Lost Two Gen 3 LS Engines in my 1986 C10 2WD

[SquareRoot]

I got an idea. But having failed at it twice already, you're gonna have to start shopping at a more reputable place. Buy once-cry once.

 

[TotalyHucked]

Spitball is what I'm looking for. The injector theory sounds probable because I used the same fuel rail and injectors on both motors. Also using an aftermarket PCM harness which had numerous wiring issues that I discovered. I went through the whole harness looking for shorts and opens and had to change like 8 mistakes. If it's cylinder washing, the harness could still have something I missed. Thanks for the feedback.

I'd agree with Rick, I'd compression check all 8 on the next engine before you fire it. Also, definitely get new injectors (Fuel Injector Connection in *******, Ga is who I use) or at least get yours flow checked/cleaned.

When I swapped my truck, it was actually running on 7 when we tried to tune it initially. Turns out I'd missed one rocker hold down bolt and it spun, causing #1 intake valve to not open. So also pull the valve covers off and inspect all the rockers/pushrods before firing too.

 

[Hunter79764]

While it is possible it's a coincidence, the number of 160k LS engines running just fine and then 2 dropping compression and failing in short order makes me think its a related issue vs bad luck of the draw. Rick and Huck are probably on to something, look at what was in common with the two engines. If the same fuel rail was used, that seems like a good start. It might be possible the injector is stuck open and causing issues, might be restricted and running lean enough to burn up a piston. If you don't want to invest in a new, tested set, at least swap in a different set from a known running engine, and/or soak yours in SeaFoam to clean them up a little. Run compression test on everything if you can, and pull valve covers to see if all the valves are moving reasonably.

And what else is in common? Harness could cause injector issues, if you didn't mess with timing chain and/or rockers, then I don't think that can realistically be the problem. If you have a different intake, you might try that as well (if it was the same factory intake). Look at what changed vs what didn't change and I'm guessing you'll find a smoking gun somewhere.

 

[Ricko1966]

Run compression on the engine you have now,that way you know whether to focus on cylinder number 2 or have an even bigger issue. At this point from what I've read,you checked number 2 on the first motor because it was easiest found zero,went no further Ran 2 on this one just because you knew# 2 failed on the last one but you don't know if all the cylinders had zero compression on the last engine and you only know for sure that #3 is good on this engine,find out if you have 1 problem cylinder or 5,7,2,3,bad cylinders. Maybe you have 4 bad on one bank.

 

[1lejohn]

Was the 5.3 an AFM, DOD engine? If so, the lifters might be stuck in the collapsed condition.

 

[Edelbrock]

Are these

Was the 5.3 an AFM, DOD engine? If so, the lifters might be stuck in the collapsed condition.

That's exactly what I was thinking. My guess is that the engines started having oil pressure issues, or lifter noise - so the motors went to the junk yard, and then this guy bought them.

 

[shortboxin]

You need to run compression on all 8,maybe you havev7 dead cylinders and 1 good cylinder. 1 dead cylinder it should still start,run and go down the road with a p0302 code. Jumped timing does not just affect one cylinder,leaning out like I mentioned earlier could. Which was why I asked about intake,which sorry I didn't make myself clear enough when I say intake I mean air and fuel. Somethings very strange it should still start and run even with 1 dead cylinder. I'd be checking fuel supply,spark and injector signal. Once it's running again you can figure out what's wiping out number 2 cylinder.

I should have mentioned that I pulled the engine out yesterday. I definitely will not be running the same injectors though just in case. I'll run a compression test on the rest of the cylinders and see what's up. This is definitely a strange one for sure. Thank you so much for your help!

 

[shortboxin]

Was the 5.3 an AFM, DOD engine? If so, the lifters might be stuck in the collapsed condition.

No, I should have mentioned the years originally. The 4.8 was a 2004 and the 5.3 was a 2002. I ran the fuel rail, injectors, and drive by wire throttle body from the 2004 on the 5.3.

 

[Bextreme04]

Run compression on the engine you have now,that way you know whether to focus on cylinder number 2 or have an even bigger issue. At this point from what I've read,you checked number 2 on the first motor because it was easiest found zero,went no further Ran 2 on this one just because you knew# 2 failed on the last one but you don't know if all the cylinders had zero compression on the last engine and you only know for sure that #3 is good on this engine,find out if you have 1 problem cylinder or 5,7,2,3,bad cylinders. Maybe you have 4 bad on one bank.

I'm just going to point out that 130psi on a 2002 5.3 is not OK compression. That should be 150-185psi AT LEAST.

No, I should have mentioned the years originally. The 4.8 was a 2004 and the 5.3 was a 2002. I ran the fuel rail, injectors, and drive by wire throttle body from the 2004 on the 5.3.

You need to verify everything. Run compression on all cylinders. When you go to get a new motor, run compression test on all cylinders BEFORE you try to run it in the truck. You should be cranking the engine for ~30 seconds with the coils unplugged and full throttle before you start up the new engine anyways. The motor could have been sitting for years and have bone dry oil galleys. You want to pump fresh oil everywhere before starting it for real. Unplugging the coils and full throttle will put it into flood clear mode and shouldn't fire the injectors so that you can crank the engine to prime it with fresh oil.

I would also be inspecting the inside of all cylinders with a bore scope on a junkyard engine before installation and do the initial prime cranking with the valve covers off so you can see the valves move normally as well. I always send injectors to my guy on any major top end service or before putting a new motor in. It runs about $10-20 per injector to have them cleaned, flow checked, new seals and filter, and shipped back to me.

 

[shortboxin]

You need to run compression on all 8,maybe you havev7 dead cylinders and 1 good cylinder. 1 dead cylinder it should still start,run and go down the road with a p0302 code. Jumped timing does not just affect one cylinder,leaning out like I mentioned earlier could. Which was why I asked about intake,which sorry I didn't make myself clear enough when I say intake I mean air and fuel. Somethings very strange it should still start and run even with 1 dead cylinder. I'd be checking fuel supply,spark and injector signal. Once it's running again you can figure out what's wiping out number 2 cylinder.

Okay, I'm going to put the starter and flywheel back on it and run a compression test on the rest of the cylinders and post that up next week. Additionally, when I put the next engine in, I think I will remove the fuel pump fuse and check for signal on the injector on cylinder #2 to make sure it's not constantly on. I will also be running the fuel injectors and fuel rail from the replacement engine to alleviate the possibility of the injector on cylinder two being stuck open mechanically.

 

[90Supurban]

Are you using the same intake manifold each time? Transfer of debris from a previous failed engine? Stuck open injector is another likelihood.

 

[shortboxin]

I got an idea. But having failed at it twice already, you're gonna have to start shopping at a more reputable place. Buy once-cry once.

Different sources for the engines. Last thing I want to do is blast a new rebuilt motor.

 

[Edelbrock]

Found that the cylinder #2 intake valve was very slow to close back up, all others on that side acted normal.

Lets talk about this.

 

[shortboxin]

Are you using the same intake manifold each time? Transfer of debris from a previous failed engine? Stuck open injector is another likelihood.

Different intakes, same injectors. Another member mentioned the injector possibility. I'm thinking that or wiring short causing it to stay open.

 

[Camar068]

check the compression before you install it.....be better before you buy, but a little difficult to do in the field. All you'd need tho is a battery and a starter along with the comp. gauge.

Not sure how critical, but did you prime the oil system before you started it or just went dry?