Running very lean after cam change
Discussion
I got my 450 back with its new cam shaft, and I thought everything was running nicely.
That is until I took it to Surrey Rolling Road, and that revealed that it's running horrendously lean - over 16 at some points.
I've plugged Rovergauge in, and that shows that both long-term fuel trims are at or near 100% rich.
To my mind this rules out a lambda sensor fault. Partly because I'd expect only one of the fuel trims to be wild, but also if a lambda were saying "full rich" you'd expect the ECU to put the trims to fully lean, and if a lambda were saying "full lean" you'd expect the trims to go fully rich - but in that case you'd also expect to see a rich mixture at the tail-pipes, which isn't what we see.
For similar reasons I doubt it's a MAF sensor fault either.
So I reckon this possibly supports the theory of a fuel supply issue - pressure? filter? pump? And the 100% rich trims show that the ECU is aware of the excessively lean mixture and is doing everything it can to correct, but it can't do enough so we still see a lean mixture at the tail-pipes.
Can you think of anything else? Is my logic correct?
I also looked for fault codes, and there's nothing at all. When dynoed a few weeks before Christmas, the mixture was spot-on correct.
That is until I took it to Surrey Rolling Road, and that revealed that it's running horrendously lean - over 16 at some points.
I've plugged Rovergauge in, and that shows that both long-term fuel trims are at or near 100% rich.
To my mind this rules out a lambda sensor fault. Partly because I'd expect only one of the fuel trims to be wild, but also if a lambda were saying "full rich" you'd expect the ECU to put the trims to fully lean, and if a lambda were saying "full lean" you'd expect the trims to go fully rich - but in that case you'd also expect to see a rich mixture at the tail-pipes, which isn't what we see.
For similar reasons I doubt it's a MAF sensor fault either.
So I reckon this possibly supports the theory of a fuel supply issue - pressure? filter? pump? And the 100% rich trims show that the ECU is aware of the excessively lean mixture and is doing everything it can to correct, but it can't do enough so we still see a lean mixture at the tail-pipes.
Can you think of anything else? Is my logic correct?
I also looked for fault codes, and there's nothing at all. When dynoed a few weeks before Christmas, the mixture was spot-on correct.
Classic Chim said:
Air Induction leak.
If your readings were good before the cam change then it suggests a badly fitting or re used valley gasket that’s not sealing very well.
Yes, that does seem likely. The valley gasket was replaced.If your readings were good before the cam change then it suggests a badly fitting or re used valley gasket that’s not sealing very well.
I’ve done further experimentation today, and the problem is quite erratic and intermittent. I’ve seen the trims stuck at 100% for long periods of driving, then they’ll start dropping for no apparent reason. I had them stay at sensible values (around +20%) for a 20 minute period, only to climb up to 100% again. And I’ve even seen just one bank reduce to about 50% for a minute or two, then climb back to 100%.
I’m almost wondering if there’s an induction leak that opens and closes with temperature. The trims do seem to go on the move whenever I stop for a minute or two. (Or is it just because I’m able to watch more closely?)
But the fact that I’ve seen sensible trims for a while today makes me wonder if I was just lucky during the session at Surrey Rolling Road a few weeks before Christmas - did it coincide with the problem temporarily disappearing for long enough to give an apparently good reading?
I’ve emailed the well-respected specialist just off the M40 to see what they say.
It would have to be the mother of all air leaks to give you any significant change in afr on full throttle, ie plenum elbow half hanging off or something.
Also if you are looking at the long term trims (as per your pic) then they are only updated at hot idle. Only the short term trims change on the fly ..
If it really was fine before the cam change then don't touch anything and take it back to whoever did the work for their opinion. It might be co-incidental or it might be something they've done (though can't think what ..) but if you've been playing around with it without letting them take a look at it then you might be giving them the perfect excuse to wash their hands of it.
Also if you are looking at the long term trims (as per your pic) then they are only updated at hot idle. Only the short term trims change on the fly ..
If it really was fine before the cam change then don't touch anything and take it back to whoever did the work for their opinion. It might be co-incidental or it might be something they've done (though can't think what ..) but if you've been playing around with it without letting them take a look at it then you might be giving them the perfect excuse to wash their hands of it.
spitfire4v8 said:
It would have to be the mother of all air leaks to give you any significant change in afr on full throttle, ie plenum elbow half hanging off or something.
