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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 09-27-2011, 12:59 PM
rockypool rockypool is offline
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Cool 90 460 Motorhome Wont start

I have had this MH 2 years and changed all fluids and Batteries It wont start I changed Fuel relay and Ignition tfi I can start it with start fluid I just put 12v to the pink/black at the inertia and the fuel pump works I read on here how the oil pressure switch can be bad I have a engine wiring diagram and it does not show that oil switch in the wiring plan what else can effect power to the fuel pump?

I also get a slow response with the first 3 turns of the key ...not a click but a buzz those first trys then away it goes strong starter I have checked
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Old 09-27-2011, 03:02 PM
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First, welcome to FTE. I say that because what I'm going to say next might come across as rude or condescending and I don't mean it that way. I only say this because your post is very hard to understand.

Please learn to use punctuation and complete sentences. No one wants to slog through a post like yours to try and figure out what you're asking. It's much easier to click the back button and spend time helping someone who can write a coherent sentence.
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Old 09-27-2011, 05:35 PM
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A 1990 is a Fuel Injected engine so it does not have a oil pressure switch like the Carb 460's did.

You said that you put "12v to the pink/black at the inertia and the fuel pump works".
Witch fuel pump ran?
The one in the tank or the one on the frame?
Did you try resetting the Inertia switch?
Does the fuel pump relay click when the key is turn on and drop back out one second later with just the key being turned on?

If you can start it with starter fluid why did you change out the TFI (ICM)?

Is this a class "A", "B" or "C" Motorhome?
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Old 09-27-2011, 06:03 PM
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See if when you apply power to each pump, that they spin and sound OK. You could use a battery charger, or a temporary wire from your battery's positive side to each pumps + side, doing so one pump at a time. Have your key in the run position for the test. If they seem OK, install a test fuel pressure gauge to the valve on the fuel rail, cycle the key to run position a few times, take note of the final reading. If they don't spin with the key, but do with the auxiliary power source, then you will need to examine the circuit, to isolate the problem. If with auxiliary power, one or both fail the test, examine/repair the circuit, and/or replace the pump if at fault.
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Old 09-27-2011, 11:11 PM
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Hi Thanks This is a 1990 Southwind with the 7.3 EFI It only has 1 fuel pump in the tank I havent checked the inertia switch How can I check it Its right in the middle of all my problems I did put power to the pink / black wire the comes out of the inertia switch and the pump worked great.
I took off the Inertia switch and no power in the brown so I will have to check the relay now I got a new one so I wiil start with the yellow lead into it
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Old 09-28-2011, 12:03 AM
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You will only get power to the inertia switch for the first 2 seconds after you turn the key to on. It won't have power again until the computer gets a signal that the engine is running.

You could temporarily hook the pink and brown wires together and bypass the inertia switch. If it starts then either the switch is bad, or it needs to be reset.

Your slow cranking sounds like it might be the battery cables or a ground. Would be worth checking them out.

(Advice worth what you're paying for it)

Good Luck,

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Old 09-28-2011, 12:21 AM
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I have given up for tonight the inertia was getting something like 1.2 v so I have to go back to the fuel relay and the eec power relay
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Old 09-28-2011, 08:07 AM
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OK so you have a Class "A" Motorhome with a 7.5L (460) EFI on a Ford F53 Chassis with one high pressure fuel pump in the tank.

The 1.2 v is coming from the Computer pin #8 over the Brown wire that checks the fuel pump relay and fuel pump status. The Brown wire also carries the current from the fuel pump relay NO contact to the input of the Inertia fuel shut-off switch.

The fuel pump relay is closed when the Computer pin #22 (Tan wire with a light Green stripe) grounds the coil of the relay. This wire also goes to the EEC self-test pin #6 and can be grounded or shorted to pin #2 of the self-test plug to run the fuel pump for testing. The computer will ground the fuel pump relay for one second when the key is first turned on and again for one second every time it sees a PIP pulse. The fuel pump runs at no other time pressure or no pressure.

The common contact of the fuel pump relay is fed from a fuse link by the starter relay over a yellow wire. There is a fuse link at the starter relay that will cut power to the fuel pump wiring and the yellow wire going to the fuel pump relay Common contact.

Power to the fuel pump relay coil is fed from the NO contact of the EEC Power Relay over a Red wire.

The fuel pressure regulator just bypasses fuel back to the tank when the fuel pressure goes over what the spring and vacuum says it should be. With the engine not running the regulator will by pass fuel to maintain 40-45psi with pin #6 of the EEC self-test plug grounded or shorted to pin #2 of the EEC self-test plug with the key on.
With the engine at idle and at max vacuum the fuel pressure will be about 30-34psi.

The HP frame fuel pump will pump to about 95-100psi into a closed head and will run all the time it has power on it. But the fuel pressure has nothing to do with the running of the fuel pump.

A PIP pulse comes faster than a second from the distributor when the engine is cranking or running so the pump will run all the time the engine is cranking or running and has nothing to do with pressure. When the engine is not cranking or running their is not a PIP train so the pumps will not run with the key just on.

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Old 09-28-2011, 08:07 AM
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