I have a 2000 GMC sanoma its got the 4.3 in it 4wd. In the past 2 months i have blown up 3 engines they are junk yard motors but all very clean inside and out all newer 2002-2003 with less than a hundred thousand miles all from the same mechanic with a great rep. We have changed everything starting with the obvious oil pump, water pump, intake gaskets, and then stuff like oil cooling lines and radiators even the little valve in the oil filter housing. It will run great like a new truck and all of a sudden the transmission will act like it doesn't want to shift when it does that you look and the oil presure is on 0! and the motor will rev up but its like the trans doesn't want go you put another engine in it and it runs, drives, and shifts great until it does it all over again and once its drops oil presure like that its done you have spun a bearing get another engine! 3 engines in 2 months SOMEBODY PLEASE TELL ME WHAT NOBODY SEEMS TO KNOW WHAT THE H*LLS BLOWIN MY ENGINES!!!!
HELP! im blowing up 4.3's
- Thread starter simpleman
- Start date
Molson02536
New member
You need to flash your ECM for your engine, your 4.3 should shut down when the rpm's go past 6,400 PRM or when your oil pressure drops below 8 psi. As for your transmission shifting at high rpm's you may need to have that also programed not to shift so high and if it does once and a while, that's a common sign of your TPS being bad and giving erratic readings to your ECM.
Your transmission is electronically controlled by the ECM and takes reading from your TPS and input shaft sensor in your transmission. One of these sensor's are faulty can lead to delayed WOT shifts causing your engine to over rev. Remember the 4.3 was not built as a high RPM engine, but was built as a high torque engine. Even the 4.3 turbo charged Syclone engine was not a high RPM engine and at WOT the 1-2 shift was around 4,200 RPM as to our normal aspirated 4.3 at 5,400 RPM
Good luck and try Dyno tuning your ECM to match your engine's performance.
Thanks ill check that out the only thing is the oil pressure isn't always droping out at high rpms in fact the second engine he put in blew up at about two grand leaving the shop with in ten min. just driving down the road. The trans only has about 60 thousand on it now and always shifts great until the engine blows which really doesn't make sense bc thats the only time it acts up and as soon as you put another motor in it its back to shifting great. And ive never got it over or even to the rev limiter in fact the last engine that blew was the only one of the 3 that blew at a high rpm and it was still below the rev limit. I really don't know it doesn't make any sense something really werd and out of the ordinary is causing it to drop oil pressure the original engine wasn't doing this i mean i blew it up but it was over the coarse of 5000 miles and it was already ticking when i bought it and even gradually got worse naturaly it was to be expected but the trans never acted up even when it got to the point where i had to replace the first engine. Idk it just started this crap when i got those other motors put in and you could say it was bad engines but 3 out of the different cars i don't think so. And he is a good mechanic he does about 500+ engine jobs a year and none of them ever come back, not bc they are blowing up anyway. Idk there is something everybody is missing and true this is a very uncommon problem with the 4.3 they're great engines they just don't tear up. Something started this when i had the motor replaced ther has to be an answer and either somebody more knowledgable than me is going to tell me or im going to have to sell it and it breaks my heart i love that the truck but tapped out i just can't afford to put anymore money in it so if anybody knows or can find out and tell i would be much apprecitive thanks again for the advice!
Molson02536
New member
It could be just 3 bad engines for sitting there for a long time, if you are going to install another engine, drop the pan and replace the lower end bearings since it's not in the engine. Once everything is back together and engine installed, try adding 1 liter of Marvel Mystery oil for the first 500 miles and then give it another oil change and have the oil analyzed.
The Marvel Mystery oil will clean out the engine's oil journals and you may have to add Marvel oil 500 miles before each oil change for a while until you think your engine is clean enough.
For each time your engine has failed, what was the reasoning??? Just wondering, you mentioned spun bearing. (lack of oil pressure and or worn out bearing to start with). What was the cause of the other two engines??? I used to work at a speed shop and had many blown engines go through there for the common running lean, detonation, oil pressure failure, or parts failure like oil pump shaft breaking.
They all blew the same way just droped oil pressure. Idk somethings making them drop oil presure all of a sudden its really. Idk im bout out of any ideas. I feel like in my heart of hearts its got to be something simple thats why i hate to just sell it. Somebody will buy it will be a 20$ problem or even just a lack of knowledge problem idk what to do! And Know as well as i do generally speaking motor don't just blow up without a warning sign. F.Y.I i put all new melling or however you spell it oil pumps on it every time.
Molson02536
New member
Most 4.3s that I've dealt with have died due to oiling issues so when I rebuild them I throw in a Melling Z28 oil pump, HD pump drive shaft with steel sleeve, and shim the bypass that's in the block with a 1/16" washer. You also got my thinking on your oil pressure issue, i know the oil pressure relief valve is a part of the "Melling" oil pump and i can't see all the oil pumps you have installed have pressure failure.
Keep me posted eh, be glad to work with you on getting your Sonoma running again. I'd buy it from you, but i just picked up a 1996 2 door blazer for my son. So we can work together as a year project, he's only 15 now and i don't want to give up my toy to him
