V8 - Load stalling driving me crazy

[disconc]

G'day everyone,

after searching and reading a lot, I have found some things, but yet can not solve my problem.

Here is the story (sorry, long post) :

Discovery autobox with a 3.9 EFI engine, 8.13 low comp, no cats, "Australia / Rest of the World" specs.

The engine has been entirely rebuilt 2000 km ago by a friend.
No problem for starting, either hot or cold, never !
No problem when running...

The problem is as follows, ONLY WITH WARM ENGINE:

When engine is warm ONLY, the idle on Park, or Neutral is ok and smooth.
When driving around and you stay at the lights with Drive engaged and braking, Idle is perfect.

The problem is :
-> when I am idling in Park or Neutral, and engage reverse or drive, well adding a significant load to the engine, the revs drop to below 500, and sometimes stall, sometimes recover.
When it recovers, it then idles ok with the load applied
When it stalls, you can re start again no problem

-> when offroading, like rock crawling, this is irritating, as you come to a stop with a tire on a rock, you give it a little gas to come over, then release... and it stalls when returning to idle.

-> you could make it happen also by giving it a little gaz with drive engaged and the left foot on brake and release gaz... same effects... it stalls when returning to idle.

It seems like it does not cope with a load apply on idle...
Does not do it with AC or lights, but have not had chance to try with a winch, but I believe that a good load on alternator might generate the same stalling.

Here is what I have done up to now :
=> brand new GENUINE cap, rotor, plug leads, plugs
=> timing set warm, with no vacuum at 6 BTDC
=> CO idle trim set at 1.4 V (have no CO tester around) and I feel it is worse when this value is lower
=> base idle speed set up warm with air by pass pluged at about 750/800 rpm
=> checked for vacuum leaks

The only thing (crazy) that I found is :
If I disconnect the vacuum hose which goes from the vaccum port just below the stepper motor to the fuel pressure regulator, the engine takes a few revs (of course with more air, say from 750 to 1000), that I would bring down to the previous idle revs by tightening the base idle screw.
Leaving this vacuum port sucking outside air, and the fuel regulator not connected with vacuum, THE PROBLEM COMPLETELY DISAPPEAR.

You can now switch from park to drive, go rock crawling, rev in drive while braking, and release gaz... it always goes back to its clean idle !!!

This is CRAZY and I can not run the car with the fuel regulator like this and air entering the plenum by the sideway, unfiltered...

By the way, I believe the problem is not from the fuel regulator, as if I just replug the vacuum port, so leaving just the fuel regulator unconnected, I have the same problem.

Seems like engine wants a little more unrestricted air, but when everything is plugged as it should, I can not give it this amount of required air from the base idle screw !!

No problem when cold, I believe the stepper compensate for this.

I do not know what else to try, if anyone could please give me any ideas ?

Thank you all

Erik
Cheers from New Caledonia

[BigJon]

Is the throttle plate adjusted properly? When the throttle is closed there should still be an airgap where the throttle plate doesn't quite touch the throttle body bore.

[PhilipA]

This behaviour is a characteristic of a 14CUX and I still have it a little even after changing the whole inlet manifold to a Thor. LOL. So my conclusion is it is not mechanical but electronic in nature.

I believe that it is caused by the stepper( ie the ECU confirming the revs) not being able to react quickly enough to the change in load. With mine I find if I let the idle stabilise for about 10 seconds ( which seems an eternity at the petrol pump) that it minimises the issue. This is after start in neutral where mine revs because of the Unichip aligning, then it steps down and may fall to 500 then up to 650-700RPM. Then wait 10 seconds then into drive. My theory is that the stepper closes right up which cause s the revs to drop but the time delay in the ECU recognising the lower revs causes the revs to drop below 500 and the ECU then to shut off fuel.

Also mine got MUCH worse when after I had a dyno tune where they advanced the timing at idle by adding 5degrees to my Unichip. I had the tune reversed to have nil additional advance under 1000RPM and it became much better.
So if you have a lot of static advance , you should back off to 7-8 degrees.

It should IMHO have got a bit better when you set the base idle up a bit . How did you do it? Did you block the hoses to the stepper on both sides?Then set the base/curb at say 600RPM. Also mine seemed to get better after I cleaned all the gunk from around the throttle butterfly.

It is only a minor problem for me now and mainly happens in reverse, where I think the load is higher from the trans.

But to repeat it stayed the same with a different complete manifold, stepper, temp sensor, TPS, adding o2 sensors, richening the MAF to 1.5 Volts ( recommended with 02 sensors). I think it may have got a tiny bit better after I fitted Iridum plugs also.

Not much left but the ECU. But they do not all do it.

