Kirby@PCMTec Posted October 19, 2021 Share Posted October 19, 2021 Hey Guys, One support query I get often is related to issues with gear detection in manual transmissions (especially FG+) where the gear detection fails and the gear indicator on the dashboard clears, cruise control keeps dropping out in 3rd/4th or CustomOS boost by gear isn't obeying the commanded boost target. Why does it happen? Basically, there is no gear detection sensor in any factory manual transmission (other than Reverse) and unlike the autos (BTR, 5r55 or 6hp26) where either the PCM or TCM knows the gear by the commanded clutch/brake states (along with some plausibility) the manual gearboxes are dependent 100% on a computational method. The computational method works like this (simplified): 1) Measure Engine RPM > 2) Measure OSS (Transmission Output Shaft Speed) > 3) Calculate RPM/OSS > 4) Wait for Stable > 5) Compare to Gear Ratio Table > 6) Select Closest Gear > 7) Lock Selection > 😎 Start Timer In some calibrations the guys at Ford made particularly tight allowances for the gear ratio's for part 5/6 of the method: A number of factors (clutch slip, jitter in RPM or OSS) can cause the instantaneous ratio (e.g. RPM/OSS) to move out of range and the gear detection program will fail. When this happens, the "gear selected" will go to '0' (e.g. Neutral) and any number of routines in the PCM relying on gear will quit or 'go funny' due to the gear changing from say 3 to neutral, or in this case the cluster displaying an error. How to detect? If you think its happening you can use the PCMTec Datalogger to verify. The following logging channels are useful: MID36381 Estimated Gear Selected - MTX MID61215 Instant Transmission Ratio - MTX MID37788 Current Gear Ratio - MTX MID110730 Time In Gear - MTX Along with Throttle, RPM, VSpeed and VSS Fail Flag. Here is a classic example. You can see the orange trace (MID37788) getting "bumpy" at a few locations, at the same time you can see the estimated gear (MID36381) drop from 3rd to '0'. (Yellow Arrow, Red Arrow). Time in gear (MID110730) resets to zero (green arrow). When the gear estimator can't 'snap' to a gear it will change to and reflect the instantaneous ratio (green trace, MID61215), NB: these are not exactly the same at my marker due to some delay -and- different logging rates and polling times. At the indicated point you can see the instant ratio is "1.3431" (indigo box). If you look at the image above for the tuning parameters, you can see this is just outside the detection range (auF0337). So with the instantaneous ratio being out of range for the required plausibility time (few ms) of any gear, the gear selection program reverts '0' - Neutral or unknown gear. NB: this is a valid selection because if OSS = Zero and RPM > 1 (clutch in or in neutral), this ratio will actually go infinite (there is actually a clip parameter to set the default value) and this routine must accommodate that and provide some method of detecting Netural. Why? Assuming this particular example is driving on the road or a dyno (with a decent amount of drivetrain inertia) the rapid stabs of the throttle are casing a decent torque increase (and not so much rpm increase) which is likely slipping the clutch just enough for the above check to fail momentarily. Depending on the car, its age and power targets, it might be due for a new clutch. 😇 How to fix? Once you have identified the cause and found the offending gear, usually opening up the ratio limits are sufficient (as mentioned, our opinion is they are a little tight from factory for 3rd and/or 4th). In this particular example 3.6 on the upper limit (auF0337) of the 3rd gear ratio was sufficient and the problem of gear detection abated. Hope someone finds this interesting! Happy Tuning. 2 Quote Link to comment Share on other sites More sharing options...
Bill Posted October 19, 2021 Share Posted October 19, 2021 Great write up @Kirby@pcmtec 2 hours ago, Kirby@pcmtec said: How to detect? If you think its happening you can use the PCMTec Datalogger to verify. The following logging channels are useful: MID36381 Estimated Gear Selected - MTX MID61215 Instant Transmission Ratio - MTX MID37788 Current Gear Ratio - MTX MID110730 Time In Gear - MTX This issue is one I've previously investigated with version 1.25 & found that the channels were not as clearly named. The updated naming & ID in Version 2.10 has really tidied this up. I've just connected to a BA F6 HAAT3VC, didn't actually go for a drive & can find all channels except MID110730. I'm guessing it might not be available with the BA PCM or it's something that's still being investigated. All the MID channels above, are available on the BF XR6T. MID110730 is workshop only 1 Quote Link to comment Share on other sites More sharing options...
Kirby@PCMTec Posted October 19, 2021 Author Share Posted October 19, 2021 12 hours ago, Bill said: Great write up @Kirby@pcmtec This issue is one I've previously investigated with version 1.25 & found that the channels were not as clearly named. The updated naming & ID in Version 2.10 has really tidied this up. I've just connected to a BA F6 HAAT3VC, didn't actually go for a drive & can find all channels except MID110730. I'm guessing it might not be available with the BA PCM or it's something that's still being investigated. All the MID channels above, are available on the BF XR6T. MID110730 is workshop only I actually had to work through this recently and found our default names really needing some improvement, so I did this for 2.1, but generally I am trying and refer by MID numbers whenever talking about datalogging for clarity. We are putting alot of effort into names at the moment - expect continual improvement in this space. Time in gear is definitely not needed to diagnose this, its just nice to confirm in logging. If you look it has a much higher MID number than the others, which generally (but not always) means that it was identified later - which might mean it didn't appear until later model PCM's. 1 Quote Link to comment Share on other sites More sharing options...
pma Posted August 1, 2023 Share Posted August 1, 2023 Hey very informative write up, im just going through same issues programming gear ratios for cruise in a patrol. When I try datalog, cannot access MID36381, MID61215, MID37788. FG turbo manual ecu, PCM tec pro version 2.11 Any ideas why? Quote Link to comment Share on other sites More sharing options...
Kirby@PCMTec Posted August 17, 2023 Author Share Posted August 17, 2023 From memory these are workshop only MIDs' 1 Quote Link to comment Share on other sites More sharing options...
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