96 GMC Yukon 5.7 Vortec, Swap to Carbed

[BigSwid79]

My 96 GMC has the 5.7L vortec. But is has 181K on it and I've been having a ton of problems, mostly computer issues and timing issues. Bad distributor, and I've been told I could have jumped a tooth on the timing chain... I did a tune up took it out for a ride that night and it ran the best it has ever had, and then the next day took it, ran fine for about 10 minutes, got to stop sign went to take off and then all the sudden misfires, popping, lack of power, vibrating, I then confirmed that the timing was way off when I plugged it into a scan tool and the cam was 24 degrees retarded. I even tried resetting the timing several times and no luck. Has spark, fuel, air, just not firing. Needless to say I'm sick of working on something I feel like whatever I do cannot fix it. So I have this grand idea What would it take to drop a Carbureted engine in, with a th350 on the back of it?

I have plenty of parts for the conversion and what I think enough knowledge to do it. I've seen it done on a 87 tbi, and it worked great. So please give me your thoughts.

[argonaut]

While carbureted motors do run fine and well I think that swapping from EFI back to carb is a step backwards. The computer can control combustion over a wider range of conditions better than a carb can. I would say get to the root of the problem. Either you have a bad distributor rotor, distributor clamp, or bad gear teeth between the cam and distributor, or a problem with the timing chain. I don't see how else the base ignition timing could change that drastically. A new roller chain timing set is pretty cheap nowadays,and should probably be done anyway after nearly 200k miles. You can inspect the distributor rotor and gears teeth pretty quickly just by pulling it out. Do a compression check on all 8 cylinders while you're at it and make sure your piston rings and valve guides are in good condition.

[Dalaigh]

Honestly if you're going to go through the trouble of swapping motors, I look into an LS. Each swap has it's pros and cons.

Carb'd engines are simple easy to work on and cheap to upgrade. But, they kinda suck in the cold, they're not that great on gas (especially if you start putting speed parts on), and the only 4 speed auto you get is the 700r4 (not saying its a bad thing, just pretty much one option).

LS motors on the other hand are much better on gas, depending what year LS you, get you can go with a 6 speed auto. There are plenty of go fast/aftermarket parts for them and tuners can net you more power with increased fuel economy. But, they are a little higher on the difficult level (mostly from the computer/wiring harness), and the cost is a little to a lot more (depending what combo you go).

I'm not nocking one or the other, I run a carb'd 350 in my 84. It's a strong motor and reliable, but the fuel economy isn't there.

I found a used 5.3 locally with 45000kms for $800, and it got me looking into the swap. And I think it can be done for about $1800-$2000, using my th400.

Edit: this is Canadian funds too, so may cost you less, because **** cost 2x as much over here for no reason other then greed.

[Zoomad75]

The plastic bodied distributators used on the vortec 5.7 are notorious for getting loose with high mileage. The bushings that the dist shaft rides in loosen up and allow timing to bounce around. Then the next issue is with the dist gear wearing down to a knife edge on the teeth. That also lends to irregular timing. The problem there is if the gear on the dizzy wore down, chances are the gear on the cam is pretty worn too.

181,000 miles is a hell of a lot on a 350. I know some have gone further without rebuilds, but with the issues you have it might be time to freshen it up. It would be better to fix what you have than going backwards to a carb'd 350. Going back to a carb would require dealing with the high pressure fuel system and getting it down to under 10psi for a carb if you don't want to try and make a mechanical fuel pump work in there.

If you are going to pull the engine why not rebuild it instead? I'd upgrade the injector spider to a later style that has real injectors at the ports instead of the crappy leak prone poppet valves.

[BlackhillsHD]

Also if you get rid of the injection, get ready to to a trans swap as well because your computer controlled trans isnt going to do anything without the injection there.