Misfire From Hell
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From: Indianapolis
Got my new ignition control module in. Applied the new thermal paste. Car doesn't stall anymore so that's good.
But it still idles a little weird like it wants to stall. It bogs down a bit now to where it almost stalls then catches it's breath. Turned off the engine and unplugged the ESC module on the passenger side but the engine ran just the same. I think that means the ESC is good? So at this point I've replaced EVERYTHING ignition related. It runs great until it warms up then everything falls on it's face. Unplugging EST wire and starting engine it'll idle great all day long.
I guess at this point I just need to wait for my cable to see what the £!*k is going on.
But it still idles a little weird like it wants to stall. It bogs down a bit now to where it almost stalls then catches it's breath. Turned off the engine and unplugged the ESC module on the passenger side but the engine ran just the same. I think that means the ESC is good? So at this point I've replaced EVERYTHING ignition related. It runs great until it warms up then everything falls on it's face. Unplugging EST wire and starting engine it'll idle great all day long.
I guess at this point I just need to wait for my cable to see what the £!*k is going on.
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Joined: Apr 2000
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From: Texas
Got my new ignition control module in. Applied the new thermal paste. Car doesn't stall anymore so that's good.
But it still idles a little weird like it wants to stall. It bogs down a bit now to where it almost stalls then catches it's breath. Turned off the engine and unplugged the ESC module on the passenger side but the engine ran just the same. I think that means the ESC is good? So at this point I've replaced EVERYTHING ignition related. It runs great until it warms up then everything falls on it's face. Unplugging EST wire and starting engine it'll idle great all day long.
I guess at this point I just need to wait for my cable to see what the £!*k is going on.
But it still idles a little weird like it wants to stall. It bogs down a bit now to where it almost stalls then catches it's breath. Turned off the engine and unplugged the ESC module on the passenger side but the engine ran just the same. I think that means the ESC is good? So at this point I've replaced EVERYTHING ignition related. It runs great until it warms up then everything falls on it's face. Unplugging EST wire and starting engine it'll idle great all day long.
I guess at this point I just need to wait for my cable to see what the £!*k is going on.
- TPS sensor not adjusted properly
- Minimum idle air incorrectly set
- IAC valve out of range
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From: Indianapolis
What does IAC valve out of range mean?
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From: Texas
When you look at the IAC counts with a scanner while at idle you'll see a number. Going from memory, the IAC counts at idle are something like 20 or 30. Get to far outside of that and it's....out of range. When the IAC is to far out of range, it can't adjust the idle properly.
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From: Indianapolis
Checked timing chain
So since this thread is starting to have a theme with the Electronic Spark Timing, I thought I would test the timing chain slop until my ALDL cable arrives. Using the breaker bar method in conjunction with watching the rotor button move I rotated the engine until it was dead on 0 and made sure that there was no slop on that side of the timing chain. I then went the other way and rotated until I saw the button begin to move. It was anywhere between 3 and 4 degrees on the timing tab. I did this test multiple times to validate. I read on another thread that anywhere from 6 degrees and on is too much slop and could mess with the timing. Also read that the distributor gear could add an additional 1 or 2 degrees extra slop. I would say that my timing chain isn't the issue based on this test. That's good news and I kind of thought that before checking due to it holding base idle at 6 degrees without wavering with the EST bypassed. But I wanted to be sure.
Drifting
Joined: Jul 2022
Posts: 1,805
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From: Central Florida
This is kind of unscientific but, put the timing light on it with the timing wire CONNECTED. It should be under the water pump about an inch above the timing tab at appx 1:30 (clock) position. It also bounces around a tiny bit. Unscientific but it should be in the ballpark of 30° advanced at idle.
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Last edited by Vets-Vet; Apr 6, 2024 at 07:55 AM.
Thread Starter
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Joined: Jun 2022
Posts: 57
Likes: 19
From: Indianapolis
This is kind of unscientific but, put the timing light on it with the timing wire CONNECTED. It should be under the water pump about an inch above the timing tab at appx 1:30 (clock) position. It also bounces around a tiny bit. Unscientific but it should be in the ballpark of 30° advanced at idle.
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Right now it's hanging around 12-15 degrees after warmup. That brings me full circle right back around to the closed loop misfire. I think the misfire isn't allowing the timing to advance more than a few degrees. It does advance when you rev the engine and it still runs a tad rich. Thinking that maybe the misfire is causing a knock signal I depinned the brown ground pin on the ESC module (bypassing the knock sensor; the computer still sees the sensor but it doesn't send a knock signal) It's a trick I found on these forums. No change to anything. So I reinserted the ground pin. That would eliminate the knock sensor causing it to only allow timing to advance to 15 degrees at idle.
My cable should be here on May 9th.
Using my timing light I'm getting a steady flash on all sparkplug leads with and without the EST bypassed.
I'm going to try to advance the timing with the brown wire bypassed to where the EST is supposed to have it. Checking to see if it misfires by manually advancing it. If it does then that could eliminate the EST circuit as the cause for the misfire.
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Joined: Jun 2022
Posts: 57
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From: Indianapolis
Right now it's hanging around 12-15 degrees after warmup. That brings me full circle right back around to the closed loop misfire. I think the misfire isn't allowing the timing to advance more than a few degrees. It does advance when you rev the engine and it still runs a tad rich. Thinking that maybe the misfire is causing a knock signal I depinned the brown ground pin on the ESC module (bypassing the knock sensor; the computer still sees the sensor but it doesn't send a knock signal) It's a trick I found on these forums. No change to anything. So I reinserted the ground pin. That would eliminate the knock sensor causing it to only allow timing to advance to 15 degrees at idle.
