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Old August 12th, 2011, 09:04 AM   #1
SHARPMACHINE
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5.3 diagnostics

I have a 5.3 in my jeep. It ran great when installed and I probably have ~ 300 miles on it since. It has no cats, and the rear O2s are removed with tuning.

It has developed some issues:

Starts a little hard.
No power and lots of "stink" from the exhaust.
Runs better with the maf unplugged.

I will start this weekend with:

Checking fuel pres..
Try cleaning maf and tb.
Check fp reg. to make sure there is no fuel in the hose.
Check pcv valve.

Any other ideas much appreciated.
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Old August 12th, 2011, 09:22 AM   #2
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I would also check for intake manifold/vacuum leak, lazy O2 sensor. Best bet would be to get a scanner that will capture live data stream like a TechII or Snapon Solus then you will be able to see what is actually going on when it is running.
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Old August 12th, 2011, 10:53 AM   #3
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pull codes and go from there.
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Old August 12th, 2011, 11:01 AM   #4
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pull the codes and check fuel pressure
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Old August 12th, 2011, 11:10 AM   #5
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Sorry, I should have said = no codes.

thanks
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Old August 12th, 2011, 11:16 AM   #6
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Do you have a scanner that shows live data?
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Old August 12th, 2011, 11:34 AM   #7
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Quote:
Originally Posted by buttercr125 View Post
Do you have a scanner that shows live data?
Yes. I looked and confirmed that tps and iat look correct. What else should I check?

thanks everyone
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Old August 12th, 2011, 03:29 PM   #8
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Quote:
Originally Posted by SHARPMACHINE View Post
Yes. I looked and confirmed that tps and iat look correct. What else should I check?

thanks everyone
Check O2 cross counts and A/F ratio, it should be 14.7 to 1 any less is going to be a rich mixture and any more is going to be a lean mixture.
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Old August 12th, 2011, 09:43 PM   #9
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I only have 21 psi of fuel. I pulled the regulator vacuum hose and it does not go up (Mitchell's said it should). No fuel in the vacume line either. I tried another or spare regulator and no difference? Lookinglike a bad pump?
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Old August 12th, 2011, 09:50 PM   #10
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surprising it even fires up with that little fuel psi. the injectors should require more than that to open/close. double check with a different gauge before buying a pump, but that sounds like your issue.
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Old August 12th, 2011, 09:50 PM   #11
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Doing this on a phone is gay. Anyways. I have only 21 psi of fuel. I looked at Mitchell and it said it should go up if you pull the vacuum line while it is running. It does not go up and there is no fuel in the line. I tried the same test with a spare regulator and it was the same. Looks like a bad pump? I just need to confirm it.
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Old August 12th, 2011, 09:55 PM   #12
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surprising it even fires up with that little fuel psi. the injectors should require more than that to open/close. double check with a different gauge before buying a pump, but that sounds like your issue.
Thanks and I didn't think it took my first responce. I am going to test the pump on another car to confirm. Thanks.
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Old August 12th, 2011, 10:01 PM   #13
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should spec between 55-61 psi, if i'm remembering the right pump
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Old August 15th, 2011, 09:11 AM   #14
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Did not end up being anything I would have guessed it would be. Everything pointed at the pump, so we dropped the tank.

As soon as we started pulling the sending unit, we found the problem. I had used good-year fuel injection hose with injection clamps to go from the pump to the sending unit. The hose was obviously not designed for the outside to be in contact with fuel. It was swollen and mushy, allowing it to slide partially off the pump any bleed off most of the fuel pressure into the tank. We put some new line in and it works great.

PS While finding a new pump I learned that you can use a pump from a 96-99 2-door yukon or tahoe. The reason this is good to know is that it can be bought as just a pump, and is much cheaper.

EDIT = More fuel pump info.....


What fuel pump is best to use in my swap? 2002 6.0 going in an 1988 c1500 Chevy truck. I was considering using a Mallory or Holley fuel pump in case I decide to go further with this project later. For now it will remain a stock engine.

If you're doing a fuel injected setup, use a walbro 255 and be done.
If you go with a walbro check out part # es2448 at advance. even says walbro on the pump
It's going to retain all the stock 02 fuel injection
Go to e-bay and buy a pump for a 96-98 vortec truck. costs $20 and works perfectly, part number e3270
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Last edited by SHARPMACHINE; January 21st, 2013 at 08:23 AM.
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