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?
------------------ 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?
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05:50 PM
PFF
System Bot
buddycraigg Member
Posts: 13620 From: kansas city, mo Registered: Jul 2002
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.
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09:29 PM
Master Tuner Akimoto Member
Posts: 2267 From: South Florida,USA Registered: Jul 2003
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
------------------ 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
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11:11 PM
Nov 21st, 2003
buddycraigg Member
Posts: 13620 From: kansas city, mo Registered: Jul 2002
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).]
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04:39 PM
buddycraigg Member
Posts: 13620 From: kansas city, mo Registered: Jul 2002
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.
------------------ Be alert. The world needs more lerts...
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.