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87 2.5 auto backfire thourgh throttle body - HELP by buddycraigg
Started on: 11-20-2003 05:50 PM
Replies: 14
Last post by: goldiron on 11-27-2003 01:28 AM
buddycraigg
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Report this Post11-20-2003 05:50 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
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 isnít there anymore but under quick acceleration it back fires through the throttle body.
Itís not a muted back fire, it sounds more like a 22 rifle being fired.
As long as you drive normally itís ok, but a quick throttle opening will cause it at any speed or rpm.

He doesnít know if it was happening before because he was babying it with the new motor.

New plugs and new wires didnít 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
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got a broken stud?
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buddycraigg
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Report this Post11-20-2003 09:01 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
ttt
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ARKaiser
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Report this Post11-20-2003 09:29 PM Click Here to See the Profile for ARKaiserClick Here to Email ARKaiserSend a Private Message to ARKaiserDirect Link to This Post
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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Master Tuner Akimoto
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Report this Post11-20-2003 09:59 PM Click Here to See the Profile for Master Tuner AkimotoClick Here to visit Master Tuner Akimoto's HomePageSend a Private Message to Master Tuner AkimotoDirect Link to This Post
Bad cam lobe,tight valves or timing chain stretched or jumped a notch.

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red85gt
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Report this Post11-20-2003 10:18 PM Click Here to See the Profile for red85gtClick Here to visit red85gt's HomePageClick Here to Email red85gtSend a Private Message to red85gtDirect Link to This Post
Deff cam my old camaro did exact same thing. 2round lobes
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buddycraigg
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Report this Post11-20-2003 10:33 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
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

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GTDude
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Report this Post11-20-2003 11:11 PM Click Here to See the Profile for GTDudeClick Here to Email GTDudeDirect Link to This Post
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
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buddycraigg
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Report this Post11-21-2003 12:36 AM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
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?

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fierofetish
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Report this Post11-21-2003 04:39 PM Click Here to See the Profile for fierofetishClick Here to Email fierofetishSend a Private Message to fierofetishDirect Link to This Post
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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buddycraigg
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Report this Post11-21-2003 06:39 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
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.

Iíll wont see the car till Monday night so keep those suggestions coming.

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theogre
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Report this Post11-21-2003 07:13 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreDirect Link to This Post
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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buddycraigg
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Report this Post11-21-2003 07:47 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
.

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

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buddycraigg
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Report this Post11-22-2003 03:16 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
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?

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buddycraigg
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Report this Post11-27-2003 12:27 AM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggDirect Link to This Post
ok tried the EGR and the CPS.
still shooting up through the TBI

next...

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goldiron
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Report this Post11-27-2003 01:28 AM Click Here to See the Profile for goldironSend a Private Message to goldironDirect Link to This Post
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.

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