It backfires when accelerating in gear, but not at the park position

G

gpadilla1071

Member
Joined
Jul 30, 2007
OK my friends, so I did some research on the site about the subject and took all advice and went with it. I changed my plugs, wires, cleaned the MAF, changed O2 sensor, coil pack is good to go. Before I continued, when my exhaust manifolds cracked to the point of no return, the car sat for approximately 3 months. Once I gave in and bought the headers and did my test drive, that's when the backfire started. Also due to this issue I'm having it takes a little longer for the turbo to spool. One more thing, while the car is in the park position I can start it, accelerate it and no backfire, only while I'm driving... My scanmaster should be here by tomorrow or Thursday and hopefully I can get some readings that can help me decifer my issues. Any thoughts or anything else that I miss on doing, your opinions are greatly appreciated.:)
 
do you have your wastegate jacked up to the moon from when you were trying to overcome header cracks?
 
Did u ohm the coil. ??
Did u ck for crossed wires

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I'm wondering if you ever figured out what was causing this. I have the same exact issue!! I suspect ignition but before I got the car, my buddy had swapped out the coil pack and ignition control, I think, so I don't want to buy more and try the same route. It could be he put used/wrong stuff in but nearly everything else on the car has been checked and replaced. It's not fuel delivery, and I'm getting good spark, but haven't ohm'd under load.
 
I tried several coil pack and ignition modules and was never able to completely solve my backfire and stutter at wot issue until I went to the Bailey TR6 ignition. It's a really really good upgrade.
 
Whats your fuel pressure at full boost ?
Have you messed with the cam sensor at all ?

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I haven't tried to get it up to full boost but from what I saw, fuel pressure was increasing pound for pound with boost. The car seems to run great at idle in park and I can hit the gas and there is no or little "pops." It only runs garbage and backfires once I put it into (any) gear and move it. I haven't tried gunning it or hard acceleration because I'm afraid of a massive backfire ruining things. I just hobbled it around the block. It is a little hard to start, too. It will not start right up. I have to turn it over for a while and it sounds like it's catching and I have to pump the accelerator to get it to run. This makes me think it could be the Cam sensor, but I'm not sure. Because it idles well I didn't think the cam sensor could be that far out of line. I was going to try starting the car and disconnecting the cam sensor and then put it in gear. I also need a buddy to help me so I can check vacuum, etc while in gear. Thoughts?
 
Did replace the cam sensor
Or was it removed before you had this problem.
?


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I haven't touched the cam sensor at all. I am saying I was going to disconnect it while the car was running to check it. If the sensor is indeed bad, how would I know/test? I don't want to buy a new one as a 'test'
 
I think you may have crank sensor issues: loose wire, bad wire, balancer ring rubbing, etc. Go below and report back. :) Backfire through the exhaust means rich mixture FYI. Intake backfire = lean. Rich mixture can be due to spark issue hence my questioning the crank sensor.
 
Thanks, I'll check the crank sensor. But I'll point out that it runs fine in idle. If the crank sensor was really bad, would the car run at all? I don't have to be moving, just putting the car into gear with the brake on causes the pops/backfires. I'll check anyhow.
 
Could be ignition module or coil pack as well. Ohm the coil pack towers and see what you get. Do a search for specs, I think it's 11K ohms between each pair. Best to find a buddy to swap with if you have one near, the parts are expensive just to guess at.
 
"afterfire" more clearly explains what's going on, so thanks for the hints. Probably running rich in gear and the waste spark is igniting whatever fuel is left on exhaust. The popping sound is pretty regular. Also, this car has no cat so that might add to the issue. I haven't really driven it hard, but maybe I will try since I know it isn't backfiring through the intake. Maybe it cleans up under harder accell instead of just rolling.
 
I had a back fire and blew the up pipe off. But that was when I was accelerating. Turned out to be a dead spot in the TPS sensor. I think I would second the bad LT-1 MAF like Steve V said.
 
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