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I have a 1983 El Camino that I put a 2002 5.3L with a 4l80E in. I used the LT1Swap guide for wiring/relays.
I haven't been driving it much, but put some decent miles on it last weekend.
A few times throughout the weekend it seemed like it was taking a little longer than usual to fire up. For an unrelated reason, I replaced the coolant temperature sensor/pigtail and then when I went to start it, the fuel pump (Walbro 255 in-tank) wouldn't turn on. The car wouldn't start. Engine turns, all the lights seem to work. I check the voltage and it seemed relatively normal, so I assumed I got a bad fuel pump and went and got another Walbro 255 off Craigslist.
I installed the craigslist pump and still, no fuel pump when key is turned on. No priming, nothing. I swapped around the relays and replaced all fuses for the relays, still nothing. I then took the old fuel pump (non-craigslist) and connected it directly to the battery with alligator clips, it turned on and sprayed leftover fuel all over my shirt.
After that, I took my voltmeter and connected it directly to the connector that clips onto the fuel pump from the sending unit. This video is that volt meter reading:
I'm not an expert at all regarding voltmeters, but it looks like when I turn the key (where it should be priming) it flashed 12V, but then drops. Then I turn the key to ON and it struggles to get up to 12V.
My buddy suggested that it could be the ignition switch (located on the column), so I went and picked a new one up from O'Reillys tonight. I'll be installing that tomorrow.
But, I really am looking for any advice here. I'm moving out of state shortly and need this to start. I'm happy to answer any additional questions that may help solve this mystery.
If it were the igntion switch, I'd expect you'd be seeing symptoms from other things intermittently not wanting to work as well, not just the pump.
In any event, keeping checking your electrical connections. The ECU provides a ground under the circumstances required to have the fuel pump running. That ground closes the contacts in the fuel pump relay allowing the pump to run. You should see - prime for a second or two with ignition on/engine off; if the ECU "sees" the engine turning over properly and/or starting/running - then it keeps the ground in place allowing the pump to run. If it's not running, and you don't have a bad pump (sounds like you have 2 good ones) then there's an electrical problem somewhere. Did you check the pump ground itself?
If it were the igntion switch, I'd expect you'd be seeing symptoms from other things intermittently not wanting to work as well, not just the pump.
In any event, keeping checking your electrical connections. The ECU provides a ground under the circumstances required to have the fuel pump running. That ground closes the contacts in the fuel pump relay allowing the pump to run. You should see - prime for a second or two with ignition on/engine off; if the ECU "sees" the engine turning over properly and/or starting/running - then it keeps the ground in place allowing the pump to run. If it's not running, and you don't have a bad pump (sounds like you have 2 good ones) then there's an electrical problem somewhere. Did you check the pump ground itself?
This is what its going to take to diagnose the problem, but wanted to let you know that the PCM supplies 12v to the fuel pump relay rather than a ground. Its the odd one, fans and check engine light it supplies a ground to make those work.
Using DVM, check for 12v from wires at PCM. Are there any wire unions from front to rear? Check wire for nicks or damage.
Is the relay getting constant 12v? Good constant ground? I always re-look up SPDT relay connections because I forget, you could have a terminal mixed up. I don't believe it's ignition switch. Good luck.
...but wanted to let you know that the PCM supplies 12v to the fuel pump relay rather than a ground.
Thanks for clarifying -- mine was all pre-wired by PSI so I only had to connect the relay output to the fuel pump circuit. I assumed it was a ground as all the other efi set ups I've had have been. Wonder why they went a different way on this series of engines? In any event - the trouble shoot process is the same.
Using DVM, check for 12v from wires at PCM. Are there any wire unions from front to rear? Check wire for nicks or damage.
Is the relay getting constant 12v? Good constant ground? I always re-look up SPDT relay connections because I forget, you could have a terminal mixed up. I don't believe it's ignition switch. Good luck.
