need help debugging total instantaneous cutouts while driving

[jeff parker]

I had the exact same problem on my car. It ended up being the Permatune, but a poor ground was the root cause. Apparently a poor ground will cause the Permatune and probably the CDI to fail. I added a 0 gauge ground cable from the engine to the side of the engine compartment. A new Permatune and problem solved. It took me about a year to solve this probem. That was before I found this forum

[Early_S_Man]

Michael,

No, don't do anything to the existing harness!

Regular female spade -- 1/4" Faston connectors of the solderless type fit the male terminals on the Bosch/PermaTune units ... you just have to use a pair of needle-nose pliers to connect them individually, and the CDI-unit needs to be removed from the relay/regulator/CDI panel when you connect the wires! Then bolt the CDI-unit to the panel. Good luck!

[mhackney]

Warren, I got the stuff and rewired - bypassing the entire CDI harness. I put the Permatune and original Bosch blue coil back in. I also too the entire fuse panel bracket off and lo and behold, I found an absolutely corroded ground wire. I cleaned everything up, cleaned all the contacts and reassembled. Then I made the new wiring harness and wired it up. I tapped the red into the Sportomatic slot on the power side and grounded directly to the coil bracket as you suggested.

It fired right up (a good sign!) and I took it out for a 15 minute spin. No problems yet but I need to put some more miles on hot days. One thing though, that panel ground was really bad!

Cross those fingers! And Thanks again to everyone for helping out!

Michael

[Early_S_Man]

Michael,

It sounds like you found the source of your problems!

You probably don't need the 'bypass' harness, now. Wouldn't hurt to throw it in the trunk with tools and spares, though!

If the Bosch CDI works well, that is the system I would leave on the car! The PermaTune can be a good spare for you in case of future emergencies!

[mhackney]

I think I'll swap over to the Bosch CDI and new coil tomorrow and see what happens. Given how much worse it was with that combo the problem would certainly show up sooner. Then, once the problem appears to have been corrected, I'll leave the new direct ground wire and replace the temporary 3 wire harness with the stock. Would you suggest soaking the connectors in vinegar to make sure they are clean? They are nearly impossible to clean mechanically.

Thanks again! I hope I'm on the right track.

[mhackney]

Well, I left the original CDI (Permatune) and Bosch blue coil in because I wanted to eliminate variables - basically testing the new "temporary" wiring harness and cleaned up ground. I have to say the car just felt a lot stronger and more responsive overall. On the way home just now - its 90 in Boston - I was free and clear and it was pulling strong. Then, I got a stall, immediately followed by several more then a backfire. I finished the trip home uneventfully. So, the question is, why?!

Warren, would you recommend that I put the Bosch CDI and new Bosch (non-blue) coil in and see what happens? Is it possible that I had a couple of problems that were complicating diagnosis. The engine really did sound and feel much better after the ground cleanup and new harness (I know it wasn't my imagination!).

Thanks again,

Michael

[jeff parker]

Make sure you have a good ground , then replace the Permatune. That is why it took me a year to solve. I would go through cleaning contacts and replacing wires just like you. It would seem to be fixed and then BAM!! fail again. I wouldn't consider it fixed until you put about 500 failure free miles on it.

[mhackney]

Ok, so I removed my Optima battery and cleaned all the contacts (ground & +). The positive feeds back t the engine compartment were loose and needed recrimping. For grins I thought I would check my dwell with my new Gastester Pro (the one with voltage, dwell & rpm built in along with CO -very cool). Well, it was 24.2! I pulled the points and although they were not horrible I replaced them, gapped to what ultimately was .014" and got the dwell right at 40.0. At least my idle problem went away! The idle dropped from the 1600 or so I had befre down to 800 RPM.

Any chance that such a low dwell could lead to intermittent stalls? It seems resonable that if the gap was just on the verge of too great that it could be a contributor to stalls.

thanks again!
Michael

[mhackney]

Ok, so the situation is better but not perfect! In the last 3 days I have had 1 quick "stall" during the evening comute home. It has been relatively cool and dry in Boston this week - perfect New England driving weather! Anyway, these were very quick flickers - not even completely down to 0 RPM. No backfire either. This is still with the Permatune and original Bosch Blue coil and bypassed wiring harness. I'm chomping at the bit to put the Bosch CDI and new coil in and see what happens - should be able to do that tomorrow evening.

