edco

Hey Guys,

One side of my exhaust is running hotter than the other. Difference at idle on a warm engine is 50 degrees. I had the car on a lift today and both cats are good and no obstructions in the mufflers. So my driver side is much hotter at idle.

Bill Ball asked me to check for a loose spark plug or plugs and everything was good. We are thinking that the previous owner might have the timing belt off a tooth. Any thoughts on what might cause the difference in temperature from one side to the other?

atb

Where are you taking your measurement?

edco

We checked it from front to back but measured the heat right at the h-pipe where it bolts to the manifolds

IcemanG17

Matt
What adam said.....is it right at the header-cat or further back (tailpipe area).....

Hot typically means lean....but cam timing could be a factor...but thats a BIG difference....hopefully its the passenger side bank, since its easier to check.....I would say bad injectors...but you just had them fixed along with the fuel pressure reg too.....

IcemanG17

One more thing.....how is the engine running...smooth with good power....seemed like it in the ORR?

edco

We took the reading where the exhaust manifold enters the H-Pipe, before the cats, before the two sides mix in the H section. At idle on a warm engine Drivers side 260 degrees / Passenger side 217 degrees

Engine is running fine, almost got 21mpg on the trip up and back, 11mpg on race day

IcemanG17

your mileage is fine....not running rough....about the only other thing that would tell if you truely are running lean is a smog check....when is your next one?

I know that the headers are not quite the same length....one side is slightly longer than the other (don't know which one)...its not much...but might explain it a little bit.....

I would test someone elses 928 (bills)....maybe its normal?

edco

Brian,

There is a problem it's hot enough that it is discoloring the bumper cover at the RMB on the same side that is hot at the manifold. So it's not if it's to hot or not but what would cause it to be 45 degrees hotter than the other side at idle. Who knows what that temp difference might be at freeway speed? I took it to a shop today to have a look on the rack thinking it could be a bad cat or blocked muffler they all checked out ok. The tech is not a 928 guy but said it was not the norm to have such extreme difference in temps before the cats

John Speake

I have known a GT where the cam timing was off about a tooth, and that caused a temp differential sufficient to trigger the "ignition protection relay".

SwayBar

If all of the tubes on one bank are cooler than the other bank, then it must be the cam timing.

IcemanG17

Hmm
Since matts is an 88 it doesn't have that circuit...could be dumping fuel which is burning in the header?? Just a little bit anyway?

time to check the cams

John Speake

I appreciate that Matt's S4 doesn't have that circuit, but I was making the point that incorrect cam timing can make a significant difference to exhaust temps.

The incorrect timing may also mess up the mixture on the correctly timed head because the O2 loop will be fooled by possible incomplete combusition from the faulty side.

edco

Thanks John,

That is what Bill Ball suspected, I just thought it never hurts to see what the group thinks as well. Well check it out today and report back.

Bill Ball

I asked Matt to shoot the temps for each cylinder to see if it is one cylinder or the whole bank. Also, I asked him to look through the inspection hole at the timing notch on each cam gear per chance it is that simple. It is real easy to be a tooth off on a TB job if you aren't careful. If the temp difference is the whole bank but the gears are right on, then we need to pull the cam covers and do a factory cam timing job.

Matt, if you need help with this, I am free today.

PorKen

I've seen where someone (dealer?) has installed the belt a tooth off, then adjusted the gear as far as it could go in the slot to try and match up to the follower lift specs, but gave up and left it.




I've heard there is a less invasive way to check/set the cam timing.