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Old 01-29-2021, 05:52 PM   #41
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Originally Posted by Magnet18 View Post
That's odd
Did you hear the hissing noise?
Did cycling the key a second time do anything?

Fuel inlet is disconnected from throttle body and connected to gauge. Seems its slowly leaking down. I do have a spare new fuel pump, I will install tomorrow.
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Old 01-29-2021, 07:23 PM   #42
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I've done this repair hundreds of times. You're done troubleshooting the fuel system. The fault is in the ignition system. The primary ignition side of the system supplies the signal to operate the ignition spark and triggers the fuel injection.


Deep down in the distributor you can find the pickup coil and rotating magnet. Those are the parts that supply the ignition module and the electronic control module,(which operates the injection solenoids).


I can get photos and post them if it would help, but if you are doing the work yourself the distributor has to come out of the engine to replace the shaft with the magnet and the ignition pickup coil.


This might also be a good time to change to a high performance distributor and coil, like MSD.
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Old 01-30-2021, 04:18 AM   #43
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Why is the fuel pressure so high? Can the TB/regulator/return line handle that pressure given that it is only expecting about 15 PSI. As far as I am aware, the stock pump was spec'd low pressure and only gave out about 14-16 PSI.

Do you have one of the bluetooth ALDL gizmos so that you can capture the various readings e.g voltages against stock parameters? It should give you the fuel pump voltages over time. I assume fuel pressure would drop relative to a lower voltage.

Is the pressure falling back to 40 PSI without power? The pump may be designed to allow some back flow when not powered, although that is guesswork on my part.

I assume that whiff of gas you picked up was due to the loose supply line. Thank God you picked that one up. Very nice Church BTW. You lucky fellow. Having multiple careers is very 2021, so you are bang on trend!

Good luck with your investigations.
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Old 01-30-2021, 07:45 AM   #44
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Why is the fuel pressure so high? Can the TB/regulator/return line handle that pressure given that it is only expecting about 15 PSI. As far as I am aware, the stock pump was spec'd low pressure and only gave out about 14-16 PSI.

Do you have one of the bluetooth ALDL gizmos so that you can capture the various readings e.g voltages against stock parameters? It should give you the fuel pump voltages over time. I assume fuel pressure would drop relative to a lower voltage.

Is the pressure falling back to 40 PSI without power? The pump may be designed to allow some back flow when not powered, although that is guesswork on my part.

I assume that whiff of gas you picked up was due to the loose supply line. Thank God you picked that one up. Very nice Church BTW. You lucky fellow. Having multiple careers is very 2021, so you are bang on trend!

Good luck with your investigations.

Yes, Nick, confirmed 13-15.
Revised readings:
Line pressure from pump to throttle body 40 psi, (the 60 was an initial fluke), bleed down overnight to 20 .
Next I will try to get the output reading with the regulator in the loop.
Had an early Morning brainstorm with Brad and now we are wondering if a second pressure regulator at the pump is needed to get the line pressure down.
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Old 01-30-2021, 07:54 AM   #45
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Originally Posted by Guyfromiowa View Post
I've done this repair hundreds of times. You're done troubleshooting the fuel system. The fault is in the ignition system. The primary ignition side of the system supplies the signal to operate the ignition spark and triggers the fuel injection.


Deep down in the distributor you can find the pickup coil and rotating magnet. Those are the parts that supply the ignition module and the electronic control module,(which operates the injection solenoids).


I can get photos and post them if it would help, but if you are doing the work yourself the distributor has to come out of the engine to replace the shaft with the magnet and the ignition pickup coil.

This might also be a good time to change to a high performance distributor and coil, like MSD.



Thanks for your input. It has been established that this is a fuel delivery problem and not an ignition problem.
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Old 01-30-2021, 08:19 AM   #46
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Originally Posted by PeterH-350LE View Post
Yes, Nick, confirmed 13-15.
Revised readings:
Line pressure from pump to throttle body 40 psi, (the 60 was an initial fluke), bleed down overnight to 20 .
Next I will try to get the output reading with the regulator in the loop.
Had an early Morning brainstorm with Brad and now we are wondering if a second pressure regulator at the pump is needed to get the line pressure down.
Out of interest, why did you shoot for a high pressure pump rather than a replacement low pressure version?

For info to anyone who gets into TBI rebuilds. I think they can be quite picky on specifics e.g. the precise rebuild kits, gasket sizes and, i think, injector flow rates. Chris Craw and I were both in TBI hell a few years ago. I'm pretty sure he had a 350 and the same Rochester 220. His TB looked the same but had a different casting number from mine and strangely it didn't seem to be an exact match on the rebuilt kit. I am 99% sure mine is a stock unit. Casting number on mine was 17091045. Chris had found a replacement via Autoline should anyone ever be interested. Anyhow, the point I am trying to make to anyone who works on a TBI rebuild is to undertake due diligence on the casting number, rebuild kit type and the injectors. Hope this helps someone one day!
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Old 01-30-2021, 09:01 AM   #47
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Out of interest, why did you shoot for a high pressure pump rather than a replacement low pressure version?
....

