My engine will not start up and run

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
It is wierd how they route wires sometimes!
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Tuesday, May 4th, 2021 AT 11:51 AM (Merged)
Tiny
POSSUMFL
  • MEMBER
  • 6 POSTS
We have driven the vehicle about 5 times, less than 100 miles, started up and ran fine all week until this afternoon when it wouldn't start again. I examined the wiring harness and everything is nice and tight, no chaffing, everything looks and fits like it should, but I'm having the same problem with the fuel pump not kicking on. What else do you recommend I try? Thanks, Robert.
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Tuesday, May 4th, 2021 AT 11:51 AM (Merged)
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
I dont know who linzsmith is. Not a big help. Did you remove the plastic conduit under the seat and inspect the wiring inside it? That would be my next step, then test for power at the pump connector. Something in the wiring or the pump needs a look.
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Tuesday, May 4th, 2021 AT 11:51 AM (Merged)
Tiny
RAUL OROZCO
  • MEMBER
  • 2 POSTS
  • 2003 CHEVROLET TAHOE
  • 5.3L
  • V8
  • TURBO
  • 2WD
  • AUTOMATIC
  • 180,000 MILES
While driving home from work going sixty on freeway my gas pedal suddenly stopped working. I pressed down on it twice and did not feel or hear motor rev up or the car speed up. However, on the third time I stepped on the gas pedal it felt like engine started back up and the car sped up. Then it happened again same scenario, I exited freeway made right turn and my SUV turns off. So I turned off key then on and started back up and then it turned off again. So I pulled over and tried starting it again and it would start up again but for only three to five seconds then turned off.
I changed throttle body and still the engine turns but no start. There is no check engine light turning on. Please help. I hope I explained myself.
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Tuesday, May 4th, 2021 AT 11:51 AM (Merged)
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I am Danny.

Well since there is no check engine light on I would suggest first to check your Fuel Pressure. There is a Schrader valve located on the fuel rail to check. Most auto part stores have a tool loaner program (AutoZone, Pep Boys, O'Reillys) that can rent you one. Your fuel pump is an in-tank unit and they wear out after time.The fuel pressure should be 48-52 PSI if your engine is 5.3L VIN code Z. All others should be 55-62 PSI. I have included a link as a tutorial to give you an idea as to what is involved. Hope this helps and feel free to ask any questions as needed.
Danny-

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Tuesday, May 4th, 2021 AT 11:51 AM (Merged)
Tiny
RAUL OROZCO
  • MEMBER
  • 2 POSTS
Hi Danny, thanks for the fast reply.
About checking the fuel pressure I have not checked it with actual gauge, but a friend that used to be a mechanic took off the cap and looked at it and said that it is good. That it is spitting out the right amount off pressure but I will double check it with a gauge. And what if pressure Is good since I replaced the throttle body (but I got it from junk yard from 2003 Silverado) and someone told me that it needed to be reprogrammed or program it to my cars computer. What are your thoughts on that? Thank you.
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Tuesday, May 4th, 2021 AT 11:51 AM (Merged)
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.
Yes, You definitely need to test the fuel pump with a gauge (directions in last my last post). In my last post I also gave you the fuel pressure specifications. When you installed the throttle body did it give you a code? Check engine light? Happy 4th! Danny-
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Tuesday, May 4th, 2021 AT 11:51 AM (Merged)
Tiny
TYLERESSARY1990
  • MEMBER
  • 4 POSTS
  • 2002 CHEVROLET TAHOE
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 173,000 MILES
We have replaced the starter, and also the ignition switch, and can’t get SUV to start. It will start every once in awhile, but then you turn it off, and it just cranks and won’t fire up. Please help.
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Tuesday, May 4th, 2021 AT 11:52 AM (Merged)
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This sounds like it could be a problem with your Crankshaft Position Sensor (CKP). The CKP sensor tells the Power-train Control Module(PCM) AKA, "computer" where the engine is in its cycle. When the PCM loses track of where the engine is in its four stroke cycle, it will not know when to fire the spark plugs or when to send the duty cycle to the fuel injectors.
I have included a few links down below for you to go to:

https://www.2carpros.com/articles/how-a-crank-shaft-angle-sensor-works
https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor
https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

Please go through these links and get back to us with what you find out.

Thanks,
Alex
2CarPros
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Tuesday, May 4th, 2021 AT 11:52 AM (Merged)
Tiny
TYLERESSARY1990
  • MEMBER
  • 4 POSTS
I also wanted to add now it’s not even cranking. Could it still be the crank shaft position sensor out even though it’s not cranking at all now? Like I said, we have tried the ignition switch and the starter. I initially thought it was the ignition cylinder, but we haven’t replaced that yet. Should we start with the crank shaft positioning sensor or the ignition cylinder? I forgot to add the security light will blink sometimes too. Just started doing this.
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Tuesday, May 4th, 2021 AT 11:52 AM (Merged)
Tiny
TYLERESSARY1990
  • MEMBER
  • 4 POSTS
I may have forgot to tell you something very important. Before all this happened, we replaced the oil pan gasket, and rear main seal. She had one of those DUI blower things and it started acting crazy and would start to reset itself and wouldn't let her start her truck for thirty minutes sometimes. So then she took it to the place thinking it was the blower, and they took the blower off, and still having problems. There’s no wires or anything I could have accidentally hit when fixing the rear main or oil pan gasket right? I know kinda stupid question because there shouldn’t be anything electrical, but everything started happening after we did the work on the rear main and oil pan gasket. I may should have told you that from the get go. I do apologize. I do want to add, my grandpa fixed a toggle switch that you can crank it right up with, but you take the toggle switch out, it does nothing. No crank, the lights on the dashboard do light up, though. I hope this is more helpful for you to diagnose.
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Tuesday, May 4th, 2021 AT 11:52 AM (Merged)
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

Okay, are you guys trying to replace the toggle switch? I am not sure what is going on? Please get back to us with what you guys are trying to do please.

