Ok, I tested the voltage at the pump terminals with the key in the START or CRANK position and the transmission in R (in other words, no starter action, but the pump should run) and I get 8.8 volts. There is 12.5 Volts at the battery terminals.
My diagnosis: the pump is getting voltage, but does not run, so the pump is bad. This squares somewhat with a report that the late owner had trouble with the car dying intermittantly; i.e. failing fuel pump. An '86 model with 91,000 miles, not unexpected.
Comments?
Also: I noticed there are several brands (and prices) for replacement fuel pumps, so I am open to advice as to quality and what brand to buy/what to pay.
Regards!

 

Is 8.8 volts enough to run a pump designed for 12+ volts? I dunno. I'm asking!








Or isn't grounded




I'm not much help as I've never had to buy a fuel pump for my Jags (what luck, eh?)

But....


The system doesn't know what brand you've picked or what price you paid....so long as the pump delivers enough flow/volume.....and enough ooomph to produce about 75-100 psi "deadhead" pressure.....which is then regulated down to about 35-40psi.

The original pumps were pretty high grade stuff.....usually lasting 20+ years. I think this is where higher price vs. lower price might come in. It's not that they work better. It's that that last longer.

If yours is original it might have some Bosch numbers. If so, Google 'em for some alternatives. The same pump was used on other cars, not just Jags.

Some of the lower prices choices might be sorta semi-generic and require changing wiring connectors or other minor mods.

I can't remember the details and history of your car but if there's a chance of rust in the fuel, take care of that first. Or add filters between the tanks and the pump. Not unusual to hear of brand new ($$$) pumps being ruined by rust in the fuel



Cheers
DD

 

My car's existing pump is a Pierberg, so that is what I ordered. I don't know if that is the OEM pump. There were a lot of choices on the internet: Bosch, Denso, et al. and prices from $45 to $400. The Pierberg was just under $200.
I figured the 8.8 volts is because the pump itself is bad and could be dropping voltage. I plan to test with the leads disconnected from the pump.
Ther is a ground wire right there, fastened to the floor pan of the boot. I will check it, but the car is very clean and not rusty at all, plus there are two harness wires to the pump (it is mounted in rubber so it does not ground to the body). One of the harness wires may in fact be the ground which is connected to the floor pan.
More later.
Thanks!

 

I would think checking the ground for the fuel pump, the fp relay (and its wiring) and the wire from the relay to the pump before you spend $200 on a pump would be a good idea. Given the voltage readings you have I'd venture to guess replacing the pump isn't going to fix anything.

 

Good points; when the weather clears I am running 12V direct and see what happens at the pump.
Hey, you're the technician, I am an amateur. Thanks for the information. What I did not know was: should I expect the full 12V at the terminals, even if the pump is faulty somehow? You confirm: yes, should be 12v.