Glowing Exhaust Manifolds 1992 454 TBI 7.4L P30 Motorhome

[Kaweh]

Hello, after reading a lot here i decided to join and ask my question with hope that some of you grearheads may have an answer. I drive a 1992 p30 chassis motorhome with a 7.4L 454 tbi in it. A while back I had a backfire and then loss of power. I brought the RV back to my friends' shop and if I remember correct we replaced the ignition module the ECM had fried and that was that. The car then seemed to run good until I went up a hill.

Long story short I rebuilt the motor with a new timing chain, lifters, (didn't touch the cam, it showed no wear), machined heads and new exhaust manifolds. I had the catalytic converter out and the muffler they are fine. There was no restriction. New spark plugs, rotor, cap, actually a new distributor, coil, map sensor, EGR was fine, new coolant sensor and oxygen sensor, started it up and it fired right up. We played with the timing at 4 degrees TDC, 8 and now it's at 12 and it is back to the way it was running. Good power in the city. Engine does not overheat it purrs. Now, when I go up a hill I still have the same issue! Both sides of the exhaust manifolds glow and if I give it more gas they just glow more. I noticed when I give the car a good amount of gas on a straight road for let's say 10 seconds, it's no problem and before you know it I am at 75 mph. If I do the same amount of gas going up hill, after ten seconds they glow.

I hooked up the shop's snapon computer again today and it didn't show any codes. I replaced the knock sensor also. When the car goes up a hill it does not overheat. Temperature is steady at 200 degrees and the clutch motor fan comes on as it should. Oh, I also put in a new thermostat. I replaced the fuel pump also because I had an extra one and I put a fuel pressure gauge in line. It reads steady at 10.5 psi (9-13 is spec.) By the way the MAP sensor tested out good so did the ignition coil.

I made friends with the shop foreman at the local GM dealership and he put his scanner on it and he says at idle it runs a little rich but not alarmingly much. I checked the engine ground and it's good. So is the battery ground. I rebuilt the fuel pressure regulator also. There are no leaks and all the vacuum lines have been replaced. The intake manifold has a steady vacuum reading. Everything was torqued to spec and the car runs great, idles great, and sounds like a killer chevy. Lastly, I took the injectors to a shop here and had them flow tested. This shop does it with the injectors sitting in the throttle body so I had to bring the whole thing to them. The test outcome was that they are both good and they both flow 510cc. Now I found an online calculator and that turns into almost 50pph. The part number on the injectors reads GM17084304RPD. Now, my online studies point toward the fact that they indeed are the correct part number for this vehicle (p30) but that these injectors should flow 75/80pph. Some say the fuel pump should be at a solid 13 and not between 9 & 13. So this is now overwhelmingly confusing. I learned a lot on this journey and it's now at a point where everyone I have asked about this is out of ideas.

The computer that is in it is a replacement one and it has no part number on it. it just shows this: NUMBER: 7-7060 and DC CODE: 1212GD The old prom was used and it says this on it: AWUJ. The gentleman at tbichips.com says that he can reprogram my prom and all of this stuff will go away but I am holding off on that because the vehicle wasn't doing this and I shouldn't have to modify things in order to get it back on track. I know I can do a lot of work and programming to make it better but I feel it shouldn't have to come to that. So there it is. I'd love to hear some suggestions from you folks. Thank you in advance for your time and knowledge.

[partero]

Replace the EGR Valve. I had this same problem with my 454 chevy chassis Motorhome & pulled the heads & had the valves done, thinking I had a burned intake Valve! I still had the same problem after putting the heads back on! A leaking EGR Valve allows exhaust flame to get past the valve & ignite the fuel in the intake manifold. It only happens under hard acceleration, when there is a lot of pressure in the exhaust manifolds.

[joegreen]

I'm sure other more knowledgeable people will chime in but i believe your timing should be set to 0 degrees with the brown wire unplugged. Also these systems are not super modern or sensitive so don't be alarmed if its not throwing codes.

[Kaweh]

i believe your timing should be set to 0 degrees with the brown wire unplugged.

Hello and thank you for your comment. The book says 4 degrees TDC and I have played with the timing several times. Timing is not the issue in this case! And last year, before all this, the engine was advanced 12 degrees which is where it's at now.

[ony]

some one else had a post sometime ago about manifolds glowing, you might do a search at the top of the page and find what they did.

[Kaweh]

Thank you for your reply. We had already tested the EGR valve and because you brought it up I just tested it again (20 seconds hold) and it holds vacuum.

