Making sense of LTFT readings - causing S60 2.0T to stall
Discussion
Evening all,
Hoping someone with me knowledge than me can point me in the right direction on this. Recently bought a 2004 S60 2.0T that has a a cutting out/stalling issue. In summary:
- Started off fine, other than the occasional flatspot during WOT
- Idle started becoming a little erratic, but wouldn't stall until switched off. When restarting, engine fires for a couple of seconds before cutting out completely
- Scanned with Torque app, codes (sometimes live, somtimes pending) have been P0101 (Mass of Volume Air Flow Circuit Range/Performance Problem) and sometimes a P2188 (System Too Rich at Idle bank 1) to go with it
- If I clear codes, car starts again and the cycle repeats after about 15-20 miles
- During this time, LTFT slowly climbs from 0 to around 8 or 9. When it gets to this point, when I restart it will stall
- Just before it last stalled, I turned the car off with LTFT of 6.something. When I turned it back on, it was showing -23.4! Predictably it then choked and stalled when I tried to start it. See screenshot.
I was reluctant to start throwing parts at it so took the car in to a local specialist. They've plugged into VIDA but suggested other than the MAF reading a little low, everything looks ok. They've suggested it may be the throttle body, apparently the internals (not the butterfly valve) can cause these symptoms. I'm not convinced as throttle readings in Torque appear ok, plus I'm not sure it would cause the steady rise or sometimes erratic LTFT readings.
Their suggestion is to let the problem develop but I can't really run a car that needs a DTC reset every other time I want to start it! Before I start replacing parts (MAF or throttle body) does anyone have any suggestions based on the figures recorded from Torque? My knowledge is limited so I may be missing something obvious - all I can ascertain is that something is causing it to (usually) run lean and think it needs more fuel to the point of overfuelling and stalling - or in the case of the screenshot above, majorly underfuel and stall.
Thanks in advance.
Hoping someone with me knowledge than me can point me in the right direction on this. Recently bought a 2004 S60 2.0T that has a a cutting out/stalling issue. In summary:
- Started off fine, other than the occasional flatspot during WOT
- Idle started becoming a little erratic, but wouldn't stall until switched off. When restarting, engine fires for a couple of seconds before cutting out completely
- Scanned with Torque app, codes (sometimes live, somtimes pending) have been P0101 (Mass of Volume Air Flow Circuit Range/Performance Problem) and sometimes a P2188 (System Too Rich at Idle bank 1) to go with it
- If I clear codes, car starts again and the cycle repeats after about 15-20 miles
- During this time, LTFT slowly climbs from 0 to around 8 or 9. When it gets to this point, when I restart it will stall
- Just before it last stalled, I turned the car off with LTFT of 6.something. When I turned it back on, it was showing -23.4! Predictably it then choked and stalled when I tried to start it. See screenshot.
I was reluctant to start throwing parts at it so took the car in to a local specialist. They've plugged into VIDA but suggested other than the MAF reading a little low, everything looks ok. They've suggested it may be the throttle body, apparently the internals (not the butterfly valve) can cause these symptoms. I'm not convinced as throttle readings in Torque appear ok, plus I'm not sure it would cause the steady rise or sometimes erratic LTFT readings.
Their suggestion is to let the problem develop but I can't really run a car that needs a DTC reset every other time I want to start it! Before I start replacing parts (MAF or throttle body) does anyone have any suggestions based on the figures recorded from Torque? My knowledge is limited so I may be missing something obvious - all I can ascertain is that something is causing it to (usually) run lean and think it needs more fuel to the point of overfuelling and stalling - or in the case of the screenshot above, majorly underfuel and stall.
Thanks in advance.
Your problem is why the STFT is maxed out surely? The LTFT will average the STFT over a period of time.
STFT is what the engine thinks is happening now. It thinks it’s running rich so is trying to trim back fuelling.
Think you need a good poke around other sensor readings to see what isn’t making sense. Could be something like throttle needing adaptation or duff injector or air leak etc etc.
STFT is what the engine thinks is happening now. It thinks it’s running rich so is trying to trim back fuelling.
Think you need a good poke around other sensor readings to see what isn’t making sense. Could be something like throttle needing adaptation or duff injector or air leak etc etc.