So do you think a fuel supply issue is a possibility?Edited to add: I notice that “low fuel pressure” is a fault code, and mine hasn’t raised any codes. So that seems to rule it out.
spitfire4v8 said:
Also if you are looking at the long term trims (as per your pic) then they are only updated at hot idle. Only the short term trims change on the fly ..
Aha! Now I understand why nothing seemed to change while driving, but the trims would often go on the march when I stopped.spitfire4v8 said:
If it really was fine before the cam change then don't touch anything and take it back to whoever did the work for their opinion. It might be co-incidental or it might be something they've done (though can't think what ..) but if you've been playing around with it without letting them take a look at it then you might be giving them the perfect excuse to wash their hands of it.
I agree. I haven’t (and won’t) do anything. All I’ve done is wiggle the stepper motor to confirm it’s secure and I pushed the vacuum line a few millimetres further onto its nipple at the distributor end.As others have said, massive air leak.
I had similar issue as I had bent the valley gasket when refitting the plenum.
Get hold of a smoke tester and use it inject smoke into the plenum intake hose between plenum and AFM.
Machine like this is brilliant https://m.youtube.com/watch?v=URRId6fTrGo
I had similar issue as I had bent the valley gasket when refitting the plenum.
Get hold of a smoke tester and use it inject smoke into the plenum intake hose between plenum and AFM.
Machine like this is brilliant https://m.youtube.com/watch?v=URRId6fTrGo
Here is the dyno printout from Saturday, with a comparison to the previous numbers. Blue is a few weeks before Christmas (before the cam change); red is the latest from Saturday.
As you can see, the AFR is well north of where it should be...
As you can see, the AFR is well north of where it should be...
Edited by Dr Mike Oxgreen on Tuesday 22 February 17:55
Dr Mike Oxgreen said:
As you can see, the AFR is well north of where it should be...
hmm your graphs don't make a great deal of sense right now ..you've basically gained power everywhere which is great, but .. with mixtures as weak as they are reported now you should have the power nowhere near where it is. To illustrate, my old V8S had a regulator issue, it had low fuel pressure with mixtures very weak like you have. It made around 130hp. When corrected it made 198hp .. my graph comparison is attached .. dotted lines weak mixture, solid lines with regulator clamped to raise the line pressure.
Also on your graph the massively weakened area at 3200rpm shows no corresponding change in the power graph at that point, not does the changing afrs prior to that point .. I would have expected the power graph to have a distinct clear reduction in power as that mixture change happened, yet there is none.
I'm not saying the graph is wrong or that you don't indeed have an issue with the fuelling on the car, but it doesn't make a great deal of sense at the moment that you should see such wild mixture swings yet no distinct change in the power line, and if I had just recorded a run like that on my dyno I would be re-visiting the lambda system to make sure what I had just recorded was correct and valid.
The AFR was measured using a lambda up the tail pipe, not the car's own lambdas. And Charlie did try both tail-pipes, with similar results.
I see what you're saying about the lack of power change when there was a big swing in the AFR. It is a bit odd.
Regarding the power, bear in mind that the blue line from before Christmas was with a worn cam and well down on what I expected, the maximum being only 241 bhp. Previously this car has produced 278 bhp on the same rollers. The cam it now has is the 885, replacing the 435, and as I understand it that should give at least as much power as the factory original (possibly a bit more). So the 255 bhp produced on Saturday on the new cam seems well down on what it should have been - I was expecting 280+. Charlie commented that he felt the engine was struggling.
I'm inclined to say that there must be a problem, given that an external sensor (lambda up the tail-pipe) and the car's own reported fuel trims both indicate something amiss.
Am I right in assuming that the long-term fuel trims should never go to 100% in either direction?
I see what you're saying about the lack of power change when there was a big swing in the AFR. It is a bit odd.
Regarding the power, bear in mind that the blue line from before Christmas was with a worn cam and well down on what I expected, the maximum being only 241 bhp. Previously this car has produced 278 bhp on the same rollers. The cam it now has is the 885, replacing the 435, and as I understand it that should give at least as much power as the factory original (possibly a bit more). So the 255 bhp produced on Saturday on the new cam seems well down on what it should have been - I was expecting 280+. Charlie commented that he felt the engine was struggling.
I'm inclined to say that there must be a problem, given that an external sensor (lambda up the tail-pipe) and the car's own reported fuel trims both indicate something amiss.
