97 GMC Safari Tuneup after 137K Miles

97 GMC Safari Tuneup after 137K Miles

Postby K-TRON [OP] » August 25th 2016, 6:14am

On Tuesday the 4.3 in our 1997 GMC Safari started to stumble and miss. I pulled off and let the engine idle for a minute without a load. The miss went away after about twenty seconds, so I decided to drive it the four miles to our local mechanic. Sure enough it had a misfire on the #5 cylinder. After talking with our mechanic, we figured it was some crud in the fuel injection system, dirty oil causing the lifter to stay open, or some carbon was holding a valve open. The van had about 4300 miles on it since its last oil change. Knowing that the van hasn't had a tuneup since the 58,000 mile marker, and it now has 137,000 miles on it, I decided that it was time to give the van a tuneup with new sparkplugs/plug wires/distributor cap and rotor. So for $200 I was able to buy all brand new AC Delco/Standard parts and some good synthetic oil. (AC Delco 41-993 Sparkplugs - 19256067), Standard 7673 plug wires, Standard DR475T distributor cap, Standard DR331T distributor Rotor) Since about the 32,000 mile marker our van has been using 10W40 Valvoline synthetic blend motor oil. I saw the overwhelming love of the Mobil 1 oil on this forum and decided that it would be best to go to full synthetic motor oil. We have been averaging 4000-5000 miles on the Valvoline oil over the years, and the last dozen times I've changed the oil its been red. The only explanation I can come up with is that the oil is not a real synthetic oil and has broken down before its regularly scheduled oil changes. I drained the old oil out, stuck my air blow gun down the oil fill and blew a good amount of oil out of the drain plug that would normally not come out. 5 quarts of Mobil 1 10W30 Full Synthetic went in, and a new Fram 3980 filter. I immediately noticed how much quieter and smoother the engine idled. Oil pressure was in its normal range, 36-38psi at idle and ~ 50psi going down the road. I drove the van around the block and for the first time an oil change seemed to actually make a difference in how the engine ran. I jacked the front of the van up, pulled the tires, mud guards and proceeded to replace the sparkplugs. #1 and #6 have the longer straight body plug boot and both came apart in pieces. The rubber hardened and became brittle over the years. The four 90* elbow boots came out without much trouble, but they were still not easy. I noticed right away that the old Iridium plugs were all within spec. I measured 0.057- 0.063" electrode gap. The plug wires on the other hand were in need of replacement. Im sure the last time we paid $550 to have the plugs done (almost 11 years ago) the wires, distributor and rotor were not changed. The wires were somewhat melted and chaffed in spots partially due to the plastic plug wire block clips being broken. I found the torque rating of the sparkplugs and saw that GM recommended 11lb/ft torque for reassembly, and 22lb/ft torque recommended on new parts. I torqued the plugs to 18lb/ft torque with my techwrench. I applied some Permatex Anti-Seize to the plug threads, and some di-electric grease to the porcelain plug bodies. I mainly work on antique engines and was surprised to see that GM was not using crush washers on the sparkplugs. Installing the new plugs and wires went without a hitch. The distributor rotor and cap was also pretty easy to replace. The tang on the old rotor was quite worn, and the distributor had some dried up salt/moisture deposits in it which I cleaned away. Thankfully some folks on here explained how to remove the doghouse without needing to remove the front seats! I fit everything back up, and it fired right off. Oh it runs so nice! I have not put the doghouse back on, as I want to clean some of the dirt/grease off of the valve covers and the top of the engine. This is the first time I have pulled the doghouse off myself, its pretty easy! Is there anything else I should check before I button the van back up? Are the EGR valves at all problematic? To my knowledge it has never been off or cleaned. I have not done anything to the fuel injectors or spider injector, I simply added 20 ounces of Chevron Techron complete fuel system cleaner to the ~ 20 gallons of fuel in the tank.

