74 J20 360 v8 Ignition

[beartrace]

Went to install new points and condenser. Pulled the ignition cap, the rotor and a plastic dish and saw what is in the photo. Never seen this before. ( I thought the Jeep had a bad condenser as it started irregularly, may run for a while and the quit.)

j20 s.JPG

[img]j20%20Ignition.JPG[/img]

[Nikkormat]

Bad news, you somehow got a prestolite distributor. Not a points distributor.

[Stuka]

'73 was the last full year for points. They changed to the Prestolite in '74.

The Prestolite is the worst ignition system to ever come in a Jeep. From the sounds of it your magnetic pickup, or more likely, the ignition module is failing. The ignition modules are very expensive, and the ones being built now fail continually.

However, good news. You can buy a points distributer and drop it right in, almost. You have to slightly change the wiring, but nothing major. Took me all of an hour to do the whole swap in my '75. That, or put an HEI in it from CRTPerformance or the like.

[Nikkormat]

74 was the last year for points and some early 75's still received points.

[tgreese]

74 was the last year for points and some early 75's still received points.

Yep, Prestolite was used '75 through '77. Easiest way to identify it is by the plastic vacuum advance can.

[Stuka]

74 was the last year for points and some early 75's still received points.

I have never actually seen a '75 with points (anecdotal I know).

But either way, he really should get rid of that ignition.

[beartrace]

Thank you..

[FSJunkie]

Prestolite works great if you know how to fix it. 30,000 trouble-free miles on my own Prestolite so far.

You're problem is likely the module. One of the solder connections inside has cracked and breaks contact when it gets hot then makes contact again when it cools. Replacing the module for $35 is the easiest option, or you could melt the potting material out of the control module and resolder the connection. There aren't many components inside a Prestolite module, just a few capacitors, resistors, and transistors. You could probably build one from scratch with generic components. A good module will last 50,000 miles or more.

Sensors seldom go bad but they can get out of adjustment and hit the rotor. They should be adjusted to never hit the rotor no matter what vacuum is applied to the vacuum advance. The sensor wires are fragile and the electrical signal within is sensitive to the length and gauge of the wire, so splices and repairs must be handled with care to duplicate the original. Try to keep the sensor wires away from the spark plug wires and use dielectric grease on the connections to prevent corrosion.

A few drops of oil on the wick under the rotor will help prevent wear. It's a good idea to clean and lubricate the mechanical advance weight pivots and cams once every 40 years along with the upper bearing.

Carry a spare module and ignition coil with you.

[Jeepguyp]

Wow, I've heard few people praise the much-maligned prestolite. I did once upon a time. I drove a CJ, Wagoneer and a J10, all V8 (well the CJ was a 258 for a while before I put in a 360) and all had the Prestolite (formely owned by Studebaker) system. I rode on many a trip and 4-wheel outing. Sometimes on a gravel road "wash board' It would backfire and buck. A few times my CJ would just up and quit with no warning. Along the way I learned how to set the gap on the reluctor(so the pick-up was in spec), I even modified a small puller for trigger wheels. How to shim the bottom so the gear would TURN FREE AND NOT HAVE TO MUCH END-PLAY. BUt I found myself carrying around a spare dizzy and module in whatever Jeep I was using. sad to say, just couldn't get where I totally trusted it, good connectors or not. Going back to a AC Delco points type, with a Petronix conversion, and I never had another problem. Did a HEI on 1, its a bit better, but more aggravating to install. The petronix is EASY, no giant cap with a coil in the middle..... Sorry FSJunkie, just my 2 cents..... Want my old Presto stuff? Got some marine-grade distributor caps, dizzies, etc

[Stuka]

Wow, I've heard few people praise the much-maligned prestolite. I did once upon a time. I drove a CJ, Wagoneer and a J10, all V8 (well the CJ was a 258 for a while before I put in a 360) and all had the Prestolite (formely owned by Studebaker) system. I rode on many a trip and 4-wheel outing. Sometimes on a gravel road "wash board' It would backfire and buck. A few times my CJ would just up and quit with no warning. Along the way I learned how to set the gap on the reluctor(so the pick-up was in spec), I even modified a small puller for trigger wheels. How to shim the bottom so the gear would TURN FREE AND NOT HAVE TO MUCH END-PLAY. BUt I found myself carrying around a spare dizzy and module in whatever Jeep I was using. sad to say, just couldn't get where I totally trusted it, good connectors or not. Going back to a AC Delco points type, with a Petronix conversion, and I never had another problem. Did a HEI on 1, its a bit better, but more aggravating to install. The petronix is EASY, no giant cap with a coil in the middle..... Sorry FSJunkie, just my 2 cents..... Want my old Presto stuff? Got some marine-grade distributor caps, dizzies, etc

I agree with you, it was a pain in my Cherokee. Always had to have spare modules. The magnetic pickup in the prestolite dizzy was picky on temps. I had a lot more trust in my Jeep when I pulled it and put in points.

[Stuka]

Prestolite works great if you know how to fix it. 30,000 trouble-free miles on my own Prestolite so far.

You're problem is likely the module. One of the solder connections inside has cracked and breaks contact when it gets hot then makes contact again when it cools. Replacing the module for $35 is the easiest option, or you could melt the potting material out of the control module and resolder the connection. There aren't many components inside a Prestolite module, just a few capacitors, resistors, and transistors. You could probably build one from scratch with generic components. A good module will last 50,000 miles or more.

