Discussion
Shunting. (The insoluble!)
I thought I would share my experiences-observations.
I have a 1995 Griffith 500 bought in the UK in 2002 and shipped out to Oz. During 2002 and 2009 the car ran beautifully, good power and was taken to the track regularly. Having got my license suspended in 09, I decided to pull the engine and replace the cam (38k miles). (Also purchased MS2Extra for later fitting). Cam was local and nothing wild, heads were reconditioned, big ends, rings, performance clutch, trigger wheel, WBO sensor fitted and the Pre-Cats removed, everything else standard.
In 2010 after my rebuild there were signs of shunting/hesitation. I tried all the usual tweaks for a std engine including variable fuel regulator, but could not resolve. Having purchased the Megasquirt (fuelling & ignition- now 3.2.5) I thought I would install this and tune out the problem.
Continuous tuning 2010-2015 and I still have the problem. This is how I define my shunting – light or easing throttle between 1200-2100rpm causing a light snatching in the transmission. If not corrected by dipping clutch or more throttle, becomes shunt proper (kangaroo).
Only evidence in the log is 50-100rpm superimposed on revs. (TPS, and other datalogs – nothing.). Here is my list of extensive tuning tests (4yrs) attempting to cure:
Non-Mechanical tests:-
- Untold logging runs varying every combination of tune maps (VE, AFR, Spark) plus/minus 3/4 points
- Multiple Req.Fuel ratios settings (14-17)
- Speed Density (variable MAP/TPS) based tuning for 3yrs
- AlphaN / TPS tuning based for 1yr (current)
- Simultaneous/alternating fuelling
- Idle PID, CL PID, no PID
- Ignition events (12 – 32)
- Loads of MSQ and logs available
Mechanical tests:-
- Timing 9 - BTDC, 28 – 3000rpm
- CAM (Dur 283, overlap 60, phase 112)
- Plenum spacer (3mm), no spacer
- New stepper
- With and without stepper
- Base idle adjustment (0 – 6 turns)
- Injectors, change from std to 4 pintle (19lb)
- New fuel regulator
- Flared carbon trumpets
- New coil packs(2)
- No detectable air leaks, servo, PBR, dip stick, breathers, etc (except inlet manifold)
- Oil catcher added
- HT Cables /boots interchanged (spare sets)
- Plugs – BP7ECS / BP6ES
All of these and combinations thereof have not resolved. Suggestions from Phil and Shaun have been incorporated at various stages all to no avail!!
As a final test, I have now removed Megasquirt and re-installed dizzy/14CUX, rechecked the setup (ignition, MAF, TPS, base idle, etc). The car fires up beautifully and runs well, BUT still shunts !!
I have concluded that it is not a ‘soft’ issue, but mechanical. The slight easing of the throttle presumably causes a small increase in vacuum which starts the shunt. It is that balance point when holding the throttle in any gear between 1200 – 2000rpm. (especially 3rd and 4th) These tests appear to point to:-
- CAM
- Induction / manifold changes?
- Exhaust back pressure (no pre-cats)
- ?????
I will be in UK (Aug/Sept) and have an opportunity to buy parts (i.e. cam, etc), but really at a loss for a solution.
- Experts advise that it will not be the CAM.
- Induction manifold/plenum/butterfly,etc has not changed (manifold gasket leak?)
- Put cone baffles in the exhaust?
- Desperate !
Anyhow I thought I would share my experiences and my disappointment that she does not run as sweet as when I bought her!! (I have learnt a lot and it has kept me occupied for 4 years.) I have not really looked at Roverguage, but as an aside, would be interested to hear if it could be used to create an exact copy of the 14CUX maps for MS (i.e. spark, AFR) and let it create the VE?
Feel free to add your pennies worth!!
(I have probably not included all the tests I have done, - just off the top of the head.)
I thought I would share my experiences-observations.
I have a 1995 Griffith 500 bought in the UK in 2002 and shipped out to Oz. During 2002 and 2009 the car ran beautifully, good power and was taken to the track regularly. Having got my license suspended in 09, I decided to pull the engine and replace the cam (38k miles). (Also purchased MS2Extra for later fitting). Cam was local and nothing wild, heads were reconditioned, big ends, rings, performance clutch, trigger wheel, WBO sensor fitted and the Pre-Cats removed, everything else standard.