LordLoveLength said:
Your problem is why the STFT is maxed out surely? The LTFT will average the STFT over a period of time.
STFT is what the engine thinks is happening now. It thinks it’s running rich so is trying to trim back fuelling.
Think you need a good poke around other sensor readings to see what isn’t making sense. Could be something like throttle needing adaptation or duff injector or air leak etc etc.
The 2 are synonymous as you say, albeit the STFT is reading high and low during the same run, but averaging out high on the LTFT.STFT is what the engine thinks is happening now. It thinks it’s running rich so is trying to trim back fuelling.
Think you need a good poke around other sensor readings to see what isn’t making sense. Could be something like throttle needing adaptation or duff injector or air leak etc etc.
My mechanic friend had a poke about this evening and spotted this:
The breather pipe to the PCV has disintegrated. The hole at the bottom had nothing going to it.
It needs replacing regardless but would this mess with the AFR? Or a separate issue completely?
Belle427 said:
I would expect it to be close to 0%.
I think this is normal for Torque... I'm going to plug it into the other car and see what it says. Quick Google search suggests the reading is based on absolute position rather than relative but should be something fairly easy to rule out - or conversely highlight an issue. Tc24 said:
LordLoveLength said:
Your problem is why the STFT is maxed out surely? The LTFT will average the STFT over a period of time.
STFT is what the engine thinks is happening now. It thinks it’s running rich so is trying to trim back fuelling.
Think you need a good poke around other sensor readings to see what isn’t making sense. Could be something like throttle needing adaptation or duff injector or air leak etc etc.
The 2 are synonymous as you say, albeit the STFT is reading high and low during the same run, but averaging out high on the LTFT.STFT is what the engine thinks is happening now. It thinks it’s running rich so is trying to trim back fuelling.
Think you need a good poke around other sensor readings to see what isn’t making sense. Could be something like throttle needing adaptation or duff injector or air leak etc etc.
My mechanic friend had a poke about this evening and spotted this:
The breather pipe to the PCV has disintegrated. The hole at the bottom had nothing going to it.
It needs replacing regardless but would this mess with the AFR? Or a separate issue completely?
Important thing is it is a current reading so you can chase a fault in real time.
Obviously replace the breather and have a good look at other similar pipes which are presumably the same age and may have deteriorated as well!
Some time off work and other projects means thread revival time!
- Vehicle has been smoke tested, a small leak was found near the turbo (from memory). Pipe replaced, thought this would resolve, but unfortunately not.
Further updates:
- MAF was plugged into an oscilloscope and reading a little low. Replaced with a new Bosch unit but still no immediate change.
- Throttle body cleaned out, again seemingly made no difference
While I've still had both stalling and error codes since the new parts, interestingly it hasn't stalled in the last couple of hundred miles or thrown any error codes. It's either as a result of the work to date OR a couple of longer journies with minimal WOT have helped average out the LTFT so that it doesn't spike them every time I do put my foot down. Maybe there were multiple issues at play and I've only fixed one or some of them.
The issue is still there in some form however, as STFT still shoots up to 25 under load without fail. Idle and part load seem to be ok for now.
I read somewhere that an air leak would cause issues with idle rather than WOT so really my question is now - what could cause lean running under load/at WOT?
If going down the parts route (that I was hoping to avoid) common sense would suggest O2 sensor is next...
LordLoveLength said:
Any air leak has the potential to upset the MAF reading dependent on where exactly it is - small leaks having a larger proportional effect at idle which is probably why it is high and low over a run.
Important thing is it is a current reading so you can chase a fault in real time.
Obviously replace the breather and have a good look at other similar pipes which are presumably the same age and may have deteriorated as well!
This breather has now been fixed... but made no difference. Needed doing regardless, so nothing lost here. In summary since my last post:Important thing is it is a current reading so you can chase a fault in real time.
Obviously replace the breather and have a good look at other similar pipes which are presumably the same age and may have deteriorated as well!
- Vehicle has been smoke tested, a small leak was found near the turbo (from memory). Pipe replaced, thought this would resolve, but unfortunately not.
Further updates:
- MAF was plugged into an oscilloscope and reading a little low. Replaced with a new Bosch unit but still no immediate change.
