fng w/TBI Fuel Pump and ECM Issues

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530dan

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So I need some mother truckers that can help trouble shoot or help me prove what's not wrong with my truck.

My name is Dan and my truck is a 90 v2500 gmc burban 5.7/th400 with 307k miles yes motor, trans and transfer case have all been rebilt at least twice each front and rear axles are about to be redone again I do all of it myself

Now my problem is no signal from ecu/ecm to fuel rela. so no power to fuel pump!(don't really care what's you want to call it as long as we both know what we are talking about)
 

1987 GMC Jimmy

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The SES light comes on as soon as you turn the key? Can you interface with your ECM by pulling codes and everything looks good there? Are you saying the orange wire isn't getting 12V? If so, the best bet is a bad oil pressure safety switch. It's located by the oil filter. If you're talking about the green/white wire, that would probably be a bad ECM. Also, double check that your ECM B fuse is good if you're not getting an SES light. I wasn't sure which wire you were talking about, but those should be your solutions barring a wiring problem.
 

530dan

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Drk grn/ wht stripe wire, as far as I can tell is the wire in a1 slot from ecu to relay. if I ground the tan/ blk stripe wire relay clicks. as far as I can tell it's oil presure switch, from wire diagrams I can find. my oil pressure gauge works. Is that sensor same for signal To ecu and gauge? Yes ses comes in when I turn on the key and no codes to pull
 
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530dan

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Yes see light comes on and no codes to pull
 

1987 GMC Jimmy

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Drk grn/ wht stripe wire, as far as I can tell is the wire in a1 slot from ecu to relay. if I ground the tan/ blk stripe wire relay clicks. as far as I can tell it's oil presure switch, from wire diagrams I can find. my oil pressure gauge works. Is that sensor same for signal To ecu and gauge? Yes ses comes in when I turn on the key and no codes to pull

Your gauge sender is by the distributor, accessible from the top of the engine, and is a one wire unit that only communicates with the pressure gauge. The safety switch is down by the oil filter and is a two wire unit that mediates power to the pump granted that engine is in the correct pressure range. It's just a precaution that kills your pump in the event of a rollover or a crash. You could always bypass the switch temporarily to test it out.
 

530dan

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Wow ok I'll check it out because it seems to be an on going issue with my truck the really smart people I bought it from drilled two holes in the the top of the old fuel sender to hard wire a toggle switch for the fuel pump. I rewired it correctly with factory wires from a junk yard truck and it ran great for 6 weeks or so other then it died at a stop light three different times. It fired right back up and that's when I started trying to figure out the problem
 

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The only reason I could think to do that is if the ECM stopped sending out power to drive the relay, and they just bypassed the whole thing. That's so stupid, though. The fact that you were able to make it work by rewiring it properly makes it sound like everything's working right so I'd check on that switch.
 

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Welcome Dan, This turned out to be more of an Intro thread, so I've moved it to the TBI category and put a description in the title for others to follow.


Soooo you guys got to avoid the big expected dam break not long ago? I remember back in about 1986 or so when the levy broke and Marysville and Yuba City wasn't so lucky.
 

530dan

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Welcome Dan, This turned out to be more of an Intro thread, so I've moved it to the TBI category and put a description in the title for others to follow.


Soooo you guys got to avoid the big expected dam break not long ago? I remember back in about 1986 or so when the levy broke and Marysville and Yuba City wasn't so lucky.

I was 2 in the 86 flood but in 97 when it flooded we were under water. This time around they made a big deal out of nothing the dam is about 200 yards from the spill way that came apart the only thing that was a little nerve racking was when the water came over the emergency spill way
 

530dan

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So I couldn't find the two wire sender you were talking about are you sure there is supposed to be one a the 90 v2500 small block?

Anyway I put a new pump in and filter and turned the key and now there is power to the pump I'm kinda thinking that the pump failed in a way that it couldn't complete its circuit and that's way it seemed to be no power at the pump I'm not sure. I'm pretty good with cars and trucks and it's mind boggling to me
 

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I'm absolutely sure it's supposed to be there, but I wouldn't be surprised if it wasn't. Anything with some sort of factory in-tank electric fuel tank is supposed to. Here's a stock photo of one. It's threaded on one end, and it's a black tube looking thing with a plug on the other end.
 

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HotRodPC

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So are you saying it's fixed and working now with the pump replacement?
 

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Later years had oil pressure sensor/switch combo with three wires. Two for the switch and middle for the signal
 

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