My cable should be here on May 9th.
Using my timing light I'm getting a steady flash on all sparkplug leads with and without the EST bypassed.
I'm going to try to advance the timing with the brown wire bypassed to where the EST is supposed to have it. Checking to see if it misfires by manually advancing it. If it does then that could eliminate the EST circuit as the cause for the misfire.
My cable should be here on May 9th.
Using my timing light I'm getting a steady flash on all sparkplug leads with and without the EST bypassed.
I'm going to try to advance the timing with the brown wire bypassed to where the EST is supposed to have it. Checking to see if it misfires by manually advancing it. If it does then that could eliminate the EST circuit as the cause for the misfire.
Cold:1. 165, 2. 170, 3. 165, 4. 166, 5. 165, 6. 165, 7. 163, 8. 170
Hot:
1. 166, 2. 171, 3. 167, 4. 167, 5. 166, 6. 167, 7. 165, 8. 171
These look pretty good to me. All within range. Would this indicate that nothing in the cylinder is contributing to the miss?
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Drifting
Joined: Jul 2022
Posts: 1,805
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From: Central Florida
Can't wait to see O2 sensor readings. What part number was used ?? was the car this way at time of purchase ?? Have you checked for supplied voltage at the O2 sensor.
And you have re affirmed several times the car can idle all day with the EST wire disconnected right ??
And you have re affirmed several times the car can idle all day with the EST wire disconnected right ??
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Joined: Jun 2022
Posts: 57
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From: Indianapolis
Can't wait to see O2 sensor readings. What part number was used ?? was the car this way at time of purchase ?? Have you checked for supplied voltage at the O2 sensor.
And you have re affirmed several times the car can idle all day with the EST wire disconnected right ??
And you have re affirmed several times the car can idle all day with the EST wire disconnected right ??
But, It had compression and a clean title. I paid 800 dollars for it and got to work. Took everything that wasn't in the block off and cleaned it, gave it new gaskets, valve seals. (Thus the parts cannon). Paid way to much for a brand new transmission with a 3 year 150000 warranty.
The clear coat and previous respray had failed. Spent months sanding it smooth and getting it ready for paint. Right now it's just in primer and sealer. I'd like to finish it but I'm stuck on, this misfire.
At this point I could have just put the money I had already put into it for an actual proper running good looking C4. But here we are. I have a thread on here somewhere about the project.
Edit: The pictures are clearly out of order.
Last edited by LarryBoyG; Apr 6, 2024 at 04:48 PM.
Drifting
Joined: Jul 2022
Posts: 1,805
Likes: 365
From: Central Florida
Don't feel bad. My car had nice paint, a great interior and good tires and was basically stock and I have over 12K in mine. The decision point to stop is difficult because after a certain amount of time and money I felt stuck. You are not alone.
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From: Indianapolis
I feel like it's close to being drivable minus the misfire and primer paint job haha. Some of the smaller items I still need to tackle. U-joints and rear hub assemblies are a couple I can think of.
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From: Indianapolis
I ran the datalog and from what I could see the ECM, ECS and EST were running as they should. I Took the headers off for more investigation into this and I may have found the issue. There was a pinhole about the size of a pencil lead right dead center of the 4 pipes going into the collector on the exhaust side. Would a hole this small on the upstream of the O2 contribute to a rich air fuel ratio? Also I don't know how but downstream of the O2 the inside of the exhaust somehow became seperated and was loose inside the outer layer of the exhaust. This contributed to an even bigger exhaust leak that I could imagine and was probably the reason I was hearing all that popping noise I posted in a video at the beginning. I am searching for a new set of headers and a down pipe to see if that ultimately fixes my issue.
I thought the popping noise was a misfire could it have been an exhaust leak this whole time?My question is why would the popping noise go away when the EST was unplugged. Could it have been messing with the timing?
I thought the popping noise was a misfire could it have been an exhaust leak this whole time?My question is why would the popping noise go away when the EST was unplugged. Could it have been messing with the timing?
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From: Indianapolis
It has an x-pipe where the cat used to be. 85 was the year it had a single large cat in the center. It has a full Pypes racepro exhaust from the front Y pipe back to the tips. It is clamped on about a foot past the O2 sensor on the downpipes. The headers and downpipes are original. Yesterday I took the headers and downpipes off and saw that the downpipe was cracked about 5 inches downstream of the O2 sensor and the headers had a pinhole in the collector. Can't really see it unless you hold it up to a light.
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From: Texas
I ran the datalog and from what I could see the ECM, ECS and EST were running as they should. I Took the headers off for more investigation into this and I may have found the issue. There was a pinhole about the size of a pencil lead right dead center of the 4 pipes going into the collector on the exhaust side. Would a hole this small on the upstream of the O2 contribute to a rich air fuel ratio? Also I don't know how but downstream of the O2 the inside of the exhaust somehow became seperated and was loose inside the outer layer of the exhaust. This contributed to an even bigger exhaust leak that I could imagine and was probably the reason I was hearing all that popping noise I posted in a video at the beginning. I am searching for a new set of headers and a down pipe to see if that ultimately fixes my issue.
I thought the popping noise was a misfire could it have been an exhaust leak this whole time?My question is why would the popping noise go away when the EST was unplugged. Could it have been messing with the timing?
I thought the popping noise was a misfire could it have been an exhaust leak this whole time?My question is why would the popping noise go away when the EST was unplugged. Could it have been messing with the timing?