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printjunky
02-12-2011, 04:57 PM
I have a 25d with a pertronix in it. It has run fine recently, but the Rover's been grounded for other issues for a couple of months. And now there's a problem. The main symptom seems to be (sounds like it's) not firing on 4 cylinders all or most of the time. And while it will start and run.it has very low power under load. Also noticed very rapid carboning of plugs.

After some diagnosis, its clear I have a weak, intermittent spark condition. All of which could support those symptoms. Also, I've noted a struggle with the plugs carbon-fouling even when I've reigned in some carb adjusment issues (Zenith). So while it's true that there could be other things going on, I'm confident that the root of my most immediate issues are ignition-related. And specifically this weak-intermittent spark problem.

Here's what I've tried:

New cap, new rotor.

Checked all multiple times: Power to coil and continuity of all connections and grounds, checked dizzy base plate ground, coil resistance, etc, etc, etc.

Set timing from scratch several times. Beer, gear (light) and ear.

Tried 2 new coils, new wires.

So, even though it is somewhat unlikely, given how little could go wrong with it, that the problem must be the pertronix unit. (I'm still researching some way I might test it.)

Obviously I can dig out a set of points (if I can find them) swap them in and try that. But I'd have to find them (and condenser and that plastic lead thing) and try and remember how to mount and set them ...

So while I mull my next step, any other insight?

printjunky
02-12-2011, 07:12 PM
Scratch that. Pertronix seems to be working OK. Did a test-light test on it. Light flashed in an expected way. It appears the spark problem might be related to a bad coil wire. The spark is still pretty weak and yellow. But it's there.

And now there's a no start situation. Though I didn't try too much now that it's dark.

We'll see what the morning brings.

Lord Icon
02-12-2011, 08:38 PM
You can take the coil down to autozone and they will bench test it for you.
I have had pertronix in every thing that I ever got with points, it's the first thing I replace. great stuff and I have never had ( or heard) of one going bad, solid state being so robust. I would go with the coil as the problem maker...

I Leak Oil
02-13-2011, 07:11 AM
They can go bad. Ask Bostonian about his experience at Mini-Mar a few years ago. His just went completely dead though. No spark at all if I remember correctly. We replaced his dist. with a spare and got it back on the road.

You didn't mention changing the coil wire or plug wires but you could try that along with checking out the coil.

bkreutz
02-13-2011, 12:21 PM
Pertronix (s, not sure what the plural should be:D) do fail especially if you leave the key on with the engine not running (which voids the warranty). But my experience is that they fail completely and don't exhibit a weak spark symptom. I've installed quite a number of them in the past few years in various makes mainly due to the unavailability of quality condensers. My SIII still has points though, I haven't had any ignition issues so I'm leaving well enough alone for now.

printjunky
02-17-2011, 04:59 PM
Yeah, it occurred to me that, as the Pertronix is basically just a switch, there's no way it could be causing a weak spark.

As mentioned in my original post, I did try all new wires two new coils, switched wires around, etc.

I'm going to try a few things this afternoon, but weak spark could also explain why I've been plagued with carbon fouling even after adjusting the carb to what seemed like it should be a little lean.

Any way to shadetree assess the veracity of a spark, other than looking at it? (Right now, I've got #1 hooked to a grounded plug sitting where I can see the electrode when I crank it over.)

Bostonian1976
02-19-2011, 12:58 PM
Pertronix (s, not sure what the plural should be:D) do fail especially if you leave the key on with the engine not running (which voids the warranty).

Pertroni? Pertronix? Pertronixes? :)

Yeah that's exactly what I did and it didn't work out so well for me. Funny thing is I'd done it a few other times with no problem - I think this time the rotor was perfectly aligned to maintain contact and burn the unit out. Complete failure for me - prior to that it was extremely reliable!

Nium
02-19-2011, 01:43 PM
How's the bonding strap from engine to chassis?

printjunky
02-23-2011, 11:02 AM
Walker,
That's often the first thing I say to OTHER people. Should take my own advice, huh? Definitely had all kinds of gremlins that seemed to come down to simple grounding issues on many vehicles in the past.

I know the main chassis-block strap is intact and looks like it's in good shape, and pretty much all meter tests seem OK. Though, I'm not 100% sure on the condition of the batt-chassis connection.

Maybe I'll just redo (and overdo) my grounds. Weather's slowing my shadetreeing way down right now, of course.

Shawn

printjunky
03-19-2011, 06:01 PM
Finally getting back out there now that the weather and my schedule has let up some.

To catch you up quickly. After having run fine for a few months as I worked gremlins out, several weeks ago it started running very poorly, sometimes obviously not on all 4. Terrible power under load.

Assume everything below is triple-checked
Timing
Wires
plugs
Coil
Distributor (note: pertronix)
Carb (adjusted)

I have, in the past had excessive carbon-fouling of the plugs. That seems to be the only consistent and unchanging feature (and of course severely affects running when it gets bad enough pulled the plugs).

Today, started up fine, running a little rough, but sounds ok. Certainly all 4 firing. Did not do a road test to asses power under load today.

Adjusted valves. All were pretty good. Nothing alarming at all. Ran it without the rocker cover, everything seemed to be acting as expected (yes, I know that doesn't really tell me anything about valve operation).

Did a compression check. 4 tests on each cylinder averaged: 139, 140, 140, 138. No problems there.

Have not tried improving the grounds yet (but that all looks and tests good with a meter).

And I have not done a vacuum test yet to see if I can diagnose any valve problems. Maybe tomorrow.

So far the carboning (fuel fouling effectively - which could definitely lead to the "less-than-4-cylinders-firing scenario) leads me back to the carb. (I understand it could still be valve-related). The carb is a rebuilt and de-warped Zenith, with a non OEM rebuild kit. I have reverted back to some of the original parts (idle adjustment screw, and something else, I forget) because I found the non-OEM kit parts to be extremely inferior. I have busted it open a few times and adjusted and re-adjusted the float polished up the pump cylinder and double checked everything (jets clear, etc). I've tried adjusting the idle to its leanest and even then, seem to still be getting a lot of fuel through. (Though admittedly, I haven't run it very much fully leaned out). Plus that only affects idle.

Any other insights?