Working on my FIL's 94 lightning. It has some other issues, and has been sitting for almost a year and a half. Bought a new battery and was going to try and get it started and pulled in the garage. Would not start. Fuel pump(s) not priming and 0 pressure. Swapped fuel pump relay, checked inertia switch, checked to make sure there was fire so I would know EEC relay was good. My fear is the computer has went south while sitting. I know there is a procedure on diagnosing this but I can't find it. If someone could post the link it would be great. Any ideas welcome. The truck has some other issues, so I will probably have more questions later.

 

You have a dead fuel pump.

 

Two dead fuel pumps that both worked fine when then truck was parked?

 

Truck started missing and cutting out with the
O/d light flashing when you tapped the gas. So it sat in the driveway waiting on another project that was in the garage. He started it regularly and would let it run until a freeze plug in the back of the head rusted out. That was about 8 months ago.

 

These pumps don't like sitting.. I can tell you that. It's easy enough to figure out if the PCM is bad, put a jumper across the STI and Sig_Rtn pins in the EEC Test connector, turn the key to the run position and the check engine light should begin flashing stored codes. If nothing happens then check that the EEC power relay is engaging when the key is turned on, because if the PCM doesn't get power then the pumps won't either since the PCM engages the pump relay.

 

Thanks, will check this afternoon. Is using a little code reader the same as counting the check engine lights? And since the truck sat so long with a completely dead battery(actually unhooked for a while) will there be any codes to read?

If the truck has spark, doesn't that mean the EEC relay has to be good?

 

You should still get the 11 or 111 all clear codes with the code reader or the jumper method.

No. Ignition pulse is delivered directly to the coil from the distributor so you will still get spark even with the PCM completely removed from the vehicle.

 

Check the red wire at any fuel injector with a loading test light with the key on. If the test light lights with the key on then EEC (PCM) relay is made and is sending power out of its NO contact.

 

Thank you guys so much for your wisdom, I ended up not being able to make it over there today, but he was able to get the code reader hooked up.

542. Fuel pump circuit open electronic control assembly to ground.
625. Electronic pressure control driver open
Continuous memory codes -- fix last
542. Fuel pump circuit open electronic control assembly to ground

It gave the 542 twice.

 

I dough that you got a 625 from that truck as it does not have a Electronic pressure control driver.
If you did get a 625 I would guess that you have a bad PCM Computer.

Most of the time a 542 means that you have a bad fuel pump but I would ground pin #6 in the self-test connector and turn on the key and see if each of the fuel pumps run when selected.

KOEO DTC 542 indicates that one of the following has occurred:

No Start:
-- Inertia Fuel Shutoff (IFS) switch not reset or electrically open.
-- Open circuit between the fuel pump and FPM circuit connection to the power-to-pump circuit.
-- Poor fuel pump ground.
-- Fuel pump electrically open.

Engine Starts:
-- Fuel pump secondary circuit short to power.
-- Fuel pump relay contacts always closed.
-- Open in FPM circuit between PCM and connection to the power-to-pump circuit.
-- Left/front HO2S short to power (dual HO2S applications).
-- Damaged Powertrain Control Module (PCM).

A Continuous Memory DTC 542 indicates that one of the following intermittent conditions has occurred:
-- Fuel pump circuit activated when PCM expected circuit to be off (i.e., fuel system test or prime procedure).
-- Inertia fuel shutoff switch tripped, then reset.
-- Open circuit in or between the fuel pump and FPM circuit at the PCM (refer to «Schematic»).
-- Poor fuel pump ground.
-- FPM or power-to-pump circuit short to power.
-- Fuel pump relay contacts stuck closed.
-- Left/Front HO2S circuit short to power (with/dual HO2S).
-- Engine stall due to excessive load.

NOTE:
For trucks with dual fuel tanks, perform Key On Engine Off (KOEO) Self-Test twice, once with the front tank selected and once with the rear tank selected. If KOEO DTC 111 and Continuous DTC 542 is present both times, continue with this test (intermittent concern). If KOEO DTC 542 is present in only one test, refer to the Fuel/Engine Group of the Service Manual to check for open circuit between select switch and suspect pump circuit ground./

 

Wow subford, I feel like a third grader talking to the professor.

This was not one of the little cheap code reader where you count the flashes/beeps, he has one of those, he borrowed this one from a friend, It's a snap on that digitally reads out. So that was the code given, and as soon as he said driver, I suspected the computer. Can you elaborate on jumping the number 6 pin. I have no idea where to start there.

 

Just got over here
Attachment 150999

 

The self-test plug is where he plugged in the code scanner.
You just ground pin #6 of that plug or short pin #2 to pin #6, select one of the fuel tanks and turn on the key. The selected fuel pump will run until the key is turned off or the ground is removed. This bypasses the PCM Computer and takes the Computer out of the ball game.





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Ok, got to playing with the code scanner. Ran the test for no start/no fuel pressure. Gave that 625 code again, then it gave me a option to run a test. I assume it would be the same as jumping the #6 pin? The fuel pumps kicked on. I primed it a few times then cranked it and it started. Shut it off an unhooked the scanner and the pumps are still working and truck is starting. I don't understand, but I hope it's fixed, at least that issue. The truck also didn't go to cutting out and o/d light flashing when you hit the accelerator. I'm sure something will come back up, but at least we can move it around and get the major issues fixed.

Going to pull the transmission to replace front seal. His plans are to try and unbolt 1 side of motor at a time and rotate it around to try to replace freeze out plugs in the back of the heads while the trans is out. Anyone ever done this? Maybe I should start a new thread on this. I don't look forward to this, mainly because of the numerous wasp nest under the truck.

 

I will try my best to remember this for future reference, super simple. Thanks for spending the time to write that up, excellent job.