Technical 1981 Spider low voltage at fuel pump relay

[seankb]

Hi all,

I have an '81 Spider (FI) and I'm on my 3rd fuel pump/filter and it won't run (yet again). I've gotten more mileage riding in the tow truck than in the car behind it:bang:.

So far I've replaced all the fuel lines, injector hoses and seals, air flow meter, and combination relay. I also had the fuel tank cleaned by a radiator shop.

I found a diagnostic guide and started trying to locate the problem in the FI circuit. This is where I get real confused, real fast. The combo relay seems to be feeding the fuel pump via terminal 88d. The power appears to come from terminal 88y (white/brown wire with inline fuse). The fuse was also blown but I've replaced that. What I found strange was that the voltage at the relay from terminal 88y to ground reads 12.25 volts, but the voltage at terminal 88d to ground is only about 8.3 volts.

Am I looking in the wrong place? Any suggestions on how to proceed would be greatly appreciated!

Thanks,

SeanKB

 

[GeorgeT]

88d should be 12v. I would clean all connectors to the combo relay and apply dielectric grease and re-check voltages. It may be that you have 12v going to the relay but are experiencing a drop due to corroded connectors.

 

[seankb]

I cleaned the connectors and tried again but still no luck. The voltage was still about 8.2. Although the motor did start for a split-second and while it was running the fuel pump voltage did jump up to close to normal. Is it normal for the circuit to have low voltage while the engine is cranking but not yet running? If so then I'm looking at replacing my 3rd fuel pump in 12 months.

I'm going to double check all the ground connections next.

Thanks!

 

[seankb]

My fuel pump is definitely dead. I took it out of the car and put it on the bench and applied power just long enough to hear if it would turn. It clicks but doesn't do anything else. Definitely bad!

I guess I'll be purchasing my 4th fuel pump. Seems there must be something causing them to go out so frequently but I cannot figure what that is.

Still, if anyone has any ideas I'd be happy to hear them.

Thanks!

 

[kregester]

You might want to do a postmortem on the fuel pump.
Looking for trash in the pump.
IAP mentions this in the tech stuff.

I am thinking of adding a filter between the fuel pump and the gas tank to keep the junk out of the pump.
That should be low pressure so generic std filter would work as long on low pressure side of the fuel pump?

What do you all think?
-=Ken=-

 

[mbouse]

not having an electric fuel pump, i cannot explain my answer... but i have read NOT to put a filter between the tank and the pump.

additionally

Voltage should be 12 volts where ever you check on this circuit. if it is not, suspect a dirty ground in the circuit. trace the circuit back to its origin, clean and re-establish all connections.... especially the grounds. if there are splices in the wire, replace that section of wire with the proper gauge replacement wire.

 

[GeorgeT]

Be careful when installing a filter before the fuel pump: This will add an exrtra load on the pump and increase the possibilty for premature failure. These pumps are designed to "pump" not "suck".

 

[seankb]

I wound up sending the fuel pump back to IAP the manufacturer. I'm waiting for their word.

I also wound up buying a performance clear glass filter (inline) and put it in the trunk between the fuel pump and the fuel tank. The filter has replaceable elements. I figured that if I purchased a large diameter filter I could safely do this. The hardest part was finding fittings sized for the 12mm hose from the fuel tank. I had a couple of older cheap fuel pumps with threaded 12mm ends, so I used those. Almost immediately upon starting the car, I noticed there was junk getting in the filter. I've been checking the filter screen every day and it isn't even close to clogged-up, but there are several little pieces in it.

I don't think that flow will be affected, the filter was designed for performance cars. Also, the filter is on the input-side of the fuel pump so it shouldn't have pressure on it. I will just need to keep an eye on the filter screen and buy a new one if it starts looking clogged-up so it won't burn-out the fuel pump.

By the way, the car is running great again!