AFR Bad on cylinders 456

[SteveTusc]

Hi, I'm getting an AFR fault logged on cyclinders 456. I hooked up the diagnostics and I could see the adaptives were sky high. Completed a re-set and watched them climb back up while the car was at idle. Checked the throttle bodies and they are all in balance. I then noticedd that the Lambda value was sat at 0 - 0.01 volts (other bank was fine). I believe this is a lean signal hence the adaptives keep going up til AFR fault is logged? So I've chucked in a new Lambda sensor (did them both while I was there). I still have the same problem.

Reading the user guide for the software it suggests a constant Lambda value will be a duff sensor, sensor wiring or air leak to the intake/exhaust. The engine has just been rebuilt so both the bodies and exhaust have been off the car. I guess it possible they haven't sealed properly when being re-fitted but is this likely? Could it be that my throttle bodies are worn? Would this cause the Lambda to behave as it has? I know a couple of people on here had issues with RTV sealant washing out after the bodies were re-fitted, did you see the same symptoms I am? I'm wondering if it is worth putting on some of TVR Powers gaskets for the TB's. Or is this unlikely to do anything other than lighten my wallet?

Unfortunately I'm fast running out of patience with the car, and dare I say it, falling out of love with it.

Edited by SteveTusc on Wednesday 13th March 15:59

[DAVEY DEE]

Has it had its running in service & check up?Have you spoken to Dave & Chris about it Steve?

I have had the Power gaskets fitted,which do seem to work well by all accounts,but its only going to help if the prob is the air leak in the throttle bodies.

I've no idea if I needed the gaskets but as It was being rebuilt,& it seems to cure a common problem,I did it anyway.

Good luck.

[shep1001]

I would check the (lambda) plugs for a good connection first. It could be a bad earth. No voltage would as you have suggested mean a faulty or non operative sensor

Edited by shep1001 on Wednesday 13th March 17:43

[SteveTusc]

DAVEY DEE said:

Has it had its running in service & check up?Have you spoken to Dave & Chris about it Steve?

I have had the Power gaskets fitted,which do seem to work well by all accounts,but its only going to help if the prob is the air leak in the throttle bodies.

I've no idea if I needed the gaskets but as It was being rebuilt,& it seems to cure a common problem,I did it anyway.

Good luck.

Hi Dave, it's not had it's service yet. I've been caught up over the last few weeks so haven't got round to it. Just spoken to Dave though and will be booking it in with Chris tomorrow. Don't want to jump the queque and delay any of engine builds he has on.

shep1001 said:

I would check the (lambda) plugs for a good connection first. It could be a bad earth. No voltage would as you have suggested mean a faulty or non operative sensor

Edited by shep1001 on Wednesday 13th March 17:43

I'm planning on swapping the sensors over to rule out a duff one. They are both new, so assuming they are ok then I'd expect the issue to stay with the second bank. If it doesn't then at least it's an easy fix. Do you know where they are earthed? Does each sensor have it's own earth point? If it's shared then I'd get the issue on both presumably.

[shep1001]

SteveTusc said:

I'm planning on swapping the sensors over to rule out a duff one. They are both new, so assuming they are ok then I'd expect the issue to stay with the second bank. If it doesn't then at least it's an easy fix. Do you know where they are earthed? Does each sensor have it's own earth point? If it's shared then I'd get the issue on both presumably.

I don't know where they are earthed to but I am aware lambda earthing can be an issue and TVR power have a work round for it, there was on a thread not long ago

[ninetynine]

check no air leak on cat/exhaust join this caused some odd readings on mine

[SteveTusc]

Quick update.... Chris/Dave from RND called me and the car is now booked in for it's post rebuild service. If I haven't resolved the AFR fault by then they will take a look. Also Dom from Power pm'd me and kindly ran through some tests to complete that should pin point the issue

I swapped the sensors over at the connectors which swapped the 0v to Lambda 1, and Lambda 2 showed a voltage. So I now know there is no issue with the loom receiving the voltage back from the sensor. Dom suggested this almost certainly points to the sensor not working, most likely due to being of dubious quality. So I've ordered a new pair of sensors from Dom and will pop them in over the weekend. Fingers crossed this sorts the issue.

[bionicjim]

Hi Steve
That must be very frustrating given its had a rebuild
How ever I would hope it's nothing that can't be
Sorted with ease
Apart from that problem how's she driving
Have you noticed any benefit
I'm sure Chris will get it sorted
Mines on and off the rollers at the mo
So I would expect to get mine back in the next couple
Of days
Fingers crossed

[DAVEY DEE]

Any news Steve?

[SteveTusc]

DAVEY DEE said:

Any news Steve?

I've fitted the new sensors and rebalanced the throttle bodies (they were a little out). I'm still getting high adaptives on that bank. I blocked off the inlet on one of the bodies to see if it was running on just air leaks. This didn't make the lambda spike like I was expecting if there were leaks, the revs dropped so I think that means air leaks are ok? The sensors (both) are still slow to switch so I'm wondering if its a heater issue. Will check to see if there is current getting to them. The last test I did was from a cold start, so it might have just been a symptom of that the the switching was slow.

Chris has me on stand by for a service, looks like he is busy finishing off a few builds. I'll get him to take a look as well.

[shep1001]

SteveTusc said:

I've fitted the new sensors and rebalanced the throttle bodies (they were a little out). I'm still getting high adaptives on that bank. I blocked off the inlet on one of the bodies to see if it was running on just air leaks. This didn't make the lambda spike like I was expecting if there were leaks, the revs dropped so I think that means air leaks are ok? The sensors (both) are still slow to switch so I'm wondering if its a heater issue. Will check to see if there is current getting to them. The last test I did was from a cold start, so it might have just been a symptom of that the the switching was slow.

Chris has me on stand by for a service, looks like he is busy finishing off a few builds. I'll get him to take a look as well.

Lambda sensors are fused at position 36 on the fuse board. 7.5A 6th up from the bottom