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If you haven't already you should try this product called cataclean if your mech suspects the cat is the issue. A while back I had an issue passing emissions because my cats wouldn't ready for thousands of miles. I used this stuff and ran pretty hard on the freeway for about 10 miles and it finally readied. Not sure if it's a coincidence or the product actually worked but for now i'll assume this thing actually helped. I have also disconnected my battery numorous times since this happaned and have not had issue since. All you'd be losing is 20 ish bucks if it doesn't work.
I still haven’t resolved the issue with the high fuel trims and lower than normal boost. I got a CEL P2099 Post catalyst fuel trim system too rich.
The high positive fuel trims indicate a lean condition that the computer tries to balance by adding fuel. Why am I getting a rich code though?
I smoked the turbo vacuum lines that tend to break and they passed the test. I found though that the diaphragm of the check valve on the vacuum pump is gone. Pic attached. Looking for a replacement so I won’t have to do the entire pump. I don’t think though that this has anything to do with the high fuel trims on idle since the valve is supposed to be open on idle anyway.
That made me think of other check valves have gone bad too and let air in the intake when they are not supposed to do. That would be the crankcase ventilation valve located under the HPFP. I think that one is supposed to be closed on idle. If the diaphragm is bad, then I guess it would let unmetered air in the intake. Any way to confirm that without taking it out?
Any other ideas?
I haven’t pressured tested the turbos to see if they seal properly. From what I see when I start the car, the arms move straight to the front in a steady controlled way. Also, whatever the problem is, I believe it lies somewhere where it affects both banks equally. I think it is unlikely that both turbos leak exactly the same.
I still don't have an answer but I can tell you more stories about my '16 E550 that may help? Some info is better than no info.
My little check valve dealie took a dump on me too, but instead the cage holding it simply fell apart. Not broken, it just slips together and it seems nothing really holds it together so it didn't stay together, per the pix. I simply reassembled it and melted the plastic to hold it. I looked for a replacement assy but only found complete pumps, which I think were ~$150 and a pita to replace. So I bought one and at the very least I have a spare valve.
Mine, when it fell apart, was lowering vacuum to the turbos and I discovered a wee bit of oil in the vac line leading to the turbo solenoid. Since oil can only get there via the pump, I removed the valve and you know the rest. Once I fixed it the turbos had more vacuum, especially at idle. But note the vac to the turbos has nothing to do with your fuel and idle issue. You can have the wategates fully open or closed and it doesn't matter. Even if closed and you get a teeny bit of boost, it isn't enough to matter at idle. Disconnect the vac line if you like, to test it.
As for trims and idle I can tell you I've had similar and worse issues trying to run E85. I'm not running 100% E85, so my actual alcohol content in the tank I've been experimenting with is 10-30%, excluding any that is in the normal gas which may be 10%? What happens is the more alcohol I add the higher the fuel trims. Seems obvious, but no. I adjust the fuel to match the alcohol % but trims not only go up, they up more than they should even if I didn't adjust for them. It's like it doesn't understand what to do or something. So if I add ethanol that would call for 5% more fuel across the board, fuel trims go up more like 10%. At idle it's much worse than cruise, and full throttle is more or less what it should be. Full throttle fuel mix/trims are almost what they should be regardless of E85 % or none, then cruise less so and idle is much worse. Open loop idle is worse because it doesn't see that it's off and delivers too little fuel. It gets surgy too, with rpms going low, then it opens the throttle to compensate and revs too high, closes the throttle, repeat. Frustrating. But the trims are very similar to what you're seeing, the lower the rpm/load the higher the trims.
