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MikBoje Thursday 13th September 2012    
Unfortunately I don't own a a TVR smile - but this forum seems to be the place where a lot of knowledge is held regarding the Rover V8/14CUX ECU, so I hope it's ok I'm asking for help anyway, as I'm getting pretty desperat.

I have a RRC with a brand new Turner Engineering 3.9 V8 long block just fitted - and I'm a lot of problems with hot idle. Startup and cold idle is fine, as well as normal driving - but when hot, idle gradually gets worse and worse and the lambda figures are not that far off it seems to me, but when iddling hot, the lamda figures raises to 18-22 (where the lamdba gets out of range), and the engine nearly stalls.

It has gasflowed performance heads, a H180 Sports torque camshaft, and stainless steel headers and 3" exchaust system - all brand new. It's a non-cat 1990, so in order to see whats happening I've put on an Innovate LC1 wideband lamba connected to a Innovate MTX-L gauge.

I'm not big mechanic myself, but have read a lot on the subject - all of the testing and fitting has been done by proff. mechanis, but specific 14CUX experts appears to be non-existant here in Denmark smile

While trying to take some of the old parts out the equation, the following has been exchanged for new parts, testing it at along when fitting it:

The AFM, fuelpressure regulator, stepper motor, fuelt temp, water temp, and injectors are all new. Crank-case breather has been checked and all components of the PCV system has been changed too.

Brake Cleaner/Diesel starthas been sprayed directly onto the various joints around the plenum - with no change in rpm - so no clue of false air as far as we can detect.

The throttle heater pad is not removed. The T-piece of the PCV system has still got the small restrictor in place.

The Ignition system is a programable 123Iginition electronic unit, running a very modest ignition curve. This was fitted with brand new Magnecor HT leads and an genuine Land Rover coil.

AFM is set to 1.3V, TPS is set to 0.35V, Fuel pressure is set to 40 psi.

Would it help increasing fueling on hot idle via a Mark Adams chip or a Megasquirt ? - or would that just cause more problems ?

I'm running out of ideas

Please advice
Thank you
shpub Thursday 13th September 2012    
You might want to download the ECUmate user manual as it explains in detail how the idle is controlled by the ECU. It does depend on a lot of things and simply replacing parts is very expensive way of doing things. I designed ECUmate to extract the data from the ECU so you can see what is going on.

It could be that the new engine setup is not compatible with the original 14CUX mappings and what you are seeing is simply a result of the hardware changes that make the engine different from the original setup. If it is not running a cat mode then the ECU runs open loop and cannot adjust the fuelling to compensate.

It could be as simple as the temperature sensor - ECUmate will show what the value that the ECU is seeing. There may be other faults that are causing the ECU to run in a limp home mode.

If there is an ignition problem this will cause the lambda to go lean because of the misfire and you could be seeing this.

MikBoje Thursday 13th September 2012    
I've monitored the temps and stepper motor with Rovergauge and everything seem to be behaving correctly. Temp sensor show Ohm readings corresponding to the manual as well. Base idle has been set according to the manual as well.

Its running the correct resistor for a non-cat car, so you're right it won't be able to do any adjustments.

No errors are showing in the ECU, according to Rovergauge.
shpub Thursday 13th September 2012    
ECUmate displays more idle data and fault codes than Roverguage does including when the ECU is or not in the idle state. This is affected by several parameters. Any one of them can change the idle behaviour. Also bear in mind that the stepper operation by the ECU is very crude: there is no feedback just because the stepper is moving, it doesn't mean that it is actually in the right place to start with.

Pages 37 to 40 in the download describe in detail exactly what the ECU does and why. I suspect that the mapping is either completely out and running lean but when the engine is cold, the fuelling enrichment is compensating or there is some other fault that is causing the ECU not to implement the idle mode correctly.

Also bear in mind it could equally be a problem with the ignition that is contributing to it. Misfires will cause the mixture to appear lean.

MikBoje Thursday 13th September 2012    
Hi SHPub

Thank you for your comments. I don't think the ignition is misfiring - the 123Ignition has a pretty good reputation, and the timing at idle is spot-on when checked with a timing gun.

The AFM is set to 1.3V on Red/Black and Blue/Red when ignition is on, but engine not started - shouldn't that be correct ? I've read somwhere that Ohm measured between "the two outside pins should read 300 Ohms" - mine does only measure 120 - would that be an indication of something smile ?

robrover Friday 14th September 2012    
Sounds like you’ve got an unmetered air leak into the plenum somewhere. Does it run ok off idle? That’s a fairly mild cam but with good low down torque ideal for a 4x4.

These same issues have come up before on the forums at
See especially their Technical Assistance, Electronic Diagnostics, Disco 1 and RRC sub forums.
From what I gather, generally when going bigger – eg from 3.9 to 4.6 - the fuel map in the 14CUX is ok at lower rpm but can’t supply enough for the larger capacity higher up in the range.

MikBoje Friday 14th September 2012    
Two different mechanics have checked for air-leaks using Brake Cleaner/Diesel start, which has been sprayed liberally around the plenum area - with no no luck in detacting any airlieaks.

