Discussion
I'm at work so have not had time to look at the detail of the thread but I successfully mapped out some shunting from my Chim using megasquirt. I can drive at 1300rpm in any gear comfortably.
low load (TPS or vacuum) between 1000rpm and 2600rpm is not a part of the map you'll be at during any kind of driving except 'gentle'.
- I pulled a lot of advance (10-15 degrees I think?) from this area of the map, and re-tuned the fueling so the AFR was back to 14 ish. Job done.
- If you have no control over advance, you can enrichen the mixture until you reduce the power made to alleviate the shunting.
easy enough to back up the tune and try this out.
with much less torque in the gentle area of the map you'll less likely excite the positive feedback loop that gives you the shunt.
low load (TPS or vacuum) between 1000rpm and 2600rpm is not a part of the map you'll be at during any kind of driving except 'gentle'.
- I pulled a lot of advance (10-15 degrees I think?) from this area of the map, and re-tuned the fueling so the AFR was back to 14 ish. Job done.
- If you have no control over advance, you can enrichen the mixture until you reduce the power made to alleviate the shunting.
easy enough to back up the tune and try this out.
with much less torque in the gentle area of the map you'll less likely excite the positive feedback loop that gives you the shunt.
Edited by 977 on Friday 31st July 11:41
977 said:
I'm at work so have not had time to look at the detail of the thread but I successfully mapped out some shunting from my Chim using megasquirt. I can drive at 1300rpm in any gear comfortably.
low load (TPS or vacuum) between 1000rpm and 2600rpm is not a part of the map you'll be at during any kind of driving except 'gentle'.
- I pulled a lot of advance (10-15 degrees I think?) from this area of the map, and re-tuned the fueling so the AFR was back to 14 ish. Job done.
- If you have no control over advance, you can enrichen the mixture until you reduce the power made to alleviate the shunting.
easy enough to back up the tune and try this out.
with much less torque in the gentle area of the map you'll less likely excite the positive feedback loop that gives you the shunt.
Unfortunatly one fix dont cure all on my previous engine advance taken out fuel added cured lurching but on my new build of a totally different tune the fuel stays but advance as been added to reach the same low load (TPS or vacuum) between 1000rpm and 2600rpm is not a part of the map you'll be at during any kind of driving except 'gentle'.
- I pulled a lot of advance (10-15 degrees I think?) from this area of the map, and re-tuned the fueling so the AFR was back to 14 ish. Job done.
- If you have no control over advance, you can enrichen the mixture until you reduce the power made to alleviate the shunting.
easy enough to back up the tune and try this out.
with much less torque in the gentle area of the map you'll less likely excite the positive feedback loop that gives you the shunt.
Edited by 977 on Friday 31st July 11:41
different strokes for different specs I guess, I have even known stock TVR 400's to shunt like b
ds even though AFR's are within spec and present engine condition i.e cam condition ignition condition are all in a good state even inc my own 400 years ago I always put that down to it being fitted with the 500 cam but then later found that out to not be the case although it don't help 
in fact my present light shunting with this new build that's to be expected is far better than those previous examples even though I am using a cam spec that certainly not ideal for the road and an enlarged inlet track inc blended trumpet base I thought it would be far more unhappy at low speeds TBH I count my blessings I use an aftermarket ECU otherwise the car would be unbearable I'm sure 
Edited by Sardonicus on Friday 31st July 14:36
OK guys, thankyou for your thoughts. I have been fairly desperate and thinking desperate solutions.
Taking on board the comments, and after my Holidays I will start a brand new project and start to tune again from scratch. I will get my dizzy curve plotted and use that as start point for Spark, (because it feels good under 14CUX).
I have noticed under CUX during a 20min logging session, the mean AFR for the whole run was 14.7 exactly! So the ECU is doing its job and seems to run comfortably between 14.4 and 15. Drops into the 12's when accelerating. The idle AFR is around 14.4, whereas with MS I was using around 13.8. I would be interested to know what most 500 MS users are using for their ReqFuel? Mine is currently set to 16.1, 2 squirts Alternating. This gives a VE=54 at idle and VE's of around 130 peak rpm .
If I were to use the MS calculated value for my injectors (Ford Bosch 18-19lb, 4 pintle - from US, 280-150-943)this would give a ReqFuel = 21, which I have never actually tried!! I presume the VE's will simply adjust accordingly? Does anybody use the calculated value? Comments welcome.
Also any useful comments on Squirts and Simultaneous settings choice?
I won't be putting baffles in to replace the Pre-Cats.
I won't change the Cam.
I will go back to Speed Density/MAP/TPS, since there does not appear any difference shunt wise between that and AlphaN/TPS.
Cheers
D.
Taking on board the comments, and after my Holidays I will start a brand new project and start to tune again from scratch. I will get my dizzy curve plotted and use that as start point for Spark, (because it feels good under 14CUX).
I have noticed under CUX during a 20min logging session, the mean AFR for the whole run was 14.7 exactly! So the ECU is doing its job and seems to run comfortably between 14.4 and 15. Drops into the 12's when accelerating. The idle AFR is around 14.4, whereas with MS I was using around 13.8. I would be interested to know what most 500 MS users are using for their ReqFuel? Mine is currently set to 16.1, 2 squirts Alternating. This gives a VE=54 at idle and VE's of around 130 peak rpm .
If I were to use the MS calculated value for my injectors (Ford Bosch 18-19lb, 4 pintle - from US, 280-150-943)this would give a ReqFuel = 21, which I have never actually tried!! I presume the VE's will simply adjust accordingly? Does anybody use the calculated value? Comments welcome.
Also any useful comments on Squirts and Simultaneous settings choice?
I won't be putting baffles in to replace the Pre-Cats.
I won't change the Cam.
I will go back to Speed Density/MAP/TPS, since there does not appear any difference shunt wise between that and AlphaN/TPS.
Cheers
D.
Edited by DaveG on Sunday 2nd August 08:38
Gassing Station | Griffith | Top of Page | What's New | My Stuff