need help - pertronix trouble at low idle speeds?

[MTribe]

Anyone know if low idle speeds can damage a Pertronix Ignitor unit?

Here's what I'm experiencing--car runs great (71 TR6) at 1200 rpm idle. I drop it down to 850. Runs fine for a few minutes, but then engine suddenly loses power and starts sputtering and popping. It isn't a slight loss of power--the car barely runs, as if only one cylinder was firing.

I did a bunch of debugging, including increasing idle speed again, and couldn't make the engine run smoothly--no change at all, still sputtering and popping with almost no power. Until I put a new pertronix unit in there--bam, works great again, at 1200 rpm idle speed.

So I drive around the neighborhood. Then pull over and decrease idle again to 850. About two minutes later, same thing--sputtering and popping with almost no power.

I do have a GP2 (streetable, mildly tuned) cam, and CR of 9.5. I wonder if the lumpy idle of the cam is causing trouble?

At this point I'm about out of ideas. Anyone experience this or have any ideas?

 

[poolboy]

Can you measure the voltage that your alternator is putting out at 850 ?

 

[TR3driver]

You won't have that problem with points ...

 

[TR3driver]

You won't have that problem with points ... or just about any other 'electronic' conversion. And you've already had the Pertronix "easier starts, better running, better gas mileage, more reliable" experience ...

BTW, my guess would be that you're not getting good thermal contact between the module and the adapter plate. The module both generates heat and can be damaged by too much (which makes attaching it to the engine a Bad Idea IMO).

 

[SkinnedKnuckles]

I'm curious. With the Crane ignition (which I have) you go through an exercise in "phasing", as they call it, to be sure the rotor is in the correct position when the spark fires. If the rotor is leading or lagging the distributor electrodes when firing you can get low or high speed misses, or it may not run at all. Is there a similar check with Pertronix?

 

[MTribe]

OK--going out to measure voltage at 850...

RE overheating... do you think the slower idle could make the unit heat up more?

 

[donbmw]

Change your plug wires, distrubort cap and rotor. I have had simalar problems on my TR3 with the pertonix isntalled. I went back to points have not had any problems in over two years now.

Don

 

[MTribe]

poolboy-- battery voltage 14.15V @ ~850 rpm, 14.20V @ ~1200 rpm. Doesn't vary much with rpm.

Don--the rotor and cap are new. Wires are new-ish... though I could try a new set of those.

Brent--no phasing process. Only thing is setting the gap between the magnetic rotor and module, but I'm back to using my old one which is non-adjustable anyway.

Randall--hmm, sounds like you're not a fan? ; ) I wonder if the lower idle speed causes more heat in the module?

Just went out and started car. Was rough as before. However, it smoothed out after about 5 min of idling at ~1200 rpm. Drove around the neighborhood, very smooth for about 5 minutes, then lost power going up a hill. Then cycled through running fine and a little rough next 5 minutes, then got very rough again. Limped home and checked plugs--not fouled.

Does that provide any more clues? I think I'll go try the points to see if the problem persists.

 

[TonyPanchot]

When is the last time you bought petrol ?
sounds like water in the carbs

 

[SkinnedKnuckles]

I guess the Petronix set-up is built so the phasing isn't supposed to be a problem. But it's still unclear to me since I've not seen one. Has to be tied to the cam lobes... How is the "module" secured or centered? I'm curious because electronic timing should be the only way to go, yet quite a few go back to points for stumbling/performance reasons.

 

[MTribe]

Tony, RE gas, the car was sitting quite a while while nearly empty while doing some work on it. I actually noticed this problem for the first time soon after (maybe 5 miles) after filling up.

How does water commonly get in the carbs? I actually had the car at a body shop, and I don't know how they washed it, but the carpets were soaked implying lots of water, so it's possible they washed under the hood too.

Could a bad tank of gas cause this?

 

[poolboy]

I guess the Petronix set-up is built so the phasing isn't supposed to be a problem. But it's still unclear to me since I've not seen one. Has to be tied to the cam lobes... How is the "module" secured or centered? I'm curious because electronic timing should be the only way to go, yet quite a few go back to points for stumbling/performance reasons.

There's a magnet that slips over the distributor's shaft. The ID of the magnet conforms to the lobes of the shaft, the OD is circular.
You remove the points and condensor, replace them with an adaptoor plate that is specific to the distributor type. Upon the plate the "pick up module" is mounted.
2 wires exit the distributor where the old low tension wire was attached. One Pertronix wire goes to the - terminal of the coil and the other to an 8 to 12 volt keyed source..
I sense a Randall moment along about now..
At any rate, those 2 wires are the only visual evidence that the distributor is anything but stock..no external module, it's all under the cap.

 

[TonyPanchot]

You can get water in gas from the station
been there done that
and was perplexed until, lucky for me the rubber hose under the fuel pump was leaking and I noticed droplets of water on top of the floor
I too thought it was a dist issue

 

[SkinnedKnuckles]

Thanks, Poolboy. That's exactly my question - how does that "pick-up module" know where the rotor is in relation to the distributor/plug electrodes? Sounds like it doesn't - you're either lucky (stock setting), or not. If there's been a change to the dizzy in relation to the drive gear - moved a cog or two - the "phase" has been shifted. Does this sound plausible?

