Hi I have been trying to trace a stop a stalling problem with my car. I used the data logging function to record the load figures and timing etc. However I'm not sure what I'm looking at
What load figures should I be looking at when coming down from high revs to a stop? So I can compare against my log.
I presume you should see a low figure as the car pulls a vac (15KPA) and then should rise as we get close to the idle speed? to around the 30-40 KPA?
http://www.theiansons.co.uk/mini/testlog190209.csv
Thanks for any help
datalogging
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Spockie-Tech
- Posts: 152
- Joined: Wed Jan 02, 2008 12:52 pm
- Location: Melbourne, Australia
Hmm, I had a look through your log file. Some weirdness in there.
It seems there are a few occasions where the RPM drops to 0 for a second or two then jumps back up again.
Are you sure your VR sensor is mounted securely and close to the teeth ?
They could be showing for some other reason. Does that log represent a single run with no switch offs ?
There also looks to be a point where the advance drops to 0 for a bit , at around 5600rpm. Rev Limiter maybe ?
The actual load numbers will depend on lots of factors.. your cam, induction, whether you shut the throttle completely or keep it open a bit as you decelerate and so on.
If you rev it up, slam the throttle closed and leave it closed with carbs you can sometimes dry up the manifold and the engine will often sag before the idle circuits manage to get things fuelled up again.. depends on how fat your idle circuits are running and so on.
What induction are you running ?
Can you point out a time (seconds from the end of the log) that a particular stall occurred and what you were doing at that time ?
It seems there are a few occasions where the RPM drops to 0 for a second or two then jumps back up again.
Are you sure your VR sensor is mounted securely and close to the teeth ?
They could be showing for some other reason. Does that log represent a single run with no switch offs ?
There also looks to be a point where the advance drops to 0 for a bit , at around 5600rpm. Rev Limiter maybe ?
The actual load numbers will depend on lots of factors.. your cam, induction, whether you shut the throttle completely or keep it open a bit as you decelerate and so on.
If you rev it up, slam the throttle closed and leave it closed with carbs you can sometimes dry up the manifold and the engine will often sag before the idle circuits manage to get things fuelled up again.. depends on how fat your idle circuits are running and so on.
What induction are you running ?
Can you point out a time (seconds from the end of the log) that a particular stall occurred and what you were doing at that time ?
to be honest Its not an mj thing. the car used to do it before mj but it was on a dizzy that had to be retarded to 0 TDC to stop the det later in the rev range. This was the reason I switched to mj to allow accurate control of the advance curve.
11:07:54.974,0 the car stalls after being driven down the road and coming to a stop at a junction. I'm out of gear and the clutch disengaged, no throttle applied. . At this point when I re-started the engine, I had to raise the idle screw to keep it running. This is why I'm now starting to think it a cold thing introduced by the air running through the carb. and maybe freezing the dash pot piston a little? The cars fuel and air has been setup on a rolling road so it should be spot on. I have tried a heavier spring, rebuild the carb and replaced the dashpot, piston and damper for new old stock.. I did think the MJ would stop it as the timing would have been dropping to 0deg on the dizzy and making it harder for the car to catch-up...
I can get it setup at idle in the garage fine and always drop back to idle but after the car has been under load it wont always return to idle without stalling..
Its a low CR engine running 8.7:1 and an sc12 blower at a max of about 10 psi full throttle. The 5500 to 0 deg was the rev limiter in the MJ software.
I have attached my current map, we have increased the off boost advance to try and tune the problem out.. I might try some copper pipe around the dashpot to the heater pipes to see if this helps..
11:07:54.974,0 the car stalls after being driven down the road and coming to a stop at a junction. I'm out of gear and the clutch disengaged, no throttle applied. . At this point when I re-started the engine, I had to raise the idle screw to keep it running. This is why I'm now starting to think it a cold thing introduced by the air running through the carb. and maybe freezing the dash pot piston a little? The cars fuel and air has been setup on a rolling road so it should be spot on. I have tried a heavier spring, rebuild the carb and replaced the dashpot, piston and damper for new old stock.. I did think the MJ would stop it as the timing would have been dropping to 0deg on the dizzy and making it harder for the car to catch-up...
