Glowing Exhaust Manifolds 1992 454 TBI 7.4L P30 Motorhome

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.

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.

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.

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.

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Originally Posted by joegreen

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

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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.

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.

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Originally Posted by 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.

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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.

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

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

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Originally Posted by PJG1173

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

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^^ Which is why everyone that has TBI knowledge tells you that even a stock engine needs ATLEAST 13 psi to run correctly. I had a TBI L03 F-car that merely had shorty headers and exhaust on it and was running at 10.5 psi from the factory. The narrow band o2 sensor would go to ZERO at wide open throttle above about 3,000 rpm. Needless to say I understood very quickly why that engine got a bad reputation for not responding well to modifications. Bumped the pressure up to 14 and suddenly had a little fuel to play with. I

I will say to the OP what I said on Chevytalk.... 510cc is not enough fuel for a stock 170 hp 305, much less a 454. Its only enough fuel for about 160 HP at 85% duty cycle and .5 BSFC. If those injectors were used in a 454 it was at 28-32 PSI!

And to expand on what I said earlier , when your injectors were flowed , there had to be a pressure they were flow tested at .

We can assume the 510cc was flowed @ 10.5 psi (which is what GM originally flowed the 17084304 at) , but it does no good to assume . If it was in fact flowed @ 10.5 psi 510cc is not enough fuel .

If the injectors were flowed at a lower or higher pressure , flow will be proportionally different. Without a PSI for a given flow rate , the flow rate is useless .

FWIW , the 17084304 was flow rated by GM engineering @ 75 lb/hr @10.5 psi.

From an email message from Walt Sherwin dated 8/25/03:

"17084304 is the stock (1990 - 1993 454) SS injector. The service part number is 17112560. It is rated at 75 lbs/hr of spec fuel, at 10.5 psig differential pressure.

HTH

TOM

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Quote:

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Originally Posted by Nasty-Z

Without a PSI for a given flow rate , the flow rate is useless .


TOM

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The flow test was done at 13psi. Just found that out. I just wonder if the injectors are indeed the problem. And why did I have no problem all of last year?
How can I bump up the pressure of the fuel pump without going to something extreme like the ACDelco 381 pump (60psi)?

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Originally Posted by billygraves

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

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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.

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Originally Posted by Kaweh

The flow test was done at 13psi. Just found that out. I just wonder if the injectors are indeed the problem. And why did I have no problem all of last year?
How can I bump up the pressure of the fuel pump without going to something extreme like the ACDelco 381 pump (60psi)?

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If the flow test was done @ 13 psi that means your injectors now flow 48.6 Lb/hr @ 13 psi , they are really flowing around 42.6 lb/hr @ the 10 psi you say you have ,not nearly enough to fuel your BBC under load , i'm actually surprised it runs as good as it does .

For those injectors to supply the fuel you would need around 35.5 psi at the injectors (this would give you a theoretical flow rate of 80.5 lb/hr) , this can be accomplished by an externally adjustable pressure regulator or modification to the factory regulator with either an aftermarket spring or the 94-95 454 TBI spring and a high flow pump such as the Walbro 255 LPH or a factory TPI or CPI pump. Only thing to remember is that this injector you have is rated from GM @ 75 lb/hr , for it to flow check as low as it did , something is wrong . I would not raise the pressure with these injectors.

If it were mine and I had hard data like that in front of me , I would get a set of flow matched injectors either on the 17084304 platform that you already have or the 5235231 platform injectors , both are around the same flow rate stock (75 lb/hr for the 17084304 and 80 lb/hr for the 5235231) . Mr injector is referenced on this board a lot although I have never had anything done by them , or if you could pick up another 454 TBI unit from a reputable source that has the injectors you need in it . Parts stores would be a last resort for me as you never know what you get unless it has flow rating @ stated PSI.

Quote:

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Originally Posted by Kaweh

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.

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EGT is exhaust gas temperature and A/F is air / fuel.

Unless you have specialized gauges in your unit or the test equipment to check you would have no way of answering either without a substantial investment in both a Wideband gauge to monitor A/F and a Pyrometer to measure the EGT.