In 2010 after my rebuild there were signs of shunting/hesitation. I tried all the usual tweaks for a std engine including variable fuel regulator, but could not resolve. Having purchased the Megasquirt (fuelling & ignition- now 3.2.5) I thought I would install this and tune out the problem.
Continuous tuning 2010-2015 and I still have the problem. This is how I define my shunting – light or easing throttle between 1200-2100rpm causing a light snatching in the transmission. If not corrected by dipping clutch or more throttle, becomes shunt proper (kangaroo).
Only evidence in the log is 50-100rpm superimposed on revs. (TPS, and other datalogs – nothing.). Here is my list of extensive tuning tests (4yrs) attempting to cure:
Non-Mechanical tests:-
- Untold logging runs varying every combination of tune maps (VE, AFR, Spark) plus/minus 3/4 points
- Multiple Req.Fuel ratios settings (14-17)
- Speed Density (variable MAP/TPS) based tuning for 3yrs
- AlphaN / TPS tuning based for 1yr (current)
- Simultaneous/alternating fuelling
- Idle PID, CL PID, no PID
- Ignition events (12 – 32)
- Loads of MSQ and logs available
Mechanical tests:-
- Timing 9 - BTDC, 28 – 3000rpm
- CAM (Dur 283, overlap 60, phase 112)
- Plenum spacer (3mm), no spacer
- New stepper
- With and without stepper
- Base idle adjustment (0 – 6 turns)
- Injectors, change from std to 4 pintle (19lb)
- New fuel regulator
- Flared carbon trumpets
- New coil packs(2)
- No detectable air leaks, servo, PBR, dip stick, breathers, etc (except inlet manifold)
- Oil catcher added
- HT Cables /boots interchanged (spare sets)
- Plugs – BP7ECS / BP6ES
All of these and combinations thereof have not resolved. Suggestions from Phil and Shaun have been incorporated at various stages all to no avail!!
As a final test, I have now removed Megasquirt and re-installed dizzy/14CUX, rechecked the setup (ignition, MAF, TPS, base idle, etc). The car fires up beautifully and runs well, BUT still shunts !!
I have concluded that it is not a ‘soft’ issue, but mechanical. The slight easing of the throttle presumably causes a small increase in vacuum which starts the shunt. It is that balance point when holding the throttle in any gear between 1200 – 2000rpm. (especially 3rd and 4th) These tests appear to point to:-
- CAM
- Induction / manifold changes?
- Exhaust back pressure (no pre-cats)
- ?????
I will be in UK (Aug/Sept) and have an opportunity to buy parts (i.e. cam, etc), but really at a loss for a solution.
- Experts advise that it will not be the CAM.
- Induction manifold/plenum/butterfly,etc has not changed (manifold gasket leak?)
- Put cone baffles in the exhaust?
- Desperate !
Anyhow I thought I would share my experiences and my disappointment that she does not run as sweet as when I bought her!! (I have learnt a lot and it has kept me occupied for 4 years.) I have not really looked at Roverguage, but as an aside, would be interested to hear if it could be used to create an exact copy of the 14CUX maps for MS (i.e. spark, AFR) and let it create the VE?
Feel free to add your pennies worth!!
(I have probably not included all the tests I have done, - just off the top of the head.)
Edited by DaveG on Sunday 26th July 14:12
Edited by DaveG on Sunday 26th July 14:17
Thanks for responses and suggestions. I have taken onboard the comments with the following reservations:
Leads & shrouds:
I have different leads used for 14CUX and MS (Both could be faulty?). The shroud's are original, used when it was good and when shunting.(Possible culprit? Maybe one, but not all eight)
CAM.
One expert who specialises in RV8 race engines indicates that you can probably be up to 2 deg out and still not show those distinct problems. Also said the pre-loads could be up to 80 thou and still work ok. My first instinct was to change the CAM again, but 400Pds and a lot of work for possibly no result?
14CUX vs MS
I only reverted back to prove a point. You would imagine that after 4 yrs of mapping that I would have had more success - hence the mechanical focus.
AFR's
I have set the map down in the 12's and varied the spark +-3/4 degrees. Also in the 15's. ??
Vacuum/MAP
My vac is 51-53Kpa at idle (875rpm, can drop it to 49-50 at 900-1000rpm) It has been consistent with this CAM.
My MAP noise is pretty good. (Lag Filter=40) I tried an inline fuel filter - no change. I now have inline restrictor, probably similar to your Weber jet.
Exhaust back pressure?
No comments here. It will not be easy putting baffles back into the exhaust manifold and may also be a no result effort.
