Hot Rod Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
58 Corvette with 1987 L98 engine: Running great for months, then died 5 miles from home one day, but restarted after coasting to a stop - drove home with no problem. Four day later, again about 5 miles from home, started coughing through the intake and sputtering (just like earlier) - eventually died after turning around to head back home. Waited 40 minutes restarted but hardly ran – had to call a tow truck - embarrassing. Once home the car restarted - barely ran. No codes were thrown. Vacuum is good at 15 - 17". Checked compression and it was all around 120-130 PSI. Later started and it was smooth and solid - went for test ride and performed well. Stopped at a neighbors about 300 yards from home - spent maybe 3 hours - went to drive back home and barely made it back. Engine would run right for a few seconds and then start sputtering and backfiring. Thankfully it ran strong for a few seconds to get me up my driveway and into the garage. The above happened before summer heat set in here in AZ so the car has been on jacks all summer. A few days ago I started it up and it ran just fine. I let it idle for maybe 10 minutes occasionally rapping the throttle and all was good. Then the next day it ran like crap. Just like the description above – coughing and sputtering. I could keep it running by constantly feathering the throttle but once I stopped it died while back firing through the MAF meter. I could never get the RPMs past maybe 700. Disconnecting the connector to set advance made the engine run worse. The TPS is smooth in its output voltage. Still no codes, suggestions please.
 

·
Registered
Joined
·
3,466 Posts
Sounds like grounds or coil.

I would replace the cap, rotor, coil, module, and inspect the wiring going to the hei for bad connections.

Then make some new grounds out of 4 gauge wire and copper ends.

Stuff wont break the bank but can cause the issues your describing. It is good preventive maintenance if it turns out this is something ecu related. The hei components being bad are more likely.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #5 ·
58 Corvette with 1987 L98 engine: Running great for months, then died 5 miles from home one day, but restarted after coasting to a stop - drove home with no problem. Four day later, again about 5 miles from home, started coughing through the intake and sputtering (just like earlier) - eventually died after turning around to head back home. Waited 40 minutes restarted but hardly ran – had to call a tow truck - embarrassing. Once home the car restarted - barely ran. No codes were thrown. Vacuum is good at 15 - 17". Checked compression and it was all around 120-130 PSI. Later started and it was smooth and solid - went for test ride and performed well. Stopped at a neighbors about 300 yards from home - spent maybe 3 hours - went to drive back home and barely made it back. Engine would run right for a few seconds and then start sputtering and backfiring. Thankfully it ran strong for a few seconds to get me up my driveway and into the garage. The above happened before summer heat set in here in AZ so the car has been on jacks all summer. A few days ago I started it up and it ran just fine. I let it idle for maybe 10 minutes occasionally rapping the throttle and all was good. Then the next day it ran like crap. Just like the description above – coughing and sputtering. I could keep it running by constantly feathering the throttle but once I stopped it died while back firing through the MAF meter. I could never get the RPMs past maybe 700. Disconnecting the connector to set advance made the engine run worse. The TPS is smooth in its output voltage. Still no codes, suggestions please.
I may have found the problem. The male connector to the TPS had a broken tab that locks it to the TPS proper. I replaced the connector and so far so good. Its restarted in good health several times now. You'll hear more if it starts its old habits again.
 

·
Registered
Joined
·
3,466 Posts
Did you put "stable" in the tank before putting the thing on jack stands.

If not pull the fuel filter, replace it and I would blow out my lines before pouring a cleaner in the tank with new gas. Ethanol does not like to sit.

Look at your injector spray. Tbi is pretty good with ethano sledge. But it can still get clogged if bad enough.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #7 ·
Sounds like grounds or coil.

I would replace the cap, rotor, coil, module, and inspect the wiring going to the hei for bad connections.

Then make some new grounds out of 4 gauge wire and copper ends.

Stuff wont break the bank but can cause the issues your describing. It is good preventive maintenance if it turns out this is something ecu related. The hei components being bad are more likely.
Cerial, I've already replaced the module but I'll take your other suggestions too. Do you think the ESC could be the problem?
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #8 ·
Did you put "stable" in the tank before putting the thing on jack stands.

If not pull the fuel filter, replace it and I would blow out my lines before pouring a cleaner in the tank with new gas. Ethanol does not like to sit.