- Throttle body cleaned out, again seemingly made no difference
While I've still had both stalling and error codes since the new parts, interestingly it hasn't stalled in the last couple of hundred miles or thrown any error codes. It's either as a result of the work to date OR a couple of longer journies with minimal WOT have helped average out the LTFT so that it doesn't spike them every time I do put my foot down. Maybe there were multiple issues at play and I've only fixed one or some of them.
The issue is still there in some form however, as STFT still shoots up to 25 under load without fail. Idle and part load seem to be ok for now.
I read somewhere that an air leak would cause issues with idle rather than WOT so really my question is now - what could cause lean running under load/at WOT?
If going down the parts route (that I was hoping to avoid) common sense would suggest O2 sensor is next...
Another question for those who know - which sensors should I be recording data from/graphing in Torque to try and pinpoint this? You can see those I've used to date but I think these are more helpful in showing there's an issue rather than what it is... perhaps some combination of:
- Engine load/air flow
- Throttle position
- O2 sensor voltage (not equivalence?)
- Commanded AFR
As is probably clear, I'm no mechanic so feel like I'm shooting in the dark a little bit with the data I'm currently recording!
- Engine load/air flow
- Throttle position
- O2 sensor voltage (not equivalence?)
- Commanded AFR
As is probably clear, I'm no mechanic so feel like I'm shooting in the dark a little bit with the data I'm currently recording!
Tc24 said:
Plugs are new and correct spec. Coils are original as far as I can see but wouldn't I be getting codes for a misfire if they'd degraded?
You need to have a certain number of misfires before they will register a fault code.You might find codes shown in the 'Pending codes' section if you have one, and sometimes the live data will show the number of misfires on a specific cylinder.
On the other hand it might be nothing to do with misfires.
bearman68 said:
You need to have a certain number of misfires before they will register a fault code.
You might find codes shown in the 'Pending codes' section if you have one, and sometimes the live data will show the number of misfires on a specific cylinder.
On the other hand it might be nothing to do with misfires.
I think I can probably find a way to log this in Torque, likely worth monitoring.You might find codes shown in the 'Pending codes' section if you have one, and sometimes the live data will show the number of misfires on a specific cylinder.
On the other hand it might be nothing to do with misfires.
No pending codes (other than the ever-present clutch position sensor I've not got round to fixing yet). It'll occasionally throw the P0101 originally mentioned, but less frequently.
Chris32345 said:
Ask a mot station if they can put the emissions machine on it for a few quid see if it is really running rich or lean
As it could be a o2 sensor misreading
Good shout, however it went through the MOT fine and from memory the emissions printout showed lambda at pretty much bang on 1.00 and low HC. With the lean condition only happening under high load we'd have to poke the probe from a rolling 30mph start in 4th or something! Doesn't tend to lean out so much when static even if revved, only under load.As it could be a o2 sensor misreading
To add some further info that may or may not be of use, I've been playing around with the Torque app again today and found some useful data I hadn't used before. Rather than looking at fuel trims to measure how lean it's running, I've instead looked at actual AFR.
Nearly all the time in normal driving it's close to 14.7:1 (good). At WOT however it's nearer 17:1. Not horrendously out when compared to stoich BUT it should be running rich at WOT by my understanding - something like 12:1. Even with STFT at 25%, to me that sounds like it's running in the region of 40% leaner than it should be. Can't be good for the engine.
Also interesting that the other car I tested this in (admittedly not a Volvo) goes open loop when approaching WOT. The S60 stays closed loop all the time other than when off throttle. Any significance in this?
Tc24 said:
Good shout, however it went through the MOT fine and from memory the emissions printout showed lambda at pretty much bang on 1.00 and low HC. With the lean condition only happening under high load we'd have to poke the probe from a rolling 30mph start in 4th or something! Doesn't tend to lean out so much when static even if revved, only under load.
To add some further info that may or may not be of use, I've been playing around with the Torque app again today and found some useful data I hadn't used before. Rather than looking at fuel trims to measure how lean it's running, I've instead looked at actual AFR.
Nearly all the time in normal driving it's close to 14.7:1 (good). At WOT however it's nearer 17:1. Not horrendously out when compared to stoich BUT it should be running rich at WOT by my understanding - something like 12:1. Even with STFT at 25%, to me that sounds like it's running in the region of 40% leaner than it should be. Can't be good for the engine.
