Have similar issues, enough where the truck's not dependable. On my '95 there's a ground strap from the frame to the heater box to the engine. It had been rubbing against the exhaust manifold & was frayed. Truck will start sometimes but not always, why I parked it. When it decided to start I moved that cable with my fingers & it ran better. Haven't cleaned the frame connection yet, gonna tho.
Your oil pressure on these tbi trucks is a dual function oil pressure switch with the engine not running the oil sending unit is in bypass to supply fuel to the injectors for start up once running it comes out of bypass and fuel pump relay takes over. Thats why the truck wont start until oil pressure guage shows pressure your not making contact because your oil sending unit is bad. Its also a safte gaurd if you lose oil pressure it should shut the engine down
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
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
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 ,
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
Your oil pressure sending unit behind the intake manifold may be your problem, they can cause low voltage or no voltage. Also, the distributor pickup coil could also be your problem, I'd also test the ignition control module, ICM, and make sure it's working properly, they're notorious for causing intermittent problems both electrical and fuel pump operation
You need a new oil pressure sending unit. It's not closing the circuit to the fuel pump relay. Once it realised it has oil pressure it will close the circuit to the fuel pump and run
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!
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.
Having issues with crank/no start. Have replaced plugs, wires, distributor cap, rotor, coil, and ICM. Have spark at distributor/coil/and plugs. No fuel spray thru injectors when cranking. Will start if primed and continue running rough but may quit when idling, has to be primed to re-start. I have been told that the new ICM may be bad. What are your thoughts? '92 Chev K2500 5.7 L
I'd look for either: (1) a clogged fuel filter (2) a weak fuel pump (3) a bad fuel pressure regulator (this is built into the throttle body) or (4) clogged injectors. Since it continues running, it sounds like the computer may be working, so I wouldn't suspect a bad computer until I ruled out the other 4 things. To know for sure that the injectors are getting a signal to open, get a noid light and plug into the injector plug.
@@farmboy30117 Thanks for your reply! Yes, I forgot to mention that I had changed the fuel filter to start with, so we can rule that one out. Yesterday I decided to bite the bullet and went to the local NAPA store and got another ICM (the previous one came from an outlet online, made in China) at triple the price. My reasoning was that since the ICM supposedly controls both fuel and spark during cranking (GM by-pass system), and I wasn't getting fuel spray at cranking, I would go with the idea that the new online replacement was faulty. After installing the NAPA module, the engine fired up in a normal amount of cranking time and ran extremely rough for about 10 seconds, then smoothed right out on its own. I was really happy for about 10 minutes... went sailing down the road about 5 miles with engine running better than it has for months! Then the engine started to miss, dropping a cylinder here and there. Turned around and headed back home, sputtering and choking under heavy throttle until it got back up to speed. Have driven it a couple of more times with the same results: runs great for a little while then chokes and pukes. Will have mechanic check the fuel pump pressure tomorrow. More fun than I can stand. BTW, the ol' Chevy has 440K miles on him, original engine & 5-sp tranny. I'm cutting him plenty of slack!
Have a 92 chevy Silverado 1500 4x4 I had a no spark issue i replaced the icm and i have spark now but now its acting like it's out of time it will crank it will start but then it will die like it can't find its self
Distributor cap is new plugs are new button is new icm is new and wires are new it's in the correct firing order and all fuses are good and its gets fuel but it still acting like it's out off time any ideas
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.
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?
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.
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
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?
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.
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?
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.
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.
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.
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!
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.
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.
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.
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.
That's what I thought as well, but the oil pressure comes up fine and it starts and runs after the oil pressure comes up. Come to find out the new fuel pump relay was bad..see part 3.
You are a wizard sir, not every one can read and understand those wiring schematics, hope you've solved your issue
Check motor grounds and one behind the throttlebody
Have similar issues, enough where the truck's not dependable. On my '95 there's a ground strap from the frame to the heater box to the engine. It had been rubbing against the exhaust manifold & was frayed. Truck will start sometimes but not always, why I parked it. When it decided to start I moved that cable with my fingers & it ran better. Haven't cleaned the frame connection yet, gonna tho.
Your oil pressure on these tbi trucks is a dual function oil pressure switch with the engine not running the oil sending unit is in bypass to supply fuel to the injectors for start up once running it comes out of bypass and fuel pump relay takes over. Thats why the truck wont start until oil pressure guage shows pressure your not making contact because your oil sending unit is bad. Its also a safte gaurd if you lose oil pressure it should shut the engine down
What that Las fuel on the left for
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.
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
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
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 ,
I need help with my 1992 Chevy blazer. I'm only getting 8.7 volts at the fuel pump connector. Where is my 12 volts going?.
