Shunting/power loss
Discussion
I know its been covered and have tried several the ideas but no go.
450 98 serp top end rebuild with a stealth cam fitted, bedded in, and timed in. Take it for a spin and the first 200 metres i can give it the full beans and complete rev range.
After 200 metres immediate power loss above 1800 rpm with it only coming back in at 1000 rpm. Limp mode i suppose.
It does reset after being left for a few minutes then repeats ie. Full beans for 200 metres is ok then instant power loss.
Fyi - I measured tappet preload and was out 75 to 100 thou so installed 30 thou shims (48 thou at rocker cover) to get it back close to spec
So far I've tried, one step a time,with no improvement (exact same cycle as above):
Clean rotor
Remove fuel vacuum
Remove dizzy advance
Disconnect stepper (engine then idles at 1800 so constant powe loss)
Reset ecu
The obvious engine changes are the cam and shims - is there anything obvious I'm missing or is a fuel remap required due to stealth cam?
Cheers. Matt
450 98 serp top end rebuild with a stealth cam fitted, bedded in, and timed in. Take it for a spin and the first 200 metres i can give it the full beans and complete rev range.
After 200 metres immediate power loss above 1800 rpm with it only coming back in at 1000 rpm. Limp mode i suppose.
It does reset after being left for a few minutes then repeats ie. Full beans for 200 metres is ok then instant power loss.
Fyi - I measured tappet preload and was out 75 to 100 thou so installed 30 thou shims (48 thou at rocker cover) to get it back close to spec
So far I've tried, one step a time,with no improvement (exact same cycle as above):
Clean rotor
Remove fuel vacuum
Remove dizzy advance
Disconnect stepper (engine then idles at 1800 so constant powe loss)
Reset ecu
The obvious engine changes are the cam and shims - is there anything obvious I'm missing or is a fuel remap required due to stealth cam?
Cheers. Matt
I always thought that a new cam of a different torque and power curve to the original requires an ECU remap to work properly. There are several flavours of stealth cam.
I agree it sounds like limp home mode, you have done an ECU reset, but perhaps the new cam is what is throwing the ECU into limp wrist mode?
On the ECU front I do have a spare 400 ECU you are welcome to borrow. I can post it.
Also my car has a chip specifically mapped to my bigger 20AM AFM, 72mm plenum, 5 litre engine and stealth cam, and you are welcome to try that too if we can arrange to meet up.
I think I may even have another 4litre chip somewhere, which I can post to you.
However, I would initially recommend giving Jools (kits and classics dot co dot uk) a ring. Great guy, describe what you have done, he will immediately know if you need a remap and won't just be trying to get your business. He's not expensive, but it does mean getting the car to Chesterfield if work is required, as he will need to put it on his rolling road to map it. Do you have a suitable tow car and access to a trailer?
I agree it sounds like limp home mode, you have done an ECU reset, but perhaps the new cam is what is throwing the ECU into limp wrist mode?
On the ECU front I do have a spare 400 ECU you are welcome to borrow. I can post it.
Also my car has a chip specifically mapped to my bigger 20AM AFM, 72mm plenum, 5 litre engine and stealth cam, and you are welcome to try that too if we can arrange to meet up.
I think I may even have another 4litre chip somewhere, which I can post to you.
However, I would initially recommend giving Jools (kits and classics dot co dot uk) a ring. Great guy, describe what you have done, he will immediately know if you need a remap and won't just be trying to get your business. He's not expensive, but it does mean getting the car to Chesterfield if work is required, as he will need to put it on his rolling road to map it. Do you have a suitable tow car and access to a trailer?
Edited by QBee on Saturday 25th June 19:47
cheers blitz and qbee, especially for the loan of a chip.
No MIL light came on but will get a rovergauge cable and software and so what it shows up. I'll buy one of the classifieds.
I should add that whilst static and during cam bed in it'll rev to the max quite happily, so only under load does it limp.
I'll give V8D A call tomorrow and see if Rob/Ray have any ideas and if stealth cam 450 cars need a set up.
The previous owner had put on a straight through exhaust with large bore tail pipes. In case back pressure can cause a fault.....
No MIL light came on but will get a rovergauge cable and software and so what it shows up. I'll buy one of the classifieds.
I should add that whilst static and during cam bed in it'll rev to the max quite happily, so only under load does it limp.
I'll give V8D A call tomorrow and see if Rob/Ray have any ideas and if stealth cam 450 cars need a set up.