Thanks,
Alex
2CarPros
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Tuesday, May 4th, 2021 AT 11:52 AM (Merged)
Tiny
TYLERESSARY1990
  • MEMBER
  • 4 POSTS
Sorry no, I shouldn’t have mentioned the toggle switch. Okay, here’s what we did first: First off, my girlfriend has a Interlock system in her car. We did the rear main seal and the oil pan gasket, put that back together, and then the interlock started acting weird after that and would make you wait thirty minutes after blowing to start, and then wouldn’t start at all after, would just crank over. We thought maybe it was the interlock messing up, but we took it to the place, and they took the interlock out, and the car is still just cranking. Almost like it’s not getting fire to the starter, but we have replaced the starter and the ignition switch. Could it be the cylinder itself that needs to replaced, or could it be the crank shaft positioning sensor like you mentioned? Sorry for the misunderstanding.
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Tuesday, May 4th, 2021 AT 11:52 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,329 POSTS
When you turn the key to the on position without cranking the engine over can you hear the fuel pump run in the tank for five seconds? It sounds like they may have bumped the connector for the crankshaft angle sensor as well. here is a guide that can help. See if the engine will run on starting fluid.

https://www.2carpros.com/articles/car-cranks-but-wont-start

Please run down this guide and report back.

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Tuesday, May 4th, 2021 AT 11:52 AM (Merged)
Tiny
AUDLEY
  • MEMBER
  • 0 POST
  • 2002 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 240,000 MILES
2002 tahoe 5.3, 48 psi fuel pump pressure, spark at plug wire, installed crank positioning sensor won't start, cranks a little faster and sounds as though it wants to start, but won't. Battery is up and there is plenty of fuel. I don't want to start putting any more sensors on at random. Audley
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Tuesday, May 4th, 2021 AT 11:54 AM (Merged)
Tiny
ERNEST CLARK
  • MECHANIC
  • 1,730 POSTS
You're computer needs to see both a crank speed reading and cam position reading for it to tell the coils to fire a spark to the plug.

Since you've checked spark and fuel pressure, use an automotive stethoscope to listen for your injectors firing. You'll hear a distinct clicking sound. If your injectors are firing, the valve timing may be off (bad timing chain). You can verify this by doing a compression test.

If your timing chain has slipped, just replacing the timing chain wouldn't be economically sound, as that would be like putting a band aid on a gunshot wound. The rest of the motor will be just as worn as the timing chain. However, I do not recommend rebuilding this motor unless you want to keep this truck for 10 more years. There are too many low-mile used engines for dirt cheap.

It isn't your ignition switch. If that were the case, you wouldn't be getting spark at the plugs. Your ignition timing is controlled by the computer. If that's out of wack, your computer would be bad. Sometimes an intermittent fault with your sensors will fail to set a code. Depending on which sensor is faulty, the computer will have to determine it has been faulty for a certain amount of drive cycles or time. If the sensor acts good, the computer will shut off the light by itself.

If a scan doesn't produce anything, you'll need to continue your diagnoses on the systems components the computer can't always read. These would be the mechanical components of the engine.

If the crank sensor was bad and to replaced it the sensor will sometimes need to be programmed to the car a shop can do this for about $130.00.
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Tuesday, May 4th, 2021 AT 11:54 AM (Merged)
Tiny
ERNEST CLARK
  • MECHANIC
  • 1,730 POSTS
Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help

Cheers
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Tuesday, May 4th, 2021 AT 11:54 AM (Merged)
Tiny
MJESSICA
  • MEMBER
  • 1 POST
  • 2002 CHEVROLET TAHOE
  • V8
  • AUTOMATIC
  • 200,000 MILES
I pushed truck to the pump and put gas in it. After I got gas tried to start the car but it wouldn't start, and it said I had low fuel even though I just put gas in it. I'm not sure if it's the fuel filter or the fuel pump. I also wanted to know where the reset switch is located if this module has one. I've recently had the alternator replaced as well as an oil change/tire rotation. And just put in transmission fluid.
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Tuesday, May 4th, 2021 AT 11:56 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,650 POSTS
Hi,

The fuel pump relay is under the hood in the power distribution box. There is no reset on it. I attached a pic below (picture 1) and circled the relay. If there is a relay with the same part number, switch them. If not, here is a link that explains how to test it:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Here is a link that explains the most common causes of a crank no start. Take a look through it to see if it helps.

https://www.2carpros.com/articles/car-cranks-but-wont-start

Next, check fuse 30 also (under hood). It powers the fuel pump relay. (see picture 2 and 3)

Now, the first thing I would be checking is if there is fuel pressure at the engine. I can provide the manufacturer's specs, but I need to know which engine is in your vehicle. There are 4 different V8 engines.

Here is a link that explains how to test fuel pressure in general:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Next, if fuel pressure is good, then we need to determine if the ignition system is working. Here is a link that explains how to test for ignition spark:

https://www.2carpros.com/articles/how-to-change-spark-plugs

________________________________________

Here are a few links you may find helpful when testing.

https://www.2carpros.com/articles/how-a-car-fuse-works

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

________________________________________

Let me know what you find. I will watch for your reply.

Take care,
Joe
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Tuesday, May 4th, 2021 AT 11:56 AM (Merged)

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