Low rev misfire

Low rev misfire

Author
Discussion

Thom

1,689 posts

189 months

Monday 20th May
quotequote all
If 0.7mm is the plug gap originally specified for an AJP running on the standard ignition set up then I would not try another value for the plug gap, regardless of the type of plug used.
If your engine has a slightly higher compression ratio than standard then it might even benefit from a gap tighter than 0.7mm.
A good thing about setting the gap down is that it's free smile

Jhonno

Original Poster:

3,515 posts

83 months

Monday 20th May
quotequote all
Thom said:
If 0.7mm is the plug gap originally specified for an AJP running on the standard ignition set up then I would not try another value for the plug gap, regardless of the type of plug used.
If your engine has a slightly higher compression ratio than standard then it might even benefit from a gap tighter than 0.7mm.
A good thing about setting the gap down is that it's free smile
Yep, agree. It says they come pre-gapped, and not to change it, but could be worth a gentle go. Or just wait for the NGK's to arrive.

FarmyardPants

3,470 posts

160 months

Monday 20th May
quotequote all
Is it possible to revive a borderline o2 sensor by blowtorching it, or is this an urban myth?

Jhonno

Original Poster:

3,515 posts

83 months

Monday 20th May
quotequote all
FarmyardPants said:
Is it possible to revive a borderline o2 sensor by blowtorching it, or is this an urban myth?
I have read that too.. I don't know how true it is either!

Jhonno

Original Poster:

3,515 posts

83 months

Monday 20th May
quotequote all
Lambda from the bank that keeps dropping out..

https://photos.app.goo.gl/DudTUHnp5bkrG74h8

No idea what it should look like.
Advertisement

Thom

1,689 posts

189 months

Tuesday 21st May
quotequote all
The symptoms you initially described with the car missing below 3k rpm and fouling the plugs suggested an excessively rich running condition which would have had the lambda sensor(s) look positively black, at least for real world road driving where going full load all the time does not happen.
If the engine is now running better with the replaced plugs and after setting the throttles again then the lambda sensor(s) may not be sooted anymore, however this picture suggest an excessively lean running condition.
How does the other lambda sensor look like and can you swap them to see how or if the adaptives and lambda voltages change?

Jhonno

Original Poster:

3,515 posts

83 months

Tuesday 21st May
quotequote all
Thom said:
The symptoms you initially described with the car missing below 3k rpm and fouling the plugs suggested an excessively rich running condition which would have had the lambda sensor(s) look positively black, at least for real world road driving where going full load all the time does not happen.
If the engine is now running better with the replaced plugs and after setting the throttles again then the lambda sensor(s) may not be sooted anymore, however this picture suggest an excessively lean running condition.
How does the other lambda sensor look like and can you swap them to see how or if the adaptives and lambda voltages change?
So I went back to the car and it was refusing to idle again, well it will idle at 1300rpm+.. The missing is better, but still there. I noticed that the Lambda 1 value kept dropping to 0.01-0.04 (remaining stationary, whilst Lambda 2 flicked) and it would miss when you tried to accelerate. When it "came to life" again it would pull cleanly from any revs.

I was thinking the lambda condition was showing lean, but wasn't sure, I had a couple laying about which looked darker/more sooty. The plugs from that bank looked OK.

Edited by Jhonno on Tuesday 21st May 09:12


Edited by Jhonno on Tuesday 21st May 09:52

Jhonno

Original Poster:

3,515 posts

83 months

Jhonno

Original Poster:

3,515 posts

83 months

Tuesday 21st May
quotequote all
Another..

Having to hold about 1.3k due to lack of idle..

https://photos.app.goo.gl/nhTJSVHrooqYTdqY7

spitfire4v8

2,886 posts

123 months

Wednesday 22nd May
quotequote all
In a galaxy far far away about 10 days ago ...


spitfire4v8 said:
We could do with seeing a trace of the live graphing screen showing the lambdas spiking




The adaptives trim is based on the lambda feedback .. some lambda outputs look ok on the main diags screen, but when you view it in the realtime logging they don't spike sharply like they should do, the traces might be gentle meanderings which is not correct.

Jhonno

Original Poster:

3,515 posts

83 months

Wednesday 22nd May
quotequote all
spitfire4v8 said:
In a galaxy far far away about 10 days ago ...


spitfire4v8 said:
We could do with seeing a trace of the live graphing screen showing the lambdas spiking




The adaptives trim is based on the lambda feedback .. some lambda outputs look ok on the main diags screen, but when you view it in the realtime logging they don't spike sharply like they should do, the traces might be gentle meanderings which is not correct.
laugh

I was just checking that is what you meant.. Still learning some of the more in-depth bits. Never seen a lambda trace before.

Jhonno

Original Poster:

3,515 posts

83 months

Thursday 23rd May
quotequote all
For reference..

Lambda trace with 1 new lambda and one heated with a blow torch and reused.

https://photos.app.goo.gl/rKi3M9AXxd3vbxwf8

spitfire4v8

2,886 posts

123 months

Thursday 23rd May
quotequote all
That looks better, but with the lambda traces both being the same colour its impossible to tell the two apart. Does the tvr diags not work for you?

Jhonno

Original Poster:

3,515 posts

83 months

Thursday 23rd May
quotequote all
spitfire4v8 said:
That looks better, but with the lambda traces both being the same colour its impossible to tell the two apart. Does the tvr diags not work for you?
They are different shades of green..? The issue is they follow each other quite a bit and so are over laid.

I have the rewritten version of the software on my laptop..

spitfire4v8

2,886 posts

123 months

Thursday 23rd May
quotequote all
Ah I see the 2 colours now , still its hard to see the less vibrant colour but it *looks* to be ok.

Jhonno

Original Poster:

3,515 posts

83 months

Thursday 23rd May
quotequote all
Here is an interesting one..

NGK's fitted.

Started straight up and settled into a nice 1k idle.

Adaptives about +3

Comparison of iridium vs. copper plug. I wonder if the spark position/shrouding is why some Cerbs don't like Iridiums.. Mine used to, but now maybe it doesn't?

https://photos.app.goo.gl/HcCiqQSZ3Ugaa2dU7

FarmyardPants

3,470 posts

160 months

Thursday 23rd May
quotequote all
So how does it drive now?

Jhonno

Original Poster:

3,515 posts

83 months

Thursday 23rd May
quotequote all
FarmyardPants said:
So how does it drive now?
So much better.. It still has a miss when pulling away, and brief one at 3k, but it is pretty transformed. Pulls cleanly in fifth, much harder than before. I haven't even reset the adaptives yet. Forgot to plug my phone in to do it.

Thom

1,689 posts

189 months

Thursday 23rd May
quotequote all
Would be interesting to gap the Iridium plugs down to 0.7mm. I would be really surprised if the nature of the plugs caused the issue rather than the gap.

In any case, congrats for the progress!

Jhonno

Original Poster:

3,515 posts

83 months

Thursday 23rd May
quotequote all
Thom said:
Would be interesting to gap the Iridium plugs down to 0.7mm. I would be really surprised if the nature of the plugs caused the issue rather than the gap.

In any case, congrats for the progress!
I still have the plugs, I may experiment when it is run in..

So looks like it was a combination of unbalanced cylinders, lambda, plug lead and plugs, and setup to get it to 90%..