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90 Max misfire mystery

Yes, I know it's time for a new car as I've been posting in this newsgroup for way too long about my many Maxima problems. Heres' the latest on my 90 GXE (165k mi):

Engine misfires at all speed ranges- but not all the time! Sometimes I'll start it cold and it will run perfectly. Sometimes not. Sometimes I'll start it hot or cold and it will misfire on a cyl through all speed ranges and then mysteriously, it will stop misfiring and run normally. I replaced injector #1 since it had high resistance and when I pulled the plug wire on #1, the engine showed no signs of change as it did with all other cyls. With new injector, it still misfires, but I don't think it's on #1. All plugs are getting excellent spark. New wires, NGK plugs, rotor and cap. Coolant temp sensor about 2 years old. Fairly new fuel pump and filter. I've run injector cleaner (Lucas) straight into the fuel line with no change in behavior. I ran the ECU diagnostic procedure in all modes and no codes were stored- BUT, while turning the mode screw on the ECU all the way clockwise, the idle rpm's dropped about 150rpm. When I turned it back ccw, the idle speed returned, but the misfire continued. I have never replaced the O2 sensor. The cylinder that is misfiring really is not firing at all as the engine really vibrates and the dragging cylinder really affects power. But with no warning at all, it will stop and run perfectly. This whole problem started early this summer when it was hot and I thought it had the old vapor lock problem. It only misfired when it was restarted hot. Once I got underway, the misfire/stumble at low rpm went away.

This is weird but I remember once going through a toll booth on the Dallas North Tollway and as soon as I went through the toll reader, the misfire started. I'm not sure if it was coincidence or the proximity reader emf's affecting the car's ECU.

So here's my take on this problem: I think it's either a bad microcircuit in the ECU that is not firing a fuel injector, a bad connection to the fuel injector or a sensor giving an intermittant bad signal. But why would a sensor cause only one cyl to drag?? Do ECU's behave this way?

This ng has been great through the years and have given me a lot of help keeping my cars running! Don't stop now- send me your thoughts!!

Thanks!

Chris

90 & 94 GXE's
Reply to
Chris H
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Have you performed a compression and cylinder balance test on this engine?

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Reply to
Telstar Electronics

No, but I think I have the mystery almost solved. Last Sunday, I did a resistance test on the injectors and 2 came up to 58 ohms and 78 ohms. All others were at 14 +/- ohms. So I replaced them. The motor started up and ran great w/ no misfiring since Sunday, but it still hesitates when accelerating from a stand-still. I'm thinking the O2 sensor is bad. I have to do a Mode III & V check tonight on the ECU to see if it indicates a bad sensor. When it starts up cold in Open-loop mode (assume a rich mixture) throttle response is much better than after it warms up and begins to stumble at idle and take off. I might do a compression test just for grins to see if I have any bad valves etc.

Chris

90 & 94 GXE's (& looking at '06 SE's!!)

Reply to
Chris H

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