Vortec conversion in a 1999 GMC K2500

[comeaud]

Hey everyone. I don't know if this is the place to post this but I have just about given up on this truck.

I have a 1999 GMC K2500 with a 350 Vortec in it. Over the years I have rebuilt countless 350s and other V8 engines and never before have I run into so many problems with an engine.

The story is that the motor had over 350,000 miles on it. A piston cracked which obviously put a stop to the engine. I ordered a rebuild kit, as well as new factory style heads and a distributor. I completely rebuilt the engine, installed new fuel injection and and EGR valve. After reinstalling the engine and making all of the connections the engine started and instantly popped a code. P1345 which is Cam / Crank sensor correlation error. The engine ran like junk and backfires. It was so bad that I dropped the pan and removed the timing cover to ensure that I had the mechanical timing correct. As I suspected the timing was exactly were it should have been. After beating my head against the wall I had 3 friends separately check the work and nothing was wrong.

I towed to the truck to a very well respected garage to have them look at it. They connected it to a bi directional code reader and adjusted the Cam Retard Offset to within -2 to +2 degrees as specified by the manufacturer. It still runs like ****. They changed the spider out thinking the one I installed was defective. No change. New computer, new cam and crank sensor, checked fuel pump,new distributor again, NOTHING.

Needless to say, its junk.

I love the truck, it's solid as far as the body and frame goes. I want to fix it but I want to divorce myself from this computerized bull****. SO here is where my questions come in.

Can a 350 Vortec be modified to be a carbureted engine with an MSD aftermarket ignition system for example?

If this is the case obviously there is no TPS on a carburetor. Is there a way to make a carburetor that is set up for a mechanical kick down compatible with the computerized controls required for the 4L80E?

Does anyone know if someone makes a carburetor that comes equipped with the proper connections to the computer that would allow the truck toknow when the transmission should shift?

If the 4L80E is not a viable option for this situation and I need to run traditional carb and ignition system, is there a transmission that has mechanical controls like a 350 Turbo or 400 that can be attached to this engine?

I know that it would be easier to just put a different engine that is working correctly into the truck but I just dumped a bunch or time and completely new components into this engine and I would rather not lose all of them.

Thanks in advance!

[Baddflash]

Yes you can get aftermarket transmission controllers to run the trans without the ecm.

[hugger6933]

I had that code in a truck that had to replace the dist. Now I have broken the big rule and didn't read all the way through the post before clicking reply but you have I mean HAVE to be exact on the timing[dist position] prior to restarting the engine. Also the code will not go away with out a scanner to clear it or until it is fixed and the history records no recode[for the lack of a better term]. For the history to be cleared it has to go through like 100 ignition cycles to clear the code so you see it can take a while to clear without a scanner. That being [anything] OBD2 you have to clear it and not just unhook the battery to clear the computer like with OBD1. Now with a scanner like the one I have [GM TECHII] you can hook up the scanner and turn the dist until the scanner says it is in proper position. But however like I said you can do it without the scanner and do it right[well I did anyway] and make it run properly.

Now getting discouraged and wiping out the EFI and putting on a carb and and HEI type dist will make the truck run and those vortec motors run like a raped ape with the carb on them tuned properly but you won't come out of firs gear without a stand alone computer to run the L80E trans and not to mention the $500 to $1000 bucks for it but the rest of the junk in your truck won't be right either like the transfer case shifter and what not.

I think you should try timing again. Jim

[57taskforce]

$wise your way further ahead figuring out what you need to do to get the fuel injection right than throwing more time and money at converting it to carb(carb,intake, hei,modifying fuel system, etc) plus the cost of a trans controller or new trans.

[Eddie H.]

I would recommend finding a good experienced Chevy tech and paying him to properly diagnose and repair the problem. I spent nearly 40 years working in dealerships, and I can't count the number of times I ended up with "problem vehicles" that the owners, and other shops in the area, finally gave up on trying to fix. Usually the problem ended up being something relative simple, and not even related to the hundreds of dollars worth of unnecessary parts that they had been throwing at it.

[comeaud]

Thanks for the replies! The issue is that it isn't just a hand full of backyard mechanics tinkering with it. As I stated in the post it was brought to a shop where it was removed and torn down again despite my assurance that it was done properly by a GM tech with 30 years working at a dealership and running his own garage. The only components that weren't removed were the Pistons and rods because the bolts were already stretched when torques at their proper angle.

The engine was reassembled and preloaded again to the exacts specs and in the same manner in which I preloaded it. He connected it to his diagnostic computer and adjusted the cam retard offset exactly to where the factory had it. The fuel injection was again changed. New spider as well as a new throttle body. Map sensor, mass air flow, cam, crank, knock (only cause it was leaking coolant) all changed. The distributor was replaced with and aftermarket model but after the problems I ran into the mechanic installed a brand new one from delco and then reset the cam retard offset again. New computer as well. The harness is intact and after chasing the wires there is no sign of any shorts. Compression tests have all 8 cylinders right around 165 psi.

Whatever the issue is it seems to be an anomaly. Nobody, not myself, my fellow wrench heads, or a garage filled with very experienced GM techs can nail this one down. My concern isn't that it will cost money to convert it, my concern is continuing to throw more good money at bad in order to chase a problem that as of now cannot be fixed.

I've heard that they run great carbureted. My concern mechanically is exactly what the one person mentioned and that is that the transmission won't function properly.
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[Bigdav160]

There's no bad cars just bad mechanics. Throwing parts at it is telling

[hugger6933]

The trans controller will let you make the trans shift but I'm more concerned with the transfer case it is electric, right? Also the dash stuff is gonna need ecm[BCM came on the later models] to operate and with out a carb on there it just won't. Now I've seen lots of earlier trucks that style 88-92ish mainly that have been changed over and mostly all that didn't work was the speedo. But those had a lot different set up in the dash. Jim

[Nitis]

Ok I get where youre coming from wanting to try and simplify this but you are digging a hole you don't want to dig

First things first you can pay lots and lots of shop time and I mean a lot for how expensive those trans controllers are they are not cheap

Next as previously mentioned take it to someone who knows GM inside and out. My moms 97 Yukon basically same setup you describe local mechanic threw all kinds of stuff at it and finally gave up. Took it to a GM guy fixed in 20 minutes bad distributer cap that was brand new!

[Eddie H.]

I have seen many instances where some really weird running problems were caused by outside electrical interference (like bad grounds, shorted diodes in the alternator, wiring harness problems, etc) affecting the ECM. I remember one "problem truck" that was given up on. The owner and his mechanics had replaced practically everything but the air in the tires. I checked it out and found a glitch in the electronic instrument cluster that was causing the ECM to randomly shut off the injectors. You may have had some very experienced mechanics working on it, but sometimes even the most experienced people get caught up in the trap of just replacing parts, hoping to get lucky, instead of really tracing down the root cause of the problem.
I'm not trying to be a know it all, I really do hope you can get it fixed right.
To answer your question, yes you can convert it back to a carburetor, and put an electronic transmission controller on it, and make it run and be driveable, but you may still have problems getting everything else to work correctly.