Tacho N/W changed ignition from MSD to ign.

What the P0351 code means The P0351 DTC is seen when the ignition coil A primary or secondary circuit has a malfunction. The engine control module is looking for specific signals from the ignition coil A and when these signals are not seen the ECU sets the Check Engine Light. The Check Engine Light will be illuminated on the dashboard when you switch over to the msd your ecu doesnt recognize it and adding the tach adapter wont solve need the ecu programmed or adapter harness so the ecu recognizes the msd ignition

tachos get their signal wire from the ignition (coil, ignition control module )
it the miss is in tune with the tacho movement then there may be a fault in the signal generator ( the coil) or ignition control module

the question is ---is the tacho faulty at those rpms causing a short to the ignition module
or
is the ignition module faulty causing the tacho to react accordingly
tachos get a power supply and an impulse signal from the ignition system and that impulse is registered as a rpm reading
try disconnecting the tacho and see if the problem occurs and if it makes no difference then look for the problem else where
the problem may be in the carby/s ( assuming that the engine is carby run) or if efi then run the fault codes for problem s in the maf/vaf sensors

check for a faulty wire/s to the tacho of a faulty tacho unit
the tacho gets its reading by the ignition impulses so any engine running problems may have been a result of the faulty tacho or wires.

ok what engine?
2.5L , 4.0L ? 4.2L
the tacho works by spark, signals and this varies by engine type.
1990 has the very odd, French REnix ECU (bendix-renix)
with no scan tool suport ,until 1993.
so scanning it for tacho signal good, is impossible. (DIY)
i sold min long ago. at 250k miles. now have 5 th jeep, 2008, a retired tech.
sold it with those rare books too. all 3 sets.
back then the engine has a small blue book, separate from main FSM.
ebay has them if patient, id recommend owning the FSM on any car
you do the work on. why work blind?>

alldata.com may have these facts.

too bad you didnt post engine. really, so ill will wild guess its a
4.2L
and answer for that.
the ignition model sense the spark signal to the Tacho
the tach is 3 pin meter. power, ground and signal.
if the signal is good and 12vdc across, power and ground pins
the tacho is bad.
if power and ground are bad fix that first.
if the signal is dead, the wire is cut or grounding out or the ignition wire
green is dead.and bad module,
on the 4.2L the green wire. goes dead kills the coil dead..

since it runs ok
that leaves way.
bad power to tacho, bad tacho.
easy peasy. this car.
other engine can work differently, (not stated)

the msd igniter is not connected correctly

if its a monsta tacho red wire to ignition in fuse panel black to earth in engine bay green to negative wire on coil if you have ecm there will be a tacho wire on points cover check that it dosent have power and that should be the one

I would suspect the ignition control if you have already replaced all that stuff. I personally would replace it with an MSD ignition for better running and fuel mileage, but the ignition module should be a whole lot cheaper.

BYPASS line is open or grounded

2) EST line is open or grounded

3) Poor connections between ignition module and ECM

4) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise

5) Faulty or incorrect ignition module

6) Faulty ECM If the number 1228253 is on the ecm replace it they are trash. Why did you replace the Ign. module? What was wrong with it before? Reply

Coil pack could be the Problem