89 C4 mystery misfire/stumble
06-06-2016, 01:19 PM
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89 C4 mystery misfire/stumble
Hi. Hope someone has experience with this problem.
1989 C4 coupe with auto.
Problem: misfire at idle and under load. Intermittently clears for a few seconds then back to misfire.
Replaced:
1989 C4 coupe with auto.
Problem: misfire at idle and under load. Intermittently clears for a few seconds then back to misfire.
Replaced:
- New injectors (from Fuel Injection Connection, stock size)
- " plugs
- " wires
- " fuel filter
- " distributor cap, rotor and module
- " intake manifold gasket (leaking china wall)
- Timing set at 6 degrees BTDC
- Fuel pressure check (40 #) Gauge bled down to zero after 10 min. Clamped return line, slowed pressure loss, clamped both return and feed lines, still bled down slowly. Might be that I used locking pliers to clamp off lines and pressure bypassing these.
- Checked fuel pressure at WOT during test drive and all was good. Pressure stayed at between 38 and 44 pounds.
- Injectors firing (noid light check)
- Cleaned MAF
- Vacuum test with propane
- Compression test (all cylinders good and close together readings)
06-06-2016, 03:02 PM
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06-06-2016, 03:26 PM
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St. Jude Donor '05
May or may not have a leaker have you pulled the line off the fuel pressure regulator to see whats going on there?
06-06-2016, 03:46 PM
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Yes. I disconnected the vacuum line from the pressure regulator while the car was running and the fuel pressure went up. I believe this means the diaphragm in the regulator is OK?
06-07-2016, 01:24 AM
#6
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06-07-2016, 07:33 AM
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Do you think the culprit might be the pickup coil in the distributor. It is the one thing I haven't changed yet. A PIA to change (remove and disassemble distributor to get to). Could the pickup coil cause a misfire or will the car not run at all with a bad one? The misfire does clear for a few seconds intermittently too.
06-07-2016, 02:19 PM
#8
How old is your o2 they get old and slow.
06-07-2016, 02:34 PM
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[QUOTE=antfarmer2;1592373266]How old is your o2 they get old and slow.[/QUOTE
I have only had the car since late last fall, so has sat over winter. The PO said he had done oil changes only. No maintenance or parts replaced for his five years of ownership.
Maybe I should replace the o2 just to be certain.
I have only had the car since late last fall, so has sat over winter. The PO said he had done oil changes only. No maintenance or parts replaced for his five years of ownership.
Maybe I should replace the o2 just to be certain.
06-07-2016, 02:50 PM
#10
[QUOTE=Corvince;1592373378]
My 94 would stumble and fart under the hood. Never set a code. I replaced the front two never ran better. 
Keep us posted. 
How old is your o2 they get old and slow.[/QUOTE
I have only had the car since late last fall, so has sat over winter. The PO said he had done oil changes only. No maintenance or parts replaced for his five years of ownership.
Maybe I should replace the o2 just to be certain.
I have only had the car since late last fall, so has sat over winter. The PO said he had done oil changes only. No maintenance or parts replaced for his five years of ownership.
Maybe I should replace the o2 just to be certain.
Keep us posted.
06-11-2016, 02:40 PM
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[QUOTE=antfarmer2;1592373508]
I found the problem!
when I was looking under the hood while the car was running, because I didn't have a light on in the garage, I saw a bright blue spark between the right front plug wire cap and the head. When I pulled the wire off I found that the porcelain part of the plug was cracked. this plug is a giant pain to get to (air con and air pump stuff in way). I could get a socket with a swivel on it, but it seams that as it was tightened the angle of the swivel was too much and the porcelain would break. I found that if you go in through the wheel well opening at the A arm you get almost direct access to this plug.
Put in new plug and the car runs great. I guess that 9 times out of 10, solutions end up being the simple things.
Thanks to all for the input.
I found the problem!
when I was looking under the hood while the car was running, because I didn't have a light on in the garage, I saw a bright blue spark between the right front plug wire cap and the head. When I pulled the wire off I found that the porcelain part of the plug was cracked. this plug is a giant pain to get to (air con and air pump stuff in way). I could get a socket with a swivel on it, but it seams that as it was tightened the angle of the swivel was too much and the porcelain would break. I found that if you go in through the wheel well opening at the A arm you get almost direct access to this plug.
Put in new plug and the car runs great. I guess that 9 times out of 10, solutions end up being the simple things.
Thanks to all for the input.
06-11-2016, 03:05 PM
#12
good job