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1993 Silverado Hard Starting Issues Part 2

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Having issues with my fuel pump circuit. Need some help figuring this out.
Category: Транспорт
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Chris Hood (1 year ago)
Hello...My Dad has a 94 GMC Sierra SLE 1500 WITH THE 5.7. It will start when the truck has been sitting up, then after I run it until it warms up and shut it off it will not start back up until it sits a few hours.Any ideas? Thanks in advance! I can hear the fuel pump come on.
Chris Hood (1 year ago)
Got ya!!
farmboy30117 (1 year ago)
Not sure but I think it should be 30-40 psi.  Yeah, too bad GM didn't put a service port in.  The fuel lines just screw into the TBI if I'm not mistaken.  You'd have a rig up an inline Tee.  If you're check engine light is not on, you don't have any codes.
Chris Hood (1 year ago)
I have not checked for codes or anything either,i guess i should make a jumper and check.
Chris Hood (1 year ago)
What is the pressure this truck should have from fuel pump,i know it's working i hear it kick on soon as key is turned on. There is no service port to screw in a pressure gauge on the 94 if i'm not mistaken by the fuel rail or anywhere,so do i have to unloosen fuel filter and tie in there to check fuel pressure? Thanks!
farmboy30117 (1 year ago)
Hard to say. Generally the ignition module will get hot and do this but normally it'll shut off while you're driving. I assume it's not setting a trouble code. This could potentially rule out an overheated sensor (maybe). When it does it, check for spark. If you're getting spark, I'd suspect a weak fuel pump.
antonio osorio (1 year ago)
Hello I have a suburban 1994 It is obese that when I turn off the engine the petrol pump continues to run for a few seconds And in the BIT gasoline is observed in ecxeso Can this fault be attributed to the pump relay? greetings from Mexico!!! And thanks for the comments
J Reed (5 months ago)
It your oil pressure switch it right underneath your distributor cap
antonio osorio (1 year ago)
Gracias is TBI gas in ecxeso
farmboy30117 (1 year ago)
Hi Antonio!  When you turn off the engine, is the key in the ON position or all the way to OFF? The fuel pump relay is only used by the computer to initially start the fuel pump when the key is turned to the ON position.  Once oil pressure has built up, a separate circuit is used to power the fuel pump from the oil pressure sending unit.  Not sure why the fuel pump would continue to run for a few seconds with the key off because that should disable power to the circuit.  If the key is left in the ON position, the computer may be sending power to the relay for a few seconds until the pressure builds back up in the fuel line.  I don't think the relay itself is causing the issue.  Not sure what BIT means or ecxeso?
Cody Silvers (1 year ago)
i have 95 gmc Sierra k1500 been sitting for few years we got it put fuel pump and filter on it got it running but has hesitation any idea does have exauhst leak could my back pressure be a problem?
Cody Silvers (1 year ago)
farmboy30117 so you think the timming could still be out some?
farmboy30117 (1 year ago)
That should be after the O2 sensor, so that should be ok
Cody Silvers (1 year ago)
farmboy30117 its at the y where the manifolds come down and connects to single pipe we also had to adjust the timming just a hair on it
farmboy30117 (1 year ago)
If the exhaust leak is ahead of the Oxygen sensor, then it could be causing the sensor to read a lean condition and apply too much fuel (too rich).   A leak past the O2 sensor should not effect fuel.  Also, make sure the injector spray pattern is uniform.  A dirty injector could cause it to have less fuel than what's being called for and lead to a lean condition as well as vacuum leaks.
zacatecano1986 (2 years ago)
guys this circuit is pretty easy the icm send a 3x signal to the pcm when cranking and when  pcm senses the signal it automatically sends battery voltage to the fuel pump relay control circuit wire color dark green with white . let me know if if you need more help ,
Dalton Jones (2 years ago)
Same problem with both my 93 chevy truck and my 89 Camaro. You can switch power to your fuel pump and it will run. The 89 Camaro has low power coming into the fuel pump relay switch code 54. once power is jumped on the fuel pump relay and the Camaro will start and run beautifully. But when the engne gets cold, it's hard to start again.
Jacob Dawson (2 years ago)
I have an 89 k1500 I changed the fuel pump and the fuel pump relay and it will crank but not start....any ideas?