Am I right in assuming that the long-term fuel trims should never go to 100% in either direction?
Yep long terms should be between the extremes -100 to +100 and short terms ideally oscillate around zero.
When the long terms go either + or - 100 it means the map is beyond point where adjustments by lambdas can't be made.
Hence it could be an induction air leak. I had same issue and found 3 air leaks I could not detect with the usual "squirt of easy start" around induction area.
1. Bent valley gasket
2. Shaft of throttle butterfly
3. Plenum Water heater pipes and gasket under the plenum
Once i sorted those it all started getting a lot better.
When the long terms go either + or - 100 it means the map is beyond point where adjustments by lambdas can't be made.
Hence it could be an induction air leak. I had same issue and found 3 air leaks I could not detect with the usual "squirt of easy start" around induction area.
1. Bent valley gasket
2. Shaft of throttle butterfly
3. Plenum Water heater pipes and gasket under the plenum
Once i sorted those it all started getting a lot better.
Well I've just been out for another drive, and I'm even more confused!!!
Firstly, I now understand that the long-term trims only move when stopped. You don't have to be stopped for long - just 10 seconds seems plenty.
When I started up at the beginning of today's drive the trims were both at +100% which is where they were when I stopped yesterday.
But after warming it up and stopping, the trims came down to somewhere in the mid fifties. And on the next stop they came down to 20-30. And for many stops after that, they only moved by small amounts, remaining around 20-30-ish.
Just as I was giving up and starting to head home, I made one more stop. As I watched, the trims came up to the mid fifties again and stayed there for a bit. And then, really puzzling... as I watched for a bit longer, the odd bank marched up to 100% leaving the even bank at 53%. It then stayed like this so I drove home.
When I stopped at home, the even bank marched up to 100%. So both banks were at 100% again.
If this is an induction leak, then it's a peculiar one that comes and goes, or at least varies in intensity. And how did just one bank go to 100% if it's an induction leak? Surely an induction leak would affect both sides of the engine? Or was that just a freak, or some quirk of the 14CUX? It did happen just once yesterday as well.
So just for my reference, when the engine was running with trims around +20-30% does that seem relatively normal? And what about when the trims are in the mid fifties - does that indicate a moderate induction leak that's within the ECU's ability to compensate?
I did glance at the short-term trims a few times, and these just seemed to be dancing around at small to medium numbers. No particular pattern that I could see.
Firstly, I now understand that the long-term trims only move when stopped. You don't have to be stopped for long - just 10 seconds seems plenty.
When I started up at the beginning of today's drive the trims were both at +100% which is where they were when I stopped yesterday.
But after warming it up and stopping, the trims came down to somewhere in the mid fifties. And on the next stop they came down to 20-30. And for many stops after that, they only moved by small amounts, remaining around 20-30-ish.
Just as I was giving up and starting to head home, I made one more stop. As I watched, the trims came up to the mid fifties again and stayed there for a bit. And then, really puzzling... as I watched for a bit longer, the odd bank marched up to 100% leaving the even bank at 53%. It then stayed like this so I drove home.
When I stopped at home, the even bank marched up to 100%. So both banks were at 100% again.
If this is an induction leak, then it's a peculiar one that comes and goes, or at least varies in intensity. And how did just one bank go to 100% if it's an induction leak? Surely an induction leak would affect both sides of the engine? Or was that just a freak, or some quirk of the 14CUX? It did happen just once yesterday as well.
So just for my reference, when the engine was running with trims around +20-30% does that seem relatively normal? And what about when the trims are in the mid fifties - does that indicate a moderate induction leak that's within the ECU's ability to compensate?
I did glance at the short-term trims a few times, and these just seemed to be dancing around at small to medium numbers. No particular pattern that I could see.
I've had a bit of a poke around, looking for anything disconnected or loose.
I noticed two nipples underneath the throttle area, under the entry pipe to the plenum - the two red arrows in the picture below. I don't remember having noticed them before. What are they - are they for coolant heating of the throttle body to prevent icing, or perhaps to improve cold-start? And are they simply not used in TVR's engine installation? If that's the case, should they be plugged?
Also, there's a hose that's attached at one end just behind the pair of coolant temperature sensors, but at the other end it's rather free to move. It's the hose marked with the green arrow in the picture. I can't see what it attaches to under the plenum entrance, although I can see a jubilee clip. What is this hose, should it be firmly attached, or is the movement normal?
