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Old 04-30-2021, 03:58 PM   #1
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Fuel pump wiring help

I need some help understanding the fuel pump wiring on the early 90's TBI 220 systems.
My understanding is that in "ignition on" mode, the pump will prime the system and the injectors will spray a few shots in the throttle body and then the pump should turn off.
My pump stays on.
One would assume that the fuel pump control relay would be in charge of this.
I have tried 3 different fuel pump relays with the same results, so it can be safely ruled out to be the culprit.
Can anyone look at these schematics and tell me where to look? I also would be curious to understand what the red circled C149 is?

I can not rule out that some PO wired the fuel pump to IGN on, bypassing the pump relay.
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Old 04-30-2021, 06:22 PM   #2
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The prime circuit through the relay, pins 490/120, is normally closed. It opens ( shuts off) the prime circuit when the relay is powered, which also then runs the fuel pump all the time when you start the engine.

The schematic is showing the physical connector views so 149 circled in red is just a single wire connector.

Given that your pump runs all the time in prime mode the fuel pump relay is not the problem. On the other hand If the pump was not running at all in prime the relay could be the cause of that.

So the question is what is 490 and 120 connected to? One or both have other circuit components that control the pump in prime mode. Those are not shown in your posted schematics. I'm not 100% positive but one of the upstream components is the ECU and there may other "switches" as well.

Same question of 465/150 in terms of what are the connected to? Prime is probably shut off by energizing the relay, so what in that circuit is controlling the relay?
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Old 04-30-2021, 07:20 PM   #3
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Quote:
Originally Posted by vintage6t View Post
The prime circuit through the relay, pins 490/120, is normally closed. It opens ( shuts off) the prime circuit when the relay is powered, which also then runs the fuel pump all the time when you start the engine.

The schematic is showing the physical connector views so 149 circled in red is just a single wire connector.

Given that your pump runs all the time in prime mode the fuel pump relay is not the problem. On the other hand If the pump was not running at all in prime the relay could be the cause of that.

So the question is what is 490 and 120 connected to? One or both have other circuit components that control the pump in prime mode. Those are not shown in your posted schematics. I'm not 100% positive but one of the upstream components is the ECU and there may other "switches" as well.

Same question of 465/150 in terms of what are the connected to? Prime is probably shut off by energizing the relay, so what in that circuit is controlling the relay?

Thanks for the reply. I have to admit that these schematics are difficult for me to understand.

465 goes to the ECM, 150 appears to be ground, 120 goes to the ECM as well, 490 I can only see as a pin of the ACDL, the diagnostic plug, being the predecessor of the OBD-2
edit ECM not PCM
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Old 05-01-2021, 05:21 AM   #4
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Given, the additional info, I don't think what I described above makes sense. Specifically 490 seems to be a fuel pump test point only and not involved in the prime operation, Sorry for the wild goose chase.

What I think is correct is that the prime works by the ECM energizing the relay for a few seconds when you turn the ignition on.

It's possible your ECM is not operating correctly but it could be a few other things as well. I've attached a diagram of a 90s TBI circuit which may not be 100% accurate to yours but should be more or less the same. In the diagram you can see two components, the fuel pump oil pressure switch and the hot fuel module.

The oil pressure switch is wired in parallel to the fuel pump relay, When oil pressure builds in a running engine it closes and takes the fuel pump current load over from the fuel pump relay. As long as the engine is running then you can actually de-energize the relay and the pump will still run. My point here is if the oil pressure switch is defective and stuck with its contact closed (simulating a running engine) the fuel pump will run regardless of the ECM shutting it off after the few second prime. You can test the oil pressure switch with a meter as it should be open (no continuity) when the engine is off or you can also just disconnect it's connector and see if the prime works as expected.

Similar story with the hot fuel module. When the ignition is tuned on, it over rides the ECM and runs the fuel pump for like 20-30 seconds to clear any vapor lock in the fuel lines. Leave the ignition on for 30+ seconds and see if the pump then shuts off and this will tell you if its working correctly or not. Alternately you can also remove its connector and see if the pump primes for a few seconds via the ECM when the ignition is turned on.
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Old 05-01-2021, 07:07 AM   #5
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Quote:
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Given, the additional info, I don't think what I described above makes sense. Specifically 490 seems to be a fuel pump test point only and not involved in the prime operation, Sorry for the wild goose chase.

What I think is correct is that the prime works by the ECM energizing the relay for a few seconds when you turn the ignition on.

It's possible your ECM is not operating correctly but it could be a few other things as well. I've attached a diagram of a 90s TBI circuit which may not be 100% accurate to yours but should be more or less the same. In the diagram you can see two components, the fuel pump oil pressure switch and the hot fuel module.

