4.3L V6 Hesitant To Start When hot - Fuel Pressure Test

[K-TRON]

Three years ago we had the engine in our 1997 GMC Safari Van replaced. Ever since then we have had one problem after another with it, preventing us from using it for anything other than local driving. Long story short I found that the previous shops made a lot of careless electrical and mechanical mistakes which took me months to resolve. After going through all of the electrical connectors, performing oxidation remediation, I added ground straps between the engine and the frame, the frame and the body, and from the engine to the body. I cleaned the positive wire from the alternator and the negative wire from the battery to the engine block. I pulled the starter motor, cleaned all of the contacts, and added a heat shield to the starter solenoid. All of this improved the electrical response of the controls/gauges/headlights, etc. Now the biggest issue I have with the van is it being hesitant to start when the engine is hot. We bought the van new 23 years ago, and the original engine started in half of a turn hot or cold no matter the temperature up until the point the engine died. The Jasper replacement engine starts just the same cold, or after the engine has sat at least six hours after being previously run. Starting when hot is another story. As long as the engine has run that day, a minute or an hour, the engine will be hesitant to restart. Sometimes this entails two additional seconds of cranking, sometimes an additional ten seconds of cranking is required. Cycling the ignition to run the fuel pump, or holding the accelerator down during hot starts does not change anything. I tested the alternator and battery individually, both seven years old, and both are working perfectly. I finally bought a genuine Kent-Moore fuel pressure gauge. I hooked the gauge up to the fuel rail on the engine and it reads 58psi initially, dropping down to 55psi of fuel pressure with the ignition on - engine off, and 45-50 psi (usually 48psi) of fuel pressure with the engine running. I finally caught the hesitant hot start on video with the fuel pressure gauge and tiny-tach showing rpm. You can clearly see that fuel pressure is not low or dropping during the start up process. I have let the van sit off for over two hours and the fuel pressure in the rail does not drop more than 2 psi. I am starting to think that this issue that I am having has to do with the distributor cap, or with whatever is plugged into the distributor. I bought a brand new Delco distributor when the engine was replaced. It only has 591 hours and 24,000 miles on it. This engine has the updated spider injector in it. Since fuel pressure is not dropping when the engine is off I believe the injectors are fine. The engine is not throwing any codes. The hesitation simply bothers me. I want to use the van again for long distance trips. My last trip with it, four weeks ago was 940 miles, with 3800lbs of iron in it for four hundred miles. It averaged 15.2mpg. I recently had the exhaust completely off the engine as the shop never bolted the collector to the manifolds. I took this opportunity to inspect the catalytic converter and oxygen sensors. Everything is surprisingly clean. I appreciate your thoughts on this issue.

https://www.youtube.com/watch?v=1xhuU00oYa8

I am sorry about the ringing in the video, I should have taped the open door sensor down.

Chris

[AstroWill]

Watching your video shows a slightly low fuel pressure, the specs according to the manual are 60-65psi for your year while the pump is running with the engine off. Of course to complicate things, the vans that came with the new style injectors call for 55-62psi with the pump running engine off, which you are well within.

Have you tested/replaced the ignition coil? Have you connected a scanner and watched the temperature that is being reported to the PCM, just to make sure it's in line with actual temperatures?

You can read the entire fuel system pressure test in the GM Techline eSI factory service manual(links in sig), it's a great reference.

[MechBob]

Watch your tach., engine does not start until it "sees" a signal.As you do not appear to have full shop diagnostics,I would replace crank sensor and ignition module,perhaps even the coil.

[MechBob]

Oh,and clean/tighten/replace all connectors to the above.

[Leeann_93]

Like Will said, technically you're within specs for the MFI injector, but it does seem a little low to me. Question is, is the pump questionable, is the filter plugged, is an injector or injectors plugged or stuck open, is the FPR screwed (which doesn't happen often with the MFI version)...?

My hot start problem, which progressively got worse over a year, was actually a whole bunch of problems: spark wasn't quite right (really, it was quite NOT right - initially deliberate to compensate for fuel issues to get it sold), fuel wasn't quite right and the exhaust was plugged from spark and fuel being not quite right. In fixing the spark problem, I replaced the ICM/coil/plugs/wires/cap/rotor/distributor, which actually made the van run WORSE. Then I replaced the crank sensor, knock sensor, coolant temp sensor, MAP sensor, intake air temperature sensor and PCM (not necessarily in that order). Then I replaced the spider with an AC Delco replacement MFI spider. Somewhere in there, I replaced the ignition key cylinder and ignition module (electrical wiring harness) because the cylinder was severely worn - couldn't even turn it to ACC - and the wiring harness had a couple chafes in it. Had an evap code or two, so replaced the purge solenoid and vent valve with almost-brand new AC Delco ones I'd put on my '02 (coolant temp sender, MAP sensor and blower motor also were grabbed from the '02). I replaced every vacuum line I could - they were all cracking, disintegrating and nasty. I haven't replaced the vacuum check valve, but I have one on hand to do at some point.

