car runs rough when it gets up to operating temp

They said it could be the #4 injector possibly or the piston ring or something.

Not sure what to do.

I would pull that plug and wire and check them. Could have gotten a bad plug or damaged the wire on install (ive done it before...twice)
Could also be, as they said, they injector on #4 has gone bad.
Did they tell you what the codes were on the computer?

Nope, they said no codes but there was a misfire.

Is there a way to ohm out the injector?

I checked the cylinder numbers and the ign. wires for 3 and 6 were swapped.

I originally copied the original order the car was in but it was wrong to begin with.

I changed them to the correct order. It made a small difference in idle. I'm not sure, but I might have to leave the battery disconnected to let the car relearn with the correct firing order?

I checked all the injectors, they all ohmed in at 16.2, injector 5 was 17 ohms. All had 12V with ignition on.

I'm stumped. Starting to sound like a parts car.

It also has a long crank time before it starts. It has a brand new starter.

So I tested the injectors to make sure they were getting a pulse from the PCM.

All of them pulse OK. Checked with $5 test light instead of $30+ noid lights.

All the coils are giving good spark, no CEL.

Removed MAF connector, didn't change much except throwing a CEL.

So yeah. I guess the motor really is shot.

I would think that some or all of your symptoms could be a result of #3 and #6 wires being reversed. Being that 3 and 6 share a coil, the waste spark I believe to be a weaker spark could be your bucking for sure. The dealer that checked your car should have found that. As far as the compression on cylinder #4, I would check that yourself or at least have an independent shop do it without giving them a hint of the #4 cylinder problem.

bigdave wrote:

I would think that some or all of your symptoms could be a result of #3 and #6 wires being reversed.

Forgive me if I misunderstand the waste spark setup, but I believe the two cylinders on each coil both receive full power so they can't actually be reversed even if you swapped the two wires, as long as they are still both on the same coil. Please correct me if I'm wrong.

I believe that the polarity of the signal to the coil is reversed for the waste spark and it only has maybe a 1/3 of the power of the side on the compression stroke. Which being reversed may not be all that noticeable at light load, but under load would act like a weak coil or faulty plug wires. I'm not saying this will make all his issues go away, but its a start.

The coils fire companion cylinders. 1-4, 2-5, and 3-6. When one cylinder is on the compression stroke, the companion cylinder is on the exhaust stroke. If there is a difference in the spark energy, the result from swapping wires would be a weak spark to both cylinders on the compression stroke?

That is correct. My theory being that the weak sparks on 3 & 6 may not be as noticeable at low load but would act up at higher load situations.

I did swap those back to the way they should be already.

It didn't change much, but as you mentioned at higher speeds it feels smoother.

This morning, I started the car and drove it for a bit.

While it was cold, it ran fine, fairly smooth idle and acceleration.

As it started to reach 200F temp, it started idling like shit again.

I checked the coils, just secondary for now. All of them were in the 5.30 ohm range which I've read is ok.

I need to pickup a 7/32 bit to take the packs off to check the primaries, as the car "ate" yet another bit yesterday. Lol

do you have a cold air intake? mine runs kinda crappy like when she gets hot too.I just put it in neutral at the light and she quiets rite down.have you tried this?

Do you have a scanner to check datastream? Could be a coolant temp sensor. If the car is warm but the ecm thinks its cold it would be too rich to run well at idle. You still need to find the condition of the #4 cylinder also.

robotennis61 wrote:

do you have a cold air intake? mine runs kinda crappy like when she gets hot too.I just put it in neutral at the light and she quiets rite down.have you tried this?

Robo, I don't have a CAI - still stock airbox. But, what you are talking about is exactly what I do at the stoplights when it starts shaking itself (and me) to death.

The bad idle condition is still there, but it's much less noticeable when the car is in neutral.

bigdave wrote:

Do you have a scanner to check datastream? Could be a coolant temp sensor. If the car is warm but the ecm thinks its cold it would be too rich to run well at idle. You still need to find the condition of the #4 cylinder also.

