Today I was driving on the freeway in 4th gear and right around 4100 RPM the tach started jumping wildly anywhere from 4000-6500 or so. I freaked and shifted quick and tried it in 5th... sure enough does the same thing.

I had about a 2 hr drive so I played with it a while on the way there and back and if I use EXTREMELY light throttle to nudge the RPMs up it doesn't seem to do it, but anything medium or more from ~4k on makes it go nuts. It does it in every gear, including neutral.

It's done twice before over the last 6 months, once just randomly down at like 3k RPM I saw it bounce around for like 5 seconds and thought little of it, and once last week when I took it up to about 5500 and saw it sweep all the way to >8k, then I shifted and it wobbled for a second or two.

One thing I'm not sure of is if this is affecting the fuel output at all because usually the car runs normal when its bouncing around, but sometimes it'll sweep a high and the engine will pop a little (knock? doesn't sound like it but the freeway is noisy at 80mph).

Any help would be appreciated!

 

a lot of ppl will immediately say your ignitor is going out. that may be the case, but first, clean the two contacts to your ignition coil and make sure its a clean, tight connection. (dont strip the screws tho) i had the same problem, eventually the car would actually start to stumble and stall out on me unreliably on the road. to get it to work again, i just messd around iwth the distributor, not knowing exactly what i was accomplishing, and i would start again, but would die at any time. all i did was clean the contacts and it has been fine ever since.

 

I'll try this tomorrow and assume the ignitor if it doesn't help? Any other ideas would be great since I have all day to screw with it.

 

I had the same problem on my '91 LS. This is what I did to fix the problem.
Try these steps firsrt.
Clean and tighten all engine grounds, make sure there is no corrosion on the terminals, especially the ground terminals at the thermostat housing.
Check, clean, tighten all the connections and terminals inside the dizzy
The 2 wires on the coil amd the 3 or 4 on the ignitor.. They NEED to be really clean and really tight. Use a plier to make sure they're tight. Be careful, though.
If those steps don't solve the problem, try swapping in a known good coil and/or ignitor.
HTH

 

yeah, just let us know when you fix the problem so we have a record of what worked. ive heard sometihng as simple as cleaning the connectors on the back of the guage cluster also solving just a jumping tach problem.

 

I got lazy today and didn't touch it, I'll try tomorrow and let you all know!

BTW Tyson, great faqs, I read em a long time ago but never got to thank you for the write ups!

 

Long story short, it was the ignitor. I bought that and a new cap and rotor... cap and ignitor went in fine, rotor retaining hex cap was stripped so I had to stick with the original part.

 

i had this prob on a si motor i fixed it with a new cap and rotor

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mr.Saturn &raquo;</TD></TR><TR><TD CLASS="quote">Long story short, it was the ignitor. I bought that and a new cap and rotor... cap and ignitor went in fine, rotor retaining hex cap was stripped so I had to stick with the original part.</TD></TR></TABLE>

Anyone know the best way to get the old rotor off and remove the old hex screw? I heard just rip the rotor off and use vice grips, with the rotor being plastic and most other parts being metal, will I hurt anything by going ballistic on the rotor?

 

drill the hex bolt out i guess. or pull a vlad(91civiclx) and melt the rotor off with a torch then take some pliers to the rotor screw. i dont know if enough will be sticking out to accomplish this though. drilling it out should be pretty easy since you can just use the hex hole to center the drill.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mr.Saturn &raquo;</TD></TR><TR><TD CLASS="quote">
I heard just rip the rotor off and use vice grips, with the rotor being plastic and most other parts being metal, will I hurt anything by going ballistic on the rotor?</TD></TR></TABLE>
Where do you guys get this sh%@# from?
This is possibly one of the dumbest things I've ever heard.
Please do not rip the rotor off you WILL damage the shaft that drives the dizzy. And you may not get the new rotor to seat back on right, at the very least
The shaft and the set screw are BOTH metal.
Try cutting a slot in it with a Dremel or a file. Or try a screw extractor. Use your head.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4crx4me &raquo;</TD></TR><TR><TD CLASS="quote">
The shaft and the set screw are BOTH metal.
Try cutting a slot in it with a Dremel or a file. Or try a screw extractor. Use your head. </TD></TR></TABLE>

The shaft may be metal, but there is a layer of plastic. Don't get me wrong, tearing the hell outta it would be a last choice for me, but if there was no other way it would give a little extra room to use some vice grips.

I don't really need to do anything right now because everythings working and until it breaks I'm not gonna fix it. I really don't the idea of doing anything that will make metal shavings in something thats so sensitive to magnetic interference.

 

well, glad to see at least you oslved your problem.

hmm, the set screw is stripped huh. you could remove the distributor, hack around the plastic and get a vice grip around the bolt and remove it that way. but rotors can be cleaned off and reused as long as it works and youre not asking for perfection.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson &raquo;</TD></TR><TR><TD CLASS="quote">well, glad to see at least you oslved your problem.

hmm, the set screw is stripped huh. you could remove the distributor, hack around the plastic and get a vice grip around the bolt and remove it that way. but rotors can be cleaned off and reused as long as it works and youre not asking for perfection. </TD></TR></TABLE>

my thoughts exactly (in better words than i could think of)