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Discussion Starter #1
My car is a '90 XR-7. About 3 weeks ago, after a weekend of constant rain, my CEL came on and I developed a miss.

I gave it a day to dryout, no change.

I had it scanned. First they thought an 02 sensor, so I had them change that. No difference. They pulled the plug on #4,it didn't look as though it was firing.

Then they thought a bad plug wire. More scanning and they figured a bad fuel injector (that was only a guess). I changed the plug wire, no difference. Idling fuel pressure is 40 lbs.

Here are the symptoms:

It appears #4 is dead and not firing. Runs the same with plug wire off.

Starting from cold, it will not idle.

Hard to get over 20mph when cold, pumping the gas pedal helps.

Warm, it idles but shakes.

Stumbles when accelerating below 1000 rpm

At cruise, you feel an occaissional miss. Actually, a little more than a miss. Almost like the ignition was shut off for a 1/4 second.

CEL goes off, once in a while, but running does not improve.

Well into boost while crusing at 60.

Acceleration is very, very poor.

Can a bad coil pack effect just one cylinder?
 

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my mom's car is havi ng the same exact problem one of the cylinders had a missfire changed wire plug all that. and nothing was fixing it so basically leaves 1 thing left really and thats the injector.
 

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I would guess it's in the ignition. In my experience, fuel injectors don't just go out. Considering that and the somewhat inconsistent problem, I'd guess it's electrical.

I have seen coils go out, but usually they don't run at all after that. Could it be the plug itself? How about the ignition module? I know the modules on the non-SC cars from that era tend to burn out. I suppose it could also be the ignition pickup, that could also possibly cause the same problem that I'm thinking of.

If you pull the #4 plug after it's ran for a little bit, you should be able to smell gas on it if it wasn't firing. That would eliminate the possibility of the fuel problem.
 

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give it a good tune up. and MAKE SURE all the plug wires are connected FIRMLY. you may think its snapped on good but triple check. i had the same problem
 

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Discussion Starter #5
I would guess it's in the ignition. In my experience, fuel injectors don't just go out. Considering that and the somewhat inconsistent problem, I'd guess it's electrical.

I have seen coils go out, but usually they don't run at all after that. Could it be the plug itself? How about the ignition module? I know the modules on the non-SC cars from that era tend to burn out. I suppose it could also be the ignition pickup, that could also possibly cause the same problem that I'm thinking of.

If you pull the #4 plug after it's ran for a little bit, you should be able to smell gas on it if it wasn't firing. That would eliminate the possibility of the fuel problem.
I tend to favor the idea of an electrical problem. I've never had a fuel injector go bad, but I am not of the impression that it is sudden. I think I'll hit it with my stethoscope, if it clicks I'll continue chasing electricy for a while.
 

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Discussion Starter #6
Well, I decided that it was probably electrical. After jumping another wire to the dead cylinder, I didn't get any change. So, since the scan didn't get me anywhere, I fell on changing parts to see if there was a difference. Somewhere on the net, I found the advice that if only one or two cylinders misfired, it was probably the ignition module. I swapped that out for a new one and voila, problem cured.
 

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Too bad I am in late on this, I was going to suggest the ignition module lol

I need to check the boards more often.

-Thomas
 

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Yeah, too bad I'm late on this as well. My Sable was doing the same thing several months ago. After changing plugs and wires, the coil (ignition module) was next and it fixed the problem.
 
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