Hi.

I have a 1989 E-350 motor home with the 460 (or 7.5 L) gas engine. It has a single tank with a low pressure pump in the tank and a high pressure pump on the frame.

I am having an intermittent issue with the fuel pump. If I leave the vehicle sitting for a few days, the pump won't hum when I turn the key (and it obviously won't start). The first time I did this, I jumped the fuel pump test connector to see if I was getting power to the pump. The strange thing is that after a minute of being jumpered (with the key on), the pump all of a sudden came to life. The engine then started no problems.

After sitting a few days, the same thing happened. I jumped the test connector for the fuel pump and just waited unit the pump clicked on and away I went.

Is it possible that the pump can get gummed up and needs to have that power going to it for some time before it breaks loose? Then, it sits and gets jammed up again?

Thanks for any ideas.

 

Is there a relay in your fuel pump electrical system? That's another possible problem but I'm not familiar with that chassis. I will say an '88 E150 cargo van flamed out on a trip home due a bad harness connector at the fuel tank; something else to consider.

Its entirely possible your guess about gumming up after sitting a few days is close to what's really going oniIt wouldn't hurt to run some Techron through your system for a few tankfuls---that stuff un-stuck my sending unit which was begging to be replaced before I discovered that great stuff!

Hope its nothing too serious or costly!

 

Yep, it has a relay. I will be going through the entire system looking for all possibilities (bad connections, grounds, etc.).

Hopefully I can get the engine running again so that I can try your suggestion of the Techron.

I have it stored for the winter, so I am looking for all possibilities so I know what to look at come spring.

Thanks for the reply.

Peter

 

Let us know what you find if it comes to mind----could be helpful in the future.

Good luck with it all!

 

Are you calling the EEC self-test plug the fuel pump test connector?
If so when you say you jump it are you grounding pin #6 or jumping pin #2 to pin #6 of the EEC self-test plug?
If this is what you are doing do you hear the fuel pump relay (green bottom relay) click when you ground pin #6 and turn on the key?
When you say that you hear the fuel pump come on and it will now start are you talking about the fuel pump on the frame or the one in the tank or do they both come on at the same time?
If neither pump come on at first and then together it would be and electrical problem and not a fuel problem.
I have also heard of the Inertia switch doing this so you might try jumping it out and see what happens.

 

Sorry that I wasn't very clear in my post.

Yes, I am using the EEC test plug. I jumped the #2 (which I thought was a ground) to the #6 and turned on the key. I didn't hear the high pressure pump start humming until about a minute later (I was fiddling with my tester and just about to get under the vehicle to test for power to the high pressure pump when it came to like and started to hum).

I have not listened for the low pressure pump in the tank to see if it was humming. Would I need to get my ear right up to the tank, or should I be able to hear just by standing at the rear of the vehicle?

Unfortunately, I do not have the motor home close by to check right now.

I did hear the "click" when I turn the key, and I am assuming that is the fuel pump relay (but I have not confirmed that yet).

I did make sure that the inertia switch was pushed down, but I have yet to test it directly when I am having the no start issue.

So far, the pump has clicked on after jumping pin 2 to 6 on the EEC tester before I have had a chance to see what is going on with my tester. Next time I have a chance, I will need to have someone turn on the key while I am in position so I can test for power to the pump, etc.

Again, I apologize for not using the proper terminology in my original post. I am new to this type of diagnostic work, but I am trying to learn.

Thanks for the reply.

 

Pin #2 does go to ground but it goes the long way around as it goes through the computer and then to the NEG post of the battery. Why I asked if you were using pin #2 as the ground was I wanted to know if you had a complete ground through the computer.

Also when you turn on the key the EEC Power relay (brown base) and the fuel pump relay (green base) will make (click) at the same time. The fuel pump relay should drop back out (click) again after one second if you are not grounding pin #6 of the EEC self-test plug. The fuel pump relay will not make (click) unless the EEC power relay also is made as that is were the coil of the fuel pump relay gets its power.

You can put your ear to the fuel cap hole as the key is turned to hear if the tank pump is running or not.
Note unless you run out of fuel or clime a steep hill you may run for a long time with the pump in the tank not running.

 

Thanks for that. It gives me a good starting point come Spring. Hopefully I can track down the issue quickly.

Thanks again.

 

Ok. Spring has come and I am back on the hunt for my issue.

When I turn the key (just before turning the engine over), I can hear the green-based relay click. In addition, the "check engine" light comes on.

When i jump pin #6 and #2 on the test connector, I cannot hear either pump hum (the frame pump or the in-tank pump). I also tried to ground pin #6 directly to the negative terminal of the battery and the pump still doesn't come on.

Is the next step seeing if power is getting to the pump? If the green relay clicks, does that mean power should be at the pump?

Finally, are the two pumps wired in series (I am trying to figure out if the in-tank pump will come on even if the rail pump doesn't)?

What else should I be looking for?

Thanks.

 

YES the power should be there unless the fuse link is open at the starter relay on the fender or the inertia switch has not been tripped.

No they are wired in parallel. So yes one pump will come on if the other one does not.



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I see these pumps go bad often . The supply pump usually goes first , over works the pressure pump , then bang ! . The pressure pump fails . Ck the wiring ^^^^ and go from there . Good Luck !

 

I think I may be on to something.

I simply heard a click with the key turned on, but I didn't hear the pump relay click off a second later. I can hear something else click off after a second somewhere else in the engine compartment, but it definitely is not the green pump relay.

I unplugged the pump relay and I now realize that it is the brown-based relay that is clicking. I can actually feel it click, but nothing from the green pump relay.

Can I do a temporary jump on the pump relay connector to see if i can get the pump to energize?

Thanks for those diagrams. That makes it clearer.

 

Yes you can jump the yellow wire to the orange wire with a light blue stripe.
Short pin # 3 to pin #4. The two larger socket pins.

The brown bottom relay is the EEC Power Relay.



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When I jump the yellow to the orange with blue stripe, I hear the pump start humming straight away. Unfortunately I need to charge the battery a bit before I can turn it over.

So, I guess it is safe to say that my pump relay is the issue?

Hopefully I will be able to fire it up after supper. Fingers crossed! Is it safe to run it with the jumper in there for a short time?

Here is a silly question; does the pump stay on the whole time under normal operation, or does it come up periodically to keep up the pressure like an air compressor? Sorry for all the questions, but I would like to understand the system the best i can.

 

The pump runs all the time engine is running . The jumper can be used for a short time to diagnose or geter home . Relay is likely bad .