Jacob Dawson (2 years ago)
+farmboy30117 thanks
farmboy30117 (2 years ago)
Are you getting fuel coming out of the injectors when cranking? I'm going to assume you don't. I'd remove the fuel line at the throttle body and stick it in a container. Turn the key on to see if there is any fuel coming out.  It should run a few seconds and quit.  If you have fuel, crank the engine over and see if fuel continues to run out.  If not, you have a bad oil pressure sending unit.  If it does, you possibly have some issues with the injector or PCM.  Hope this helps.
Jacob Dawson (2 years ago)
+farmboy30117 yes
farmboy30117 (2 years ago)
+Jacob Dawson Got any spark?
Brian West (3 years ago)
I have same problem on 91 Z71, it will turn over and crank after oil pressure builds. But after it warms up it won't crank back. Any ideas?
Brian West (3 years ago)
Yeah when it warms up that's it.it will crank cold after oil pressure builds up
farmboy30117 (3 years ago)
Yep, if you have no spark, that's probably the culprit.  Usually they quit working when it gets hot though.  My module went out going down the road one day and left me stranded.
Brian West (3 years ago)
Thanks, someone told me ignition module, could cause it
farmboy30117 (3 years ago)
Sounds like your fuel pump relay is bad (mine was).  I'm guessing that it may not build up enough oil pressure when it is warm to run the fuel pump.  If that doesn't fix it, check for fuel and spark when trying to crank it when warm.  You should be able to see the fuel being injected in the throttle body.    
TRILLA BOSS (3 years ago)
Im having the same issue now. Did you ever find a solution?
Jacob Miller (4 years ago)
Oil pressure sensor?
farmboy30117 (4 years ago)
I checked the relay and the new one wasn't working but that still isn't the problem. Check out part 3 which should be up soon.
rob roberts (4 years ago)
I wonder if one of the wires to the relay is freyed or damaged sometimes it gets moved somehow and causes less voltage to the relay at times.
mossman381 (4 years ago)
I would still take the neg cable off the frame and make sure it is touching bare metal. Ground problems can make stuff do weird things. The system low voltage code is why I would do it. Should be easy to do and free to try. If the computer is not getting 12v it will not work right. I think the computer is behind the glovebox. I wonder if there is a ground near it?
Jerzy Wilk (1 month ago)
mossman381
farmboy30117 (4 years ago)
I checked the ground in the relay by putting my test meter probe on battery positive and it read full battery voltage. I'll need to check the one at the pump.
farmboy30117 (4 years ago)
I'm definitely not having that issue. But I will double check all the grounds.
farmboy30117 (4 years ago)
I had the entire distributor rebuilt last year. If I put the fuel pump fuse directly to battery positive, it'll fire right up. I'll get another video and do some more troubleshooting soon.
farmboy30117 (4 years ago)
Thanks Ryan. I'm not giving up yet.
farmboy30117 (4 years ago)
Thanks Pete. I'll have to do some more testing.
farmboy30117 (4 years ago)
I replaced the relay (part 1) with no result. But it is definitely firing up when oil pressure builds so it's getting power from that circuit.
arnie2much (4 years ago)
i second the ignition control module, had an issue with my 95 305 that stopped starting turned out there was corrosion on the screws grounding the ignition control module in the distributor
slowride55 (4 years ago)
Check grounds. Flip the intake lid on that! It will let tons more air in. My friends '96 had a starting issue too. It wouldn't start at all when it was hot and it got horrible mpgs. Turned out the coolant temp sensor was saying the coolant was -12*F lol so it would dump tons of fuel in all the time. Good luck!
ryan richardson (4 years ago)
Don't give up! That is a damn good truck that you have..i have two z71s ..one is a 94 and the other one is a 2000 model..
ryan richardson (4 years ago)
Did you check the ignition module under the distributor cap?
Pete The Farmer (4 years ago)
Hi Jay, I had a dodge pick-up one time and something was wrong with it. I thought it was the battery or the alternator or the starter, but what it was it had a short in the wiring. When I fixed that problem it did just fine. Your shop is really looking nice. Pete
funny2man2004 (4 years ago)
could be a faulty relay not priming the pump. power goes through both the relay and oil pressure sensor. if the relay is bad you have to build about 4 psi of oil pressure and the oil pressure sensor will send power to the pump itself
mossman381 (4 years ago)
I would check the main ground from the battery to the frame. I would take it off and clean the rust off it. There is a ground for the fuel pump down by the fuel tank filler neck. I would clean the rust off that too. We changed a fuel pump on a 88 chevy once but I think it was the ground that was the real problem. I hooked up the old pump to a battery and it still worked.

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