Yet another P0300 thread....sorry

[safaried]

Here's the background:

Over the last couple of years we've had some issues with our 2000 Safari 4.3L AWD not starting. Eventually I changed the crank position sensor and the fuel pump and things went well for just over a year. Last week the van didn't start again. Again, I changed the crank position sensor as it was still under warranty. The van started but ran very rough. Codes were thrown and read it had a P0300 and a P0135. I imagine that the P0135 was being caused by the misfires but I could be mistaken.

I installed a new cap and rotor. They weren't that old really since we had to have the engine replaced 2 years ago after my son thought it would be cool to jump rail road tracks, smash the oil pan and continue to drive it! This engine currently has right around 100k miles on it. After the cap and rotor I was getting only P0303 codes. I checked and changed all the plugs and wires. It still didn't resolve the issue and started getting P0300 and P0135 codes again.

After all this I made sure to check the engine timing thinking there might be something mechanical wrong with the engine. Everything checked out fine. TDC on number 1, the rotor points at the mark on the distributor, and the mark on the harmonic balancer points to the mark on the timing chain cover. So I took the van to a shop to have them run a diagnostic on it. The only thing they came up with was to change the fuel filter and tell me that it looked like the fuel pump wasn't delivering enough fuel to the injectors. They said that when they ran the van and sprayed ether into the intake the engine smoothed out and ran better. So I changed the fuel pump. The second time in 3 years. After this the van still continues to run rough and I was getting P0300 and P0135 codes the first time I drove it. The second time I drove it I only got a P0303 code.

I've probably read every thread on this forum about these issues. I still have a couple more things I would like to check...

Catalytic converter plugged?
Injectors clogged or bad?

I just can't figure out why the codes would be telling me random misfires one time then only misfires on number three another time.

If anyone has any other ideas please share because I'm stumped. I don't claim to be a great mechanic but I can do most things to an engine.

Thanks.

[Phantom]

P0300 is random misfire , means any plug/cylinder could misfire at any time it could be an injector , could be a few things , including a fuel pump
P0303 is cylinder 3

So I took the van to a shop to have them run a diagnostic on it. The only thing they came up with was to change the fuel filter and tell me that it looked like the fuel pump wasn't delivering enough fuel to the injectors. They said that when they ran the van and sprayed ether into the intake the engine smoothed out and ran better. So I changed the fuel pump. The second time in 3 years. After this the van still continues to run rough and I was getting P0300 and P0135 codes the first time I drove it. The second time I drove it I only got a P0303 code.

You need a better shop , how they run a diagnostic and have no idea is not a good shop

they should have run a fuel pressure test to know for sure if you need a fuel pump , you may need one , but with that level of service I surely would not let them do any work ,

A code P0135 may mean that one or more of the following has happened:

O2 Heater element resistance is high
Internal short or open in the heater element
O2 heater circuit wiring high resistance
open or short to ground in the wiring harness

Possible Solutions

Repair short or open or high resistance in wiring harness or harness connectors
Replace oxygen sensor (cannot repair open or short that occurs internally to sensor)

[safaried]

I did change the fuel pump hoping that would resolve the problem but unfortunately didn't. I was hoping the misfires were giving me a false code on the oxygen sensor. Should I just replace it as well?

[Phantom]

Did you just recently replace the pump after the shop diagnose it? You should run a fuel pressure test first to determine if it is pumping the needed 60 psi , if it is , then it would not be the pump , it could be a clogged spider "injector" , with a P0303 code telling you that there is a miss at
cylinder #3 , that is a place to look for a clog or leak , and make sure spark is good . The o2 sensor and wiring should be inspected as well test the sensor for proper resistance

[DonD]

My P0300 was a worn disty gear.

[rev_les]

My P0300 was a worn disty gear.