Once I got the spark back into spec, that showed me that the fuel was messed up. Got the fuel system back to spec and it showed me that the exhaust had been melted and plugged by the spark and fuel problems. Replaced the y-pipe and everything's been great since. I had a MAF code until I got the three things fixed; the MAF was fine, but couldn't compensate for the inability to expel exhaust gases. I cleaned it more than once with MAF cleaner and replaced it briefly with the MAF from my '02 (known-good), just in case.

I know that several things (or all things, really) I replaced were bad, thanks to readings from my knockoff GM Tech 2. Several other sensors I replaced were marginal; the readings on the Tech 2 didn't jive with ambient temp (something like a 30° difference), coolant temp (a 40° difference), actual height above sea level (about 30' here, but it thought I was 25' below), TPS, thermostat (stuck open), starter, oxygen sensors, etc. Later, I had to replace the fuel pump when the original completely died. No warning, unlike on my '93 Bravada with 4.3L V6 (it would not work only when hot, about 20 mins after starting); I drove it home after a week of driving to and from Baltimore for work and it never even coughed. My husband drove our daughter to work the next morning (2 miles from the house), brought it back and parked it, and the fuel pump never pumped an ounce of fuel again.

Supposedly, my van was dealer-maintained, but reality says ****. I had to do an awful lot of regular maintenance just to catch up with what should have been done long before I bought the van, along with replacing a few things that were stressed because regular maintenance had not been performed.


At any rate, that long-winded response was just to show that no single thing caused my hot restart problem. The whole saga is in my '05 thread, found here:
https://www.astrosafari.com/viewtopic.php?f=9&t=133162

[K-TRON]

Thank you everyone for your responses. As far as I can tell, without a specialty code reader, the van has been running flawlessly, other than the hot starting issue. It has not thrown any codes in the last six months. It idles nice and smooth, has plenty of power and pulls well. Once it starts it does not miss a beat. It has not always been smooth sailing though. After the engine was changed we immediately had problems with the van not running properly. The new engine would randomly misfire, on various cylinders, which the mechanics could not figure out. It went back to the shop at least a dozen times after the engine swap without the problem ever being resolved. Every time it was 'fixed', the problems started back up again, with no solution and more damaged interior parts from mechanic neglect. Their solution ended up being pulling the check engine light from the instrument panel. When the engine began misfiring without a service engine light flashing, I became suspicious, and what I found made me really mad. I eventuality got fed up with their negligence, and began fixing everything that had been screwed up by the first shop which destroyed the engine, and then the second shop which replaced it. I traced the problems back to a pinched high tension plug wire and a bad coil to distributor wire. Replacing those made a world of difference. They likely got pinched/damaged when the body was put back onto the subframe. After months of crawling around under the van I must say that the mechanics we have used for years did a pretty bad job re-connecting everything after dropping the body back onto the subframe. Loose brackets, wires and hoses rubbing and chaffing on the van body because they were not properly secured caused a world of problems. They clearly did not want to work on the van, a lot of glaring issues were totally ignored before they gave the van back to us. The rattling of the exhaust which we complained about ended up being caused by the collector for the exhaust which was only held onto the exhaust manifolds by two of the six flange nuts! Anyhow, that has all been resolved. The van has finally been running great and is borderline reliable again! All I need to do now is fix this hot starting issue and it will be as good as new again. Back to the history on the van, about six months before the engine failed, (four years ago/25,000miles ago) I changed the fuel pump and fuel filter out. A genuine AC Delco fuel filter was installed and a Delphi fuel pump was fitted. I did not have a fuel pressure gauge then and it started perfectly hot or cold (this was the original engine). I try to use genuine Delco parts whenever possible. I have a new AcDelco fuel filter ready to be installed/tested the next time I have the dog house off. Upon your recommendations, I went ahead and ordered a new AcDelco crank sensor, coil and ignition control module. This starting problem began after the engine was changed, so it could be a bad connection somewhere. The coil, ignition control module and crank sensor are all 23 years old. I will be checking the wires with my meter, cleaning the pins with a fiberglass pen, and replace the components one at a time and test the van to see if the problem remains. I sure hope that these parts resolve this problem. I do not want to begin replacing everything! I am fairly confident that this problem is not fuel related since the fuel pressure holds above 35psi even after it sits overnight. From what I have read if the injectors were bad the fuel pressure would leak down quickly. Since fuel pressure is the same whether the engine is cold or hot, I think I can rule out fuel pressure being a culprit. My records do not show the key ignition barrel to have ever been changed. I have not had the steering column apart other than to clean electrical contacts. I will report back in a few days when the new parts arrive and I get them installed.