Unfortunately, I don't have a OBD 1.5-compatible scanner.

That's what I paid the damn dealership $63.00 to do, but apparently they were incapable.

Yeah, as far as I know the only way to do that is to start taking the motor apart. Which is going to cost a lot of money.

edit: Wouldn't a bad temp sensor cause the temp reading on the instrument panel to be out of whack, though? Or is this a different temp sensor?

sniperdude wrote:

robotennis61 wrote:

do you have a cold air intake? mine runs kinda crappy like when she gets hot too.I just put it in neutral at the light and she quiets rite down.have you tried this?

Robo, I don't have a CAI - still stock airbox. But, what you are talking about is exactly what I do at the stoplights when it starts shaking itself (and me) to death.

The bad idle condition is still there, but it's much less noticeable when the car is in neutral.

I wish I knew why it does that? I had it diagnosed but they couldnt find anything.My OBD1.5 doesnt even read my car anymore! ithas no problem reading other cars tho.go figure.

sniperdude wrote:

edit: Wouldn't a bad temp sensor cause the temp reading on the instrument panel to be out of whack, though? Or is this a different temp sensor?

Not necessarily. Some GMs of the mid-90s had two CTS - one for the gauge and one for the computer. I had this exact problem in my '96 Chevy van - ECM CTS was bad causing it to run rich but the dash gauge read normal. I had convinced myself it was the TPS, but when I replaced that and nothing changed, I was watching the TBI literally gush fuel into the engine, and I realized it had to be the CTS... pulled it out and it was covered in old/baked dexcool coating...

That sounds very plausible. Wish I could afford the scanner to find out.

'cant remember who else has my problem,the temp gauge and dash gear not showing,but i bought a known good used dash online from instrumentclusterstore.com and my gauges still dont read.guy over there sed 98% of the time its the computer thats faulty.
looks like Im sending cluster back.

All the sensors on an engine work the same way. The PCM sends the sensor a 5 volt reference signal, and the sensor sends back a voltage to the PCM. The computer interprets that return voltage as a reading. Not sure about the ECT sensor, but the TPS has 3 wires. One would be the 5 volt reference signal, one would be ground, and one would be the return signal. You might be able to take some readings with a volt meter, and see what going on with the sensor. Measure cold, and see where the signal goes as it warms up. I know it's easy to check a TPS this way. Closed throttle is about .40 volts, WOT is about 4.5 volts. When checking a TPS, you would move the throttle slowly from closed to wide open and watch the voltage. Should increase uniformly . If it skips around, you know the TPS is bad. Maybe you could figure out how to do that with the ECT. What do you think Big Dave, and Derek?

LARRY70GS wrote:

All the sensors on an engine work the same way. The PCM sends the sensor a 5 volt reference signal, and the sensor sends back a voltage to the PCM. The computer interprets that return voltage as a reading. Not sure about the ECT sensor, but the TPS has 3 wires. One would be the 5 volt reference signal, one would be ground, and one would be the return signal. You might be able to take some readings with a volt meter, and see what going on with the sensor. Measure cold, and see where the signal goes as it warms up. I know it's easy to check a TPS this way. Closed throttle is about .40 volts, WOT is about 4.5 volts. When checking a TPS, you would move the throttle slowly from closed to wide open and watch the voltage. Should increase uniformly . If it skips around, you know the TPS is bad. Maybe you could figure out how to do that with the ECT. What do you think Big Dave, and Derek?

This would definitely work except that you don't know what value you are looking for. Plus some ECT have a one-wire setup, so it's just a resistance to ground. I'm not sure what the '95 uses though. If the PCM uses a 3 wire TCS then this would work. If it's a one-wire then you would need to test it with an ohmmeter. You'd also need someone else to give you the 'normal' value you are looking for.

Saw this older post from Eldo.

Quote :

There is just the one temperature sensor that feeds the PCM, then the PCM sends serial data to the IPC 'brain', which decodes it and actuates the gauge motor.