Early Efi Madness

Working on getting our backup truck running right today so we can get a for sale sign on it. Truck is a 96 f250 460 2wd zf5 with 86k miles, so it has sat most of its life.

For years it ran great but it started having some tank issues so it got parked till it could get some attention. Well it took a year before I’ve gotten to it, and I’ve drained all the gas, replaced both sending units and pumps, along with fresh gas a fuel filter. I replaced the cap and rotor, wires and plugs, with a new battery too.

Truck fires right up and has good fuel pressure, but sounds like it has a wicked cam, and is running pig rich with no power. Obd1 scanner will not read the computer, and the manual way isn’t triggering the self test. I know the computer is working because the check engine light is on and the truck runs.

Checks all the continuity at the EEC and everything looks good there. I replaced the map, fpr and o2 sensor and now the truck runs and drives, but has no power.

Timing is right, firing order is correct, it’s running on all 8, just super rich. No exhaust leaks, and is completely stock other than a flowmaster muffler.

I’m at my end with this antiquated efi, and if I can’t get it working right I’ll pull a carb intake off the shelf and put a Holley on it...

I really don’t mess with these efi trucks much so anyone’s thoughts are appreciated!

So these symptoms sound just like a bad fpr to me, causing the injectors to overfuel. Well I pulled the relay for the fuel pumps with the engine running and the engine smoother out and idled perfect for about a minute before starting to run out of fuel. Interesting...

So wen you turn your truck to run and not start it does the fuel pump pressure up and turn off? Or does it just keep running constantly? Followed with hard starts and If you do a throttle snap test does it want to bog and die and possibly backfire through intake or exhaust?

Continuously runs with key on engine off. I put the old fpr and have no change. Starts great and has decent throttle response but pours black smoke when you rev it. I put my gauge on it and it’s building too much fuel pressure. As soon as I pull the relay and it drops into the 30 psi range it runs great again. I pulled the return off and ran it into a sealed can so there would be no back pressure on the return of the rail and still no change

Fuel pump continuesly running was a sign of the computer being bad in my buddies truck though a little older it was a 91. We replaced every sensor on his motor and cleaned basically everything searching for the problem. It was the computer after all of our work. It did run and drive still. Also it wouldn't let us read obd1 codes from it either. It did after we changed the computer out though

Get a fuel gauge connected up the fuel rail, before proceeding farther. What are you using for a reader. I really suggest flashing light style, takes some practice but less stuff to go wrong or

hce said:

Get a fuel gauge connected up the fuel rail, before proceeding farther. What are you using for a reader. I really suggest flashing light style, takes some practice but less stuff to go wrong or

You must be registered for see images attach

Click to expand...

I’ve got my ford ob1 scanner and tried the light style with no response from the computer, I’ve already mentioned my fuel pressure readings.

pelky350 said:

Fuel pump continuesly running was a sign of the computer being bad in my buddies truck though a little older it was a 91. We replaced every sensor on his motor and cleaned basically everything searching for the problem. It was the computer after all of our work. It did run and drive still. Also it wouldn't let us read obd1 codes from it either. It did after we changed the computer out though

Click to expand...

I’ve got a computer coming, that makes a lot of sense. Just didn’t expect the engine to run and have engine lights on with a dead computer, but it’s usually something you don’t expect after all.

I have a 96 f150 5.0 and its got the obd2 port under the dash. Yours is obd1? That thing has fuel issues too, low power, poor fuel mileage but no check engine light. Maybe we oughta stick to Idi’s lol


Sent from my iPhone using Tapatalk

This is a weird truck, it’s a December 95 build with obd1 and no maf. Once this truck is sold I’ll have a 7.3 only fleet, it’s not a bad lookin truck but the efi 460 is just a gas guzzler

Thewespaul said:

This is a weird truck, it’s a December 95 build with obd1 and no maf. Once this truck is sold I’ll have a 7.3 only fleet, it’s not a bad lookin truck but the efi 460 is just a gas guzzler

You must be registered for see images attach

Click to expand...

They must’ve started obd2/maf like Jan 1st 1996 then lol


Sent from my iPhone using Tapatalk

Well kudos to @pelky350 computer fixed the truck up, big thanks for all the help