Hey guys; Ive got my 3.4L installed running in my 88 GT. It has these symptoms: It runs poorly down low, above 3000 RPM it runs pretty well. It will backfire out the intake when its between 1000 and 3000 rpm sometimes. It sounds like I hear someone knocking on my back window right behind my head when it backfires. The engine bay gets very hot even after only driving it for a minute or two, so hot that i can barely touch the rubber air hose.
I swapped the EGR tube out with a new one from the fiero store, no change. I checked for a vaccum leak, its all solid.
I am pretty sure the problem is the timing, what do you guys think? Is it advanced or retarded? Which way should i move the distributor? And how much?
A vacuum leak wont make it backfire.. sounds like a timing issue.. sounds like one tooth off the gear on the distributor. (to check for vacuum leaks..just spray some carb cleaner.. the RPM's will drop when you find the leak.....)
Seems like you recovered from your car accident well enough to install your 3.4 .... Why do I not get any response from you by e-mail or PM. You still have my 3.8 scII in your garage ready to ship to europe. Please send me an email or PM!!!! I can understand that you may have gotten fed up with the hassel trying to get shipping organised, but you must understand I would like to get the engine I have allready payed for shipped to me "some time".
Iwan from the Netherlands
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07:54 AM
Mickey_Moose Member
Posts: 7568 From: Edmonton, AB, Canada Registered: May 2001
A vacuum leak causes backfires thru the INTAKE, whereas valve timing or ignition timing can cause backfires thru the EXHAUST.
I still say look for a vacuum leak.
Arn
...not entirely correct, I have personally heard backfiring though the intake with the valve messed up (this seriously affected the power output of the motor). I had a post on here at one time that included a audio file and pictures of the valve once I got it apart. Of note, the sound was not your typical exhaust back fire sound, but more like a leather belt being slapped together.
If you have no vacuum leaks, I would then be looking at valves.
Tim
[This message has been edited by Mickey_Moose (edited 05-16-2005).]
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10:44 AM
May 25th, 2005
fiero-iwan Member
Posts: 352 From: Eindhoven,Netherlands,Europe Registered: Mar 2003
It looks like the pickup from Matts place is going to happen tomorrow or friday. GREAT! Thanks to Matt for seeing this thing through to the end, aspecially after all the setbacks we've encountered. Also thanks to Fiero-dave for his help and advice. And last but not least thanks to Vince Clarke for making the necessary arrangements on such short notice.
Iwan
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07:24 AM
Aug 14th, 2005
fiero-iwan Member
Posts: 352 From: Eindhoven,Netherlands,Europe Registered: Mar 2003
I really thought Matt would come through this time... I did get my engine in the end but it was missing a lot off stuff that I had payed for. The complete engine wiring harness and PCM , the engine mounts and brackets, engine cover etc were all not on the pallet when it arrived. I have been trying to get in touch with Matt since I picked up the engine and noticed the stuff missing. He does not respond to pm's and emails. I have can only conclude he is avoiding me again. I did pay him a $200 for his troubles not including the expensens which I also payed. After Matthian collected the money via paypall he has been non responsive. I'm still waiting on the pictures he was supposed to email me of the engine and all stuff mentioned missing above strapped to the pallet, ready for pickup from his home by a shipper that I had arranged with the help of Fiero-dave.
Matthian (Matt Dorneman) if you read this you can still set the record straight by returning a PM or email. Once I have the missing stuff I will be glad to edit this message to make it more possitive. If you continue to avoid me I have no choice than to give you the bad rep you seem to be asking for.
Fiero Iwan from the Netherlands
[This message has been edited by fiero-iwan (edited 08-14-2005).]
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05:23 PM
BERKELUSA Member
Posts: 262 From: Manchester, New Hampshire USA Registered: Apr 2005
Your engine is running lean beyond the ECM's capability to compensate for it, that is the cause of backfires through the intake. It could be because of a vacuum leak, but not likely unless you're seeing a high idle. Lean condition will produce extremely hot exhaust and is the reason your engine compartment is so hot. It will damage the exhaust valves if you drive it that way for long. If you used the 2.8's injectors, that's why you're having problems. You need at least the 17# injectors from the 3.4, and 19#'s are even better.
also, just for sh!ts and giggles...check the valve adjustment. did you recently build that 3.4? if so, you might not have gotten the valves correct. one might be too tight causing that popping. i had that happen on a 350 i built and i drove myself nuts trying to figure out what it was till i went back and did the valves again and it all went away...just an idea
------------------ Keith Topsail Beach,NC 86&87 Fiero GT 86&96 Corvette 04 HD Softail 73 Lotus Europa TC 86 Lotus Turbo Esprit
Valve adjustment could definately be the cause, I had an exhaust rocker nut back off to where you couldn't hear it rattle after installing a cam, the side effect was the intake charge coming into the cylinder being combusted and sent right back out the intake port into the plenum but in my case it sounded like someone was tapping on the intake with a wrench. Check to see if your exhaust manifolds are glowing that will point to timing.
I vote for a valve or rocker. I had the same problem when a push rod guide broke and the rocker slipped off the valve. The TBI butterfly valve was bent because of the back fire through the TB. The back fire didnot do bang but tap tap.
