Discussion
been out today for a nice little run enjoying the sunshine all going well until I came to some road works where I had to stop and she didn't want to tick over revs kept on dropping and cut out a few times. I cleaned the stepper motor over the winter. When we got home it ticked over fine ok for a couple of mins any ideas thanks.
2 sMoKiN bArReLs said:
There'll be loads of experts in a bit..
..all I can say is I've done maybe 300,000 miles in a few Chimaeras. They've all done that some of the time. I just live with it, and keep foot on both brake & throttle to stop the stall.
(and sometimes they rev to 2,000 rpm instead
)
When I first purchased mine it would idle fine when cold but stall when warm. Not being an expert it was looked at 4 or 5 times before the issue was resolved - turned out to be a rusted earth connection on one of the wiring looms. ..all I can say is I've done maybe 300,000 miles in a few Chimaeras. They've all done that some of the time. I just live with it, and keep foot on both brake & throttle to stop the stall.
(and sometimes they rev to 2,000 rpm instead
)Prior to that, more obvious items such as stepper motor and lamdas were suspected.
While I was told that 'they all do that' it doesn't help your confidence with the car, particularly when it's new to you - and I guess that my experience proved that there was a cause that (eventually) was diagnosed and rectified.
Patience and perseverance was key!
storm grey said:
been out today for a nice little run enjoying the sunshine all going well until I came to some road works where I had to stop and she didn't want to tick over revs kept on dropping and cut out a few times. I cleaned the stepper motor over the winter. When we got home it ticked over fine ok for a couple of mins any ideas thanks.
Was your petrol tank less than half full by any chance?Even when the tank is at half full you should be aware fuel can vaporise in the fuel rail on a hot day.
As we know our fuel injection is on a return system, the petrol tank acts as a heat sink on the returned fuel.
As soon as the fuel pump compresses a new supply of cooled fuel it heats it right up again, as the returned fuel gets lower that supply to the pump just gets hotter & hotter in the first place.
If you want to test this yourself just feel the tank on a hot day at idle when your half full or less.
You'll probably be surprised at just how hot that tank is to the touch, after the pump has compressed & heated the already warm fuel it travels up past the O/S exhaust manifold taking on yet more heat.
And then around the fuel rail for a final cooking before it has a chance to start the cooling process again as it returns to the tank.
After a long hot run followed by a period of idling in traffic the heat sink effect starts to lose out to all that radiant heat & fuel temps just keep escalating.
When you turn your engine off the water pump stops turning so there's a huge surge of heat that has to go somewhere, as we know heat rises and there's only the vents in the bonnet for it to escape through.
Even the fans that would ordinarily go some way to help evacuate some of this under bonnet heat are wired in a TVR so they go off when you turn the ignition key off.
It's a recipe made in hell, everything and anything under the bonnet absorbs all this heat including the fuel rail & the fuel inside it which is no longer circulating because the fuel pump isn't running.
So run your TVR at low speed through town with a lowish tank in the 30 degree heat like we're getting now, turn off the engine & nip in the local shop for a pint of milk, and when you return 5 minutes later your fuel is boiling in the rail.
Crank her over and it's going to really struggle to maintain the required fuel pressure to sustain a steady reliable idle.
Modern petrol is full of ethanol which has a vey low boiling point compared with the fuel we used to enjoy years ago, this is a real problem for classic cars running carburettors where the float bowls are near the exhaust manifolds (Ie non cross flow type engines).
This problem is well understood by the classic car fraternity but it far less common in fuel injected cars with a return type system.
But the TVR is different, there is so much heat in there you end up suffering that fuel vaporisation problem too.
My LPG conversion has a half sized petrol tank so I've been suffering the problem more than most, especially recently with all this hot weather.
It doesn't happen that often, but when it does it can be really annoying, mostly because it seems to happen when you are in a hot stop start traffic jam.
To help I've just fitted a fuel cooler from a diesel BMW E46 Diesel.
I'm hoping by positioning this little 10" x 6" fuel cooler in the O/S wheel arch to cool the fuel on the return line before it gets deposited in the tank will be just enough to solve the problem.
I'll update everyone as soon as I've given it a good test.
As we know our fuel injection is on a return system, the petrol tank acts as a heat sink on the returned fuel.
As soon as the fuel pump compresses a new supply of cooled fuel it heats it right up again, as the returned fuel gets lower that supply to the pump just gets hotter & hotter in the first place.
If you want to test this yourself just feel the tank on a hot day at idle when your half full or less.
You'll probably be surprised at just how hot that tank is to the touch, after the pump has compressed & heated the already warm fuel it travels up past the O/S exhaust manifold taking on yet more heat.
And then around the fuel rail for a final cooking before it has a chance to start the cooling process again as it returns to the tank.
After a long hot run followed by a period of idling in traffic the heat sink effect starts to lose out to all that radiant heat & fuel temps just keep escalating.
When you turn your engine off the water pump stops turning so there's a huge surge of heat that has to go somewhere, as we know heat rises and there's only the vents in the bonnet for it to escape through.
Even the fans that would ordinarily go some way to help evacuate some of this under bonnet heat are wired in a TVR so they go off when you turn the ignition key off.
It's a recipe made in hell, everything and anything under the bonnet absorbs all this heat including the fuel rail & the fuel inside it which is no longer circulating because the fuel pump isn't running.
So run your TVR at low speed through town with a lowish tank in the 30 degree heat like we're getting now, turn off the engine & nip in the local shop for a pint of milk, and when you return 5 minutes later your fuel is boiling in the rail.
