I've fitted an AFR gauge to my Escort Cosworth.
In idle it constantly oscillates between the values 14.7 and 15.6. This is without me touching the throttle and at (completely) steady rpm.

The same happens in every other driving situation with slightly different values except at full throttle. At full throttle the gauge is steady.

I've checked the gauge and sensor, petrol pressure, original lambda sensor, mass air flow sensor. I've even replaced all the hoses, changed the fuel nozzles and checked everything for leaks.

Does anybody know what the problem could be?

Thanks

 

How long does it take from 14.7 to 15.6? 1 second? 2 seconds? 5 seconds?
And how long back from 15.6 to 14.7?

 

What gauge is it?

 

maybe tps needs cleaned ?


not many cars idle bang on 14.7 mind ....it should just be there about


what afr you seeing at wot ?


tommy

 

sounds like closed loop operation to me. the fuelling will self calibrate at idle and cruise. Nothing to worry about at all.

if its a P8 you could try and reset the adaption to see if it helps stabilisation.

 

It is just about 2-3 seconds between the values at idle and about 1 second between at cruise speed.

It is an AEM afr gauge.

I forgot to say that it is the late escort t25 with the EEC-IV so I don't know whether it has tps and closed loop operation?

I'm sorry but what does WOT mean?

Thanks for all the help so far.

 

mine does this (c20let engine) 14.6-15.4 etc its spit seconds on mine...its never going to stick on 14.5 as surely the idle speed is always a bit off liek it jumps 10rpm etc.

WOT - wide open throttle, it should stay bang the numbers then.

 

mines a bag of spanners for this, it's just the nature of efi saldy, you could take some timing out or richen the mixture a bit, that stops it oscillating, but uses more fuel.
an alternative is to raise the base revs.

 

T25 escorts are closed loop,

 

Its hard to tell from your description here but if its wavering too much then it sounds like your short and long term fuel corrections maybe maxed out.

Check the dump valve diaghragm is ok. If its failed we sell uprated ones for it.

 

My turbo has been changed by the last owner of the car to a T35 turbo from "the old escort". So there is no dump valve on my car.

Could something else cause that problem?

 

Does the T25 cosworth have a TPS? At WOT it is at approx 12.5 at 6000 rpm.

 

 

Since you post those "shocked" smileys I guess that is a big NO NO to change the turbo or what?

 

Different turbo means a different map will be required, although on an mass airflow based setup rather than a speed density the ecu will cope better (still not right, just better)

 

I'd really love to give the car a different map but no one knows where I can get a custom map for the escort cosworth with EEC-IV