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pete379 07-19-2005 07:04 PM

Engine Stumbling
I am having trouble with my engine in my truck. Its a 88 with a TBI 350. It stumbles like the transmission is stumbling and backfires under heavy acceleration. The backfiring is not very loud, almost like a popping sound in the engine compartment. I took it to a local shop and the mechanic said it was the ignition coil going bad. I replaced it with a new one but it is still acting up. The timing was also checked and it was fine. It seems to be worse when the truck warms up and goes into over drive. The check engine light has not came on. Could the catalytic converter be clogged. Could the fuel filter need to be replaced? When the truck is in park and it is reved up there doesn't seem to be a problem.

NXS 07-19-2005 07:17 PM

Have you ran the codes? all it takes is a paper clip in the aldl connecter.

The cat could cause that and the fule addition to a clogged injector, a bad intake valve or exhaust cam lobe.

sbchevfreak 07-19-2005 10:45 PM

Also try a new ignition modual. They can cause problems like this. Also, and this is kind of a dumb question but.... did they check the resistance of the coil wire when they changed the coil? High resistance here will cause this too, as well as look kind of like a bad coil on the scope.

pete379 07-21-2005 08:25 PM

I checked the coil at Auto Zone myself and it needed to be replaced. I am going to check out the ignition module. The shop I took my truck to at first checked the wires and everything was okay.

HotCTruck 07-26-2005 09:43 PM

Sounds like the same problem I have!
I just bought a 1956 Chevy Truck and I changed The fuel pump, distributor, points, spark plugs plus wires, carberator, and hoses.

It seemed to run fine cruizing the neighborhood, but as soon as I took it on the highway it died and hadda call the tow truck.

When I took the truck home, I found that when I revved the engine on high speeds, it would sputter and die for no reason. I thought I heard a loud popping noise and a whine before the engine died and was hard to start up again until it cooled a little.

From what I am hearing, it's possible it's the "ignition module", or that white rectanglular block mounted to the firewall? I took it off and behind it was a copper colored wire in some transparent goo that was somewhat melted. Could this small object be the cause of all the trucks problems??

I have yet to buy it and see. Is it? It must be right? It's the only thing left! Besides the timing chain, cams and all that, but it seems to run OK at low speed (before heating up?)

What is it?

PS, glad to be here at the forums :mwink:

sbchevfreak 07-26-2005 09:51 PM

What style ign? If you have that "white rctangular block", you are dealing with a points ignition, as that is commonly referred to as a ballast resistor. This will cause a higher RPM backfire and engine kill, if it is weak(too much resistance). Basically you won't get enough voltage to the coil to produce an arc at the plug gap under high RPM or load. Not enough Kv. If the resin is melted, it's a good sign that you probably need a new one.

HotCTruck 07-26-2005 10:13 PM

I am going to try to change the "ballast resistor" tomorrow after work. I couldn't believe it's that tiny little thing that's causing all the problems. It's about 3 to 5 inches in length, and 1 x 1.

I hope that is the problem. I might have to put out the dog and the sister for sale if this doesn't work. :pimp:

HotCTruck 07-31-2005 05:42 PM

Wasn't the ballast resistor after all....
I changed the ballast resistor and the same thing happened, the engine would die at high rpms. So I decided to go down and check the fuel lines and gas tank. I found that the previous owner used an old rubber air hose to connect the fuel lines and it had swollen up and clogged the line. So I cleaned that up and it ran like a top! No dying at high rpms!

Then I screwed up the points which led to the starter being screwed up. While I was adjusting the points and cranking the starter it went out. I took it out and the teeth were cracked as well as the motor being fried. The way I see it is that it would have went out eventually anyway, at least it wasn't on the highway this time. I'm getting it rebuilt and they promise a lifetime warranty on the rebuild. Why not?

I guess it's expected that one has to change everything when restoring a car that's that old.

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