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I am helping my neighbor with his 1988 Econoline Mirada motorhome.
The van has been sitting for 6 years. He put new batteries in it the other day and it wont start. It will fire and run a few seconds on ether in the intake. I can hear what I think is the fuel pump relay under the hood on the passenger fender click, but when I crawl under it I cant hear the pump in the tank come on. When I turn the key to run the relay clicks but no other sound.
So, I am thinking the fuel pump is bad. Where is the pump located on this? I see on the frame under the drivers door what I think is a fuel pump. Is this actually the pump, or is there a pump in the tank? I don't hear a sound from the pump on the frame or from the tank.
Thanks!
deputydog03
there is a fuel pump in the tank and a booster or high pressure fuel pump in the frame rail on the driver side. If the RV has 2 tanks there will be a 3rd fuel pump in the other tank. If the relay is clicking as you say and you don't hear any action then the tank pump is probably bad. There should be a test plug on a pig tail somewhere on the driver side. You can jump 2 of those terminals to test the pump. Google 88 ford 7.5 fuel pump test and this forum has some fantastic info about how to check it . Illustrations and everything. You can study that info better than I can explain it. Also don't forget to check the inertia safety switch to see if it is tripped.
Great, thanks!
Does the booster pump on the frame kick on with the key too, or is it activated by fuel pressure? I cant hear it running either.
I will research the above items.
deputydog03
my experience comes from an 88 F350 with 7.5 with 2 tanks. So I'm going to assume the your neighbors RV is going to be similar OK? There should be 2 relays , most likely on the driver side. On the RV they may be under the "dog house" toward the rear of the engine. They are usually side by side and can have a black plastic cover over them. One should have a brown plug , the other a green plug. Locate the brown . Look for a tan wire with a green stripe. If possible put a test light on the back side of that wire terminal by stabbing the point beside the wire. ground the test light to a good ground. Turn key to on position. Tester should light for 2 seconds as the computer kicks "both" pumps on to prime the system. If you have 2 seconds of test light the EEC is sending a signal . Now try the same test by probing the brown wire.
when key goes to on position you should again see test light for 2 seconds. If you do............you have voltage going out to the pumps, If you don't have light.....the relay is probably bad.
It only has one tank. The relay under the hood clicks then clicks again after 2 seconds. The inertia switch has power to both wires a few seconds after turning the key on. So, I assume the switch is good. I also assume the relay is good as it is sending power to the inertia switch.
If I am correct I believe the power will go through the relay then through the inertia switch back to the pump. My only confusion right now is when the boost pump on the frame should kick on. Neither that pump or the tank pump is coming on when the key is cycled on.
deputydog03
The 2 pumps should come on together. The most likely canadate for failure will be the pump in the fuel tank. It's also cheaper in price than the booster. Unfortunately its not the easiest to get to. I suppose that the tank pump could somehow signal the booster to come on possibly through the EEC (computer) to prevent the booster from running with no fuel from the tank pump and burning up. Though the booster is accessible it is still somewhat hard to get to. It has an electrical plug with a black ground and a pink hot wire. You could unplug it and run a positive and negative leads and see if it comes on. Given your description of how long the RV has set , my hunch is still going with a bad tank pump. If you could confirm the voltage from the brown relay wire that would tell You the relay is in fact good.
annaleigh,
That would be a great book For deputydog03 's neighbor to have !!!! Thanks dude for sharing that !
Deputydog03, dude I sent that reply before coffee this morning
and after reading it again ,I would realize that if in fact you have voltage after the inertia switch you should have voltage to the fuel pumps (barring a break in a wire or bad ground. Speaking from past battles , I had a bad tank pump ,and couldn't hear the booster pump coming on . Turned out my booster was good. So I am wondering if the EEC keeps the booster pump from coming on if the tank pump is dead. As I said , you could run some leads to the plug and check it. My thoughts are
still that a tank pump sitting in 6 year old gas has failed. Does the gas gage work ? Or does the needle act a little goofy ?
Oh Yes ! That looks all to familiar ! My farm truck sat for about 5 months. Changed that nasty looking pump and still no start. After a very long time and a lot of reading on this forum I had eliminated everything but the injectors , all 8 of which were stuck ! Thanks again ethanol !
