Hello, I have a 1992 Buick Roadmaster sedan I recently purchased (project). The car sat for 5+ years and we dropped the gas tank to drain the crud out of it, the sending unit is in pretty bad shape, the float is seized up (all rusty) and I am looking for a replacement. Makes sense as the gas gauge was not registering at all. I'm just a little confused, as I see there are at least two different types for the same year, one will be for a wagon and the other for sedan I'm sure, but as I stated before I am a little confused. There seems to be a BAG and BAJ/BEK unit. The only hint I have is I called Autozone and he said the only one it recommended was the BAG-50. Can anybody shed some light on this for me?

 

So I figured out it was BAG-50, the tag is attached to the harness on the sending unit. So we cleaned it up a bit and put a different fuel pump in, we will probably be replacing this sending unit, but I had a spare AcDelco fuel pump (BGV00386) for my 1990 Caprice lying around new and never used, so we decided to put that in. We had no power going to the fuel pump, I am currently looking at the Fuel Pump Relay as a possible culprit, it is also possible the harness for the sending unit is bad, or the fuel pump is incompatible with this vehicle.
I have yet to test the relay, I will do that in the morning. If I understand correctly, the AC Relay and the Fuel Pump Relay are the same, and if one is working I can switch one out for the other to test it, is this correct? I might upload a picture just so I can get some clarification, as I am still not 100% sure if what I was looking at was the Fuel Pump Relay, was a Bosch relay, can post number. Anybody care to share any thoughts? Thanks a lot

 

You didn't say if you checked all the fuses .,Yes/no ?

 

No we did not check all the fuses. Everything else in the car seems to work. On a schematic I've been looking at it says there is a Fuel Pump/ECM Inline Fuse, I did not check that either, we got a light storm here in SoCal and its hard to get under the hood right now. I did switch the Bosch Fuel Pump Relay for the AC Relay sitting right next to it since they were the same exact relay, but it still did not work, I didn't hear the fuel pump running. The connectors on the relays looked pretty clean, very minimal amount of rust on them, I did not get the opportunity to test them because the rain picked up.
Is there any particular fuse I should be looking at? Also, how would I test the fuel sending unit? We will be dropping the tank again sometime in the very near future to check things out again. Thanks all

 

When I don't have all the info I would like when checking fuses, I will take a test light and start checking them all. Some will have power all the time and some will require the key to be on .The fuse should have power on both sides of the fuse and there is no need to remove them. If there is a defective fuse you will find it right away. It is quick and reliable. Once you confirm you have power to a circuit , then you confirm the ground connections are good. Once that is done , now you can go after the components.
As far as checking the tank sending unit, the better way is to remove the unit, connect the wiring and watch the readings on a meter with the key on and moving the float up an down. You don't always need to know the exact readings, just that the readings don't drop out anyplace when moving the float. Once that is done and operation is confirmed you can reinstall the sending unit and you are done there. You can also watch the fuel gauge on the dash if no meter is available. The only problem with that is you don't know if the problem is with the sending unit, wiring or dash unit. If the unit checks out ok, check the wiring and connections going up to the gauge. ~If they are good , the only thing left is the gauge itself.

 

You can check the fuel pump by running a hot lead to the loose connector with the red wire beside the relay. It will run the pump if the pump is good, and hooked up correctly. I believe the fuse is in the small capsule by the relay. You should also check the ground wire for the pump/gauge. It is the black wire in the pump harness. If the pump does not run, the next most likely culprit is the connector in the tank. The sending unit for the 94-96 cars will fit in the tank, and they have a better design to keep the pump submerged. I always hard wire my pumps in.That way, the connectors can not cause issues. The parts are difficult to solder, because the flux in the solder does not clean them well. You need a more aggressive flux, but not an acid flux. If you put a new sending unit in, and the pump does not run, it would be wise to check the ground from the tank harness to the body. There is a connection from the oil pressure switch to run the pump at prime up. As soon as the engine gets a spark signal, the computer bypasses the oil pump pressure sensor, and runs the pump itself. The Haynes Manual for 91-96 Caprice will have the wiring diagrams in the back.

You can check Rock Auto, and input your car to see what parts fit best. Check around, and you can come with a 5% discount code. Try this one: 132760143108964751

 

Hi Fred,
I think you might have made a typo error.
I believe the power to the fuel pump from the oil pressure sw is to provide power to the pump if there is an RPM signal missing. If the signal is absent the oil pressure sw supplies the power. That is one of the reasons for a long cranking time before the engine fires up.

 

It is a parallel path in case the spark signal is missing, provided there is oil pressure. If the spark signal disappears, the engine usually stops. There is a signal to run the pump for prime (about 3 sec), then the computer takes control after there is a spark signal.

I would establish the pump ground first. Check for voltage at the pump second, The fuel pressure on TBI engines is difficult to check, but if you just installed a new pump, it should be good. You can look at the injectors, and verify a spray pattern.

 

Hi Fred,
Can you clarify something for me?
I believe the fuel pump control relay gets energized when the key is turned on . That relay now sends power to the positive side of the fuel pump relay coil which now closes and sends power to the fuel pump. I believe the Computer uses the RPM signal from the ign system to operate the injectors. Would that explain why they used the oil press sw to operate the fuel pump if the control relay wasn't working because the injectors were working , but no fuel was getting to them?
Do you remember if you noticed if the injectors would fire once when you first turned the key on to prime the intake? This goes back a way for me , what do you think?

 

I have never had to look that deeply into the system. The only issue I ever had was when the hose in the tank broke.