Chris

[MechBob]

Good stuff,Leeanne,will disagree a bit about the pressure.If poster for sure has the "upgraded" MPFI,fuel pressure is less of an issue,as there are no poppet valves.old style,yes.Butthe newer and conversions ( i think gm went to this system in 2002?) is not unheard of to read stories that truck will start and idle,but cannot drive, and they only have 35-45 lbs pressure.Which would never happen with poppet valves,I think their minimum is 45-48 psi.And,heat would affect them,on a hot start. Anyway,good call on the cat(s), very good possibility.

[MechBob]

OH,if you cannot remove the electrical terminals from the housings,(they get loose from vibrations,and open up), take a good sewing needle or strong pin,and bend them closer shut,for good connection.

[K-TRON]

I replaced the fuel filter with a new AC Delco GF652. The old filter element was not terribly dirty inside, but some blackish fuel was drained out of the inlet of the filter. I also found, removed, and cleaned the ground for the fuel pump. After torquing the cleaned fastener down I coated it with a corrosion inhibitor. Fuel pressure marginally increased from 55psi key on ignition off to 57psi, and running fuel pressure increased from 48psi to 49psi. Although I will take an additional 1-1/2psi of fuel pressure, changing the filter did not help with the hot start issue.

https://www.youtube.com/watch?v=BxHnDLXY-3I


Chris

[K-TRON]

Upon the forums recommendations, I went ahead and ordered a new AC Delco 19239841 coil and 19352931 ignition control module. Replacing these parts was a little more involved than I thought it would be. I had to remove the throttle body bracket in order to remove the two fasteners which held down the ignition coil bracket. I found the mating surface for the aluminum heat sink to be quite corroded. I planed this surface before applying a fresh layer thermal paste. The installation was a snap compared to the removal. It took me about three hours from start to finish. When I was finished I turned the key and the van started. I ran the engine up to temperature and shut it down. I was surprised that it restarted without any hesitation. I then took the van out for fifteen minutes and brought it up to temperature. It pulled good and strong up to 70 mph. I noticed that when driving around 1600rpm @ 50mph fuel pressure is 55psi, and when I hammer down on the throttle it will hold about 62psi up to 3500rpm. The only thing that I heard out of the ordinary was a whirring noise coming from the back of the engine from 1600-2600rpm from about 25-45mph. I am going to pull the distributor cap and check things out. There should not be any appreciable wear on these components since they do not even have 30k miles on them. Back in the driveway I shut the engine off and successfully hot restarted it six times in a row. I am really quite happy! The van has not restarted this smooth since the engine was replaced three years ago. Tomorrow I plan to change the coolant temperature sensor and check the distributor out. I am going to pass on replacing the crank position sensor since I do not have any way to 'relearn' the sensor. Thanks again for the quality commentary on my problem. Lets hope that tomorrow the van starts and re-starts effortlessly over and over again.


https://www.youtube.com/watch?v=_akEHsSQL0o


Chris

[MechBob]

Dam,someday someone will thank me.PS crank sensors on 96 and up 4.3's can get hammered from crankshaft bearing wear,and crankshaft twisting.You can replace it without a relearn, if the new sensor is a bit off,it may throw a code.however,is still very drive-able.in the "bad old days" the only way for relearn ways revving the engine,till the fuel cutout kicked in.Not good, with older engines.But,with scan toll can be done differently.Just pull it out.If the base is nice,smooth and clean,put it back in.if it has wear marks,you should replace it,and follow the instructions for shimming it upwards.

[Rod's Trucks]

Leeann and MechBob,
Lots of good information presented there, and for a tough diagnostic problem. Those kinds problems will make ones hair turn gray! To an extent, I have some empathy for the mechanics who attempted to solve the problem...even if they may have effectively caused it in the beginning.
The only comment I can offer, and it is from years of wrenching: IMHO, 'most' of the time when a cat starts to plug, response and power is lost at the upper end, and gets progressively worse as the plugging increases.
In this case K-Tron mentioned that once it is running, it runs flawlessly and has plenty of power.
For that reason I would have discounted the cat as a potential cause of the hard warm-starting problem.
Rod Johnson
Issaquah, WA

[MechBob]

CAT problem?? Why would you bring that up from reading this thread?You kinda lost us.

