MSD ignition causing stumble on acceleration
Jack
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
do_not_...@my-deja.com
Jack wrote:
> I recently installed an MSD 5900 Blaster ignition and an 8202 Blaster 2
> coil on my carbed Dakota V6.
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 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.
The carb could explain it. Find out how to set it up right.
Jack
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
do_not_...@my-deja.com
Jack wrote:
After warmup, not before?
> 2. EGR function
> 3. Spark advance
> 4. Air switching from Exhaust manifold to catcon
> 5. Purge of canister
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?
Jack
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."
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?
Kevin
@nlpi067.nbdc.sbc.com:
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
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THUNDERSNAKE #9
Protect your rights or "Lose" them
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mako...@yahoo.com
> Jack wrote:
> > do_not_spam...@my-deja.com wrote:
> >> Jack wrote:
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
Jack
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 condition.
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.
Jack
Thanks for the commiseration, Mark. I finally did get closer to an
answer. See my reply to Kevin on this thread.
do_not_...@my-deja.com
Jack wrote:
> > do_not_...@my-deja.com wrote:
> 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.
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)
>
> 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?
Here's all the information I still have:
http://www.flickr.com/photos/33791088@N05/
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.