Intermittent misfires

hytorksc

Registered User
Gentlemen,

My '90 SC AOD is having a minor problem at idle only. It's not really rough, but I can feel frequent little misfires... it's more like the engine drops ignition for a split second and comes back on rather than a misfire. It happens so fast that it almost doesn't act as if there was a misfire. Fuel pressure is good at idle, and the car is running perfect otherwise. This is very hard to explain. I've got all new sensors/plugs/wires, including a new DIS module, but I did not change the crank sensor yet. i also noticed that sometimes it takes a little longer to crank up- nothing major though. Since i replaced the majority of ignition components and sensors, including the ignition switch fix, i'm thinking that i may have an intermittent crank sensor. I worked very hard on this SC and made sure all wire harnesses and connectors had continuity.

My question is given that everything else is working properly, could a crank sensor work intermittently and cause the engine to "bump" frequently like that?
I just thought that possibly my plugs (autolite 2544's non platinum) may also not be gapped correctly- they were approx .050, could this cause an issue with the waste spark distribution (if this makes any sense)?
What are some of your experiences with this?

Anyone-

thanks
 
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My car does this as well, very light little misfire during idle but otherwise runs fantastic.....

I went looking for the problem but couldn't find anything wrong. I noticed it after I did the H/G and installed solid rubber motor mounts....

Now I just figure its the mounts as the originals may have been absorbing the little hiccup so it wasn't noticable.

There's no leaks in the intake anywhere, both vacuum and boost.

Frit
 
fturner said:
My car does this as well, very light little misfire during idle but otherwise runs fantastic.....

I went looking for the problem but couldn't find anything wrong. I noticed it after I did the H/G and installed solid rubber motor mounts....

Now I just figure its the mounts as the originals may have been absorbing the little hiccup so it wasn't noticable.

There's no leaks in the intake anywhere, both vacuum and boost.

Frit
so is this a "quirk" of the SC that is unsolvable? Everything is working correctly including the IAC, and it pretty much settles to a normal idle (650 rpm in D) after firing up. The cam sensor is new, and it is adjusted properly.

this doesn't really bother me that much, but i thought there's got to be a reason for this because my car does not hiccup like that when at idle just after firing it up, or when the engine is cold. There's something happening when the EEC goes to closed loop mode (fully warmed up) after a few minutes. I don't think i have any burned valves or anything (no popping sounds while coasting), and the engine runs pretty cool temp wise. it's pretty healthy- got a ton of torque right now smoking the tires from a stop all the way thru 1st, 2nd, and chirping 3rd.
 
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