[K-TRON]

I was able to replace the old coolant temperature sensor with a new AC Delco 12554145 sensor. It was far more difficult than anticipated. I spent over an hour trying to install the new sensor with an open end wrench and finally deemed it impossible. Seeing that the electrical connector end of the new sensor would not pass through a 3/4" ratcheting wrench, I grabbed the cheapest 3/4" wrench I could find and cut a slit in it for the wire to pass through. I was able to install the sensor without too much trouble after that. It took a long time to burp the air out of the system. It threw up a few extended cranks upon initial sensor replacement, but it was also reading high since there was air in the system. It finally settled down and took in all of the coolant that came out. The temperature gauge seems to be reading about 2 bars lower than it used to. Going down the road with the heat in the cab on, it never seemed to get much over 170* according to the gauge. The engine has a new Stant 14119 195* thermostat. I will have to grab the infrared gun to double check that the new sensor is reading correctly. I did not get a chance to pull the distributor cap. Maybe tomorrow.

Chris

[Leeann_93]

Mine have all been 19mm...

[K-TRON]

Leeann, there is 0.012" difference between 19mm and 3/4". I literally own no metric tools. I rebuild antique engines and have no use for them. The van is the only metric anything I own. I have many antique English engines and even they did not use the metric system, they knew better! I will take British Standard and Whitworth long before the inferior metric system.

The rain kept me from getting anything substantial done on the van tonight. All I managed to accomplish was the removal/cleaning/re-installation of three crusty electrical connections under the hood. I have been going around and cleaning every electrical contact I can find, and then covering it in a marine grade corrosion inhibitor.

Chris

[K-TRON]

I found the time to pull the distributor cap today, and found quite a bit of white corrosion on the terminals of the rotor and cap. It was all surface corrosion and cleaned off nicely. It is hard to say if any improvements were made, but I was able to verify the condition of the cap with my fluke meter, and verified the condition of the actual distributor by turning the armature. It was nice and tight, with only about 5* of rotational movement noted. The engine started right up and ran just perfectly. It is still making a bit of a whirring/ticking noise from time to time between 1600-2600rpm. I did not feel any slop in the distributor bushings, so chalked it up as normal. I took the van out for forty minutes, had it good and hot and up to highway speed for a prolonged period. It ran perfect, had plenty of good power, and accelerated fine. After the little excursion, I restarted the hot engine in the van and it started right up without any hesitation. So far changing the coil/icm/coolant sensor, and cleaning every electrical connection I could find has reduced the number of extended cranking times from about 80 times out of 100 to 2 out of 100. I am not sure if those two times were a fluke or not, but they were a ~2 extra second start. I have not touched the crank position sensor, and do not plan on it. It is running and restarting perfectly as far as I am concerned. I have to check the passenger front brake caliper, all of a sudden it feels like it is pulling to the left when braking. Thanks to all for your help, I am finally feeling confident in driving the van again.

Chris

[AstroWill]

Significant improvement! That is awesome to hear.

[Rod's Trucks]

MechBob,
Sorry it took so long to reply. I've been away for a bit.

I mentioned the CAT because of the post of LeeAnne
"Once I got the spark back into spec, that showed me that the fuel was messed up. Got the fuel system back to spec and it showed me that the exhaust had been melted and plugged by the spark and fuel problems. Replaced the y-pipe and everything's been great since. "
I misinterpreted the reference to 'melted...' as referring to damaging the CAT.
Yes, rereading LeeAnn's post, it does not say it was the CAT, just the Y-pipe.
My error, sorry for causing any confusion.
Rod J
Issaquah, WA

[Rod's Trucks]

K-Tron,
You stated " I literally own no metric tools."
What do you use for the 6mm bolts (10mm hex heads) that are common on our vans?
I have grown to be comfortable with metric system, but it has taken many years to get over the Asian version of metric bolt head sizes, vs. the European version.

Is it going to be the 8, 10, 12, 14, 16 set of wrenches; or 8 10 13, 15 17 set I grab?

It was not very many years ago, when major tool manufacturers did not even include a 16mm or an 18mm in a complete set.
Also the 16 and 18mm bolt heads are not a very close match for the SAE wrenches, and in some places ( like taking out the front seat with the storage box under it) no SAE wrench allowed adequate movement, once the slop was taken up.
Ahh, the Whitworth (BSW) system...a nut and bolt sizing system which seems to have mostly gotten lost in history.
The wrench that fit the bolt on a BSW standard 1/4" threaded bolt, was labelled 1/4. How unique! When I first saw wrenches that marked :"0BA" and "1BA" I did a double-take.
We 'Yanks' decided to supply our 1/4 inch threaded bolts with matching nuts which could be in different wrench sizes.
In a previous life, I worked on some old British sports cars...that was fun stuff!
Rod J.