Imo the trims don't seem very important as long as they still have enough room to adjust. If they run out of adjustment then you have a problem. The LTFT has much more adjustment than ST, but LT doesn't work above a certain rpm, instead it freezes wherever it happened to be when exceeded that rpm. I forget but I think it's 2500 or 3k? I think it was WRC-LVR that pointed that out to me because before that I never paid attention. And unlike LT, the STFT stops at 25, or worse, it gives up trying and goes to 0 if it tries to exceed 25. So if normally you have say 20 on trims, and you were putting along with LT at 0 and ST at 20, and you floor it, you only have 5 left to adjust. If ST zeros out you're now down by 20 and way too lean. If your LT were 20 and ST 0, then you floor it, you have the 20 LT locked and 25 left on ST to adjust. The latter example is what it's supposed to do, but it doesn't always do what it's supposed to so you could randomly end up with the former example. So imo, if you adjust so you're a little rich and trims are negative, it has more room on avg to adjust richer if needed. Since the eng runs lean already, then you go even leaner under load, it could get ugly fast. The way I adjust my fuel is via HP Tuners, which is software and an OBD dongle that allows programming. There are other ways to do it but HP is easy and reasonably priced compared to other options. Key word here is easy. It also has a really nice program to monitor your engine that is much better than whatever program you're using now. I think it's $400 for the OBD dongle and software is free, then another $300 if you want to program the car. You can also use it to squeeze more power out of it so you can use it instead of buying a tune.
If I undo all my changes to the fuel and no E85 it's fine, it's similar to what you're seeing. So we may have the same issue, which is maybe a common issue since very few people check.I have no codes related to this issue. Same old story for me, codes for things that are fine, no codes for things that are bad. The dealer and indie shops are basically useless with a code telling them what to do, so you're probably on your own like me.
When I first checked the trims about a year ago they were between 0 and 5, then they slowly worked up to the 12% or so it's at now. The 12 is across the board but idle is much higher. So with fuel programmed to give me ~0 at cruise, trim will be 5-20 at idle. When I first stop and it drops to idle it's more like 0-5, then it climbs over ~30sec to 15-20. It seems the ECU thinks it somehow needs less fuel, but the O2 sensors are saying no stupid, and compensate which triggers trims to read higher. The actual fuel delivered stays more or less the same, just the trims #'s climb. Seems like the ecu to me but who knows.
I also have lower intake vaccum that started a few months ago. I assumed an intake leak which would explain that and fuel trims. Turns out it was just the throttle opening too much for the fuel, so it's too lean and that nets poor vacuum. The O2's have a much harder time adjusting at idle so this is the result. If the correct fuel is delivered then vacuum seems fine. It should never deliver as little fuel as it's trying to do so what else could it be other than the ecu? It could be my MAP sensor giving a higher vacuum reading than actual, but it's reading matches the boost sensor so they would both need to be bad by the same %, which I can't imagine. Plus with the eng off the ambient sensor also matches. An ecu issue is much easier to believe.
My fuel pressure is ~2450 at all rpm except idle, which is 1700 or something. I think it's supposed to do that but not certain.
I have never looked at evap purge but maybe I will now.
I still don't have an answer but I can tell you more stories about my '16 E550 that may help? Some info is better than no info.
My little check valve dealie took a dump on me too, but instead the cage holding it simply fell apart. Not broken, it just slips together and it seems nothing really holds it together so it didn't stay together, per the pix. I simply reassembled it and melted the plastic to hold it. I looked for a replacement assy but only found complete pumps, which I think were ~$150 and a pita to replace. So I bought one and at the very least I have a spare valve.
Mine, when it fell apart, was lowering vacuum to the turbos and I discovered a wee bit of oil in the vac line leading to the turbo solenoid. Since oil can only get there via the pump, I removed the valve and you know the rest. Once I fixed it the turbos had more vacuum, especially at idle. But note the vac to the turbos has nothing to do with your fuel and idle issue. You can have the wategates fully open or closed and it doesn't matter. Even if closed and you get a teeny bit of boost, it isn't enough to matter at idle. Disconnect the vac line if you like, to test it.