Look at your injector spray. Tbi is pretty good with ethano sledge. But it can still get clogged if bad enough.
Cerial, I'm inclined to think the issue is electrical since it runs fine SOME of the time. But I am going to replace the second filter. I have my fuel pump mounted external to the pump and it has it's own fuel filter and that one looks good and is fairly new. The one in the engine compartment is fairly old so it's time for a replacement there.
 

·
Registered
Joined
·
3,466 Posts
The computer is the last thing in a long list of things. Unless the passenger floor is wet(cowl) or the thing is not advancing timing the computer is probally good.

I would look at the key wiring and Netural/clutch switch before the computer. But only after playing under the hood/car and not finding anything.

I have had fuel pumps that showed good pressure and the thing ran great then would die intermediary. Turned out to be the ground to the fuel pump itself was corroded. I have also had bad fuel pump relay connections/wiring do the same thing.
 

·
Registered
Joined
·
382 Posts
Overheating ign module will also do that. Did you apply the heat sink paste to the back of the new module?

Sent from my moto x4 using Tapatalk
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #11 ·
Sounds like grounds or coil.

I would replace the cap, rotor, coil, module, and inspect the wiring going to the hei for bad connections.

Then make some new grounds out of 4 gauge wire and copper ends.

Stuff wont break the bank but can cause the issues your describing. It is good preventive maintenance if it turns out this is something ecu related. The hei components being bad are more likely.
The computer is the last thing in a long list of things. Unless the passenger floor is wet(cowl) or the thing is not advancing timing the computer is probally good.

I would look at the key wiring and Netural/clutch switch before the computer. But only after playing under the hood/car and not finding anything.

I have had fuel pumps that showed good pressure and the thing ran great then would die intermediary. Turned out to be the ground to the fuel pump itself was corroded. I have also had bad fuel pump relay connections/wiring do the same thing.
Well, here's the latest as of yesterday. New, cap, coil, rotor, module - almost blew my muffler off when I tried starting. I'll go through my grounding again but it's so clearly intermittent that I can't help but think it's a solid state component. It can be running fine one minute (however this hasn't happened for a few days), shut it off, restart 10 seconds later and bam - backfire and sputter if it even gets that far.
 

·
Registered
Joined
·
3 Posts
Well, here's the latest as of yesterday. New, cap, coil, rotor, module - almost blew my muffler off when I tried starting. I'll go through my grounding again but it's so clearly intermittent that I can't help but think it's a solid state component. It can be running fine one minute (however this hasn't happened for a few days), shut it off, restart 10 seconds later and bam - backfire and sputter if it even gets that far.
had rust in my tank that drove me crazy trying to figure out , blow thru line backwards and try starting tf starts and runs check for fuel when dies again
 

·
Registered
Joined
·
185 Posts
If it has backfired through the maf , I would start there. testing it. BUT something else is causing the backfire in the intake.
TPI is BATCH FIRE EFI , This means 4 injectors fire(spray) fuel at once.
Only way to have a back fire in the intake, is
1) a sticking or burnt valve
2) plug wires leaking spark energy into another plug wire and firing the wrong cyl.
3)A timing chain jumped or stripped gears
4) a timing issue, What is the timing set at, was the distributor installed correctly, if new module installed, was the paste put on the module between it and the distributor body.
5) an injector that is leaking and filling the intake with fuel, Check with a fuel psi gauge , put test gauge on fuel rail , it should hold psi, once it has built psi, even after you shut the engine off, if it is dropping psi, find out why.
Check fuel regulator also.
A fuel pump or dirt in lines, won't cause the engine to backfire, nor will the ecu 99.99% of the time.
Base timing (either from the distributor installed wrong,or set base timing being way off. ) A burnt valve, or sticking open valve(broken valve spring) , or crap plug wires., or the old palm to face, installing the plug wires in the wrong firing order.
Check these 5, and you'll most likely find your issue, but the backfiring in intake/maf sensor, most likely killed that sensor, So test and check that sensor, but that isn't the cause of your backfiring.
Good luck

p.s. my gut crystal ball is seeing timing chain jump and/or worn timing gears and chain.
Not sure if g.m. put the nylon timing gears in whatever your engine was pulled from. but my gut says, worn gear and chain jumped.
This is assuming a timing issue isn't from user error, I.E. re installing distributor wrong, plug wires following firing order correctly, and good plug wires.
A coil that is weak, die'n. won't cause a backfire. carbon tracking inside the cap can, a burnt through ign. rotor can make/cause the spark energy to be weak to the plugs and it run like crap, but backfiring, unlikely
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #14 ·
Well Chad & Karen, thank you for your thoughts. Regarding timing I keep going back to the fact that it runs good SOMETIMES. I did find an issue with my knock sensor: bad connection. So I'll replace that ASAP and report back. I'll also see if there is a procedure to troubleshoot the MAF meter. I'll report back.
 

