I have had huge problems with my fuel pump since it was first installed. I wrote Darth Fiero a few times about his modification to bypass the two way trip to the C203 connector and finally finished the switch yesterday. It works like a charm but I discovered that the probable cause intermittent pump failure to work was a bad ground. It was apparently good enough for the gas gauge but not for the pump. While I had the fuel tank out, I changed pump, sender, fuel hoses and made as direct a connection in the harness to the pump as I could. I need to take the car out to test it but I offer this advice to others: Before you go through the hassles of dropping a tank, etc make certain that ground connections are good.

Kudos to DarthFiero for his mod and his great communication with me on this matter and other problems I had with my car earlier in the year. He is a great asset to our Fiero community. And kudos to Mike Gonzalez for his great work in making the conversion. I was the idiot who installed the fuel tank and made the connections to the sender, not Mike. His wiring is neat and first rate.

A good indication you have a ground problem is when the dash lights dim visibly when the turn signal is activated. I had a bad ground to the tank which made my fuel pump oscillate audibly when the turn signal was activated. I would recommend running a hot wire directly to the fuelpump relay. The Grand National guys have a kit to boost the current flow to their pumps to help insure good fuel delivery.

The warning that should be included with this is that any 'hot wiring' of the fuel pump will eliminate a feature that GM built into the Fiero (and ALL electric fuel pump cars). That is the fact the fuel pump turns off in the event of a crash where the engine is no longer running. A hot wired fuel pump would continue to run, and in the case of a ruptured line would pump out the contents of the gas tank onto the ground where the crash occured. In the event of a crash you might be pinned in the car or incapacitated. Not a place I want 5 gallons of gas pumped on the ground at.

This has the potential to kill, severly burn or mame you.

A better fix in my mind is to get the system to work the way GM intended, using both the oil pressure switch, and the ECM/relay as redundant ways to make sure the fuel pump is running when the engine is, and make sure the fuel pump isn't running when the engine isn't.

quote Originally posted by phonedawgz: The warning that should be included with this is that any 'hot wiring' of the fuel pump will eliminate a feature that GM built into the Fiero (and ALL electric fuel pump cars). That is the fact the fuel pump turns off in the event of a crash where the engine is no longer running. A hot wired fuel pump would continue to run, and in the case of a ruptured line would pump out the contents of the gas tank onto the ground where the crash occured. In the event of a crash you might be pinned in the car or incapacitated. Not a place I want 5 gallons of gas pumped on the ground at. This has the potential to kill, severly burn or mame you. A better fix in my mind is to get the system to work the way GM intended, using both the oil pressure switch, and the ECM/relay as redundant ways to make sure the fuel pump is running when the engine is, and make sure the fuel pump isn't running when the engine isn't.

Hot wire in this application bypasses nothing but excess wire and unnecessary routing. Fusible links and the like are not to be omitted in the process of getting rid of unnecessary routing through the harness. The hot wire is to the relay not the pump, although stouter wire should be considered there also.

[This message has been edited by Joseph Upson (edited 09-15-2010).]

quote Originally posted by phonedawgz: The warning that should be included with this is that any 'hot wiring' of the fuel pump will eliminate a feature that GM built into the Fiero (and ALL electric fuel pump cars). That is the fact the fuel pump turns off in the event of a crash where the engine is no longer running. A hot wired fuel pump would continue to run, and in the case of a ruptured line would pump out the contents of the gas tank onto the ground where the crash occured. In the event of a crash you might be pinned in the car or incapacitated. Not a place I want 5 gallons of gas pumped on the ground at. This has the potential to kill, severly burn or mame you. A better fix in my mind is to get the system to work the way GM intended, using both the oil pressure switch, and the ECM/relay as redundant ways to make sure the fuel pump is running when the engine is, and make sure the fuel pump isn't running when the engine isn't.

Thanks for your concern but the term "Fuel Pump Hot Wire Modification" probably is a misnomer in this application. The computer still controls the fuel pump through a fuel pump relay directly from pin 3 (I think it is pin 3--I don't have the schematic in front of me) with a green/white wire. The 3800Sc computer supplies the 12 volt voltage to the fuel pump winding (I measured 155ma from pin 3 to the relay winding) and switches the fused 12V from a power distribution block to the fuel pump. I might be mistaken but if a crash occurs and the engine is off, the computer will sense low or no oil pressure and cut off the relay. The misnamed "Hot Wire" mod only changes the location of the fuel pump supply voltage and it is still fused. The only problem I had with Darth's instructions is that I am a "schematic person" but the way I have the mod wired definitely uses the 3800 ECM. I could draw a schematic but after I figured out what he is doing, I had the schematic in my head. http://www.gmtuners.com/fiero/hot_wire.htm

Thanks again for your concerned post and I really appreciate your posts because your knowledge about these cars and the 3800 goes deep.

Post Script: I physically hot wired the fuel pump once to get me home but that was an emergency.

Edit: Joseph beat me to it. Thanks!

[This message has been edited by starlightcoupe (edited 09-15-2010).]

Wires and +12 come out of the C203 to the FP relay and oil pressure sensor/switch. Then all back to the C203 to join in to the body C500 harness where it enters the cabin harness, and heads out of the cabin towards the C500. The fuel tank connector exits the body harness C500 and that is where the fuel tank connector plugs in. I think they are talking abut taking the 'back in to the cabin' part of the circuit, and 'out of the cabin' again out of the loop.

I have considered this myself as it is a waste.

They have not removes or 'hot wired' anything, but about 3 foot of wasted wire. If it isn't there, it isn't causing any problems. Great idea.

[This message has been edited by josef644 (edited 09-15-2010).]

Problem is not C203.
Problem is likely Fuse Link A, S206, and any/all other loads on Link A. Link A and S206 runs most of the car. Same problem with other high amp load, like power windows, or reliable loads, like fuel pump. (For example, See 88Service Man. Power Distribution drawing, 8a-10-1 8a-10-2 pages. other year uses dif pages. ) GM should use a second fuse link to split the loads up.

Another option...
keep it stock relay and oil sensor but run a new fuse and wire from main power (like gmtuner link above) to orn/blk wire next to relay. This way it will bypass Link A etc.

------------------
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 (It's also at the top and bottom of every forum page...)

quote Originally posted by theogre: Problem is not C203. Problem is likely Fuse Link A, S206, and any/all other loads on Link A. Link A and S206 runs most of the car. Same problem with other high amp load, like power windows, or reliable loads, like fuel pump. (For example, See 88Service Man. Power Distribution drawing, 8a-10-1 8a-10-2 pages. other year uses dif pages. ) GM should use a second fuse link to split the loads up. Another option... keep it stock relay and oil sensor but run a new fuse and wire from main power (like gmtuner link above) to orn/blk wire next to relay. This way it will bypass Link A etc.

Update: Drove car today, it ran very good and it may be my imagination but it seems to run a little better.

Ogre, the way I wired the modification is the same as your option and gm tuner's. I moved the relay closer to the power block (positive 12V), used a weather proof inline fuse holder but had to lengthen the ECM wire to the relay's coil. The current is about 150ma so the extra length isn't critical. The relay came from a relatively new Buick and is weather proof as well. I didn't keep the original location because I wanted one unbroken run from the relay to the pump. Using the stock location would have put the relay about halfway between the supply voltage and the fuel pump.