Hey,

I have a 1990 5.0 TPI with a T5. There's an MSD 6AL with timing control under the hood as well. Everything else is pretty much stock engine wise.

Since I bought my car about two years ago it has this horrible backfiring problem. I've been overseas and haven't driven it too much, but only have about 10 days to fix it before my leaves up!

Basically the car idles and runs fine now, but while driving it under load it backfires enough to make the car suck to drive. It seems to be backfiring through the exhaust, and does it when you let off the gas, so much that I have to stay on the gas going down hills or it will start popping. If I really get on the gas and then let off, it will backfire loudly.

I have a dual cat car, and the cats may be bad, but they don't get red hot and they don't seem to rattle, but I haven't taken them off. Also there are these POS edelbrock headers that the guy put on, they have AIR tubes coming out of them, but they are just sitting there, they aren't hooked up. They used to have tape over the holes but it didn't seem to do any good.

Any ideas? I definitely need help with this, and you guys seem to be the gurus!

Thanks.

 

I let my car sit when I was over and I had all kinds of goofy **** waiting for me lol.

The open AIR tubes could be doing it, you're getting an air leak into the exhaust and mixing with unburned fuel could give it good enough conditions to light. Or it could be sucking the air all the way through the EGR and getting too much air. Buy some cheap bolts to fill the holes for the time being and see if she settles down.

 

Thanks. I thought that the AIR tubes might be a problem, and I found out that they are supposed to connect to this thing called a "splitting valve" in the GM service manual. It sat near the alternator and the AIR tubes all crossed into it. I set out to the yards to find this valve thing to "do it right," but no luck. I'm guessing for a 90 dual cat car they are pretty damn rare. I figured I'd use some left over heater hose that I have laying around and tie all three together in a "T" to close the loop, but it started to rain and I need more hose!

Tomorrow I'll try hooking them together or just doing what you said and put some bolts into em and see how she likes it.

Thanks again.

 

If you can't get the valve just remove the small steel lines from the headers and plug the ports in the headers.