Anyone with the shunting problem near Hungerford?
Discussion
Now Ive managed to reprogram the 14CUX, Id like to try tweaking the fuelling on a car that shunts. It appears that running a slightly richer mixture will reduce the shunting, but the ECU's lambda control constantly pulls the mixture back to 14.7:1. Im thinking that if I simply set just one load cell to a much higher fuel value at the shunting point I might be able to over ride the lambda control limits, and leave the rest of the map alone. There is no risk involved, as I will use my own ECU that I can program, and its FOC as its an experiment. Anyone interested?
How bad a shunting problem do you need? Mine was bad when I got it but now only happens at very light loads and low rpm. I'm willing to be experimented on, I'm not that far from Hungerford, in Witney West Oxon. If you don't get any offers that better meet your experiment criteria let me know.
I spent many hours with Paul Stallards Griff trying to stop it shunting, but failed due to the 14CUX always running emission complaint, and I did not have the software tools to frig it. At its most basic adding an air tube to blow extra air over the AFM sensor you could literally turn the shunting on or off with a blast of extra air. This is what lead us to the conclusion that a richer mixture was the answer as a higher AFM output puts in more fuel. Not that a plastic pipe you blow down is a workable solution. 
Paul fitted a Canems system, and bingo the fault has gone, so it can be done. Ive not quite given up with the 14CUX yet though.
TVR Stef- Ill ping you a mail.
Paul fitted a Canems system, and bingo the fault has gone, so it can be done. Ive not quite given up with the 14CUX yet though.TVR Stef- Ill ping you a mail.
Well things are moving at a pace- With massive thanks to Dan Bourassa of RoverGauge fame, it appears that you can set more than one RPM point to turn the lambda switching on or off. By default its turned off at 3400 rpm as the map goes open loop, but the thinking is to make the map open loop just at the point the shunting occurs, so you will have total control of the mixture without lambda feedback getting in the way all the time, so basically it would go like this:
idle to say 1600 rpm- closed loop
1600-1800 rpm open loop
1800-3400 rpm closed loop
above 3400 rpm open loop
This means you can play about the fueling in the open loop area to your hearts content. It also means the catalyst will work normally the rest of the time, so you dont need to worry about melting it, which you would if you ran open loop all the time. Im hoping this has a big potential as a simple chip upgrade to remove or at least reduce the shunting if it works as hoped. I now have a test 3.9 map thanks to Dan, that hopefully I can test on TVR Stefs car at the weekend.
idle to say 1600 rpm- closed loop
1600-1800 rpm open loop
1800-3400 rpm closed loop
above 3400 rpm open loop
This means you can play about the fueling in the open loop area to your hearts content. It also means the catalyst will work normally the rest of the time, so you dont need to worry about melting it, which you would if you ran open loop all the time. Im hoping this has a big potential as a simple chip upgrade to remove or at least reduce the shunting if it works as hoped. I now have a test 3.9 map thanks to Dan, that hopefully I can test on TVR Stefs car at the weekend.
blitzracing said:
Well things are moving at a pace- With massive thanks to Dan Bourassa of RoverGauge fame, it appears that you can set more than one RPM point to turn the lambda switching on or off. By default its turned off at 3400 rpm as the map goes open loop, but the thinking is to make the map open loop just at the point the shunting occurs, so you will have total control of the mixture without lambda feedback getting in the way all the time, so basically it would go like this:
idle to say 1600 rpm- closed loop
1600-1800 rpm open loop
1800-3400 rpm closed loop
above 3400 rpm open loop
This means you can play about the fueling in the open loop area to your hearts content. It also means the catalyst will work normally the rest of the time, so you dont need to worry about melting it, which you would if you ran open loop all the time. Im hoping this has a big potential as a simple chip upgrade to remove or at least reduce the shunting if it works as hoped. I now have a test 3.9 map thanks to Dan, that hopefully I can test on TVR Stefs car at the weekend.
Just having a wonder! If the air filter is heavily oiled over the last 14 years of service, perhaps the AFM is not getting enough air to flow over the hot wire at closed loop and tick over, and therefore fueling is not rich enough to reduce shunting? Perhaps removing the air filter for the test may help to reduce/eliminate the shunting? Good luck, will follow your testing with interest.idle to say 1600 rpm- closed loop
1600-1800 rpm open loop
1800-3400 rpm closed loop
above 3400 rpm open loop
This means you can play about the fueling in the open loop area to your hearts content. It also means the catalyst will work normally the rest of the time, so you dont need to worry about melting it, which you would if you ran open loop all the time. Im hoping this has a big potential as a simple chip upgrade to remove or at least reduce the shunting if it works as hoped. I now have a test 3.9 map thanks to Dan, that hopefully I can test on TVR Stefs car at the weekend.