I can get it setup at idle in the garage fine and always drop back to idle but after the car has been under load it wont always return to idle without stalling..
Its a low CR engine running 8.7:1 and an sc12 blower at a max of about 10 psi full throttle. The 5500 to 0 deg was the rev limiter in the MJ software.
I have attached my current map, we have increased the off boost advance to try and tune the problem out.. I might try some copper pipe around the dashpot to the heater pipes to see if this helps..
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Spockie-Tech
- Posts: 152
- Joined: Wed Jan 02, 2008 12:52 pm
- Location: Melbourne, Australia
Hmm, dashpot ? I assume we're talking about some sort of SU or Stromberg carb then ?
I dont have any experience with them, other than the knowledge they work via a venturi vacuum driven needle/piston designed to keep a relatively constant velocity through the carb. Supercharged huh.. I assume its a draw-through setup ?
Do you have an EGO sensor on the exhaust ? Monitoring that is always a good idea for a supercharged car, since lean outs can rapidly become catastrophic.
If you put a wideband EGO sensor in and hook it up the Aux input on the MJ then you can log the A/F ratio while you drive, and see if its a deceleration leanout that is causing your stall. Rolling Roads often dont show up that sort of thing.
Freezing the carb doesnt sound likely, but like I Said I have no hands on experience with SU's, so maybe its more common than I know. I assume you're in the UK and things are probably a bit colder than I am used to in Australia.
Are you watching the fuel pressure ? Acceleration based fuel starvation is another thing that wont show on a RR (No G forces), although I doubt it would only show on return to idle - unless the carbs idle circuit is more sensitive to float levels (do they have a float ?) than the main circuit.
How about fatenning the up the idle until it barely runs from richness, then go for a drive. If the stall doesnt happen or is harder to make happen, then you know for sure its a fuel dry-out problem.
On a conventional carb, you could just pump the accelerator pump a couple of times on deceleration to keep things wet and prove the cause, but I dont think SU's have a pump do they ?
Assuming it is a dry-out, that could be tricky to fix. you probably need to set the throttle plates idle position open more to keep air moving through enough to keep the needle flowing fuel.. no doubt that would stuff the idle speed up though.
If you can confirm the cause, might be time to call for an SU guru's help. Constant Velocity Carbs are weird things to us Weber-Heads
I dont have any experience with them, other than the knowledge they work via a venturi vacuum driven needle/piston designed to keep a relatively constant velocity through the carb. Supercharged huh.. I assume its a draw-through setup ?
Do you have an EGO sensor on the exhaust ? Monitoring that is always a good idea for a supercharged car, since lean outs can rapidly become catastrophic.
If you put a wideband EGO sensor in and hook it up the Aux input on the MJ then you can log the A/F ratio while you drive, and see if its a deceleration leanout that is causing your stall. Rolling Roads often dont show up that sort of thing.
Freezing the carb doesnt sound likely, but like I Said I have no hands on experience with SU's, so maybe its more common than I know. I assume you're in the UK and things are probably a bit colder than I am used to in Australia.
Are you watching the fuel pressure ? Acceleration based fuel starvation is another thing that wont show on a RR (No G forces), although I doubt it would only show on return to idle - unless the carbs idle circuit is more sensitive to float levels (do they have a float ?) than the main circuit.
How about fatenning the up the idle until it barely runs from richness, then go for a drive. If the stall doesnt happen or is harder to make happen, then you know for sure its a fuel dry-out problem.
On a conventional carb, you could just pump the accelerator pump a couple of times on deceleration to keep things wet and prove the cause, but I dont think SU's have a pump do they ?
Assuming it is a dry-out, that could be tricky to fix. you probably need to set the throttle plates idle position open more to keep air moving through enough to keep the needle flowing fuel.. no doubt that would stuff the idle speed up though.
If you can confirm the cause, might be time to call for an SU guru's help. Constant Velocity Carbs are weird things to us Weber-Heads
mmm I don't have a wide band. and yep its a SU carb... and I'm starting to think its the route of all evil... I might try and switch it for a newer bike carb. its a hard one to tune out.... I have had a little more time to play with the settings its a difficult thing to tune out without knowing the AFR???
Thanks for the help
Thanks for the help