AAArgh! Post speedo correction box install driveability issues. HELP!

[PhoenixGTS]

Finally installed the old style Unitrax speedo correction box I have had in the garage forever so that my 3.55 gears are not goofing up the speedo. All you do is interrupt the speedometer sensor wire as it goes to the PCM, tap into keyed ignition power, and ground some other wires. Car starts fine, idles fine, but when I drive it it has no power. Totally flabby. Runs fine, just really slow and sounds more like a V8 than normal. First drive the check engine light came on. I remembered that to do the install I only disconnected two of the three PCM connectors so I disconnected them all for awhile to reset the PCM. No check engine light on second drive, but drove exactly the same. The speedometer is working so it looks like I did the box install correctly, but it seems that I have a fueling issue (does not seem to miss so I do not think it is ignition. Looking in the service manual I see that white/center PCM connector in which I interrupted the speedo wire also has the triggers for all ten injectors. Think maybe I disturbed an injector connection? Any chance tapping into the keyed power has made the PCM mad? I need some help on where to look. Dang it I hate wiring!

 

[VPRTKMIKE]

give me a call tomorrow, i'll walk you through it. mike @ 631-845-8199 after 9am est

 

[PhoenixGTS]

give me a call tomorrow, i'll walk you through it. mike @ 631-845-8199 after 9am est

OK. I am assuming that if I did not install the box correctly the speedometer would not work. Given that it works (indicated speed appeared correct during my test drives) I am assuming it is installed correctly, but I have triggered something else. I interrupted pin 27 (white with tan) on the white PCM connector for the speedo signal, and pin 2 (dark blue with grey) on the black PCM connector for the ignition keyed power.

Really wanted to drive the car to work tomorrow! Dang it!

 

[PhoenixGTS]

Bump. I was going to start my diagnosis process tonight but it was mid-90s today and I drank a bit too much wine at dinner. Go ahead and shoot out any suggestions for tomorrow night when I actually get on it.

 

[SilverSnake]

If you want i could stop bye to show you how i wired mine?


Robert

 

[PhoenixGTS]

If you want i could stop bye to show you how i wired mine?


Robert

It HAS to be installed correctly because the speedo is working fine. Something else has gone wrong.

 

[PhoenixGTS]

Rechecked install and everything is correct per the instructions - BUT - I have an idea the instructions may be wrong.

THE QUESTION NOW: IS THE PURPOSE OF THE BOX TO LIE TO THE PCM ABOUT THE SPEED SENSOR SIGNAL? OR IS IT TO LIE TO THE SPEEDOMETER BY ALTERING THE SIGNAL FROM THE PCM?

If the idea is to alter the speed sensor signal before it goes to the PCM then the instructions are wrong. If the idea is to alter the signal from the PCM to the speedo then the instructions are correct and I have some other problem.

ANYONE KNOW THE ANSWER???

[edit] Search function found a post where some people said after the box install their spedo was correct but odometer was off. That would lend to the box altering the signal from the PCM to the speedo. But in the same thread someone said the box corrected both their speed and odometer which would lend to the box altering the signal from the speed sensor to the PCM.

 

[Steve 00RT/10]

I have the Unitrax speedo box from a couple years ago. Pin 27---to the speedometer works right for me. I tried pin 28 this past weekend at Unitrax direction to see if it would work. ---no speedo/bad idle/ stalling. I'm back on pin 27 and everything works right. I did not reset the computer when I made the change, but then I never reset the computer when I hooked to pin 27 the first time and had no problem. Unitrax is handling a new box that I think will use pin 28. The theory is that the vehicle speed sensor is a better signal to interupt. It didn't work for me. I'm waiting for a reply from Devin before experimenting further. You might try pin 28, as Devin wants a few people to change theirs around and see if it works. You have nothing to lose.

Steve

 

[PhoenixGTS]

FAWK!!! Some weeks I hate this car. Here is an update. Bypassed the Unitrax box and car still ran same. Totally flabby like it had not timing advance whatsoever. So I hooked the box back in and drove until the check engine light came on. Speedomoter was working and properly corrected the whole time. Guy at Autozone was nice enough to use a hand-hald unit and pull the code "P0352 ignition coil B primary/secondary malfunction." OK that makes sense as this feels like a timing issue even though there is no blatent miss. Service manual says P0352 is "Ignition coil #2 primary circuit - Peak primary circuit current not achieved with maximum dwell time." Sounds right from the symptoms. One last kick in the **** was on the way home the speedo went dead. Aaargh! I guess question now is if there is a bad coil could the box have caused it, or, would tapping into ignition keyed power in the harness trigger something like this? I'll call Unitrax tomorrow because those guys were super helpful in finding me instructions for the older unit, but if anyone has any comments on the P0352 code shout out.

 

[PhoenixGTS]

Update. Talked to Devin at Unitrax and he suggested moving the splice from pin 27 (the line from the PCM to the speedo) to pin 28 (the line from the speed sensor to the PCM). Did that and car still runs like heck and speedo is still dead. Completely bypassed calibration box and the speedo works but the car still runs like crap. So it looks like I bought a bad box (or at least it died last night while I was driving) and I have a #2/B coil pack out. Whether the two are related - who knows??? Time to find a coil pack. I hear they are expensive. Ugh.

 

[99 R/T 10]

Call Chuck Tator, he will square you away 914-763-3136

 

[PhoenixGTS]

For archival purposes I am going to beat this thread until it dies.

GOOD NEWS! Took the last step of disconnecting the power tap from pin two of the black PCM connector so that the Unitrax box is totally disconnected. Car runs fine. So, the bad Unitrax speedo correction box was somehow dragging on that power lead, freaking out the PCM causing it not to trigger the ignition properly, and then causing it to set the P0352 ignition coil code (ODBII is a "result" finder as opposed to a "cause" finder after all).

I ordered a new box so hopefully my next post will be the last and I will report that the install is done and all is well. Thank goodness the Mopar PCM is not fried - it just runs SO good without any idle hang.