engine and drivetrain OUT OF CONTROL RPM GAUGE MET WITH VIOLENT MISFIRES

[FAST5]

Just as the title reads. The car feels as though it is running on 3 cylinders. The engine shakes when I disconnect an of the spark plug wires, so I assume those are okay. I fiddled with some adjustment screws on the Weber, but nothing helped. The car has petronix and an electronic choke. I was told it might be the coil, but from my understanding, the coil just poops out at once, and not gradually. The car spits and hesitates at WOT, and it immediately cuts all power at a stanstill.

Sounds like its more combustion-related, so why the hell is the RPM gauge OUT OF CONTROL?!?!

Thanks guys....

[c.d.iesel]

what's yer BATTERY VOLTAGE ?

AT 3000 RPM ?

AND WITH THE KEY OFF - NOTHING ON ?

[Zenon]

The crazy tach action is a major clue that one of the connections in the coil primary circuit is flaky.

Check all the spade connections at the coil and confirm your pertronix wiring is solid. Give all the female connectors a squeeze with pliers to tighten them up - they should be very snug on the spades. Also, if the original black wire for the points was not used in the pertronix install, make sure it is not dangling and shorting against something. Finally, make sure the pertronix itself is not loose in the dizzy (it grounds the coil via the mounting plate) and that the little braided ground wire between the dizzy body and points plate is still intact.

Hope this helps.

regards,

Zenon

[FAST5]

The crazy tach action is a major clue that one of the connections in the coil primary circuit is flaky.

Check all the spade connections at the coil and confirm your pertronix wiring is solid. Give all the female connectors a squeeze with pliers to tighten them up - they should be very snug on the spades. Also, if the original black wire for the points was not used in the pertronix install, make sure it is not dangling and shorting against something. Finally, make sure the pertronix itself is not loose in the dizzy (it grounds the coil via the mounting plate) and that the little braided ground wire between the dizzy body and points plate is still intact.

Hope this helps.

regards,

Zenon

Hey Zenon,

Thanks so much for your advice. Unfortunately, it did not yield any changes to the situation I am having. I did however drive it on a stretch of road just to see what the max speed was. It hit a brick wall at 65. I am led to believe that one of the cylinders might not be firing? But in this, what would explain the bouncing tach? If you don't have any other suggestions, or anyone else for that matter, it's on its way to the doctor tomorrow.

-Kevin

[Zenon]

Hey Zenon,

Thanks so much for your advice. Unfortunately, it did not yield any changes to the situation I am having. I did however drive it on a stretch of road just to see what the max speed was. It hit a brick wall at 65. I am led to believe that one of the cylinders might not be firing? But in this, what would explain the bouncing tach? If you don't have any other suggestions, or anyone else for that matter, it's on its way to the doctor tomorrow.

-Kevin

The low top speed makes sense 'cause your ignition is fubar - not gonna make much power!

Perhaps you have to look harder for the bad connection. Also, try unplugging the tach wire at the coil - I have heard of tachs developing an internal short that kills the ignition (since it is connected directly to the negative side of the coil by the black wire) so there is a chance yours is doing so intermittently on its way out. Maybe hook a test light to the coil + and see what it does when the problem occurs.

I am still firmly of the opinion that there is a 99.99% probability your problem is electrical/ignition. Think about it... Even when you completely unplug a spark plug wire, the tach does not normally go nuts. There is no kind of internal engine or carburetion problem I can imagine that would make the tach go nuts and there is no way the engine rpms are actually changing that rapidly or erratically.

A good shop will figure out it is an electrical fault very quickly, I should think. Of course, if you did let a shop, say, rebuild your carb for $500 or head for $1000, do you think they would ever tell you that the problem was really a chafed wire that they only eventually found because the problem was still there after all the other work?

(As you can probably tell, I don't have a high opinion of repair shops in general... ;-))

regards,

Zenon

[FAST5]

Hey Zenon,

Thanks so much for your advice. Unfortunately, it did not yield any changes to the situation I am having. I did however drive it on a stretch of road just to see what the max speed was. It hit a brick wall at 65. I am led to believe that one of the cylinders might not be firing? But in this, what would explain the bouncing tach? If you don't have any other suggestions, or anyone else for that matter, it's on its way to the doctor tomorrow.

