Intake Backfire
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Joined: Jun 2007
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From: Mundelein, IL
Intake Backfire
I just replaced my plugs and wires on my 32V. I have checked and made sure the wires are correct. When I started it yesterday I had a bang and the intake popped apart and dented the hood from inside. What the heck did I do?
I went with nology wire and Bosch platinum plugs, I checked the gaps rotors and caps are new last fall with no issues, wires are not cross arcing, I did notice the I knocked a line from the front of the throttle body loose and I'll take care of that tonight. I need to be up and running on Tuesday night soI know what I'm doing for Father's day...if I can figure out what to do.
I went with nology wire and Bosch platinum plugs, I checked the gaps rotors and caps are new last fall with no issues, wires are not cross arcing, I did notice the I knocked a line from the front of the throttle body loose and I'll take care of that tonight. I need to be up and running on Tuesday night soI know what I'm doing for Father's day...if I can figure out what to do.
Drifting
Joined: Dec 2005
Posts: 2,124
Likes: 103
From: ATL, GA w/a 996TT
I think the concensus is fuel vapors from a leaky injector and timing being just a nick off. The search feature here on this site is fantastic as well. Here are some good threads with some info.
https://rennlist.com/forums/showthre...ntake+backfire
https://rennlist.com/forums/showthre...ntake+backfire
https://rennlist.com/forums/showthre...ntake+backfire
https://rennlist.com/forums/showthre...ntake+backfire
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I would guess it to be more likely related to crankcase/gas tank vapors, possibly combined with bad valve timing (as mentioned in Turtle's second link).
The S³ takes what seems like a long time to start, because the EZ-F doesn't give a timing signal to the LH until it gets a good reading from the crank sensor, so injectors and spark plugs aren't firing. The oil vapor may self ignite after cranking enough to heat the air?
The valve timing is normally retarded when cold, especially on the passenger (¼) side. When the engine heats up, it expands, which advances the timing to it's 'normal' position. (Note that S³ cams are the same as GT's, except that the GT's intake cams are advanced 8°.)
Early cars with gas tank vapor recovery (carbon cannisters) get fresh air, and dump overflow to the bottom part of the airbox! Starting with '86.5, the carbon cannister fresh air/overflow goes to the back of the car, behind the bumper. Perhaps the explosion possibility prompted this?
Check the valve timing! (Buy a 32V'r from 928sRus!
)
The S³ takes what seems like a long time to start, because the EZ-F doesn't give a timing signal to the LH until it gets a good reading from the crank sensor, so injectors and spark plugs aren't firing. The oil vapor may self ignite after cranking enough to heat the air?
The valve timing is normally retarded when cold, especially on the passenger (¼) side. When the engine heats up, it expands, which advances the timing to it's 'normal' position. (Note that S³ cams are the same as GT's, except that the GT's intake cams are advanced 8°.)
Early cars with gas tank vapor recovery (carbon cannisters) get fresh air, and dump overflow to the bottom part of the airbox! Starting with '86.5, the carbon cannister fresh air/overflow goes to the back of the car, behind the bumper. Perhaps the explosion possibility prompted this?
Check the valve timing! (Buy a 32V'r from 928sRus!
)
Drifting
Joined: Jul 2004
Posts: 2,725
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From: Davidsonville, MD
I did that on my '85 (same intake) only with the intake full of ether vapors. My hood was open at the time so when mine blew, it flew across the garage and put a dent in the refrigerator. Go back and double check your wires. Seriously. I thought mine were correct but they weren't.
Under the Lift
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From: Buckeye, AZ
Finally got it right after checking it again. No explosions, but the car ran poorly until the wires were correct.
Last edited by Bill Ball; Jun 13, 2008 at 03:59 PM.
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From: Ball Ground, GA
Almost certain to be crossed plug wires...
There is a tiny chance that it could be an intake valve hanging open due to dirty stems/guides.
Timing isn't adjustable, so isn't likely to be off.
