Shunting / Misfire on the warm-up
Discussion
After a bit of advice if I can. Getting to grips with the new Tuscan, but having a real issue with engine stuttering / misfire when driving off from cold i.e. on the warm-up cycle.
As soon as I stop the car for 10 seconds or so and re-start it, the problem goes away and she drives perfectly. Have set the engine up in terms of throttle balance and adaptives – all within 1 or 2%, lambdas switching lean to rich every second or so of each other and the drive is very smooth – normally. No fault codes or fault logs.
Was thinking about fuel purging, so opened the fuel tank filler with engine running, but no difference.
The only way I can eradicate the issue is to stop the car and restart it.
Have fitted an ‘uprated’ Bosch coolant temperature sensor as part of the recommission, but I do note its accuracy compared to the pod at lower temperatures can be up to 10 Deg C out until I get to the 88 Deg C mark where they both line up. Wondering whether by stopping the car the cylinder head coolant temp increases, so the accuracy improves and the problem goes away?
Any ideas?
TIA
Nick
As soon as I stop the car for 10 seconds or so and re-start it, the problem goes away and she drives perfectly. Have set the engine up in terms of throttle balance and adaptives – all within 1 or 2%, lambdas switching lean to rich every second or so of each other and the drive is very smooth – normally. No fault codes or fault logs.
Was thinking about fuel purging, so opened the fuel tank filler with engine running, but no difference.
The only way I can eradicate the issue is to stop the car and restart it.
Have fitted an ‘uprated’ Bosch coolant temperature sensor as part of the recommission, but I do note its accuracy compared to the pod at lower temperatures can be up to 10 Deg C out until I get to the 88 Deg C mark where they both line up. Wondering whether by stopping the car the cylinder head coolant temp increases, so the accuracy improves and the problem goes away?
Any ideas?
TIA
Nick
It may be a mechincal or electrical issue but also each time you start the car the ecu looks to reset the initial throttle position, so it might be that something you or the car is doing on first power up isn't achieving that, but it does the second start up. You need to data log the diagnostics, or keep a beady eye on the live running numbers to see if you can spot anything going on there.
Edited by spitfire4v8 on Tuesday 12th June 09:16
I have noticed something similar on mine. Sometimes it seems that a stop and restart improved the light throttle low speed running. Like spitfire I'd concluded that it's something to do with the way the ecu samples the throttle pots at start up...I guess with bit of noise and uncertainty sometimes it's a few pct out and that's enough to get it running on the wrong point in the fuelling map. But just a guess on my part.
Had similar issues with both the Sagaris (05) and T350 (03)..
If both left to idle for a while (no throttle) straight after starting to warm up they were both very happy; if you drove off almost immediately (or held the throttle up to say 1000rpm to warm it) then it would "feel" a little upset at lower RPM's..
For me it was such a subtle difference, that disappeared when warmed up, that I suspect most people never really notice it.
Or.. maybe a certain revision of the MBE firmware has this 'effect'
If both left to idle for a while (no throttle) straight after starting to warm up they were both very happy; if you drove off almost immediately (or held the throttle up to say 1000rpm to warm it) then it would "feel" a little upset at lower RPM's..
For me it was such a subtle difference, that disappeared when warmed up, that I suspect most people never really notice it.
Or.. maybe a certain revision of the MBE firmware has this 'effect'
Thanks all for your response. Not had a chance to play with the car since, but what I have also noticed is that if I set the air flows between the two banks identically at idle I find that the throttle pot value is about 5% higher on the front and the adaptive on the rear goes consistently - ve (10-15%) whilst the front will trim nicely to around 0% even after a throttle reset and with an idle of around 900rpm. So I end up offsetting the balance to line it up. Is this a school boy error on my part and should I just let the adaptives do their thing from the base map ie with two banks balanced?
I do note the LHS exhaust occasionally 'chuffs' but not sure if that is because the airflow is set wrong...
Nick
I do note the LHS exhaust occasionally 'chuffs' but not sure if that is because the airflow is set wrong...
Nick
I've always noticed an inbalance in the adaptives after replacing the airbox top even when they're nigh on identical during the set up routine with the airbox top off.
I've always put the inbalance that occurs afterwards to the fact that the breather is towards the front of the airbox, but I've no evidence of that .. moving the breather to the centre or rear would prove it I guess.
I always leave the adaptives to do their thing (with the airflows set up as close as possible with the airbox top off) and accept the difference in values front/rear .. I doubt your issues are anything to do with the inbalance youre seeing bearing in mind 99 percent of other sp6 cars set up this way drive very nicely, but you never know. Why not try a variety of slight butterfly balance changes and report back?
I've always put the inbalance that occurs afterwards to the fact that the breather is towards the front of the airbox, but I've no evidence of that .. moving the breather to the centre or rear would prove it I guess.
I always leave the adaptives to do their thing (with the airflows set up as close as possible with the airbox top off) and accept the difference in values front/rear .. I doubt your issues are anything to do with the inbalance youre seeing bearing in mind 99 percent of other sp6 cars set up this way drive very nicely, but you never know. Why not try a variety of slight butterfly balance changes and report back?
Thanks both.
Agree Joolz that the adaptives seem to screw up once the airbox lid is refitted.
Hopefully will get a chance to have a play tonight and try it with a balanced throttle set up and also see how the airflows differ at say 1500 RPM when balanced at idle...