These motors are known for eating them. Grab the rotor and see if you can turn it left/right. If you can , it should rise and fall a bit as it moves. If you have more than maybe an eighth inch of play, pull it and check the gear. If you see any groove at all on the gear, it needs to be replaced. ( truthfully, if has play, plan on replacing it, checking it is just a formality) Good luck
I'd keep an eye on the injectors too. Yours is sequential,so any individual injector in the module, or any given poppet, may be sticking. If there's no distributor problem, a professional injector cleaning might be in order. ( the cleaner they inject into the fuel rail, not the FLAPS cleaner in a bottle you add to the gas).

[cowboydan]

phantom was on to something. but i will add the forgotten always.... coil. everyone forgets about it. random mis is most common when you have weak spark.

[safaried]

Thanks all for the replies and suggestions. I've done a bit more checking on things (mostly electrical) I'm really starting to think coil/ignition module on this one. There is some play in the dist. I can only move it counter-clockwise about a quarter inch and it does move up and down when twisting it. The ignition module can be tested, correct? To show how stupid I am when it comes to this engine I didn't realize the injectors were under the intake until I started looking at the manual more in-depth. I really hope it's not an injector problem. I can work on engines and have rebuilt many but I'm not sure I'm up for the task of removing the intake on this thing.

Thanks again

[Jasen]

Safaried,
I haven't removed the intake on one of these, but I have seen others here that are on the lower end of a shade tree mech (no offence intended) that have done it. There's also some good info here as to how to do it. As with most engine repairs on these, it's just a bit cramped.
I just did my coil and did a little write up on it, because it is, just a bit cramped in there.

https://www.astrosafari.com/viewtopic.php?f=76&t=13086

[chevymaher]

Safaried,
I haven't removed the intake on one of these, but I have seen others here that are on the lower end of a shade tree mech (no offence intended) that have done it. There's also some good info here as to how to do it. As with most engine repairs on these, it's just a bit cramped.
I just did my coil and did a little write up on it, because it is, just a bit cramped in there.

https://www.astrosafari.com/viewtopic.php?f=76&t=13086

Hey I resemble that remark.At least I do it in the shade and not in the blazing sun LOL.

[Jasen]

Chev, go play with your rear end

[redfury]

Misfires could also be caused by a bad alignment of the camshaft position sensor to the crankshaft sensor...it's called CMP retard. A good shop will have a scanner that can see the CMP retard. If it's too far out of adjustment, you can get misfires. The computer will compensate for most of them.

However, you stated that you had replaced the cam sensor once and it solved the problem. I wonder what exactly killed the first one. There really isn't any reason for that particular sensor to get damaged, unless it's physical damage.

The thing about the O2 sensor, that could be causing your bad running and your codes, so I'd look into that first and make sure that everything in regards to that is working properly. There's only 4 wires to deal with, so it should be relatively easy to trace down what the problem is. If you have wires that have exposed wire, fix that first before anything else. If the wiring is shorting out, it's going to cause all sorts of problems because the computer is trying to compensate for a false positive.

[cowboydan]

Thanks all for the replies and suggestions. I've done a bit more checking on things (mostly electrical) I'm really starting to think coil/ignition module on this one. There is some play in the dist. I can only move it counter-clockwise about a quarter inch and it does move up and down when twisting it. The ignition module can be tested, correct? To show how stupid I am when it comes to this engine I didn't realize the injectors were under the intake until I started looking at the manual more in-depth. I really hope it's not an injector problem. I can work on engines and have rebuilt many but I'm not sure I'm up for the task of removing the intake on this thing.

Thanks again

yes, modules can be tested, but you must bring it to them when it fails. disconnecting while your van runs, it will test good. one common symptom of a failed module is in a hot condition. after it cools, you can restart usually 2hrs. be careful though, fuel pumps can fail the same way (intermittent fail).

[cowboydan]

i wonder if running data on the scan tool could help. it will freeze frame when the miss occures. i'd get those printed out, cause it may take some time to analize it all. my scan tool can freeze fuel/air maps, timing, temps and it runs diagnostics and freeze frames that too. i didn't pay that much for mine so i might assume other brands are capable of it and more. i think this could help cause you don't have to have a check engine light on.