Hope this helps

TOM

Thanks Tom for all that info. And so, here are a couple of questions. Does anyone know where to obtain the injectors that will be right. I ask because the ones in now say the right part but
don't flow according to what they should be. The fuel pump is within manufacturer's specs (9-13psi). so is it safe to say then that the pump is ok? And why is this now a problem. I drove this 34 foot RV to Burning Man (super long climbs ) last year with these injectors in and it wasn't an issue. And thank you for everyone's input. I/We will get to the bottom of this.

I came across this gadget a long time ago and was thinking about modifying the current set up.

http://marine-performance-parts.com/...843505774.aspx

Does anyone know how one knows to what psi one would be changing the pressure? The gadget doesn't have read out on it so how do we know
what we are feeding the engine? And here is another thing I am totally in the dark with:

The fuel pump is in the tank right, way in the back, over 20 feet back, so the pressure shows up before the tbi at currently 10.5psi, then it goes into the
regulator. What happens there? then it goes into the injectors and then depending on their flow it shoots gas into the engine. I've learned that the computer
handles the injectors output but I don't quite understand how all that works. The GM Foreman says my engine is running little rich at idle. Not too much but a little.
Then other's have said the reason the manifolds glow under load is because I'm running lean, Others say no, it's burning excess fuel in the manifold and it's running
too rich. So which one is it under load? rich or lean and the computer doesn't control the regulator so how the heck does all of this work?

Thanks to anyone who can shine some light on this for me. And do it in really plain kid's English! LOL

I found this tonight on IRV site:

"454s do have exhaust manifold issues from excessive heat. My last 454 went through 7 manifolds prior to changing the engine T stat to a 160. After that never had a manifold issue. The engine ran perfect and had no ill effects due to the colder T stat. Even the mpg stayed the same...BUT>>.......once outside temps got to 50...mpg did drop(engine didnt warm enough to go into closed loop operation) and the heater was poor.

If you dont plan to use the RV in the cold months....this may be something to consider."

Before all of these problems, last year when the car engine was rocking solid, I had taken out the thermostat, my engine regularly ran around 100 to 120 degrees. Of course it went up a bit more on climbs but never exceeded 200 which is what it idles at now once it's warm. I bought a 160" thermostat and I haven't put it in yet. Does anyone have any objections to this? yes my heater wasn't so warm but that was no problem because I have rear heater also. It just seemed like the engine was happier (figure of speech).

Why is it a problem now you ask. All those other parts you replaced weren't a problem at some point either. You used it, use creates wear, use causes things to fail. Why is your engine oil black when it was brand new 5000 miles ago.....same theory.

The adjustable fuel pressure regulator, great idea somewhat. When you put that on you're most likely going to read your pumps dead-head pressure which isn't going to be much. And running a pump like that will kill it. The adjustable fuel pressure regulator has to be used with a pump that can output more pressure than you plan to run. For my '92 454 I used the pump for a '95, it's a higher pressure pump.

The problem with doing this is it's going to make it run richer at all rpm and loads, it's going to run rich at idle because it was programmed to run at 9-13 psi from the factory. So you really need to reprogram the chip if you do this. Another problem is measuring the fuel pressure, theres no place to just plug in a gauge, you either have to run the gauge inline for testing only or buy a special fitting with a test port like this one http://marine-performance-parts.com/...ifitting.1.JPG

Then the next problem is adjusting the fuel pressure, you have to take the pod off, make an educated guess, put it all back together and read the pressure. You can't just turn a screw with it running while watching a gauge.

You can go all out and remove the stock regulator, and do some other modifications to the TBI so you can run a remote adjustable regulator with a return line and a guage, like this one http://www.jegs.com/i/Mallory/650/43...FUFk7AodJFwAgA
But it's all going to have the same effect, it'll run too rich at idle and correct at wot under load, or a little too rich at idle and a little closer to ideal under load.

The best fix is to get the injectors to flow properly, install a remote adjustable fuel pressure regulator and remove the regulator from the pod and modify it accordingly, then get into the computer and lean out the lower operating range and possibly richen the under load range.

