chrysler vehicles and tach signals

So about a month ago I did a r/s in a 03ish Jeep Grand Cherokee. I have gone about 3 years with just using voltage sensing, but ever since learning that hooking up tach is SOP, I have started using tach sensing. So I finished it up, tested it with my normal procedure (once before putting dash back together, once after the vehicle is put back together, and once more when I park it for good luck). Then I called the customer to let him know it was all set. When he got there, we went out so I could demo it for him, and when i hit the r/s button it cranked for literally about .3 seconds (less than the lowest setting on the unit) and of course doesnt start. I explain to the customer that the unit wasnt cranking long enough, and reset it to voltage sensing and it worked perfectly. I didnt think anything of it, but now today I finally got around to finishing my own r/s (rewired everything b/c I didnt like the way it looked, and hooked up tach). Now my truck is doing the same thing the jeep did. I would prefer to keep it in tach mode because it is definately a lot smoother of a start. My truck is a 2000 Dodge Ram 1500 fuel injected. The Jeep was a 4.0L I4, and I used the opposite colored fuel injector wires for the tach signal, both were tested with the DMM and the LED came on showing that the tach signal was learned. So what exactly would cause this???? This is two problems I've had with tach already (been using it about a month now), and I have never had a problem with voltage sensing... lol.
Thanks again guys/gals.

Kenny

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Kenny
Owner / Technician
KKD Garage LLC
Albany, NY 12205

Are you using DEI units? I have come across this on about 80% of the Chrysler's I have done recently. The tachometer connection is the best way to install the starter, it prevents overcrank, undercrank, etc. What I have found with the DEI units I put into the Chrysler products is that I have to 'raise' the idle just a hair when programming the tachometer. I take the idle to about 1000-1200rpm and then program the tach. I am not sure what causes this, whether it is a Chrysler issue or if it is with the DEI pieces but the programming at a slightly higher idle has worked 100% of the time for me.

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Installer, IT support, and FFL. I need less hobbies.

that would actually make a lot of sense b/c both times i have tried programming the tach, the truck was warmed up and it idles very low (around 600-800)... and it is the same on my jeep as well... Thanks for the insight. The other thing I noticed on the audiovox tech services site is that the tach signal can be found in the data connector... I havent looked yet, but that would just suck (since i already brought it through the firewall and fought with the injector harness to free up the wire enough to solder it.. lol).

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Kenny
Owner / Technician
KKD Garage LLC
Albany, NY 12205

another note for DEI products. as a rule of thumb for tach signal: Chrysler = coil; Ford = fuel injector

get the tach signal at the coil instead on your chryslers.

Had the same problem on my 98 ram.  Got it off the fuel injector and intermittent tach signal.  Went to ign. coil and works every time.

Have a similar problem with my '99 Galant, refuses to R/S when cold, should I look to raise revs and then set tach (off fuel injectors) or do I have a cold start wire off the ignition (as A second wire to go live with starter wire) that I've missed? G4 Clfford with I/Start IV

also remember when using key in box to have it tight because when its cold it will act up...