88 IROCZ28 Stumbling/[email protected] Throttle

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  #1  
Old 10-26-06, 04:35 PM
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88 IROCZ28 Stumbling/[email protected] Throttle

I have an 88 IROCZ28 that having some issues. It has a new engine in it and it has been running excellent till this started. It runs great at anything more then partial throttle. If it's barely cracked open or you slightly accelerate it stumbles/backfires and or surges. I've replaced Plug wires, distributor cap and rotor, fuel pump, fuel pressure regulator, coil. I even regapped all the spark plugs. Any ideas?.
 
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  #2  
Old 10-26-06, 04:47 PM
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I would check the rocker arm adjusment and make sure none of the valve springs or broken.
 
  #3  
Old 10-26-06, 04:48 PM
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stumbling IROC

You haven't told enough, but from what you have said, there are a number of obvious possibilities. Vacuum leak, failure of timing advance (which could be due to a vacuum leak.) Less likely, but possible, is slipped timing belt -- usually a slipped timing belt makes a huge difference, the engine wont run at all, but in some engines a timing chain or belt can slip one cog, and the engine will run, but barely.
Easiest thing to do is to check timing, and make sure advance is working -- for vacuum leaks, a small leak will be temporarily plugged by a spray of water (use a pant mister) -- another trick is to spray a bit of brake cleaner, with a vacuum leak , the cleaner will get scked into the intake and immediately produce clouds of exhaust smoke.
 
  #4  
Old 10-26-06, 04:54 PM
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Originally Posted by Junk Doctor
You haven't told enough, but from what you have said, there are a number of obvious possibilities. Vacuum leak, failure of timing advance (which could be due to a vacuum leak.) Less likely, but possible, is slipped timing belt -- usually a slipped timing belt makes a huge difference, the engine wont run at all, but in some engines a timing chain or belt can slip one cog, and the engine will run, but barely.
Easiest thing to do is to check timing, and make sure advance is working -- for vacuum leaks, a small leak will be temporarily plugged by a spray of water (use a pant mister) -- another trick is to spray a bit of brake cleaner, with a vacuum leak , the cleaner will get scked into the intake and immediately produce clouds of exhaust smoke.
Iroc does not have a timming belt, and a vacuum leak would cause poor idle, he said idle was good.
 
  #5  
Old 10-26-06, 08:14 PM
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Telling you more

Ok some imformation, It is a ECM controlled car. New ditributor also. Everything was new when installed about 5,000 miles ago. I've checked all my vaccum line and they are all new rubber lines. It could be rocker arm adjustment as thats one of the last adjustments I made to the car a couple months back. The timing chain is a cloyes true roller and the cam timing is still where I set it at. My plugs are all burning great.
 
  #6  
Old 10-26-06, 08:30 PM
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You might check the vacuum at idle - should be around 18 to 22. It'll tell you a lot about timing, valves, vacuum leaks, general engine condition, etc. Post back with the reading.

Hope this helps,

Bob
 
  #7  
Old 10-27-06, 03:45 PM
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Originally Posted by IROCnRoll
I have an 88 IROCZ28 that having some issues. It has a new engine in it and it has been running excellent till this started. It runs great at anything more then partial throttle. If it's barely cracked open or you slightly accelerate it stumbles/backfires and or surges. I've replaced Plug wires, distributor cap and rotor, fuel pump, fuel pressure regulator, coil. I even regapped all the spark plugs. Any ideas?.
i had the same problem the other day with my trans am and i could not figure it out, but under the air cleaner there was a electrical cable not plugged in to it, try that.
 
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