[jay72]

Thank you for your reply. We had already tested the EGR valve and because you brought it up I just tested it again (20 seconds hold) and it holds vacuum.

What you did only tests the vacuum diaphram. The problem mentioned is the exhaust gas pressure opening the valve.

My '92 dually used to cruise with the headers glowing, I think the reason why GM stopped using iron exhaust manifolds and changed to steel header type manifolds is because the heat would crack the iron.
Another cause of backfiring is the screens on the distributor base getting clogged and not allowing any airflow, not that it needs much, but the screens need to be removed.

You can have the problem tuned out, or replace the whole eprom, that AWUJ code was updated, I don't remember with what. I put a BAMM code in my truck and it runs better, it has to run on at least 89 octane, thats the factory recommendation.

If the injector flow numbers are off why don't you correct that? The problem points almost directly at a fueling issue and you said you found one.

[Nasty-Z]

If (and its a big "if") the injectors you have are only flowing 510 cc (48.6 lb/hr) you have found your problem.

Possibly the flow is enough at idle and part throttle that it runs good , but when you load the engine (your uphill runs) it runs out of fuel causing the lean glowing red manifolds you describe.

A sure fire way to prove a fuel related problem would be to run the vehicle with the scanner connected and keep an eye on the O2 sensor reading , you will find out fast if it's going lean.

HTH

TOM

[PJG1173]

^X2 had that problem with a stock S10. not enough fuel in high load area

[Kaweh]

Jay, i use 91 octane at the moment. I ordered a BAMS chip from Harris Performance. I just received it today and haven't put it in yet. I had the injectors tested and they were too low for this motor according to many sources. now I have 90 lb/hr injector in there and a EP381 AC delco fuel pump which is overkill but Harris recommended the upgrade as well. The backfire happened because of a ground short from the injectors. i bout this rv used and someone had messed with the injectors. and no matter what, it had great power and up the hill to burnin man six years in a row yielded no problems. anyway, the backfire is gone. engine runs great just up the hill the manifolds start to glow in a matter of seconds and it's scary. I am going to make a video of this before i put in the prom just to show the level of the severity.

[Nasty-Z]

Jay, i use 91 octane at the moment. I ordered a BAMS chip from Harris Performance. I just received it today and haven't put it in yet. I had the injectors tested and they were too low for this motor according to many sources. now I have 90 lb/hr injector in there and a EP381 AC delco fuel pump which is overkill but Harris recommended the upgrade as well. The backfire happened because of a ground short from the injectors. i bout this rv used and someone had messed with the injectors. and no matter what, it had great power and up the hill to burnin man six years in a row yielded no problems. anyway, the backfire is gone. engine runs great just up the hill the manifolds start to glow in a matter of seconds and it's scary. I am going to make a video of this before i put in the prom just to show the level of the severity.

You don't know what injectors you have unless they have been flow tested @ a specific PSI , I have asked multiple times for you to provide where these new injectors came from but never received an answer , there were never any 90#/hr injectors EVER released from GM so I know for a fact you do not have those . I still contend the engine is running out of fuel or has a vaccum leak as it gets hotter and works harder. Again I will say , Unless you get hard data out of either a datalogging software program or a scan tool , you are pissing in a fan throwing parts at this thing . You need data to support weather a change you make is doing any good or not , simply using the manifolds as a tuning tool is a poor way to diagnose. You are already pissing in a fan ordering anything from TBI Chips , you can do your own research on that on this very site. You can have all the fuel pump in the world and as big of injectors as you can find , if the calibration and the input from the related sensors is incorrect , it will still perform like a$$ ........

FWIW , my '94 3500 with the 502 (509) regularly sees 14K# of 5th wheel camper , add that to the 6440# the truck weighs and its over 21K# with my not so small a$$ in the seat and full fuel tanks , EGT stays right around 1300 at the collector merge , never do the headers glow under load . I run Edelbrock coated TES headers to Dual 2-1/2" exhaust with an X pipe . This isn't my first rodeo here .......


Diagnose first , then change parts as necessary .

TOM

[Kaweh]

I replaced the EGR valve last week and still the same problem persists. It made no difference although we did find a tiny tiny leak with the EGR that was only found when spratying starter fulitd right into from the bottom. But it was so tiny. Either way the same problem persists.

[billygraves]

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[Kaweh]

Yes there are some things that can help. Without EGT and A/F ratio readings how is anyone suppose to help?

What is EGT and A/F?
I use AC Delco when possible and available. I've done pretty much all of the labor myself and I have owned this vehicle for the past six years.