1227747 to 16197427 Conversion PCM Swap with Wiring Pinout Directions!

[d21turbo]

Yes, the multimeter method is the surefire way to figure out the knock sensor wiring. It is also how I ended up figuring it out. I believe that the pin designations on the modules are the same on passenger cars vs. trucks but the wiring colors are different. I could be wrong though, I don't have both to confirm this.

I also used the Standard Motor products KS6 knock sensor. It is working great.

I would have to agree with the people who state this conversion won't make your vehicle run better if you had the original ECM tuned right to start with, but the datalogging is so much better! There is one quirk my van had with the 7747 that has went away now, that I could never get tuned out on the 7747. On cold start at an ambient temp of around 40-50*F I would have to push the accelerator a little bit or it would just flood out with the 7747. If temperatures were colder or warmer than that range it would fire right up with just a turn of the key. Since the change to the 97427 that issue has went away. This could just be an issue with my setup, this engine is far from a stock 350 with more cam than most would consider EFI friendly, and I am sure it could have been tuned out on the 7747 but I couldn't figure it out and the conversion to the 97427 eliminated the need to figure it out. In any case there is definitely something superior about the cold start up routines in the 97427 and it is great having that problem gone after 4 years of dealing with that on daily driving.

[Fast355]

I would have to agree with the people who state this conversion won't make your vehicle run better if you had the original ECM tuned right to start with, but the datalogging is so much better! There is one quirk my van had with the 7747 that has went away now, that I could never get tuned out on the 7747. On cold start at an ambient temp of around 40-50*F I would have to push the accelerator a little bit or it would just flood out with the 7747. If temperatures were colder or warmer than that range it would fire right up with just a turn of the key. Since the change to the 97427 that issue has went away. This could just be an issue with my setup, this engine is far from a stock 350 with more cam than most would consider EFI friendly, and I am sure it could have been tuned out on the 7747 but I couldn't figure it out and the conversion to the 97427 eliminated the need to figure it out. In any case there is definitely something superior about the cold start up routines in the 97427 and it is great having that problem gone after 4 years of dealing with that on daily driving.

GM loves to switch around the wire colors. I recently swapped my L31 black box to a 0411 in my 97 Express using a guide for a 97 C1500. Found several discrepencies with that swap as well.

The 427 swap was very new when I wrote that guide on TGO, very few had done it and the info was scattered across numerous posts and sites. I swapped my 83 G20 first using a 92 G20 harness, followed by th 87 GMC Jimmy 2.8 and a RS Camaro.

Having done 3 different swap, all on well tuned setups, I have to say the newer 7427 has noticeably better driveability than an earler TBI ECM. They ran smoother, were more responsive, responded to changing conditions better and just all around performed better. The real improvement was E-transmissions however.

I will also add I have a 95 G-series calibration I found with the a/c high pressure switch active and I believe the 95 trucks used them too.

[CDeeZ]

Chris how did you find this website?!?! That's it, Fast has made his arrival, time to shut the forum down! LOL JK man, glad to have you on here with your EFI-veteran status!



I agree on trying to eliminate the confusion on the knock sensor wiring when upgrading from the 747 ECM to the 7427 PCM, I went through the same thing myself. Blue to brown gives you two grounds on some GM vehicles (which obviously won't work b/c that's only half of the circuit). The multimeter is the only surefire way. It also doesn't help that the wire colors underhood are further obscured by fading/grime accumulation.


Also, I'm not as learned as some of the guys on here, but I have to agree, with what little I know, that the 7427 does indeed have better cold start routines, and also is just better all around in my opinion. Perhaps part of this is the additional resolution on things like fuel tables?

[dave w]

I think this is a good tread to post a budget update about converting a vehicle with the 1227747 / TH400 combination to a 16197427 PCM which does not have a TH400 Kick Down control.

On vehicles with a 1227747 the TH400 Kick Down Relay is controlled by ECM pin A7 (tan wire with a black stripe), which sends a ground to the Kick Down Relay. The simple budget fix is to install a TH400 Kick Down Switch on the Accelerator Pedal, just like the older non-computer controlled GM Pickups used. The HUGE difference is ECM pin A7 will be switched to ground (black wire with a white stripe) through the Kick Down Switch to make the TH400 Kick Down Relay work. One side of the Accelerator Pedal Mounted Kick Down Switch will be connected to ground and the other terminal of the Accelerator Pedal Mounted Kick Down Switch will be connected to pin A7.

For a long term trouble free service, solder splicing the wiring is HIGHLY RECOMMENDED!

The pictures below are from a 1987 C3500 454 / TH400 that has been updated to a 16197427 PCM that is using an Accelerator Pedal Mounted TH400 Kick Down Switch. The older Accelerator Mounted TH400 Kick Down Switch is a direct bolt in, no modifications required.

dave w

[Fast355]

I think this is a good tread to post a budget update about converting a vehicle with the 1227747 / TH400 combination to a 16197427 PCM which does not have a TH400 Kick Down control.

On vehicles with a 1227747 the TH400 Kick Down Relay is controlled by ECM pin A7 (tan wire with a black stripe), which sends a ground to the Kick Down Relay. The simple budget fix is to install a TH400 Kick Down Switch on the Accelerator Pedal, just like the older non-computer controlled GM Pickups used. The HUGE difference is ECM pin A7 will be switched to ground (black wire with a white stripe) through the Kick Down Switch to make the TH400 Kick Down Relay work. One side of the Accelerator Pedal Mounted Kick Down Switch will be connected to ground and the other terminal of the Accelerator Pedal Mounted Kick Down Switch will be connected to pin A7.

For a long term trouble free service, solder splicing the wiring is HIGHLY RECOMMENDED!

The pictures below are from a 1987 C3500 454 / TH400 that has been updated to a 16197427 PCM that is using an Accelerator Pedal Mounted TH400 Kick Down Switch. The older Accelerator Mounted TH400 Kick Down Switch is a direct bolt in, no modifications required.

dave w

Dave,

Interesting idea however I am thinking a small patch could be added to control the downshifts similarly to the shift light logic. No extra hardware created.

[dave w]

Dave,

Interesting idea however I am thinking a small patch could be added to control the downshifts similarly to the shift light logic. No extra hardware created.

I agree, a small patch would be a good option.

dave w