This problem seems to be getting worse. Basically if I am cruising at say 2000 rpms the actual needle on my Tech. starts to bounce up and down several hundred rpms at least. This is happening more and more frequently now (say about 10-15 minutes out of a 1/2 hour drive). The actual engine/tranny is not effected (so just the gauge is reading wrong).

Any advice?

Odds are that you need a new tach filter.

Also the battery could be going out. My 84 would bounce like that when the battery was dying.

Here is a great website article about this subject. He also has a link to the schematic of a tach filter if you are so technically inclined as to build your own replacement or you have the option of purchasing one from www.rodneydickman.com...

Here is the tach filter info:

http://www.fieros.de/en/main.html

Hope this is of help,
Marty

Are the 4cyl and 6 cyl tach filters the same? IF so I have one available for sale. pm me

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4.9 Caddy in Garage! Car in Driveway! ACK!

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http://home.cfl.rr.com/fierose
Central Florida Fieros
http://www.centralfloridafieros.org

Crap crap goes your ignition module. Mine did that and then my ignition module died. The tach filter could also be going. Relativly easy fixes so not to worry. Good luck.

A bouncing tach is one of the early symptoms of ignition module failure. If you don't have a spare module on hand, this would be an excellent time to obtain one.

Tach filter? Easy to test; disconnect it and jumper the wires that led to it. If this restores normal tach operation then the tach filter is bad. Don't leave the wires jumpered; over time this will damage the tachometer.

In my old fiero, the tach needle would bounce with the bass from my stereo

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Ok Guys, I noticed something the last few days that I dident at first. The bouncing is getting worse, and I think its effecting my engine. When its bouncing I can def. feel surges in the engine , this is both accelerating and at steady highway speeds. I cant really explain what the surging feels like, but its almost as if someone is putting the ebrake on. The surges are very quick, but may come as 5 or 6 in a 10 second span. At the time of teh surge the rpm needle will be higher then its supposed to be, but not bouncing. For example. If I know im at 2000 , then needle will bounce a little up and down and then stay at 2500 for a 1/2 second and fall back to bouncing.

Does this still sound like my Tach Filter? If I unplug the dammed thing till my replace part shows up will the far still run? (san tachometer?) or am I looking at a much bigger problem here?

Like it was mentioned, you are looking at a problem with your tach filter or the tach signal coming from the ignition coil. The white wire that comes out of the gray connector on the ignition coil is the tach signal wire. If the tach signal is jumping or shorting out it will mess with the ECM's control over the engine. If the tach drops out the ECM thinks that the engine is decelerating and trys to adjust to it and you get the surge. Try Rodney Dickmans tach filter replacement and if that doesn't work then I would look at the gray connector on the coil and then the coil.

Mine is jumping right now too but I know that the wires for the tach filter were burned when I had a little fire.

Edit: What does the ignition module have to do with the tach signal? The tach signal comes from the ignition coil, not the module.

[This message has been edited by carbon (edited 09-27-2004).]

You can temporarily disconnect your tach filter and jumper the connections together in the plug. This wil still let your tach work and will let you know for sure if it is your tach filter that is going bad. When the tach filter goes bad, it creates a direct short to ground. This can damage other parts of your ignition when it happens. Rodney Dickman is the only source that I know of for a replacement part.

thanks guys. If I disconnect and short is it safe to drive the car like that for a few days untill my part arrives, or shouldI just be parking it?

If you really are concerned, you can just drive with the tach filter disconnected. You won't have a working tachometer if you do this, but you also will not have to worry about blowing anything up. If you jumper the connections in the plug that goes to the tach filter, your tach will work, but it might get damaged from running it that way.

As has been mentioned, you can disconnect the tach filter completely - this will disable the tachometer but won't affect the way the car runs.

However, if the tach filter isn't your problem this won't help any, either.

Have you got your spare ignitiion module yet? I've got a strong hunch that you'll be wanting to change it in the not too distant future...

Ok Guys,

Heres the deal. I unplugged the Tach Filter (which of course solved the bouncing needle because it dosent move at all). The engine still surges.. and its def getting worse. ...

Judging by the suggestions I should look at the ignition module next. Is there a good way to test this (other then to swap it out with a new one?)...

Ok then... I was mistaken. You can take it to a parts shop like Autozone and they have a test althought some will pass and still fail in the car becuase of the heat that it is exposed to in every day conditions that aren't present in the test.

