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Strange VE numbers around motorway cruise

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Could someone shed some light on why it is when I'm trying to do some road tuning when I give what the logs/CLL/LTFT ask for my fuel table looks like this? What am I missing? This is specifically at motorway cruise and at first I thought it was due to transients on and off the throttle. I've checked it live though and when cruising steady it's consitantly asking for these VE numbers around the 3kRPM sites.

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Try changing the length of the MAP sensor hose and/or the take off point, sometimes resonance in the hose can cause a ridge like this. Also you you can get similar resonance in fuel pressure. If you ecu log both at 500 or 1000Hz you may be able to spot something.

Otherwise it is possibly just intake/exhaust resonance effects.

Related discussion: https://youtu.be/4QF5BmQtXZA

Thanks for the reply Adam, just when I thought I was getting my head around tuning thing another previously unheard of issue rears its head ha ha.

Is this something that only appears on Modelled fueling? With you actually monitoring air as opposited to %DC of fuel.

It is common for cars with large aftermarket injectors and no fuel pulsation damper to have some significant resonance problems which can lead to very odd fuelling demands seem in maps if high speed fuel logging isn't done. You can also get aliasing in manifold pressure readings depending on sample frequency/signal processing.

I've attached a log which is recording fuel pressure and MAP at 1000hz. Theres not noticable fluctuations in either but you can see clear as day the huge lean spike at 3krpm which is about 200rpm wide. I've shortened the FPR hose length from around 500mm to 100mm and it's made no difference (id plumbed it into the original location but the regulator has been moved to the other side of the inlet manifold).

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The spike is so lean, you might suspect an issue with the Lambda sensor, cracked exhaust, or vibration / wiring issue. Does changing the fuel table as you've shown actually cure that? If so it has to be in intake / exhaust resonance that is affecting the actual VE of the engine.

I've had exhaust systems that caused the exact opposite (a super rich area where flow seemed to stall), so it's not unheard of.

Since this appears to be a turbo charged engine (100kPa MAP with 20% throttle), perhaps there is some plumbing issue that is introducing extra air into the manifold (leaking blow-off valve), or the boost control is holding the manifold pressure steady, but the exhaust pressure is changing resulting in a change in efficiency. Either way -- if its reproducible, I would modify the fuel table to give it what it wants, and keep the engine running properly.

BTW -- Lambda sensors change their reading with pressure, I wonder if that could be related. Interesting data would be exhaust pressure and/or turbo speed.

Thanks for the reply David. The plot thickens I've just been out to do another run and I've added egt to the log. There doesn't seem to be any increase in EGT across the lean area. Seeing as the VE numbers are similar either side of the region i'm starting to thing the VE is in the ballpark and there's something up with what the sensor is seeing. Weather that be the sensor itself or an exhaust leak before the sensor. I have a spare sensor from my old wire in Wideband. I'll swap them over and see if there's any change.

Ive got forge BOV fitted but I can't remember what spring is in it, I do have stronger springs so I could fit a really strong one to seal it just to see if it makes any difference.

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Now, you are showing the same trend in a lower load area (15% throttle, 70 kPa MAP). I would tune the fuel table -- if you have a "ridge" at a particular RPM that is most certainly an intake/exhaust resonance and tuning the fuel table is the correct thing to do.

Yeah the hump seams to be from 50 to 100kPa map and always around 3krpm. I'm assuming there's nothing I can do to reduce this resonance without major modifications to be intake/exhaust system? Is this meaning that my Lambda values are likely to be accurate? That being the case would I not expect to see and increase in EGT?

I'll be ashamed to show anyone this VE table once I'm finished ha ha.

If the engine has some form of variable valve control, you may be able to tune it out - or at least confirm if it's related to that as it will affect the resonant characteristics.

I'm a little surprised you haven't noticed any sort of 'surge'when passing through that section of the rpm/load when driving - additional fuelling would suggest additional air requiring it. Actually, that may be another indication of a 'standing pressure wave' in the fuel line at that particular point.

Well I couldn't resist having one last run out tonight. I changed the lambda sensor for a spare I had just incase although I don't think it made any difference.

I then added the fuel it looks to be wanting and although the table looks hideous at least it's solved the problem of the lean spot. I don't have variable valves so other than what I have done I'm not sure what else I can to make the table look any better in this area?

Could this be as simple as at this point its spinning the turbo up causing the additional air and therefore fuel needed?

Would it still be advisable to fit a fuel pulsation damper?

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The Link software uses the min and max value from the fuel table to scale the span of the height axis for the surface graph, so in many cases this tends to exaggerate any height differences compared to for instance if you graphed the same table in Motec software. So I wouldn't be too worried about what you have here, it probably looks worse than it really is. The more important thing is if you are repeatably getting the correct mixture when moving through that operating range. Give it what it wants rather than what you think it should need. You can possibly add some finer RPM breakpoints around that region to round it off a bit if needed.

Ill be honest if i was just looking at the table i probably wouldnt of batted an eylid and just give it what it wanted, it was the graph that threw me. I have added an additional point at. 3250 rpm to try and isolate it from the rst of the table as much as possible. Would you say it's more likely to be air related than fuel now? and not to bother with a pulsation damper?

ust a little update, I've now got my cruise area pretty much dialed in within 2% of target. There's obviously something going on at about 3125 rpm as I've added a few sites either side of it and it's like a knife edge! I was tuning this car with the standard injectors/rail in traditional mode and there wasn't anything like this so i'm going to assume the resonance is something in the fuel system. I've ordered a damper so fingers crossed it sorts the problem.

Thanks for everyone's input

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I thought I would post an update just incase this becomes usefull to someone down the line. Since my last post I've fitted a pulsation damper to the fuel rail and the issue has pretty much dissapered. Have a look at the pics of before and after. Thanks for everyones input and pointing me in the right direction, I would have never figured it out on my own!

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