What brand O2 sensors did you use? Also, did you fix the damaged wire on that one O2 (or replace the O2)?
I'm not good with my kms-to-mile conversion, but when was the last time spark plugs and wires were changed? Also when changing the plugs, stay with AC Delco or NGK (if you have BOSCH plugs in their now, dump'em, they are known for peroformance issues in GM v6 engines).

If you read any non-Dex bottle of anti-freeze at the parts store, almost all of them will state "compatible with any coolant" and the stuff is green out of bottle. Prestone makes a coolant that is long life Prestone Coolant with Dex (that's what's in my Monte now). I think I've seen only one bottle that did not have that statement. Odds are, the coolant your brother-in-law put in is fine. But if you don't flush the cooling system regularly, it does tend to get sludgy. I believe the recommended flush interval is every 5 years or sooner.

Short answer, you want FelPro MS98014T. Reason, it's aluminum and the old stuff is nylon, nylon is crappy and fails easily.

Old/original style gaskets are made of nylon. Crappy material, should NEVER have been used, yet GM (and I'm sure others) used that for LIM gaskets for years. People blamed DexCool for the gaskets failing, but Dex was a scape goat. The old green stuff does it too (my '94 Grand Am needed LIM gaskets on the 3100 twice, failed running nothing but ol' green non-DexCool). Dex was found in it's ORIGINAL formula (which was discontinued in mid-to-late 90's) to "promote" deterioration of the LIM gaskets (hence the class action law suits and people now calling it "DeathCool"). But anything present day, has been revised and as long as it's flushed regularly (which also needs done with ol' green) it's fine (otherwise, you would think GM would STOP using it).

Sorry, that's my soap box and now I'm stepping off of it.

 

Hi Maniac, I changed both O2 sensors with AC Delco. They were both original so it was time anyway. Last month I changed the plugs and wires using the most expensive NGK stuff I saw (they had a great sale). My long term fuel trim is above 16% at idle and it is misfiring at any rpm with no load on the engine. I'd like to replace all the vacuum lines and intake gaskets. I don't know what else to do at this point. It also had a new fuel pressure regulator installed last year, as well as a fuel filter.

 

Unfortunately for me and a bulk of people, fuel trim information does not do much for us (the people into performance tuning a car may be able to make better use of that information).

I assume you have no Check Engine lights or even failed trouble codes? If you have access to a good enough scan tool, it can tell you trouble codes that have occurred but may not be enough to set off the CEL. Also, modern ODB-II systems should be able to show the individual cylinders and their mis-fire data.

At this point, I would be curious about:
- is the firing order of the car correct
- failed coil
- failed injector
- failed ICM

If you can see the mis-fire data (per cylinder), then you can try trading positions of two coils and see of the problem changes to a different cylinder. If not, you can trade injectors and again, see if the problem moves to a different injector.

You can also pull the ICM off (remove the coils from it, disconnect the wiring harness and it comes right off) and then take it to the parts store and have them bench test it.

 

i just finished my plenum change today, it was leaking coolant out the side of the plenum but it would not run hot, now after the change the car is running hot, seems that the water is not circulating in the radiator and i have not seen the fans come on. i removed the radiator to clean it out since i had everything cleared out of the way. at what temperature should the fans come on and where is the sensor that controls that function? 2000 monte carlo ss

 

Thanks very much for the advice maniac, I am suspecting coils or injectors but i didnt think about the ICM. Recently I noticed that under load at low rpm it feels like I have a weak cylinder kicking in and out, but not failing to fire completely. Well it may be one or 2 or more if I have coil issues. Next step is to figure out what cylinders I am having trouble with. I don't know if I mentioned the lean bank one code that comes and goes or not.

Magic Madoff, it sounds like your coolant system may be air locked. There is a bleed screw on the thermostat housing.