Fuel Pump Testing and Fuel Issue Diagnosis (Page 1/3)
jumpmonkey MAR 05, 10:10 PM
Context: I just purchased my first Fiero, a non-running 85GT that has been sitting for some time(10-15 years). I am a GM apprentice tech and student at a technical school. My knowledge is limited but I can understand car-speak. Electrical diagnosis isn't super foreign to me, either. That being said, I'd like to hear your thoughts on my current situation.
After installing a new battery, my friend and I attempted to crank the engine. It siezed up. We removed the spark plugs and attempted to crank the engine, again. It cranked great. Put the spark plugs back in and it was still cranking, however, not starting. After some digging, we found that fuel was not being delivered to the engine. We got inside the car and listened for the fuel pump. We could not hear it priming.
We went through diagnosis steps we found on this thread about fuel pumps. We checked the 10A Fuel Pump fuse and it was good, along with the Fuel Pump relay in the engine compartment. I did find a blown 5A V6 Fuel Injection fuse, though I don't know of it's signifigance. I replaced it. Still, nothing from the fuel pump.
The only option left that I found was to try and send 12v directly to the fuel pump via the ALDL. I did so with wiring from the battery, and still nothing. We disconnected the line coming off the fuel filter to see if there was any fuel coming out, and there was nothing. And please don't worry; there is gas in the tank.

I wanted to ask if there's anything else to really check before I rip out the tank and replace the fuel pump. I do have a multimeter and can conduct any tests that you guys suggest. I thought about bench testing the fuel pump, but a tech at my dealership did that once and started a fire. Maybe not the best idea. There was mention in the forum I linked saying that there could be a short to ground in the TAN/WHT wire that powers the fuel pump, but I'm not sure the specs to possibly test that wire with once the fuel pump is out. Any advice would be great. I think as soon as I can get the fuel issue figured out, the car will run. When spraying in some starter fluid, it really does go for a bit!

Thank you!

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Jumpmonkey

1985 Fiero GT MAR 05, 10:25 PM

quote
Originally posted by jumpmonkey:

Context: I just purchased my first Fiero, a non-running 85GT that has been sitting for some time(10-15 years). I am a GM apprentice tech and student at a technical school. My knowledge is limited but I can understand car-speak. Electrical diagnosis isn't super foreign to me, either. That being said, I'd like to hear your thoughts on my current situation.
After installing a new battery, my friend and I attempted to crank the engine. It siezed up. We removed the spark plugs and attempted to crank the engine, again. It cranked great. Put the spark plugs back in and it was still cranking, however, not starting. After some digging, we found that fuel was not being delivered to the engine. We got inside the car and listened for the fuel pump. We could not hear it priming.
We went through diagnosis steps we found on this thread about fuel pumps. We checked the 10A Fuel Pump fuse and it was good, along with the Fuel Pump relay in the engine compartment. I did find a blown 5A V6 Fuel Injection fuse, though I don't know of it's signifigance. I replaced it. Still, nothing from the fuel pump.
The only option left that I found was to try and send 12v directly to the fuel pump via the ALDL. I did so with wiring from the battery, and still nothing. We disconnected the line coming off the fuel filter to see if there was any fuel coming out, and there was nothing. And please don't worry; there is gas in the tank.

I wanted to ask if there's anything else to really check before I rip out the tank and replace the fuel pump. I do have a multimeter and can conduct any tests that you guys suggest. I thought about bench testing the fuel pump, but a tech at my dealership did that once and started a fire. Maybe not the best idea. There was mention in the forum I linked saying that there could be a short to ground in the TAN/WHT wire that powers the fuel pump, but I'm not sure the specs to possibly test that wire with once the fuel pump is out. Any advice would be great. I think as soon as I can get the fuel issue figured out, the car will run. When spraying in some starter fluid, it really does go for a bit!

Thank you!




Best thing I would do is to find the wire going directly to the pump, whether that's The output of the relay or whatever, whatever connector is as close as possible to the pump and put 12v directly into it from there, if you hear it, it can be traced to some other electrical issue, if not, it most likely was a mouse that ate the wire, or the pump is somehow clogged/dead. Test with the multimeter on that wire, to make sure it isn't shorted before applying voltage. Sometimes to make it easier, I use a 2s LiPo from an RC car to do testing on stuff like that, smaller then lugging around and wiring up a lead acid battery, less dangerous to, as it is less powerful, only about 8v, could use a 3s LiPo, that would be right around 12v.
jelly2m8 MAR 05, 11:02 PM
85 the connector to the Sending unit harness is located on the forward engine bay bulkhead just below and to the left of the right side Deck lid hinge / spring box. It is a 3 wire connector. test at the vehicle side, if you have power and ground there, then your going to have to drop the tank.
jumpmonkey MAR 06, 10:07 AM

quote
Originally posted by jelly2m8:

85 the connector to the Sending unit harness is located on the forward engine bay bulkhead just below and to the left of the right side Deck lid hinge / spring box. It is a 3 wire connector. test at the vehicle side, if you have power and ground there, then your going to have to drop the tank.



I will look into that. Any good threads on dropping the fuel tank that you know of?
1985 Fiero GT MAR 06, 10:29 AM

quote
Originally posted by jumpmonkey:


I will look into that. Any good threads on dropping the fuel tank that you know of?



I don't know any threads off the top of my head, I'm sure someone will post a good thread, I'll be dropping my tank soon too, it's finicky, but should be fairly easy just a lot of little connectors and hoses to disconnect, then wiggle the tank out.

This video should have some good info:
https://m.youtube.com/watch?v=hcu78RFGj9k
CSM842M4 MAR 06, 12:21 PM
Greetings, jumpmonkey. '85 is right; dropping the tank is not HORRIBLE, just involved. I've dropped mine with the rear of the car off the ground a little. Seems like 6 or 8 inches is enough for the tank to slide out. Remove the nuts from the t-bolts in the tank straps. One 3-wire connector and three or four hoses to disconnect as they expose themselves as the tank is coming down. Easy peasy! You're gonna have a good time with it! Keep us up to date on your progress.
theogre MAR 06, 01:15 PM
Dropping the tank "easy" to start ignoring rusty hardware problems.

Is much easier having some extra tools like https://www.fiero.nl/forum/Forum2/HTML/146426.html Hose removal tool(s)
That one tool will push every hose off except big fuel fill.

If have a lot of gas, Drain tank by sucking the return line joint near the tank w/o bothering w/ F-pump. Return line w/ added hose will siphon "easy."
Don't need to drain all & may help have a couple gallons as weight to help you drop the tank.

Many time you have to loosen or remove all supports the small pipes for Heater to clear the fuel tank & often find other problems...
Example: http://www.fiero.nl/forum/Forum2/HTML/146198.html Hidden Fuel and Coolant Leaks...

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

jumpmonkey MAR 06, 03:53 PM
1985 Fiero GT, CSM842M4, theogre. Thank you!

I will update you with any extra test results and how dropping the tank goes.

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Jumpmonkey

Patrick MAR 06, 04:19 PM
Another tip for dropping the tank... Remove the heat shield that's attached with four(?) screws. It'll make access to the hoses a helluva lot easier.

[This message has been edited by Patrick (edited 03-06-2024).]

CSM842M4 MAR 06, 07:24 PM
Listen to Patrick, for he is wise. I've done it every time with the shield in place, and wished for more room.