Sensors seldom go bad but they can get out of adjustment and hit the rotor. They should be adjusted to never hit the rotor no matter what vacuum is applied to the vacuum advance. The sensor wires are fragile and the electrical signal within is sensitive to the length and gauge of the wire, so splices and repairs must be handled with care to duplicate the original. Try to keep the sensor wires away from the spark plug wires and use dielectric grease on the connections to prevent corrosion.

A few drops of oil on the wick under the rotor will help prevent wear. It's a good idea to clean and lubricate the mechanical advance weight pivots and cams once every 40 years along with the upper bearing.

Carry a spare module and ignition coil with you.

So did you swap out your points for a prestolite then? Or was this in another Jeep that you don't have currently?

[Dusty]

My Presto Junko distributor works GREAT now!





















As a oil priming tool for new motors!

[FSJunkie]

So did you swap out your points for a prestolite then? Or was this in another Jeep that you don't have currently?

No, it's in my daily driver 1977 AMC Hornet with a 232 I6. My Jeep is currently on a Pertronix because my distributor shaft bushings are too worn to give stable dwell on points, but when I rebush it I might go back to points.

I don't know what to say about people having problems with their Prestolite ignition. Like I said, mine has given me 30,000 miles and three years of trouble-free service. I read the manual and understand how it works and how to repair it. Prestolite is actually kind of neat because it gives hotter spark than points and also has variable dwell to produce exceptionally long spark times at idle, making for extremely stable combustion. By everything I've found it seems like a great ignition system.

Sorry I'm the only one who has good luck with it.

[Stuka]

So did you swap out your points for a prestolite then? Or was this in another Jeep that you don't have currently?

No, it's in my daily driver 1977 AMC Hornet with a 232 I6. My Jeep is currently on a Pertronix because my distributor shaft bushings are too worn to give stable dwell on points, but when I rebush it I might go back to points.

I don't know what to say about people having problems with their Prestolite ignition. Like I said, mine has given me 30,000 miles and three years of trouble-free service. I read the manual and understand how it works and how to repair it. Prestolite is actually kind of neat because it gives hotter spark than points and also has variable dwell to produce exceptionally long spark times at idle, making for extremely stable combustion. By everything I've found it seems like a great ignition system.

Sorry I'm the only one who has good luck with it.

No need to be sorry, I am just seriously wondering what you have done differently. As just about everybody, myself included, has had rotten luck with them.

[Jeepguyp]

Well, it was a flawed design, even AMC recognized that.Thats why they went to the more robust and reliable Motorcraft set-up. I worked for a shop, back in the 90s, run\owned by a former AMC\Jeep tech from the 70s. He told me how they held tech classes about it, and how they connected or soldered the connections directly. I have an ORIGINAL 76 service manual, it addresses the connectors and so forth. Electronic ignition was a new thing, Prestolite was what our guys had. .... No, I don't think youd wanna take points OFF a vehicle to switch to Presto. Heck, that would be a wiring job with the module and all, and not really an upgrade of any kind even though its electronic. You got points, then put on Petronix! I've had that on my rigs, ZERO trouble.... until you leave the switch in the "on" position all night, LOL. oops, kills the module.
Yea if your gonna rebush your worn dizzy, why fool with points? Stay with the Petronix. They offer upgrade coils, where you can open the plugs gap more. My CJ loves it. ... HEI seems to work superbly, I just don't like the cluttered area close to the power steering, just opld fashioned and like an external coil. Bigger wires with female ends required (late 80s Ford V8).... Once again, I aint flaming the Presto, I'm only a practical guy is all

[babywag]

Yep prestolite was a really bad system only used for 3 years for several reasons.
Couldn't pay me to run it, and no reason to keep it on any vehicle.

[letank]

Pertronix rules, when I swapped points to pertronix, even the 8 year old kids asked me if I had replaced the engine...

[Tatsadasayago]

Having owned many Presto-Lite jeeps and working on them at the dealership I learned that there were the occasional PL systems that worked great and never seemed to break.
Being an old school Maico dirt bike rider I learned a saying about the Bing carbs they used: "He who has a good Bing has a good Thing".
Most of them were garbage, but every so often a good one would appear and surprise everyone.

I would never willingly drive an FSJ with a PL ignition system. I have enough things to worry about that are likely to strand me as it is!

[Nikkormat]

Prestolite: well desinged but poorly executed.

[Jeepguyp]

A little side bar.... Petronix. Great product. However, this recently happened:
My CJ-5 (360) developed a skip, particularly detectable at low RPM\ "lugging". Did some checking, pull wires on cap...one doesn't change. nervously checked compression. good. Thank goodness. sTART HER up, pull wires again... That one isn't even firing!
Cap comes off. there, on the rotor shaft is a strange item. A small magnet is riding there. Its one of the 8 that are imbedded in the reluctor ring (part of the Petronix kit), covered by a layer on cellophane. I think contamination from oil or antifreeze caused this, making the epoxy break down. No fault of Petronix. I recently had a coolant issue, didn't drain the radiator prior to pulling a plug out of the thermostat housing. oops.