Ok, 90 iroc tpi speed density. Came home from work one night, car was running fine...next day won't start. Changed plugs, wires, cap, rotor, coil and module.....car runs but acts like it's only hitting on 6 out of 8 cyl. Have gone on to check the timing, replace egr, 02, map, cts, changed fuel filter, fuel pressure is 42, compression is around 150 on all 8, replaced ecm, pcv, checked fuel injectors with a noid light, had the car on a sun machine which says everythings fine....but still acts like its running on only 6 cyl....no power..backfiring, motor shakes like it's out of time... etc. I have no idea what to try next! The fact that it went from running fine to this overnight leads me to electrical...but I don't know what else to try!

 

Gonzo,

Did you try bypassing the ESC? The ESC could be flaking out and causing irregular timing.

Is the reluctor and/or pickup coil cracked, slipping, or shorting? A cracked reluctor will kill the spark timing pulse at the cylinder where the crack passes the pickup coil. A failing pickup coil can cause irregular ignition timing and spark intensity.

Is the valve timing correct? Timing chains have an odd way of slipping just as the engine winds down to a stop.

Are you getting any error codes?

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

not sure about the pick up coil...that was my last idea to check.....not getting any codes....as far as the timing is concerned....it looks fine with the light....and look ok on the distributor....but haven't actaully pulled the timing cover off to verify this (lot of work as you well know).....by bypassing the esc....do you mean disconecting the wire over by the blower motor (as if you were going to time the motor) if this is what you meant...I've done this for timing purposes obviously...but didn't drive the car in that state.

 

Check the COMPUTER!!! Mine is MAF but it did the same thing to me last year ended up somehow the computer got messed up and they just had to reprogram it. 40 bucks and that was it.

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TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph

"Speed kills, wanna live forever, drive a Ford."

 

When Vader mentioned valve timing, he's talking about cam timing changoing because of a stretched belt, not ignition timing.
The only way that I know of to check for a stretched timing chain is to pull the timing cover, and inspect it.

 

I had an El camino not to long ago that had a broken valve spring.

Compression was PERFECT in all holes, but while running it would miss really bad.

Everything seemed perfect. Pulled the valve covers and there it was. (you REALLY have to look good)

Just my two cents.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

 

ok have new pickup coil in hand....getting ready to install it tomorrow....will let you knoew what happens.....also have checked the TPS and that's functioning perfectly....it the pickup coil doesn't do it...I might have to break down and take it into the shop.

 

also checked my vacuum at the brake booster hose. At Idle it held 15" (which seems low to me) blip the throttle and it drops to zero naturally...then up to around 24 as it coming back down to idle....and settles back into a steady 15". Does this sound low to anyone else? Anyone have any idea what my normal vacuum reading should be at idle (completely stock motor) have done the old "spray test" and didn't find anything...so would love some input.

 

Well....just put a new distributer in it....no change......I think I'm going to have to break down and send it into the shop

 

I agree with the valve spring idea. Did you check those? with what youve done already it shouldn't be too hard to pop the valve covers off. Good Luck

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'87GTA w/ SLP Cold Air, MSD Coil, Airfoil, Gutted MAF, AFPR, TES Headers, HI-FLOW CAT, Flowmaster Catback, Energy Suspension Master Bushing Kit

 

In reading your original post, you say you went from a car that was running fine, to a no start condition, to a starts & runs, but runs like it is on 6 cyls. Go back & check the plug wires you changed to make sure they are properly connected & in the correct firing order.
Relative to a timing chain failure, if you checked your BASE timing with a light & it has not changed, your timing chain & valve timing are OK.
Regards, FJK