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Re: 97 GMC Safari Tuneup after 137K Miles

Postby chevymaherchevymaher is online! » August 25th 2016, 12:27pm

K-TRON wrote:Are the EGR valves at all problematic?
Chris

The entire purpose is to pump engine waste back through the engine. Air with no oxygen to be used for combustion. Trading one waste product in lower numbers for another in higher numbers. Oil, carbon and air with out oxygen which fouls the engine and kills efficiency making a second trip past injectors and plugs. It is just another failed engineering experiment. Exactly why newer vehicles don't have them anymore. They suck they don't work and they never did.

But how do I really fell about them right?
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby Leeann_93 » August 25th 2016, 11:49pm

EGR is at the front of the motor so it doesn't need work while you have the doghouse off ;)

Nice job on the other stuff, though. I've never had any luck with Valvoline, but my engineer uncle absolutely swore by Mobil 1. He had 355,000 miles on an Audi 4000 CS Quattro when the NJ salt ate up the internal 'frame'. The motor was still going strong...

Check and clean the IAC valve (driver's side up by the gas pedal) and replace the PCV valve (driver's side valve cover) while you're in there.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby K-TRON [OP] » August 26th 2016, 2:48am

I watched a few videos on youtube about the EGR cleaning procedure, but the engine in our van seems to be configured differently. I see that the line which feeds the EGR valve is threaded into the driver side exhaust manifold. The line runs straight up, then alongside the driver side valve cover and then disappears behind the AC compressor.

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Is it possible to just remove that line and thread a plug into the exhaust manifold? Or do you have to actually dig to the EGR valve to block it off? I drove the van over to our local mechanic, he gave me the big thumbs up. I asked him about the EGR valve and he wanted to say it was underneath the intake manifold. Thats uncharted territory for me. I havent dug that deep into it yet.


I did however clean all of the grease/dirt/grime from the valve covers and whatever I could reach with the doghouse out of the way. I also ziptied the plug wires to the plastic locating tabs. I am confident at this point that the misfire was partially due to a melted plug wire on the #5 cylinder. The wire was burned in several places as it was laying on the exhaust manifold. I made sure the wires were tied up away from the engine before I put the doghouse cover back on. Unfortunately I did not see Leeann's response before I did so. I will take note and look into whats involved in cleaning the IAC and PVC valves.

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I took this opportunity to clean and grease the entire front end of the van, as I had the van up on jackstands. I cant tell you when the last time all of the steering rods/linkages, and the bottom of the engine have been thoroughly cleaned and degreased. I regularly grease all 14 zerk fittings on the steering linkages, with the front axle on the ground, so its pretty difficult to clean the underside of the van without getting absolutely covered in grease and grime. Today I spent three hours degreasing the underside of the van. I was able to clean the outside of the oil pan, the bottom of the starter, the oil lines, the oil filter housing, the bellhousing on the transmission, the front differential, the front cover of the engine (around the crank position sensor) and all of the nooks and crannies in between. It looks pretty decent for its age!

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I took the van through its paces, and am very pleased with the way it is running. We have a lot of big long hills around where I live. Racing through 1, 2 and 3 I was able to get about 4mph more than average going up the big hill. It seems to accelerate well from a stand still, and passes well on the road. To finish the tune-up I installed a new Fram CA7421 air filter.


At this point, the engine has been tuned up, last year I changed the oil in the front/rear differentials, the oil in the transfer case, the oil and filter in the transmission, I changed the fuel filter, and replaced the in tank fuel sending unit. I resealed the rear window, replaced the door hinge pins and locks, replaced the rear leaf springs, bump stops, and shocks front and rear. Right now it looks like I just need to replace the universals (as they are non-greaseable), replace a couple AC condenser lines, clean the IAC/PCV valves, perhaps perform an EGR Delete, and then start collecting everything I need to replace all of the brake lines. The windshield needs to be re-sealed, and the lights in the radio/climate control switches need to be replaced. Then perhaps some body work and a fresh coat of paint! I guess it never really ends. We love our van, and wouldnt replace it with anything else. Thanks again for all of your help!