Will run a log hopefully when it's misbehaving to see what's s going on.
Nick
Agree Joolz that the adaptives seem to screw up once the airbox lid is refitted.
Hopefully will get a chance to have a play tonight and try it with a balanced throttle set up and also see how the airflows differ at say 1500 RPM when balanced at idle...
Will run a log hopefully when it's misbehaving to see what's s going on.
Nick
Well, after a bit more tinkering, I managed to get her running sweet only for her to go off the boil after stopping and restarting. So this time the opposite to my original issue.
So decided to swap the NVRAM in the ECU as suspecting trim values were being lost etc. and hey presto... I think...
Running sweet as a nut all day today. I can only assume the 10 year lay-up was enough to kill the backup lithium battery.
Will do a run to work in it tomorrow to see whether I've spoken too soon (or not).
So decided to swap the NVRAM in the ECU as suspecting trim values were being lost etc. and hey presto... I think...
Running sweet as a nut all day today. I can only assume the 10 year lay-up was enough to kill the backup lithium battery.
Will do a run to work in it tomorrow to see whether I've spoken too soon (or not).
Did it make a difference ?
The other odd thing I find is that I can set the idle speed at cold to between 800 and 850 and its good...until the next day when it seems to undo the tweak on the adjuster screw and it starts & idles at 700. Its almost like the ecu nulls out the idle screw adjustments if they are small. But for sure, if you go silly and set a very fast idle, then you deffo get a fast cold idle next time. All very frustrating
The other odd thing I find is that I can set the idle speed at cold to between 800 and 850 and its good...until the next day when it seems to undo the tweak on the adjuster screw and it starts & idles at 700. Its almost like the ecu nulls out the idle screw adjustments if they are small. But for sure, if you go silly and set a very fast idle, then you deffo get a fast cold idle next time. All very frustrating
Hi Pete,
Glad you sorted yours...
I still have an issue. The car runs OK, but sometimes still hesitates or holds back (sometimes) around the 2.5k RPM mark. It definitely improves if I stop the engine for a minute or so and then restart.
Since the re-commission, its had new coil, plugs and leads as per my original posts.
What I can see is very occasionally I will see a spike on the leading throttle pot, but I am not sure whether its the no.1 butterfly causing it or vice-versa. I can have the hesitance when the pot output is rock stable (as much as can expected for the one the leading pot).
I want to:
1) get the valve clearances checked
2) Check the throttle springs again
3) try a new throttle pot (but this one is new and thy are as rare as rocking horse s###e)
4) Apply a d-throttle to the pot by either s/w update (eprom) or just by putting a small capacitor across the pot wiper and 0V at the ECU
6) Try another set of plug leads
Just need to get thee time and inclination to make progress...
Nick
Glad you sorted yours...
I still have an issue. The car runs OK, but sometimes still hesitates or holds back (sometimes) around the 2.5k RPM mark. It definitely improves if I stop the engine for a minute or so and then restart.
Since the re-commission, its had new coil, plugs and leads as per my original posts.
What I can see is very occasionally I will see a spike on the leading throttle pot, but I am not sure whether its the no.1 butterfly causing it or vice-versa. I can have the hesitance when the pot output is rock stable (as much as can expected for the one the leading pot).
I want to:
1) get the valve clearances checked
2) Check the throttle springs again
3) try a new throttle pot (but this one is new and thy are as rare as rocking horse s###e)
4) Apply a d-throttle to the pot by either s/w update (eprom) or just by putting a small capacitor across the pot wiper and 0V at the ECU
6) Try another set of plug leads
Just need to get thee time and inclination to make progress...
Nick
I'm glad too...really was starting to despair. Such a simple fix in the end...amazing what a difference a few mm of missing travel on the butterflies made (it was 5 and 6 not moving enough).
Not sure if you recall but i've changed my whole throttle set up...all cylinders are ganged together using oldham shaft couplers, and I have just one throttle pot right in middle directly on the lever (I chose to use the rocking horse blue one
bad choice! but will use a white one flipped over some day when I need to). So actuation is nice a sharp and the nice thing is the pot gets to know about small throttle inputs immediately not after all the slack of the balance arms (by which time the middle cylinders have tended to lean off as they have opened a bit but 1 and 6 still haven't taken up the slack and hence haven't started to move->3 and 4 have too much air). While its a big improvement, there's still shunting. I'm fairly sure its down to cylinder mixture in-balance and randomness at light throttle. I'm really starting to think there is no fix as-such, its just down to the "simplicity" of the control setup. Unless someone knows otherwise ?
Not sure if you recall but i've changed my whole throttle set up...all cylinders are ganged together using oldham shaft couplers, and I have just one throttle pot right in middle directly on the lever (I chose to use the rocking horse blue one
bad choice! but will use a white one flipped over some day when I need to). So actuation is nice a sharp and the nice thing is the pot gets to know about small throttle inputs immediately not after all the slack of the balance arms (by which time the middle cylinders have tended to lean off as they have opened a bit but 1 and 6 still haven't taken up the slack and hence haven't started to move->3 and 4 have too much air). While its a big improvement, there's still shunting. I'm fairly sure its down to cylinder mixture in-balance and randomness at light throttle. I'm really starting to think there is no fix as-such, its just down to the "simplicity" of the control setup. Unless someone knows otherwise ?Gassing Station | Speed Six Engine | Top of Page | What's New | My Stuff