Is This a Normal Fuel Trim Value?

[Denio24]

Just logged my car, and I'm seeing a LTFT value of 17% and the STFT value is around 0%. Any explanation why the LTFT is 17? I will post more information later regarding the MAF, just wondering about possible causes for now.




UPDATE #1

So the car felt kind of slow today all of a sudden, as if it wasn't boosting all the way. General complaint is lack of power, though it still not bad, but noticeable enough to raise a concern. Boost was logged and is a solid 20 psi.

On measuring block 32, which is fuel trim at idle and partial, the partial fuel trim is 21.5% and the idle fuel trim is a good -0.3%. What else should I log to figure out why the partial is 21.5%?

[gavin_j]

Not normal. That's getting close to throwing a too rich code. Could be as simple as a boost leak. Ideal ltft are a few percent +/- 0 with respect to a few conditions.
Maf can definitely cause this too.

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[Denio24]

my MAF max reading @ wide open throttle is 182 g/s so I highly doubt that is the issue. Also, I'm able to boost to 21 lbs, in most gears. Note I'm tuned with JHM stage 1.

I actually did have a code in the past around 300 miles or so, and it was P1093. I took the HPFP off and took a look at the follower and it was fine - some wear, but nothing major. Camshaft looked fine as well. I have a 2008.

[Charles.waite]

Boost leaks happen after the MAF. Not before. Probably a boost leak as has been stated.

[Denio24]

Boost leaks happen after the MAF. Not before. Probably a boost leak as has been stated.

As I said before, my boost is able to go to 21 psi which is normal for my tune. At the moment, I am not worried about boost leaks as I have already checked for them, but another underlying cause to my high LTFT values. I'm thinking LPFP in the back of my mind. I'd like to add I also recently replaced the fuel filter. Any way to diagnose a bad LPFP?

[mtroxel]

I'm thinking LPFP in the back of my mind. I'd like to add I also recently replaced the fuel filter. Any way to diagnose a bad LPFP?

Check the duty cycle. Group 106, value 2. Anything in the 60-70% range and the LPFP is questionable.

[Denio24]

Check the duty cycle. Group 106, value 2. Anything in the 60-70% range and the LPFP is questionable.

The max value I saw in my logs was 84.7% duty cycle at 110 bar in the fuel rail. At idle it seems to be at 55%

[Charles.waite]

As I said before, my boost is able to go to 21 psi which is normal for my tune. At the moment, I am not worried about boost leaks as I have already checked for them, but another underlying cause to my high LTFT values. I'm thinking LPFP in the back of my mind. I'd like to add I also recently replaced the fuel filter. Any way to diagnose a bad LPFP?

Yea mainly boost dut readings are the way to test short of removing the pump and physically measuring it's flow. I thought more about this and I was wrong about the boost leak as you said. Basically your ECU is adding a ton more fuel. Could be a bad fuel filter? Are your rail pressures in spec? If the rail pressure is dropping it could be a culprit. Could be lpfp I suppose. Maybe HPFP but you would probably have low rail pressures across the board of that we're the case. In theory your rail dump valve could be cracking too early as well.

[Denio24]

Rail pressures are in spec. I do see something though in my logs; is it normal for the lpfp pressure readings to drop to around 3 bar when pressure in the rail is highest? (around 120 bar).

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[Denio24]

Here is a 3rd gear log from 2k rpm to 6k WOT. LTFT values are still 15-17% even after resetting ECU. At idle, the LPFP duty cycle is 57.6%.

[Charles.waite]

I don't THINK it is but I'm honestly not sure. Might want to run these by the guys at jhm and ask since you're tuned they would be able to tell you for sure whether that's in spec for their tune. My gut says it's not but I'm not sure...

[MrBigglesworth]

When you say LTFT - do you mean LTFT at idle/add or throttle/mult? I'm assuming its throttle/mult. Do you know what your ide/add numbers are?

Also when you say STFT, I'm assuming this jumps around alot for you but generally flicks between positive and negative?

Your log has an interesting blip at time stamp 8.1 - where the MAF and fueling go down before then going up again. Did you have your traction control off?

Some more logging that you could try would be HP fuel vs request, boost vs request, misfires. Also if you can return to stock and see if there is any impact, that could be useful.

With those additional items, might help in pointing at a particular issue.

[MrBigglesworth]

Yea mainly boost dut readings are the way to test short of removing the pump and physically measuring it's flow. I thought more about this and I was wrong about the boost leak as you said. Basically your ECU is adding a ton more fuel. Could be a bad fuel filter? Are your rail pressures in spec? If the rail pressure is dropping it could be a culprit. Could be lpfp I suppose. Maybe HPFP but you would probably have low rail pressures across the board of that we're the case. In theory your rail dump valve could be cracking too early as well.

Yep - a boost leak should cause running rich not lean.

Thinking about the rail valve (assume you mean PRV) - if this cracked early then I think you would see HP fuel dropping well away from actual and LP doing a corresponding spike. So thinking about VCDS this should relatively easy to spot - but as I haven't had the problem myself, I haven't really seen anyone confirming this using VCDS - so that's only a guess.

In terms of LP - if you are at 55/58% idle, then that seems good. LPFP dropping at high HPFP request is normal too - mine drops to c.3.7 bar (not tuned) and duty cycle goes to low 80%s.

[Jake@JHM]

Why are you logging LTFT at WOT?

Is there a specific issue you are chasing?


To check LTFT drive normal for a day, and then log the block at IDLE the next to see where your trims are at.

[Denio24]

Why are you logging LTFT at WOT?

Is there a specific issue you are chasing?


To check LTFT drive normal for a day, and then log the block at IDLE the next to see where your trims are at.

