C4 miss fire
Thread Starter
Intermediate
Joined: Feb 2014
Posts: 29
Likes: 0
C4 miss fire
Start car and it runs and drives fine, but when it reaches normal temp and I accelerate from stop it pops and bangs out the intake ,Come off throttle and gently accelerate and it's fine. Or if I'm on motorway doing say 60 mph it's fine come off throttle then try and accelerate it pops and bangs. Change down a gear on the automatic and ok. It seems if revs are high it's ok.
Opti is new, I have changed cap rotor,plugs ,plug leads. No difference ! Any ideas anyone? This is a 1992 Lt1
Opti is new, I have changed cap rotor,plugs ,plug leads. No difference ! Any ideas anyone? This is a 1992 Lt1
Race Director
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From: Compound in the Grove, Ga.
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Well if you changed the opti you changed all you can as far as cap & rotor. First I would go back and check the plug wires to be sure you did not cross one. If all is good you may want to check the injectors. run a compression check, check for codes.
Drifting
Joined: Mar 2012
Posts: 1,492
Likes: 61
From: New Jersey
All good suggestions - if you don't already have the FSM (factory service manual) get one. Use the method in post #18 of this thread -http://forums.corvetteforum.com/c4-general-discussion/2647036-the-ultimate-c4-diy-thread-write-ups-w-pics.html and pull the codes if any.
Until you use the FSM diagnostic charts do the following as said before -
check fuel pressure at and after warm-up
check spark plug wires for arcing
check opti harness connections for corrosion
how many miles - have the oxygen sensors ever been changed
have you checked out the fuel injectors themselves and are they original
check icm and coil
Until you use the FSM diagnostic charts do the following as said before -
check fuel pressure at and after warm-up
check spark plug wires for arcing
check opti harness connections for corrosion
how many miles - have the oxygen sensors ever been changed
have you checked out the fuel injectors themselves and are they original
check icm and coil
Thread Starter
Intermediate
Joined: Feb 2014
Posts: 29
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Hi, thanks for reply. I have now tryed a new coil ,removed icm and put heat sink on mount. Stil no better. I'm thinking poss faulty opti, but don't want to buy one till I'm 100% ,that's the prob. Anyone know how to test it in situ?
Safety Car
Joined: Aug 2009
Posts: 3,751
Likes: 275
From: Melbourne, Victoria, Australia
Have you checked the throttle position sensor is good? that is one of the main sensors the ecm uses to calculate fuel delivery.
I am not sure on the TPS voltage setting for your model, however i am sure someone will let you know.
Also seeing you have the dreaded optispark, ignition module issues of retarded ignition can give you back fire problems.
I am not sure on the TPS voltage setting for your model, however i am sure someone will let you know.
Also seeing you have the dreaded optispark, ignition module issues of retarded ignition can give you back fire problems.
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Pro
Joined: Jan 2009
Posts: 686
Likes: 4
From: Austin Texas
Start car and it runs and drives fine, but when it reaches normal temp and I accelerate from stop it pops and bangs out the intake ,Come off throttle and gently accelerate and it's fine. Or if I'm on motorway doing say 60 mph it's fine come off throttle then try and accelerate it pops and bangs. Change down a gear on the automatic and ok. It seems if revs are high it's ok.
Opti is new, I have changed cap rotor,plugs ,plug leads. No difference ! Any ideas anyone? This is a 1992 Lt1
Opti is new, I have changed cap rotor,plugs ,plug leads. No difference ! Any ideas anyone? This is a 1992 Lt1
Drifting
Joined: May 2012
Posts: 1,623
Likes: 51
From: Gastonia North Carolina
Order yourself a new or rebuilt set of injectors from John at FIC. Replace the old injectors and I bet your running smooth as ever again.
Make sure the FP is to specification first and if it is, I will bet you a dollar there is one, two, and maybe all your injectors are clogged and not operating correctly.
Keep us posted.
Make sure the FP is to specification first and if it is, I will bet you a dollar there is one, two, and maybe all your injectors are clogged and not operating correctly.
Keep us posted.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Start car and it runs and drives fine, but when it reaches normal temp and I accelerate from stop it pops and bangs out the intake ,Come off throttle and gently accelerate and it's fine. Or if I'm on motorway doing say 60 mph it's fine come off throttle then try and accelerate it pops and bangs. Change down a gear on the automatic and ok. It seems if revs are high it's ok.
Opti is new, I have changed cap rotor,plugs ,plug leads. No difference ! Any ideas anyone? This is a 1992 Lt1
Opti is new, I have changed cap rotor,plugs ,plug leads. No difference ! Any ideas anyone? This is a 1992 Lt1
When you replaced the opti, did anything change with the new replacement or is it the same problem.
What kind of opti did you use and what did you pay for it. (not to be nosey). Some of the cheep opti's have had problems in the price range under $200.
My first impression is the symptoms do sound like an opti.
Thread Starter
Intermediate
Joined: Feb 2014
Posts: 29
Likes: 0
I bought the car from a guy that got ill and didnt finish putting back together. Water pump was off and a new ac delco pump and ac delco opti was with the car unfitted. They were bought in 2006. I fitted them a month ago and always had the problem. Car had stood since 2005.the rotor arm fell to bits a couple of weeks ago so I have fitted new cap and rotor. So I'm thinking was this a faulty unit?
Pro
Joined: Jan 2009
Posts: 686
Likes: 4
From: Austin Texas
yes, TPS and MAP. Symptoms section begins in FSM page 6E3-B-5
Drifting
Joined: May 2012
Posts: 1,623
Likes: 51
From: Gastonia North Carolina