Help Ive got Gremlins 5.3 sonoma

[Hazmatt81]

Ok guys anyones input will be greatly appreciated.

First off heres the run down. 1997 GMC Sonoma Ext Cab 2wd. 2001 5.3 engine and matching transmission(4l60e) 40,000miles with 2001 Zo6 Cam, pushrods, rocker arms and springs. Current Preformance wiring, motor mounts, and sanderson headers. Into a 2 1/2 exhaust running dual with an x-pipe and 2 hooker aerochambers continuing out the back.

Im having problems.
And this is what i know.

Fuel Pressure, 50 at idle and about 55 as soon as you flick the gas. This is the stock fuel pump and setup that was in the truck factory. Fuel pressure regulator is new and not leaking.

Egr. is blocked off at intake manifold.

I did the carb and choke cleaner test looking for leaks at intake manifold. none found

Engine got the seafoam treatment throught the brake booster hose. Just about brought on the 2nd Ice Age blocking the sun

Seems to be missing/stuttering on cylider 4 (second from the from on the passeger side) and cylinder 5 (third from the front on the drivers side.)
I figured this out by unplugging power to the coil(s) while running and feeling/listening for a difference. The Scan tool (snap on) registers 0 missfires on all cylinders. The only thing that the scan tool told me is the passenger side o2 is reading low.

I started swapping coils from a buddys pickup this DID NOT HELP.

Replaced the Brand new Jegs wires with new wires.

Pulled the new spark plugs out of the motor and looked at them. No Cracks. NGK TR55 platinums. One did seem to be a little gassy looking but other than that everything seemed ok.

I am kind of at a loss the only thing I can think of is I have 2 lazy injectors. Lucas Cleaner is in the tank mixing with sea foam. and is not helping.

I have the battery grounded directly to the block and the two extra ground wires comming off of the regular ground lead. one is grounding to the fender and the other to the radiator support.

There is not a engine ground strap on yet. just the ground from the battery to the block.

I also pulled the valve covers to look for valve motion to check to see if the cam went flat on those cylinders. Didn't look to unusual.

When Idling the truck rocks like a miss and when you try to rev it sputters and then kinda comes out of it. when you floorboard it in gear it hesitates and sputters and then takes off like a stock 4.3 and it you leave it in 1st and just wind it up like a top it cuts out like a rev limiter at 4500 rpm.

I am at my wits end here and about the sell the truck. Suggestions

[downdimedown]

I work at a GM dealer in Stratford, from what I hear, it sounds awefully familiar to a plugged cat. Are you even running a cat(s)?

[Hazmatt81]

sorry no cats.

[sparkinak]

Mine missed and chugged for a while. If the motor has been sitting for a while it could be the rings need to reseat. Swap injectors around and see if that does anything. Last measure where did you get your computer and how was it tuned??? Don't do the ebay way I got screwed!!!

[Hazmatt81]

I'll try swapping injectors around and see what happens. Current Performance did the Deletes on the computer, but there has been no dyno tune or tuning of any sort so far. Just what the computer has learned itself

[91sonomast]

these LSx motors are notorious for injectors getting clogged, GM even has bullentins and PI's out about them. i would pull ur fuel rail and inspect ur injectors carefully. they make the injector cleaner in the spray can, spray off ur injectors and let it get inside the injectors and soak inside them. might end up replacing injectors. but like said above, swap injectors around to see if it follows, i nearly bet it will.

[philntx]

Injectors are cheap. I'd replace them all if the motor sat for any extended period of time before the install.

[Hazmatt81]

UPDATE:

Decided to swap around injectors no help.

I pulled out the temp gun and the 4, and 5, cylinders which i expected to be the culprits are about 100 degrees cooler the the proper firing cylinders.

so i voltage tested the injectors all injectors seem to be in spec and to the higher end of the scale. so thats good.

I got out the noid light and started checking the injector leads/pigtails. The noid light fires nice and bright on all cylinders except 4 and 5 which leads me to believe that the injectors not getting enough juice, making it run crappy, which is bringing the cylinders temp down.

what is the remedy? The Current performance wiring harness is grounded to the back side of the heads on each cylinder head. Im going bonkers

[97 SS 350]

Verify the integrity of the wires going in to the injectors, tug on the wires some and make sure they don't come out.

Injector 4 ground wire goes to the computer Blue connector, pin 44 (Blue/Black wire) Make sure it is in the right spot, and that the terminal is seated properly in to the connector.

Injector 5 ground wire goes to the computer blue connector, pin 76 (black/white wire) Make sure it is in the right spot, and that the terminal is seated properly in the the connector.

Beyond that, I would say to physically check the wires going from the injector to the pins I mentioned with an OHM meter. If all that checks out, it may be a bad injector driver in the actual computer.

[4x4zr2GA]

i thought minimum fuel pressure was supposed to be 58 psi.

[lalitopalito]

Rail pressure definitely has to be in between 58- and 62 psi.

[Hazmatt81]

UPDATE::

OK guys i got it figured out. After retracing all of my steps checking over everything once more. I found that during my injector test (swapping injectors to see if the miss followed). I was disrupted during the first test and actually replaced the same injector in the same hole. DUMB@SS!!! So i that was my problem all along.

I would like to thank everybody that posted with their ideas and support.