MSD ignition causing stumble on acceleration

I recently installed an MSD 5900 Blaster ignition and an 8202 Blaster 2 coil on my carbed Dakota V6. I now have a slight shudder on moderate to heavy acceleration from a dead stop. Light acceleration gives no problem. With the MSD ignition removed and using just the Blaster coil or the stock coil, I have no problem. All the other ignition components are fairly new.

I tried advancing the timing by 2 and 4 degrees and retarding the timing by 3 degrees, but that did not eliminated the problem.

The wiring is all correct according to the MSD schematics. Funny side note - while checking the Chrysler service manual for this truck, I found the ignition coil wired backwards in the wiring diagram for the

3.9L spark advance system. It shows the negative terminal of the coil wired through the ignition switch to the positive terminal of the battery. The same diagram for the 2.2L engine shows it wired correctly.

I wonder what would happen if the coil were wired backwards... wouldn't that just reverse the flow of current through the plugs?

anyway...

The spark advance on this truck is computer controlled, and since I swapped out the original feedback carb with the non-feedback variety due to not being able to get a replacement mixture solenoid, the only thing that the computer controls is the ignition advance.

I put a message up at the MSD board, but they are all on vacation until Jan 5th, so I thought I might see if anyone here has any insight on this problem.

Jack

Reply to
Jack
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Why? Stock ignition systems since the days when cars started to be sold with catalytic converters in them, about 1975, have been very good and hard to improve upon, Ford TFI being an exception because of its reliability problems. MSD is good but not worth paying extra for.

The carb could explain it. Find out how to set it up right.

Reply to
do_not_spam_me

It *is* set up right. The problem that I described does not occur without the MSD hooked up. I got the MSD unit in the hopes that it would contribute to a better smog test result after having to replace the feedback carb with a regular carb.

Since I posted the original question I have come to find out that the problem does not occur when the engine is cold. The shudder on medium to heavy acceleration occurs only after about 3½ minutes from startup. I have confirmed this after 4 or 5 cold starts. This at least gives me something to work with.

Things that I know change after warmup:

  1. Choke (richer mix) and faster idle
  2. EGR function
  3. Spark advance
  4. Air switching from Exhaust manifold to catcon
  5. Purge of canister
Reply to
Jack

After warmup, not before?

I'd expect a regular carb that's jetted, metered, and set up just like the feedback carb equivalent to run the engine leaner at times, and stumble on warm acceleration seems like a lean mixture problem. Still I don't understand why a multi-strike discharge (MSD) ignition can't fire the mixture anyway because a multi-strike I built in a hurry from plans in a circuit encyclopedia noticeably reduced the cold stumble of my 1975 Dodge Dart 6-cyl. with 1-barrel Holley, as did a double-strike CD ignition I tried later (cracked the distributor cap, but by then I found a mechanic who knew how to fix that infamous Chrysler problem). I'm sure that professionally designed multi-strikes do much better, so is it possible MSD now sells regular ignitions as well as multi- strikes?

Reply to
do_not_spam_me

The Blaster 5900 is not a multi strike ignition, but a prolonged, stronger spark. I think the duration is 20° of rotation. It is combined

with an MSD Blaster 2 coil.

Today, I disconnected everything that I am aware of that changes with engine warmup. This includes everything listed prior:

  1. Choke (richer mix) and faster idle
  2. EGR function
  3. Spark advance
  4. Air switching from Exhaust manifold to catcon
  5. Purge of canister

All these things, except what the choke controls, operate in engine cold mode when disconnected. The choke takes longer to to disengage because the electric heater no longer takes the choke out of action and the engine must fully warm up to disengage it.

The result was that the onset of the stumble took longer to kick in. This points to the leaning out of the mix and decrease in the rpms at idle as being the cause of the stumble, as the choke took longer to disengage with the heater unplugged. However, when I cheated the disengaging of the choke conditions, richer mix and higher rpms, the stumble still occurred. When I disengage the MSD 5900 Blaster Ignition, the stumble from a dead stop is completely eliminated. If I can't make this MSD unit mesh with the rest of the system, I can always chuck it. I just got it in hopes that it would help pass smog without the feedback carb that was stock.

But I can't seem to walk away from a mystery like this one.

Like the guy said that Clint Eastwood had covered with a .44 Magnum,

"I gots to know."

Reply to
Jack

I want to re-emphasize... the stumble from a dead stop does not occur with the MSD 5900 Blaster Ignition out of the picture. With just the Blaster 2 coil or the stock coil, the take off from a dead stop is smooth as silk and powerful.