Since his car was working correctly before, but has begun to "act up" -- doubt it's a terminal mix-up...sounds to me like a connection disruption somewhere along the line.
Since his car was working correctly before, but has begun to "act up" -- doubt it's a terminal mix-up...sounds to me like a connection disruption somewhere along the line.
Thanks, I missed that part! Should also note, soldier and heat shrink all connections.
To the OP, you do have a fuel pump relay wired in, right? Because running the pump straight off the PCM power will cook it in short order....
I really appreciate all the replies.
Yes, I have a fuel pump relay wired in. This is the setup I went with.
I checked the -30 slot (orange wire on the fuel pump relay in picture) in the relay with a test slight initially to see if it was getting constant power, and it testing good with the test light. I haven't ran the multimeter on it. I'll hold off on the ignition switch for now. I had a hard time finding the 2 wires I had cut for the coolant sensor, and did some digging around the wiring. I'm wondering if I knocked something loose in that process.
Any additional details or advice is greatly appreciated.
Test the orange wire in that photo, the one you already tested and said was good, by grounding it at the black wire in that plug. What that will do is let you know if the ground is good. If that checks out, check the green wire with a meter, with one probe on the green wire and the other on the black ground. That should give you 12v for a couple seconds, so you may have to have someone turn the key for you while you check it. If that checks out good, then you should be getting 12v on the wire coming out of the relay plug going to the pump, again, only for a few seconds. If all that checks out and you're getting power out of the relay, check your pump ground at the tank.
The only thing I'll add is that, when hunting for the coolant switch wires, I meant to get the little plastic cover off the blue side of the ECM to expose the pins and loosened the bolt that holds the blue side in a little bit (i forgot that this is unrelated to the plastic cover). I didn't pull it out, but it did push out of the ECM a little bit. This may be nit picking, but just wanted to mention that. I tightened it backdown immediately after I realized I was loosening the wrong thing.
Figured it out! One of the key on power terminals had come loose on the relays.
Put it back in more securely and everything works great again. Figured it was something simple like that.
alex the reason I suggested the ign switch is that odd run-on problem you have. is that still present?
did adding back the ECT sensor to the PCM make the transmission shift correctly?
I think you might wanna pony up for a proper drivability tune too.
anyways good luck in California!
Run on problem seems to be reduced if not gone. I’ll have to keep an aye on it but I still have the ignition switch so maybe I’ll give that a try when I’ve got some time.
ECT sensor did not fix the transmission issue. It did fix the high idle and there is no longer a check engine light, ie no longer a CASE Learn code throwing anymore either.
There’s no pulse coming from the the Speed sensor wire off the PCM, so I’m wondering if that would have any effect on the shifting... gonna try to get that working and go from there.
Good call on a proper tune... ordered cats to pass DEQ, but that might be my next purchase.
Thanks for all your help along the way dude. It’s been huge.
Not moving just yet. I was in Texas visiting family for the last week. I'll be leaving friday for CA and will live out of a hotel until 12/23, then fly back here for about a week and move everything before 1/1.
Ordered 2 new speed sensors for front and back while i was out and just replaced them as soon as i got home. Definitely didn't fix the transmission shifting issue.... I didn't fully mess around with attempting to calibrate the speedo, but it didn't show any activity, so i'm willing to bet that's not fixed either.
I might try to swap the plugs around after reading that thread. I remember when I first did the wiring, I accidentally cut one of the VSS' and later put a new plug back on, which could easily mean I got them confused.
Well i swapped the plugs and it seems to have fix the shifting issue.
It still didn't seem like I was getting any signal to the speedo, but I stopped in a church parking lot to see if I could calibrate it and the damn thing died on me.
It was the same terminal that had fallen out previously, but the locking tab completely broke off. Had to rig something up since O'reilly didn't sell terminals with locking tabs.
i'm really looking forward to validating that the speedo works so I can get all this wiring in a safer condition...
11-21-2017, 12:42 AM
Fuel Pump Issues 
