Hi everyone.

Vehicle specs:
'89 cobra motorhome.
7.3L gas engine.

The vehicle sat for about a year after I drove it last. A month ago I tried to start it and had to keep feathering the throttle to keep it running.

Eventually it idled like it should and I let it run for a couple hours but then it died even with a quarter tank of fuel.

I figured maybe bad gas so I siphoned the fuel out and put in a fresh 1/2 tank full of gas plus some fuel stabilizer/water treatment and let it sit for a month.

I tried to start it yesterday and it wouldn't run without spraying starting fluid.

I searched the internet for solutions and decided to try jumping the connector for the fuel pump relay to bypass the relay.

The rig started but I still needed to feather the throttle to keep it running then after several minutes I couldn't get it to run anymore.

I let it sit for about an hour and when I went out to try again I check the jumper wire I had put on the connector and it was very hot (why?) so I unhooked it.

I plugged the connector back in and tried to start the MH but of course it just cranks.

I have spark and am unable to test the fuel pressure at the rail because I don't have access to a gauge at the moment.

From what I've described does it sound like the fuel pump relay is bad? If so, why did the MH start after jumping the wires and then not want to start again a few minutes later? And why did that jumper get so hot with the key off?

Thanks and sorry for the long post.

 

Welcome to the site.

7.3 is diesel, 7.5 was a gasser.

Fuel pump failures are pretty common, and pressure and volume is always a starting point if any doubt, or starts with a short shot of ether, and more so if the pump is excessively noisy or undetacable while running. Generally a healthy pump will have a slight high pitch whine. Easily heard from below or through the tank fuel neck running and even more noticeable when you cycle the key ON (no cranking) Pump should run for a few seconds to pressurize.

The test connector when jumped shouldn't get hot, but should really only be done as a test point. Are you certain the correct connections were bridged on the DLC? I'd think is there were a dead short it would have had fuse issue..

 

I think you mean a 7.5 engine, anyway, maybe the fuel pump is working too hard to push fuel through a plugged fuel filter. The jumper should not have reached so hot a temp unless the pump is pulling too much current and not pumping which could also possibly explain why the relay might have been damaged because over time it would also get overheated, but the fuel pump fuse should have opened if it was pulling too much current. The fuel pump electrical system will need to be thoroughly checked out. All connections from the battery on down should be checked and confirmed to be in good condition and clean with no corrosion. Technically , the pump doesn't run without a signal from the dist showing that the engine is actually running. In this case it was trying to pump against an engine that was not using any fuel.

 

Yea, sorry 7.5L.

Thanks for the replies. I crawled under the MH and found the filter secondary pump on the frame rail.

My thought is to relieve the pressure (like I've read) and detach the input hose to the filter then turn the key on to see if fuel pumps out of the hose. At least that will tell me the tank pump is working to some degree and that the filter may be the problem.

Sound like a decent plan?

 

Just a reminder,
The fuel pump should run for 1-2 seconds when you first turn the key on, then after that it will only run if the engine is cranking or running providing the computer with an RPM signal. The better thing to do would be to have a fuel pressure gauge connected to confirm adequate pressure. The pump on the rail could be getting tired also. The pump in the tank is a low pressure pump and the one on the rail provides the higher pressure required for fuel injection. As Hayapower stated, fuel pump problems with those were common. Let us know what you found, thanks.

 

I have an 81 Brougham motor home, 460 V8, on an E350 chassis. It has dual tanks and I am experiencing similar problems when either tank is selected. So are there 3 pumps? One on each tank and one on the frame rail? Do you have to drop a tank to replace the pick-up fuel pumps? Since it occurs with either tank selected, I am assuming that it is most likely the pump on the frame.