Breaking up, popping at around 14 lbs. Help!

TR Custom Parts

Mark Hueffman - Owner
Joined
May 25, 2001
Haven't needed any advice in a long, long time so here goes. My 87 GN is usually flawless and consistent performance wise. Late last year I began to have a popping, backfiring thru the intake. Years ago I took off the original ignition module and coil to save for the future and installed replacements. Car always ran great that way for years and figured I would just swap back to the stock ones on the shelf. Problem solved! Numerous 100 plus mph tests without any issues. Running 20 lbs of boost with alky.

Fast forward to last week and the same symptoms are back with the original parts. Ordered some replacements from Rock Auto and installed. Ignition module was AC Delco made in USA and coil was AC Delco made in China. Took the GN to a car show yesterday and about 5 minutes into the 30 mile drive I romped on it and ran like it should, no issues. Tried a couple more times and still all good. After about 20 minutes of driving and almost to the show hit it one more time and same damn thing again. After the show, ran great again but after about 15 minutes of run time back to the popping. Making me think it is heat related.

Neither of the previous ignition modules showed any signs of the gooey mess I have read about so no signs of them overheating. Drive the car normally and runs fine, no missing, no stalling or stumbling. I have grounds going to the firewall AND the block for the coil mounting bracket and all attachment points are scraped to bare metal.

GN only has 45,000 miles on it, original short block. About 5,000 miles ago, I changed out the timing set and put on a set of Champion heads and Champion ported stock intake manifold. All grounds were relocated from back of head, all fusible links relocated to fenderwell. Alkycontrol kit with fresh pump and alky gauge is showing normal pressure. Hood mounted fuel pressure gauge showing the normal 1 to 1 rise in fuel pressure. The car has always been ultra reliable so this has me stumped. Haven't used my Powerlogger in years so needed to find my tablet and charge it up before I try to document what it is actually doing. I know the replacement coils, modules are crap now so maybe I got a clunker? Like I said when car is about 10 minutes into a drive it runs perfectly normal. After that is when it starts acting up. Plug wires and plugs are good, Same AC 42's I have run for years gapped at .028. No pre turbo exhaust leaks. Cam sensor was gone thru and the tab repair kit was installed. Haven't really gone any more in depth on it since replacing the module and coil as I am still recovering from recent hip surgery.
 

TurboTGuy

Gray Beard Member
Joined
Sep 24, 2010
Could the battery have gone dead or the ECM get unplugged and the tune in the chip was lost? I had those same issues when first got my new combo installed. Lot's of phone calls back and forth to Lou and with the help of a local named Dennis Spivak, we figured out. We had a fueling issue and it was dumping way too much fuel in @ WOT. I'm assuming you have a v6.1 Turbo Tweak chip or other simi-tunable style chip.

Good luck!
 

Chuck Leeper

Toxic old bastard
Staff member
Joined
May 28, 2001
Mark, try the cold rag trick to narrow down the heat failure aspect.
Get it into the "failure mode", put a cold/wet rag on the sides of the module and the base plate.
Run ok now?
 

TR Custom Parts

Mark Hueffman - Owner
Joined
May 25, 2001
Could the battery have gone dead or the ECM get unplugged and the tune in the chip was lost? I had those same issues when first got my new combo installed. Lot's of phone calls back and forth to Lou and with the help of a local named Dennis Spivak, we figured out. We had a fueling issue and it was dumping way too much fuel in @ WOT. I'm assuming you have a v6.1 Turbo Tweak chip or other simi-tunable style chip.

Good luck!
Always on a battery tender. Wouldn't explain why it only does it after a longer drive and car is fine from cold start to about 10-15 minutes of driving.
 

TurboTGuy

Gray Beard Member
Joined
Sep 24, 2010
Always on a battery tender. Wouldn't explain why it only does it after a longer drive and car is fine from cold start to about 10-15 minutes of driving.

Like I said, same symptoms. Same temp situations. It may not be the issue, but there's no real reason to not at least check it out. Or, just discount it, no skin off my nose.

I hope you get it fixed and you post up the problem/solution here.
 

SCOOBY DOO

I'M NOT A MONSTER, I'M JUST AHEAD OF THE CURVE!!!
Joined
Feb 18, 2007
This is an extreme case of a bad module I've run across. I've seen them look absolutely normal when split from the coil pack and be bad. Hard hot starting, breaking up in high gear when load is the highest, backfiring is a few tell tale signs.

 

Mr.Spool

Well-Known Member
Joined
Nov 6, 2006
Haven't needed any advice in a long, long time so here goes. My 87 GN is usually flawless and consistent performance wise. Late last year I began to have a popping, backfiring thru the intake. Years ago I took off the original ignition module and coil to save for the future and installed replacements. Car always ran great that way for years and figured I would just swap back to the stock ones on the shelf. Problem solved! Numerous 100 plus mph tests without any issues. Running 20 lbs of boost with alky.