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Re: 97 GMC Safari Tuneup after 137K Miles

Postby chevymaherchevymaher is online! » August 26th 2016, 12:18pm

It it has a tube from the exhaust and you block it. Best thing for the exhaust tho. It will suck air from the open tube when the EGR functions. It would probably run better because that air has oxygen but it will make a uneven air fuel distribution. So it would still run rougher than it should.

Dad's firechicken has that set up. It still needs the plate put between the EGR and the adapter bolted to the intake.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby K-TRON [OP] » August 30th 2016, 3:19am

I took our van for a 225 mile road trip yesterday. It ran really well, had good power and never missed a beat. The only thing I noticed which was odd was that the oil pressure was down. Hot, the engine had 25 psi oil pressure at idle and 45 going down the road. Oil pressure is down about 10psi across the board with the 10W30 full synthetic Mobil 1. Perhaps I should have used 10W40?

This evening I was at the stop light and the engine started running rough again. I lightly tapped the throttle and it cleared right up. The service engine light did not come on. About 1500 feet down the road the engine started violently shaking. This time the service engine light came back on. I took note of the oil pressure, should the lifters be binding up. 40-45psi oil pressure was noted. The shaking quickly stopped after about 5 seconds and it ran fine the rest of the way home.

Tomorrow I plan to head to the station in the early morning and see what the error code has to say. Chances are its going to say: "Cylinder #5 Misfire" again. So what in the world can it be this time? I have new plugs, new wires, new distributor cap and rotor, the wires are ziptied in place and away from the hot exhaust manifolds. Oil pressure is good and the oil has just 230 miles on it. It cant be a chipped valve, bad head gasket or loose plug wire. The erratic behavior comes and goes. Im thinking it HAS to be within the fuel injection system. I put 20 ounces of the Chevron Techron complete fuel system cleaner in the last tank of gas. The injectors must be too dirty for one dose of fuel injector cleaner to sort out. Perhaps I need to blend more of it into the fuel supply? The fuel filter has less than a thousand miles on it. Has anyone actually had success with this fuel injector cleaner? or is it just a bandaid fix until the injector can be replaced?

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Re: 97 GMC Safari Tuneup after 137K Miles

Postby sadglad » August 30th 2016, 3:55am

K-TRON wrote:....our van has been using 10W40 Valvoline synthetic blend motor oil.....5 quarts of Mobil 1 10W30 Full Synthetic went in
Chris


Any particular reason to use 10W40? The recommended oil is 5W30 and Mobil 1 even say 0W30 is an acceptable option if using their oil. The last thing I want to do is start a useless oil war but I am curious if I'm missing something. Thanks.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby chevymaherchevymaher is online! » August 30th 2016, 12:32pm

sadglad wrote:
Any particular reason to use 10W40? The recommended oil is 5W30 and Mobil 1 even say 0W30 is an acceptable option if using their oil. The last thing I want to do is start a useless oil war but I am curious if I'm missing something. Thanks.


Reason for thinner oil is striving to get the minuscule .00001 MPG better mileage. But in hot environments thicker is better. I am in a heated garage so winter starvation on start up is not a issue. 0 and 5 for the first number is actually for arctic type start up situations. 20 degrees and lower.

But I run 15-40 year round. I enjoy having hot idle oil pressure myself. 100 degrees with the air on breaks oil down fast and thins it out, And I occasionally flog it tractor pull style. Those 100 MPH your LS motor isn't squat get back behind me and stop trying to cut me off runs.

It is a recommendation nothing else. Same motor as in the 60's same bearings the whole nine yards. When they recommended 10-40 or higher in severe duty situations. Like towing and racing. Back when it wasn't taboo to have power and use it.

