1993 Gmc k1500 no fuel at start

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Old 05-18-2013, 09:27 PM
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Default 1993 Gmc k1500 no fuel at start

Ok Im seriously stumped at this point...new fuel pump/sender, temp sensor,swapped out injectors and regulator out of another running truck and distributor, ops is new, plugs/wires o2 sensor, no vacuum leaks...ok went through the obvious here. I get no fuel at start, prime with gas and it runs until I shut it off injectors spraying fine... shut it off and no gas pulses out at cranking, fuel pump runs the relay is new and it also idles between 1500 and 1000 rpms, no codes, seriously stumped. I drive truck for a living and don't have time to be fiddling with it all the time, any suggestions would be helpful except the obvious ones that I have just mentioned, Thanks
 
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Old 05-19-2013, 01:03 PM
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The oil pressure sending unit is part of the injector relay circuit, if I recall.

Looks like you have a fuel pump relay issue.

You should have 12 volts from the ECM on the dk grn-wht wire with the key on and possibly cranking, should have a good ground on the blk-wht wire, 12 volts at the orange wire.

Basically if you jumper the orange wire to the gray wire the fuel pump should run all the time. Sounds like your truck is running off of the oil pressure switch after the engine builds oil pressure, the switch bypasses the relay giving you fuel pressure.

So my guess is you have a problem on the control side of your relay. Check powers and grounds with what I said above and see what's going on.

Did you replace your fuel pump relay already? It's on the firewall behind the cover above your coolant overflow tank.
 

Last edited by NullHead; 05-19-2013 at 01:08 PM.
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Old 05-19-2013, 01:07 PM
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Basically your fuel pump lives off of the gray wire, and the orange wire is the power one. The fuel pump is grounded by the relay through the ECM is what it looks like:


Orange should be hot all the time, the gray wire has the fuel pump on it. The wires I talked about in the other post are the "control" side of the relay. Really, you should be able to do most of your diagnosing from the base of the relay with a test light/volt meter. Just be careful probing around and don't short anything.
 
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Old 05-19-2013, 08:24 PM
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I checked that everything is good for whatever reason it is starting everytime now worked on it all day today, thanks for the info NULL. I ran new ground for temp sens and I replaced the sensor with new one last night now the problem is idle is between 1400 and 1100 rpm found vac leak at tb base...changed gasket, and egr gasket today...every once in awhile it will drop then pick right back up to 1100 rpm, I unhooked tps and idle dropped rite down to about 900-1000 rpms hooked it back up and walla right back up to 1100-1400 rpms, sprayed brake clean all over and its not stumbling or nothing.. so I ruled out vac leak now
 
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Old 05-19-2013, 09:04 PM
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When it's idling high like that, take the end of a screwdriver and tap on your IAC screwed into the side of the TBI. If your idle drops, pull out the IAC and clean all the carbon out of it. I would recommend replacing it, and then cleaning out all the carbon.

I would also recommend cleaning your throttle blades with carburetor cleaner and a toothbrush. Don't use brake cleaner to check for vacuum leaks or to clean the throttle blades, cause when it's burned it makes a poison gas that will come out of your tail pipe. Use brake cleaner for brakes.

The IAC is the large cylinder looking thing on the top left of this picture:
http://www.diyautotune.com/jwplayer_..._7952_1024.jpg
 
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Old 05-20-2013, 05:18 PM
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I swaped IAC out with a working one that I know works cleaned it all out, when I unplug the TPS the idle drops down to 900 or so rpms, that's why I was wondering if it was the TPS but I guess I will be paying some autopart store employees wages for the week with these parts haven't even priced em yet gunna do that in a few
 
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Old 05-20-2013, 08:17 PM
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I taped on the IAC I swapped out and no change, think Im going to go over the fuel pump relay again and check the voltages, you say the relay grounds through the ECM? If that is the case, and its not grounding and running off the ops, the ECM could possibly have takin a dump or bad ground some where? I noticed on my 88 2wd previous owner had ran a new wire from fuse for pump all the way back to the connector at the tank. I swapped the relay out of the truck that ran to the 93 with same results (the 88 is a chevy 1500 2wd, parts donor/former daily driver with a 5.0)
 
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Old 05-20-2013, 11:55 PM
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You can test your TPS sensor if you want:

It should have 5 volts on the gray wire, key on. It grounds to the ECM with the black wire, and has a splice that connects the grounds of the ECT sensor to the TPS sensor.
 
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Old 06-23-2013, 08:57 AM
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It was the TPS sensor changed it and starts every time sorry took so long to reply thanks for the help
 
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Old 06-23-2013, 07:52 PM
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Thanks for coming back and telling what happened!

I'm glad you got it figured out. At least it's an easy simple fix
 

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