Disco 1 V8 - Throttle Potentiometer fault???

Just when I thought I was winning!!!

1st start up after major surgery to the top of the engine, Timed correctly, good fuel, good spark etc.

It coughed & spluttered then started.......ran for a couple of seconds then died. Tried again, did exactly the same. Put the diagnostic on it and error
17 Throttle sensor Sensor needs adjustment, is faulty or has wiring fault. This can cause low speed misfires 18 Throttle sensor output high when air flow low. Large air leak or faulty throttle sensor or A/F meter.

Seems like I got a faulty one? I tested it and closed it measures 0.58V closed but move it ever so slightly it goes to 4.99V. Measured it when the engine briefly runs and it dances all over the range with no throttle then goes to 4.99V and the engine dies.

Take it I'm correct in my diagnosis and its FUBARED????

Jasonmichael said:

Take it I'm correct in my diagnosis and its FUBARED????

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Although I have no experience with the V8 engine, as an electronics engineer I can say that generally there are two sorts of problems which usually afflict potentiometers are either a dirty or scratched track which can result in "noisy" operation, causing the voltages or the signal to jump about erratically or a break in the track which can give the symptoms of the voltage or output signal remaining low until the break is crossed by the wiper and then it jumps to its full level with no control between low and high output.
I would say that you're on the right track with your diagnosis.

HELLS TEETH!!!!! Just seen how much a new one is.....that is if you can get hold of one!!!!

Well, spent hours looking for a reasonably priced one, like trying to find a golden egg

There's no reason why you couldn't use a good second user one.
Try a search for "Gentlemen of Salvage". They appear to have a reasonable reputation, as far as second hand parts sellers go.

I've done every scrapyard, ebay, gumtree etc. every well known 4x4 spares eg, Paddocks, Rimmer Bros etc. Because they are now obsolete they're nowhere to be found!

From some research it seems that the p/n is ERR4278 and for that p/n it appears as interchange this one https://www.ebay.co.uk/itm/Throttle-Position-Sensor-Fits-Land-Rover-Discovery-Range-Rover-4-6-4-0-RTT6LR/173328660522?_trkparms=aid=555018&algo=PL.SIM&ao=1&asc=52945&meid=d923a82ea8f74ea09ac0669dcfc5a34b&pid=100005&rk=1&rkt=12&sd=113007774838&itm=173328660522&_trksid=p2047675.c100005.m1851 , but make sure yourself, even if the connector doesnt fit get a connector from a RR with the same engine, or from a D2 cos i have a strong feeling that the pot is the same just maybe the plug is different

other p/ns http://www.kakapart.com/oem/partscrossinterchange/land-rover-err4278.html

or this https://www.johncraddockltd.co.uk/l...ntiometer-throttle-multi-point-injection.html

ERR2263 is the correct part for the disco 3.9 300 series and is totally different from the iinfo posted above, also the 3.9 TPS can’t be adjusted unlike the one for the 3.5 ‘flapper’ EFI engine (RR).

I was just trying to help, as i said it was the result of some research which i made not long ago for a friend(that's definitely not from my own experience), my bad that i wasnt clear enough, the whole story is here: https://forums.lr4x4.com/topic/103142-39-hotwire-plenum-tps-replacement/ while ... too bad that part sellers dont know what they are doing cos ERR2263 appears for up to '95 modells while then OP has '97 in the profile...

ERR2263 is completely obsolete so whatever's i do seems like it's gonna have to be 'judge's is i want to ever get it running again!

BODGED!!!! Not judged. Predictive txt

Jasonmichael said:

ERR2263 is completely obsolete so whatever's i do seems like it's gonna have to be 'judge's is i want to ever get it running again!

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It surprises me that the item isn’t available label now, anywhere. I understand from info years a go that the RR 3.5 item can be used as that is adjustable due to the elongated fixing holes, I’m miles away from my RR parts catalog so don’t have the part number on that one at the moment, also the the correct method to set the adjustment in the the RR workshop manual, for the the 3.9 it’s just undo the two screws an replace.

I believe the 3.9 ecu is a bit more advanced therefore it makes its own judgment on the settings hence plug n play with a replacement.

sierrafery said:

I was just trying to help, as i said it was the result of some research which i made not long ago for a friend(that's definitely not from my own experience), my bad that i wasnt clear enough, the whole story is here: https://forums.lr4x4.com/topic/103142-39-hotwire-plenum-tps-replacement/ while ... too bad that part sellers dont know what they are doing cos ERR2263 appears for up to '95 modells while then OP has '97 in the profile...

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Just look in a genuine D1 parts catalogue and don’t bother on sellers info or the online version as their descriptions are are not always for the uk market.
Both my RR and D1 were purchased before the on-line stuff and any parts that were required by me were from a main LR dealer, with a ‘trade discount’, hence owning parts catalogues.

Yeah, I'm surprised too (one way of getting rid of old Gas guzzlers I suppose)

On all the sites I've looked into (spent 3 hours) its either not stocked or as I say obsolete. there's no 'its been superseded by ***** number' and yes the Disco one you cannot adjust it, it just screws into the throttle body. Mine is well & truly goosed, at idle it sits at 0-5v but as soon as there's any hint of vibration from the engine it goes 4.99v. I took it off and had a mess about with it still connected to the plug with my diagnostic plugged in and it won't go through the range. its either all or nothing so even me with no real electrics knowledge think its Donald Ducked.

Ok also check the idle control valve at rear of the Plenum as that can upset starting I believe, perhaps running as well.

discool said:

Ok also check the idle control valve at rear of the Plenum as that can upset starting I believe, perhaps running as well.

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Oh believe me I have I've checked & triple checked everything. But it does as it says in the diagnostic book of the 14CUX fault finding. It starts and runs normally (Really smooth too should I say after a whole new top end) and I thought 'YEAY I'VE CRACKED IT!!!" then it suddenly died. Fire it up again, runs smoothly then dies. It says in the book that it will run for approx a minute I think it was before the signal from the faulty POT goes to the ECU then the ECU will spit its dummy out and kill the engine, thus the code 17 & 18.

Try cleaning the ICV valve with carb cleaner and a light tooth brush. Reinstall then give'r ago.
If it works, don't forget to reset your adaptive values for the engine's ECU.

In my despair, I started to look at potentiometers online, ie. electrical retailers. Would it be beyond the realms of possibility to adapt one of them some how, or am I talking rubbish???

Did you read that link i posted with the conversion to the cheap sensor? i know it works cos it was made on a friend's D1 by a very skilled mechanic, it's beyond my knowledge how to do it but i know it works and he was inspired by that link.

Sorry Sierrafery, I've looked at that many websites Yep, it looks doable, with a bit of bodging. I'm gonna buy one just to try it, I won't loose anything I suppose. Just have to figure out its size compared to the old one, make sommat to replicate the little probe on the old one & the female plug. As long as its a 5v one.