Re: [GMCMH-EFI] Blowing Mufflers

[James Hupy]

If you are blowing mufflers up, you have unturned fuel in them. That should NEVER happen, no matter if you have a Carburetor, or anyone's fuel injection. That is unburned fuel passing completely through the engine. Because you stated that you have had it more than once, I would look first at your O2 sensor placement. Then, fuel/air ratios. That should give you a place to start.

Jim Hupy

Salem, Oregon 

On Sat, Jul 15, 2023, 9:39 AM Dave G <vidg...@gmail.com> wrote:

Hello friends, my first time posting here. Some of you may know me on FB as Dave Gee.

I have made every mistake possible in trying to convert to EFI on my GMC coach. I am now on my 3rd TB and am still exploding mufflers. The coach seems to run well enough but I have now destroyed 4 mufflers. I started with the Holley Quadrajet and Hyperspark. After multiple hardware failures I decided to try AFI's GM TBI system for a mid 90's truck. It runs very well but has blown up mufflers. I may have fixed the problem by installing a new retrofitted HEI with computer control. The old distributor was in pretty bad shape despite the engine running well. I also switched from E3 plugs to NGK Iridium. Since I am not sure the problem is solved I want to do further diagnostics and have purchased an AEM wideband sensor/gauge set and also purchased the ALDL to USB cable for use with Tunerpro.

I am trying to find the files to load for a $31 mask as well as a concise tutorial for using Tunerpro. It seems that every site I have looked at was either gone or no longer administrated.

I know I should have started here first. Bill Van Vlack and others were kind enough to reach out to me a long time ago before I went with Holley. What a mistake that was!

Any guidance and links to the resources I need are appreciated! Thank you!

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[Dolph Santorine]

Nearly all the muffler problems I’ve seen are related to excessive spark plug gaps (greater than .038), coil failure, leading to dumping fuel into the air pump that is the engine, which then pumps it into the muffler. Should the ignition system decide to throw a couple of sparks, it blows out the muffler. 

Recommendations -

1. Make certain your charging system is making the right amount of DC, and that it’s not all noisy indicating rectifier failure. I’ve seen many bad alternators cause module problems. 

2. Replace the Coil and the Module with new, Delco parts. 

3. fresh wires

4. Clean those plugs and gap at .038

HTH

Dolph Santorine

Do...@DolphSantorine.com

Excuse me for not being my usual wordy and sporadically verbose self. This message is sent from my iPhone.   

No trees were killed in the sending of this message and few long dead dinosaurs were involved. A large number of electrons were terribly inconvenienced.

On Jul 15, 2023, at 1:08 PM, James Hupy <james...@gmail.com> wrote:



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[MICHAEL ORLANDI]

Start off with a set of AC spark plugs for the year and motor in your coach. In the dealerships and aftermarket shops that I have worked in I have fixed numerous misfires and drivability concerns with OEM spark plugs. I have that the aftermarket just doesn’t work correctly. Stick with copper core as anything else is a waist and a potential problem.

Do you have a scan tool to read live data with?

If so what is the blocklearn and intergrader at? Ideal is 128+-10. What is your fuel pressure? When you turn off is there any fuel in the intake, TBI at full open throttle?

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On Jul 15, 2023, at 10:08 AM, James Hupy <james...@gmail.com> wrote:



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[Jon Roche]

Maybe…. 

My experience was failed cheap mufflers.    Local Shop installed them on mine and a friend’s coach…. So 6 failed mufflers between us in just a couple summers.   Then another shop swapped out the last blown ones to a good quality one and that has been fine for a long time.  

Never really noticed any backfiring.  But sure have seen many blown up cheap mufflers. 

On Jul 15, 2023, at 12:08 PM, James Hupy <james...@gmail.com> wrote:



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[Eric Schmidt]

If you are having the same problem with different FI systems installed, my guess is that it isn't the FI system causing the problem. Ignition components, intake and / or exhaust leak.

[George Beckman]

We have to remember our long time guru friend Dick Patterson’s wry comment on issues like this. 90% of all carburetor/EFI problems are ignition. I cannot begin to tell the oddities caused by the ignition module, but here is a recent example: 

Fitech was running very lean with other problems.(The rear bumper was blued from the exhaust heat.) The handheld showed that upon throttle release, the RPMs went to idle. The analog tach connected to the same tach post showed proper (e.g. 2300 RPMs). Owner changed the module and the handheld and other problems corrected. I still say, that this is impossible—can’t happen. Apparently, the Fitech is analyzing the "tach signal” differently. I always assumed it was a simple pulse signal.