One thing I noticed with the stock ignition: when I replaced the stock main jets with smaller ones, I seem to recall that I would get a stumble from a dead stop. I thought this was unusual because I did not think that the smaller jets would cause this problem when accelerating from a dead stop. These were the smaller jets from the feedback carb. The stock jets were flow rated at 311 cu cm a minute. The smaller feedback jets were flow rated at 175. That's a radical difference, I know, but I had the smaller jets on hand and at the time I didn't know how much smaller they were because Holley changed how they designated jet size and I wasn't sure what the 175 stamped on the jets referred to. I have since determined that it can only refer to flow rate and not size.

So know I am thinking that perhaps bigger main jets or bigger idle jets might alleviate the stumble from a dead stop, but it still doesn't make sense to me why the problem only occurs with the MSD ignition and not the stock ignition. Plus, this carb was jetted for a 318 and this engine is a 239.

I put in a colder Champion plug on the possibility that the hotter, longer spark was creating a pre-ignition condition, but that didn't help.

At this point, all signs point to the carb, as you suggested, but again, there is no problem with the stock ignition. At this point, it is turning into a quest for answers. I already have an ignition system that runs beautifully, but I want to understand why the MSD unit has the stumble problem from a dead stop and the stock ignition doesn't.

BTW, I'm impressed that you built your own ignition unit from plans. Are they are the net somewhere?

Reply to
Jack

Jack wrote in news:DqZ5l.15696$ZP4.5747 @nlpi067.nbdc.sbc.com:

combined

Ignition,

the good msd 6000 series will deff. help your running. but that worthless 5900 is a joke. I will give you another one I took off years ago. KB

Reply to
Kevin

I had an 1989 Celebrity 4 cyl TBI engine all stock that had a similar symptom, occasional stumble when starting out from a red light, only after the car was warmed up. It would stumble bad enough to stall usually. I never did figure out what it was. I changed the throttle position sensor but that did not help. The intermittent and transient nature of the problem made it impossible to troubleshoot. I could not even figure out if it was a spark or fuel problem. The car ran perfectly other than that. There was a thread on here a few weeks ago about a similar problem. I don't know if your problem is related or not. I understand how you feel about the quest for an answer.

Mark

Reply to
makolber

Hi Kevin, thanks for the offer. I could use another paper weight!

1) After exhaustively checking everything on the engine system, I discovered that if I cheat the choke to it's cold starting position after the engine warms up, the 5900 and Blaster 2 coil do not cause any problems. I tried this because the stumble from a dead stop was not occurring when the engine was just started from a completely cold conditi on.

2) With just the 8202 Blaster 2 coil alone, which is spec'ed by MSD for use on the 87 Dakota 3.9L, and *without* the 5900, the truck runs beautifully.

3) With just the Blaster 5900 alone, and using the stock coil, the truck runs beautifully. I just finished this last test because I had the 5900 installed for a while before getting the Blaster 2 coil and couldn't remember having this stumble problem. I got the Blaster 2 coil because I noticed that the stock coil was getting awfully hot with the 5900 driving it.

4) MSD specs for the resistance of the 8202 Blaster 2 coil is .7 ohms primary and 4.5K ohms on the secondary. The 8202 Blaster 2 coil that I have measures correctly for the primary, but 5.4K for the secondary. The reading was the same using both an analog and a digital meter. This may not be a factor and probably isn't, but I just don't know for sure. The Blaster 2 coil works fine by itself, without the 5900 installed.

5) MSD recommends this coil for use with the 5900, as well as all 5, 6 and 7 ignitions

I registered at the MSD site, but have not yet been cleared for take off in their posting forums. I think everyone is on vacation til Jan. 5th. It should be interesting to see how they spin this.

Reply to
Jack

Thanks for the commiseration, Mark. I finally did get closer to an answer. See my reply to Kevin on this thread.

Reply to
Jack

I'm going to say the MSD ignition is lousy, maybe because of their coil or plug wires. There's not much advantage to special wires, and stock coils are usually best, even for CD ignition (the instructions for the Delta CD kits from Radio Shack and Heathkit recommended them)

Here's all the information I still have:

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Many articles about electronic ignitions were published in electronics magazines from about 1965-1980. They're actually simple to built, but I learned it was very important to make them waterproof (glop on silicone sealer) and highly resistant to heat (derate parts by a factor of 2-3 more than normal 2-3 times) and vibration (more silicone sealer). I almost always used mechanical points so I could easily bypass the system if it failed, but magnetic pickups, including Hall effect sensors, are cheap and easy to hook up.

Reply to
do_not_spam_me

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