I ordered new fuel injectors 90lbph, it fired right up. good power. floor it a couple of times and the manifolds got hot red again. I didn't even have to go on the hill to test it. Now I feel really stuck! So we know then that the injectors are not the problem. Any thoughts ?

I have a friend who had a similar problem with his motorhome. What he found was there is a second in lined fuel pump in addition to the pump in the tank. His in line pump had failed causing his problem. Trace your fuel line and check to see if you also have a second fuel pump.

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Originally Posted by Kaweh

I ordered new fuel injectors 90lbph, it fired right up. good power. floor it a couple of times and the manifolds got hot red again. I didn't even have to go on the hill to test it. Now I feel really stuck! So we know then that the injectors are not the problem. Any thoughts ?

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I would say if the power is good and its not overheating there is a good chance its just the load on the engine making the manifolds glow. The 350 in my Express has damn near burned the ceramic coating off the Doug Thorley headers on it and melted the plastic loom over the transmission that shielded the wiring harness. I had to reloom that section of harness.

My Titan made so much heat pulling a heavy trailer that the exhaust system made of stainless discolored from the front of the truck all the way to the rear and even discolored the T304 tips!

Before getting run hard...
http://i243.photobucket.com/albums/f...psg8me2c7y.jpg

After
http://i243.photobucket.com/albums/f...psywdxhb0s.jpg

These are just a few of the things that truck pulled while I had it.

http://i243.photobucket.com/albums/f...ps4wyjlw4g.png

http://i243.photobucket.com/albums/f...ps35tekseh.jpg

I am sure the headers were just glowing when it was under load, especially on long uphill pulls. The stock manifolds are quite crack prone on these trucks and the catalytic converters built on the ends of the manifolds often burnout and become hollow.

Quote:

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Originally Posted by Kaweh

I ordered new fuel injectors 90lbph, it fired right up. good power. floor it a couple of times and the manifolds got hot red again. I didn't even have to go on the hill to test it. Now I feel really stuck! So we know then that the injectors are not the problem. Any thoughts ?

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Where did the injectors come form ? Were they flow tested ? There were no 90#/hr injectors offered by GM so I would assume these were aftermarket? Do you have a spec sheet from them ?

10.5 PSI from the fuel pump is still way to low for my liking FWIW.

TOM

Just throwing this out there, is it possible that the catalytic converter is blocked up? maybe something else causing a restriction?

if you're late to this post: I put in a new catalytic converter and rebuilt the engine. Today I put in the acdelco EP381 pump. This is a higher output pump and my gauge finally went up to 12psi for the fuel pressure. I also put in a 160 degree thermostat and went on a test drive. The same thing is happening. Under load, the manifolds turn red. Now what?...... to be continued!

Quote:

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Originally Posted by Kaweh

if you're late to this post: I put in a new catalytic converter and rebuilt the engine. Today I put in the acdelco EP381 pump. This is a higher output pump and my gauge finally went up to 12psi for the fuel pressure. I also put in a 160 degree thermostat and went on a test drive. The same thing is happening. Under load, the manifolds turn red. Now what?...... to be continued!

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Once upon a time I saw a GMC motorhome with the quadrajet fed oldsmobile 455 crack an intake manifold and under heavy throttle the crack would expand and hot exhaust gasses would shoot into the intake manifolds, leaning out the air/fuel mixture and cause the engine to run poorly and the headers to glow.

Quote:

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Originally Posted by Fast355

Once upon a time I saw a GMC motorhome with the quadrajet fed oldsmobile 455 crack an intake manifold and under heavy throttle the crack would expand and hot exhaust gasses would shoot into the intake manifolds, leaning out the air/fuel mixture and cause the engine to run poorly and the headers to glow.

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Thanks for your thoughts! I put brand new exhaust manifolds on as part of my rebuild!!

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Originally Posted by Kaweh

if you're late to this post: I put in a new catalytic converter and rebuilt the engine. Today I put in the acdelco EP381 pump. This is a higher output pump and my gauge finally went up to 12psi for the fuel pressure. I also put in a 160 degree thermostat and went on a test drive. The same thing is happening. Under load, the manifolds turn red. Now what?...... to be continued!

