'90 fuel pump

[ChrisWhewell]

Haha, lucky me !   I let the 90 sit a couple years and when I went to start it, no dice.   Spraying ether into the intake made it fire up momentarily however, which is nice.   But,

applying +12V to the green connector by the brake booster results in.... nothing.   No sound from fuel pump.    Fuse #8 is fine and the relay is good.    So I s'pose it's time to pull the tank, ugn.    One last question.... does anyone know where the ground wire for the in-tank fuel pump runs ?   I'd like to check if it's grounded b/c maybe that's the problem and if it turns out to be a simple ground connexion fix, I'll buy myself a bottle of beer !!!    Thanks a lot, hope y'all are doing well.  

 

EDIT:   I checked the resistance btw. the green connector(gray wire) and chassis ground, it showed 70 ohms.  

Edited April 11 by ChrisWhewell (see edit history)

[wufibug]

Replacing the fuel pump is not a fun job unless you have access to a lift.  There is no access to the pump from the car; you have to drop the tank.  The pumps are cheap enough, and the gasket is available though. The are easy to replace once you have the tank out from under car.   Another possibility is trying to add some octane booster to your stale gas.  BTW, I was told that the product usually labeled as "starter fluid" is very hard on engines because of its extreme combustibility. 

[EmTee]

3 hours ago, ChrisWhewell said:

One last question.... does anyone know where the ground wire for the in-tank fuel pump runs ?   I'd like to check if it's grounded b/c maybe that's the problem and if it turns out to be a simple ground connexion fix, I'll buy myself a bottle of beer !!!

Try connecting an Ohm meter between the pump's 12V input and chassis ground.  If the motor is grounded, you should get continuity (i.e., a couple of Ohms resistance).  If it reads 'open' (i.e., infinite Ohms) try attaching a temporary ground wire between the tank and a good chassis ground.  If it still reads open circuit then there's a problem with the hot wire to the pump, the ground to the pump, or pump motor (internal).  I had replaced the pump on my father's '84 Corvette three times because the car would sit idle/unused for long periods (a couple years at a time) and the pump would fail to run when it finally came time to 'wake-up' the car.

[ChrisWhewell]

Hi, thanks.   My limited understanding is that the under-hood grey wire which terminates with a green connector just hanging there is itself in effective electrical contact with the motor of the fuel pump.   I re-measured the ohms and got 38 ohms in a second sampling, which I'm inclined to attribute to contact resistance given the apparent discolouration likely stemming from oxidation from the thing just hanging there for  decades     In some modes of failure I might expect an open, or infinite reading, and another mode wherein possibly a short circuit in the motor winding or elsewhere would yield a zero ohms reading.  But to get 38 ohms is odd, but yet still shines a glimmer of hope that it may be a dirty connection somewhere.  With 38 ohms at 12V that only permits c.a. 1/3 ampere of current to flow, which is clearly not sufficient given the fact that the fuse is a 15A fuse, suggesting normal operating current is around maybe enough for the pump to dissipate approx 25Watts, so, a couple amps.   Temptation arises to jolt it with 60 VDC just for S&Giggles, since I"m sensing it might be time to part this one out as I've found other matters to spend what little time I have left on !    If the grey wire dangling with green connector is not in effective electrical contact with the power input to the pump, I'd sure like to learn of a convenient access point, thanks for your reply !   

[EmTee]

If you can find a connection point closer to the fuel tank you could remeasure there and see what the resistance is.  My gut says the pump motor is probably bad (dirty and/or partially stuck brush).  Try a few hard raps on the tank with a block of wood (or your shoe ) with 12V applied and you might get lucky and get it unstuck...

 

 

Edited April 12 by EmTee (see edit history)

[ChrisWhewell]

Thanks.   Maybe I'll force some xylene in a reverse direction from the hood bay into the fuel line w/hope of spinning the impeller in a reverse direction and the solvent would dissolve any thin film of boogers inhibiting impeller spinning due to olefinic polymerisation.  

Edited April 12 by ChrisWhewell (see edit history)

[wufibug]

Chris, wouldn't the fuel filter prevent that from reaching the pump?.  I thought those had a built in one way valve?  Might work if you disconnected the inlet line to the filter and used that to backflush the pump.

[ChrisWhewell]

On 4/12/2024 at 4:17 PM, wufibug said:

Chris, wouldn't the fuel filter prevent that from reaching the pump?.  I thought those had a built in one way valve?  Might work if you disconnected the inlet line to the filter and used that to backflush the pump.

You're probably right.   I should have changed the fuel filter years ago, but I failed to do so.   So, since I have the new fuel filter anyway, I could pull the old one off and maybe blow a little compressed air, but, maybe that would blow the sock off, haha.   Funny, I disconnected the fuel line from the fuel rail and tried suction , to suck out the gas but had a bear of a time, and it was not productive.   Perhaps the fuel filter is so clogged up that the pump could'nt pump against it.  Or else, it could be the fact that the pump is 34 years old might have something to do with it :)