OK, the underlying issue was a hesitation when accelerating usually over 3k RPM with higher engine loads (greater throttle positions). This also happened in idle and revving the engine. This prompted me to check fuel trim values which is when I noticed my high long term fuel trim. I still have yet to figure out why my LTFT values are higher than expected.

[Jake@JHM]

OK, the underlying issue was a hesitation when accelerating usually over 3k RPM with higher engine loads (greater throttle positions). This also happened in idle and revving the engine. This prompted me to check fuel trim values which is when I noticed my high long term fuel trim. I still have yet to figure out why my LTFT values are higher than expected.

A hesitation during load sounds more like a misfire. Have you checked your plugs and coils? Do you have any codes?

[Denio24]

Plugs and coils were recently . I had a P1093 - Malfunction - Intermittent , but I cleared codes and it hasn't come back.

[MrBigglesworth]

The blip in your fueling coupled with that code is coincidence or pointing to an issue on your fueling side - but at the moment could be one of several issues (sensors, filters, pumps) and if its a sensor then VCDS may be giving you readings that are out.

Just to check there's not an injector playing up - have you logged misfire and timing on all four cylinders to check that there is nothing unusual?

[Denio24]

The issue has subsided since the past couple of days after changing my cam follower, so I will post up pictures of the follower later today. The two may be related, since I have experienced no hesitation or surging as i described originally. The multiplicative long term fuel trim has also gone down to 10.9-12%. So for me this is really a non issue until i start seeing 15+%.

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[MrBigglesworth]

By the way - my mult fuel trim seems to go up by about 3.5% when its colder too, so not sure how much temp variation there is where you are but some of the difference could be due to just temp changes.

However, does sound like that has made a reasonable difference. Did you have any lobe wear or the piston show any damage?

[Denio24]

Just completed some measurements on the cam follower, and it looks like a new one is just over 2 mm at 2.066. The one I took out measured at 1.956 mm after 10k miles & tuned...so a .1 mm wear

It's just so weird that there is no more hesitation & surging when accelerating anymore. I will keep my eye out on this as something had to be causing it, and will update this thread once I have more information.

Just a comparison, a camshaft has a wear limit of about .1 mm of radial play for 2.0t fsi engines before things start going south. However I have no idea what effect a .1mm wear will do to a hpfp system. Maybe someone

can chime in here to help my try to rule out this. Or, perhaps my camshaft has worn down, but that is unlikely as the follower has never broke through and the car was meticulously maintained.

[derrek]

Just completed some measurements on the cam follower, and it looks like a new one is just over 2 mm at 2.066. The one I took out measured at 1.956 mm after 10k miles & tuned...so a .1 mm wear

It's just so weird that there is no more hesitation & surging when accelerating anymore. I will keep my eye out on this as something had to be causing it, and will update this thread once I have more information.

Just a comparison, a camshaft has a wear limit of about .1 mm of radial play for 2.0t fsi engines before things start going south. However I have no idea what effect a .1mm wear will do to a hpfp system. Maybe someone

can chime in here to help my try to rule out this. Or, perhaps my camshaft has worn down, but that is unlikely as the follower has never broke through and the car was meticulously maintained.

What kind of fuel trims are you expecting? .1mm isnt going to make your fuel trims go way out of wack.

[Denio24]

Just updating this thread. My high multiplicative fuel trim values were most likely due to my heavy foot on the accelerator! As long as there is no CEL it does not usually signify an issue.

[Denio24]

UPDATE #1

So the car felt kind of slow today all of a sudden, as if it wasn't boosting all the way. General complaint is lack of power, though it still not bad, but noticeable enough to raise a concern. Boost was logged and is a solid 20 psi.

On measuring block 32, which is fuel trim at idle and partial, the partial fuel trim is 21.5% and the idle fuel trim is a good -0.3%. What else should I log to figure out why the partial is 21.5%?

[mtroxel]

You're running lean. If it was an air leak it should show up at idle and you should adding a lot of fuel at idle. So I might think about looking at fuel rail pressure readings? Might also look at MAF readings, should be about 160 g/s at WOT.

[Denio24]

I'm tuned and its running ~ 200 g/s. Fuel rail pressure at load is also spot on. I'm stumped. What are your block 32 values?

[mtroxel]

I'm tuned and its running ~ 200 g/s. Fuel rail pressure at load is also spot on. I'm stumped. What are your block 32 values?

I looked last week. At idle it flips between + and -like it should, never more than about 3 either way. i just looked at a log and my lambda control can do the same when I'm driving, but usually stays within 5 either side of 0. Sometimes in double figures but not often.

Anything you want me to log so you can compare to a healthy one?

[Denio24]

I'm pretty sure you're referring to block 33 values, which monitor the lambda control values from the ho2s sensor. Those values fluctuate constantly. In block 32, they are the learning values at idle and at higher loads - these stay pretty much constant and do not fluctuate.

Can you log block 31 with block 2, then 32 with 2, and then 33 with 2 with turbo mode enabled first a couple of seconds at idle then wot to like 4k rpm?

[Okedokey]

HPFP pressure release valve venting too early? Need to upgrade to RS4 one?

[mtroxel]

I'm pretty sure you're referring to block 33 values, which monitor the lambda control values from the ho2s sensor. Those values fluctuate constantly. In block 32, they are the learning values at idle and at higher loads - these stay pretty much constant and do not fluctuate.

You're right, my bad. I will do some logging tomorrow]

[Denio24]

I have logs from a bit ago, and the fuel rail pressure holds to 126-129 bar at wot. I'll post up a log of the fuel rail pressure tomorrow when i get the chance.