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
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.
Your oil pressure sending unit behind the intake manifold may be your problem, they can cause low voltage or no voltage. Also, the distributor pickup coil could also be your problem, I'd also test the ignition control module, ICM, and make sure it's working properly, they're notorious for causing intermittent problems both electrical and fuel pump operation
You need a new oil pressure sending unit. It's not closing the circuit to the fuel pump relay. Once it realised it has oil pressure it will close the circuit to the fuel pump and run
I had the no start on a 76 chevette. Bad oil pressure sensor. Easy fix? Not! The switch was located under the A/C compressor.
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!
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.
Having issues with crank/no start. Have replaced plugs, wires, distributor cap, rotor, coil, and ICM. Have spark at distributor/coil/and plugs. No fuel spray thru injectors when cranking. Will start if primed and continue running rough but may quit when idling, has to be primed to re-start. I have been told that the new ICM may be bad. What are your thoughts? '92 Chev K2500 5.7 L
I'd look for either: (1) a clogged fuel filter (2) a weak fuel pump (3) a bad fuel pressure regulator (this is built into the throttle body) or (4) clogged injectors. Since it continues running, it sounds like the computer may be working, so I wouldn't suspect a bad computer until I ruled out the other 4 things. To know for sure that the injectors are getting a signal to open, get a noid light and plug into the injector plug.
@@farmboy30117 Thanks for your reply! Yes, I forgot to mention that I had changed the fuel filter to start with, so we can rule that one out. Yesterday I decided to bite the bullet and went to the local NAPA store and got another ICM (the previous one came from an outlet online, made in China) at triple the price. My reasoning was that since the ICM supposedly controls both fuel and spark during cranking (GM by-pass system), and I wasn't getting fuel spray at cranking, I would go with the idea that the new online replacement was faulty. After installing the NAPA module, the engine fired up in a normal amount of cranking time and ran extremely rough for about 10 seconds, then smoothed right out on its own. I was really happy for about 10 minutes... went sailing down the road about 5 miles with engine running better than it has for months! Then the engine started to miss, dropping a cylinder here and there. Turned around and headed back home, sputtering and choking under heavy throttle until it got back up to speed. Have driven it a couple of more times with the same results: runs great for a little while then chokes and pukes. Will have mechanic check the fuel pump pressure tomorrow. More fun than I can stand. BTW, the ol' Chevy has 440K miles on him, original engine & 5-sp tranny. I'm cutting him plenty of slack!
it's straight piped
Thanks Pete. I'll have to do some more testing.
Have a 92 chevy Silverado 1500 4x4 I had a no spark issue i replaced the icm and i have spark now but now its acting like it's out of time it will crank it will start but then it will die like it can't find its self
Any ideas
Distributor cap is new plugs are new button is new icm is new and wires are new it's in the correct firing order and all fuses are good and its gets fuel but it still acting like it's out off time any ideas
Chevys are damn good trucks my grandmother's 99 Yukon still runs good it's loud though
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.
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?
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..
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.
will brown Betty smoke the tires faster then the 93
I watched the brakes trying to lock up.on the 6 point 2 on one of youre old videos
@@dustinkey8116 No, the dually has a lot more traction than the '93 so it doesn't spin as easy.
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
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?
Gracias is TBI gas in ecxeso
It your oil pressure switch it right underneath your distributor cap
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.
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.
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?
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.
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
That should be after the O2 sensor, so that should be ok
farmboy30117 so you think the timming could still be out some?
Oil pressure sensor?
Thanks Ryan. I'm not giving up yet.
I'm definitely not having that issue. But I will double check all the grounds.
change the pcm
@@dustinkey8116 It was the fuel pump relay. The new one I bought was defective.
does the ac still in the 93 I noticed.it kick the compressor on foure a minute then kicked back off
@@farmboy30117 wheres the ole dually at
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.
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.
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!
I have not checked for codes or anything either,i guess i should make a jumper and check.
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.
Got ya!!
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 Got any spark?
+farmboy30117 yes
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.
+farmboy30117 thanks
Temperature sience
Did you check the ignition module under the distributor cap?
Im having the same issue now. Did you ever find a solution?
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?
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.
Thanks, someone told me ignition module, could cause it
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.
Yeah when it warms up that's it.it will crank cold after oil pressure builds up
Oil pressure sensor or oil pump. GM cars if oil pressure is less than 4psi it will not start!!!
That's what I thought as well, but the oil pressure comes up fine and it starts and runs after the oil pressure comes up. Come to find out the new fuel pump relay was bad..see part 3.