MS
I can easily re-install MS. I could go to MS3, but if I cannot fix with MS2?? If it is 'mechanical' then I should be able to fix with 14CUX?
Keep the comment coming guys.
Thanks
D.
Leads & shrouds:
I have different leads used for 14CUX and MS (Both could be faulty?). The shroud's are original, used when it was good and when shunting.(Possible culprit? Maybe one, but not all eight)
CAM.
One expert who specialises in RV8 race engines indicates that you can probably be up to 2 deg out and still not show those distinct problems. Also said the pre-loads could be up to 80 thou and still work ok. My first instinct was to change the CAM again, but 400Pds and a lot of work for possibly no result?
14CUX vs MS
I only reverted back to prove a point. You would imagine that after 4 yrs of mapping that I would have had more success - hence the mechanical focus.
AFR's
I have set the map down in the 12's and varied the spark +-3/4 degrees. Also in the 15's. ??
Vacuum/MAP
My vac is 51-53Kpa at idle (875rpm, can drop it to 49-50 at 900-1000rpm) It has been consistent with this CAM.
My MAP noise is pretty good. (Lag Filter=40) I tried an inline fuel filter - no change. I now have inline restrictor, probably similar to your Weber jet.
Exhaust back pressure?
No comments here. It will not be easy putting baffles back into the exhaust manifold and may also be a no result effort.
MS
I can easily re-install MS. I could go to MS3, but if I cannot fix with MS2?? If it is 'mechanical' then I should be able to fix with 14CUX?
Keep the comment coming guys.
Thanks
D.
Edited by DaveG on Monday 27th July 07:37
Edited by DaveG on Monday 27th July 07:38
Thanks again for the additional suggestions, thoughts.
My thinking at present has 4 possible options all of which would revert back to MS2 for the extra control:
1. Look at installing some cone baffles to compensate for removed pre-cats.
2. Book a comprehensive Dyno session and get a good spark map to suit the engine (always a bit of an unknown) and good AFR's.
3. Change the induction side characteristics with these:-
4. Swap the CAM again for say a 885. (Could be just repeating my past tuning experience?)
Those are probably in preferred order, but would need to find good Dyno tuner to work with MS (Has anybody used dyno-tuning for the spark map across the range?)
The twin throttle kit is from a Triumph/Rover specialist here in Oz and I like the idea of some 'mechanical' change?
On the controller side, I too have felt that there is some positive feedback getting introduced (I can see this 50-100rpm cycle superimposed on the 'steady state' revs log.) However similar must be happening with 14CUX, I just have no way of seeing it?
I am going to be in the UK/Europe for 6 wks so have some time to ponder/review.
Thanks, more comments and experiences please.
D.
My thinking at present has 4 possible options all of which would revert back to MS2 for the extra control:
1. Look at installing some cone baffles to compensate for removed pre-cats.
2. Book a comprehensive Dyno session and get a good spark map to suit the engine (always a bit of an unknown) and good AFR's.
3. Change the induction side characteristics with these:-
4. Swap the CAM again for say a 885. (Could be just repeating my past tuning experience?)
Those are probably in preferred order, but would need to find good Dyno tuner to work with MS (Has anybody used dyno-tuning for the spark map across the range?)
The twin throttle kit is from a Triumph/Rover specialist here in Oz and I like the idea of some 'mechanical' change?
On the controller side, I too have felt that there is some positive feedback getting introduced (I can see this 50-100rpm cycle superimposed on the 'steady state' revs log.) However similar must be happening with 14CUX, I just have no way of seeing it?
I am going to be in the UK/Europe for 6 wks so have some time to ponder/review.
Thanks, more comments and experiences please.
D.
Edited by DaveG on Tuesday 28th July 01:40
Edited by DaveG on Tuesday 28th July 08:20
Thanks DNB. Points noted. I am hoping a "steady state" dyno can be used to give me a good cross range result. I must say the std dizzy gives a pretty good result. I'm surprised nobody has mapped the std dizzy - KPa vs RPM for MS. I guess it means plotting with weights only and adding a 'band' of advance for the vacuum? (I might see what dizzy reconditioners do and what they can plot?)
The back pressure is an interesting one and I personally think it could be a contributing factor - just don't fancy pulling the exhaust manifolds again now they are nicely sealed!
The back pressure is an interesting one and I personally think it could be a contributing factor - just don't fancy pulling the exhaust manifolds again now they are nicely sealed!
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
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