Now your not supposed to do it so you don't need it is the attitude. Once a oil is heat soaked it is thinner. And it offers less protection. The lubricating layer is thinner. Which is all fine and dandy if you drive like grandma don't tow and are making short trips and the engine is in perfect shape.

So it is a judgement call. So far the smog gods are not failing you for using better than stock oil. But some newer cars actually have sensors that tattle tail you if you use thicker oil. It throws a engine light.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby K-TRON [OP] » August 30th 2016, 6:12pm

Well I went to the station this morning and the service engine light went away. The code was still in the computers history. Sure enough it was a cylinder #5 misfire. So I took the mechanics advice and went to the parts store to put two more bottles of the Techron fuel system cleaner in the tank. Literally the entire ride to and from the parts store (about 6 miles round trip) the van was running on 5 cylinders. It was not an intermittent miss today, it ran poorly the entire trip. I put the fuel injector cleaner in at the parts store and drove it back to the station. Looks like its in for an injector replacement.....The only other thing I noticed was that the blender valves were not working for the climate control, so a small vacuum line must have broken or come undone. I do not suppose something as simple as that could cause the problems I am experiencing?

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Re: 97 GMC Safari Tuneup after 137K Miles

Postby WimpTech » August 30th 2016, 7:12pm

This is starting to sound a lot like my stuck valve problem, especially since its #5 (hottest of the 6).... did someone do a leak down test?
Here's my issue, starting on page 2... viewtopic.php?f=43&t=86977&hilit=misfire&start=40

I would recommend my favorite, magic smoke trick to further isolate stuck valve. For stuck lifter, I recommend BG engine flush, see if it gets any better.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby TurnNburn » August 30th 2016, 7:33pm

I use BG products at work all of the time. but its not in a whole lot of stores around here. Seafoam will have the same results and is cheaper and easier to find.

I used the BG flush before I deleted my oil cooler and it was amazing how dirty the fresh oil had become.

And subarus are notorious for getting stuck lifters and making a horrible noise that sounds like main bearings. I have fix a lot of "blown up" engines by flushing them.

Get the engine up to operating temperature, add the seafoam, and hold the RPMS high. I know without a tach its hard to tell, but shoot for 3-4k rpms, and hold it there till the noise goes away. Usually a minute or less. Then do an oil change. I usually let it drip longer then usual because I would prefer to get as much of that additive out of the engine.

And seafoaming the intake is also capable of freeing up stuck valves. There are a bunch of youtube videos on this that are pretty funny.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby Mmusicman » August 30th 2016, 7:53pm

K-TRON wrote:The only thing I noticed which was odd was that the oil pressure was down. Hot, the engine had 25 psi oil pressure at idle and 45 going down the road. Oil pressure is down about 10psi across the board with the 10W30 full synthetic Mobil 1. Perhaps I should have used 10W40?

Lower pressures are typical with thinner oils and synthetics. Your pressures still look fine... so no worries.
Personally, I prefer 10w40 (for ANY engine with over 100,000 miles on it)
5 quarts of Mobil 1 10W30 Full Synthetic went in, and a new Fram 3980 filter. I immediately noticed how much quieter and smoother the engine idled. Oil pressure was in its normal range

Personally, I believe you likely just "imagined" the "quieter and smoother" part. I think we all do this from time to time. Oil change does not typically "affect" noticeable changes on how an engine runs... it simply provides lubricant to bearings and other frictional moving internal parts, as well as pressure to pump up lifters. Quality (proper weight) oil (with proper oil changes) will extend the life of parts, but that won't usually be seen (or felt) until much later in the engine's life. Since the "new" oil is running at the same pressures... I doubt it actually "ran" quieter.. or "felt" smoother. But it certainly can may the owner "feel" better! :D

I noticed your "tune-up" did include all good quality parts, but did not include "AC Delco" cap and rotor, which is typically recommended. Probably won't matter. Ironically (side note), the price of a quality cap and rotor can often be almost as much as what a complete Skip White new distributor (with cap and rotor) costs. With over 100K miles, you may want to check distributor for excessive play and wear. Fuel injectors may also fall into this same category... as well as many other parts too. Hopefully they just need cleaning.

