91 RR Classic stalling under load

**aussiebushman** · 25th October 2019, 05:28 PM

This is a 91 Range Rover Hi-Line with a new 4.0 top-hatted engine installed just a few months ago. Initially it was OK, but a weird condition has developed.

After sitting for a while - like several days (I only drive it once each couple of weeks), the engine is hard to start - coughs and stumbles but eventually fires. To me this suggests a fuel delivery problem. Eventually it starts and then it runs well on the open road but if the vehicle has to stop for any reason like traffic lights, halted traffic etc, obviously the foot comes off the accelerator pedal. As soon as pressure is reapplied to the pedal, the engine cuts out. I have discovered that the engine does not cut out IF very light pressure is applied to the accelerator but any attempt to provide more throttle causes immediate stalling

On the open road,there is plenty of power but if throttle is eased off, there is a distinct hesitation when power is reapplied

it has already been back to the workshop to have this rectified - plug leads were replaced as well as the vacuum tube from the Plenum to the MAF, timing was adjusted. Seemed OK for a while but now the problem has returned:

Part of my problem is my location - 75 Km from the nearest town (where I have learned never to trust the local mechanics) and 3.5 hours from Sydney so it is no simple job to get it fixed - even if it makes it there

I have a spare fuel pump but no diagnostic tools so if it the MAF or the ECU, it will be way beyond my abilities to fix it.

If anyone is familiar with this issue and can offer advice (other than set fire to the car) it would be appreciated

16PMark · 25th October 2019, 05:35 PM

TPS....?
Clean/Inspect.
If you are handy with a multimeter, then can be easily checked.
It (the TPS) can also be adjusted (tweaked) via its mounting screws.

Also.. cold start injector.....
Disconnect hose, and block it off.
(Not needed here in Oz)

16PMark · 25th October 2019, 06:24 PM

Also, (just sitting here thinking about your issue) .... the air flow meter, being the "flappy" type, rings a bell somewhere in my noggin as also being a contender in this scenario...

**aussiebushman** · 26th October 2019, 10:03 AM

Originally Posted by 16PMark

TPS....?
Clean/Inspect.
If you are handy with a multimeter, then can be easily checked.
It (the TPS) can also be adjusted (tweaked) via its mounting screws.

Also.. cold start injector.....
Disconnect hose, and block it off.
(Not needed here in Oz)

Thanks but assume I'm too stupid to follow that. I'm certainly OK with a multimeter but which contacts should be measured? Are you referring to the unit under the passenger seat?

**PhilipA** · 26th October 2019, 03:17 PM

A 91 is a 3.9 with 14CUX, no flapper and no cold start injector.

I agree the TPS could be worn just off idle which is where they wear.

You could also check the temperature sensor on the RH front of the engine which has 2 wires. should be 300 Ohms at 88C if it seems to be rich.

Some weird ones are ,Has the T piece into the plenum from the large tube that goes from the rocker cover to the TPS got just a pinhole into the manifold, or has someone put just a normal T piece there?

Have you thoroughly cleaned around the Throttle body and blade ?
Is the stepper motor clean and the housing where the cone goes in clean. Do not attempt to rotate or pull apart the stepper as bye bye if you do.
Are all the vacuum hoses in one piece and not cracked or holed, particularly the one to the FPR?
Regards PhilipA

16PMark · 26th October 2019, 05:53 PM

Originally Posted by PhilipA

A 91 is a 3.9 with 14CUX, no flapper and no cold start injector.

I agree the TPS could be worn just off idle which is where they wear.

You could also check the temperature sensor on the RH front of the engine which has 2 wires. should be 300 Ohms at 88C if it seems to be rich.

Some weird ones are ,Has the T piece into the plenum from the large tube that goes from the rocker cover to the TPS got just a pinhole into the manifold, or has someone put just a normal T piece there?

Have you thoroughly cleaned around the Throttle body and blade ?
Is the stepper motor clean and the housing where the cone goes in clean. Do not attempt to rotate or pull apart the stepper as bye bye if you do.
Are all the vacuum hoses in one piece and not cracked or holed, particularly the one to the FPR?
Regards PhilipA

Whoops! Yes. Thanks PhillipA.
Too many cars, too many years, too many drinks in between all that.

Sigh...

Sorry aussiebushman for the error.

**justinc** · 26th October 2019, 08:24 PM

First thought with your comment about off idle stall is TPS adjustment. 290mV to 320mV at closed position. Also .05mm air gap around cleaned throttle plate.

J

**aussiebushman** · 27th October 2019, 11:33 AM

Thanks guys. All good information.

I changed the fuel pump yesterday and the engine started immediately without the previous stuttering. I'll take the car our for a drive shortly to see if the throttle problem has gone.

Re your comments Phillip - I shall do as you suggest.

The temperature sensor on the RH front of the engine which has 2 wires. should be 300 Ohms at 88C if it seems to be rich.
Has the T piece into the plenum from the large tube that goes from the rocker cover to the TPS got just a pinhole into the manifold, or has someone put just a normal T piece there?
Have you thoroughly cleaned around the Throttle body and blade ?
Is the stepper motor clean and the housing where the cone goes in clean. Do not attempt to rotate or pull apart the stepper as bye bye if you do.
Are all the vacuum hoses in one piece and not cracked or holed, particularly the one to the FPR?

And Justinc - not sure I know how to do this, but I'll try:

First thought with your comment about off idle stall is TPS adjustment. 290mV to 320mV at closed position. Also .05mm air gap around cleaned throttle plate.

**PhilipA** · 27th October 2019, 02:35 PM

Its not too crucial on a 14CUX to have the exact value at idle . Anything under .49 volts is OK. It has to be under .49 for the ECU to know when to cut the injectors on override.

What is important is to move the throttle/TPS slowly from idle upwards while looking at a voltage meter. It is important that there are no gaps or backtracking as you move the TPS. It's just like a volume control inside (carbon track) and is the most "wearable" part of the injection. You can test by back probing the connector with a needle and attaching multimeter. One terminal will show 5Volts and the other a variable voltage . AFAIR there is a third which is earth.
Regards PhilipA

**aussiebushman** · 28th October 2019, 09:57 AM

Originally Posted by PhilipA

Its not too crucial on a 14CUX to have the exact value at idle . Anything under .49 volts is OK. It has to be under .49 for the ECU to know when to cut the injectors on override.

What is important is to move the throttle/TPS slowly from idle upwards while looking at a voltage meter. It is important that there are no gaps or backtracking as you move the TPS. It's just like a volume control inside (carbon track) and is the most "wearable" part of the injection. You can test by back probing the connector with a needle and attaching multimeter. One terminal will show 5Volts and the other a variable voltage . AFAIR there is a third which is earth.
Regards PhilipA

Haven't checked it yet but is it worth changing the TPS? Doesn't look too hard to change unless you tell me otherwise

Here is a used one for $125 https://www.ebay.com.au/i/2333758307...iABEgIi-fD_BwE

OR can this one be used? https://www.ebay.com.au/i/1536334422...SABEgJKmvD_BwE

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