I have another ECU at home and they changed the part numbers several times. probably trying to fix glitches like this. I really cannot be bothered to fit it to see as now it is only a minor prob.
Regards Philip A

[Landover]

Mine was doing this when my coil was failing. I would try to back up over a lip into my shed and it would stall when I took by foot of the accelerator. I replaced the coil and it's all good now. Very responsive and doesn't stall. I was also getting a bit of a miss when warm as well. Might be worth a look.

[disconc]

Hi Guys,

thanks for your answers.

I will have a look at cleaning the throttle plate... I have checked it as per the manual, where it says the difference between top and bottom with a depth vernier should be less than 0.5 mm which is ok on mine... but I am not sure about the remaining airgap... maybe it is too much sealed at now ??
BigJon, can this gap be seen/checked/adjusted easily ?

Philip :-) I have been looking at going Megasquirt for a while, to forget the 14CUX, but have not found the energy to go this way yet... mainly because of the tuning involved.
I did the base idle as you say, and set static idle advance with no vac at 6 deg BTDC.

Landover, one of the few things left unchanged by now on the ignition side was the coil... your description is similar to my problems, so maybe I should try a new coil... the only thing is, if it was the coil (ignition related), why would it behave perfectly with additionnal air entering the plenum ??

Thanks again... any other ideas welcome :-)

Cheers

Erik.

[BigJon]

I usually use a piece of paper to check the air gap. Slide a slip of paper into the intake and let the throttle close on it. You should be able to pull it back out without the throttle plate jamming it in place.

[PhilipA]

if it was the coil (ignition related), why would it behave perfectly with additionnal air entering the plenum ??

Because you are speeding up the idle, there is just more headroom above the ECU cutoff point. Even though it is unmetered the difference in leanness is not enough to matter.
You could do the same by increasing the base idle to 800 RPM or so.
Regards Philip A

[disconc]

BigJon,
Thanks for the tip, I will try that.

Philip,
this is where it becomes crazy... with everything plugged as it should, I even nearly completely unscrewed the base idle once, taking it to about 1000 rpm... and it will still make the same trouble, with an irritating then high idle !

On another hand, if I unplug the fuel regulator vacuum line and let the plenum suck air by this port, even if I set back the base idle just at about 600/700 rpm, it never make the stall problem !!! crazy.

I have also tried something else. I plugged everything as it should and tried giving the plenum some air by using the charcoal canister port on the plenum... guess what, the problem is still here !!!
The only way by now to get rid of it, is to let air get into the plenum by the fuel regulator vacuum port on the stepper housing... you still say crazy ?!?

Last try... I ran a hose from the pressure regulator vacuum port on the stepper housing to a nipple on the side of the air filter box (which normally takes a breather hose from the LHS rocker cover)... and the problem is still present. Unplug the hose from the air filter box, and no stalling then !!! not enought air when plugged there maybe... more and more crazy I say :-)

Thanks again

Cheers

Erik.

[PhilipA]

On another hand, if I unplug the fuel regulator vacuum line and let the plenum suck air by this port

If you unplug the fuel regulator then you are richening the mixture which also will give a more stable idle.


<LI id=jsArticleStep1 itxtvisited="1">
<LI id=jsArticleStep1 itxtvisited="1">When the engine is suddenly under heavy acceleration, the vacuum drops off momentarily and then recovers within a very short period of time. This sudden drop in pressure during acceleration also affects the fuel pressure, as the injectors are suddenly opened longer. The fuel pump takes a second to catch up with the pressure, so the fuel pressure regulator reacts to the drop in vacuum by closing the fuel return line momentarily. This gives a momentary boost in fuel pressure. <LI id=jsArticleStep1 itxtvisited="1">





Read more: How Do Fuel Pressure Regulators Work? | eHow.com (http://www.ehow.com/how-does_5002088_fuel-pressure-regulators-work.html#ixzz0xPLAklhn) How Do Fuel Pressure Regulators Work? | eHow.com (http://www.ehow.com/how-does_5002088_fuel-pressure-regulators-work.html#ixzz0xPLAklhn)<LI itxtvisited="1"><LI itxtvisited="1">Regards Philip A

PS hmmmm, i wonder if it is the fuel pressure regulator not increasing the pressure quickly enough when teh load comes on? I have a new one that I have been meaning to fit but haven't yetr got around to it.

[mike 90 RR]

The problem is as follows, ONLY WITH WARM ENGINE:

When engine is warm ONLY, the idle on Park, or Neutral is ok and smooth.
When driving around and you stay at the lights with Drive engaged and braking, Idle is perfect.

The problem is :
-> when I am idling in Park or Neutral, and engage reverse or drive, well adding a significant load to the engine, the revs drop to below 500, and sometimes stall, sometimes recover.
When it recovers, it then idles ok with the load applied
When it stalls, you can re start again no problem

-> when offroading, like rock crawling, this is irritating, as you come to a stop with a tire on a rock, you give it a little gas to come over, then release... and it stalls when returning to idle.