But don't fall into the trap of just changing lots of parts until you "fix" a problem. Good "diagnostics" can go a long way to saving money and aggravation!

PS: If you want a change you can REALLY feel (if you feel any vibration) ... try changing the motor mounts! Been there.. done that! It can really make it "feel" like a new van!

Two funny stories... I drove a brand new 2000 Astro Cargo work van for MANY years, without a single tune-up until it hit over 100,000 miles! While it was still running perfectly, the boss figured it MUST certainly need a "tune-up" by now. So after the tune-up... the engine developed an immediate stumble, and intermittent misfire at idle... which stayed with it for the next 100,000 miles and pretty much still to this day! No codes... but just an occasional stumble at idle. It was perfect.. until we broke it's cherry. Despite stumble.. it still got very good fuel mileage though. My 92 (also once a previous work van) always got "random" oil changes with the cheapest conventional oils possible... and it ran strong (with excellent oil pressure) all the way to 282,000 miles. Maybe with better oil I'd still be running with that V6! :)

Good luck!
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby K-TRON [OP] » August 30th 2016, 8:44pm

I picked up the van from the station. Our mechanic thinks that the valve is binding up and potentially not turning. He pressure tested the injectors and he says they all appear to be fine. He said to put some miles on it and see if the fuel system cleaner cleans the injectors and valves. I really do not like how the engine sounds and pretty much refuse to drive it. Have any of you heard this noise before? It really sounds like a valve is ready to let go,

https://www.youtube.com/watch?v=IHt50z_h1Dk


After the oil change the engine did idle quieter. It wasnt just my ears. My brother and dad also noticed it running smoother. We originally went to the synthetic blend oil many years ago because we had problems with the lifter on #5 ticking. When I put the Mobil 1 full synthetic oil in, that ticking went completely away, and it was indeed quieter. Something is definitely wrong now and I havent pinpointed exactly what it is yet. There is no way the brand new distributor cap and rotor are worn after ~250 miles. It ran perfectly during that time. If I didnt have a million projects on the workbench I'd be inclined to pull the cylinder heads and touch up the valves. I am starting to think that a valve has chipped and all of a sudden its running bad full time.

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Re: 97 GMC Safari Tuneup after 137K Miles

Postby TurnNburn » August 30th 2016, 8:54pm

since your willing to post videos, can you take one from the engine bay while its running? And no offense, but don't talk, I had my volume turned up really loud to try and hear the noise since its not very loud in the video and damn near blew my speaker out when you said something.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby Mmusicman » August 30th 2016, 9:22pm

K-TRON wrote:When I put the Mobil 1 full synthetic oil in, that ticking went completely away, and it was indeed quieter.

Sounds LOUDER to me... I listened to the video! (just kidding)
Something internal definitely wrong.
Maybe some oil additive might help (if it's minor and something just sticking)

Good luck.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby WimpTech » August 30th 2016, 9:33pm

Wimpy stood by his original recommendation.... magic smoke, until he watched the video. That is a completely DEAD HOLE! When the SES blinks like that... it's not a good thing.

In case you wanna do the Seafoam trick....

1) Get yourself some Seafoam, about 8oz should do it. Get a funnel or something ready to make sure you get it into the TB.
2) Pull the air box/ throat all the way down to the throttle body.

3) Startup your van, rev up and slowly (over about 10 secs) add about half the seafoam, revving the motor to keep it from dying. Then dump the other half in and let off the throttle.

4) Let sit for a while, I like to go overnight.

5) Start 'er up and let the smoke F L Y!!! Seriously, I can fill up my whole street in a few seconds.

6) After a few minutes, the smoke will subside and if my theory is correct, she should run a whole lot better.

