1987 2.5 auto
Recently a club member replaced a bad motor and has been driving around for a week or so without any noticeable problems.

He was driving in the rain and it started to spit and sputter.
I looked at it for him and discovered a crack in one of the coils on the coil pack.
Got a coil pack off of a running parts car from the fiero farm.
The sputtering isn’t there anymore but under quick acceleration it back fires through the throttle body.
It’s not a muted back fire, it sounds more like a 22 rifle being fired.
As long as you drive normally it’s ok, but a quick throttle opening will cause it at any speed or rpm.

He doesn’t know if it was happening before because he was babying it with the new motor.

New plugs and new wires didn’t help.

Ideas anyone?

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Buddy - there are two "G"s in my name
Ling = 84SE-350-N2O-Poly-Mr.Mike seats-Sequential turn signals-short shifter
Julia C = 85GT stock (mostly)
KCFOG
got a broken stud?
car doesn't crank over?

ttt

Nothing but theroy here... Backfire is a timing issue. Backfire into the TBI would mean either an intake valve is sticking open or that there is pre ignition. Since you say that it happens only upon acceleration I would think it is more likely pre ignition. It's possible that the timing is advanced to the point that upon acceleration it acts faster then the valves do. The first thing I would do is recheck the timing. With all the work you have done you might be just a couple of degrees off. Then I might check the compression.

As I said this is a couple of guesses.

Bad cam lobe,tight valves or timing chain stretched or jumped a notch.

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Tuners of the Quickest 4.9
12.51@118 mph
Being replaced by a "New" improved and even quicker 4.5 HY-BRID (In progress.)

Deff cam my old camaro did exact same thing. 2round lobes

cant play with timing as it is a DIS system.

there is no cam chain

and i really dont like the idea of a cam problem.

i'm looking for that warm and fuzzy magic answer

Most common problem with a DIS ign prob is the crank sensor located under the module. Be careful not to break it off in the engine when you take it out. Cheap item and definitely a common prob. Good luck.

Phil

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87 FIERO GT 2.8 5spd
0-60 in 6.8 seconds!
If you found my advice helpful, please take the time to give me a positive rating. Thanks

thanks, i'll swap out the CPS with the old one on the coil pack.

i wont see the car for 4 more days.

anyone else wanna throw a suggestion my way?

Hi buddycraigg...
I had the same problem with my Firebird Formula and my wife's 88 L4...on both it was a crossfire between the coil to distributor cable, and and a plug cable very close to it, and only happened when the atmosphere was damp.I hate to ask, but did you change this cable as well? Sometimes the tracking from coil cable to a plug cable can burn a track across the outside of the distributor cap, and it becomes obvious at night,with a nice bright spark jumping the gap: I guess you know this anyway, but might have overlooked it...and also assuming this car has a distributor...I'm unfamiliar with the car,but hope only to help!!
fierofetish
OK!!! I had a look at my Haynes, and see that it doesn't have a distributor!!!Sorry to waste your time folks...

[This message has been edited by fierofetish (edited 11-21-2003).]

[This message has been edited by fierofetish (edited 11-21-2003).]

Thanks for the suggestions, but as you discovered it has DIS. Distributor less Ignition System some times referred to as Direct Ignition System

And I have changed the plugs and the wires.

I’ll wont see the car till Monday night so keep those suggestions coming.

Every time mine does this it means the EGR needs cleaning again.

With one exception... It used to have a Wells EGR on it. That POS went bad in about a year. I put a cleaned used OE unit on it and haven't had a problem since except that it needs cleaning about every other year. EGR gaskets are about $1.

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Be alert. The world needs more lerts...

The Ogre's Fiero Cave (It's also at the top of every forum page...)

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[This message has been edited by buddycraigg (edited 11-22-2003).]

oooh.
i like that idea.
keep em coming, and i'll post back what solved the problem. and the first person to have the right suggestion gets a cookie.

anyone from the saturday group wanna take a stab at it?

ok tried the EGR and the CPS.
still shooting up through the TBI

next...

Last resort, read the instructions?? I've think the book's material has been covered in prior replies, but to make sure, here's what the manual attibrutes backfiring ("making a loud popping noise") to.

EGR being open all the time
Output voltage of the coils
Crossfire between plugs (at coils, wires,)
Faulty plugs, wires, boots
Perform compression check looking for sticking or leaking valves
Proper valve timing
Broken or worn valve train parts.

The culprit will be found.