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roflwaffle 05-24-2008 07:10 PM

Question for you Chevy/engine gurus
My friend's dad has a 90 GM pickup w/ a 350/TBI in it. It also has 307 heads instead of stock. For whatever reason, when a lot of load is put on it, the temps would go sky high and power will drop immensely. On one trip, it was noted that the DS manifold, the one w/ the O2 in it, was glowing red, while the other one (no O2) was still the usual color. He was told it was the "cat" although IMO whoever said that is just trying to rip 'em off, since the manifold that was glowing was farther than the cooler one, not to mention if a cat was plugged up enough to make a manifold glow, it would probably blow out the honeycomb pretty quickly.

The only thing I can think of that would cause this kind of issue is obscenely off fuel maps compared to air. I've read that in the event of a vacuum leak, OBDI and older systems with two banks will run proportionally richer or leaner if the other side is off. I've also read that way retarded timing can cause this, but wouldn't both manifolds glow if that was the case? Any other ideas would be great!

Johnny Mullet 05-24-2008 11:12 PM

Best way to check is to drop the pipe and see if it's plugged or temporarily replace the cat with a patch pipe.

JohnnyGrey 05-24-2008 11:22 PM

A few questions...

1. How many injectors are there and where are they?
2. What is the exhaust layout?
3. How many cats?

Duffman 05-24-2008 11:32 PM


Originally Posted by JohnnyGrey (Post 28240)
1. How many injectors are there and where are they?

TBI = 2 Injectors, likely on a dual plane manifold, so one injector would feed a bank of the engine.
I imagine if there was a large imbalance, it would run like a total bag of crap. Does it have air injection pumps into the exhaust manifolds?

I would run some injector cleaner through it as it is pretty cheap stuff and could solve an imbalance issue.

JohnnyGrey 05-24-2008 11:45 PM

2 injectors, yet only one bank has an O2. If the non-O2 bank was running rich or lean, the ECU would never know. Injector cleaner sounds like a good idea. To know for sure, I'd swap the injectors to the opposite manifolds and observe. On an 18 year old pickup, I'd consider replacing them based on their age. You don't have a lot of data to work with, and no way to see how much fuel the other bank is getting.

roflwaffle 05-26-2008 02:08 AM

Off-hand I'm thinking that pulling the spark plugs would allow me to get a good idea if one bank is running richer/leaner than the other and as for obstructions I can pull off the DS manifold and run a snake down it to check there. No air injection AFAIK, I just saw EGR.

COMP 05-30-2008 11:39 PM

why 307 heads ??? could they be 305 heads ???

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