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Hello fellas. I could use some guidance using the Hex editor in TPRT. I'm working on a 1989 GTA that we converted from MAF to SD (165 to 730 ECM) and now the VSS input is non-existent in the datalog. Most of you have probably seen the instructions, but they say, "requires PROM change: MAG VSS at 0x18 b6 for $8D PROM". Unfortunately for me, I have no clue how to make this change; never worked with the Hex editor before.
The car is a 1989 GTA with a newly rebuilt 383 HSR, 230/236 cam, hooker 2055's and a T56. It's running but it's really down on power and sluggish. Every data point in the log is pulling 6+ degrees SA right now and I'm not sure if it's because of the VSS or not. I've been pulling timing and fuel, but want to eliminate the VSS as a problem. I'm using TPRT with Moates Ostrich 2.0 to tune the AXCN bin with matching XDF and ADX files. I was hoping the XDF would have had this field defined, but it doesn't. Any help I could get with the Hex editor is very much appreciated. Thanks in advance!
Hello fellas. I could use some guidance using the Hex editor in TPRT. I'm working on a 1989 GTA that we converted from MAF to SD (165 to 730 ECM) and now the VSS input is non-existent in the datalog. Most of you have probably seen the instructions, but they say, "requires PROM change: MAG VSS at 0x18 b6 for $8D PROM". Unfortunately for me, I have no clue how to make this change; never worked with the Hex editor before.
The car is a 1989 GTA with a newly rebuilt 383 HSR, 230/236 cam, hooker 2055's and a T56. It's running but it's really down on power and sluggish. Every data point in the log is pulling 6+ degrees SA right now and I'm not sure if it's because of the VSS or not. I've been pulling timing and fuel, but want to eliminate the VSS as a problem. I'm using TPRT with Moates Ostrich 2.0 to tune the AXCN bin with matching XDF and ADX files. I was hoping the XDF would have had this field defined, but it doesn't. Any help I could get with the Hex editor is very much appreciated. Thanks in advance!
Make sure you disable the checksum if you're using the Ostrich. Need to change it from 8D to AA.
i don’t know what Youre looking at but if x18 means x018 address bit 6 you can simply create a new flag in tuner pro by right clicking and adding one at address x018 bit 6 and when you open it check or uncheck it.
Thanks fellas. I first started with S_AUJP_V4 with WBO2 enabled (that's what I run in my IROC). I see it (S_AUJP) already has that switch available, so it's simple enough to revert back to AUJP. When we ran the S_AUJP it bucked /jerked like crazy on acceleration and died when depressing the clutch. Switching to the AXCN bin cured that; that's why I was moving forward with it. I'm pretty sure the jerking (on acceleration) with S-AUJP was too much timing, which I've since reduced. I can also adjust all the IAC parameters in AUJP (copy from the AXCN bin to the AUJP .bin.) as I've read that cures the stumble/dying when slowing/stopping with clutch depressed.
Screenshot; this is S-AUJP, VSS X 018 bit 6 I believe. It was checked, if unchecked, does it enable the ECM to receive/interpret the VSS signal for the 165 ECM? I say that because without going back in to change the SGI-100, the ECM is receiving the old signal that the 165 ECM required. Hope that makes sense...
Yep, but I don't believe S_AUJP sets it to AA by default.
Magman => You might want to give my Miniram start bin a shot... Other people have used it as a starting point with short runner manifolds and have had better luck than starting with a stock TPI bin.
BTW, I'm helping another member with a 383 HSR and very similar cam using S_AUJP_v7, as well as starting with my Miniram start bin.... and I'm advising him to just go open loop and tune via the WB. Even though his BLM's are very good and the car seems to run pretty decently, and he's adjusted his O2 thresholds quite a bit richer, he's getting these part throttle lean spots that we can't seem to get rid of. I think it's a function of the 7730 being essentially an "emissions oriented" ECM and not a performance oriented one (as opposed to say, the EBL, or a Holley or other aftermarket setup).
I was running into similar stubborn part throttle lean issues with my 383, Miniram and much milder cam (215° @.050 on a 114 LSA)... I only get away with closed loop due to how much I restricted the ECM from trimming fuel with the INT and BLM (a configuration I dubbed "quasi-closed loop").
Hello fellas. I could use some guidance using the Hex editor in TPRT. I'm working on a 1989 GTA that we converted from MAF to SD (165 to 730 ECM) and now the VSS input is non-existent in the datalog. Most of you have probably seen the instructions, but they say, "requires PROM change: MAG VSS at 0x18 b6 for $8D PROM". Unfortunately for me, I have no clue how to make this change; never worked with the Hex editor before. Every data point in the log is pulling 6+ degrees SA right now and I'm not sure if it's because of the VSS or not. I've been pulling timing and fuel, but want to eliminate the VSS as a problem.