The previous owner had put on a straight through exhaust with large bore tail pipes. In case back pressure can cause a fault.....
Cable ordered. Not a fan of guesswork either.....
Would fuel delivery problem create limp mode? I understand fuel starving would result in power loss but the engine is still turning not cutting out. I admit i have no idea on fuel flow rates under load.
I take it to test fuel pressure you connect a gauge up to fuel rail valve point. Ok at idle but whilst driving take it rovergauge can monitor fuel flow.
Forgot to say before that the oil warning light is always on but reading from a mechanical gauge I've got good pressure (electric one confirmed this too) would a faulty oil sender switch put car in limp mode as it assumes oil isn't circulating? I'd be surprised if this were true though.
Would fuel delivery problem create limp mode? I understand fuel starving would result in power loss but the engine is still turning not cutting out. I admit i have no idea on fuel flow rates under load.
I take it to test fuel pressure you connect a gauge up to fuel rail valve point. Ok at idle but whilst driving take it rovergauge can monitor fuel flow.
Forgot to say before that the oil warning light is always on but reading from a mechanical gauge I've got good pressure (electric one confirmed this too) would a faulty oil sender switch put car in limp mode as it assumes oil isn't circulating? I'd be surprised if this were true though.
Edited by Chimp871 on Sunday 26th June 18:06
Probably utterly irrelevant.
My turbo diseasel Merc used to do this for a while on hard acceleration, but on those cars it cuts the power completely, leaving you to coast to a halt. Not funny if you were half way past 32 tonnes of fun on a busy single carriageway A road at the time.
On that car it was the sheer amount of carbon all the way through the engine......or so we thought, until on the 6th visit to the garage they discovered the cracked inter cooler.
I have also seen a 6 month old XF go into limp mode on a track day - they said they thought it had simply exceeded a pre-set parameter in the ECU and the nanny system told them to take it back to a franchise dealer for a wallet-fleecing.
Point I am making is that on those cars the ECU thought a parameter has been exceeded - is that true of our pre-Boer War systems, Blitz?
My turbo diseasel Merc used to do this for a while on hard acceleration, but on those cars it cuts the power completely, leaving you to coast to a halt. Not funny if you were half way past 32 tonnes of fun on a busy single carriageway A road at the time.
On that car it was the sheer amount of carbon all the way through the engine......or so we thought, until on the 6th visit to the garage they discovered the cracked inter cooler.
I have also seen a 6 month old XF go into limp mode on a track day - they said they thought it had simply exceeded a pre-set parameter in the ECU and the nanny system told them to take it back to a franchise dealer for a wallet-fleecing.
Point I am making is that on those cars the ECU thought a parameter has been exceeded - is that true of our pre-Boer War systems, Blitz?
Chimp871 said:
Cable ordered. Not a fan of guesswork either.....
Would fuel delivery problem create limp mode? I understand fuel starving would result in power loss but the engine is still turning not cutting out. I admit i have no idea on fuel flow rates under load.
I take it to test fuel pressure you connect a gauge up to fuel rail valve point. Ok at idle but whilst driving take it rovergauge can monitor fuel flow.
Forgot to say before that the oil warning light is always on but reading from a mechanical gauge I've got good pressure (electric one confirmed this too) would a faulty oil sender switch put car in limp mode as it assumes oil isn't circulating? I'd be surprised if this were true though.
There are no sensors on the fuel pressure or oil pressure you can read with RoverGauge- but first off check for error codes (the ECU warning light is not always enabled or even wired in), then you can check basic sensor data like AFM and throttle pot and you may see some some odd lambda trim values. You can see physically a lean off with a test meter across the lambda probes (Black and white wires ), where the voltage will drop to zero, from a switching signal of 0 to 1.2 volts. Fuel pressure can only be read with a pressure gauge on the rail when the car is under load, and thats not easy! Worth checking the air intake hose is not crushed- that causes some real funnies. Ive never seen Limp home mode do anything that drastic.Would fuel delivery problem create limp mode? I understand fuel starving would result in power loss but the engine is still turning not cutting out. I admit i have no idea on fuel flow rates under load.
I take it to test fuel pressure you connect a gauge up to fuel rail valve point. Ok at idle but whilst driving take it rovergauge can monitor fuel flow.
Forgot to say before that the oil warning light is always on but reading from a mechanical gauge I've got good pressure (electric one confirmed this too) would a faulty oil sender switch put car in limp mode as it assumes oil isn't circulating? I'd be surprised if this were true though.