On Jul 16, 2023, at 8:46 AM, Eric Schmidt <jjjmi...@gmail.com> wrote:

If you are having the same problem with different FI systems installed, my guess is that it isn't the FI system causing the problem. Ignition components, intake and / or exhaust leak.

---------

Best Wishes,

George
gbec...@graestone.org

[Keith V]

Yeah, sounds to me like one or two cylinders arent firing and are dumping fuel into the exhaust

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Sent: Monday, July 17, 2023 8:55:57 PM
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Subject: Re: [GMCMH-EFI] Blowing Mufflers

 

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[George Beckman]

And the O2 sensor couldn't care less about extra fuel in the exhaust. It only registers the O2 levels. When a cylinder misses, no O2 is used, and the O2 sensor assumes there was not enough fuel to use up the O2—a lean condition. The EFI adds more fuel to the mixture. The firing cylinders run richer, and more fuel is dumped by the missing cylinders until the O2 sensor is satisfied enough O2 is being used in the burn.

On Jul 21, 2023, at 10:49 AM, Keith V <my4...@hotmail.com> wrote:

Yeah, sounds to me like one or two cylinders arent firing and are dumping fuel into the exhaust

[James Hupy]

The signal from the O2 sensor is an analog signal. The computer only recognizes a digital signal. So, some conversion is happening before the data from the O2 sensor gets to the computer, that equates to time in milliseconds between when the signal is read and the computer sends signals to the fuel injectors. No wonder mufflers suffer as a result. Cheap ones flat out don't. 

Jim Hupy

Salem, Oregon 

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[Dave G]

Thanks to everyone who replied with suggestions! I have considered all of them and am very grateful for your thoughts. With some guidance from Dick Patterson I have installed an all-new ignition system. ATM I am addressing the fuel system which I think delivers way to much pressure for my throttle body (rated for 30) psi. I am boiling my gas and processing copious amounts of fuel through my system, most of which is returned to the tank. The current pump easily puts out 100 PSI and I believe it is overpowering the built in regulator. I would like to know what external fuel pump/filter others are running and hoping to drop the pressure significantly. This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi.

[Bill Van Vlack]

I used an Airtex 8094 for one of my pumps for my GM TBI. It seems to be out of stock. I think the pressure rating of the pump needs to be just a little higher than what the built-in regulator supplies so that the amount of return fuel is minimized. The 8094 is rated for 17psi. I also bought a Herko K2000 from a friend. They both work fine.

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[Jon Roche]

I believe i am running fuel pump spec from a 1990 e-150 van.   Works well. 

On Jul 31, 2023, at 3:17 PM, Bill Van Vlack <bill.va...@gmail.com> wrote:



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[Bruce Hislop]

There was a GM throttle body EFI system used in 94 or 95 that used smaller injectors at about 30 psi. I believe that is what Randy Van Winkle is using and also KevinV (or is Kelvin? Sorry on my cellphone)

Check with them to be sure which system you are using before ordering a new pump.

Bruce Hislop

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[MICHAEL ORLANDI]

Any pump that you use is going to be regulated by the throttle body, depending on the spring in the regulator. What is the regulated pressure running at? What is your target PSI?

On a jeep I put together I was running a 100 PSI pump but had a had 12psi regulated at the throttle body . The pressure return is not a problem. One problem that you can run in to is lack of volume. What size fuel line are you running?

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[Dave G]

I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30 but I am sending it 100 resulting in a large volume of very hot fuel being sent back to the tanks and they boil. I did try deadheading it with a regulator set to 30 (the minimum I could get to with a Holley regulator) and it ran but I did not drive it having been suggested that I may end up with vapor lock. I currently run 100 PSI to the throttle body and I think it's overwhelming the internal regulator so I have been looking for the specs of a 94 - 95 454 chevy  fuel pump but have not found the data yet. The units suggested so far are for the earlier TB that uses a larger injector with lower pressure.

[MICHAEL ORLANDI]

Look around for as set of injectors from a 88-93 GM truck with a 7.4L 454 motor. Replace the pressure regulator spring with a 0-20 pi’s spring set at 13psi. If you feel that the fuel is boiling in the return then install a fuel cooler like a 1st gen Deramax used. 