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I gather that, but it doesn't mean it isn't causing a restriction. If you run raw fuel through a cat, it will clog up really quick. There are other things that can clog it as well. There could also be a restriction somewhere else.

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Originally Posted by Markmx6

I gather that, but it doesn't mean it isn't causing a restriction. If you run raw fuel through a cat, it will clog up really quick. There are other things that can clog it as well. There could also be a restriction somewhere else.

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it's no the catalytic converter. I ran it for a month without the catalytic converter in it. IT is NOT the Cat.

Put a scan tool on it and watch the O2 readings , I believe I mentioned doing this in an earlier post .

I also questioned the validity of the "90 #/hr" injectors you installed , were these from a reputable source such as Mr. Injector , or parts store specials ?

You need hard data to find the problem , scan tool data , at this point I am lost , both here and on Chevytalk.

TOM

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Originally Posted by Kaweh

Thanks for your thoughts! I put brand new exhaust manifolds on as part of my rebuild!!

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I am confused at how the exhaust manifolds have anything to do with the intake manifold.

What I was saying is the 455 Oldsmobile manifolds were known to crack under the carburetor in the exhaust crossover passageway and when the engine was working hard and hot the crack would expand and dump exhaust gasses right back into the intake charge.

Did you confirm that the TDC mark on the balancer is actually TDC?

If you look-up the ultimate TBI mods you can find info on how to make the stock regulator adjustable. It's not as easy to adjust, but there is a screw you can release so you can make small adjustments without buying any parts.

The timing is correct and I tried it at 4 degrees TDC, 6 and 12. We also did it by ear once. When it started to knock we backed off a bit. And that's where it's at right
now, 12 degrees. Great power. just the harder I push it to go up a hill, the hotter they get. Supper bright! Some folks think this is normal and that chevys were prone to cracks and glowing exhausts because of the restrictive nature of the exhaust. They say maybe I didn't notice it. But this is scary red past the Y pipe. The GM foreman agreed to go on a test drive with me with his scanner next week so we'll go and see what he says. I say it's time for headers and dual 3" exhausts. Let's face it everyone I have been in touch says the design is poor and should have never been made like that and that is why in 96 GM changed it.

You're going to swap manifolds for headers so then you'll have glowing red headers.
On my '92 454 I have headers to dual 3" exhaust all the way back to the bumpers. What I said before about GM changing to a steel "shorty" header type manifold, the point is steel is less prone to crack. IMO headers are more likely to glow red because they're thinner than cast iron manifolds.
Heres a video I made several years ago, this is whats going on inside your exhaust. https://youtu.be/CLYi4JDnTSQ
And BTW, haven't changed anything on that engine since, except oil and filters, and it's been run several times for 24 hours straight fully loaded in the bed while towing a car on a trailer. Do I care if my headers are red? No I don't.

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.

by the way thanks for sharing this video Jay. I wonder what might happen if i take the manifolds off and run it. But on my rv there are a lot of power, oil and what not lines running right next to the driver side manifold. Do you have a link to the right steel manifolds that you are referring to?

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Originally Posted by 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.

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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

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The injectors are from RockAuto:
STANDARD MOTOR PRODUCTS Part # TJ11 {Click Info Link for Alternate/OEM Part Numbers} Throttle Body Injector; 90.77 lbs/hr

https://www.rockauto.com/catalog/moreinfo.php?pk=47657

Quote:

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Originally Posted by Nasty-Z

You don't know what injectors you have unless they have been flow tested @ a specific PSI ,

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STANDARD MOTOR PRODUCTS Part # TJ11 {Click Info Link for Alternate/OEM Part Numbers} Throttle Body Injector; 90.77 lbs/hr

LINK: https://www.rockauto.com/catalog/moreinfo.php?pk=47657

I just got off the phone with Rock Auto and I was transferred to technical. The gentleman said that they were test at 14.75psi.
For me to test them means taking the whole tbi out and dropping it off at the shop here in San Jose, Ca. Rockauto said they'd take
them back if I find anything different than 90lb/hr provided i include the data sheet. That'll work I say.