Lambda is showing:
Cold idle approx 12.5 - 13.5
Cruising at 50 mph approx 14-15
Kickdown at 50 mpx approx 11.5 to 12.5
Warm idle starting around 16, and gradually rising to 22 if left idling, at which point it can barely keep itself alive.

I know that the cold fueling will be compensating a bit, but wouldn't an air leak also be more apparent when cold ?

The last mechanic who checked for an airleak commented that the vacuum was too low - but I don't know if that can be related?

Cold and stable idle: 0,41 bar
Warm idle starting to get rough: 0,38 bar

Edited by MikBoje on Friday 14th September 06:03

tvr marvin Sunday 30th December 2012    
Hello MikBoje,
Your problem does look like an air leak. Because the mixture seems to lean out slowly at closed throttle (idle) while there is no leaning when throttle is open (even partially). It seems there is air introduced into the intake, which is not measured by the AFM.
You said you tested for air leaks by spraying combustible stuff around the plenum and found nothing - alright, but there are other ways air could get into the intake:

The Brake booster is fed with engine vacuum and the hose is connected to the plenum after the throttle and AFM. If you have a hole in the hose or in the break booster, it ma mess up your mixture without showing air leaks when spraying carb cleaner, because the hole is far away from the engine.
Just disconnect the hose for testing (you know it does not brake anymore if you drive like that cool).

Crankcase breather
The crankcase breather is the large tube going across the engine from the right bank head cover into the plenum (again, after throttle and AFM). Usually it routes fumes from the oil into the intake for environmental reasons. It also creates a vacuum in the crankcase which naturally prevents oil leaks.
Now if you have a hole in your crankcase somewhere (see the breather filter on the back of the left bank! And put back oil stick back in wink!) that may suck too much air into the plenum.

Ignition vacuum advance
Same as with brake booster. Make sure the distributor membrane has no holes.

Fuel pressure regulator.
Same again. there is a membrane that controls fuel pressure on the rail as a function of plenum pressure. However, since this is behind the plenum, you should have seen it by spraying carb cleaner behind the plenum.

Idle control stepper.
The idle stepper bypasses air around the closed throttle. Since its position is on the backside of the plenum it needs a hose for this. This hose may be porous or slipped from the connection (I have seen loose hoses on breather and idle control hoses). But again, this all is close to the plenum and you should have found it by spraying carb cleaner...

That is all the vacuum hoses on a rover V8 I remember now. maybe there are more and I hope others can add information if there is any. In old cars sometimes even wipers and windows were vacuum operated. So make sure you find all hoses.

The best way to test this is to just disconnect all hoses at the plenum and plug the holes.
This will not work for your ignition advance, since a missing advance will change timing, which may change idle etc. Best way here is to test the hose, distributor, and all connected stuff with a hand vacuum pump (reverse leak-down test wink).

I hope you find the problem.


Big Ron Wednesday 11th September 2013    
Hi MikBoje,
Did you ever resolve your hot idle probs? I have exactly the same issues, and been around all of the suggestions to no avail. I have a very similar spec engine, with the kent h180, ss exhaust etc. cold runnig is all good, but the hot idle is poor, and usually ends up cutting out - especially when putting into gear( auto box drag). I suspect its either a faulty ECU, or the original Map isn't coping with the new engine set up. If you figured it out, well done, share the knowledge!

MikBoje Wednesday 11th September 2013    
Hi Ron,

Well in the end after spending a lot of money and hours on checking out different error sources, it turned out that the bloody &/%&/(% mechanic that put in the new Turner engine had put a copper washer on the stepper motor - thereby not enabling it to close properly and sucking in false air...

Suddenly I had a lot of spare time because the thing was now running fine with the 14CUX - so I decided to MegaSquirt the beast - haven't looked back since smile

Big Ron Wednesday 11th September 2013    
Hi Micheal,
Thanks for the reply, I wasnt holding out much hope on a year old postsmile
I know that my idle valve is ok, 1 - its new, 2 - new and old perform the same, and 3 - it is running in the right area of its range. 130-140 steps from open. The base idle setting governs where the idle valve operates. My AFR is showing a pretty stable mixture of around 13.5 - 14 even when she starts to stall - which is odd. Its as if the ecu is reacting too slowly to move the idle valve. its only on hot starting, and putting into gear.
I dont really understand how your readings were showing lean when you were having problems. even if your idle valve wasnt closing fully, the afm would still be measuring all of the air into the pleunam, so should maintain the correct mixture?
Anyway, i've got one more idea to try. Ive built a little timer circuit that will give a small volt increase to the tps input, when the gears are selected for a few seconds. this will hopefully overcome the stalling effect. If that doesnt work I may take a look at the MS route myself. Which MS did you go for 1 or 2?


MikBoje Wednesday 11th September 2013    
It's an MS2 Extra.

I went through 5 (!) stepper motors - each acting differently from the other. Try and see if you have any gasket/spacers on them.

I also found a cheap spare 14CUX on Fleabay that I tested with - may be worth a shot in your situation smile

Bluebottle Wednesday 11th September 2013    
one other thing to check would be for a lazy lambda sensor and probably the one on the bank not monitored by the afr gauge...I have had this in the post where it sticks telling the ecu to lean the mix out which it does to the max instead of the usual lambda failure where it richens the mix.