madhatter

98 SS M6
GM ASA racing cam, 921 springs, full bolt ons

My buddies car is running rough. It has ~70k on the engine. I pulled the plugs and replaced them. They were pretty bad with normal wear and tear, nothing out of the ordinary. Replaced them with TR55s - no change. It is not a miss, more of just running ****ty, almost like bad gas. No codes are being thrown. Does not matter if cold or warmed up. Fuel pressure is normal.

Any ideas?

Sean

AL SS590 M6

Sometimes a MAF will screw up without throwing a code.

CamaroFan71

Dirty Maf, fuel filter, dirty injectors, small vacuum leak etc etc etc.

trans_am7935

did you change your radiator fluid any time recently? if it is all dirty and cloged it will cause your water pump to rotate irraticly there for your engine will not idle right

Kraest

????

johnny6

I really hope that was a joke


If you got some bad gas it would have to be REAL bad for it to throw a code. I got a bad tank of gas from an Exxon a while back, the car idled like crap with a sputter etc. etc. and it didn't throw a code, i threw a couple of bottles of gas/fuel injector treatment and it slowly started to improve and eventually ran fine. Get a can of MAF cleaner and see if that helps you out any.

99ztwty8

Try running a bottle of SeaFoam through the gas tank, I guess it could be a O2 Sensor going out on you too?

Red89GTA

Not to simply throw out a guess, but does the 98 have egr? if so it could be a stuck open egr. I'd first look at a vacuum leak, remember, look for the simple things first!! Vacuum leak/ bad gas, running some fuel system cleaner (Sea foam for DIY, most dealers/shops have access to fuel system cleaners also which work well) won't hurt.

madhatter

EGR was taken off long ago. If I remember correctly the O2s are not in use when the engine is cold. MAF was cleaned and also changed with another MAF with no change. Hear/see no vacuum leaks. Even sprayed down the whole engine bay with brake cleaner with no change in idle, so I don't think there is a leak. Fuel filter done ~9k miles ago. Maybe try the fuel system cleaner next. I used to work at a shop so I still have a drip bottle in my toolbox.

BTW, wicked avatar. I am somewhat of a fan.

jrm1493

My truck did this last year, couldn't figure it out. It is a Ford but sounds kinda like your problem. It turned out to be a bad coil - it was bad enough to run crappy but it was still either putting out some spark or just dieseling enough that it never threw a misfire code (not even a random misfire).

The input & output resistance on all the coils was perfect the whole time so I was really surprised when the coil ended up being the problem - I thought I was going to have to just sell the thing it was driving me so crazy but I tried replacing the coil as a last-ditch effort (its all one block on that truck) and it fixed it!

Air-Adam

K&N air filter? Might have a dirty MAF from the oil in the filter... I've seen it many times.