Any GM techs around???

[RCSConstruction]

I recently found a 2000 L29 7.4l replacement motor for my truck (1997 Chevy Silverado 3500 SRW) It was in a wrecked truck exactly like mine with 29,000 miles. We replaced all the gaskets in the motor and used most of the original sensors. The only sensors used off the old motor were the oil pressure sensor and MAF. The truck spits out two codes. 102 and 340. Low voltage MAF, shows ZERO on scanner but has voltage going to it. The other is a cam sensor that was cleared but then came back. You can pull just about any sensor on the truck and it will not run any different. Maf,Dist.,knock,O2, Even a spark plug wire!!! I swapped out MAF's with no change. Can't get to the camshaft sensor and don't want to unless you think it is the culprit.
The truck smells heavy of raw gas, spits raw gas out of a small exhaust leak where the cat attaches to exhaust and has an extremely erratic idle. It also has no power and backfires hard enough to sound like my muffler is self destructing inside.
I have spent a grand getting it analyzed and worked on with no difference. The dealer will not touch it since the longblock is from a 2000.......... I can't imagine the year model number is the culprit? Different ecm program? I am at a loss.
Thanks for any insight

P.S.
What was wrong with the old motor you ask? NOTHING.... LOLOLOL it had 140,000 on it and a tap in the valve train but no problems. I just wanted to get a new motor in so I didn't have any issues later down the road.

 

[Kenneth Brown]

Re: Any GM techs around???

Not a GM tech but in quite a few motors in my time.
Is it wired correctly? It really sounds like the firing order is switched around.

 

[RCSConstruction]

Re: Any GM techs around???

Yeah, I checked twice on the wiring. I was positive that was what it was...

 

[jimr]

Re: Any GM techs around???

Did you use the wiring harness and ECM off the newer motor? is it timed correctly? if some of those chevy's are off by 1 tooth they will not run correctly. Cracked cap possibly burned through rotor.

 

[RCSConstruction]

Re: Any GM techs around???

To be honest I am not sure if the distributor is in correct. The book says to install back into the previous marks that were made, I didn't mark anything. I figured the dist. went in like they all do. Find TDC on compression stroke number 1 cylinder and install distributor to were the rotor is pointing to the number one terminal on cap, is that right for this type distributor?
I took out the dist. this AM and installed a cam sensor but it's worse, will not even start now. No doubt from the distributor being in wrong but I realigned it twice the way I mentioned above, rechecked all the wires,too.
I did not use the old ecm. When I go to get parts they always say 1996-2000 7.4l, no difference in sensors or part numbers, so I figured my computer would be fine. All sensors are identical and hook up to current wiring harness. Two new caps and rotors just in case one was a bad.
Thanks for your help.

 

[puddle jumper]

Re: Any GM techs around???

Just a gess but are your injectors pulsing.It kinda sounds like one or all of your injectors are stuck open.Remeber that you have a constant power to them and thay switch on the ground side. You may also have missed a ground
to the engine or the ground wire from the engine to the fire wall.

 

[Reel Poor]

Re: Any GM techs around???

You can't put the distributer in like that. The crank sensor fires the ignition coil. The cam sensor is what is in the distributor. Follow the installation procedure outlined in the manual. Once you get the distributor installed you have to set the cam syncronization, that requires a scanner that will read data.

 

[RCSConstruction]

Re: Any GM techs around???

This is a hybrid dist.
It has a rotor in it and the cap has the 8 posts and coil button.
The manual states nothing about sync'ing the cam???
I got it set properly now but it's still all wacked out. When I put my scanner on it today and there wasn't even power to the port, I closed up shop and called the tow truck.
No doubt it's shorted wire or missing ground somewhere. Maybe a ruptured fuel pressure regulator?? Maybe a fried ECU now? I dunno and am done screwing with it. In my younger days I would still be out there freezing my arse off with the motor partially disassembled..
Wish me luck.