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Thread: Glowing Exhaust Manifolds 1992 454 TBI 7.4L P30 Motorhome

  1. #16
    Fuel Injected!
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    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.

  2. #17
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    GM Adjustable Fuel Pressure Regulator

    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

  3. #18
    Fuel Injected!
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    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).
    Last edited by Kaweh; 04-18-2015 at 11:11 AM.

  4. #19
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    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.
    Last edited by jay72; 04-18-2015 at 04:49 PM.

  5. #20
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    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 ?

  6. #21
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    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.

  7. #22
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    Quote Originally Posted by Kaweh View Post
    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 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...


    After


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





    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.
    Last edited by Fast355; 04-28-2015 at 08:19 AM.

  8. #23
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    Quote Originally Posted by Kaweh View Post
    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 ?
    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
    1994 3500 Dually , 502 (509) , 264HR , Edelbrock MPFI , PFI '7427
    1992 S-10 434 SBC/Tremec - '7427
    1986 Monte Carlo SS
    1984 S-10 , SAS, 496/700R4/205 , D44/14BFF -'7427
    1980 Z-28 496/700R4
    1979 Corvette 496/700R4
    1977 Olds 98 Regency 403/700R4

  9. #24
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    Just throwing this out there, is it possible that the catalytic converter is blocked up? maybe something else causing a restriction?

  10. #25
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    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!

  11. #26
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    Quote Originally Posted by Kaweh View Post
    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!
    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.

  12. #27
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    Quote Originally Posted by Fast355 View Post
    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.

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

  13. #28
    Electronic Ignition!
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    Quote Originally Posted by Kaweh View Post
    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!
    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.

  14. #29
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    Quote Originally Posted by Markmx6 View Post
    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.
    it's no the catalytic converter. I ran it for a month without the catalytic converter in it. IT is NOT the Cat.

  15. #30
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    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
    1994 3500 Dually , 502 (509) , 264HR , Edelbrock MPFI , PFI '7427
    1992 S-10 434 SBC/Tremec - '7427
    1986 Monte Carlo SS
    1984 S-10 , SAS, 496/700R4/205 , D44/14BFF -'7427
    1980 Z-28 496/700R4
    1979 Corvette 496/700R4
    1977 Olds 98 Regency 403/700R4

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