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6.0 poping/hesitating. What could it be?

y5mgisi

y5mgisi

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Aug 11, 2002
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Hey guys, Just finished a swap putting a 6.0 in a 92 jeep cherokee. the motor is an '07, has a walbro 255 pump, vette filter, computer and harness by S&P, and ls6 intake with truck injectors/fuel rail. Runs really good...for the most part. The problem is it feels underpowered and will sort of hicup and stumble at WOT. Im wondering mostly if the problem is revolving around the ls6 intake/ truck injector situation or maybe the fact that the computer was programed for the truck intake. any ideas on where to start?
 
I think lean also. No the check engine light is not connected yet. Im telling him to dyno tune it also but just trying some cheaper easyer things first.
 
Hooking up the CEL is #1, it will probably point you to the problem (something that is bad or didn't get hooked up). Failing that, it's a tune deal.
 
Gotta hook up your check light frist.the ECM will know if it's not hooked up. Besides that, people program these things so different from each other that it has to go on a Dyno to do it correctly.
I had my ECM reprogramed by Howell Injection, biggest waste of money I ever put in my project. Found a local guy with a dyno and a hour later the truck runs great.
 
I doubt just an intake is causing such a tune issue though, but I could be wrong.

Do the truck motors and the car motors run at the same constant PSI?
 
I also doubt the problem is the intake you need to get the light hooked up and make sure you dont have any codes it may be a called a dummy light by some but you can learn alot from it.

All n/a ls motors need the same psi to run properly I dont know exactly but I pretty sure it 50-55psi.
 
Check your fuel pressure on the rail, I had an issue just like yours a couple times.


once.. some wires were fubar

2nd time fuel issue

3rd time the new tune, m guy had the rear non existent o2 sensors turned on, and my fronts not turned on. The back fires turned this place into Compton with a quickness:thumb:
 
texas4x4rebel said:
I also doubt the problem is the intake you need to get the light hooked up and make sure you dont have any codes it may be a called a dummy light by some but you can learn alot from it.

All n/a ls motors need the same psi to run properly I dont know exactly but I pretty sure it 50-55psi.
Click to expand...


Yeah I believe its 56psi constant.
 
What about the fact that we have 5/16" fuel line between the filter and fuel rail? Could that cause this?
 
y5mgisi said:
What about the fact that we have 5/16" fuel line between the filter and fuel rail? Could that cause this?
Click to expand...


hmm, mine is 3/8, but that could be it, you do need to check for codes, i could be wrong but as long as you have a adl port i doubt you would need a actual light..the code will still set you just wont know you have one till you hook up and scan.

A light is stupid easy to add though id you already have the diagnostic port really really easy.


These motors are very common for intake gaskets too. But you need to get a scanner on there and it should read out some codes like low manifold pressure or something.


Have you sprayed around the intake or looked for leaks? I had a leaky intake gasket on my 5.3 in the buggy too btw
 
I will get the codes checked and help him hook up the CEL. The thing does run really well and has good throttle response. The only problem is above 2/3 throttle or so. Even then its not bad but definitely under powered and is more pronounced when its cold. So that leads me to insufficient fuel. But we shall see.
 
Was the IFR table done correctly for using the Vette fuel filter? Being that it produces a constant 58 psi the IFR table needs to be sloped to take account for the reduced flow of the injector as the intake pressure approaches 100 kpa
 
I couldnt tell you. The guy i did the work for had the computer tuned by street and performance and told them everything he was going to run so if i had to bet, I would say yes, that has been accounted for.
 
I am not sure if this has been suggested, but I know the 5.3 is notorious for clogged injectors. I had swapped my 5.3 into my s10 and it would not start. Pulled 1 injector to test if it was opening, and it was, so I figured the others were. Boy was I wrong. I had 7 injectors out of the 8 that had a frozen pintle. After cleaning them, and doing everything I could, I got them all free, put them back in and it fired up first crank. Your problem is completely different, but check your 8th cylinder injector, if its not that one, check them all. The 8th one is known to clog, though.
 
I had the the thought about dirty injectors too... Think im going to have him start by pulling all 8 plugs and analyzing them.
 
y5mgisi said:
I had the the thought about dirty injectors too... Think im going to have him start by pulling all 8 plugs and analyzing them.
Click to expand...

You can pull the injector rail up and look at it with it running. I had one that was crap and it was very easily spotted. Just loosen the two 10mm bolts and have someone fire it up, do one side at a time and if they check out to be ok, use petro jelly and lube the o-rings, then put them back in.
 
Definately let us know if you find out what it is. I am curious myself. It could be anything really, but always start at the simplest of places, make sure you are getting fuel, spark and air. Those are the 3 main things you need for a running motor (atleast thats how it is with the old carbed motor).
 
Im not sure i get what your explaining here. Are you saying to pull on side of the fuel rail up out of the intake, then start it and watch the spray pattern?
 
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