I've got a new to me 1998 S10 with the factory 4cylinder 2.2 engine. I bought it not running and it had been sitting for a while. The fuel pump was bad, so I replaced it with a Sparta (apparently made by Delphi) unit. That got it started. The fuel was varnished and amber, so I drained the tank and put in fresh fuel. Changed the fuel filter. The plugs that are in it are Autolites and I have the correct AC Delco plugs on the way. I replaced the spark plug wires. I replaced the two ignition coils. It was acting like an ignition problem, but I was getting spark on all four wires, albeit weak in my opinion. It will start and then buck because of a miss. OBDII says P300, general misfire. Nothing specific to one or two cylinders. Fuel pressure is 42 static without the car running. it will go down about 2 pounds per minute. So, I'm guessing leaking injector (the varnished fuel was obviously bad) or the falling pressure is caused by a bad fuel pressure regulator, but the leak down is slow. I'm assuming its not the check valve in the brand new fuel pump. Compression is good in all 4 cylinders.

Let me know if you have any ideas but mine are as follows: Injector(s) stuck; bad ICM; bad plugs, potentially defective new coil on one of the banks. I'm throwing parts at it, but if anyone has seen this before, I'd appreciate any input. I'm not sure even if the injectors leaking like they might be could be the culprit. I'm also thinking IAC valve, which I'm going to clean tonight, but that seems like a longer shot.

Thanks

 

1. Do you have a scanner with live data capability?
2. If so, can it graph parameters?
3. You should check the fuel pressure leak down at the fuel filter per the sticky before attacking the intake plenum
4. Do you have a misfire capability with your scanner and if so what are the cylinder counts?

A partial ICM failure is not likely. If you have an LED test light or scope you can look at the pulses into and out of the ICM

In the past when I have had a vehicle sit and then have varnish for fuel I have always been successful draining the fuel as you have and running a good fuel like Chevron or Sunoco and by the second tank it stops running like crap. My Blazer sat for 5 years at 105,000 miles and barely started and then ran like crap initially. I am now at 210,000, with original fuel injectors, ICM and coil.. I replaced the fuel pump with a Delphi at 110,000.

The flat spotted tires on the other hand have almost never been recoverable.


George

 

I've been working on my issues with the misfires.

It was difficult, but I got the fuel rail and injectors out. The fuel pressure regulator was bad, so I replaced that. I was just going to swap out injectors for new, but the new ones spec'd out and about 12 ohms and my old ones were 2.7 ohms. So I opted for cleaning my injectors. I got them all clean so that they worked fine. I cleaned the fuel rail and put it back together. I got some slight improvement as to how it runs, but the car still misses and will only start when it's stone cold. I got my misfire counter working and learned that cylinders three and four we're both misfiring the exact same amount. Zero misfires on one and two. I was not able to confirm or not confirm pulse to the injector wiring to those cylinders. I used my LED test light and it looked like they were going to ground (the light flashed while cranking), but given the fact that the only thing I see that cylinders three and four have in common is the computer, I'm thinking it must be a bad computer. I put the timing light on the spark plug wires for each of the plugs and they all seem to be consistently firing. I'm thinking it's a fuel / computer injector firing issue. I've seen two posts on the internet where people have had the similar p0300 code and it turned out to be a bad computer. I hope that's what it is because I don't know what else it could be. I suppose the crank sensor or the cam sensor could be bad in some way, but you would think it would throw a crank cam sensor code and the only code it throws is the p0300.

I've replaced the plugs and wires and cleaned the iac and throttle body. Exhaust is not plugged. Intake is not plugged. I also pulled off the timing cover because this vehicle has no timing marks to check, and learned that the timing is dead on and that there is no slop in the chain.

Any thoughts?

 

The engine computer can go bad but its rare. I have seen many replaced but that is seldom the problem. I would save that for last. Let break down your update:

1. You need to verify your fuel system repair and measure the ten minute leak down. What is it cold and what is it when the motor heats up and starts running like crap? This subject ain't over till it's over. "You'll know where your going when you get there". lol.
2. Those two cylinders have physical proximity to each other. What were the results of your compression test? Warm or cold engine? We can consider a dynamic compression test which can find more problems. Could be head gasket, valves, leaks. What do the plugs look like?
3. What do your fuel trim numbers look like. Cold and running good and then when it start running crappy? Weak fuel pressure or starved injectors will go lean. Flooding or lack of detonation will go rich.
4. Can you graph O2 sensors?
5. Have you measured CMP retard yet?
6. If there are fuel injector control problems then that can be many things besides the engine computer.:

• Power/wiring issues to the injectors
• The injectors themselves
• The ground side wiring back to the engine computer
• Finally the engine computer itself

How uniform were your injector coil resistance values?

