AFR ?

[mike454]

I have a 1993 Chevy Truck 3500 4 door ramp truck that I just acquired, it has a 7.4 4l80e 16147060 BAMP

The previous owner said it had always, since day1, had problems with turning the exhaust manifolds cherry red while pulling.....

Well sure enough it does, just sitting here idling the manifolds are at 635* deg on my infrared temp checker....isnt normal like 300to 400?

My question is what can cause it to do that? He said its had 4 sets of manifolds on it over the years, and has pretty much done this since it was new.

My thought was originally that it was too rich and the unburned fuel was causing the overheated manifolds.

But I just got a new AEM Wideband,and it shows under wot 15.8/16.5,and cruise 15.3/15.5 to 1,which is pretty lean right?

Have been thru all the tune up stuff, and timing settings its at 8 degrees now with connector unplugged, and I tried it at 2 and 4 degrees and it still did it but was down on power a little,
'seems to run best and not ping at 8.

Exhaust is new 2 1/2 back to 2 brand new flow masters,no converters, so everything there seems to be ok, no restrictions.


Fuel pressure is a little low at 11 psi.....

I'm getting ready to work on getting that up to 15 or 16?

And to do some logs, over the weekend.

any thoughts ? or anyone else ran into this?

I know I've heard about this year motorhomes doing it

[tayto]

check injector part numbers, perhaps they're the wrong ones.

[PJG1173]

I have seen this before. my tbi 4.3 used to do this under a load for extended periods of time (chewing through the mud). manifolds would glow read hot. had a buddy tell me that this is typical of tbi's. I turned up fuel pressure and no more glowing manifold problems but was a little rich in other areas.

[In-Tech]

If your fuel pressure gauge is accurate, shim that regulator till psi is 13, huge difference in fueling with a couple lbs of fuel pressure on a low pressure TBI system. Note, there is a 70 second power enrichment delay in the BAMP program. That's not doing you any favors either.

[mike454]

yes I had ran into that before on the fuel pressure too. I will get it up to 13 and double ck my gauge, its an older Mac but on low pressure a lb or 2 either way wouldn't help.

I talked to the guy that bought the truck new and he says its had this issue since before the warranty was out and the dealer couldn't straighten it out after swapping everything....engine and all.

so we'll see.
on that pe delay set it to 0 correct?

mike

[In-Tech]

During tuning I usually set the delay to 0, then after finished I like to add a short delay as it helps fuel economy when driving around town and lot's of transients that might trip un-needed PE.