[chefred112]

I hope you figure this out..i too have a mis fire (p0305 last I checked)...since i wanted to smog it quickly back in Feb i took it to dealer to have them look and take care of it if it was simple...their answer, "need to replace the engine"..what? Til this day I've been driving it and it runs fine while driving, at idle or stop you can feel the hesitation...but no tappin in the valves and the engine still feels strong. I've replaced plugs, wires, distributor, rotor, cap and 2 02 sensors and still get the misfire... in mid nov I'm gonna pull the heads and do a little rebuilding to see if there is anything physically wrong with cyl 5... have 242k on motor and i figure it's time..

[Phantom]

i too have a mis fire (p0305 last I checked)...since i wanted to smog it quickly back in Feb i took it to dealer to have them look and take care of it if it was simple...their answer, "need to replace the engine"..what?

Need to replace mechanic

since you have it pinned down to cylinder 5 ,,a live scan diag would show more specifics as to what is happening,, could be a leaking injector dropping raw fuel in cylinder , maybe some dirt , or maybe some dirt caught in plug, valve not fully closing , plug wire not fully seated , cracked insulator on new plug ......

[safaried]

The engine seems to run decent without being under load. Just a little stumble when I hit the accelerator at first. At higher rpms it seems to do better but as soon as I put it in gear and try to drive it misses horribly. I'm really beginning to think it's a weak coil.

[cowboydan]

The engine seems to run decent without being under load. Just a little stumble when I hit the accelerator at first. At higher rpms it seems to do better but as soon as I put it in gear and try to drive it misses horribly. I'm really beginning to think it's a weak coil.

do you have trouble in the rain? sorry, did the problem start out as a problem in the rain? how long has the problem persisted?

[cowboydan]

I hope you figure this out..i too have a mis fire (p0305 last I checked)...since i wanted to smog it quickly back in Feb i took it to dealer to have them look and take care of it if it was simple...their answer, "need to replace the engine"..what? Til this day I've been driving it and it runs fine while driving, at idle or stop you can feel the hesitation...but no tappin in the valves and the engine still feels strong. I've replaced plugs, wires, distributor, rotor, cap and 2 02 sensors and still get the misfire... in mid nov I'm gonna pull the heads and do a little rebuilding to see if there is anything physically wrong with cyl 5... have 242k on motor and i figure it's time..

add coil. be sure to disconnect the battery. check your ingectors. when all is done, use a bottle of intake medic and lucas in the tank. i usually go with stp black bottle, but i'm leaning towards liking lucas more. i wouldn't take it apart untill you can prove something internal is wrong. it's only an engine. if it can run normally, it can run well. if internals are needed, you will know. anything internal, is going to make noise. alls it is imo, is and dirty. removing the heads will yeild nothing unless you know what your looking for. but, if it's not making noise, it's not internal. a p anything code is fuel and emissions, but if not fixed, will result in a tow, the hesitation you get tells me that your computer has backed off the timing. it will continue to remove timing untill it removes all it can. if still allowed to run, that is when you need ama cause you won't have the money fo the tow.... damn murphy.

[safaried]

Since my last post I've changed the coil and ignition module. No changes, still misfires. So, I took it to the GM garage and had them run a diagnostic on it. They told me injectors for cylinder 3, 4 and 5 are bad and need replaced. They also said my O2 sensor tested a little under spec but shouldn't need changed right away. I'm checking out parts for it. I haven't taken the plenum off yet so I'm not sure what injectors I actually need. The mechanic said it's not a fuel spider but checking around I see 2 different types of injectors?? One seems to have a supply line attached while the other looks like an inline type with o-rings on either end.

Oh on another note, thanks cowboydan, we were also having problems with the van starting on very wet humid days. At least it seemed to happen most often then.

Thanks much