There is a tiny chance that it could be an intake valve hanging open due to dirty stems/guides.
Timing isn't adjustable, so isn't likely to be off.
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Thread Starter
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Joined: Jun 2007
Posts: 316
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From: Mundelein, IL
I'll give the wires another check. Porken, I've been to your sight and I'll get some liftbars someday, I've got Carl's springs and shocks on my blueprint table in my office, that'll come next after I get this sorted out. I need more time...
Thanks to everyone on the list. I've been here about 8 month and am still learning. I use the search function constanty but I could not find anything about intake missles.
TIm
Happy Fathers Day to all Fathers!
Thanks to everyone on the list. I've been here about 8 month and am still learning. I use the search function constanty but I could not find anything about intake missles.
TIm
Happy Fathers Day to all Fathers!
Nordschleife Master
Joined: Apr 2003
Posts: 9,601
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From: Abbotsford B.C.
I have had this happen a couple of times on my 1981 with 86.5 engine.
Each time it has happened I have not had
a) crank case vented to intake
b) gas tank vapour system hooked up
I had it happen once with the 86 LH/EZF, and have had it once (maybe twice) with the stand alone.
Neither time it has dented the hood.
With the standalone I run 10 deg of advance for starting, the injectors were cleaned not too long ago either. I also run 1 deg of retard on both passenger and drivers side camshafts.
My plug wires were untouched before and after all times.
I have yet to figure out as to what has caused this,
but I have no fuel tank vapour system, or crankcase vent gasses to cause this to happen.
and I know my timing is bang on.
IMO it is either an injector with a very small leak, or vapours left from the last run, probably pooled on a valve and as you crank it gets blown back into the intake.
How it ignites though I remain clueless.
Each time it has happened I have not had
a) crank case vented to intake
b) gas tank vapour system hooked up
I had it happen once with the 86 LH/EZF, and have had it once (maybe twice) with the stand alone.
Neither time it has dented the hood.
With the standalone I run 10 deg of advance for starting, the injectors were cleaned not too long ago either. I also run 1 deg of retard on both passenger and drivers side camshafts.
My plug wires were untouched before and after all times.
I have yet to figure out as to what has caused this,
but I have no fuel tank vapour system, or crankcase vent gasses to cause this to happen.
and I know my timing is bang on.
IMO it is either an injector with a very small leak, or vapours left from the last run, probably pooled on a valve and as you crank it gets blown back into the intake.
How it ignites though I remain clueless.
Intermediate
Joined: Jun 2008
Posts: 41
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Im looking at buying an 86 928 that owner said was running really rough and with some difficulty starting, sprayed some starting fluid into intake that exploded through air intake and blew out the air filter box, ect. It hasnt been started since but what can happen to engine when this happens?? Selling as-is for 2K with perfect interior and 56K. Thoughts?
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Joined: Jan 2003
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From: Honolulu and sometimes L.A.
Based on just watching ebay for years, I think that 85/86 cars just do this sometimes. Usually just a matter of putting the intake manifold back together. I have heard of several cases of folks getting great deals when this had happend to the P.O. who assumed (reasonabley) that something major was broken.
Drifting
Joined: Dec 2005
Posts: 2,124
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From: ATL, GA w/a 996TT
I was thinking (and maybe read this somewhere) that if there was a leaking injector and during the initial cranking that the vapors made it up to the MAF wire and were ignited by the "burn-off" window that the MAF wire goes through. I think it would get hot enough to ignite fuel vapors. maybe maybe not? Any thoughts?
Nordschleife Master
Joined: Apr 2003
Posts: 9,601
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From: Abbotsford B.C.
Rng Trtl,
The MAF does its burn off time if the car was run for more than 5 min, and turned off for more than 2 min. As well I do not have a MAF in my setup and it still happens.
Just reconnect the airbox and all is good to go.
The MAF does its burn off time if the car was run for more than 5 min, and turned off for more than 2 min. As well I do not have a MAF in my setup and it still happens.
Just reconnect the airbox and all is good to go.