-Kevin

The low top speed makes sense 'cause your ignition is fubar - not gonna make much power!

Perhaps you have to look harder for the bad connection. Also, try unplugging the tach wire at the coil - I have heard of tachs developing an internal short that kills the ignition (since it is connected directly to the negative side of the coil by the black wire) so there is a chance yours is doing so intermittently on its way out. Maybe hook a test light to the coil + and see what it does when the problem occurs.

I am still firmly of the opinion that there is a 99.99% probability your problem is electrical/ignition. Think about it... Even when you completely unplug a spark plug wire, the tach does not normally go nuts. There is no kind of internal engine or carburetion problem I can imagine that would make the tach go nuts and there is no way the engine rpms are actually changing that rapidly or erratically.

A good shop will figure out it is an electrical fault very quickly, I should think. Of course, if you did let a shop, say, rebuild your carb for $500 or head for $1000, do you think they would ever tell you that the problem was really a chafed wire that they only eventually found because the problem was still there after all the other work?

(As you can probably tell, I don't have a high opinion of repair shops in general... ;-))

regards,

Zenon

EXCELLENT! I was hoping that it would not be an internal problem. The erratic tach sort of kept me in high hopes, and your valid points simply exemplified my thinking.

You are very right...repair shops can be swindlers. That's what I'm trying to avoid. I have posted this issue on another BMW forum, and people say it could be the fuel filter.

Possible?

[Zenon]

I have posted this issue on another BMW forum, and people say it could be the fuel filter.

Possible?

Still would not explain the crazy tach. Besides, when a fuel filter is restrictive the car will still idle and run at low power as if nothing was wrong, then only start to die when you need more fuel for higher power over more than a few seconds - usually on the highway or going up a long hill.

Electrical, electrical, electrical!

;-)

regards,

Zenon

[_z_]

ya why I suggested the coil on the other forum. The tach is wired into the coil so its got to be something within that part of the system (like Zenon said theres no way the carb can make your tach peg like that ).

If you can't find a bad connection and you can't track down a short It might worth while to spring for a new coil .. what like 20-30 bucks or something? That'll be cheaper than a mechanic, and if its not that you've got a new coil!

Beyond doing all that stuff Zenon said that is -- good advice

[Zenon]

Seems that great Z's think alike. ;-)

One more tip: Look not just for loose connections but also carefully check the wires where they attach to the connectors. Four out of five proctologists agree that 99% of wire breaks are at the connector. Give them a light tug and see if they pull out/break off or feel extra flexy - the most intermittent of intermittents happen when the wire strands are broken but still slightly touching under the misleadingly OK-looking insulation.

regards,

Zenon

[Anthony]

I agree with Zenon, After experiencing these exact symptoms at the track on my 4 throttle injected motor I reviewed the entire ignition circuit.

My tach would start to jump and bounce, I could gingerly work the throttle to keep the car running but ultimately it would backfire and die.

In the end it was actually a ground. Make sure all of your grounds are clean!

[John_in_VA]

if you still have one with the Pertronics setup.

I've only had a problem like this once in >26 yrs of ownership, and the '70 would backfire and the tach drop to zero before firing back up. We pull the distributor/checked it/rechecked cap, rotor, etc. - loose wire at the condensor = cheap fix but time-consuming to track down!

[FAST5]

Just wanted to say thanks to everyone, especially Zenon, for their recommendations. It turned out that it was an electrical problem, something to do with the distributor and the petronix. I fiddled with it a little bit, and it drove fine dor about 5 mins, and the hesitations and erratic RPMs came back again.

My girlfriend followed me to the mechanic shop yesterday and she said she saw in full view, foot-long flames come out of the exhaust. It was met with every backfire. Kind of cool. I almost wanted to not get it fixed.

Hahaha. But thanks again to everyone, at least I know not to let the mechanic take me to the cleaners.

-Kevin

[Zenon]

You are most welcome. Please be sure to let us know what the exact cause turns out to be.

regards,

Zenon