The oil pressure switch is wired in parallel to the fuel pump relay, When oil pressure builds in a running engine it closes and takes the fuel pump current load over from the fuel pump relay. As long as the engine is running then you can actually de-energize the relay and the pump will still run. My point here is if the oil pressure switch is defective and stuck with its contact closed (simulating a running engine) the fuel pump will run regardless of the ECM shutting it off after the few second prime. You can test the oil pressure switch with a meter as it should be open (no continuity) when the engine is off or you can also just disconnect it's connector and see if the prime works as expected.

Similar story with the hot fuel module. When the ignition is tuned on, it over rides the ECM and runs the fuel pump for like 20-30 seconds to clear any vapor lock in the fuel lines. Leave the ignition on for 30+ seconds and see if the pump then shuts off and this will tell you if its working correctly or not. Alternately you can also remove its connector and see if the pump primes for a few seconds via the ECM when the ignition is turned on.

Excellent description, thank you. I will check the oil pressure switch, which has been dimming in run at various intensities, seemingly getting worse. I assumed a bad ground to be chased down soon.
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Old 05-01-2021, 07:27 AM   #6
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One thing to note on the oil pressure switch is to make sure it's the one for the fuel pump and not the gauges/idiot light. It could be a combo switch with three wires or sperate switches. If separate, one has a single wire for the gauge/light and the other 2 wires for the fuel pump circuit. Locations could be near the distributor, near the oil filter or both if separate switches.
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Old 05-01-2021, 02:23 PM   #7
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One thing to note on the oil pressure switch is to make sure it's the one for the fuel pump and not the gauges/idiot light. It could be a combo switch with three wires or sperate switches. If separate, one has a single wire for the gauge/light and the other 2 wires for the fuel pump circuit. Locations could be near the distributor, near the oil filter or both if separate switches.

its a three wire combo switch in the front behind the Oil lines going to the condenser. The power steering bracket is conveniently in the way of getting 1 3/16 wrench on it. What a pain to get out!

I replaced it hoping it would also fix my dim warning light. No such luck and pump is still running with ign on.
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Old 05-02-2021, 05:30 AM   #8
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Peter, when I rewired my Argosy I connected a toggle switch to 490 which allows me to run the pump for an extended period if I need/want to. The other side of the toggle switch goes to the battery (through a fuse). With the surge tank between the pump and the throttle body it can be handy to be able to fill the surge tank prior to cranking the engine.

My guess is someone connected the ignition circuit to 490 to keep the pump running all the time the ignition is on.

Brad
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Old 05-02-2021, 06:37 AM   #9
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Peter, when I rewired my Argosy I connected a toggle switch to 490 which allows me to run the pump for an extended period if I need/want to. The other side of the toggle switch goes to the battery (through a fuse). With the surge tank between the pump and the throttle body it can be handy to be able to fill the surge tank prior to cranking the engine.

My guess is someone connected the ignition circuit to 490 to keep the pump running all the time the ignition is on.

Brad

Thanks for your insight, Brad! I don't mind for the pump to be on at Ign on, except it will burnout the pump after a few hours, as I experienced when I left it on by mistake, taking the front end apart.

I really don't have a need for a manual fuel pump switch for my application, but what I do need is a manual Airbag compressor switch. In case, heaven forbid, I ever need to be towed, I need for the Air compressor to be in operational mode to keep the rear axle up.
I suppose, I can just run a secondary circuit with a red warning light, to over ride the signal power wire to the Airbag solenoid.
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Old 05-02-2021, 06:56 AM   #10
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Originally Posted by bkahler View Post

My guess is someone connected the ignition circuit to 490 to keep the pump running all the time the ignition is on.

Brad
Looks like even if 490 were connected to a voltage source to turn the fuel pump on for priming, etc., when the ignition is turned on the relay would open 490 and connect power to the fuel pump via 440 and the normal ECM control. Unless someone has done some similar overriding via 440 465.

If the wiring is still original, then it looks like that there is really only 3 things that can keep the fuel pump running:
1. Oil pressure switch. Eliminated as a cause due to replacement. Can be also be verified by just leaving it unplugged and turning the ignition on.

2. Fuel module if it used in this application. I didn't see it in the originally posted schematics. If it does exist it can be eliminated as a cause by unplugging it and turning the ignition on. In normally operation it should run the fuel pump for around 30 seconds. In testing to see if the fuel pump remains running did you let it run for at least 30 seconds to see if it then shuts off?

3. ECM control failure. If 1 and 2 checkout fine, then that would be the suspect. By process of elimination leaving both the oil pressure and fuel control module disconnected and turning the ignition on would verify the ECM as the problem because it would be the only thing left controlling the fuel pump.
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Old 05-02-2021, 06:57 AM   #11
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..
My guess is someone connected the ignition circuit to 490 to keep the pump running all the time the ignition is on.

