Accelertation Issue, HELP!
Thread Starter
4th Gear
Joined: Jan 2010
Posts: 4
Likes: 0
Accelertation Issue, HELP!
I know there's a ton of similar topics, but I have gone through them all but have not come to a conclusion
I have an
87 Coupe. 4+3 120,000 Daily Driver.
When accelerating, there is a miss. When cruising theres a small bumpbumpbump but usually not noticeable. But while accelerating, it really struggles and bumps. There is also an occasional pop sound by the air filter when trying to accelerate hard.
What I've checked/ done:
New SLP Air Filter
MAF Sensor Checked (tapped on, car continued to idle perfect)
New Fuel Filter
ISO HEET Dry Gas w/ FI Cleaner
Brand New tank of 93octane
Timing is Right on
New Plugs and Wires about 1000 miles ago.
New Distributor Cap and rotor about 1500 miles ago.
Clutch is pretty strong.
Full New Exhaust.
Checked for vaccum leaks but couldnt find any?
New o2 sensor
What am I missing? Any ideas?
I have an
87 Coupe. 4+3 120,000 Daily Driver.
When accelerating, there is a miss. When cruising theres a small bumpbumpbump but usually not noticeable. But while accelerating, it really struggles and bumps. There is also an occasional pop sound by the air filter when trying to accelerate hard.
What I've checked/ done:
New SLP Air Filter
MAF Sensor Checked (tapped on, car continued to idle perfect)
New Fuel Filter
ISO HEET Dry Gas w/ FI Cleaner
Brand New tank of 93octane
Timing is Right on
New Plugs and Wires about 1000 miles ago.
New Distributor Cap and rotor about 1500 miles ago.
Clutch is pretty strong.
Full New Exhaust.
Checked for vaccum leaks but couldnt find any?
New o2 sensor
What am I missing? Any ideas?
Instructor
Joined: Dec 2009
Posts: 162
Likes: 18
From: Newark ca
Just a few ideas:
knock sensor while cruising-my 90 l98 zf 6speed sometimes miss because of a false knock signal during acceleration and at a cruise (not pinging, feels like no spark) I checked with a scaner at idle had a few random counts with a smooth idle-would not explain poping/backfiring
Over advanced base timing: I know you said you checked the timing but did you check base timing in "diagnostic mode"? I am preety sure L98's timing need to be checked with out the ECM spark control active. This could explain back-firing thru intake.
Partially stuck open intake valve: If the intake valve hangs open every time that cylinder fires, it will back fire.
Just food for thought, good luck
knock sensor while cruising-my 90 l98 zf 6speed sometimes miss because of a false knock signal during acceleration and at a cruise (not pinging, feels like no spark) I checked with a scaner at idle had a few random counts with a smooth idle-would not explain poping/backfiring
Over advanced base timing: I know you said you checked the timing but did you check base timing in "diagnostic mode"? I am preety sure L98's timing need to be checked with out the ECM spark control active. This could explain back-firing thru intake.
Partially stuck open intake valve: If the intake valve hangs open every time that cylinder fires, it will back fire.
Just food for thought, good luck
Thread Starter
4th Gear
Joined: Jan 2010
Posts: 4
Likes: 0
ill look into the knock sensor. you said that yours would miss occasionally, mine is missing practically every gear throughout the tach range.
i checked the timing with the ecm spark control unplugged as according to the shop manual.
ill keep looking tomororw morning. thx for the help so far, any other ideas?
i checked the timing with the ecm spark control unplugged as according to the shop manual.
ill keep looking tomororw morning. thx for the help so far, any other ideas?
Melting Slicks
Joined: Mar 2002
Posts: 3,105
Likes: 126
From: S.L.C. UT
Double check your firing order. It is easy to get spark wires crossed especilliy #5. but double check your firing order, especially #5 and number 7.
Firing order is 18436572 turning clockwise inside your distributor cap.
If it is something different, you have found your problem, and that will solve that.
Jim Barth
Firing order is 18436572 turning clockwise inside your distributor cap.
If it is something different, you have found your problem, and that will solve that.
Jim Barth
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Every tuneup should have a compression test if being done to fix a driveability problem. You have the plugs out already it is an additional 5 minutes work and with a screw in tester a one man job. That will eliminate everything internal right off the bat and you can concentrate on codes vacuum leaks etc. Parts that can be checked should be checked before being installed new. Plug wires in particular it is just too easy to do the make sure they are within spec. I got a brand new set of AC Delco wires last year that were no good out of the box.. Checking the injectors resistance hot and cold is a good quick check and pull the codes.
Dave
Dave
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
I also think a compression check might be a good thing to do considering the problem.
I guess there is also the possibility of a weak coil and spark.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
I have a friend with a tahoe, and the knock sensor is right near where the exhaust maniforld down pipe is.
There was a slight exhaust leak at the down pipe junction at the exhaust manifold.
THe knock sensor was interpreting the slight exhaust leak as detonation on one cylinder, and retards the timing intermittantly.
we changed the header flange gasket on the engine, and tightened the exhaust manifold down pipe.
problem gone........
his engine sounded a lot like what you describe
There was a slight exhaust leak at the down pipe junction at the exhaust manifold.
THe knock sensor was interpreting the slight exhaust leak as detonation on one cylinder, and retards the timing intermittantly.
we changed the header flange gasket on the engine, and tightened the exhaust manifold down pipe.
problem gone........
his engine sounded a lot like what you describe
Last edited by coupeguy2001; Jan 6, 2010 at 11:57 PM. Reason: info
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