Need Fuel Pump Circuit Help!!!! At Wits End

Turd Furgeson · Aug 23, 2005

HISSIN50 said:
Turd , your best bet is to probe the relay terminals when it wont start. Clicking in the relay indicates the coil is energized and that it is a power-side issue (feed from the solenoid to the pump) or the relay itself.

THe first thing I would do is swap a known good relay in and see how it does (The WOT relay should be the same relay and can be used for this test).

Good luck.

Hissin, I just checked the power at the relay. I have power at the orange and light blue wire with the key on. I have power at the pink/black wire when the key is turned on. It shuts off in what im assuming is the time after the pump is done priming? I also had power at the red and black wire constantly with the key on. So from the large post above, Im thinking it's safe to say the pump is toast?

I just find it strange that the car will sit over night and then fire up the next morning, but then after a few starts, it's dead. Shouldn't when a pump go bad, it goes totally bad? This intermittent thing is strange!

HISSIN50 · Aug 23, 2005

Turd Furgeson said:
Hissin, I just checked the power at the relay. I have power at the orange and light blue wire with the key on. I have power at the pink/black wire when the key is turned on. It shuts off in what im assuming is the time after the pump is done priming? I also had power at the red and black wire constantly with the key on. So from the large post above, Im thinking it's safe to say the pump is toast?

I just find it strange that the car will sit over night and then fire up the next morning, but then after a few starts, it's dead. Shouldn't when a pump go bad, it goes totally bad? This intermittent thing is strange!

yep, after 3-5 seconds, the pump is done priming. The puter pulls the ground pulse from the relay's coil (the only wire at the FP relay socket which shows ground) to accomplish this.

I think you got it - either the pump or the wiring at the pump itself. I have had pumps go bad only when hot (they crap out altogether shortly thereafter). The diaphram gets weak, and pumps ok when the diaphram is cold, but once it warms up, it gets too loosey-goosey and wont pump decently.

A quick test would be to see how your pressure is when it does this.

Good luck.

Turd Furgeson · Aug 23, 2005

HISSIN50 said:
yep, after 3-5 seconds, the pump is done priming. The puter pulls the ground pulse from the relay's coil (the only wire at the FP relay socket which shows ground) to accomplish this.

I think you got it - either the pump or the wiring at the pump itself. I have had pumps go bad only when hot (they crap out altogether shortly thereafter). The diaphram gets weak, and pumps ok when the diaphram is cold, but once it warms up, it gets too loosey-goosey and wont pump decently.

A quick test would be to see how your pressure is when it does this.

Good luck.

I will check the pressure at the schrader tomorrow when I get it running. The car seems to run fine with it's actually running which is what I find strange.

In my old 88, I would drive around for hours, and then the pump would start crapping out. in my 91, one day it just up and died. I was sooooo hoping it wasn't the pump, I really don't feel like dropping the tank!

HISSIN50 · Aug 24, 2005

Turd Furgeson said:
I will check the pressure at the schrader tomorrow when I get it running. The car seems to run fine with it's actually running which is what I find strange.

In my old 88, I would drive around for hours, and then the pump would start crapping out. in my 91, one day it just up and died. I was sooooo hoping it wasn't the pump, I really don't feel like dropping the tank!

Actually I meant to check FP when it wont start (we know pressure is good when it does run). If the electrical is good and pressure is not, that basically leaves the pump's connection, the pump or a bad FPR (the latter-most is not at all likely).

ALso, if you happen to yank codes, 95 and 96 would indicate an electrical issue in the FP circuit (these are often ghost codes, but in your case, I would not dismiss them so easily).

Good luck.

Turd Furgeson · Sep 4, 2005

HISSIN50 said:
Actually I meant to check FP when it wont start (we know pressure is good when it does run). If the electrical is good and pressure is not, that basically leaves the pump's connection, the pump or a bad FPR (the latter-most is not at all likely).

ALso, if you happen to yank codes, 95 and 96 would indicate an electrical issue in the FP circuit (these are often ghost codes, but in your case, I would not dismiss them so easily).

Good luck.

I finally had time to play with it today. Like I said earlier, the power at the relay under the seat is all fine. I went under the car, and disconnected the connector by the tank to check for power. All I get back there is the 5 second power. No constant, no key on power. I figured the wiring in the connector at the tank would be the same coming from the realy, but they change colors somewhere. Am I reading too much into this? and I only supposed to have that 5 second power at the pump when it's priming? I figure it would have to have constant key on power as well

HISSIN50 · Sep 4, 2005

The computer sends the ground pulse to the FP relay coil. So whenever that pulse is present, the pump gets power. When that pulse is not present, there is no output at the N.O. terminal on the relay (the output to the pump) and no power at the pump either.

You can jump the relay and pump via the self test connector. You ground the ground wire that the computer pulses. This is nice for diagnotics like this (Unless you are really really fast. ).

But what you describe is normal.
Good luck.

Turd Furgeson · Sep 5, 2005

HISSIN50 said:
The computer sends the ground pulse to the FP relay coil. So whenever that pulse is present, the pump gets power. When that pulse is not present, there is no output at the N.O. terminal on the relay (the output to the pump) and no power at the pump either.

You can jump the relay and pump via the self test connector. You ground the ground wire that the computer pulses. This is nice for diagnotics like this (Unless you are really really fast. ).

But what you describe is normal.
Good luck.

That's the one thing I didn't do, jump the test connector. The links in the previous posts were dead to show me where the connector is, and which pin to jump.

slick88GT · Sep 7, 2005

As long as you get power coming out of the relay and into the pump for that 5 sec prime period and the relay always has constant power going into it, seems like everything is working fine. Your pump is bad, I bet 20 bux. The eec relay supplies the trigger signal to your fp relay to tell it to send power to the pump. Since your fp gets power for 5 secs in that initial prime when you first turn the key on, that means the eec relay is indeed working just fine. I had to research every friggin circuit that deals with all of the fuel injection components (and I do mean ALL of them) and it sounds to me like your pump is bad. The intermitent thing is pretty common as well.

tmoss · Sep 8, 2005

You get 5 second power in the "key on" position to pressurize the system. Once the EEC sees the engine is running (PIP), it turns the pump on all the time.

Need Fuel Pump Circuit Help!!!! At Wits End

Turd Furgeson

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