tach dancing around like a ho-down! (NOT fixed)

[E-Rue]

history:

well ive been trying to figure out a slight intermitant tach dance problem iv had for about 6 months now in my typhoon (daily driver). i started with new plugs, then i tried new wires, then i swaped the complete distributor, and coil with the ones that used to be on my sy before i went with MSD. no dice. still dancing a little bit at steady cruize around 45mph.

lastnight:

tach starts dancing like nuts. looks like its gonna go off the damn scale. lol. anyway shortly afterwards the check engine light comes on, and then the tach goes deadly accurate like its lost the dancing problem. i ignored it since i was on the way to class and it seemed to be running alright. just babyed it into the parkinglot and sat thru calculus. get back in the truck to go home, no light, no big dance display, just the usual.......
then when i get about half way home, it goes nuts again. BIG dancing like a fat man goin round and round. check engine light again, and then dead on the money movement from the tach. follows like a brand new truck. so once again i baby it home and into the garage. hook up the scan tool, and it reads code 42. code 42 is a short or grounded ignition while in operation. so i go back outside, start the truck pop the hood, get a misting bottle from amy, and turn off the lights. i shoot the mist all over the ignition and wires, and nothing is arching.

i am so pissed about this.

e

 

[smeagol]

Considering you've changed all the ignition components, and the issue remains, but is inconsistent, you should look at what has remained constant, namely:

- same grounds
- same harness & physical connections
- same ecm


I suspect the main ignition wires may have a short or something. Short or grounded ignition leads to tach dance, kinda like a bad plug wire firing through the block leads to tach dance.

 

[E-Rue]

nice plan. very similar to the one i had.

already swaped in a different ECM with MEMCAL and 2 bar map.
no dice.

also removed all the grounds in the engine bay and cleaned them/reinstalled them.
no dice.

doesnt leave much to do other than try and manually trace out the wiring between the ECM and distributor. (already checked out the wiring between the distributor and coil)

its prolly something small and stoopid causing me all these problems, but its making me nuts trying to find it.

e

 

[sytyguy]

Eric.....I had a somewhat similar problem years ago. I discovered it to be that some of the wires from the module to the ECM had come out of the wire loom and gotten chaffed right around the heat shield where the harness enters the cab. Instead of doctoring the connection right there, I traced the 4 wires to the ECM and snipped 'em......then ran my own separate harness for these 4 wires to the module. It solved my problem and was probably a little overkill, but I damn sure didn't want to get stranded again.

Had tach dance various other times and it always pointed to the 1 ignition component I hadn't replaced in a while.

Michael

 

[Mad Mike]

E - replace the wire harness running from the coil to the back of the distributor and connects to iginition module. They are pink and white in color.

 

[Sy Guy 0024]

What about the ignition module in the distributors? I found that BOTH my MSD and my stock distributor that came with the truck had pinched/bare wires that led from the module to the distributor. This could be an ignition short. It's awful ez to pinch them between the cap and dist base. Just a thought.

Corbin

 

[1quikAWD]

Have you checked your dash grounds? There should be 2on the drives side, if one comes loose, it can cause guages to go haywire.
John

 

[E-Rue]

the braided ground on the driverside firewall was bad.

i had to use a bigger bolt cause the 10m was stripped and not making good connection. dont know who did it, but im glad its fixed. i ended up using a body bolt from autozone, that was a little bigger.

e

 

[E-Rue]

MOTHER FUCKER ITS BACK AGAIN!!!!!!!!!!!!

why didnt i buy a supra.

anyone want a mint ty that wont run right?

e

 

[myclone]

Calm down... Bring the ty up to lumpys garage and I'll make it all better. Seriously though, you fixed it temporarily so IMO you were either on the right track with the ground or in the process of replacing the ground you accidentally improved the contact of whatever connection is causing the problems.

Why do you want a supra anyway? You suddenly wanna be the envy of every person in the neighborhood that thinks neon lights and colored vacuum hose is a mod? Wait, you had colored vacuum hoses on your sy till I took em off and wouldnt give em back. Never mind.

 

[cloneman315]

tach flutter

tach flutter

erue i found a bug last night in my truck i have all msd on it.It was the msd box grounding out on a bolt make sure its rubber mounted not with bolts.

 

[E-Rue]

thanks for the heads up, ill go check out the MSD6A box that is sitting on a shelf in a summit racing box in my garage to see if its making my truck run bad. i bet its not grounded. lol

e

 

[Daron]

Re: tach flutter

Re: tach flutter

erue i found a bug last night in my truck i have all msd on it.It was the msd box grounding out on a bolt make sure its rubber mounted not with bolts.

This perplexes me. My MSD case has not been electrically isolated from ground from day one and works fine. From the MSD installation manual:

"MOUNTING
The MSD can be mounted in most positions, except directly upside down (if upside down,
moisture or water cannot escape). It can be mounted in the engine compartment as long
as it is away from direct engine heat sources. It is not recommended to mount the unit in an
enclosed area such as the glovebox.
When you find a suitable location to mount the unit, make sure the wires of the ignition
reach their connections. Hold the Ignition in place and mark the location of the mounting
holes.
• If you have a 6A Ignition, use an 1/8" drill bit to drill the holes. Use the supplied self
tapping screws to mount the box.
• If you have a 6AL, 6T, 6BTM, 6-Offroad or "N" Series, use a 3/16" drill bit and drill the holes
for the supplied vibration mounts. Install the vibration mounts, then mount the Ignition."

I do not think the MSD case needs to be isolated from ground, and if yours does you have one weird MSD imho...

 

[cloneman315]

msd

msd

i didnt think so either i turned the lights off in my shop and checked it sure enough there was rf getting into the wiring i seen a litte arch jumping so i rubber mounted it, its all gone now i know rf is weird stuff and can make systems do funny things.

 

[Daron]

Re: msd

Re: msd

i didnt think so either i turned the lights off in my shop and checked it sure enough there was rf getting into the wiring i seen a litte arch jumping so i rubber mounted it, its all gone now i know rf is weird stuff and can make systems do funny things.

Your wiring is/was the issue, not the case of the MSD. Radio Frequency interferance and arcing are two different issues.