5.3 falls on its face

hjpcummins · Oct 14, 2015

Some know a little history of my 5.3.
Pretty much full rebuild besides heads

A Little info on engine 01 5.3 0 miles , cam & springs, psi harness and ecm.

While driving around the yard I can cruise just fine, after 1 or 2 half throttle pulls it starts to run like complete dog ****, damn near just falling on its face and shutting off. So shortly after I just let it sit and idel to test the new water temp gauge and try to get air pockets out of the system, during that time the idel is just stumbling.

Oil sits at 40 psi at idel (fluids checked)
Vacume leaks checked
Fuel rail air bleed
And so on..

This happened last time I had it in the yard, Parked it and started researching for someone with similar issues,with not much luck.

Scanner didn't find any trouble codes
Just looking for a little advice.
Thanks

TBItoy · Oct 14, 2015

The trend in "LS runs like ****" threads has been dirty injectors...

Cracksrubi · Oct 14, 2015

Was just about to say that. We had two ls motors that sat and all 16 injectors were bad clogged.

hjpcummins · Oct 14, 2015

Re:

Yeah iv been thru those threads but..why wouldn't it do this from first start? But that was going to be my next step

Diamond B · Oct 14, 2015

If the motor sat for a while, there is a good chance that the injectors are fouled. Every LS our local shop has dealt with has had to replace the injectors on motors that sat, including mine. If the injectors are good, check your O2 sensors: make sure they are the correct ones for your ECM program, and properly plugged in and installed correctly. IIRC, they are supposed to be as close to horizontal and between 9 and 3 on the exhaust close to the collector.

Bumpers · Oct 14, 2015

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Probly fuel or tune related if no vaccum leaks

wizzo · Oct 15, 2015

I had a similar issue, you may have read my thread. Ended up being trash in the injectors. Pull the injectors and reverse clean them first, I bet you get trash out. Runs like a champ again. Just my .02

altfuel1991 · Oct 15, 2015

Engines that have sat for extended periods with fuel(E10 gasoline) in the rails will generally have clogged injectors due to the gas turning to a varnish-like substance that is nearly impossible to get out. We have had generators and RV's come in the shop that have sat for 90 days without being started and had to replace carburetors on the generators and fuel pumps in the RV gas tanks as well as injectors. We have had no luck cleaning these parts.

ALLJ · Oct 15, 2015

I have done 2-3 LS motors I always soak them in seafoam cleaner you will be surprised what it will cut loose in them remove the o rings first

croes · Oct 15, 2015

Injectors plugged
Fuel pressure too low
Clogged fuel line
MAP sensor going bad
Bad o2 sensors

If you're running the factory fuel pressure regulator pull the hose off it with the engine running and make sure its not bad and dumping fuel straight in the intake.

bigun0604 · Oct 15, 2015

I HAVE A SIMILAR PROBLEM WITH MINE TOO.ITS A 5.3 WITH A SMALL CAM AND LS2 INTAKE. IT WILL CUT OUT ON HARD ACCEL AND DIE OUT WHEN LETTING OFF ACCELERATOR AT TIMES. I HAVE A FAST FUEL LS TRANSPLANT KIT. ALREADY PUT NEW FAST INJECTORS IN IT, IAC, TPS AND NEW INTAKE GASKETS. I HAD A 92 MM THROTTLE BODY ON IT AND THOUGHT THAT MIGHT BE THE PROBLEM SO I REINSTALLED THE STOCK THROTTLE BODY AND SAME ISSUE?? ANY INPUT. IVE EMAILED FAST FUEL SEVERAL TIMES AND THEY NEVER RESPOND.

hjpcummins · Oct 15, 2015

Re: Re: 5.3 falls on its face

wizzo said:
I had a similar issue, you may have read my thread. Ended up being trash in the injectors. Pull the injectors and reverse clean them first, I bet you get trash out. Runs like a champ again. Just my .02

I soaked the injectors for a few hrs today cleaned the o rings and so on. They had a lil trash in them but not like yours.

Also soaked the rails and cross over pipe. Just picked up some monster intake gaskets just to cancel one thing out and hopefully more forward on resolving this pos .

hjpcummins · Oct 15, 2015

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Ok got everything back togeather, run a tad better ( probably since injectors are cleaner) my neighbor walked over and noticed the entire right side header was warm but not to hot to touch (exhaust wrap) but the left side was to hot to touch. Now I'm thinking electrical issue.. I tried to get different idel results by unplugging each coil pack on right side and barley a slight change. I unplugged the entire right coil gang and their was a little more difference in idel but not much still

I continued to do the left side and the changes were night and day compared to the right side of the engine. So I went ahead and disconnected the whole coil gang on the left side then the motor died...hmm not sure what to think of it at this point. Thinking someone with computers skills need to take a look?

croes · Oct 16, 2015

Re:

hjpcummins said:
Ok got everything back togeather, run a tad better ( probably since injectors are cleaner) my neighbor walked over and noticed the entire right side header was warm but not to hot to touch (exhaust wrap) but the left side was to hot to touch. Now I'm thinking electrical issue.. I tried to get different idel results by unplugging each coil pack on right side and barley a slight change. I unplugged the entire right coil gang and their was a little more difference in idel but not much still

I continued to do the left side and the changes were night and day compared to the right side of the engine. So I went ahead and disconnected the whole coil gang on the left side then the motor died...hmm not sure what to think of it at this point. Thinking someone with computers skills need to take a look?

If you have o2's on each bank, unplug them and run it and see if its any better.

zjtrey · Oct 16, 2015

The harness connector for the coils has been known to be a trouble spot in my experience.. see if any of the pins look bad or other evidence of a poor connection.. I think you are calling it the gang connector... coils could also be bad.. maybe try swapping a couple coils from one bank to the other and see if the EGT's changes.

hjpcummins · Oct 16, 2015

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02s are new but I do recall when I had it mounted to the stand and running it ran great considering no vacume was blocked off.. so I'll be swapping things around today.

Does anyone know of a fuel pressure adapter for a truck fuel rail.. I'm not trying to splice into fuel system

ALLJ · Oct 16, 2015

Have you had any tuning done on this motor ? are these problems pre dyo tune ?

hjpcummins · Oct 16, 2015

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No the motor has not been tuned for new cam. Ecm has vats deleted but that is all

croes · Oct 16, 2015

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hjpcummins said:
02s are new but I do recall when I had it mounted to the stand and running it ran great considering no vacume was blocked off.. so I'll be swapping things around today.

Does anyone know of a fuel pressure adapter for a truck fuel rail.. I'm not trying to splice into fuel system

To check the pressure? If so there is a schrader valve to hook the gauge to on the factory rail.