Running lean?

[Beadybc]

Car is a 1997 945 b230fk with an Owens 19t running at 1.3 bar on 450cc injectors.

Recently the car has decided to start running lean when off throttle.

Normally on the AFR gauge I'd get around 15 at idle however the other day I hot started the car and it idled very low at around 500 rpm with an AFR reading of between 17 and 18, after a few little blips of the throttle it went back to where it should be.

When driving if I apply throttle - then lift off, first the reading will drop to around 10-11 for a second, then up to 20-23 for upwards of 5 seconds, then back to 15.

Under throttle the readings are where they should be from 1-100% throttle.

The fuel pumps are the original ones and are on 175k miles. There is an audible whir from them when the ignition is turned on.

The fpr and injectors have only done 2k miles from new.

My best guess is that the fuel pumps are knackered and/or too weak but I have a melon for a brain so could someone help identify the problem please?

[Laird Scooby]

Originally Posted by Beadybc

Car is a 1997 945 b230fk with an Owens 19t running at 1.3 bar on 450cc injectors.

Recently the car has decided to start running lean when off throttle.

Normally on the AFR gauge I'd get around 15 at idle however the other day I hot started the car and it idled very low at around 500 rpm with an AFR reading of between 17 and 18, after a few little blips of the throttle it went back to where it should be.

When driving if I apply throttle - then lift off, first the reading will drop to around 10-11 for a second, then up to 20-23 for upwards of 5 seconds, then back to 15.

Under throttle the readings are where they should be from 1-100% throttle.

The fuel pumps are the original ones and are on 175k miles. There is an audible whir from them when the ignition is turned on.

The fpr and injectors have only done 2k miles from new.

My best guess is that the fuel pumps are knackered and/or too weak but I have a melon for a brain so could someone help identify the problem please?

Sounds like fuel vapourisation to me. I'm guessing you're also running on E10/95 octane fuel as well? Switching to E5/98 octane (aka BP Ultimate and similar) might improve matters but have you noticed the problem is worse when it's hotter?

[Beadybc]

Originally Posted by Laird Scooby

Sounds like fuel vapourisation to me. I'm guessing you're also running on E10/95 octane fuel as well? Switching to E5/98 octane (aka BP Ultimate and similar) might improve matters but have you noticed the problem is worse when it's hotter?

It’s only had that rough start up once the other day whilst on a hot start I haven’t started it again since out of fear. The lean idle when coming off throttle has been happening for about a month. (I drive it about once a week normally)

[Laird Scooby]

Originally Posted by Beadybc

It’s only had that rough start up once the other day whilst on a hot start I haven’t started it again since out of fear. The lean idle when coming off throttle has been happening for about a month. (I drive it about once a week normally)

It should go lean on the overrun due to fuel cut-off above 1200rpm with a closed throttle. Some systems are set up so that between 15-1800rpm they introduce a little fuel (about 20-50% of normal if memory serves) so it's a more gradual reintroduction of fuel but i can't remember all the details or which systems specifically do that.