help car running rough

[dapbmw]

idles like a freight train and runs like it is only firing on 4 or 5 cylinders. check engine light is on.

i just did the intake and head gaskets, replaced one cylinder head as it was badly corroded. new ac delco platinums and bosch plug wires.

double check all the wiring harnesses and all are connected properly. mechanically it is good no clicking noises from the engine, no water or oil leaks, engine temp at 1/3 only. so no more intake or head gasket leak but still have the runniing rough problem.

could it be the coil pack? plugged up fuel injectors? what else could it be?

tia,

dave

[1999montana]

Originally Posted by dapbmw

....idles like a freight train and runs like it is only firing on 4 or 5 cylinders. check engine light is on....

Hi Dave,

Welcome to the forum.

It might be beneficial to read the codes the computer (ECM) has stored rather than guess at what it might be.

I hate to be the one to tell you this, but GM cars generally run flawlessly on AC Delco parts; - that includes plugs and wires. To use anything else, particularly after a partial tear down is just asking for more grief than you need.

Incidentally, didn't CanTire have a pro series diagnostic reader on sale this week?

Having done the head(s) and intake, as you well know, there is/was a ton of stuff you moved or disconnected in order to get at the top end.

If you are sure you have the coil packs and plug wires connected to the right plugs, do you get spark at all 6 plugs? If the answer to that one is yes, move on to the fuel system.

Could it be an injector, I suppose. But how long was the engine sitting while the work was performed? If only a few days, I wouldn't expect any injector to be clogged.

I know with these new technology engines you aren't supposed to disconnect the wires and let them short to ground , but that's what we used to do in the old days to determine if spark was getting to the plugs. So, the best way to zero in on what it might be is by reading the diagnostic codes.

Not much help...but a stab in the right direction I hope.

[Frzninvt]

Our '03 Pontiac Montana just started doing the same thing out of the blue with about 96,500. We've never had any trouble before this. Wife was coming home engine feels like you say running on 4 or 5 cylinders with "Service Engine Soon" light on. Took it to a shop, they changed the plugs, I had them changed about 45,000 so they had about 52,000 on them. They replaced the fuel filter and the problem persists. They checked the coil packs and then replaced pressure backwashed the fuel injectors, then replaced 3 of them. The problem is still there and it comes and goes, he is now thinking it is a stuck valve so he put some Marvel Mystery Oil in it and is letting it run through but it is not solved yet.Got any more clues on what the heck this issue could be? It has the mechanics a bit stumped and me pretty pissed off.
OBD2 codes were indicating misfires.

[rkvons]

Did it rain there about when your wife first saw the problem? Maybe water in your tank.

[dapbmw]

it turns out to be a broken camshaft! don't know maybe just scrap this p.o.s. van!