Glowing Exhaust Manifolds 1992 454 TBI 7.4L P30 Motorhome

[Nasty-Z]

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

[Kaweh]

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


TOM

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)?

[Nasty-Z]

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)?

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.

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.

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

[Kaweh]

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.

[Kaweh]

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

[Kaweh]

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).

[jay72]

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.

[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 ?