Beautiful looking truck! I don't want to remove my upper plenum and am thinking about using one of the tools to inject cleaner directly into the fuel rail. I want to do a little research and make sure it is safe and that method does not wash the cylinders and cause problems.
Deputydog03 should tell his friend to buy a Ford factory service manual also if he/she plans on keeping the motor home. They are so much better then any after market book.
1988 Ford Truck Shop Manual 5 Book Set on CD F150 F250 F350 Bronco Van Service
https://www.ebay.com/itm/1988-Ford-Truck-Shop-Manual-5-Book-Set-on-CD-F150-F250-F350-Bronco-Van-Service/162679993713?hash=item25e07bb571:g:rX0AAOSwaMhZwYT h
annaleigh
The manual you are referring to must be the disk on Amazon for 30 bucks ? I will probably be getting one!!! Thanks for sharing that !!!!
my F350 was down for some time with fuel issues due mostly to not being used. I took the bed off and eliminated one fuel tank and powerwashed the other .New fuel pumps ,filter , fuel preasure reg. and had the fuel rail off and the injectors out (they were stuck) . I built a little frame to pressurize them and apply voltage and got them cleaned. new O-ring kit and back in business. Sounds easy , but worked on it nearly a year. After that a make over of fresh paint for the cab and bed and some exhaust stacks. Most recently had to replace the EEC. Here in Missouri you can put historical license tags on a vehicle 25 years or older (with some limitations).
I have seen on YouTube people cleaning injectors like you described by hooking through the Schrader valve on the fuel rail. Are you having issues now?
I have been gone out of state for the past week, just now getting back to the computer.
Thanks for all of the great information and the diagrams! Next week I am going to get back on this little project. Now I feel like I have a direction to look. I was a little afraid that mice chewed up the wiring, but I cant see any breaks or bad spots in the wires.
I might not get back to work on this project until next weekend, but will post updates as I go.
Thanks!
deputydog03
Just understanding the sequence of the fuel system of this generation of trucks is a big help in diagnosis. A lot of things have to happen in the right order to make them run. In the case of a 1988 , we are looking at a 32 year old vehicle ......technically an antique. I recently replaced the EEC (computer) on my 88 F350 7.5 . Understanding the fuel sequence helped me to come to that diagnosis. I don't consider myself a mechanic . I just responded to your post because of the very familiar description of your issue hoping I could help. Listing the start sequence in steps clarified it for me and helped me to troubleshoot my issue. So if the following is something that you already know ,Then I apologize for stating the obvious.
key on ,EEC signals brown relay to turn both pumps on to pressurize the system for 2 seconds and shuts off
EEC is now looking for an RPM signal from a sensor in distributor
Key to start pos. engine cranks , EEC sees RPM signal , turn on both pumps with green relay until RPM signal is gone (key off or engine dies)
Tank pump deliver's fuel to booster pump that pushes fuel through filter then through fuel pressure regulator
FPR delivers fuel to the injectors and returns un-needed fuel to tank.
My hunch , based on what you have described is a failure of the tank pump. This forum has descriptions of how to energize the pump with 12 volts to see if it will come on (out of sequence) Dropping the fuel tank in a motor home is not something I would look forward to .
Best of Luck with your diagnosis and repair. Would love to hear how you are getting along with the project.
I've been wrestling with fuel pumps also. Mine is 1990. If yours is fuel-injected, then you will have an in-tank pump, and a frame-mounted booster pump. Both are on the same circuit, and both route through the inertial cutoff switch and the same relay.
You should easily hear the frame-mounted pump if you open the driver's door while turning the key to on when the relay clicks. To hear the in-tank pump you'll have to crawl under the RV and listen to the tank. A mechanic's stethoscope is useful here also. You can touch it to the frame pump and touch it to the tank to listen.
Another thing to do is hook up a fuel pressure gauge to the Schrader valve on the fuel injection rail under the hood and see if you are getting pressure. You should be reading 30-40 PSI there.
Be aware that if the in-tank fails, the frame-mounted pump is strong enough to suck gas through the dead in-tank pump, masking the problem. I am now fairly certain this is what has caused many a "die while hot" issue you find on the internet for our era vehicles. I suspect when the gas gets hot and the in-tank pump dies, the high pressure pump pulls enough of a negative pressure between itself and the tank that the fuel in the line boils, and then the high pressure pump cavitates, giving no fuel pressure until things cool down.