Meanwhile, it does seem that my timing is too far retarded - about 0 degrees at 1400 RPM. My plan is to find the advance curve for my dizzy (which I posted on another thread and Early _S_Man is going to provide later!) and pick 1500 rpm as my "taarget" to set the advance to. I don;t have enough experience to know how this will affect the idle speed. If my timing is that much retarded and I advance it to where it should be - will the idle speed drop, raise or stay the same? I don't want to start mucking with too many things at one time and it seems logical to get the timing as close as possible given that it seems pretty far out right now.

Does this make sense or am I going mad?

thanks!
Michael

[jkeyzer]

If you screw the bleed screws all the way in and your idle is still above 1000 rpm there is something wrong. Make sure your throttle linkages are fully returning to the stops and not stuck open.

Does your car have an RPM transducer (that works) and a microswitch? Could that be cutting off fuel and then intermittently causing the car to stall since your idle speed is so high?

Just a thought. Sounds ignition related (backfires after it restarts, I had this problem when I had bad points) though.

[mhackney]

Jeff,

I have cleaned, greased and checked all of the throttle linkages and they seem to be in good working order. They were adjusted/correlated by the PO's wrench and my check measurements look good.

I have not completely screwed in the bleed screws so I don't know what the results would be - sounds like a good test. I do know that #4 seems to be very insensitve to adjustments whereas the other 5 cylinders respond to adjusting the bleed screw.

I have checked and adjusted the microswitch and it seems to be in good working order.

I don't know about the RPM transducer. I have not verified that my car has one. How does one check this?

I should say that I have not had a single backfire or complete engine stall after installing the new points and setting the dwell properly and cleaning the ground and power connections. Now I just get the occasional "blib" on the tach. It has been quite mild in Boston this week (low 70s) so I haven't had any good hot driving days to put it through its paces. Sounds like I have a few things to test/do.

Perserverance!

thanks,
Michael

[jkeyzer]

If the microswitch works then you have a working RPM transducer. It is on the engine electrical panel next to the regulator and rear window defrost relay if your car has both.

Try opening the throttle and pushing on the microswitch by hand. Does the engine rpm drop drastically and then come back up again in a slow oscillation? If so, the system is working. You could try removing the wires that go to the microswitch and see if your stalling problems persist.

[mhackney]

Ok, after installing the Bosch CD and new Bosch (non blue) coil, the car has been running great. I've put >100 miles w/o a hickup but it has been relatively cool. Today it gets to 90 here in Beantown so that will be the ultimate test. That said, when I first installed the Bosch CDI it wouldn't even make it 1/2 mile without severely dropping out. I think I traced that to the faulty grounding of the panel in the engine compartment. Also, I've noticed with the Bosch CDI and new coil that my idle speed is down to 1400 rpm - a drop of 200 over the Permatune unit? I triple checked this and there really is a measurable difference. Does this make any sense?

Finally, I did check the RPM transducer, microswitch, etc and everything is functioning normally. After I make it trough the hot weather today (hopefully), I plan to work on lowering the idle. I've read the Bosch MFI docs and they have some instructions on cleaning dirty bleed screws. I even picked up a can of their recommended cleaner (basically a carb cleaner).

Michael

[Steve Marshall]

I had a similar problem that turned out to be the coil. But the guy that helped me run it down had an identical problem to the one you are experiencing. His car is a 70 911s with MFI. After going through everything, like you have have, the problem persisted, although in a diminished capacity. BA recommended new plug wires and low and behold that was it.

[mhackney]

Ok, so I drove over 50 miles in 94 degree heat and humidity without a hickup. I haven;t been able to do that for over a month!

So to recap, I believe my stalls were due to a combination of factors. The things I did to make noticible improvements included 1) cleaning the grounds at the battery, transmission and the panel in the engine compartment. Cleaning the + lead at the battery and cleaning all of the contacts and bypassing the 4 wire harness to the Permatune CD with a home made harness, 2) replacing the worn points and especially regapping them to increase the dwell from 24.2 to 40.0. And finally, the ultimate "fix" was replacing the coil and Permatune with a used Bosch CD and a new Bosch coil.

For those in the future reading this thread for help - my problem was ultimately a combo of a bad panel ground and faulty coil (or CD).

Thanks again to everyone offering help/comments/suggestions and experiences! A special thanks to Warren who truly is the "early_s_MAN"!

Michael