Petronix Ignitor Problem - PeachParts Mercedes-Benz Forum

thorsen · #1 08-21-2008, 09:47 PM

I replaced the points in my 250C with a Petronix Ignitor and Flame Thrower 3.0 ohm coil this Spring. The car has been running perfectly until the last 2 weeks.

The car will start and run fine, but after 10-15 minutes of driving the engine will begin to sputter and eventually die. It will usually start right back up and run for another minute or two before it dies again.

The Petronix module is usually fairly hot (I can not leave my finger on it for more than 5 seconds) and that is the only thing I can see wrong with it. I know that the Ignitors do not like to be left key-on without the engine running, but I never left the key on for more than 5 minutes.

Does anyone have any suggestions for what to look at next? I have been chasing this down for over a week and I am at my wit's end.

Arthur Dalton · #2 08-21-2008, 10:14 PM

If the module is runnng hot , the suspect is coil or bad ground on the dist plate.
Take a voltage reading from the plate to the battery pos and compare it to bat voltage ..they should be equal.
Test the coils primary resistance when HOT.

The problem w/Pert is you can burn up the module in 30 secs w/key On if the reluctor is lined up at that time. [ which is why I always install a kill sw on Perts]

http://www.vintageperformance.com/retrorockets/troubleshooting.htm

thorsen · #3 08-21-2008, 10:45 PM

Thanks for the links. I did diagnose a bad ground earlier in the week and added a ground wire between the Petronix mounting tab and the distributor body. I just checked and there is no resistance between the breaker plate and the battery negative terminal.

The coil is at 3.0 ohms which is what Petronix recommends for the Ignitor.

I think that the bad ground early in the week probably fried the Ignitor and left it in a condition that it would work until the temperature reaches a certain point, and then it goes intermittent. If I felt like being stranded on the side of the road (again) I could easily test my theory.

I have a new ignition system on the way and we will see if that solves my problem. If not I will start looking at the coil.

Arthur Dalton · #4 08-21-2008, 10:51 PM

You have eliminated the orig. transistor switchgear, correct ???

thorsen · #5 08-21-2008, 11:10 PM

Correct. The transistor box is still located behind the fender but all electrical connections have been taped off.

I am beginning to second-guess my ignition coil set-up. I used the 3-ohm Flame Thrower coil and did not wire in the ceramic resistors.

Arthur Dalton · #6 08-22-2008, 11:23 AM

3 ohm coil should be OK, although you could put the .6 in series w/coil ..I would verify the coils R factor.

thorsen · #7 08-22-2008, 01:52 PM

I actually just went and tested my coil. 1.5 ohms between the + and - terminals. I assumed a 3-ohm coil would be 3 ohms.

Arthur Dalton · #8 08-22-2008, 02:42 PM

Quote:

Originally Posted by thorsen

I actually just went and tested my coil. 1.5 ohms between the + and - terminals. I assumed a 3-ohm coil would be 3 ohms.

They sent you the wrong coil or the primary winding has a short, likely caused by overheating.
I would change the coil rather than add the ballast.

thorsen · #9 08-23-2008, 08:51 PM

Added a new coil and a new ballast resistor. Did a couple of laps around the block and it seems to be running well. The Petronix is no hotter than the ambient under-hood temperatures so I think I am good. I have a Crane Xr-700 on standby as the next move in the event things stop turning.

Thanks for your help Arthur.

Arthur Dalton · #10 08-23-2008, 08:57 PM

Very Good.

I have worked w/both units for years and prefer the Crane , simply on the technical aspects of Optical Switching over Hall Effect switching.
..but either is an big improvement to the old mechanical switching, for sure...........

As I mentioned, a good idea w/Pert is to use a cabin toggle between the ign sw and ballast/coil b/c then you can kill ign when doing other service to the car that requires Key ON w/o fear of burning up the Pert module..that also give one a Theft Deterent kill sw at the same time.
I put a Blinking Led onthe same circuit as the kill sw so passer-bys see the LED Alarm/ARM lamp and it is also a reminder to the owner that ign kill is active...cheap and practical..killing 3 birds w/one stone.

