Misfire and backfire only when hot

F

funkyturbo

New Member
Joined
Feb 29, 2016
I have a baffling situation after my 87 gets hot. It runs great for 20 minutes or so but when it gets warm it starts missing out and sputtering - at first only during acceleration, then at steady driving and finally it will do it at idle and finally die! Changed injectors/chip from TurboTweak, changed ignition module, coil pack, plugs and wires. Replaced cam sensor cap from Casper's yesterday. Still have the same exact problem!!!! Has anybody experience similar problem and HOW DID YOU FIX IT????
Going crazy!!!!
29,000 miles mostly original and runs decent EXCEPT for that!!!!:mad:
 
Start with some data logs, Scanmaster readings....
MAF taking a dump?
29,000 miles mostly original.. Fuel pump new? Fuel psi is?
 
Sounds to me like a closed loop vs open loop problem. Closed loop ignores the MAF and O2s, open loop takes them both into account once everything is warmed up. The datalogs would show where the issue lies, but maf/O2 would be my first guess. I could have closed/ open loop backwards.

If the engine is running and hot, tap on the MAF, if the engine stumbles then the MAF is the problem. What are the O2s reading? What type and age of MAF/translator/settings do you have?

I would have asked the same questions regardless of mod list or your repair list for what it's worth.
 
Here's what i have for readings I could get between break downs. MAF 804 - 29, BL - 128, ATS 83, TPS .44 idle (can't remember at WOT but all readings were within acceptable limits). Fuel pump has been replace and pressures are good line off, line on and during boost. When it stranded me today with not enough power to make it home I unhooked the Cam sensor and i smoothed and ran normally - even at WOT. Plugged it in at home at it killed the car. The cap is new from Casper's and since I had the same problem with original cap I don't think it is defective. The cam sensor is DEFINITELY involved but like I said the other one did the same thing! Tab on the reluctor ring in sensor is intact. Ordering a new Delco ignition module today but orriginal one and aftermarket replacement acted exactly the same. The car runs great until hot, plenty of power, no misses and 0 retard at 16lbs boost.
??????
 
Have seen many GN's with your symptoms, I found the coil pack/module being the culprit many times, so that is where would I start.

That procedure is easy for me as I have spare everything for a 1986-7 GN, maybe you can borrow one?

Do not get carried away with Delco, as all their parts are now made by outside suppliers.
 
Nick Micale said:
Have seen many GN's with your symptoms, I found the coil pack/module being the culprit many times, so that is where would I start.

That procedure is easy for me as I have spare everything for a 1986-7 GN, maybe you can borrow one?

Do not get carried away with Delco, as all their parts are now made by outside suppliers.
Click to expand...

Thanks - I have a new coil/pack module coming in next week, that makes sense as a good place to start. The ones on it are new also but I may have gotten a bad one. Does unplugging the cam sensor while it is running bad put the car back in some sort of default mode that makes it run normal again?
 
I would look at the coil pack and ignition module as the problem..

I too keep a spare coil pack and ignition module to have on hand for troubleshooting purposes. And no matter which one goes bad and causes a problem. I replace both to keep them matched as a set. I bought them with a lifetime warranty so it doesn't cost me out of pocket to replace them. I got lucky i think with the brands i use.they work for me. I've seen on here others have tried them and they didn't work for them..
 
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I would take a look at the TR6 ignition system as a replacement. The newer ignition modules being reproduced use a different circuitry as some original components are no longer available.
 
I can double check cam sensor timing, I installed Casper's Cam sensor cap with LED indicator and am pretty sure it is right, besides it did the same thing as old cap or is that an indication of something....
 
S0 when you replaced the coilpak and ignition module, it made no change? Did you replace them? Seems odd it would be the cam sensor. I never had one go bad on me in 20 years.
 
Exactly - no one else thought it would be a bad sensor either! Maybe I just finally got it set correctly, but everything was set several different times prior to the new one. The gears were fairly worn on old one - maybe enough to cause issue when hot?
 
funkyturbo said:
Exactly - no one else thought it would be a bad sensor either! Maybe I just finally got it set correctly, but everything was set several different times prior to the new one. The gears were fairly worn on old one - maybe enough to cause issue when hot?
Click to expand...

Well, in any event, I'm glad you got it sorted out. That kind of shit is so frustrating.
 
Watching this thread. Glad you figured it out. Mine did something weird yesterday. I did a full pedal blast, first during my outing, from a roll for about 4 or 5 seconds, dump open, boost about 21-22 pounds, alky working fine, let off quickly after the blast and got a backfire out of the dump. Scared the crap out of me. O2s were fine and the knock was about 1.00. Prior to this, the car has been running perfect. It was hot and humid too yesterday. Car ran fine afterwards. Very odd.

Sent from my SAMSUNG-SM-G900A using Tapatalk
 
Exactly - no one else thought it would be a bad sensor either! Maybe I just finally got it set correctly, but everything was set several different times prior to the new one. The gears were fairly worn on old one - maybe enough to cause issue when hot?
SpeedRacerX said:
Watching this thread. Glad you figured it out. Mine did something weird yesterday. I did a full pedal blast, first during my outing, from a roll for about 4 or 5 seconds, dump open, boost about 21-22 pounds, alky working fine, let off quickly after the blast and got a backfire out of the dump. Scared the crap out of me. O2s were fine and the knock was about 1.00. Prior to this, the car has been running perfect. It was hot and humid too yesterday. Car ran fine afterwards. Very odd.

Sent from my SAMSUNG-SM-G900A using Tapatalk
Click to expand...
Do you think it had anything to do with the weather conditions? I am wondering just how much it affects it - i am losing up to 2-3 lbs of boost when everything is hot...
 
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