Sent from my iPhone

On Jul 31, 2023, at 2:42 PM, Dave G <vidg...@gmail.com> wrote:

I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30 but I am sending it 100 resulting in a large volume of very hot fuel being sent back to the tanks and they boil. I did try deadheading it with a regulator set to 30 (the minimum I could get to with a Holley regulator) and it ran but I did not drive it having been suggested that I may end up with vapor lock. I currently run 100 PSI to the throttle body and I think it's overwhelming the internal regulator so I have been looking for the specs of a 94 - 95 454 chevy  fuel pump but have not found the data yet. The units suggested so far are for the earlier TB that uses a larger injector with lower pressure.

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[Bruce Hislop]

The pump supplied by Howell was rated for 100psi to a 12 psi injection system.

The 100psi is the max the pump can deliver.  The regulator bypasses the extra fuel fuel back to the tank so the system never sees 100psi.

I have two Airtex pumps, but I can't find the North American website.  Something tells me they were purchased and are now called something else?

Bruce Hislop

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[BruceHislop]

Opps, my bad, its Keith Vasilakes who I believe has a GM based EFI system with the higher pressure Rochester TB.

-------- Forwarded Message --------

Subject:	Re: [GMCMH-EFI] Blowing Mufflers

[James Hupy]

Several GMC owners here in the Northwest have home brewed efi systems using the GM throttle bodies and 7747 computers. Various 02 sensors and ignitions. Most work well with minimal "twiddling" with BIN files. Most are not very complex. 

Jim Hupy 

Salem, Oregon 

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[MICHAEL ORLANDI]

If memory serves me I believe that those systems ran at 20 psi. They would have intank pumps.

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[Bill Van Vlack]

Dave G:

 " This is a modified TB from a '95. I think a 50 psi output would supply plenty of fuel given these were originally using 9 - 11 psi."

" I am using the 94-95 setup slightly modified by AFI. Its internal regulator is set to 30"

If you can provide the Rochester and injector part numbers, we might be able to research their specs and recommend a pump.

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[Dave G]

I wish I could give you exact part numbers but I can't, or at least it wouldn't be certain. My current TB was updated by using an earlier TB and increasing the bore to 1.8 or so and using the higher pressure/smaller injectors. There was some guy somewhere that had been doing it for awhile. I have had very good performance from it but feel I am wasting a lot of energy to overheat my fuel. I think a pump that produces 35 - 50 PSI would be ideal, the lower the better. I may add an accumulator if pressure loss on acceleration becomes a problem. Looking for best flow but not high pressure. What did GM use in the 94-95 Chevy trucks, or at least what was the spec output. I have even considered using a regulator with a pre-TB return in addition to the return on my TB just so I get pressure under control. Thanks!

[Dave Stragand]

Something isn't right with that.  I can't imagine any fuel pump being able to actually heat a tank full of fuel to boiling.  Even if it were specifically a 12v heater, it would have a heck of a time doing so.  Are other heat souces like exhaust located too close to the tank?

-Dave

1978 Transmode near Pittsburgh

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[MICHAEL ORLANDI]

So you are using a modified 4.3/305/350 TBI unit. Not a 7.4/454 unit(2”). 

Leave the pump alone. If you want the fuel cooler you will need to use a fuel cooler , something like a transmission cooler.

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[M B]

Fuel pressure for 94-95 7.4 L was 26-32psi.  I checked the fuel pumps for that year 7.4l TBI offered by RockAuto and they range from 43 to 55 psi.  

If you have a set up from AFI you probably have the 4.3L injectors with a stronger spring to duplicate the 7.4L inj flow or 7.4L injectors if they had them in stock. 

Summit racing offers fuel coolers for $58 +. 