On carb engines the opposite is true. Restricting the air flow resulted in rich fueling in particular to help start up.
The RV8 engine runs as nice as pie on an AFR of around 13:5:1, but Lambda control constantly forces it run around a mid point of 14.7:1, which you can just about get away with most of the time. Problem is this engine was never designed with emissions in mind in the first place, so adding emission control as an afterthought is far from ideal, especially if you tune it as well, over the lazy old range Rover set up. You cant think of it in terms of air restrictions from the air filter, as the AFM simply measures the available air, even if it was restricted it would simply add the required amount of fuel to keep the mixture correct. I do believe that shunting varies with air temp however , and tends to be worse in hot conditions when the air density is lower, as is the available oxygen. Its all very subtle.
If you're decatted, is there any point running with the lambda sensors in? Shunts under 2.5-3.0k. Is it worth changing the tune resistor and lambda control and permanently running open loop?
As above, shunting is worse in hot conditions. I gather it is because colder air is denser, giving a more efficient burn.
As above, shunting is worse in hot conditions. I gather it is because colder air is denser, giving a more efficient burn.
Edited by Chuffmeister on Saturday 9th May 10:53
Well TVR Stef turns up, but his car refused to shunt to order- it was running very sweetly indeed and refused to mis-behave. However it gave me a change to try the map with lambda control turned off at the shunting point - unfortunately this bit did not work at all, it just kept cycling. However not to be beaten, we briefly tried a modified non cat map with the catalysts to see if they got hot or caught fire- but could see no difference at all in catalyst temp. Not that I could guarantee this on a blast down the M-way however.
So next test is to "overload" the short term trim simply by lifting the fuel map at the shunting point. Bingo this worked a treat without a huge lift in the amount of fuel going it, it simply stopped cycling. It cant reduce the fuel with long term trim as its well above tick over, so it simply runs out of short term trim, and the mixture becomes richer. I could see this from the direct reading off the back of the lambda probes. The ECU will eventually throw a fault code if the lambda's stop switching, but it takes some minutes, and as they only stop cycling at the shunting point, they will cycle normally above and below this point, so an error will be prevented unless you stick at the shunting point for a long time. My concern is if this is a fix, why has it not been done before? Im sure MA would have looked at this.
A picture of the map with the uplift point with the blue points.
As for switching to the non cat map as a fix- please be aware that TVR only ever optimised one map in the chip, so you will be using a stock Range Rover map that runs horribly lean if you just use green tune in the TVR chip.
So next test is to "overload" the short term trim simply by lifting the fuel map at the shunting point. Bingo this worked a treat without a huge lift in the amount of fuel going it, it simply stopped cycling. It cant reduce the fuel with long term trim as its well above tick over, so it simply runs out of short term trim, and the mixture becomes richer. I could see this from the direct reading off the back of the lambda probes. The ECU will eventually throw a fault code if the lambda's stop switching, but it takes some minutes, and as they only stop cycling at the shunting point, they will cycle normally above and below this point, so an error will be prevented unless you stick at the shunting point for a long time. My concern is if this is a fix, why has it not been done before? Im sure MA would have looked at this.
A picture of the map with the uplift point with the blue points.
As for switching to the non cat map as a fix- please be aware that TVR only ever optimised one map in the chip, so you will be using a stock Range Rover map that runs horribly lean if you just use green tune in the TVR chip.
Edited by blitzracing on Sunday 10th May 18:00
There are three 4 ltr test cars, and the test map appears to be smoother, but the problem is they did not shunt badly in the first place, so its not a very good test. What I have done is put the "non shunt " map into the "blue " map position, so you can simply switch between the original TVR map and the blue map with just a tune resistor change. This means you dont have to switch chips at MOT time, just a resistor. I really need a better test car that shunts to order for more testing to be sure. I cdould simply try modifying a stock TVR map for one of the bigger engines in a similar way to the 4ltr if anyone fancies being a test bed, but I do want a stock car, nothing modified.
As for aftermarket ECU- then fine you can tweak the fueling as much as you like, but we can do this on the 14CUX now, so its big bucks re inventing the wheel. Where an aftermarket really wins is if you have spark control included, so it works hand in hand with fuel control and this is bound to help.
As for aftermarket ECU- then fine you can tweak the fueling as much as you like, but we can do this on the 14CUX now, so its big bucks re inventing the wheel. Where an aftermarket really wins is if you have spark control included, so it works hand in hand with fuel control and this is bound to help.
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