The problem with the parts cannon is not only expense but you are often replacing the highest quality AC Delco components with reman's or inferior after market parts. As vehicles get older, the cause becomes increasingly wiring, relays, etc.

The way the injector circuit works is that fused power comes to the injectors on the pink power wires and then goes through the injector coil and the computer provides ground side switching with transistors. The best test is to insert a noid light for the injector because that loads the circuit which is key for wiring issues and demonstrates ground side switching, all without overloading the computer and bricking it. We can get creative and do the test without the noid light but we need to prove:

1. Adequate power on the pink wires under a load
2. Uniform injector coil resistance (what are they when the truck craps out?
3. Good ground side wiring back to the computer
4. Lastly, engine computer control

Can you be more specific on how you did this test? If any of the results were suspect do they line up with the misfiring cylinders?

Be careful with confirmation bias, it destroys successful problem solving. I spent my entire career solving technical problems, its a skill you have to develop.

George

 

The fuel pressure held with the new regulator.
All of the injectors were 2.7 ohms. All the pintles opened with applied voltage.
I put in the correct AC Delco plugs.
Compression was good on all cylinders. All the old plugs looked like they were running rich. All similar. Thought that could be fuel being sucked into intake by the bad diaphragm on the fuel regulator.
I tested the continuity of the 4 ground switching wires for the injectors at the connector going into the fuel rail wiring. These correspond to ECU connector pins 75 and 76 on the blue and black connectors. I might be able to get to the connectors on injectors 1 and 4, but access is tight. I won't be able to get to 2 or 3 I tested the grounds with a digital test light (led) while cranking and observed the led going off and on indicating the injectors were going to ground. I figure that is essentially a noid light in a different form.
I have not tested the hot pink wire under load. I figured it's running at least two of the injectors just fine.
I banged the computer while running and it affected how the truck ran. It kicked and spat. It kept running once. Once the engine died. It won't restart after the engine heats to a certain point.
I'm nowhere near having it run well enough to see a closed loop or fuel trims.
Cylinder 1 timing (advance), measured by Dashcommand is jumping all over the place.
No other DTCs.

 

Not entirely sure what fixed it, but I did some soldering on the connectors inside of the computer, specifically those affecting pins 75 and 76 on the blue and black connector. I did this figuring it was crap anyway I wasn't going to hurt it.

That didn't seem to resolve anything. Then I got concerned that perhaps I had transposed plug wires on cylinders three and four. I used a multi meter to confirm which wire was which down at the coil and at the plug and couldn't get any sort of ohms reading on plug wire 4. I put back on the old plug wire to 4 and it showed remarked improvement in the miss. Oddly, wire for cylinder 2 was dead, but 3 was good. Replacing the wire for Cylinder 2 solved all misfires. Truck is running normally with normal power. The timing advance normalized and does not jump all over the place. Short term fuel trim is like 3, so that's good.

Moral of the story is not buying parts out of advanced Auto unless you're buying expensive ones. They even refused to take them back. I'm pretty aggravated with Advance as I spent a lot of time in the Texas heat working on this vehicle. only to be led astray by brand new parts. My timing light showed that the wires were definitely working when I installed them, but, but running them must have been too much . In the end, I reach the following conclusion: If it were just plug wires, the vehicle would have run fine with the old ones since it is now running fine with the old wires installed. So, there must have been a second or possibly third issue with the injectors and/or the computer. A couple of the injectors were pretty plugged and that was a definite problem. Banging on the computer showed some change and that makes me think it was a likely culprit too. I think it refusing to start after it was warmed up indicates an expanding cold solder joint in the computer. I'll never know, but I'm suspecting that those two things were both a problem and that the bad brand new wires were just making it impossible to diagnose.

 

Its a rule here to only use AC Delco/Delphi for ignition parts and fuel pumps. Its almost never the engine computer.

Glad your fixed up.

George