Fast forward to last week and the same symptoms are back with the original parts. Ordered some replacements from Rock Auto and installed. Ignition module was AC Delco made in USA and coil was AC Delco made in China. Took the GN to a car show yesterday and about 5 minutes into the 30 mile drive I romped on it and ran like it should, no issues. Tried a couple more times and still all good. After about 20 minutes of driving and almost to the show hit it one more time and same damn thing again. After the show, ran great again but after about 15 minutes of run time back to the popping. Making me think it is heat related.

Neither of the previous ignition modules showed any signs of the gooey mess I have read about so no signs of them overheating. Drive the car normally and runs fine, no missing, no stalling or stumbling. I have grounds going to the firewall AND the block for the coil mounting bracket and all attachment points are scraped to bare metal.

GN only has 45,000 miles on it, original short block. About 5,000 miles ago, I changed out the timing set and put on a set of Champion heads and Champion ported stock intake manifold. All grounds were relocated from back of head, all fusible links relocated to fenderwell. Alkycontrol kit with fresh pump and alky gauge is showing normal pressure. Hood mounted fuel pressure gauge showing the normal 1 to 1 rise in fuel pressure. The car has always been ultra reliable so this has me stumped. Haven't used my Powerlogger in years so needed to find my tablet and charge it up before I try to document what it is actually doing. I know the replacement coils, modules are crap now so maybe I got a clunker? Like I said when car is about 10 minutes into a drive it runs perfectly normal. After that is when it starts acting up. Plug wires and plugs are good, Same AC 42's I have run for years gapped at .028. No pre turbo exhaust leaks. Cam sensor was gone thru and the tab repair kit was installed. Haven't really gone any more in depth on it since replacing the module and coil as I am still recovering from recent hip surgery.
Hi mark.if the coil pack doesn't fix it.here are some options.test the fuel injectors and have them cleaned,Fp can rise 1 to 1,but it doesn't mean the cylinder is getting fuel.compression test the motor see where its it's at.verify timing on the motor and see what the afr is doing when it starts to pop (rich or lean).
 

GNVYUS 1

Well-Known Member
Joined
Dec 15, 2002
Crank sensor
Cam sensor
Ignition module

You can usually pick one of the red cups, swap and get it running. I went to the TR6 and then swapped the other 2 anyways, ran great again. LOL
 

87_gn2fast4u

New Member
Joined
Jan 14, 2021
Haven't needed any advice in a long, long time so here goes. My 87 GN is usually flawless and consistent performance wise. Late last year I began to have a popping, backfiring thru the intake. Years ago I took off the original ignition module and coil to save for the future and installed replacements. Car always ran great that way for years and figured I would just swap back to the stock ones on the shelf. Problem solved! Numerous 100 plus mph tests without any issues. Running 20 lbs of boost with alky.

Fast forward to last week and the same symptoms are back with the original parts. Ordered some replacements from Rock Auto and installed. Ignition module was AC Delco made in USA and coil was AC Delco made in China. Took the GN to a car show yesterday and about 5 minutes into the 30 mile drive I romped on it and ran like it should, no issues. Tried a couple more times and still all good. After about 20 minutes of driving and almost to the show hit it one more time and same damn thing again. After the show, ran great again but after about 15 minutes of run time back to the popping. Making me think it is heat related.

Neither of the previous ignition modules showed any signs of the gooey mess I have read about so no signs of them overheating. Drive the car normally and runs fine, no missing, no stalling or stumbling. I have grounds going to the firewall AND the block for the coil mounting bracket and all attachment points are scraped to bare metal.

GN only has 45,000 miles on it, original short block. About 5,000 miles ago, I changed out the timing set and put on a set of Champion heads and Champion ported stock intake manifold. All grounds were relocated from back of head, all fusible links relocated to fenderwell. Alkycontrol kit with fresh pump and alky gauge is showing normal pressure. Hood mounted fuel pressure gauge showing the normal 1 to 1 rise in fuel pressure. The car has always been ultra reliable so this has me stumped. Haven't used my Powerlogger in years so needed to find my tablet and charge it up before I try to document what it is actually doing. I know the replacement coils, modules are crap now so maybe I got a clunker? Like I said when car is about 10 minutes into a drive it runs perfectly normal. After that is when it starts acting up. Plug wires and plugs are good, Same AC 42's I have run for years gapped at .028. No pre turbo exhaust leaks. Cam sensor was gone thru and the tab repair kit was installed. Haven't really gone any more in depth on it since replacing the module and coil as I am still recovering from recent hip surgery.
Have you ever considered maybe using a different type of ignition? Distributor or COP? It's a lot of work and definitely not cheap, but it beats using that cheap Chinese crap. Seems like those modules keep getting worse and worse. And, wouldn't waste my money on AcDelco parts, either. Also, thanks for the great parts and customer service. It's always a pleasure.
 
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