Tachometer problems with new Permatune

Lambotsavy · #1 (**permalink**) 04-28-2007, 10:12 AM

I have had to reinstall my Bosch ingnition as the Permatune cannot go past 5500 RPM's in any gear. What happens is when it surpasses 5500 RPM's the car sputters and the RPM's drop to about 2500 RPM's. Has anyone experienced this and is their a simple fix as I would like to reinstall the permatune. Thanks in advance.

raymond · #2 (**permalink**) 04-28-2007, 03:23 PM

That's strange I didn't experience such problems, not with the permatune nor with the msd...

You can send the unit back for inspection, Lonnie will check it and also change the rev limiter wherever you want.

Did you check your distributor cap, and timing advance, perhaps you have these problems because of the stronger spark?

Lambotsavy · #3 (**permalink**) 04-28-2007, 03:43 PM

Raymond as always thanks for your help. My mechanic has checked everything you mentioned and had isolated the problem to either the ignition system or the fuel pump, but as soon as we put the Bosch back in the problem went away. My problem now is the response on the Bosch is nothing like the Permatune. I will send it back to Lonnie tomorrow and see if they can figure it out. Thanks again.

lxmichaels · #4 (**permalink**) 04-28-2007, 03:49 PM

Just a thought here...

When I first got my car the rotor was a Bosch part that had a cut-off rev-limiter (5850rpm) mechanism as part of it. Basically a plunger that extended because of the centrifugal action and grounded against a post that made contact with the center shaft of the distributor.

- Larry

raymond · #5 (**permalink**) 04-29-2007, 12:14 AM

interesting to know about this rotor, i think in this particular case it must be the box since with the original bosch it works as it should.
What we found out with all these tachos, the accuracy is a nightmare, they all show too much rpm at low revs but about 500 too less at 7000...

On my tacho the engine cut at about 6400-6600 but the engine turned already 7000.

Lambotsavy · #6 (**permalink**) 12-09-2007, 03:14 PM

I finally found out what had caused the shutting down of my Permatune after approching 5,000 rpm's. It only took 8 months, but Lonnie was away for almost 3 months, so nothing was done. The problem was as simple as someone over at Plasmatronics putting a Model 930902 (identical looking box and connector for 76-77 porsche 911 6 cylinder) in a Model 931902 (for the Jalpa) box. The new one works like a charm and does not have a rev limiter.
This was why no one on this site had heard of or experienced a similar problem. pics below to show both identical boxes. The one on the left is shown on the Permatune site as the Porsche model 930902 and the one on the right as the Jalpa model 931902.

raymond · #7 (**permalink**) 12-09-2007, 10:37 PM

Unbelievable, but since the model is not stamped outside this can happen.
I ordered the first Jalpa box from Lonnie about 3 years ago, he raised then the rev limit to 7200 but I later found out that the box was correct, the tacho in our cars is inaccurate...
The Jalpa box was mainly invented by Lonnie for me and Bill Overhauser, he found that the Porsche 930 box is almost the same, that's also the reason for the confusion.

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