Running horribly, missing, not getting enough fuel?

Tiny
DB123
  • MEMBER
  • 2002 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 175,000 MILES
Trucks was running horribly, missing, not getting enough fuel, vacuum leaks, well fixed the vacuum leaks, changes out the MAP sensor, put new injectors, coil packs, spark plugs and wires, changed fuel filter also ran scan again cleared codes, trucks harder to start now than before I changed everything, turns over with key if foot is holding pedal down, shakes real bad then after 15-20 seconds RPMs go up and feels smooth as can be, let foot off the pedal stays idling but just barely, starting fluid changes nothing on idle spraying around to see if RPMs changes or not, and another scan afterwards no dtcs, foot on the gas blinking service engine light, foot off barely idle no engine light.
Monday, May 19th, 2025 AT 1:14 PM

9 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
If the check engine light blinks it is usually the throttle body is bad. I would try running it a little longer to see what codes are stored, also, when you say MAP sensor do you mean MAF sensor? This engine has both, I would replace the MAF sensor as well, also what brand parts did you use for the spark plugs etc., if they are the wrong spark plugs it will cause this issue, please go over this guide as well:

https://www.2carpros.com/articles/engine-cranks-excessively-before-starting

Also, if you have defective fuel injector it will cause this issue as well due to leakage. I would also remove the vacuum line from the fuel pressure regulator to see if fuel is present and if so, the regulator is bad (located on the fuel rail). Please go over this guide and get back to us.

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Monday, May 19th, 2025 AT 6:37 PM
Tiny
DB123
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MAF is okay, changed the manifold absolute pressure sensor MAP, AC Delco spark plugs, injectors and coil packs, K and N fuel filter, everything that's been done hasn't changed repetition of the idle, all live data looks good and within range, only getting wheel sensor type codes. Completely tore everything down on top half of motor down to intake and tested spark plugs, coil packs and injectors, no vacuum leaks, put it back together, same result, it's missing an 02 sensor but throwing no code for it, could cats be plugged maybe, or junk inside block or intake somewhere, it's an old farm truck not maintained very well by customer.
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Tuesday, May 20th, 2025 AT 4:43 AM
Tiny
KEN L
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So the EGR valve can leak slightly and cause the same effect as a vacuum leak. Also, here is a video we just did which is a better way to find vacuum leaks:

https://www.youtube.com/watch?v=LRKWV4Are5c&t

I would try swapping out the EGR to see what happens or you can try testing it using this video:

https://www.youtube.com/watch?v=DqUCbbKdWf4

Check out the images (below). Let us know what you find.
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Tuesday, May 20th, 2025 AT 8:56 AM
Tiny
DB123
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I did the vacuum leak test already with some starting fluid couldn't find a change in rpms anywhere, going to test the EGR now and I'll get back to you, maybe with a video of truck idling and foot on pedal.
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Tuesday, May 20th, 2025 AT 11:51 AM
Tiny
KEN L
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Yes that would help. Let me know how the EGR test goes.
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Thursday, May 22nd, 2025 AT 9:36 AM
Tiny
DB123
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Still having problems with it sounds way better than it did, may just be the engine is worn out it's got 3 or 400,000 miles on it ol farm truck.
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Thursday, May 22nd, 2025 AT 4:42 PM
Tiny
KEN L
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O ya, low compression will definitely make it hard to start, to confirm you can do a compression test on a few cylinders to get an idea if this can be the problem, this guide will help:

https://www.youtube.com/watch?v=KOxIm1F8AW0

Please go over this guide and get back to us.

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Friday, May 23rd, 2025 AT 11:08 AM
Tiny
DB123
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  • 28 POSTS
I got it running and sounding better still wasn't 100% but he picked it up yesterday no complaints so far haven't heard anything from him, ran some seafoam in the tank and adjusted the throttle cable, seemed to be doing much better, it's just worn out everything on the truck rattles, thanks for the help and quick responses, I'll be back eventually, but thank you guys.
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Friday, May 23rd, 2025 AT 12:16 PM
Tiny
KEN L
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Np :) have a good weekend!
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Friday, May 23rd, 2025 AT 1:04 PM

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