Edited by Chimp871 on Sunday 26th June 18:06
Edited by blitzracing on Sunday 26th June 20:28
New fuel filter less than 1000 miles ago but intake hose unchecked
I'm back Thursday and will check fuel rail pressure and rover gauge it. Will find a way to measure pressure on the move. Something like this may help
http://www.ebay.co.uk/itm/252419059081
I'm back Thursday and will check fuel rail pressure and rover gauge it. Will find a way to measure pressure on the move. Something like this may help
http://www.ebay.co.uk/itm/252419059081
The 14CUX needs a road speed signal to implement it's anti-stall idle strategy, basically as you come to a stop at a junction (especially rapidly from speed) the ECU will open the stepper motor to catch and eliminate an engine stall.
This happens when the ECU sees speed signal below a certain road speed, this speed is quite low, something like 6mph or possibly even less. When driving in the 1700 -1800 your road speed is typically quite low too and it's often the case in Chimaeras that the speedo doesn't even register anything from the inductive pickup on the diff until 20mph or so.
The problem is often the rather crude TVR made speed signal box, this was required because obviously the Range Rover speedo which was designed to partner the 14CUX ECU was not used on the Chimaera. Like all TVR made electronic components from the period the quality and reliability left quite a lot to be desired.
So it's quite possible your ECU thinks the car's road speed is actually lower than it really is, you're happily driving through town at say 20-25mph when the ECU loses the speed signal so thinks you're approaching a junction, it then starts to implement it's anti-stall strategy just when you don't need it.
If you're driving along at 20mph at 1700rpm and the ECU is indeed getting an unreliable road speed signal it may very well start to open the stepper motor, this would have all sorts of undesirable effects, indeed I wonder if this might be one (if not the) true causes of "Shunting"?
Could the infamous shunting problem be something as simple as an unreliable speed signal and the ECU going into it's anti-stall strategy when it shouldn't?
I'd say it's quite possible
This happens when the ECU sees speed signal below a certain road speed, this speed is quite low, something like 6mph or possibly even less. When driving in the 1700 -1800 your road speed is typically quite low too and it's often the case in Chimaeras that the speedo doesn't even register anything from the inductive pickup on the diff until 20mph or so.
The problem is often the rather crude TVR made speed signal box, this was required because obviously the Range Rover speedo which was designed to partner the 14CUX ECU was not used on the Chimaera. Like all TVR made electronic components from the period the quality and reliability left quite a lot to be desired.
So it's quite possible your ECU thinks the car's road speed is actually lower than it really is, you're happily driving through town at say 20-25mph when the ECU loses the speed signal so thinks you're approaching a junction, it then starts to implement it's anti-stall strategy just when you don't need it.
If you're driving along at 20mph at 1700rpm and the ECU is indeed getting an unreliable road speed signal it may very well start to open the stepper motor, this would have all sorts of undesirable effects, indeed I wonder if this might be one (if not the) true causes of "Shunting"?
Could the infamous shunting problem be something as simple as an unreliable speed signal and the ECU going into it's anti-stall strategy when it shouldn't?
I'd say it's quite possible
Sardonicus said:
wont be possible Dave as the TPS angle will need to be 0 for the ECU to do that, the ECU wont be just looking for road speed 
Are right, got ya Simon 
I didn't realise it needs the two rules (TPS = 0v + Road Speed below 6mph) to instigate the idle strategy.
Interesting
But what if the delicate TPS wires were fracturing or insecure, this is quite common apparently, would the ECU see 0v from the TPS and think the car is coasting to a junction if combined with an iffy road speed signal?
The thing is you do hear of people solving their shunting problem by either disconnecting the stepper motor of removing it all together, this does seem to support the theory that unwanted stepper activity could have something to do with the problem.
The one Chinmaera I drove with serious shunting issues was almost undrivable, literally like the driver was violently coming on and off the throttle and felt like the whole drive train would break at any moment. I never did try disconnecting the stepper but I can easily see how the stepper... or at least what the ECU was telling the stepper to do as being at fault.
It's just a theory, but it does have a good helping of logic behind it, perhaps the OP should check his delicate TPS wiring, set his base idle & make sure his TPS is correctly adjusted too. If the shunting remains he could then disconnect the stepper at idle and go for a drive to see if there was any improvement.
A few simple things he can do himself for nothing that may just solve the problem? He certainly wont cause any harm and it's free to try too
ChimpOnGas said:
Are right, got ya Simon
I didn't realise it needs the two rules (TPS = 0v + Road Speed below 6mph) to instigate the idle strategy.
