7747 to 7427

**scooterwrench** · 09-05-2023

Figured I'd better start a thread for Q&A on this swap.

The 7427 that I've bought came out of a '95 1/2 ton van with a 350 and automatic tranny.
The truck that it is going into is a '91 1/2 ton 2WD with currently a 305(not for long)and auto tranny.
I know already that the 4L60E shifting parameters are going to have to be 0ed out with the exception of the TCC lock.

Correct me if I'm wrong but doesn't the 7427 have the ESC built in?

How far downstream can I run a HEGO? Right now it can go in the exh. manifold but eventually it will be going into the exhaust possibly 36" from the collectors.
My plan for exhaust on this truck is 3" coming off the collectors with the left side crossing over under the tail housing of the tranny then going into a muffler with two 3" inlets and one 3" outlet then up over the rear end and out the right rear in the stock configuration. I would like to put the 02 in a crossover pipe right in front of the muffler,that way it reads both sides.

I read that you can hook a WB02 to the input for EGR position. Is that just for datalogging or can it be set up for BLM?

**scooterwrench** · 09-06-2023

I was doing some research on the 7427 inputs and it has two for driveshaft speed. One is 2000PPM(DRAC) and the other is 40PPR(VSS). Do I need both?

**TriumphR3** · 09-06-2023

WBO2 sensor has nothing to do with blm. It’s only purpose is for data logging and tuning.

**scooterwrench** · 09-06-2023

Originally Posted by TriumphR3

WBO2 sensor has nothing to do with blm. It’s only purpose is for data logging and tuning.

Will it read in air/fuel or just the voltage it produced?

**tplasek** · 09-06-2023

You only need a single 2 pulse per revolution VSS sensor connected to up to the Pin F13 on the ECU. Yes, the ESC is built into the 7427 ECI.

https://jagsthatrun.com/collections/...ce-holder-4pac

Howell also used to sell a 2pulse VSS, but I couldn't locate it via a Google search. Mine came from Howell.

**tplasek** · 09-06-2023

Originally Posted by scooterwrench

Will it read in air/fuel or just the voltage it produced?

The ECU will require an OEM type narrow band O2 sensor to adjust fuel. Do yourself a favor and make sure to get the heated narrow band sensor. The wide band sensor is an additional separate sensor and control box that displays the AFR and outputs I believe a 0-10Volt signal to the 7427 ECU. This allows you to record your wideband O2 readings into your datalog.

**scooterwrench** · 09-07-2023

Originally Posted by tplasek

You only need a single 2 pulse per revolution VSS sensor connected to up to the Pin F13 on the ECU. Yes, the ESC is built into the 7427 ECI.

https://jagsthatrun.com/collections/...ce-holder-4pac

Howell also used to sell a 2pulse VSS, but I couldn't locate it via a Google search. Mine came from Howell.

I've already got that covered.
When I bought ol Smoky the fuel and oil pressure gauges didn't work and new sensors didn't fix it. I had bought a set of Marshall instruments for a 98 S-10 that I was going to put my 355 in but lost interest in that POS so they went into Smoky. The original gauges were moonies with the VSSB/DRAC built into the gauge board that I wasn't going to be able to use so I bought a DRAC module,re-pinned it for my gear ratio and wired it in. The DRAC has four outputs. 40 ppr(tail shaft speed)for ECM,2000 ppm for speedo and ECM,4000ppm for cruise control and 128,000ppm for anti lock brakes. I used the 40ppr to run the speedo because it needed 4000-200,000ppm for it's input. The 2000ppm signal went to the ECM and the 4000ppm to the cruise control. I dropped kicked the RWAL brake module and valves into the garbage can,the dump valve was toast. So now I have the 2000ppm signal for pin F13 on the 7427 and the speedo has a 1:1 output that will pass the 40ppr signal to pin F12,,,,,,,,,if I need it! Do I need the 40ppr for correct TCC lock up on a 700R4?

WB02 signal is 0-5V off the controller.

**scooterwrench** · 09-07-2023

The swap tutorial states that I should use pin E11 to drive the TCC but that is a pulse width modulated output. Pin E10 is the direct ground output for the TCC. Would using pin E11 allow the TCC to slip because it is not getting a direct ground signal?

**scooterwrench** · 10-09-2023

Getting ready to swap the ECM's and got to thinking of how big a PITA it was going to be changing chips because of where the ECM is mounted. It's tucked up behind the glovebox on the extreme right hand side of the cab with not much wire to pull it out to change chips. I've made a remote mount chip socket mounted to the inside of the glovebox.
Y'all check this out.

**dave w** · 10-09-2023

Originally Posted by scooterwrench

Getting ready to swap the ECM's and got to thinking of how big a PITA it was going to be changing chips because of where the ECM is mounted. It's tucked up behind the glovebox on the extreme right hand side of the cab with not much wire to pull it out to change chips. I've made a remote mount chip socket mounted to the inside of the glovebox.
Y'all check this out.

That is a very clever solution.

I'm wondering if there might be some signal loss or signal delay from the ZIF to the adapter board?

Possibly the ribbon cable will act like an antenna and pickup unwanted noise?

I've always let the PCM hang down from the connectors during the tuning process. (messy looking but convenient)

Attached are my notes for a 7747 to 7427 conversion.

**scooterwrench** · 10-09-2023

I used the pin detect on my prom burner and a blank chip to test with and the first time it didn't pass. Broke out my ohm meter and discovered the small header connector didn't make a connection on pins 13,17 and 28. Pulled that one off,trimmed the cable back and pushed on another one and rechecked with the meter and then again with the burner,passed both tests that time. I read that the 7747 didn't play well with this setup and needed a signal amplifier but the 7427 didn't have that problem. That proto board was a little bit of a PITA. I had to solder in traces to make sure the ZIF socket got a good connection with the box header. That ribbon cable is only about 12" long so I'm hoping that will keep signal loss down to a minimum. If I do get noise I can shield the cable if need be.

**scooterwrench** · 10-09-2023

I studied the tutorial on the site for the 7747 to 7427 swap and crossed referenced with the pinouts for the two and got a lot of notes written down.
I've pulled the .bin on the 7427 and read it. It's written for a 95 G series van with a 350 and I'm reading it with Fast 355's $OD 700R4 mask. It's going in a 91 C1500 with a 700R4 and 305. I haven't pulled the .bin on the 7747 yet.

**scooterwrench** · 10-09-2023

Thanks for posting your pinout notes. It confirms that I need the 2000ppm VSS signal off my DRAC for pin F13 on the 7427. Pin F12 receives the 40ppr buffered signal from the DRAC which is now feeding my speedo. The speedo has an output to pass whatever signal it is receiving. If someday I ever decide to go with a 4L60-E or 4L80-E would I need that 40ppr hooked up to pin F12?

**dave w** · 10-10-2023

Originally Posted by scooterwrench

Thanks for posting your pinout notes. It confirms that I need the 2000ppm VSS signal off my DRAC for pin F13 on the 7427. Pin F12 receives the 40ppr buffered signal from the DRAC which is now feeding my speedo. The speedo has an output to pass whatever signal it is receiving. If someday I ever decide to go with a 4L60-E or 4L80-E would I need that 40ppr hooked up to pin F12?

1994 VSS
1994 VSS.jpg

**tayto** · 10-11-2023

no TBI ecm/pcm requires a 40ppr signal directly. i believe either 2000 or 4000 ppm and can be selected in the calibration. you're VSSB is in the speedo housing IIRC.