: Northstar Help

03-12-05, 04:33 PM
Help from Northstar owners please,

I have a 97 STS that I bought 6 months ago with 85K miles. I had the car checked at the dealer and they gave the car a very favorable review.

After a month or so the engine started misfiring and was pulling an O2 sensor code. I looked at the plugs and wires as initial troubleshooting steps. The plugs looked ok, but I went ahead and replaced them and the wires. I used AC plugs and Bosch wires. I also added injector cleaner. The O2 sensor code went away and we were good to go for a few months. Recently, the missing has started again, along with the O2 sensor code. I pulled the O2 sensor (before CAT) last week and cleaned it thoroughly. The code went away but the misfire returned.

The misfiring has continued, so today, I took things apart again, plugs great, wires looked good. They measured 500-700 ohms/foot. The resistance across the ignition packs was consistent as well. (about 750 ohms between the spark plug wire connectors).

Now I am working on the injectors, and they all look pretty dirty. I should have it back together in a couple of hours and will try a road test again.

Thoughts, ideas from you experienced Northstar people???



03-12-05, 08:57 PM
If the misfire is primarily at idle, clean the throttle body and disconnect the battery for 30 seconds. You can search the forums for throttle body cleaning and there are lots of posts with everything you'll need to know. I've never had any luck cleaning an O2 sensor. Maybe for a week or so it will be OK, but it will probably need to be replaced soon. It's not just soot that stops them, it's also the trace amounts of sulphur and lead in the fuel that destroy the element over time combined with the extreme thermal cycling. Those things are in a pretty harsh environment.

If you can nail the misfire down to a particular cylinder, swap that coil with another one and see if it moves. If it's hard to start sometimes, check the fuel pressure regulator by removing the vacuum line while it's running. If you see fuel coming from the vacuum nipple on the FPR, it's bad and will need to be replaced. That will cause it to run rich.

Well, a few thoughts anyway... Good luck and keep us informed...

03-12-05, 09:25 PM
I would say replace the O2 sensors since the code for it keeps coming up. I don't think they can be cleaned, they wear out.

03-12-05, 10:52 PM
Thanks for the feedback. The plugs are running very clean. It doesn't look like there are problems there. The misfiing is random and happens wherther the engine is cold or hot. I got hung up working the injectors this afternoon. (Had a little problem with the o-rings) Did you know that AutoZone does not stock them. I'll pull the connectors tomorrow and see if I can make those work. (I had one leak when I tried to start the engine.)

All of the injectors were fairly dirty. I cleaned them all thoroughly, and I hope that when I get it back together the misfire will be gone.

Yeah, I will end up changing the O2 sensor, but so far, it's working ok.

By the way, what should the fuel pressure be? I'll check it at the test port tomorrow.



03-12-05, 10:58 PM
Fuel pressure should be about 45-50 psi as I recall.