Red Hot Manifold, Bad MPG, etc

FORSFED · 12-16-2004

So I'm working on another car right now, a 90 Talon AWD, that's got a couple of issues that I'm looking for a few opinions on. After filling the first tank I only got 16.5 mpg which is the worst I've seen on any of my dsm's. Secondly, I noticed one night after laying my foot into it a little bit, the exhaust manifold got red hot.

I'm not sure if these two are related, but the possibility exists that there is too much fuel and some of it could be coming out of the head still in flames heating the manifold up..... I fixed the base timing (which was off) to 5 degrees and the car felt noticebly better but still wasn't quite right. I can't test the fuel pressure right now because I don't have the right fitting for the top of the fuel filter. I'm also pretty sure there aren't any vacuum leaks since the boost gauge reads 16 in hg at idle.

The car has a new o2 sensor which seems to only cycle while cruising and not at an idle (reads lean then). New plugs and wires, fuel filter, timing belt, and a list of many other parts not related to this situation. Also note that it's got a 3" exhaust, whineboro and UICP.

Matt D. · 12-16-2004

Exhaust manifolds can turn red hot with a noticeable loss in power because of retarded timing. In essence the fuel is still burning as it is exiting the cylinder and into the manifold creating extremely high EGTs.

FORSFED · 12-16-2004

That's what I was getting at. The car runs real strong and it doesn't feel as though the timing is being pulled so that's sort of what has me confused. I'll get my logger cable back and hopefully read what it's doing this weekend and go from there. Just wanted to know if anyone else had problems like this...

12-17-2004

I would start with a compression check, check the ignition and cam timing and see what those say

FORSFED · 12-17-2004

I don't have a compression tester readily available so I can't test that right now. As for ignition timing, it was off and I fixed it (see first post). Not too sure what you mean by cam timing, but all the marks are lined up after installing the timing belt.