5.7-545rfe speedo fix

Discussion of the 5.7L-6.1L-6.4L HEMIs.

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5.7-545rfe speedo fix

Post by 56buick » Wed Jan 08, 2014 4:21 pm

I recently completed a build of a 1956 buick special using a salvaged 5.7 hemi and 545rfe transmission out of a 2005 ram. I used the intake and front cover from a 5.7 magnum (they look way better) . There are several challenges involved, but the most frustrating one was finding a way to get the speedo and factory cruise to work . Chrysler uses wheel sensors and the ABS controller to feed ppm (pulses per mile) into the pcm. On four wheel abs there are two feeds ,on rw abs there is only one. For my application I was trying to pick up the signal from the pcm and decode it through a Dakota Digital Bimm (bus interface module ) to supply info to the custom guage panel they made for me. Everything worked but the speedo., DD was stumped and so was I ,until , through research , I found out that the speed signal came from the now long gone abs computer. Here is how I solved the problem ,and this will work for any hemi swap that uses the 545rfe transmission.
The output sensor on the rear of the trans will need to be tapped, not the ground , just the signal . On my application it was circuit T-18 (dg/br) that goes from the output sensor to the PCM plug C-4 #32. Just tap into it and run a 18 ga wire to the dash. Now you need to find the signal wire to the pcm, on my 2005 PCM it was C-1 #13 (dg/yl) circuit B-22. This is the signal wire that feeds the info from the abs controller to the pcm. If you are using Dakotas bimm or factory cruise your pcm will need this signal, If you are just feeding an aftermarket electronic speedo or cruise you won't need this wire.
The output sensor on the transmission puts out 34000+ ppm (not a typo) and you will need to step this down. Rostra part number 250-4379 will split this four ways and make the signal usable by the next little gem.
You will need a Dakota Digital SGI-5 Universal signal interface in order to change the input to a 4000 ppm oc output. You need a switched hot to power up the SGI-5 and the Rostra 250-4379, they can both be powered from the same source . plus a good ground for both .Hook the wire from the transmission output sensor to the input on the rostra and the output on the rostra to the Sig IN terminal on the sgi-5. Output four on the SGI-5 will now have a usable 4000ppm oc signal. Hook this to the pcm C1 #13 if using DDs bimm or the Factory electronic cruise. If you only need to run a speedo you can go directly to the speedo input if it needs 4000ppm. If your speedo uses a different signal the DD SGI-5 is infanitly adjustable.
Get the GPS out and dial in the speed using the up and down buttons on the SGI-5 while cruising down the road.

I posted this so that maybe someone else can save thereselfs the time to figure this out.

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Re: 5.7-545rfe speedo fix

Post by scottm » Mon Jan 20, 2014 8:38 pm

Great technical information, thanks!

Now where are photos of that Buick? :)
Scott Moseman
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