: Advice on engine miss and motor mount

06-02-04, 01:19 PM
Hello all,

New to the forum and to owing a 98 STS. I just got the car at auction with 72K on the clock. I have really enjoyed the car so far but I have already encountered some problems.

The water pump was leaking so I replaced that this Saturday and flushed the cooling system.

Also the engine had a miss at idle. First I ran a take of 91 with Chemtool fuel system cleaner, but no change.

I have read every post about idle or hesitation problems. After an inspection of the plugs and wires the appear to be new and a good shape. The plugs are the correct Delco gaped at.050, and the wires are aftermarket carquest brand. Note that 2,4,6,8 plugs were very clean and looked like new. I have only removed and checked # 3 on the starborad side becuase I saw that wire boot was not flush with the cam cover. It looked normal.

Fuel pressure regulator does not appear to be leaking when the vac, hose is removed. The #2 injector looks newer then the rest.

In a post from last year a member said that he his misfire turned out to be caused by a leaking head gasket, and that it was leaking just enough to cause the misfire at idle. After reading this I remembered how clean the plugs looked on the port side of the engine. I started to think that I may have a gasket problem.

Can anyone give me some advice on this theory and how prove or disprove it?

I also found out today from reading the post here that I have a bad motor mount. I had the wife rev the engine in drive and the passenger front came up about an inch. NAPA say they can order them in, but not sure on which one to order.

Any advice here would be great also

06-02-04, 06:06 PM

First off, don't get the motor mount from Napa.. Try going to P & G, talk to Bill sr or jr. 1-888-870-0280 ext 214 or 724-947-9590 ext 214. Great people to work with, I've spent a bunch of money with them. If you comparing prices between them and Flow or GMpartsdirect.com make sure you check out there shipping charges as well.

In this case I like talking to a person not e-mailing someone and hoping you get the right part.

When you changed the coolant did you add the bars leak gold to the lower rad hose before refilling? If not you need to.

Other will jump in with suggestions about the hesitation and your other questions.

06-02-04, 10:42 PM
Don't worry about headgaskets unless you get overheating after hard driving.

If you want to be sure do a cylinder leakdown and/or compression test.

06-03-04, 02:47 AM
i keep telling people this and no one tells me if it worked

check your coil packs if one is going bad it could do what you describe
let me know

06-03-04, 06:18 AM
Yea check the cap and rotor a crack would cause a misfire.

06-03-04, 03:24 PM
Yea check the cap and rotor a crack would cause a misfire.
Unfortunately, (or fortunately) a Northstar won't have a problem with a cracked cap or rotor........ they have nether.

Try the late night arcing test as Bbob and others have suggested in the past. On a dark night open the hood and start the engine. Use a small spray bottle filled with water and spray the plug wires and coil area, if you see any arcing you've found your problem.

06-09-04, 11:50 PM
If you do the spray bottle trick I would suggest that no part of your body was touching the car or you might light up instead of a plug.

06-10-04, 12:01 PM
I have heard other say before that they had an engine miss problems after replacing ignition wires with aftermarket wires. I have read before that the Northstar runs best with OEM wires. Just a thought.

06-12-04, 09:16 AM
I recently had a bad miss. Changed plugs, wires, got better but still not good. Tried all kinds of fuel injector cleaners. Nothing. Changed air filter, fuel filter, pcv. Nothing. Took a wire off the coil pack, started engine, checked for spark. Took me 3 wires to find out I had one bad pack on coil. Cost $22.25 at Advance Auto. Car is much better now.

06-12-04, 05:27 PM
Thanks for all the advice.

I pressurized the cooling system and checked for leak down. Pressure held steady for 30 min at 15 psi. Next I pulled all the plugs and wires.

After closer inspection of the # 4 plug I found that it had a big crack in the insulator. I replaced it the engine misfire is gone!

This morning I found out that the motor mount behind the front right tire had lost the nut that attached it to the motor. It looked like it was removed and never reinstalled.

I took the motor mount from NAPA (not the right one anyways) back and got a new 12mm nut and lock washer. Problem resolved.

I still have a rough idle and its more noticeable at a cold start up. I was told it may be necessary to rest the PCM and then go out and drive the car hard to get engine calibration back to normal.

This information came from CJ Batten, chief engineer for the Olds. Aerotech race program. They were working with the 4.0L engine during that program. He was familiar with the oil consumption problem and has the solution to correct it.

My problem now is how to reset the PCM, I tried to disconnect the 2 + leads coming up to the fuse box under the hood 60 sec. After I reattached and started the car it looks like it did not work because all the settings were still the same i.e. clock radio, seats ect.

Thanks for the advice,