I noticed two nipples underneath the throttle area, under the entry pipe to the plenum - the two red arrows in the picture below. I don't remember having noticed them before. What are they - are they for coolant heating of the throttle body to prevent icing, or perhaps to improve cold-start? And are they simply not used in TVR's engine installation? If that's the case, should they be plugged?
Also, there's a hose that's attached at one end just behind the pair of coolant temperature sensors, but at the other end it's rather free to move. It's the hose marked with the green arrow in the picture. I can't see what it attaches to under the plenum entrance, although I can see a jubilee clip. What is this hose, should it be firmly attached, or is the movement normal?
The red pipes are where I had leaks. Smoke poured out of those.
They are cold start heating not used by TVR.
They attach to to plate which is bolted from below with a gasket. I think my gasket was perished.
They other hose is all about engine fumes being sent back through for combustion to reduce emmissions. I have fitted jubilees on all the hose connections as preventative measure. Those hoses harfen over time and could let air in.
Trying not to overstate it but smoke tester could help identify or at least eliminate causes.
They are cold start heating not used by TVR.
They attach to to plate which is bolted from below with a gasket. I think my gasket was perished.
They other hose is all about engine fumes being sent back through for combustion to reduce emmissions. I have fitted jubilees on all the hose connections as preventative measure. Those hoses harfen over time and could let air in.
Trying not to overstate it but smoke tester could help identify or at least eliminate causes.
blaze_away said:
They other hose is all about engine fumes being sent back through for combustion to reduce emmissions. I have fitted jubilees on all the hose connections as preventative measure. Those hoses harden over time and could let air in.
What Frank says plus......
When disturbed this could have happened, the Tee crumpled on mine when removing the hoses.
Or maybe the small hose aint been pushed on its stub.
Got my new ones from from ebay.......
HTH
Lance
Dr Mike Oxgreen said:
I've had a bit of a poke around, looking for anything disconnected or loose.
I noticed two nipples underneath the throttle area, under the entry pipe to the plenum - the two red arrows in the picture below. I don't remember having noticed them before. What are they - are they for coolant heating of the throttle body to prevent icing, or perhaps to improve cold-start? And are they simply not used in TVR's engine installation? If that's the case, should they be plugged?
Also, there's a hose that's attached at one end just behind the pair of coolant temperature sensors, but at the other end it's rather free to move. It's the hose marked with the green arrow in the picture. I can't see what it attaches to under the plenum entrance, although I can see a jubilee clip. What is this hose, should it be firmly attached, or is the movement normal?
They look like the plenum heater pipes usually not used on the Tvr.I noticed two nipples underneath the throttle area, under the entry pipe to the plenum - the two red arrows in the picture below. I don't remember having noticed them before. What are they - are they for coolant heating of the throttle body to prevent icing, or perhaps to improve cold-start? And are they simply not used in TVR's engine installation? If that's the case, should they be plugged?
Also, there's a hose that's attached at one end just behind the pair of coolant temperature sensors, but at the other end it's rather free to move. It's the hose marked with the green arrow in the picture. I can't see what it attaches to under the plenum entrance, although I can see a jubilee clip. What is this hose, should it be firmly attached, or is the movement normal?
They are not open to the inlet if that makes sense so shouldn't be an issue.
Worth checking the small fuel regulator vacuum hose is connected too, situated at the back under the plenum.
Edited by Belle427 on Thursday 24th February 07:42
Edited by Belle427 on Thursday 24th February 07:45
The short pipe you arrowed should be fixed to a spigot on the side of the trumpet base. If not connected it is an air leak which will do a couple of things.
firstly it will introduce un-metered air into the plenum, secondly it will reduce the air going through the airflow meter so it's output will be less than it should be, meaning even more weakening effect.
It's fair to point out though that these effects are more pronounced at closed throttle where the air leak will be a significant proportion of the total airflow .. at wide open throttle its effect will be significantly reduced but should still be corrected.
firstly it will introduce un-metered air into the plenum, secondly it will reduce the air going through the airflow meter so it's output will be less than it should be, meaning even more weakening effect.
It's fair to point out though that these effects are more pronounced at closed throttle where the air leak will be a significant proportion of the total airflow .. at wide open throttle its effect will be significantly reduced but should still be corrected.
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