Brad

My question is where should it go. Obviously first to a 20 amp fuse, but then where?
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Old 05-08-2021, 08:48 AM   #12
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My question is where should it go. Obviously first to a 20 amp fuse, but then where?
This guide has all the pin-outs and some wiring info. Not sure if it helps.
http://www.73-87chevytrucks.com/tech...TBISystems.pdf
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Old 05-09-2021, 06:49 AM   #13
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My question is where should it go. Obviously first to a 20 amp fuse, but then where?
Positive from battery to fuse, from fuse to toggle switch, from toggle switch to 490.

This switch would be used for troubleshooting purposes or priming after sitting for a long time. Not for use while driving.
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Old 06-20-2021, 06:54 PM   #14
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Has been a while since I started the "Hunt" for the elusive power on the fuel pump with the ign in "ON"
I finally found out that in 1991/92 they added a "fuel module" or "hot start module" that would over ride the ECU signal. I located the module and removed the circuit board. This is NOT the fuel pump relay.
Now I no longer have the HOT fuel pump wire with IGN in ON position, that would eventually burn out the fuel pump.
Its located very close to the ECU/PCM

With it removed, I lost the hot start or vapor lock function this unit provides. But it seems I can over ride it with a simple toggle switch, which is something Brad has been saying all along, without him knowing that there is a unit like that in existence.
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Old 06-21-2021, 04:04 AM   #15
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Quote:
Originally Posted by PeterH-350LE View Post
Has been a while since I started the "Hunt" for the elusive power on the fuel pump with the ign in "ON"
I finally found out that in 1991/92 they added a "fuel module" or "hot start module" that would over ride the ECU signal. I located the module and removed the circuit board. This is NOT the fuel pump relay.
Now I no longer have the HOT fuel pump wire with IGN in ON position, that would eventually burn out the fuel pump.
Its located very close to the ECU/PCM

With it removed, I lost the hot start or vapor lock function this unit provides. But it seems I can over ride it with a simple toggle switch, which is something Brad has been saying all along, without him knowing that there is a unit like that in existence.
Glad you found it! FYI - Check out post #4, last paragraph and the schematic below it.
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Old 06-21-2021, 05:32 AM   #16
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Glad you found it! FYI - Check out post #4, last paragraph and the schematic below it.

Yup, you nailed it right there. At that time, I did not understand the workings of the entire fuel circuit and I had to process information and work through this stuff at my own pace in order to understand every aspect of it, before I move on to the next. The benefit of this approach is that I completely understand the workings of this particular element and will be able to trouble shoot problems later. Thanks for your input!
And btw, I did try the third item, you mentioned as a possible source of the problem, the ECU. I found a supposedly plug and play replacement and had a bear of a time removing the old and installing the new. It did not change the voltage problem at the pump, so I reinstalled my old ECU, since it did not throw any codes. I did not know of the existence nor location of the hot start module until I saw a picture of it on the web. And lo and behold, one of the wires on the module was the elusive tan/white wire (120) I have been chasing all over the place.
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Old 06-25-2021, 04:46 PM   #17
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found a replacement fuel module on Ebay ACD 10052954 and it works!! that was the only one I saw, NLA everywhere else.
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Old 06-26-2021, 04:00 AM   #18
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found a replacement fuel module on Ebay ACD 10052954 and it works!! that was the only one I saw, NLA everywhere else.
Nice find! Since it's such a common automotive part this made me wonder if there is a cross reference to another part number. It looks like there is and it's a more widely available part. For future reference:

Part 10052954 Has Been Superseded
10052954 is interchangeable with 10052973 since April 1, 1988 for the U.S. market;

Part Number: 10052973
Supersession(s): 10052973; 10052955; 10052954

MODULE,F/PMP CYC CONT(HOT FUEL HANDLING)(ACDelco #10052973). MODULE,F/PMP CYC CONT(ACDelco #10052973).
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Old 06-26-2021, 05:33 AM   #19
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Nice find! Since it's such a common automotive part this made me wonder if there is a cross reference to another part number. It looks like there is and it's a more widely available part. For future reference:

Part 10052954 Has Been Superseded
10052954 is interchangeable with 10052973 since April 1, 1988 for the U.S. market;

Part Number: 10052973
Supersession(s): 10052973; 10052955; 10052954

MODULE,F/PMP CYC CONT(HOT FUEL HANDLING)(ACDelco #10052973). MODULE,F/PMP CYC CONT(ACDelco #10052973).

yes, I found that info as well, but got NOT Available from all the sources I checked. All I can assume it's not a crucial part to operate the vehicle and detecting the failure of the module requires digging deep into the fuel system. In addition, Brad's suggestion for an over ride switch is an easy fix for this. I just didn't want to add just another switch to my already growing collection of switches.
https://www.summitracing.com/parts/ado-10052973

https://www.wholesalegmpartsonline.c.../10052973.html
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Old 06-26-2021, 06:10 AM   #20
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Might want to try here:

https://www.stockwiseauto.com/acdelc...olet&Model=P30

or here:

http://oemcats.com/oem-parts/10052973.html
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