hotwire on a 3.5

A

Austin Shackles

Guest

• Sep 20, 2004

• #1

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?

 

E

EMB

Guest

• Sep 20, 2004

• #2

Austin Shackles wrote:
>
> any ideas?

Educated guess from your description of the symptoms and my experiences
- Throttle Position Sensor.


--
EMB
change two to the number to reply

 

A

Austin Shackles

Guest

• Sep 20, 2004

• #3

On or around Mon, 20 Sep 2004 21:29:17 +1200, EMB <[email protected]>
enlightened us thusly:

>Austin Shackles wrote:
>>
>> any ideas?
>
>Educated guess from your description of the symptoms and my experiences
>- Throttle Position Sensor.

....

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

 

A

Austin Shackles

Guest

• Sep 20, 2004

• #4

On or around Mon, 20 Sep 2004 21:29:17 +1200, EMB <[email protected]>
enlightened us thusly:

>Austin Shackles wrote:
>>
>> any ideas?
>
>Educated guess from your description of the symptoms and my experiences
>- Throttle Position Sensor.

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.

 

T

Tim Hobbs

Guest

• Sep 20, 2004

• #5

On Mon, 20 Sep 2004 10:04:10 +0100, Austin Shackles
<[email protected]> wrote:

>
>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?

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.
--

Tim Hobbs

'58 Series 2 88" aka "Stig"
'77 101FC Ambulance aka "Burrt"
'03 Volvo V70

My Landies? http://www.seriesii.co.uk
Barcoding? http://www.bartec-systems.com
Tony Luckwill web archive at http://www.luckwill.com

 

A

Austin Shackles

Guest

• Sep 20, 2004

• #6

On or around Mon, 20 Sep 2004 19:48:19 +0100, Tim Hobbs
<[email protected]> enlightened us thusly:

>On Mon, 20 Sep 2004 10:04:10 +0100, Austin Shackles
><[email protected]> wrote:
>
>>
>>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?
>
>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.

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.

 

T

Tim Hobbs

Guest

• Sep 20, 2004

• #7

>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.

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?

--

Tim Hobbs

'58 Series 2 88" aka "Stig"
'77 101FC Ambulance aka "Burrt"
'03 Volvo V70

My Landies? http://www.seriesii.co.uk
Barcoding? http://www.bartec-systems.com
Tony Luckwill web archive at http://www.luckwill.com

 

E

EMB

Guest

• Sep 20, 2004

• #8

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

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?


--
EMB
change two to the number to reply

 

A

Austin Shackles

Guest

• Sep 20, 2004

• #9

On or around Tue, 21 Sep 2004 08:19:45 +1200, EMB <[email protected]>
enlightened us thusly:

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

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

 

A

Austin Shackles

Guest

• Sep 20, 2004

• #10

On or around Mon, 20 Sep 2004 20:11:26 +0100, Tim Hobbs
<[email protected]> 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.
>
>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?

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.