That was recommended to me, but upon further investigation the Walpro GSL-395 rated at 15 PSI would be the correct one to use.

The GSL-392 at 43.5 is the one I used.

See Nick, we are doing all this just for you, so when you get rid of your internal pump, you will know exactly what to use.
Ok, may bad on the pump choice, but that's only part of the story.

Onward to rebuilding the throttle body.

https://walbrofuelpumps.com/walbro-g...ine-fuel-pumps
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Old 01-30-2021, 10:07 AM   #48
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Wink

Quote:
Originally Posted by PeterH-350LE View Post
That was recommended to me, but upon further investigation the Walpro GSL-395 rated at 15 PSI would be the correct one to use.

The GSL-392 at 43.5 is the one I used.

See Nick, we are doing all this just for you, so when you get rid of your internal pump, you will know exactly what to use.
Ok, may bad on the pump choice, but that's only part of the story.

Onward to rebuilding the throttle body.

https://walbrofuelpumps.com/walbro-g...ine-fuel-pumps
Exactly. I need to replace my fuel lines so will copy your set up once you've worked it all out!
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Old 01-31-2021, 04:15 PM   #49
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Waited since Friday for the injectors and regulator rebuilt kit "express" delivery from Rockauto. Its Sunday and still not here.
Put it all back together, tried to start- no go, squirted some starting fluid, vroom fired right up. No pre priming observed, just a shallow squirt when I turn the key to start the engine.
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Old 01-31-2021, 08:06 PM   #50
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Hard Cold Start

Your fuel injectors require high pressure to function. If your system is not holding pressure during a long shut down period, the engine will not start until the pressure builds up. When you turn the ignition on, the fuel pump will run for a few seconds providing sufficient pressure if the system hasn't leaked down. If it has, turning the key on and off several times will build pressure and the engine will start more easily.
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Old 01-31-2021, 11:09 PM   #51
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Originally Posted by PeterH-350LE View Post
454 , factory fuel injection, all new hoses, filters, external fuel pump at low point of tank.
Always used to start on the first crank, regardless of cold or hot. Now i have to turn ignition on 2-3 times to let the relay build up the pressure before it will fire up. No fuel in oil analysis (thanks Keyair for Blackstone link)

Leaky Injectors? I would say most likely fuel related. What else could I be looking at?
It is NOT leaky injectors as you would have some serious fuel codes. The options are two, fuel or spark. Access to the engine compartment is not one of the strong points on that vehicle but you DO need to know what the fuel delivery/pressure is so pulling the cowl is in order.

There are two issue with the fuel delivery, a clogged fuel filter or a sluggish fuel pump. Installing a new pump MAY not have solved the problem for you but the ONLY way to find out is to do a fuel volume/pressure test. They are two tests done individually. Find the fuel pump relay in the engine electrical distribution box and remover the relay. Look at the pin end of the relay and locate Pin #30 and pin #87. Identify the female side of these pin numbers and insert a jumper with a 1/4" male terminal on each end and determine if the tank fuel pump pump comes on. If so remover ONE terminal lead from the relay plug.

https://i.pinimg.com/originals/30/8a...8e10c0c120.jpg


You need to break the fuel line AFTER the fuel filter and route a hose into a gallon or larger container. Be sure that no fuel can be splashed onto the floor/ground as it can be dangerous under a vehicle. With the hose securely routed into the bucket and a timer in hand, plug in the jumper wire for 30 seconds. You SHOULD deliver at least 1 qt. of liquid in that period of time.

IF the delivery rate for 30 seconds is not adequate and the pump is new you will need to check the pump power wiring. But before that you should check the ability of the newly installed external fuel pump to see if i can actually pull enough vacuum to cause fuel to be raised from the tank pickup line. I know of NO system, properly engineered, that has a fuel pump ATTACHED to the bottom of the fuel tank directly so I am assuming the pump is merely hanging onto the tank or on the frame in a low position and is drawing fuel from the top of the fuel sender as the factory intended. If there are any dry rot problems with the rubber hoses (suction side of the pump) or hose compression due to a hose being caught between the tank and the body/frame mount, this can affect the fuel delivery by creating a negative side air leak that will stymie the pumps ability to start fuel flow. You mentioned that the issue was predominately when the vehicle was cold so this is a place I would give lots of attention to.

This is something for a qualified technician to do as it requires an oscilloscope and a low amp AMP clamp. What you are looking for is a voltage drop or other fault in the circuit. We at Atlanta Diesel do these kind of tests initially before we start replacing parts as it can get expensive.

If the pump volume passes the volume test AFETR the fuel filter, the next thing would be the pressure test. There is tool for this but most RV owners have no need for it. One way (the easiest) is to locate the pressure port on the fuel rail that feeds the throttle port. Tie into this with a proper fuel pressure test gage and again plug in the really jumper wire to start the pump. The gage SHOULD read 60psi. NO LESS.

Now it can get a bit pricy. I believe that engine is a multi port fuel injector system (injectors at all intake ports) but if GM has snuck in a CMFI system on me then the issue of fuel pump pressure gets very critical. Here is an article I came across 3 year ago while working on this issue it MIGHT be of help to you.

https://www.underhoodservice.com/gmc...ion-diagnosis/

For the most part the first two fuel issues will save most starting problems but if not I can take you through the spark portion of the diagnostic. But you will have to repost the complaint.