Graham · #11 08-24-2008, 11:17 AM

Arthur,

I have only done step one of the Pertronix installation on my '72 350SL. It just replaces the points but the original electronic module is still in the circuit (I know this is not what you recommend

)

I am concerned about the burn-out possibility, but wondered if this would apply if the Pertronix is not connected directly to the coil, but rather through the MB "switchbox"?

BTW, Only change I have noticed after converting from almost new points to Pertronix, is that engine has to spin a little longer to fire up the Pertronix. If I install a new coil and eliminate the switchbox, what kind of improvement might I see? Car runs well now.

Arthur Dalton · #12 08-24-2008, 12:50 PM

Running the org. SG is like having a switch to switch another Switch.
The Pert module has the switching gear contained in the modulle, so why would you want two S/Gears??
You want direct Pert w/proper coil..nothing else in the circuit.
If one does use a Ballast, you put that on the coil feed ONLY..you always want 12 V feed to the Pert Module or it will have problems at start/low RPMs b/c it is Hall Efeect [ Hall sig ampitude INCREASES with RPM..which is their weakness and why many like Optical switching]

So, 12 V suppy to Pert is the solution to both problems...and the cabin sw is for Pert Model 1, not Pert11...the second generation has a thermal cut-out in case the key is left on when the reluctor is aligned , but the Pert 2 is not as good as the 1......so , cabin sw w/Pert-1 is my recommend....and any good coil w/proper R factor [ dependant on cyl number]

Graham · #13 08-25-2008, 01:17 PM

Quote:

Originally Posted by Arthur Dalton

Running the org. SG is like having a switch to switch another Switch.
The Pert module has the switching gear contained in the modulle, so why would you want two S/Gears??
You want direct Pert w/proper coil..nothing else in the circuit.
If one does use a Ballast, you put that on the coil feed ONLY..you always want 12 V feed to the Pert Module or it will have problems at start/low RPMs b/c it is Hall Efeect [ Hall sig ampitude INCREASES with RPM..which is their weakness and why many like Optical switching]

So, 12 V suppy to Pert is the solution to both problems...and the cabin sw is for Pert Model 1, not Pert11...the second generation has a thermal cut-out in case the key is left on when the reluctor is aligned , but the Pert 2 is not as good as the 1......so , cabin sw w/Pert-1 is my recommend....and any good coil w/proper R factor [ dependant on cyl number]

Arthur,
I have the two switch system, just because I like to take one small step at a time

I do have 12V to the Pertronix - took connection from hot side of first resistor, so no problems there and tach does work.

My question was whether having the two switches in series may actually be safer in that Pertronix would have to be aligned and MB Switchgear closed in order for Pertronix to burn out. Maybe? I don't know, but must put in a disconnect for Pertronix sometime.

I will probably go for a Flamethrower too, but to be honest, don't know why when car runs fine as it is.

Arthur Dalton · #14 08-29-2008, 04:58 PM

You may not be in series , you just are using power from SG.

Some guys do that so the Tach will work.

Regardless, if the Pert hall is energized, it is still on the completed side of a circuit for more time than the module wants to see.
The trick with Pert is to get as much R factor from the coil circuit so as to still have a good spark, yet low amp draw for the Pert module. Most seem to run fine with 4 ohms, but they call for 3 b/c they want the extra spark availability.

Cranes will take a low R coil b/c the SG will handle the extra load ..their XR300 tells you to use NO ballast, but I know guys who have burnt up the module when using that model for steet application.. Normal Driver is best done with the XR700. And they want that mounted where there is airflow for the heat sink fins. The Pert has very little heat disapation b/c it is inside the dist and relies on the base contact.
For Normal operation , either is fine and Pert ! is the preferred model that everyone I know recommends. Pert 2 has some feature for thermal cut out, but they have other ignition wire problems the Pert 1 does not.
Hence , the kill sw...................