Thread: V8 - Load stalling driving me crazy

I do not know where this TPS thing came from . It applies to flapper AFAIK but not to 14CUX which learns what is the idle voltage , or doesn't care under 0.545 volts
The manual does not say it and I have found in practice it does not matter as long as it is in a band from whatever to 0.545volts.

The override injection cutoff , cutoff point is 0.55 . I know this because I found with my setup that I was not getting to the 4.6 so I adjusted it up until I got as high a voltage as possible on WOT and then backed down until I again got injection cutoff. this is only needed because of my jury rig TPS using 14CUX on Thor.
This is flapper from the manual _1987 model year USA model

Correct voltmeter readings-
Proceed to Test 17
Throttle Throttle
closed open
0.29 ) ( 4.6 Volts
) smooth (
) __....__...___________ (
0.36 ) swing ( 5.0 Volts
Incorrect voltmeter readings
Check:-
- I -

Continued

This is 14CUX from the manual 1989 model year

Throttle closed: 0.085-0.545 volts ) smooth
) swing
) between

RR2642E

Continued

And the wide range I adjusted made absolutely no difference to the idle or the stalling. You can see the narrow band for flapper and 0.32 is right in the middle.
Regards Philip A

Originally Posted by disconc

I remember I have checked the TPS with a voltmeter , and the value was fine...

Hi Eric

I won't pretend to be the "Brains trust" on the subject of the 14cux ... All my knowledge comes courtesy from a mix of PhillipA and LOVEMYRANGIE ... With a dose of Cockie55 thrown in for good measure ... All whom, I hold in high regard ... cause without them, I'ld be stuffed

But I hear ya on the idle issue ... Mine suffered big time, on it .... great when cold , then stutters when warmed

The TPS was the main culprit ...with the MAF not far behind it ... as it was not right for voltage
My TPS now has a voltage setting of 0.34 volts ... No less than 0.33 ... no greater than 0.35

You have to oval-ate the screw holes sometimes to achieve it


Since the TPS & the MAF have been set voltage wise ... I've never had the issue again .... I'm unsure of your "Later ECU" ... Mines the 1990RRC hot wire version with a replacement ECU out of a 94 Disco


Keep in mind that if you turn the screw on the butterfly to adjust Base idle ... then you are also changing the TPS voltage position = recheck & adjust



BY the way .... Have you checked the values of the (ECU) fuel rail and Temp sender units?


Cheers
Mike

Mike , I copied the above pages from the Injection Troubleshooting Guide in the Land Rover Workshop Manual for 1987 (Flapper) and 1989 (14CUX).

I would appreciate it if you could copy a quote from an official Land Rover publication that says that the TPS on a 14CUX has to 0.32 volts. If so I will have to change mine again as I have many times with no change to anything.

Don't list the Rpi site as I originally believed as I am sure it is a simple mistake of saying 14CUX instead of Flapper.
Regards Philip A

Hi guys,

thanks again for your answers.

I have rechecked the value of my TPS : 0.31 V when closed, and smooth operation after that.

Philip confirms what I have read somewhere about the TPS values being "self adapted by the ECU" on later ECU.

Mine is a 1998 production engine, maybe one of the last batches of the 3.9, as it is a funny (no one could ever explain me the difference) suffix C engine.
In all the manuals, there are the before suffix B and the suffix B V8... but never seen anything about a suffix C.
Engine : 38D38976C / VIN : SALLJGMM4 WA765 679

We had the biggest problems finding the main bearings for this engine, part number STC 3724... which was impossible to order from various companies in UK and USA, everyone saying it was backordered and even LR could not give an estimated supply date !!! Believe it or not, I found a set at British4wd in Tasmania... Alan is a KING :-))

Back to the TPS, from my understanding, there are two screws around the throttle plate area :
-> the base idle air bypass screw (which is the one I was adjusting) and does not alter the butterfly position, but just let air pass on the side of it.
-> The other one is accessed by under the plenum (removed from engine) and is the butterfly stop screw, which is the one which should mess with the butterfly position and the TPS value I believe (not touched !)

Coolant and fuel temperature sensors seems ok ohm wise.

Thanks for the feedbacks

Cheers

Erik.

Originally Posted by PhilipA

Don't list the Rpi site as I originally believed as I am sure it is a simple mistake of saying 14CUX instead of Flapper.

I hear what your saying Phillip ....

You are correct ... I have No LR information ...

All I can say is that I have performed this setting to 4 separate cars ... all being 1990 to 1994 models .... and it got the idle issues back under control ...


Cheers
Mike

In my humble opinion the TPS is the first port of call (after a quick air leak and stepper check) if you have any idle to mid range fueling related problems, particularly over fueling. Too often the MAF gets blamed first when in reality the TPS is shot.

The 14CUX TPS is said to be “self adaptive” which simply means if there is any wear in the throttle stop, the voltage value in the TPS for idle remains fixed. To reinforce that point Lucas no longer elongated the TPS mounting holes in 14CUX TPS’s, no doubt to discourage people from fiddling with TPS’s and or for emissions control specs..

The main problem with a TPS is the first section of wiper arm movement wearing the most and as expected being the section which gets the most use. Some of the most worn TPS’s will show they are within the desired idle range of 0.32 – 0.34 volts with the ignition on (but engine off). Many people see this and assume their TPS is fine when in reality it is not.

I recommend starting the engine and checking the TPS idle voltage as quite often the vibration will cause that section of the worn wiper to come into and out of play and the voltage will spike to maybe >1.0 volts at idle. Beware this may only occur intermittently. I would automatically ditch a TPS after 10 years of short trip life.

I have always thought the 14CUX ECU idle fault range for the TPS (fault display #17) was outside 0.28 – 0.38 volts (and the genesis to the 0.32 - 0.34 desired range many speak of), however the fault code range may well be the 0.085 and 0.545 volts referenced by PhilipA. I must check one day and see.

BTW my "problem " used to be like yours many years ago, however the only time mine plays up is If I stop the engine and restart say five minutes later.

Again mine is complicated by the fact I have a Thor manifold, and the plenum heavily shields the injector rail from cooling air so it may be fuel evaporation.

Now I note that you said you have the problem with the engine "warm". Do you mean during the warm up phase before it is at normal operating temperature ie the gauge not quite at the normal 88C operating position or has just got there. I am assuming you have an 88C thermostat as any lower may cause the engine to be in warm up mode.

If that is the case the answer is very simple. Since the 14CUX was designed and tuned in the early 90s the volatility and constituents of petrol have changed enormously. This has reduced the vapour pressure of fuel ie its ability to vapourise when in a cool combustiion chamber.
I had a similar problem with my 1995 M3. It used to fart and spit when warming up, and it had very sophisticated Motronic.
So what was an appropriate enrichment curve vs temperature in the early 90s is too lean in 2010.

However if it happens when hot it is a different ball game.

I had another idea occur to me. You may or may not be aware that you can be unaware of a misfire at idle because the stepper increases the idle to the target 750RPM even if one cylinder is not firing. Maybe revisit the plugs , leads etc while having the stepper disconnected and ground out each cylinder individually.
Regard sPhilip A

Originally Posted by disconc

Mine is a 1998 production engine, maybe one of the last batches of the 3.9, as it is a funny (no one could ever explain me the difference) suffix C engine.
In all the manuals, there are the before suffix B and the suffix B V8... but never seen anything about a suffix C.
Engine : 38D38976C / VIN : SALLJGMM4 WA765 679

A bit off track here but we've had a few late D1s come through here with a C suffix engine. I don't know the difference though but you're not alone with one.
You also have recall A156 (fuel tank leak check) outstanding on your car.