WHY? According to my Dealer's mechanic, these motors have narrow valve guides with only about 0.001" clearance as opposed to 0.0015" like others. Over time, these guides will get gummed up and cause the valves to stick open to varying degrees. Why #5? That's the hottest hole in this motor, so more likely to bake on crud.
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Re: 97 GMC Safari Tuneup after 137K Miles

Postby K-TRON [OP] » September 1st 2016, 4:57pm

Since my last post I was able to fog the intake with Seafoam. Once the smoke subsided I shut the engine off and let it sit. About two hours later my neighbor who is a retired mechanic came home. I wanted him to listen to the noises the engine was making. Of course when I went to start it up it ran perfectly fine. I figured maybe it only happens when the engine is hot, so we took a drive and it did not miss a beat. The next day, as in yesterday, I pulled the dog house and replaced the one questionable vacuum line which I had spliced together years ago. I regained the blender controls for the climate control :P I spent the night thinking about what could have possible caused the noise in the engine that day, and then put it all to the test:

- Perhaps the intake plenum warped and it was sucking air and leaning out on one cylinder so much it was not firing? --- but that would theoretically make more than one cylinder run erratically, and probably would not cause the shaking I was experiencing. (I sprayed ether around the plenum and waited for the engine to race, but that never happened, so the plenum is not warped and the gasket is still good)
- Perhaps a plug wire came loose causing the dead cylinder? - but why would it run so smooth after restart?, and why was the engine laboring so much? (I checked that the #5 plug wire was still attached, which it was. I tested the resistance on the #5 plug wire and the #5 sparkplug, both were fine)
- Perhaps the bearings in the distributor are bad and there is a lot of shaft play? That could cause an excessive air gap on one side and result in the ignition arcing inside of the cap and no fire at a plug. ( I pulled the distributor cap, checked run out on the shaft and found only about 0.002-0.003" of run out, no problem there! I checked the distributor cap, no arcing to be found)
- Perhaps the head has cracked and putting coolant in the cylinder killing the ignition? (I checked that there was no coolant in the oil, and no oil in the coolant)
- Perhaps a ring has cracked on the one piston? - but that would only result in a lower compression in one cylinder, it would not make that much noise unless the top ring landing cracked. Regardless it would not clear up and go away on restart.
- Perhaps there is carbon deposited on the valve seat? That would cause a no compression scenario in the cylinder which would not drop idle rpm as much. I would also have heard backfiring through the exhaust.
- Perhaps the valve chipped and the compression blowing past is causing the noise I am hearing? but in my experience a chipped or cracked valve will not seal up in a hurry.
- Perhaps the new Delphi fuel pump is not pumping enough fuel for the engine to run right? (without knowing where to test the fuel system pressure) I decided that was not the case, if anything it would idle fine and stumble at speed if the fuel pressure was too low
- Perhaps there is some moisture in the fuel? yes I live on Long Island, sometimes the rain water has no where else to go. The fuel filter looks fine, no moisture to be seen after shaking it out. The fuel filter only has about a 1200 miles on it.
- Perhaps there is another vacuum leak somewhere I am missing? I removed the PCV from the driver side valve cover, and hooked up my vacuum gauge. 18mm/HG at idle, and 10-12mm/HG going down the road. The needle was not jumping all over the place, so I know the valves are working just fine right now.
- Perhaps a lifter is collapsing, preventing a valve from opening? I did not hear any ticking noise when the engine was running rough, but that could have been masked by the mechanical noise. Okay, on restart I heard no ticking noise two hours later. The check valves in the lifters seem to be working just fine.