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Old 02-01-2021, 01:51 AM   #52
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This is a useful document http://www.73-87chevytrucks.com/tech...TBISystems.pdf

Did you manage to swap out the fuel pump for the low pressure version or are you still on the 40 PSI version?

Voltages at fuel pump can be measured via Bluetooth ALDL OBD1/ALDLdroid which I think is a useful investment. Only about 60 bucks. I think I got this one. There might be other newer variants available. http://www.1320electronics.com/products.html
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Old 02-01-2021, 02:31 AM   #53
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[QUOTE=DubleDeuce;2456170]

Peter's 350 has the earlier TBI set up. It has a lower pressure. It's for a 1992 7.4L 454 4L80E P-series chassis. I think the EFI you are referring to came in about 1994.
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Old 02-01-2021, 02:32 AM   #54
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Also, see attached from fuel manual. Might help.
Attached Files
File Type: pdf X9136_1991_Fuel Control System.pdf (6.67 MB, 23 views)
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Old 02-01-2021, 05:17 AM   #55
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Also, see attached from fuel manual. Might help.

Thanks Nick, that already answered a lot of my questions!
For example, why I had no line pressure after the engine is shut off:
>>>The internal constant bleed feature of TBI Model 220 relieves fuel pump system pressure when the engine is turned "OFF.” Therefore, no further pressure relief procedure is required<<<
One could assume a faulty check valve at the pump, because of this feature

Also the 2 seconds Brad quoted is correct. What I heard was the fuel pressure moving through the regulator relieving pressure.

and third, several very shorts shots of priming should happen upon Cranking, I get 1 very very brief one. Something to look into for sure.


Still on the GLS-392 40psi version, Nick.The GSL-395 is on order. I do not expect that to be the major issue.





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Old 02-01-2021, 06:08 AM   #56
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When the key is first turned "ON” without the engine running, the ECM/PCM turns a fuel pump relay "ON” for two seconds. This builds up the fuel pressure quickly. If the engine is not started within two seconds, the ECM/PCM shuts the fuel pump "OFF” and waits until the engine starts. As soon as the engine is cranked, the ECM/PCM turns the relay "ON” and runs the fuel pump. On the 5.7L engine in the G van and all other 5.7L and 7.4L engines in vehicles over 8500 GVW, a fuel module will override the ECM/PCM and the fuel pump will run for approximately twenty seconds. The fuel module corrects a prolonged hot restart (vapor lock) during high ambient conditions. When the engine is cranking or running, the ECM/PCM receives distributor reference pulses which in turn energize the fuel injectors.
As a backup system to the fuel pump relay, the fuel pump is also turned on by an oil pressure switch. When the engine oil pressure reaches about 28 kPa (4psi), through cranking the oil pressure switch will close to complete the circuit to the fuel pump. An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The oil pressure switch will turn on the fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).
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Old 02-01-2021, 08:02 AM   #57
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Jeez....and to think I asked Rob if the Holley kit could be used for Bella's 350.

At the moment (with an electric fuel pump and carburetor) she starts first time (first click on the ignition switch starts the pump running, wait 5 secs, second click fires and starter, and she immediate catches) and with the GVOD we get 13-15mpg (UK gallon), or I could do the 'upgrade' and have starting issues and worst fuel consumption?????

(Lobs hand-grenade and runs for cover)
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Old 02-01-2021, 08:18 AM   #58
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Jeez....and to think I asked Rob if the Holley kit could be used for Bella's 350.

At the moment (with an electric fuel pump and carburetor) she starts first time (first click on the ignition switch starts the pump running, wait 5 secs, second click fires and starter, and she immediate catches) and with the GVOD we get 13-15mpg (UK gallon), or I could do the 'upgrade' and have starting issues and worst fuel consumption?????

(Lobs hand-grenade and runs for cover)
Martin, you must be getting bored during lockdown

It's 28 degrees here today, with all this talk about starting, not starting I just might have to go see if my Argosy will start this morning
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Old 02-01-2021, 08:19 AM   #59
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[QUOTE=Boom Sounds;2456186]
Quote:
Originally Posted by DubleDeuce View Post

Peter's 350 has the earlier TBI set up. It has a lower pressure. It's for a 1992 7.4L 454 4L80E P-series chassis. I think the EFI you are referring to came in about 1994.
The 1994/1995 trucks had a higher fuel pressure of 30 psi. Multi port injectors came in later, at least on the trucks.
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Old 02-01-2021, 09:23 AM   #60
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Jeez....and to think I asked Rob if the Holley kit could be used for Bella's 350.

At the moment (with an electric fuel pump and carburetor) she starts first time (first click on the ignition switch starts the pump running, wait 5 secs, second click fires and starter, and she immediate catches) and with the GVOD we get 13-15mpg (UK gallon), or I could do the 'upgrade' and have starting issues and worst fuel consumption?????

(Lobs hand-grenade and runs for cover)
Peter and I have the 4L80E. It's very good once it starts up.
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