Strange problem on 95 Z-28, please help!
I have heard of a lot of people having this problem. It also seems like there are a alot of things that exhibit the same symptoms.
I have had a similar problem with my car and progressively gotten worse. it eventually started to throw a code for the egr system. Mine was stuck open. It also caused a vacuum leak because of a hole in the diaphragm. this is off of shboxes webpage for symptoms.
Engine stops after cold start
Engine stops at idle after deceleration
Vehicle surges during cruise
Rough idle
I haven't had a chance to start the car since I removed it. Its most likely not your issue. but food for thought.
I have had a similar problem with my car and progressively gotten worse. it eventually started to throw a code for the egr system. Mine was stuck open. It also caused a vacuum leak because of a hole in the diaphragm. this is off of shboxes webpage for symptoms.
Engine stops after cold start
Engine stops at idle after deceleration
Vehicle surges during cruise
Rough idle
I haven't had a chance to start the car since I removed it. Its most likely not your issue. but food for thought.
Thread Starter
TECH Regular
Joined: Dec 2005
Posts: 444
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From: Kailua-Kona, HI
So I finally got around to changing the ignition switch, and the same problem persists. Doesn't want to fire (cold start-up) while cranking, takes about 5-8 key cranks to finally get it running. For some reason as its turning over, it doesn't really seem like it wants to fire, but after letting off on the starter, it fires like pre-ignition. After the first start-up, it fires right up everytime.
So now its on to the next possible cause.
I'm thinking I should change out my ICM just in case the one from my Tran's Am is no good. The T/A hasnt ran for 2 years so it could be bad.
After that I'm leaning towards the OPTI. Loose rotor seems like it could be the issue like SS RRR said.
You can do live data on OBD 1 scan tools right?
So now its on to the next possible cause.
I'm thinking I should change out my ICM just in case the one from my Tran's Am is no good. The T/A hasnt ran for 2 years so it could be bad.
After that I'm leaning towards the OPTI. Loose rotor seems like it could be the issue like SS RRR said.
You can do live data on OBD 1 scan tools right?
Teching In
Joined: May 2012
Posts: 7
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From: Portsmouth, Va
So I finally got around to changing the ignition switch, and the same problem persists. Doesn't want to fire (cold start-up) while cranking, takes about 5-8 key cranks to finally get it running. For some reason as its turning over, it doesn't really seem like it wants to fire, but after letting off on the starter, it fires like pre-ignition. After the first start-up, it fires right up everytime.
So now its on to the next possible cause.
I'm thinking I should change out my ICM just in case the one from my Tran's Am is no good. The T/A hasnt ran for 2 years so it could be bad.
After that I'm leaning towards the OPTI. Loose rotor seems like it could be the issue like SS RRR said.
You can do live data on OBD 1 scan tools right?
So now its on to the next possible cause.
I'm thinking I should change out my ICM just in case the one from my Tran's Am is no good. The T/A hasnt ran for 2 years so it could be bad.
After that I'm leaning towards the OPTI. Loose rotor seems like it could be the issue like SS RRR said.
You can do live data on OBD 1 scan tools right?
TECH Fanatic
Joined: Oct 2006
Posts: 1,106
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From: POULSBO WA.
Check fuel pressure when u turn on key when it is cold...at the prime cycle, before u turn key to start. Mine turned out to be faulty pump relay behind drv kick panel. Took me several tries to start, till i changed mine out...use AC DELCO parts.
Teching In
Joined: May 2012
Posts: 7
Likes: 0
From: Portsmouth, Va
With a test light on the fuel pump connector near fuel tank check to see if when key is turned to on position (not start) the test light should light up for a few seconds. If it lights fuel pump relay is good and pcm is sending initial power to prime fuel pump. The next thing I would check would be the opti. Shbox is an awesome website and help you check for correct opti signals.
Thread Starter
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Joined: Dec 2005
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From: Kailua-Kona, HI
Guys, I checked the fueld pressure AGAIN last night when I finished up the ignition switch. The values are good. It reads 39psi on the prime, about 40 at idle, and 47 at WOT.
So are you guys saying I need to test the pressure while cranking it?
So are you guys saying I need to test the pressure while cranking it?
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Verdad Gallardo Thread Starter
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Joined: Dec 2005
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From: Kailua-Kona, HI
I came to a conclusion over the weekend about this issue I am having, it ONLY occurs when the car is completely COLD. (the cold start issue I am now having, not the miss/stumble).
As much as I want to agree with a few of the people on here about the loose OPTI rotor, I dont see how the temperature of the motor would have any effect on that. If the rotor was loose, it would be loose regardless of the temperature of the block, right? Unless its another electrical component inside the OPTI?
I also want to correct my previous decription of the issue. It does not take 5-6 cranks (separate turns of the key to the starting position), its more like 10-12. While cranking it over I am playing with the throttle, and its not until the 7th or 8th crank over that the car seems like it might start. Once its started, it runs fine, and after it is warm, I dont have to play with the throttle or anything to start it, I can just reach in with one hand and fire it up. It still seems like the car has no spark while I am cranking over initially, and when I am cranking it, it tries to fire after the starter has dis-engaged. Eventually, after 8 or 9 tries, it will fire right up, and proceed to a high idle to warm up just like normal.
Over the weekend I changed out the water temp sensor in the water pump, and the air intake elbow. I changed the intake elbow because I was thinking I might have a vaccum leak based on the condition of the old rubber one.
What Gives?
What are some common issues that could cause this during a Cold start-up?
Maybe I need to adjust my TPS? Maybe the O2 sensors I put on are no good?
I'm getting annoyed. Please help.