With all objectives tested for, I decided that THIS IS WHAT HAPPENED:
Before my tuneup the engine had an intermittent miss, caused by excessive carbon deposits on the valve stem. I performed a tuneup, replaced the sparkplugs, plug wires, distributor cap and rotor. I put a can of Techron fuel system cleaner in the fuel supply. I changed the synthetic blend oil out for full synthetic 10W30 Mobil 1. The first 225 mile trip went fine. The fuel system cleaner sprayed on the back face of the valves and all was good. The detergents in the full synthetic oil were doing there job. After my trip, doing local driving the engine started misbehaving and running really rough. More fuel injector cleaner did not help. What happened? My educated guess is that the detergents in the full synthetic oil finally started cleaning up the old deposits in the hydraulic valve lifters. The lifters became spongy again and were finally able to pump back up to full capacity. The ticking went away, and ticking can only happen from excessive clearance or lack of oil. The deposits that the oil cleaned up went circulating through the engine and some either deposited in a valve guide, binding a valve up, or are sitting in the oil pan waiting to be flushed out. What likely happened causing the dead cylinder is this: The hydraulic lifters pumped up enough on #5 that the pushrod and rocker were able to push the exhaust valve down further than it was able to in the last maybe 50,000 miles. The excessive carbon built up on the valve stem from an otherwise unused part of the valve, now wedged into the valve guide. The valve got stuck and you could hear the engine labor trying to compress already compressed air. Fogging the intake with Seafoam and pouring a pint of Marvel Mystery Oil in the engines lubricating oil, and a pint in the fuel supply helped clean up that deposit on the valve, allowing the engine to run normal again. So how could the valve be stuck in the closed position? surely it would have bent the push rod. Well, perhaps the check valve in the lifter failed and only relies on operating oil pressure to keep it open. Perhaps the 20-40psi oil pressure could not overcome the pressure required to move the stuck valve, and the pushrod held strong. The engine has been running absolutely wonderful the last 25 miles. The valves seem to be operating normally without any noise at all. For kicks I pulled the plug wire on the #5 cylinder when the engine was running flawlessly. Removing the ignition hardly changed the idle rpm. The engine did not run rough, and did not make any more noise. You could only hear the noise from the ignition having no where to go. So that all makes sense, so what is the cure? Just continue to fog the intake with Seafoam and run Marvel Mystery Oil in the engine and fuel source? Or pull the cylinder heads - grind the valve seats - replace the valve guides and valves, replace the hydraulic lifters, and perhaps the pushrods, clean the throttle body, replace the cheap sensors perform an EGR delete, and hope it lasts another 100,000 miles....

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Testing the vacuum on the engine:
https://www.youtube.com/watch?v=2YYjzLD6vtQ

Testing how removing plug wire #5 changes idle rpm: (I wish I taped over the door open sensor)
https://www.youtube.com/watch?v=UuZwDFB4mDM

4.3L running after all of the diagnostics, Seafoam and Marvel Mystery Oil
https://www.youtube.com/watch?v=hgH1VhC0wj0

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Re: 97 GMC Safari Tuneup after 137K Miles

Postby WimpTech » September 1st 2016, 6:14pm

WOW

OK first off Chris, I believe you are resetting the bar when it comes to giving info to help explain the issues you are having. Don't be surprised if this becomes the new standard for over-the-web-troubleshooting. Also, good job on your method of deduction.. the scientific method... well done sir.

I should have been more specific in my magic smoke description... When you dump the other half in, that should kill the engine. If not, shut her down and let it sit for a while... THEN start her up and watch the smoke fly. The longer that seafoam has to soak into crud, the better it works.

I noticed in your second video to test #5 misfire... you were actually pulling the wire for cyl #3. That side of the cap is counter-intuitive, from the front its actually 1-5-3, not 1-3-5. Might want to double check that everything is hooked up correctly. FYI- this miswire would absolutely give the dead hole issue we heard in the first video.

It sounds like the seafoam trick fixed you right up, like it did for me, am I reading this correctly? According to my mechanic at the dealer, the only permanent fix is a valve job, new guides, etc. However, I have managed to keep the bat van going for the last 15k miles on 2 seafoam treatments... still running strong. That and no more cheap gas.
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