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- 1992-1999 (https://www.gmforum.com/1992-1999-91/)

- - High rpm miss (https://www.gmforum.com/1992-1999-91/high-rpm-miss-191207/)

Yup. It's puking. Mostly in passing. Plugs and wires are new, only happening at high rpm's under load. No codes, data stream is clean.

Weak spark? BTW what are you using for plugs, Will?

Steve

NGK Vpower TR55's. I'm thinking shitty alternator, and low voltage at high rpm dropout. My alt is an autozone special, only 105 amps. (emergency install).

Anyone else buy this theory? I'm planning to put the scantool on tonight and go for a sprint, watch the alt charge line and my voltmeter.

I don't know. The car itself won't pull too many amps. It's things like the windows, sunroof and rear defroster that require all those amps. I would be surprised if the voltage ever goes below 13 V. Unless the alt is toast, of course.

I have the autozone lifetime alt. So far so good. Not sure how many amps it is. When I got it, I made them switch the pulleys because the one on the autozone didn't run true with the shaft. They thought I was nuts but too bad.

Anyone got any other ideas besides the alt?

You sure its a miss? First thing that popped into my mind was EGR, but that usually can only be detected at low cruising rpm's.

If it's the EGR, I'd be throwing codes. No codes.

Ok, on the way home from work tonight using the scantool:

Headlights and foglights on, stereo off. Radar off.

Volts on idle: 13.4
Volts on Decelleration: 13.6
Volts on cruise: 13.4
Volts on ACCELLERATION @ 2500-3000 rpms: 13.0

Is this my problem? Is the ignition system that sensitive to a weak alternator? I'm assuming IF this is what's causing misfires (or just weak fires, since the PCM isn't reporting a misfire) my plugs are probably fouling also.

Quote:

Originally Posted by jr's3800

Quote:

Originally Posted by willwren

Check your plugs first..... You might have an unhappy camper... Your autozone special is functioning for now... I however don't like how its loosing voltage on acceleration.... Usually it'll be a bit higher... but the unit falls in the proper operating range... I have the same alt you do on my 91 bonneville and its usually at 13.5 to 14v for just abotu all driving situations... You may even have a clogged or dirty fuel injector... Does the miss happen a lot of just every now and again under acceleration? Check the plugs first and number them according to the cylinder number they came out of and have a good look at all of them... :wink:

I'd buy a fouled plug before an injector. It smells rich when I get out of the car after a 'misfire' run. It's a heavy miss. Feels like at least 1 or 2 cylinders missing at the same time. If I nurse it along under 2500 rpms, I don't get it at all. I'm not running lean, so I know it's not fuel delivery related, and all my injectors were cleaned when I did the Eaton rebuild. Filter is fairly new too.

I'll have to pull and inspect plugs next I suppose. Might be a couple days before I have time.

Wouldn't my ICM detect a misfire in that situation?