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Old 03-30-2016, 10:35 PM
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How much does rpm drop with TC lockup

Working on a better way to make a PCM from a TJ 3spd auto never throw a CEL with a tranny swap AW-4 or 5spd

A resistor replacing the lock up solenoid makes it mostly happy but as PCM has both speed sensor data and RPM data it occasionally objects to not seeing the RPM drop or speed increase when it thinks it locked the TC

Figure a speedo healer increasing speedo reading by a fixed number like 5% should do it and easy to wire a relay that changes speed sensor data fed to PCM from direct speed sensor to speedo healer modified data by letting the solenoid control wire trip a relay but wondered what the typical %rpm drop one sees when the TC locks up

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Old 04-03-2016, 07:15 PM   #2
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Not sure on a Jeep but most cars/trucks a couple hundred rpm,Lock Up usualy does not happen until around 40-45 mph.

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Old 04-03-2016, 07:59 PM
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The when the PCM will still control by letting its lockup solenoid control wire both feed a resistor so it looks like an appropriate resistance plus trip a relay switching speed senior data to PCM to go from pluses directly from sensor to 5-10% increased frequency as modified by the speedo healer

Seeing both an appropriate resistance plus an appropriate increase is speed for a given rpm should keep the PCM fooled into thinking the torque converter lockup is still operational and throw no codes despite the tranny swap
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Old 04-03-2016, 08:37 PM   #4
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The PCM isn't looking for a specific rpm, it's looking for an rpm drop after it signals the torque converter to lock up. It drops around 150 rpms. It'd be a lot easier to just swap the PCM to one programmed for the 5-speed.
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Old 04-03-2016, 09:18 PM
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First the resistor fools it most of the time

I think it is more interested in a relative shift rpm to speed and since rpm cannot be changed as it goes directly to spark and injection the logical answer is a speed sensor bump up which is easy to spoof

It ain't for me as I don't have a slush box but someone asked for a way and I am trying to help

As to why not change PCM well it has the correct vin already encoded and is working and already in his possession not to mention no skim issues if he keeps his PCM
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Old 04-03-2016, 09:48 PM   #6
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The pcm is doing nothing more than sending a ground to the solenoid to enable it. Replacing the solenoid with a resistor won't do anything since that's just an on or off circuit and the PCM only checks for torque converter lockup by looking for an rpm drop via the tach circuit. This is a transmission and lockup circuit that I am very familiar with.
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Old 04-03-2016, 09:59 PM
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Jerry you have for years posted that a resistor will not help but adding a resistor has made CEL much less frequent as without resistor you always get the CEL but with just the resistor you only get the resistor occasionally like ever third or so day triggered by certain driving conditions

I have seen this and others have posted similar success



The goal now is to spoof to rid the rare cel that happens after the resistor is added

That you don't think it can work fortunately has no effect on if it does or does not work
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Old 04-03-2016, 10:03 PM   #8
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Bull, I have NEVER posted anything about a resistor in the solenoid circuit, you are the first I have ever seen who thought it would help.
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Old 04-03-2016, 10:15 PM
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When researching this I found numerous posts from you saying nothing could be done various forums multiple years old

As for others discussing resistor we went thru this here about 4 weeks ago with a guy with a 5spd who bought a TJ with the wrong PCM from an auto TJ and he tried the resistor and reported success at least short term elimination of CEL

Here is info from someone else also describing improvement but not complete elimination with the resistor

http://www.jeepforum.com/forum/f9/wh...1274364?page=1

There are numerous others

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