Tach Bounces and Slight Hesitation / Misfire, Need help.

SableSal

Member
Sep 17, 2009
295
3
19
Fresno, Californ-I-A
Well, I'm guessing my dizzy has finally coming to it's end of life. I just want to ask the gurus to make sure I'm on the right track.

Last week I had some issues with an exhaust leak on my Mac Shorty Headers (I guess this is a concern on some). I could have fixed it, but I was pretty much set on getting rid of the headers. Exhaust and my Mustang have had a long battle... anyhow. So while I re-installed the headers, I took advantage and replaced the spark plugs (Thanks to Davis3 BTW for helping with this. I appreciate it VERY much so). Well, when I was installing the spark plugs, Motorcraft Standard, I failed to gap them. I figure, everytime I go to gap them, they are spot on. So I just tossed them on. Anyhow, I was wanting to get this all done, so that last week I could drive the car to San Francisco (200 miles away) to drop my sister off at the Airport SFO. The car drove perfectly fine the way there. Although, on the way back, I noticed the tachometer was kinda acting a little funny. The tach would kinda bounce around in the range of 500 RPM... Kinda hard to explain, but the tachometer looked like it was struggling as the engine reved up. I also noticed at idle, there was almost a very small misfire, but it didn't happen all the time. Just maybe a hiccup every 1/2 hour.... Well yesterday, I was driving to LA (300 miles away) to pick up my sister (damn airlines and messing up her flight). On the way there, I noticed the misfire was getting a little worse and it started to hiccup upon acceleration (very slight) and when I maintained speed, the tachometer was bouncing up and down. Lets say the engine was maintaining 2000 RPM, the tach was moving from 1800 RPM - 2300RPM. The tachometer would never stay still. Acceleration also suffered. If i punched it, and accelerated from a dead stop, it seemed to flat line around 4000RPM. So, anyhow, my plan of attack is to check the gap at all the spark plugs and to assure that all the spark plug wires are attached firmly to the plugs. (Visually the plug wires look good). Then go from there. I'm just curious if this sounds like a distributor problem?

The distributor has not been replaced by me. When I bought the car, everything was motorcraft. I don't know if the previous owner has replaced the distributor. I'm thinking it's got something to do with this mix up.

Any suggestions would be great. I appreciate it very much. :)
 
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94GTCoupe

10 Year Member
May 7, 2006
1,402
79
79
CA
I'm leaning towards the pip.
Its been pretty hot the last week.
It may be on its last legs.

Easy way to check would be to swap my dizzy in for a bit,and see if the problem goes away.
 

sixt9coug

Member
Sep 30, 2009
222
3
19
Norwalk SoCal
Sal, I would put money on it being the PIP. When I bought my car it would act up really bad too when driving around. I would nail it, and the car wouldn't rev past 3300rpms. It would bounce like it was on a rev limiter. It idled oddly too, misfire and hesitate whenever I put a load on it. I could get it to rev higher when I sloooooowly tipped into the gas but if I even farted in the direction of the gas pedal with to much vigor it would buck, shake and disapprove.

Check your plugs and wires to make sure they are still good and tight. Put a timing light on there and throw some revs, if it acts erratically I suspect the PIP.

Change the dizzy.
 

toyman

SN Certified Technician
Jul 19, 2007
1,944
53
79
Vernon BC
You say when the engine is steady at 2k rpm the tach bounces between 1.8k and 2.3k. The tack signal comes from the coil. From the attached schematic I don't see a direct link between the tach and PIP signal that would result in the engine rpm being steady with the tach bouncing. That might be a bad coil connection.

.

Perhaps I'm reading it wrong. I would suspect there may be a cracked plug or a bad wire connection that fails under load. That would account for it falling on it's face at 4k.
 

SableSal

Member
Sep 17, 2009
295
3
19
Fresno, Californ-I-A
You say when the engine is steady at 2k rpm the tach bounces between 1.8k and 2.3k. The tack signal comes from the coil. From the attached schematic I don't see a direct link between the tach and PIP signal that would result in the engine rpm being steady with the tach bouncing. That might be a bad coil connection.

.

Perhaps I'm reading it wrong. I would suspect there may be a cracked plug or a bad wire connection that fails under load. That would account for it falling on it's face at 4k.
You are exactly correct. Bad set of plugs and wires. I changed the Dizzy either way. Now I have a lifetime warranty with it. Just in case. Haha.