Mondial Fuel Pump Blowing Fuse

Two years ago I replaced my fuel pump on my '85 QV cabriolet and everything has been working fine until this week. I was driving along normally and then suddenly lost power. I was unable to start it again, as it appeared no fuel. In troubleshooting I saw the 15amp fuse was blown, so replaced it. I was able to drive another minute then it happened again. I kept replacing fuses to limp home, and then changed the fuel filter thinking it was plugged. No difference, it still keeps doing the same thing. I put in 20 amp fuses and still was blowing those, so pulling a lot more power than normal.

Is this an indication of a bad fuel pump, or is it something else? I still have the original fuseboard in my car and was going to do the GT Parts upgrade at some point - could this be the source of the failure? Open to any and all suggestions!

 

Hi Mike, thanks for the advice, will do that. It has not been failing right at the start, only after running for 30 sec to a minute so should be able to measure the voltages while running.

If the supply is showing less than 12 volts what would be the next step to identify the cause?

 

Hi Steve, the increased back pressure was my first thought as well so I changed the fuel filter to a new unit and still seeing the issue. In addition to the voltage measurements I will inspect the fuel inlet screen per the shop manual references and see if there is anything there. I had filled up with a fresh tank of gas, then saw the problem about 10 miles down the road - not sure if that is coincidence or if something happened as a result of a new full tank of gas. Really appreciate the insights!

 

I tried this and found the supply voltage at 11.74 volts . When connected to the pump the voltage was 10.9 volts, and while cranking the start it went to 9.1 volts. I inspected the fuel distributor screen and it was clean. I replace the fuel filter and no improvement. I did check the far right connector to the fuesboard and saw burn marks.

 

Thanks Mike. I measured the voltage at the battery with key off and was 12.73 volts. The measurement with key on was 12.10 volts. Do I have bad relay or something else like the fuse board?

 

I have a new fuel pump - would it be safe to replace the old one? Does a fuel pump fail intermittantly? I replaced the fuel filter and cannot find any other blockages. The fuel accumulator was replaced last year and has less than 500 miles so it should be good.

 

Hi, I don't think the problem has gone away just yet. I did clean the contacts on the fuse board so hope that helps.

I have not been able to locate the inlet filter screen to the fuel distributor. I looked in the D section of the shop manuel and cannot find it listed - any suggestions on exactly how to do that would be helpful. I can only assume to disconnect the input fuel line but not sure which one it is - there is one connection that has two lines going into fuel distributor - is that it?

 

Is this the inlet filter screen? It shows in the parts manual as a filtered union PN 115498.

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Update - I disconnected the main fuel line input to the fuel distributor and inspected the inlet screen. It was completely clean - no dirt or blockages.

 

One additional note - when I disconnected the primary power from the fuel pump to do the voltage measurements I noticed that it was only 2-3 threads engaged on the nut. When I was reconnecting it after the test I was able to secure it firmly all the way tight. I did a few test drives with a 15A fuse in slot for fuel pump and so far so good. I am thinking it might have been that the connection had worked loose and was getting intermittant shorting, resulting in the surge of current and the fuse blow. Does this make sense?

 

So a quick update - I replaced the fuel pump with a new unit. Unfortunately that did not clear the problem. I have replaced the fuel pump, accumulator, and filter with no improvement in the original problem. I'm open for any and all suggestions, especially since the voltages all check and no other obvious issues. Suggestions? It is still the original circuit board - is it time for a GT Car Parts replacement?

 

Hello, a quick update on my quest to fix the blowing fuse. I tried what Steve suggested but no luck in fixing it. I did the fusebox rebuild with GT car parts as well as a new "W" connector to replace the burned one. I took a test drive and still had the same problem. I also noticed that the relays S and T for the fuel pump and AC unit (Bosch 113 relays) started to get really warm right away. Are my relays failing? Not sure what else to do.....

 

I swapped both relays and that didnt help. I did confirm the car is a US version 1985 QV 3.0. I also pulled the 20A fuse for the air conditioning, thinking that might help as well. No luck, after about 3-4 minutes they get hot to the touch. I've been looking through the wiring diagram trying to figure out what could have failed that is causing this higher than expected current draw. Open to any other ideas!!