So last year I got a 92 6sp with a 155k on it. The engine is completely stock. If I had to guess it is the original engine, it looks like it had nothing more then one injector replaced and maybe a intake reseal. It leaks no oil (other then normal seepage), burns no oil, makes no odd sounds, and holds great oil pressure. So the bottom end is sound from what I can tell and makes me wonder if it has been replaced at some point. It ran well (not perfect)other then running rich on the right bank and backfires from right bank on decel when I got the car. Changed plugs and the right side plugs were completely black. Car had check engine light and showed right O2 voltage low. Changed both O2s and car ran great with no check engine light. This was all a year ago.

Now the car runs fine until 80% throttle, then it vibrates, runs weak, and acts like it wants to misfire without completely misfiring. Still wants to backfire on right side on decel without actually backfiring (if you get what I'm saying). While warming up car runs fine but can hear the right side trying to backfire. Can hear a slight thud from r. side exhaust.

I have a low mileage msd opti (3k miles), low mileage stock injectors (40k miles), and new msd wires for it. I also have two sets of heads. One set is used that I disassembled and they look really good. I think I could get buy with relapping the valves and new seals and springs and be good (haven't checked for warpage yet). The other set is a brand new bare set. I also have new springs, seals, locks, and retainers for the heads. And as a side note I have new 30 over pistons for it and a set of lt4 rockers.

I hope you see where I'm going with this.

My original intent was to throw the new opti, wires, and injectors at it as I'm 99% sure the opti is the culprit to my issues.

Then I got thinking that maybe I should just reseal the intake and valve covers while I'm at it. Then the timing cover since the w/p and opti are off. Then Might as well do the oil pan to. Then might as well do the timing chain since it has a 157k on it now. Then might as well do head gaskets and port the heads I have for it now and use the new springs and roller rockers. Well the ported heads aren't going to do much with the stock cam, so might as well do that. But really don't want to go that far and use a new cam on cam bearings with a 157k on them. So might as well pull it, rebuild it, and throw a new clutch at it.

But the damn thing runs so well right now. If the guy that I bought the car from told me the engine was replaced 10k miles ago I'd believe him. So I don't know what to do. Please give advice. And I'm trying to work with the smallest budget as possible. I'm poor like everyone else my age.

On a side note, I have a 70 camaro that had the oil pan started leaking. Engine was completely done 15k miles ago. The engine ended up out and completely torn apart even though the insides looked like new yet. When it was done it had a new oiling system, oil pan, cooling system, cam, rings, bearings, rebalanced, heads, intake, carb, and tq converter.

My 69 truck that was suppose to be an engine rebuild and paint ended up stripped to the frame.

So I have a bad habit of snowballing.

 

fuel pump / fuel filter / fuel pressure issue ?

 

Step away from the toolbox my friend Yes snowballing happens sometimes. Like all the time over here.


Bent (actually broke) a pushrod on a motor with 60 (sixty)miles on it last night....if I had the dough Id pull it change pistons etc and rebuild it again. its SO hard leaving things be sometimes. The what ifs can make ya

With 157k Id just get it running right and leave it alone, if youre wanting more slowly piece together a fresh motor on the side then swap it out at some point. Motor may be sound but you probably know it probably does burn some oil with that many miles and things are good and worn. Could go another 50k could go tomorrow never know.

 

Leave the motor alone and put 4.10 gears in there. I would be hesitant on putting money into a motor that used.

 

Rich right bank is most likely due to leaky right side injector/s. Connect a fuel pressure gauge on the shraeder valve on the end of the right side fuel, turn the ign to run for longer than 2 seconds and then off. Fuel pressure should be 35-42 psi and it should hold up for 1/2 hr at least. If pressure bleeds off faster than this, you have leaky injector/s or a defective fuel pressure regulator check valve.

 

Hows the shape of the rest of the car?If plan on keeping it for a long time,I would get everything slowly that you need for the complete engine rebuild.It will take time & money.That way you can enjoy the car while getting everything together instead of it sitting torn apart & waiting for more money & parts.In my experience,its cheaper to buy a corvette thats in great shape to start with than to have a cheap & poor shape corvette that needs everything to be in great shape.Thats why I bought a vette thats in great shape & basically only needs performance upgrades & not a complete going over.If you have an emotional attachment than it may be worth going over the car completely.Or if you want power just save up to have everything on hand so it will be less down time with the car.My brother torn down his 1978 corvette to completely go over it.He did it without first having everything.He has since lost his job,been divorced,& now the car has been sitting torn apart for 16 years.Now its not even worth putting back together as it would cost more than buying a low mileage 1978 corvette.He should of just drove it while slowly upgrading things here & there.Instead hes got a corvette that ain't worth $1500 that needs EVERYTHING.He only keeps it because our dad gave it to him so he would someday like to restore it but realizes its not worth it.Sorry for long post

 

I like this answer , could also be cross firing, which would be the easiest

 

Open the hood at night and see if the plug wires are arcing.

 

Thanks for all the advice. As a side note I will be performing a proper diagnosis before I do anything, I don't like to throw parts at a car. But after sleeping on it I think you guys are right and I should just get it running properly and forget about resealing the engine till I do a complete rebuild. I'm just too impatient and want it to be bad *** right from the get go.