Crank her over and it's going to really struggle to maintain the required fuel pressure to sustain a steady reliable idle.
Modern petrol is full of ethanol which has a vey low boiling point compared with the fuel we used to enjoy years ago, this is a real problem for classic cars running carburettors where the float bowls are near the exhaust manifolds (Ie non cross flow type engines).
This problem is well understood by the classic car fraternity but it far less common in fuel injected cars with a return type system.
But the TVR is different, there is so much heat in there you end up suffering that fuel vaporisation problem too.
My LPG conversion has a half sized petrol tank so I've been suffering the problem more than most, especially recently with all this hot weather.
It doesn't happen that often, but when it does it can be really annoying, mostly because it seems to happen when you are in a hot stop start traffic jam.
To help I've just fitted a fuel cooler from a diesel BMW E46 Diesel.
I'm hoping by positioning this little 10" x 6" fuel cooler in the O/S wheel arch to cool the fuel on the return line before it gets deposited in the tank will be just enough to solve the problem.
I'll update everyone as soon as I've given it a good test.
There is a fundamental issue on the 14CUX if the engine load goes up with extra alternator load say when cooling fans kick in as the stepper response is quite slow when the RPM dips. The ECU has no less that 3 extra inputs to pull the idle up when the load goes up so the RPM does not drop in the first place, (heated screen, air con and auto box drive) but I dont know if TVR use any of these at all. The easiest one to use is to put 12 volts on pin 8 of the ECU (purple yellow wire) to make the ECU think a heated screen is turned on to lift the idle without messing with the base idle screw- its only about 150 rpm or so. It would be worth checking the various 14CUX ECU loom connectors for the purple yellow wire and see if its connected or utilized in the TVR loom (??). This is not a fix for a cooking AFM or ignition amp due to high under bonnet temps. A heat shield on the AFMs a good idea as they really cook near the exhaust, and it only takes a shift of +200 mv on its output at idle to upset the mixture enough to stop the car from idling as it over fuels.
I had fuel vaporisation when I had the 14CUX when the standard tank got low on a hot day.
I still had fuel vaporisation with the Canems when the standard tank got low on a hot day.
Creating a smaller petrol tank for my LPG conversion just made the situation worse.
It doesn't matter a jot what engine management system you have, the underbomnnet temps get so hot in this weather fuel will boil in the rail.
The lower the fuel level or smaller your tank is, the more you'll experience the problem.
I know it's fuel vaporisation because the pump starts to scream when it does it.
This is classic symptom cavitation in the pump as pockets of vapour are produced by the fuel boiling as the pump compresses it.
Stick two gallons of cool petrol in my little tank while the engine is running & the pump is screaming & withing 60 seconds the pump is all quiet again.
And the car stops stalling.
Lucas 14CUX, Canems, Emerald ect ect.... it's irrelevant... they all do it to some extent, and the lower your fuel level is the less fuel you have to take the heat out of the hot returned stuff.
So the worse the problem gets.
I still had fuel vaporisation with the Canems when the standard tank got low on a hot day.
Creating a smaller petrol tank for my LPG conversion just made the situation worse.
It doesn't matter a jot what engine management system you have, the underbomnnet temps get so hot in this weather fuel will boil in the rail.
The lower the fuel level or smaller your tank is, the more you'll experience the problem.
I know it's fuel vaporisation because the pump starts to scream when it does it.
This is classic symptom cavitation in the pump as pockets of vapour are produced by the fuel boiling as the pump compresses it.
Stick two gallons of cool petrol in my little tank while the engine is running & the pump is screaming & withing 60 seconds the pump is all quiet again.
And the car stops stalling.
Lucas 14CUX, Canems, Emerald ect ect.... it's irrelevant... they all do it to some extent, and the lower your fuel level is the less fuel you have to take the heat out of the hot returned stuff.
So the worse the problem gets.
blitzracing said:
Not thought about fuel temp, but anyone with RoverGauge or ECU mate could check this one, as there is a specific sensor for it.
Actually if you're in any doubt over what I'm saying the best thing to do is rig up a fuel pressure gauge at the rail.Just watch what happens to that gauge when things get really hot at idle with just a few gallons in the tank.
Hot tank to the touch, screaming fuel pump, fluctuating fuel pressure at the rail.
They are all symptoms of the same condition.
A similar thing happened to me at the weekend on the way to a car show
Quick run up the M/way (30 miles) followed by 20 minutes stuck in a traffic jam
The idle started cycling between 1500 and almost nothing, i kept it going for a while but eventually it stalled
To it's credit the old bus started up again straight away and idled perfectly...
So; the tank was almost full. I doubt it was an air leak (not had an idle problem in 4 yrs of daily use)
Nothing had a chance to cool down in the few seconds it took to re-start the engine
Curious
Quick run up the M/way (30 miles) followed by 20 minutes stuck in a traffic jam
The idle started cycling between 1500 and almost nothing, i kept it going for a while but eventually it stalled
To it's credit the old bus started up again straight away and idled perfectly...
So; the tank was almost full. I doubt it was an air leak (not had an idle problem in 4 yrs of daily use)
Nothing had a chance to cool down in the few seconds it took to re-start the engine
Curious
Mr Plow said:
Also having the same issues.
Will idle fine for days, go on a run then starts to cut out but will start again straight away. Thought it was just me, but obviously not.
First time it's ever happened to me (in nearly 30,000 miles!) but it is also the first time I've been caught in a jam for so long on a hot dayWill idle fine for days, go on a run then starts to cut out but will start again straight away. Thought it was just me, but obviously not.
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