Just another question guys. I see both Ignition Coil & Ignition Module being thrown around. Those are two seperate but related parts? Some suggest checking/replacing coil first, others suggest replacing the mod. Which do you guys suggest (Unfortunatly theres no Autozones up in Canada so hopefully Canadian Tire does the testing)....

quote Originally posted by GodSend: Just another question guys. I see both Ignition Coil & Ignition Module being thrown around. Those are two seperate but related parts? Some suggest checking/replacing coil first, others suggest replacing the mod. Which do you guys suggest (Unfortunatly theres no Autozones up in Canada so hopefully Canadian Tire does the testing)....

yes, they are related parts, but I will bet its the igntion module. it starts with the slightly bouncy tach, then the sputter/surges, then the reluctance to accel on the freeway, then then back fires, then the complete shutdown, but will restart after a 5 min cooling, then complete shutdown with no-restart. the igntion module & the pick-up coil are both in the distributer, tho the pick-up coil requires complete removal of the distributer. the igntion module is just remove the cap, then two tiny screws, clean, grease, replace & you're on your way.

Perfect, thanks for your help. I remember seeing that black piece when I took off my distributor to change out the o-ring a few years ago. Shouldent be a problem to remove. So thats the piece I bring into my auto parts store to get checked?

oK GUYS, I took a look at the engine at lunch. Im still at work so I couldent do anything. I think there are really three parts depending on whos messages you read through the forum. I have Identified all the of their locations,

1] Pickup Coil. Inside Dist.
2] Ignition Module. Inside Dist. LIttle black box with wires.
3] Ignition Coil. Besides EGR Value. Follow middle wire on top of Dist to find it.

When I visit AutoZone do I simply walk in with #2 & #3 in my hands? Is there any way to test #1? Sorry for the confusion, I just want to make sure im 100% crystal on what I am getting tested and in what order so I dont spend 100$ on a part I dont need.

unfortunatly, the ignition module usually tests OK when cold. the chiltons manual has a test you can do on the pick-up coil & the ignition coil that just requires an ohmmeter. the pickup coil should be replaced if it looks flaky - if its original, replace it - its cheap. the igntion coil, if its original, an MSD replacement is a great thing to do, but probably not your problem. I will say its the igntion module. common Fiero failure.

Thanks for all your help Pyrthian. I only have a Haynes Manual, not the Chiltons . My wife is bringing all my tools to my work so that I can remove those parts. I actually work at a trucking company with the Mant. bay, so maybe that can give me a hand with testing those parts. You wouldent happen to have a quick and dirty version of the test procedure would you? Is it standard for all types of cars, or is this something of a fiero specialty?

Well, I swapped out the Module last night. At first the car ran pretty rough, but it soon caught up. The stutters arent 100% gone, but its much much much better.

Now, I got the ignition coil tested, and it was working, but of course that was cold. Im thinking of just grabbing 1 and popping it in anyways since its so easy to change. Im not sure if a bad coil can cause the module to fail, but Im not taking any chances.

Ill be buying the pickup coil as well, but it might take me a few days to find the time to swap that.

Thanks for your help so far guys.

get an MSD coil, not just a stock replacement - you will notice & enjoy the difference. when my coil got weak, I would get "bucking" at steady throttle around 2000 RPM.

I had what sounds like the same problem several years ago. It turns out that my distributor was bad. There was just a little play in it which threw off the timing when the engine got warm. I would also recomment replacing your rotor and cap. I had two different rotors fail on me which caused my engine to run very poorly. Check to see if there is any play in your rotor and that the terminals under the cap are clean.

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-Matthew
87 GT My transportation
86 GT My headache

quote Originally posted by GodSend: Ill be buying the pickup coil as well, but it might take me a few days to find the time to swap that. Thanks for your help so far guys.

can i suggest that you buy an ac/delco pickup coil? it is the cheapest part of the three that you are replacing but the hardest to to replace.

AH CRAP!!!

Ok, So I swapped all 3 parts, pickup coil, ignition mod, and ignition coil. Everything seemed good for a few clicks, then my rpms started bouncing ever so slightly (still using the original tach filter just as my replacement hasent shown up yet). This bounce was a little different though. Instead of swinging widly, the tach would jump about 500 rpms WITH THE ENGINE. After doing this several times then engine STAYED about +500 rpms above what its normally at at all speeds.

So wisely, I pulled over an unplugged the tech to elimated this from the equation, but it persisted. Finally the car started surging very systematically (ever 2 seconds) and about a km later I was at the side of the road dead in the water. Full power, but no catch to the start.

I got towed to a pontiac dealership and of course it started right away in the parking lot!

Everything think this is still the mysterious die once, start again, die forver igntion mod? I JUST replaced it a few days ago. Can this one be bad? If I just put in another module will is simply go back in a few days? What else could be causing this.

I have my ORIGINAL module that I suppose I could pop in, and see what happens.

Ill let you know what the dealership says, but I am more then slightly pissed at the events.. ARRRGGGGG.

maybe something went wrong with the distributer re-install. the 500 RPM surges sounds like the ECM trying to compensate for a stall. did you jump the A-B pins when setting the timing?

