replacing lambda sensors

[doddze]

Running a 91 2.9 granada engine in my TVR. Decatted.

The engine is running rich ie 12:1 at 2500 rpm increasing to 9:1 at full throttle and I am about 28bhp down on where I should be ie 140bhp rather than 168bhp and torque is down as well. On the whole the car runs ok but a bit of hesitation... pops and bangs on overrun and you can smell the unburnt fuel in the exhaust..

As it is rich I wondered if the Lambda sensors had failed in the lean setting. SO I disconnected them both and the engine fired up and ran at tickover and when I revved it exactly as before...

Should mention the car has had full service recently and exhaiust/manifolds are good, and had new map sensor which helped a bit....

So a few of questions....

as the engine running didn't change am I safe to assume they are no longer working (they are probably the original ones from 1991 although only has done 24k from new)?

Assuming this is the case when I replace them should I disconnect the ECU first to reset it or can I just stick them in and turn the key?


and finally does this seem afair assesment of the problem given the facts?


Thanks for your help

[stevieturbo]

Lambda sensors only offer closed loop control under idle/cruise, and generally low throttle openings.

At full throttle, they do nothing that could effect fuelling, so they are not your problem.

[doddze]

mmmmmm puzzling

I have been out in the car without the sensors connected and it runs fine (well as normal)at idle and mid range etc... which implies that the sensors aren't working. Also means that the system is working open loop with no way of measuring the air content as the car doesn't have air flow meters. There is a slight hesitation at 2500rpm when youopen the throttle but the ride is smooth and it returns to idle at junctions etc no problem..

Could it have gone into a default map when the lambda sensors failed and the cats previously failed (now removed)?

[stevieturbo]

It always runs default map, with lambda sensors allowing small alterations during closed loop.

It always relies on the base map aside from that.

[GreenV8S]

On the 14CUX it sems to fall back into a different map when it detects a serious sensor fault, does the Ford system do something similar?

[garage19]

Paul,

I always thought the cologne v6's ran airflow meters?

I'm sure they did in the Ford cars.

Have you got old mechanical injection with a metering head or proper EFI?

If there is no airflow meter then the ECU will be using either the throttle position sensor or a map sensor as load indicator.

As said before the lambda sensors will only have an effect on fueling at idle, light loads and cruising.

More likely to effect your MPG than your max BHP.

9:1 is rich for the top end of a N/A car. Ideally you nead to lean the AFR by about three points.

I would start by checking the fuel pressure is correct.
If someone has turned up the fuel pressure this may be the reason for the over fueling.

To be honest with you, the best way to fix it is to go to LPS, speak to Neil and get him to order you an Emerald K2 fully mappable ECU. They have been working closely with Dave Walker at Emerald lately.
It should cost you £380+VAT. LPS will be able to map
it for you on their rolling road and you will end up with spot on optimum fueling and ignition timing all over the rev/load range.

The best bit is that as it is fully mappable it will be totally compatable with any further mods you may wish to make wether it be a different inlet manifold or a full on turbo conversion.

Doug.

[cabs]

It is just a thought, but it may be the throttle pot as the ecu should shut off the injectors on overrun. This could also account for the hesitation when you accelerate.