·
Registered
Joined
·
185 Posts
Well Chad & Karen, thank you for your thoughts. Regarding timing I keep going back to the fact that it runs good SOMETIMES. I did find an issue with my knock sensor: bad connection. So I'll replace that ASAP and report back. I'll also see if there is a procedure to troubleshoot the MAF meter. I'll report back.
G.M. cam gear that is alum, with nylon teeth, the timing chain can dance back and forth.
Like I said in the other post. I don't know if g.m. was still using that type of timing gear set in whatever the donor vehicle was.
Have you put a timing light on it when it is running like crap?
Does this engine STILL have an EGR? (some back in the day removed them ,thinking they hurt performance, they don't.) if so, is it sticking partly open sometimes? Many times you can move the valve with your fingers, if you can on yours, when it is running like crap, move the valve with fingers to get it to unstick and close. If problem goes away, well you know what the problem is. 1987 TBI efi you will be able to get to it.
If this 87 engine is tune port efi (TPI) it might be hard to move the valve with fingers, it is in the middle of the unit, ( see photo,) those 2 holes in center of intake
527185

is where the egr mounts.between the upper half and lower, blocked off by the runner tubes connecting the two.
The egr is still vacuum controlled, so when it is running good, if you can unhook the vacuum line going to the valve, and then plug the vacuum line with a golf tee, now the egr won't function, if the problem goes away, you know what you will be replacing,
And will need the egr and gasket and a tpi intake gasket set, as you will be removing the tubes and upper intake to get to the egr.
 

·
Registered
Joined
·
185 Posts
Also, if you have a plumbers torch,
527186

While engine is running, but without lighting torch, just gas coming out, put tip near where the tubes connect to the upper and lower intake and see if the rpm changes from a leak. a backfire through the intake could have blow out a gasket, or from loose bolts. Check the bolts holding the tube pairs to the upper and lower.
Check that the IAC is working correctly also. But that normally will only make it idle like crap, and clean up when you open the throttle blades.

Unlikely but has happened, is a injector driver in the ecu took a crap, and/or is on way out, and when it is running like crap only 1 bank of injectors are firing, and 4 cyl, are not getting fuel other than whatever little is still floating around the intake from revertion. but more likely the egr is sticking.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #17 ·
G.M. cam gear that is alum, with nylon teeth, the timing chain can dance back and forth.
Like I said in the other post. I don't know if g.m. was still using that type of timing gear set in whatever the donor vehicle was.
Have you put a timing light on it when it is running like crap?
Does this engine STILL have an EGR? (some back in the day removed them ,thinking they hurt performance, they don't.) if so, is it sticking partly open sometimes? Many times you can move the valve with your fingers, if you can on yours, when it is running like crap, move the valve with fingers to get it to unstick and close. If problem goes away, well you know what the problem is. 1987 TBI efi you will be able to get to it.
If this 87 engine is tune port efi (TPI) it might be hard to move the valve with fingers, it is in the middle of the unit, ( see photo,) those 2 holes in center of intake
View attachment 527185
is where the egr mounts.between the upper half and lower, blocked off by the runner tubes connecting the two.
The egr is still vacuum controlled, so when it is running good, if you can unhook the vacuum line going to the valve, and then plug the vacuum line with a golf tee, now the egr won't function, if the problem goes away, you know what you will be replacing,
And will need the egr and gasket and a tpi intake gasket set, as you will be removing the tubes and upper intake to get to the egr.
Well, on top of everything I had 3 Extreme Lateral Interbody Fusions performed on L1-4 on January 7th so I'm not hopping around too well yet. I really anxious to further my investigation. Something I might be able to do is make a recording of the sound of the engine when it is "sort of" running. I'm not sure if that's something that can be posted but maybe as an attachment.
 

·
Registered
Joined
·
185 Posts
Well, on top of everything I had 3 Extreme Lateral Interbody Fusions performed on L1-4 on January 7th so I'm not hopping around too well yet. I really anxious to further my investigation. Something I might be able to do is make a recording of the sound of the engine when it is "sort of" running. I'm not sure if that's something that can be posted but maybe as an attachment.
Take it easy. get rest and heal. the vehicle can wait.
 
1 - 18 of 18 Posts
Top