89 f150 4x4 5spd, reg cab

I pulled the bed and dropped both tanks to do some frame repair work. Battery was disconnected while welding. I replaced the front tank, and reused the rear one. The truck ran off both tanks before this.

Now, it won't cycle the pumps when the key is turned on. The FP relay is new, and the inertia switch has tested good. Using my battery charger I can make the pumps run: at the pump itself, at the intertia switch and at the FP relay. I unplugged the relay and energized either the brown or red wire (can't remember) yellow is constant hot and that tests ok. It seems like there's no signal to energize the fuel pumps to this relay.

Also, banging on the eec relay with a screwdriver does nothing. Am I on the right track thinking either the eec is bad, or maybe there's a bad ground? If its grounds, where are they all at so i can clean them up. I have a haynes manual and will be digging in more this weekend. Any helpful ideas before then are appreciated. Thanks!

Kevin

 

Does the check engine light come on when you turn the key? Can you get codes from the computer?

The fuel pump relay coil gets power to one side from the EEC power relay. If the EEC relay isn't pulling in or the EEC fusible link is blown, the pumps won't run.

The computer grounds the other side of the fuel pump relay coil. The computer grounds it at power up, and then releases the ground after two seconds if you do not attempt a start. Normally, a dead PCM will sucessfully turn the pump on, but not run computer instructions well enough to turn the pump off.

One of the pins in the 6 pin diagnostic connector is labelled "FP". If you ground this wire, the fuel pump relay coil will be grounded and the fuel pump should run. If it doesn't run when you ground FP, the computer is not at fault. If it does run, check continuity between FP and the big 60 pin connector.

 

The problem was a bad EEC relay. Where one wire should have been energized at key on, it was energized all the time. Its like turning the key, the pumps run and then shut off. Only, i was stuck in a perpetual state of this because turning off the key didn't cut power to the eec relay, which cuts power to the FP relay

Now my problem is no spark. I verified this by using an old plug on the #1 wire and held the plug on the intake while the wife cranked it. No spark. Even a shot of gumout in the throttle bodies did nothing.

I have verified power to the coil at key on, no power at key off, so thats a plus. Ive been reading up on the TFI module, but im not sure where it is in the engine bay or even if its the right thing to be checking out. Cap, rotor and wires are new, and the truck has run with this configuration before i started work on it. Ideas? Is all this from welding even though i pulled the neg cable off the battery?

Kevin

 

An 89 has the TFI on the side of the distributor. It or the pickup coil inside the distributor bowl is a common culprit in a "no spark" situation.

Read my recent posts on "get a cheap $4.00 test light" for how to diagnose no-spark/bad TFI.

The real issue with welding is the flow of ground current. It is important to keep the ground clamp close to the workpiece, and to have the current flow directly from the workpiece to the ground clamp. If you slap your welder's ground clamp on the body and proceed to weld on the frame, you may well damage electrical components, no matter what you did with the battery. The reason is that the current flows the length of the frame, through various ground braids, and then the sheet metal and back to your clamp, creating elevated and damaging voltages along the internal nodes. Grounding the frame and welding the sheet metal body is similarly problematic.

If you kept the ground clamp on the frame and close to the point you were welding, I would be surprised to see much damage ensuing from that.

Sometimes, a flaky TFI or pickup coil will work OK for several weeks or months, only to randomly quit hard. It can seem to depend on the phase of the moon or temperature or whatever. So the "no spark" situation may be conincidental to the other issues.

 

Thanks for the info. I know about keeping the ground clamp close to the work area. I clamped to the frame, not more than a couple feet from where i was welding (only welded on the frame)

I may already have a testlight, ill have to look. Ill read your post on the no spark situation as well. Ill report my findings, thanks again,

Kevin