hotwire on a 3.5

ran out of gas this morning (deliberately, wanted to assess tank range to see what the "economy" was doing. I notice that the petrol isn't running smoothly at low-medium throttle. Flooring it and letting the revs go up over 3500 gets a reasonable degree of poke, considering the weight of a disco, but it's slightly rough at midrange and seems hesitant when asked to accelerate.

This is not new, in fact - when I first had it, it wan't that keen to accelerate, and if you feathered the throttle rather than flooring it, accelerated as well or better, from around 1500-2000 revs level - felt a bit like not enough fuel, but at higher revs it still pulled with larger throttle openings, so I don't suspect a restriction in the actual fuel supply.

any ideas?

Reply to
Austin Shackles
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Educated guess from your description of the symptoms and my experiences

- Throttle Position Sensor.

Reply to
EMB

On or around Mon, 20 Sep 2004 21:29:17 +1200, EMB enlightened us thusly:

...

broken? maladjusted? Hmmm. I think I have a spare one, p'raps I'll try fitting it.

Reply to
Austin Shackles

On or around Mon, 20 Sep 2004 21:29:17 +1200, EMB enlightened us thusly:

TPS passes ohm and volt checks, as does the AFM. doesn't mean that they're not faulty of course, could be an intermittent.

spare TPS isn't buggrit, different part number, different plug. Bet it's the same unit, too, buggrem. 's prolly off a range rover, or a different year.

Reply to
Austin Shackles

Sounds vaguely familiar - my Disco used to do this. Fixing the split on the vacuum pipe made lots of difference - replacing it entirely completed the job (Warren found it split at the dizzy end).

So perhaps the advance isn't advancing for whatever reason.

Reply to
Tim Hobbs

On or around Mon, 20 Sep 2004 19:48:19 +0100, Tim Hobbs enlightened us thusly:

I think I looked at all the vacuum pipes before. Might stand a second look.

forgot to say that this is a petrol-specific fault, it's running fine on gas.

Reply to
Austin Shackles

I gathered it was petrol specific from your original description, but oddly enough the gas was much less affected than the petrol when I had the problem. Am I right in thinking gas wants less advance at low rpm and more at high rpm?

Reply to
Tim Hobbs

A hairline crack in the carbon track that drops signal for a minute bit of it's operation will do this and it's bloody hard to see unless you use an old undamped analogue meter to check it - digital ones tend to respond too slowly to show the fault. Did you check the throttle closed contacts too?

Reply to
EMB

On or around Tue, 21 Sep 2004 08:19:45 +1200, EMB enlightened us thusly:

ain't any so far as I know. not according to the book, anyway. The ECU is supposed to learn the throttle positions all by itself, or somesuch.

throttle pot test is in 2 halves - resistance check end-to-end (which would show up a broken track, I guess) and voltage check from the output wire -

0.notmuch - 0.5V at throttle shut up to about 4.5V throttle open, so say the book, and smooth operation in between. which is what I got, along with the correct voltage output from the AFM.

mind, I was checking in the engine bay. I guess there could be iffy connections twixt there and the ECU, but it's a lot more hassle checking at that end :-)

Reply to
Austin Shackles

On or around Mon, 20 Sep 2004 20:11:26 +0100, Tim Hobbs enlightened us thusly:

other way about. more initial advance, and not so much less as no extra dynamic at high speeds, IIRC. so rather than say 6 - 30 BTDC say, it wants more like 12-30. those are just example figures, not known to be accurate on any real engine.

Reply to
Austin Shackles

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