Midrange misfire

[rev-erend]

All,

Wonder if anyone can help.

I have a misfire around 1800 rpm .. but as soon as it's opened up
all is great (wharp speed).

The plugs have been revently cleaned and gapped.. but I have no idea what wound cause a mid range problem but be so great at the top end.

[dickymint]

Usual suspects Rev - But I would definately check your throttle pot reading at idle.

[Gandalf]

Thats what happend to mine last year Alan - first misfiring around 15 - 2000 then progressively got worse until I had to keep revs up above 3500 to avoid misfire and stalling but the faster you went the better it ran - culprit was found to be throttle potentiometer, replacement cured the problem straight away.

[rev-erend]

I had a strange feeling some one was going to suggest this.

What's the method for checking it's knackered.

Can I just buy another and set position by voltage or does it need to get refurbished ?

[dickymint]

Just need to use a meter and check that the increase in voltage is gradual and consistant. Probably easier off the car using crocodile clips and measuring reistance. Your just looking to see if there are any breaks in the track.

You can refurb it yourself by carefully cutting the end off with a junior hacksaw, repair any break/s in the track.
Not tried it myself though. Glue the end back on when done.

>> Edited by dickymint on Thursday 16th March 17:26

[rev-erend]

Is there an initial voltage that it is set to ..

Anyone have any idea what it's actually used for - in that I mean the airflow meter must control the amount of fuel so what use is a throttle pot ?

[dickymint]

rev-erend said:

Is there an initial voltage that it is set to .. Anyone have any idea what it's actually used for - in that I mean the airflow meter must control the amount of fuel so what use is a throttle pot ?

As lifted from the EFI manual................. www.pixeltechnology.co.uk/wedge/maintenance.html

"The varying resistance signals from the air flow
meter and throttle potentiometers are fed to the
ECU for analysis and for computation of the injector
'open' time.
The information from these two potentiometers is
computed by the ECU to give a very accurate fuel/air
ratio supply to the engine."

You'r looking fror about 325 milli volt

[GreenV8S]

rev-erend said:

the airflow meter must control the amount of fuel so what use is a throttle pot ?

The throttle pot controls the transient fuelling changes as you open and close the throttle.

[rev-erend]

dickymint said:

rev-erend said: Is there an initial voltage that it is set to .. Anyone have any idea what it's actually used for - in that I mean the airflow meter must control the amount of fuel so what use is a throttle pot ? As lifted from the EFI manual................. www.pixeltechnology.co.uk/wedge/maintenance.html "The varying resistance signals from the air flow meter and throttle potentiometers are fed to the ECU for analysis and for computation of the injector 'open' time. The information from these two potentiometers is computed by the ECU to give a very accurate fuel/air ratio supply to the engine." You'r looking fror about 325 milli volt

Great - Mark Adams has confirmed the same figures..

He also said he is coming to the wedge fest - which is excellent news

[dickymint]

rev-erend said:

dickymint said: rev-erend said: Is there an initial voltage that it is set to .. Anyone have any idea what it's actually used for - in that I mean the airflow meter must control the amount of fuel so what use is a throttle pot ? As lifted from the EFI manual................. www.pixeltechnology.co.uk/wedge/maintenance.html "The varying resistance signals from the air flow meter and throttle potentiometers are fed to the ECU for analysis and for computation of the injector 'open' time. The information from these two potentiometers is computed by the ECU to give a very accurate fuel/air ratio supply to the engine." You'r looking fror about 325 milli volt Great - Mark Adams has confirmed the same figures.. He also said he is coming to the wedge fest - which is excellent news

The EFI manual has it slightly wrong (as its for the SD1) it says first set the butterfly flap at 0.000" in fact you need a gap of about 0.005" with a feeler gauge.

Thats great news about 'Mark Adams'. Techie Talk maybe?

[rev-erend]

Ohh yes..