Ranger 3.2/AUTO surging late on decel

G'day guys,

had my BT-50/Ranger (Duratorque 3.2L/6r80 auto) tuned a while back, runs great apart from surging in the bottom of 3rd gear on decel (rpm/injection timing/calc load alllllll over the shop). Once it grabs 1st its happy again.

Contacted tuner, has put it down to a trans issue... which it may be. I understand the basics of diesel tuning but by no means an expert - hence why I got a professional tune. However, i was able to log the phenomenon and wouldn't mind some of you to cast your eye over it. I won't bang on here - its all in the logs. to me converter seems to be doing what its told and I've run out of knowledge so here I am.

2 logs attached. One is a full stop in D (auto downshift to 1st), and another in 3rd in manual mode.. you'll see it sits there happily surging away in 3rd while stationary until i manually select D.

Really appreciate any time you are able to spare me.

Typically this surging happens when tuners don't know what they are doing. The usual suspect is the difference in actual torque output between the maps and how much torque the engine "post tune" is actually outputting. If a tuner makes a change to the fueling and timing and the torque value isn't updated for those changes then it won't know it actually makes more or less torque at the mapped torque output. IE: One map says it makes 200ftlbsTQ the other says 200ftlbs as well, but the tuner made changes to one of them and it actually now makes 230Ftlbs @ the 200 area. Now when the ECU is interpolating between them you'll get oscillation. This is always the most sensitive at low fuel amounts like Idle and Decel because the chance of being off by a higher percentage is... well higher.... I also see in your logs are this happens during warm up, and this is where the most interpolation between maps typically occurs as well. Before you go condemning the tune, according to the log your oil temp is a static *79F. Either that PID is wrong or your temp sensor is bad. If you can view oil temp in your cluster, verify its following coolant somewhat closely. Usually if the sensors are actually bad it will throw a correlation code for oil to coolant temp during next day cold startup. If oil temp is reading accurate my guess would be the tune needs some adjustments.

Thank you so much for taking a look and providing such a thoughtful response, J.W.

Yes you are right, that EOT is suspicious.. still 26C after a long drive today...i hadn't noticed - no gauge on cluster. Presumably that could cause issues with the tune if in fact the ECU is getting erroneous data? (And its not just a VCM Scanner display issue.) Not throwing any sensor codes, but I might unplug it see if anything changes.

You might be onto something with the interpolation issue, the problem is worse when dead cold but it still present when hot. i guess my follow up questions would be, and please excuse my ignorance:

- if this only happens at 0% throttle, at RPM where the driver demand torque is in the negatives, and all my main/base fueling tables (torque vs RPM) show zeros in those areas... ie no fuel demand.. then is the fuel demand coming from idle tables somewhere that HP Tuners doesn't show me? or is that more of a closed loop process? all i can adjust is idle RPM and Adders like AC.

-could it be caused by a wandering/low rail pressure? i refer to the obvious dip in rail pressure that coincides with onset of symptoms, but i have no idea if what im seeing is cause or effect.

-the fact that its only third gear, and doesn't do it idling in second or first... just putting that down to the extra load?? the downshift points/TCC behaviour are/is spot on for whats being commanded btw.

again thanks for taking the time.

Rail pressure surging can cause this but it has to move by more than 2k with a known good PW map and injectors to really make this happen. You can see your injection timing is moving around a lot going from -1.5 to 0 and back to 1.3. I believe this is tune related. That said I've also seen this when the PW map is messed with in the corresponding area as well. You need to log mg/stroke VCV or FCA milliamp so we know what the fuel system is doing. Could be a CP4 going bad but i'd like to look at those PIDs in a log.

Thanks again J.W.

flashed the stock tune back on and the car runs perfect so definitely somewhere in the tune.. EOT stuck at 79Fjust a red herring i think.

- PW map only changed in the very high load areas when compared to stock so probably not that?
- Agree about the timing.. there have been changes made there compared to stock in the 600-1000rpm columns at low-medium torque demand.
- unable to log fuel volume demanded or actual as far as im aware for this ecu. Unless there is PiD wizardry that can be done

I think i will mive the timing tables in the idle rpm regions back toward stock and see what happens. The fact that it exclusively happens in third gear at idle rpm and idles fine in 1st and 2nd baffles me unless there is extra load taking it to different cells to maintain idle in third gear on decel.

Im just abit fuzzy about where idle fuelling comes from when the pedal vs RPM driver torque (and therefore fuelling?) demand is negative/zero. I assume the ECU senses extra fuel required to maintain idle rpm as the rpms drop and it transitions away from overrun, and references the tables at higher torque demand in some kind of closed loop?

Thanks again mate. Ive taken up enough of your time i think but i really appreciate the ear.