Because $8D defaults to a magnetic VSS, the ECM won’t recognize the square‑wave signal your ’89 GTA uses unless you flip the VSS‑type bit. If you’re not familiar with creating a new flag in the XDF, the simpler method is to change it directly in the hex editor. Go to address 0x18 and set bit 6. That tells the 7730 ECM to use the F‑body square‑wave VSS instead of the magnetic type. Once that bit is set, your datalog will start showing MPH. As for the timing issue, when that bit isn’t set, $8D thinks the car is always at 0 mph. That keeps it stuck in idle/coast logic, so it stays in Idle Return and DFCO recovery modes. That’s why you’re seeing 6+ degrees of spark being pulled and why the car feels sluggish. Fixing the VSS bit will clean that up immediately...
Thank you guys for helping me out, it is very much appreciated!
I'm going to revert back to S_AUJP_V4 - it has many more parameters defined in the XDF. Switch 18 Bit 6 was originally checked in the AUJP .bin (pic below) and I know works fine in a 1990 IROC-Z, 700R4 with 730 ECM. I unchecked that and changed the VSS input from 4,000 PPM to 2000 PPM. That should now provide the ECM with the correct VSS input, correct?
The ECM is looking for the 1990 '730 VSS signal (2,000 PPM I believe), but the T56 signal sent through the SGI-100BT is outputting the 1989 GTA (165 required) signal which is 4000 PPM I believe. In case it matters...the speedometer works fine!
Thank you guys for helping me out, it is very much appreciated!
I'm going to revert back to S_AUJP_V4 - it has many more parameters defined in the XDF. Switch 18 Bit 6 was originally checked in the AUJP .bin (pic below) and I know works fine in a 1990 IROC-Z, 700R4 with 730 ECM. I unchecked that and changed the VSS input from 4,000 PPM to 2000 PPM. That should now provide the ECM with the correct VSS input, correct?
The ECM is looking for the 1990 '730 VSS signal (2,000 PPM I believe), but the T56 signal sent through the SGI-100BT is outputting the 1989 GTA (165 required) signal which is 4000 PPM I believe. In case it matters...the speedometer works fine!
you can simply open your non saujp $8d bin in the saujp xdf and fix the bit street lethal is telling you. Then open it with your normal xdf and go.
You can also open a second instance of tunerpro and open up the saujp xdf. Copy any flag/parameter/table defined in it with an address with only 3 digits copy it and paste it into your non saujp but still $8D xdf. Filling in the saujp well defined stuff into your non well defined xdf.
Just be careful and know that any address with 4 digits is highly suspect.
Last edited by Vanilla Ice; May 4, 2026 at 11:16 PM.
Thank you guys for helping me out, it is very much appreciated!
I'm going to revert back to S_AUJP_V4 - it has many more parameters defined in the XDF. Switch 18 Bit 6 was originally checked in the AUJP .bin (pic below) and I know works fine in a 1990 IROC-Z, 700R4 with 730 ECM. I unchecked that and changed the VSS input from 4,000 PPM to 2000 PPM. That should now provide the ECM with the correct VSS input, correct?
The ECM is looking for the 1990 '730 VSS signal (2,000 PPM I believe), but the T56 signal sent through the SGI-100BT is outputting the 1989 GTA (165 required) signal which is 4000 PPM I believe. In case it matters...the speedometer works fine!
Just to clarify... the ECM doesn’t really care whether the signal is 2000 or 4000 PPM as long as the BIN matches whatever the SGI‑100BT is outputting. The speedometer working confirms the SGI is doing its job. The part that actually determines whether $8D sees VSS is bit 6 at address 0x18. Bit 6 ON = square‑wave VSS (F‑body / 165 / 730 cars), Bit 6 OFF = magnetic VSS. Since the T56 + SGI‑100BT is giving the ECM a square‑wave signal, bit 6 needs to stay checked. Unchecking it tells the ECM to expect a magnetic sine‑wave signal, which is why VSS disappears in the datalog. Once bit 6 is ON and the PPM in the BIN matches the SGI output, $8D will read MPH correctly.
Just a quick update. I had no luck getting the VSS to register MPH in the datalog, so I went back into the wiring and discovered I have the SGI-100 wired wrong. I've got an e-mail out to the tech line to help get that straightened out. I tried multiple .bins with varied settings to no avail. Unfortunately, I stowed the SGI under the center console, so it's back apart now with the VSS wiring disconnected. I should be back in business soon. Thanks again for the tech assist, it is much appreciated!