Also interesting that the other car I tested this in (admittedly not a Volvo) goes open loop when approaching WOT. The S60 stays closed loop all the time other than when off throttle. Any significance in this?
Sounds like it's not injecting enough fuel. I wonder how long the fuel injection 'dwell' is - I guess it's up around 6ms or so.To add some further info that may or may not be of use, I've been playing around with the Torque app again today and found some useful data I hadn't used before. Rather than looking at fuel trims to measure how lean it's running, I've instead looked at actual AFR.
Nearly all the time in normal driving it's close to 14.7:1 (good). At WOT however it's nearer 17:1. Not horrendously out when compared to stoich BUT it should be running rich at WOT by my understanding - something like 12:1. Even with STFT at 25%, to me that sounds like it's running in the region of 40% leaner than it should be. Can't be good for the engine.
Also interesting that the other car I tested this in (admittedly not a Volvo) goes open loop when approaching WOT. The S60 stays closed loop all the time other than when off throttle. Any significance in this?
In which case, since it's going lean WOT, I wonder if the fuel pressure regulator is working correctly, or the fuel pump delivering enough fuel pressure. Both should be fairly easy to check.
I've certainly had it before where the fuel pressure was incorrect, leading to incorrect fuelling. In my case it was rich, and the dwell time had closed to about 2 or 2.5 ms, and it was still injecting too much fuel. Maybe this is similar. ?
bearman68 said:
Sounds like it's not injecting enough fuel. I wonder how long the fuel injection 'dwell' is - I guess it's up around 6ms or so.
In which case, since it's going lean WOT, I wonder if the fuel pressure regulator is working correctly, or the fuel pump delivering enough fuel pressure. Both should be fairly easy to check.
I've certainly had it before where the fuel pressure was incorrect, leading to incorrect fuelling. In my case it was rich, and the dwell time had closed to about 2 or 2.5 ms, and it was still injecting too much fuel. Maybe this is similar. ?
Thanks for the informative response, I'd never really considered dwell on a modern car! Fuel pressure is a good shout, and infact after the O2 sensor (going to replace due to age) it was what the garage next suggested measuring next. I'll report back with findings (albeit progress is still very slow - due to both me and the garage).In which case, since it's going lean WOT, I wonder if the fuel pressure regulator is working correctly, or the fuel pump delivering enough fuel pressure. Both should be fairly easy to check.
I've certainly had it before where the fuel pressure was incorrect, leading to incorrect fuelling. In my case it was rich, and the dwell time had closed to about 2 or 2.5 ms, and it was still injecting too much fuel. Maybe this is similar. ?
I actually thought the parts to date had collectively resolved this to a usable point - i.e. no longer stalling... however I think a lot of "light" driving in traffic = no WOT = no chance for LTFT to spike... and stall.
Foot flat to the floor on a sliproad last week, car choked and stalled while doing 70. That's a new one.
Against original plans I'll continue to replace parts, provided none of them are overly expensive. Next up is a front O2 sensor, genuine Bosch per the MAF to rule out any cheap parts playing havoc.
Pending this and the fuel pressure check, I'd be really grateful if anyone with a P2 (preferably the 2.0T) and Torque/another OBD app could plug in on their next journey and post any of the following so I know what my data should look like:
- STFT under load (ideally 40mph+)
- Whether fuel system goes closed loop under load - mine remains open unless off throttle
- How quickly fuel system goes closed loop from cold. Mine was open until coolant temp was just 8c and about 50m down the road then switched over - surely that's too soon?!
Thanks to anyone else still reading.
melhookv12 said:
Friend had a car that would stall. Similar codes. Few people looked at and scratched their heads.
Turned out to be the A/C compressor seizing up, not sure if you have A/C but might be worth removing the belt and checking.
Good luck
Now that is a left field guess, but I do have A/C. I don't know if the ECU is smart enough to know whether A/C is/isn't engaged and fuel accordingly, but if it's happened to your friend's car then clearly it can happen.Turned out to be the A/C compressor seizing up, not sure if you have A/C but might be worth removing the belt and checking.
Good luck
Nothing to lose by giving that a try, I'll see how easy the belt is to whip off. Thanks for the suggestion.
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