As much as I want to agree with a few of the people on here about the loose OPTI rotor, I dont see how the temperature of the motor would have any effect on that. If the rotor was loose, it would be loose regardless of the temperature of the block, right? Unless its another electrical component inside the OPTI?
I also want to correct my previous decription of the issue. It does not take 5-6 cranks (separate turns of the key to the starting position), its more like 10-12. While cranking it over I am playing with the throttle, and its not until the 7th or 8th crank over that the car seems like it might start. Once its started, it runs fine, and after it is warm, I dont have to play with the throttle or anything to start it, I can just reach in with one hand and fire it up. It still seems like the car has no spark while I am cranking over initially, and when I am cranking it, it tries to fire after the starter has dis-engaged. Eventually, after 8 or 9 tries, it will fire right up, and proceed to a high idle to warm up just like normal.
Over the weekend I changed out the water temp sensor in the water pump, and the air intake elbow. I changed the intake elbow because I was thinking I might have a vaccum leak based on the condition of the old rubber one.
What Gives?
What are some common issues that could cause this during a Cold start-up?
Maybe I need to adjust my TPS? Maybe the O2 sensors I put on are no good?
I'm getting annoyed. Please help.
Keep in mind that just because you aren't getting a code 16 in the PCM doesn't mean that the Opti isn't on its way out. Ignition troubles at a certain RPM, under load or intermittent otherwise 90% of the time indicate failure or impending doom of the Optispark in these cars. I see it time and time again on these forums. Code 16 will set when the computer doesn't get a pulse after x revolutions of the motor and when the coolant temperature is at a certain value and a few other conditions are satisfied.
What I am trying to say is, I think you are giving the Optispark more credit than it deserves by replacing all other parts and troubleshooting everything outside of the Optispark.
I too had a similar problem, and completely different problems at other points in time and every incident I had that seemed remotely ignition related was the Optispark. I didn't want to accept it because 1) It is expensive and 2) It is a crappy job to replace. I know it sucks, but I think you are going to be far more pleased with the results once you just replace the Optispark.
Not to mention you have troubleshot fuel and air at this point. Fuel PSI looks great for the given conditions. O2's will just make it run like garbage in the worst of situations but certainly will not cause a misfire, stumble or no start condition. TPS can be easily verified with a scan tool, but I personally think you are best of replacing the Opti with a brand new ACDelco job.
What I am trying to say is, I think you are giving the Optispark more credit than it deserves by replacing all other parts and troubleshooting everything outside of the Optispark.
I too had a similar problem, and completely different problems at other points in time and every incident I had that seemed remotely ignition related was the Optispark. I didn't want to accept it because 1) It is expensive and 2) It is a crappy job to replace. I know it sucks, but I think you are going to be far more pleased with the results once you just replace the Optispark.
Not to mention you have troubleshot fuel and air at this point. Fuel PSI looks great for the given conditions. O2's will just make it run like garbage in the worst of situations but certainly will not cause a misfire, stumble or no start condition. TPS can be easily verified with a scan tool, but I personally think you are best of replacing the Opti with a brand new ACDelco job.
It could be the optical sensor itself. Maybe there's oil down in there and it's getting on the sensor. Cranking the engine could be throwing the oil out to the sides when the opti spins and eventually letting it fire. Maybe some friction heat and electrical pulses are dissipating the oil to a mist.
Also, just some food for thought, when my Opti died a couple of months ago, it liked to do the thing where it would try to fire when you let off the key.
Also, just some food for thought, when my Opti died a couple of months ago, it liked to do the thing where it would try to fire when you let off the key.
It's either one of two things you have already mentioned....the ICM or the opti of course. Did you ever try swapping the ICM out with a known good one? I would do that as it is much cheaper/easier than replacing the opti. If that's not the cause, then it's almost certainly the opti.
Thread Starter
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From: Kailua-Kona, HI
It's either one of two things you have already mentioned....the ICM or the opti of course. Did you ever try swapping the ICM out with a known good one? I would do that as it is much cheaper/easier than replacing the opti. If that's not the cause, then it's almost certainly the opti.
The missing / stumbling issue still persisted after i swapped the ICM out, but that was also the first time that the car had this cold start issue also. I had no problems with a cold start until I replaced the Coil and ICM from my other car.
I suppose I could swap it back over and see if that cures it. If it doesn't, its OPTI time.
My friend has a brand new MSD OPTI he will sell for for $300, and I don't have to order it, so I'm leaning towards that.
Thread Starter
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From: Kailua-Kona, HI
So I went ahead and threw the old ICM back in just to see if the results would be the same, and yes, the problem still persists.
I just had to be sure because the first day it started doing this and my girl got stranded, I had swapped the ICM and coil out the night before.
Just found out that my friend with the MSD has the 92-94 application part so I'll just go with the AC unit and call it a day.
Musta been the fresh coil that just finally ended the OPTI's life as it was already on its way out, just like someone posted earlier.
Will keep you guys posted.
I just had to be sure because the first day it started doing this and my girl got stranded, I had swapped the ICM and coil out the night before.
Just found out that my friend with the MSD has the 92-94 application part so I'll just go with the AC unit and call it a day.
Musta been the fresh coil that just finally ended the OPTI's life as it was already on its way out, just like someone posted earlier.
Will keep you guys posted.
Thread Starter
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From: Kailua-Kona, HI
Its weird.
And yes, I am aware these issues may be separate.
Does the car ever just completley die while you are driving it. I had a similar problem to what you are saying where the car would run rough once it warmed up but it would cut out randomly. It ended up being the water pump was going bad and the water from the radiator was dripping onto the opti just enough to build up moisture in there. My car was a 93 though so the opti was not vented I believe 95 is vented though. But if you end up changing the opti double check the pump for signs rust or anti freeze around the weep hole.