-> you could make it happen also by giving it a little gaz with drive engaged and the left foot on brake and release gaz... same effects... it stalls when returning to idle.

It seems like it does not cope with a load apply on idle...
Does not do it with AC or lights, but have not had chance to try with a winch, but I believe that a good load on alternator might generate the same stalling.

Cheers from New Caledonia

Everything written above ^^^^^^ leads me to the bit below ....

........... Have you adjusted the TPS using the voltmeter?? .................

Cheers
Mike

[disconc]

Philip,
quote : If you unplug the fuel regulator then you are richening the mixture which also will give a more stable idle.

I agree with you, but if I let the fuel reg unpluged and I plug the vacuum port... I still get the trouble, so I though it was not fuel pressure related as the problem comes back as soon as I replug the vacuum port.
But maybe you are right on the fuel pressure not reacting quickly enough ?? One more thing to try to swap :-)

Hi Mike,
I remember I have checked the TPS with a voltmeter , and the value was fine... however, mine seems to be on the latest model 14CUX which was supposed to be self adapted by the ECU, as there is no room for adjustment on the fixing holes... can not remember where I have seen discussions about this, but up to a said model of 14CUX, there was the TPS adjustment, and after that it was not needed anymore.
Anyway, I remember having checked mine. It was in the specified voltage when closed and was smooth in operation.

Thank you all

Cheers

Erik.

[PhilipA]

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

[mike 90 RR]

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 :eek:

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

[PhilipA]

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

[disconc]

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.

[mike 90 RR]

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

[cockie55]

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.

[PhilipA]

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

[Scouse]

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.

[pibby]

Soon after getting my car it would run intermittently in limp home mode. i was learning my way around at the time and checked the TPS and it was about 0.084 volts. When you replicated the motion of the accelerator pedal on the linkage on the plenum it would sometimes return to 0.086 volts. I reset the tps to around 0.33v and that was the end of the intermittent limp home mode.

found it worthwhile to replace the coolant temp sensor for the sake of $20 odd dollars as it plays such an important role in fuelling. Even though the old one tested within spec the newer one made a noticeable improvement in the cars performance.

for what it’s worth if one can be bothered it can be prudent to check values at the 14cux pinouts rather than just on the senders/sensors in the engine compartment. Have read of cases where readings have tested ok in engine compartment but not been mirrored on the 14cux.

[disconc]

Hi guys,

Cockie55, thanks for your input. I will try to measure the TPS at idle, and see how the voltage behaves at idle and on the return of the throttle plate...

Philip, I confirm the problem only occurs when engine is hot, with thermostat opened. When cold and during warm up, everything is fine.
Changed the plugs and plug leads say 100 km ago. The plugs were all "perfectly" brown.

Scouse, thanks for the feedback, even if out of thread, you are the first one I met that has ever seen a late D1 with the C suffix engine :-) Do you have further details you could please PM me about the recall A156 (fuel tank leak check) ?

Pibby, thanks for the idea, I will double check the voltages at the ECU plug.

Cheers

Erik.

[disconc]

Hi guys,

I was a bit short on time today, so I did everything in one operation... so the shame (read stupid) part of it, is I do not know which operation seems to have improved things...

Here is all things done :
-> engine fully warmed, plugged both sides of hose, stepper to plenum, and checked base idle (only dash tacho, even if not accurate, it is all I have) : just in the middle between 500 and 750. So quite close to 600, which seems great.

-> removed the stepper : the plunger was shining clean !!! damn'it. Never mind, soaked in WD40 and a little cleaning with tooth brush.
The plenum housing side where plunger rest was like covered with a black powder (like gun powder), but not sticky... Cleaned with carb cleaner and rag. Refit.

-> removed rocker cover breather vapor trap, and cleaned it
-> removed all the breather hoses, including the little Tee, up to the plenum and cleaned everything with carb cleaner. The little side of the TEE was quite filled of sooth

-> tried to clean the area were the butterfly close on the plenum

-> checked the gap between butterfly and plenum with a piece of paper. On the bottom, no gap at all, but on the 9 to 12 o'clock part of the disk, I can feel the strip of paper moving ok.

-> cleaned the MAF with carb cleaner

-> refit everything, and checked TPS voltage, ignition on and also engine idling : voltage rock stable and always returning to the same value +/- 0,03 V, but at about 0,29 V
=> ovalate holes and made it to 0,34 V, rechecked idling and on the return to idle after a little gaz : ok to 0,34 +/- 0,02 V

Went for a test drive after that, and really seems to have improved :-))

Time will tell... I will repost in a while to tell how it is going...

If it is the cleaning that has done wonders, I am a bit worried because the engine has only done barely 2000 km after having been completely overhauled and cleaned... so that is not much before re clogging up !!

Anyway, thank you all for the ideas, and I am sorry not to have taken the time to do the tests one after the other to know exactly which one was THE ONE !

Cheers

Erik.