I just went through this with my Crane. Had a horrible stumble when winding up rpm's. This after having the dizzy rebuilt and I thought the phasing was right from previous settings. Lo & behold, when I put my glasses on during a recheck, I found the rotor was way off the dist electrode when firing. Evidence was seen when examining the rotor - the oxide "crust" was at the very end. So always wear your glasses when tuning.

 

[MTribe]

Tony--I think you might be onto something. I just took it for a 30 min drive. I live in SF with lots of hills, so tried the car under a variety of situations. I could not correlate the sputtering and lack of power with anything--loading, incline, change of incline, accelerating, etc. It sporadically gets weak, then strong again. It was improving as I was driving around, too. The way it feels and sounds would be totally consistent with water getting mixed in. I think I'll go try to burn through the tank and then refill and see if that was it.

 

[poolboy]

Thanks, Poolboy. That's exactly my question - how does that "pick-up module" know where the rotor is in relation to the distributor/plug electrodes? Sounds like it doesn't - you're either lucky (stock setting), or not. If there's been a change to the dizzy in relation to the drive gear - moved a cog or two - the "phase" has been shifted. Does this sound plausible?

I just went through this with my Crane. Had a horrible stumble when winding up rpm's. This after having the dizzy rebuilt and I thought the phasing was right from previous settings. Lo & behold, when I put my glasses on during a recheck, I found the rotor was way off the dist electrode when firing. Evidence was seen when examining the rotor - the oxide "crust" was at the very end. So always wear your glasses when tuning.

Well, the pick up being mounted on the same plate as points responds to the centrifugal advance weights the same as points and of course you can still rotate the dizzy just as with points to set the ignition timing.
All in all it's just a replacement for the points and functions as a switch for the charge and discharge of the coil.
Once the Pertonix is installed the timing does need to be reset, because from what I've seen the pick-up is not in the exact same place on the plate in relation to the lobe as the points, but ususally it just requires a few degrees rotation of the dizzy to get back to the sweet spot..
The "phasing" that you mentioned by looking at the spot on the rotor, according to Jeff at Advanced, is compensated for with the addition of the micro adjustment wheel which moves the mounting plate.
Without the wheel, I'm not sure how the phasing is adjusted.

 

[TR3driver]

Thanks, Poolboy. That's exactly my question - how does that "pick-up module" know where the rotor is in relation to the distributor/plug electrodes?

Basically the same way the points "know". The relationship between the point cam & rotor is fixed, and the magnet assembly for the Pertronix indexes to the point cam. So the phasing 'should' be fixed by the design of the magnet assembly, and the adapter bracket (which is custom for each distributor and ties into the original points mounting location).

This is different than the Crane conversions, where you get a universal bracket and have to adjust the phasing yourself.

I tried installing a Pertronix module on my TR3 project earlier this year. Didn't run as badly as yours, but it was much more difficult to start (I literally ran the battery down once, trying to get it to fire), and didn't seem to run as well as points. I initially thought the problem must lie elsewhere, so I replaced the cap, rotor, wires, plugs and coil; all with no discernible difference.

Then I removed the Pertronix and reinstalled the newish points & condenser that I had taken off. The difference was immediate and amazing! It now fires literally on the first turn (although I've got a bowl seal leaking so it won't always stay running), and runs absolutely great.

I probably should return it to Pertronix, as there is clearly some problem with the unit (either the module or the magnet ring), but I haven't tried yet.

FWIW, I had a Crane XR3000 on the wrecked TR3A and was not particularly impressed with it either. It ran OK once I got all the installation problems sorted out ... turned out the rotor was hitting the pickup and causing weird problems ... but no better than points and not as good as the MSD 6A I had been using previously (until it died).

Eventually, when I build a "hot rod" motor, I think I'll try something like an XR700 firing a MSD 6A. But for now, the points ain't broke, so I'm not going to fix them.

 

[TR3driver]

I wonder if the lower idle speed causes more heat in the module?

The Pertronix module contains a power transistor that mimics the action of the points, ie connects the coil to ground during the dwell period, then suddenly opens so the inductive kickback from the coil causes the spark. The coil is around 3 ohms DC, so once it's magnetic core is saturated, there is about 4 amps flowing through that power transistor. I don't know, but I would guess that it is a silicon type, meaning it's minimum voltage drop is around 0.7 volts and hence it dissipates about 2.8 watts while 'closed'. Pertronix has warned that it cannot handle that much heat continuously (the old warning to not leave the key on with the engine not running).

So, my theory is that the slow idle let it heat up for longer each cycle, which pushed it over the edge to "too hot". But that is strictly a WAG, I can't prove it.

Try the points, prove me wrong.

 

[TonyPanchot]

Put in some Heet and 93 octane

that will cure your woes

some times it is the simplest explanation

is the answer

 

[MTribe]

Appears to be consistent with water in the system somewhere... I have driven through two tanks of gas and less and less issue with it, although it does still happen. Also tried two bottles of heet, one in each tank. Will post more if I discover more. Thanks for all the input!