Thread: Possible TPS fault?

I am running a 3.9 hotwire engine in my RRC, the coolant through the throttle body has never been hooked up since I fitted it. No ill effects that I am aware of.

My car has always been a bit temperamental with this, especially on hot startup after a couple of minutes eg in a petrol station.

Look mine did it bog standard, After I fitted a Unichip, after I replaced the Manifold and ALL the sensors ( TPS, water temp )except the fuel pressure regulator and MAF, and added 02 sensors

Now I have had a fuel pressure regulator on my bench for about 6 months , as it is a pain to fit with a Thor manifold.

I think it is either the regulator or just may be a characteristic of the ECU in that it is a bit slow to operate the IAC, when the revs drop on load being applied.
I think I reduced mine a bit a while ago by increasing the BASE idle a bit to say 600RPM. The base idle is adjusted by the allen screw above the throttle body while blocking off the inlet end of the IAC and plugging the hole in the manifold.
Regards Philip A

My Rangie still does it even with a wolf ecu running the show and later bosch injectors.(hot starting fails at the servo etc, not stalling into drive ect)

The only way i haver found to prevent it is too run BS rich fuelling at crank.

I have put it down too the rough casting of the intake manifold tracts soaking up alot of fuel when cranking hot.

Im not sure how much smoother the Thors are internally Phillip but i's imagine rover insistance on pumping coolant through the manifold would be the same?

Im not sure how much smoother the Thors are internally Phillip but i's imagine rover insistance on pumping coolant through the manifold would be the same?

If you mean does the coolant go through the Thor manifold before to the radiator the answer is yes.
I note that someone is selling an insulator in UK for both the Thor and normal manifold, Good except that the Thor would not fit under the RRC bonnet with the insulator inserted.

I also have a feeling that the stalling may be caused by fuel vaporisation in the fuel rail . Certainly with the Thor it must get hot under there and maybe that is one reason they went to regulator in tank and no return line and higher pressure in the D2.
BTW the stalling can be eliminated ( in mine anyway) by waiting until the idle stabilises before putting in D or adding a little accelerator when changing into D. BUT you risk "Pump rage" sitting there for 10 or 20 seconds.
Regards Philip A

Interesting thoughts Phillip. Mine never stalls but cranks for maybe 15/20 seconds too start. Normally its less than 3 secs and she fires up and idles.

My idle control and idle speed and temp compensated and I also run a remote fuel pressure reg that will maintain 45psi in the rail for a good 20mins after shutdown so I dont think the fuel vaporisation is an issue in my case?


Maybe wrap your fuel rail in some header wrap and see if that helps?

Or it could just be that once at the Servo Rangie's feel they have returned too there ancestral home and dont want too leave.....

The function of the Fuel temp sensor in 13/14 CUX etc ECU is to provide for easy hot starting by enrichening the mix in response to the fuel sitting in the fuel rail approaching boiling point and vapourising or becoming less dense. Enrichening adds cooler fuel and flushes bubbling fuel through injectors. That said it is rare for this sensor (unlike coolant temp sensor) to take a dive.

PhilipA forgive my ignorance over Thor/Motronic ECU's but are you in effect saying the cause of your hot start problem is they did not put fuel temp sensors in Thor/Motronic fuel rails (and pressure regulated at the tank not at the rail) and hense this fuel temp input is not available to your piggybacked 14CUX ECU???

Could anyone explain the sequence of events when you engage drive, i.e. what components do what and in what order. I am new to the Range Rover and although I have had 3 Land Rovers in the past I have never had a V8, so it is a learning curve for me.

PhilipA forgive my ignorance over Thor/Motronic ECU's but are you in effect saying the cause of your hot start problem is they did not put fuel temp sensors in Thor/Motronic fuel rails (and pressure regulated at the tank not at the rail) and hense this fuel temp input is not available to your piggybacked 14CUX ECU???

Seeing I have a 14CUX rail, the problem does not arise. I have a fuel temp sensor but the fuel temp sensor in a 14CUX does not have a profound effect on the mixture AFAIK . From my reading its main function is to trim to about 10% , to account for fuel temperature variation as a correction for the MAF air mass.ie hot fuel will richened slightly to maintain the desired mixture due to its lower density. I don't think its prime purpose is hot starting, however maybe so.
Just to be exact the problem is not hot starting anyway. Mine starts perfectly, then revs as the IAC is opened right up on start,then stages down to idle. It is at this stage that I have to be careful to wait until idle is fully stabilised before switching to drive/reverse, and I understnd that this is a common problem.

My temp sensor is right at the front of the rail so maybe it is cooler than the rest of the rail , but this really is irrelevant as the problem has existed in mine with the standard manifold, and once upon a time I did check the resistance which was fine. ( I note that the D1 later rails shifted the sensor to half way along the left side of the rail so maybe the position was not ideal)

Thor runs the regulator in the tank, so fuel is not recirculated through the engine bay so does not heat up.( and I think this is a main reason for the temp sensor as an ongoing mixture trim for 14CUX as the fuel always heats up as the fuel is returned to the input sump for the fuel pump) In addition the Thor runs a higher fuel pressure than 14CUX 3 bar vs 2.5? and this would tend to prevent vaporisation.
All I said was that maybe this was one reason that BMW changed to the higher pressure injectors and in tank regulator , seeing the Thor manifold also completely envelops the rail and injectors and would tend to get much hotter in there.
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However , in my case the problem has existed from day one of ownership ten years ago, through heaps of combinations of manifolds, and a new set of sensors and a different manifold and different injectors.

So I think the posters problem is not his TPS, but may be just a characteristic of 14CUX, or there is a possiblity the Fuel pressure regulator is leaking pressure( which I have not yet tested).

Mine now is quite a bit better , and really only stalls in reverse only, and I think this is maybe because reverse is a lower gear than first, but I must admit that I haven't really checked the ratios.
Regards Philip A