[Dave G]

Yes, I believe it is a modified 4.3 TB. I installed an AEM AFR gauge and can see the I am achieving 14.7:1. I am also using ALDLDroid to monitor and log data. I have had fuel overheating issues since I first installed the Holley. The fuel pump has a very loud and irritating whine. The large volume of fuel being returned to the tank from the hot throttle body very quickly heats the fuel in the tank and from what I have read in other posts, the new gas formulations have a lower boiling point. I am hoping to kill two birds at once here, The loud pump and the boiling gas. The only heat source is the TB pushing a very large volume of hot fuel to the tanks. I am tired of dealing with this problem. I was going to order from Applied but when questioned on price (over $3000) JK got mad and hung up on me. I am not a rich guy and they charge every penny that the market will bear. I just bought a transmision module gear for $7 that they wanted $44 for. I believe in supporting our vendors but they need to support us too. Now I am considering finding one of the larger TB for the 7.4 that runs on lower fuel pressure 9 - 12 psi and not 100. Right now I am considering replacing my filters as pushing high volumes of fuel through them would likely clog them after this much time. Thanks for all the input!

[Dave G]

Yes, fuel pressure for 94 - 95 was 26 - 32 (THANK YOU) but is appears that is an in-tank fuel pump. I need to find an external in the same range and having difficulty finding one.

[Michael Beam]

Dave 

Walbro pumps are us made. Here is one you may like. https://www.summitracing.com/parts/vpn-f30000271?seid=srese1&gclid=Cj0KCQjw2qKmBhCfARIsAFy8buLK6z7dYS5lOxtUsalHTLpcePyX1y4CeWhOtS3QesBu1R22b4ck4QEaAtspEALw_wcB

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On Aug 1, 2023, at 8:02 AM, Dave G <vidg...@gmail.com> wrote:

Yes, fuel pressure for 94 - 95 was 26 - 32 (THANK YOU) but is appears that is an in-tank fuel pump. I need to find an external in the same range and having difficulty finding one.

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[Keith V]

About 75% of these answers are so wrong as to be dangerous. Comon people.

I highly doubt you have a 4.3 TB, it uses smaller bores and would never support 455 cubes.

(Unless it was bored out)

I also use the later 30psi TB on my .030 over 455. It does run out of fuel at the big end, but i dont run there. Otherwise its a better TB.

I use a pump.out of a ford. Im not home now, but I can get the pn tonight.

It does sound like the pump is suspect, i can barely hear mine run, but its heavily vibration damped.

Look on the photo site, i have a fuel injection album. Im sure the pn is there

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[Michael Beam]

He said he had an Affordable Fuel Injection TBI. Email response to my inquiry to their set up: 

“ Michael,

   With engines that require 7.4L throttle bodies we either use 4.3L OEM gm injectors with a stronger spring to duplicate 7.4L flow or we use OEM 7.4L injectors if we have them in stock. The larger bore throttle bodies are the 1.68" 2 bbl Rochester throttle body that we then cnc the bore out to 1.89" 2 bbl. These are not the true 2" 2bbl throttle bodies. 

   A standard 1.68" 2bbl throttle body runs 350.00. A bored out throttle body would run 550.00.”

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On Aug 1, 2023, at 4:28 PM, Keith V <my4...@hotmail.com> wrote:



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[Dave G]

Yes, bored out throttle body 30 psi to smaller injectors. Was running great on my 10 days in Ohio until a muffler blew about 40 minutes from home. I think I am going to build a new fuel sending unit with a 100 micron pre and a 10 micron post filter using the Walbro pump recommended or similar. I will likely hard connect the filters and pump using aftermarket and marine products. Still listening to all suggestions.

[Bill Van Vlack]

Some folks have mounted the filters and pump on a plate that hinges or drops down to allow inspection and maintenance; all inboard of the frame rail rather than on the more vulnerable outside.

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/47661a57-0496-4801-839b-901d517c3032n%40googlegroups.com.

[Dave G]

I have a plate (not hinged yet) I installed when I first put the holley system on. The hinge looks like a good idea but mine is pretty simple and practical, two bolts and it drops down for service. Right now I am considering ordering the Welbro pump (44 psi) and two cartridge (cleanable 10 and 100 micron) filters that have hard fittings between them and the pump. I appreciate all the input, I want to order the parts today.

[Cameron]

I will admit to wishing this was posted a week ago!  I just installed my pumps on the frame rail and they are not very serviceable in that location.

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[George Beckman]

Yes. I am not a fan of gas outside of the frame.

On Aug 1, 2023, at 6:04 PM, Bill Van Vlack <bill.va...@gmail.com> wrote:

Some folks have mounted the filters and pump on a plate that hinges or drops down to allow inspection and maintenance; all inboard of the frame rail rather than on the more vulnerable outside.

---------

Best Wishes,

George
gbec...@graestone.org