I did the standard "mark the cap location when removing the dist" from the block. Everything aligned up properly when I put it back in so I dident do the timing. Lets see what the shop says, but I will def recommend that to them. thanks.

Don't mean to hijack, but mine just started to jump last week. The engine seems to still be running fine and it's only when I'm doing between 100-100kms/hr. Please let me know what the shop says as you got me stressed about what I might have to fix if the car gets to the point where the engine starts to jump.

Thanks and good luck,
Joe

Well I have told this wacky ignition story before but it is something to think about when dealing with control modules!

I had one die one day coming home from work (highway cruising at 65mph and the car just stalled...car was running perfectly upto that point). Turned out that the control module died.
Took the suspected bad one to auto zone......they tested it and it tested bad! So I bought a new one. Put it in the car and drove off.
Well I drove the car home and it was fine. The next day I drive to work (25 miles all highway) and it ran fine. I left work heading home and all of a sudden the car starts to buck, miss, and stall out (about 10 miles into my drive home). I let it sit for about 5 mins. thinking what could be wrong now. I decided to turn the key one last time and it fired up! I threw the car in drive and off I went. Well about 2 minutes later it started acting up again. I knew it was module related.... so after about 5 stalls and 1/2 hour later I get home. I pull the module from the car run it over to AZ and have them test it (knowing it would pass because I knew the problem was heat related and the module had plenty of time to cool down). Well sure enough the module passed AZ's little test! I explained to the old guy that the failing condition is only hapening once the module heats up. He told me there is no way the module is the cause of this problem and they can not honor the warranty! Well after getting into an aguement with the guy and him telling me to take the car to a mechanic and getting the real problem fixed I told him to just get me another module...I'll pay for it! I stormed out of the store put the new module in the car and it has run fine ever since (and this hapened about 2 years ago)!

I'm not saying that your problem doesn't lie else where but these modules are real pains (especially the well's brands). I would suggest an ACdelco replacement if it is found that the module is the culprit (you'll pay more but I have never heard any bad stories of the delco modules)!

Good luck!

Well the shop said it is Arcing so bad that they cant even properly diagnose it. So they are doing a full tune up on it. I am hoping that I simply fudged up the timing so bad, and the full tune up with catch it.

OMG OMG OMG OMG OMG OMG ..

So the shop called today. Tuneup done, diagnostic done, module was bad so replaced ..... 10 minutes down the road.. BANG!!! ... dead in the water again. I know it was a new module because this one was black, the one I put in was white.

Recap. Cap, Roter, wires, plugs, pickup coil, ignition coil, and ignition module are all new.

This time car seemed to be running fine.. no surging, no jumping, no nothing... came off the highway, one turn, 1 BIG surge, 1 BIG jump (im talking rpms going from 0 to redline ... (engine staying relativly the same, hunting a little)).. surged about 3 times... got about 2 more blocks, and bam...... totally dead...

BTW I did feel the base of the the dist and it was very hot.. even 45 minutes after shutdown when the rest of the egine and exhaust was simply warm to the touch. Am I the victim of a bent shaft or something? Is there a way to test this? How freely sould the inner shaft rotate in the outer shaft when the dist is removed?

quote Originally posted by GodSend: BTW I did feel the base of the the dist and it was very hot.. even 45 minutes after shutdown when the rest of the egine and exhaust was simply warm to the touch. Am I the victim of a bent shaft or something? Is there a way to test this? How freely sould the inner shaft rotate in the outer shaft when the dist is removed?

Its highly unlikely that the shaft is bent. The distrib rotor should rotate freely. You should be able to feel the magnetic pickup coil grab ever so slightly when rotating the shaft by hand. I have seen the distributor shaft get all varnished up and needed to be cleaned as well as the bushings inside of the distrib housing that the shaft rides on. Are all the heat shields in place?
If the MAP sensor ( manifold absolute pressure) isnt working properly or if the connection is loose it can cause symtoms like you describe. Most likely it would throw a code and your service engine soon would come on but not necessarily so if the connection were loose. Check all connections at the MAP TPS (throttle position switch) and CTS (coolant temp switch). Check to make sure wiring to the sensors and the coil and distrib are all in good condition as well.

quote Well sure enough the module passed AZ's little test! I explained to the old guy that the failing condition is only hapening once the module heats up. He told me there is no way the module is the cause of this problem and they can not honor the warranty!

That's when yo go home, and either use wire jumpers to apply reverse polarity power or wall current to it and zap it dead (hopefully the smoke emiting diodes will let you know when you are done). Back to a different AZ for a test, "yep. it's shot", and Bob's your uncle.