Interesting
But what if the delicate TPS wires were fracturing or insecure, this is quite common apparently, would the ECU see 0v from the TPS and think the car is coasting to a junction if combined with an iffy road speed signal?
The thing is you do hear of people solving their shunting problem by either disconnecting the stepper motor of removing it all together, this does seem to support the theory that unwanted stepper activity could have something to do with the problem.
The one Chinmaera I drove with serious shunting issues was almost undrivable, literally like the driver was violently coming on and off the throttle and felt like the whole drive train would break at any moment. I never did try disconnecting the stepper but I can easily see how the stepper... or at least what the ECU was telling the stepper to do as being at fault.
It's just a theory, but it does have a good helping of logic behind it, perhaps the OP should check his delicate TPS wiring, set his base idle & make sure his TPS is correctly adjusted too. If the shunting remains he could then disconnect the stepper at idle and go for a drive to see if there was any improvement.
A few simple things he can do himself for nothing that may just solve the problem? He certainly wont cause any harm and it's free to try too
Valid point, you know yourself anythings possible I didn't realise it needs the two rules (TPS = 0v + Road Speed below 6mph) to instigate the idle strategy.
Interesting
But what if the delicate TPS wires were fracturing or insecure, this is quite common apparently, would the ECU see 0v from the TPS and think the car is coasting to a junction if combined with an iffy road speed signal?
The thing is you do hear of people solving their shunting problem by either disconnecting the stepper motor of removing it all together, this does seem to support the theory that unwanted stepper activity could have something to do with the problem.
The one Chinmaera I drove with serious shunting issues was almost undrivable, literally like the driver was violently coming on and off the throttle and felt like the whole drive train would break at any moment. I never did try disconnecting the stepper but I can easily see how the stepper... or at least what the ECU was telling the stepper to do as being at fault.
It's just a theory, but it does have a good helping of logic behind it, perhaps the OP should check his delicate TPS wiring, set his base idle & make sure his TPS is correctly adjusted too. If the shunting remains he could then disconnect the stepper at idle and go for a drive to see if there was any improvement.
A few simple things he can do himself for nothing that may just solve the problem? He certainly wont cause any harm and it's free to try too
I believe the Stepper Motor control routine is only active when road speed is less than 3 mph, the throttle is closed (or heading towards closed) and engine speed is greater than 50 RPM. Idle control is also influenced by the engine coolant temperature, a base idle value set in the code and the calculated target idle value.
Road speed sensing in the 14CUX code is a bit of a dog's dinner, couple this with the basic On/Off signal from the TVR speed splitter box and it maybe that the ECU has trouble catching the 'coming to a halt' event.
Road speed sensing in the 14CUX code is a bit of a dog's dinner, couple this with the basic On/Off signal from the TVR speed splitter box and it maybe that the ECU has trouble catching the 'coming to a halt' event.
davep said:
Road speed sensing in the 14CUX code is a bit of a dog's dinner, couple this with the basic On/Off signal from the TVR speed splitter box and it maybe that the ECU has trouble catching the 'coming to a halt' event.
Thanks for your input davep, this is my point exactly, the 14CUX dogs dinner arrangement as you describe it plus the dubious quality of the TVR made speed splitter box is never going to be the best recipe.If the ECU starts doing odd things with the stepper because of a temp sensor fault, a broken wire on the TPS, bad TPS adjustment or even a poor signal from the Micky Mouse TVR speed splitter box then I can very well see shunting would be a likely consequence.
There's quite a lot going on there just to manage idle, you could argue it's over complicated and complication can add unreliability. My Canems system has a closed loop system that controls idle via a two wire Bosch type extra air valve, it actually less complex than the 14CUX but works perfectly.
Perhaps it's a case of less is more?
ChimpOnGas said:
.... it's over complicated and complication can add unreliability. My Canems system has a closed loop system that controls idle via a two wire Bosch type extra air valve ....
That's the crux of the matter! I don't think complexity wrt reliability is a major factor but the fact that the ECU or code doesn't actually know where the stepper is due to no direct feedback, it's open loop rather than your closed loop. The Stepper Motor control code only has the last value of a step counter to use as a control reference. However, I've found that with all the related sensors working correctly and with base idle set at the optimum level the 14CUX stepper/idle function works just fine.Gassing Station | Chimaera | Top of Page | What's New | My Stuff