Misfire problem, specifically final stage issue?
02-20-2019, 06:15 PM
#1
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Misfire problem, specifically final stage issue?
hi all!
Great forum! I’ve looked around and followed loads of advice so far but now stumped but at least can articulate my question a little better (I hope).
Background - daily driver, standard 1990 C4 cab, no mods. 162000 miles. Owned for 8 years and put 65000 miles on myself.
recently experienced misfiring which quickly led to a non starter. First thing I did was replace DME relay with new, this didn’t cure problem.
investigated further and found primary distributor cap and rotor needed replacing. Also found that primary coil was corroded (green powder was falling out!) and coil lead damaged by corrrosion. Replaced both coils and both leads to caps with new.
After replacements, started first time and ran beautifully for two days on my ride to work and back (20 mile round trip).
misfiring started up again today however.
so I tried this:
disconnected lead to final stage for primary coil. Result - car starts and runs without misfire.
swapped secondary lead to final stage to primary coil. (So still only primary coil to primary distributor, secondary coil now disconnected). Result - car starts and runs without misfire.
swapped primary lead to final stage of secondary coil. Result - misfire.
so,
1. does this test confirm that there’s not a problem with the plugs?
2. Does this test confirm that there is not a problem with the leads?
3. Does this test confirm that the coils are not at fault?
4. Does this test confirm the distributors are not at fault?
5. Does this test confirm that both ignition final stages are not at fault?
my guess is that there is a problem on the primary route to the ignition final stage.
Does that that make sense?
if so, is there anything you guys could recommend I try? I really want to solve this problem myself, I feel like I’m so close!!!!
cheers all, looking forward to getting schooled and learning something!!!
Great forum! I’ve looked around and followed loads of advice so far but now stumped but at least can articulate my question a little better (I hope).
Background - daily driver, standard 1990 C4 cab, no mods. 162000 miles. Owned for 8 years and put 65000 miles on myself.
recently experienced misfiring which quickly led to a non starter. First thing I did was replace DME relay with new, this didn’t cure problem.
investigated further and found primary distributor cap and rotor needed replacing. Also found that primary coil was corroded (green powder was falling out!) and coil lead damaged by corrrosion. Replaced both coils and both leads to caps with new.
After replacements, started first time and ran beautifully for two days on my ride to work and back (20 mile round trip).
misfiring started up again today however.
so I tried this:
disconnected lead to final stage for primary coil. Result - car starts and runs without misfire.
swapped secondary lead to final stage to primary coil. (So still only primary coil to primary distributor, secondary coil now disconnected). Result - car starts and runs without misfire.
swapped primary lead to final stage of secondary coil. Result - misfire.
so,
1. does this test confirm that there’s not a problem with the plugs?
2. Does this test confirm that there is not a problem with the leads?
3. Does this test confirm that the coils are not at fault?
4. Does this test confirm the distributors are not at fault?
5. Does this test confirm that both ignition final stages are not at fault?
my guess is that there is a problem on the primary route to the ignition final stage.
Does that that make sense?
if so, is there anything you guys could recommend I try? I really want to solve this problem myself, I feel like I’m so close!!!!
cheers all, looking forward to getting schooled and learning something!!!
Last edited by David Garvin; 02-20-2019 at 06:34 PM.
02-21-2019, 06:10 AM
#2
Rennlist Member
Just a guess. There have been problems with 964 replacement coils. Even ones that test positive, can have internal faults. Some are switching to the 993 setup.
02-21-2019, 09:43 AM
#3
IHI KING!
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Location: Nashua, New Hampshire, USA
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How old are you spark plug wires? Are they originals? If so, I'm suspecting that you need to replace them. Try swapping just the coil to distributor cap leads to see if the problem moves with the wires. If it does, I would replace them.
02-21-2019, 02:50 PM
#4
Rennlist Member
My mistake. I browsed too fast and misread the issue as backfiring instead of misfire. Hopefully you find the culprit soon!
Matt
Matt
Last edited by Matteoagu; 02-21-2019 at 09:22 PM. Reason: Wrong answer