As for trims and idle I can tell you I've had similar and worse issues trying to run E85. I'm not running 100% E85, so my actual alcohol content in the tank I've been experimenting with is 10-30%, excluding any that is in the normal gas which may be 10%? What happens is the more alcohol I add the higher the fuel trims. Seems obvious, but no. I adjust the fuel to match the alcohol % but trims not only go up, they up more than they should even if I didn't adjust for them. It's like it doesn't understand what to do or something. So if I add ethanol that would call for 5% more fuel across the board, fuel trims go up more like 10%. At idle it's much worse than cruise, and full throttle is more or less what it should be. Full throttle fuel mix/trims are almost what they should be regardless of E85 % or none, then cruise less so and idle is much worse. Open loop idle is worse because it doesn't see that it's off and delivers too little fuel. It gets surgy too, with rpms going low, then it opens the throttle to compensate and revs too high, closes the throttle, repeat. Frustrating. But the trims are very similar to what you're seeing, the lower the rpm/load the higher the trims.
Imo the trims don't seem very important as long as they still have enough room to adjust. If they run out of adjustment then you have a problem. The LTFT has much more adjustment than ST, but LT doesn't work above a certain rpm, instead it freezes wherever it happened to be when exceeded that rpm. I forget but I think it's 2500 or 3k? I think it was WRC-LVR that pointed that out to me because before that I never paid attention. And unlike LT, the STFT stops at 25, or worse, it gives up trying and goes to 0 if it tries to exceed 25. So if normally you have say 20 on trims, and you were putting along with LT at 0 and ST at 20, and you floor it, you only have 5 left to adjust. If ST zeros out you're now down by 20 and way too lean. If your LT were 20 and ST 0, then you floor it, you have the 20 LT locked and 25 left on ST to adjust. The latter example is what it's supposed to do, but it doesn't always do what it's supposed to so you could randomly end up with the former example. So imo, if you adjust so you're a little rich and trims are negative, it has more room on avg to adjust richer if needed. Since the eng runs lean already, then you go even leaner under load, it could get ugly fast. The way I adjust my fuel is via HP Tuners, which is software and an OBD dongle that allows programming. There are other ways to do it but HP is easy and reasonably priced compared to other options. Key word here is easy. It also has a really nice program to monitor your engine that is much better than whatever program you're using now. I think it's $400 for the OBD dongle and software is free, then another $300 if you want to program the car. You can also use it to squeeze more power out of it so you can use it instead of buying a tune.
If I undo all my changes to the fuel and no E85 it's fine, it's similar to what you're seeing. So we may have the same issue, which is maybe a common issue since very few people check.I have no codes related to this issue. Same old story for me, codes for things that are fine, no codes for things that are bad. The dealer and indie shops are basically useless with a code telling them what to do, so you're probably on your own like me.
When I first checked the trims about a year ago they were between 0 and 5, then they slowly worked up to the 12% or so it's at now. The 12 is across the board but idle is much higher. So with fuel programmed to give me ~0 at cruise, trim will be 5-20 at idle. When I first stop and it drops to idle it's more like 0-5, then it climbs over ~30sec to 15-20. It seems the ECU thinks it somehow needs less fuel, but the O2 sensors are saying no stupid, and compensate which triggers trims to read higher. The actual fuel delivered stays more or less the same, just the trims #'s climb. Seems like the ecu to me but who knows.
I also have lower intake vaccum that started a few months ago. I assumed an intake leak which would explain that and fuel trims. Turns out it was just the throttle opening too much for the fuel, so it's too lean and that nets poor vacuum. The O2's have a much harder time adjusting at idle so this is the result. If the correct fuel is delivered then vacuum seems fine. It should never deliver as little fuel as it's trying to do so what else could it be other than the ecu? It could be my MAP sensor giving a higher vacuum reading than actual, but it's reading matches the boost sensor so they would both need to be bad by the same %, which I can't imagine. Plus with the eng off the ambient sensor also matches. An ecu issue is much easier to believe.
My fuel pressure is ~2450 at all rpm except idle, which is 1700 or something. I think it's supposed to do that but not certain.
I have never looked at evap purge but maybe I will now.
Thanks for your message Chevota. I feel like we are dealing with the same problem.
Before I get into it, I want to say that yes, the little diaphragm on the vaccum pump that sucks air for the turbos isn’t the problem. Worst case you will get oil in the turbo lines because of it, which hasn’t happened in my case. Also, you can buy the diaphragm alone on eBay and Amazon. BMW, Ford and Volvo have the same vacuum pump. I bought it, it fits in the plastic but the nipple doesn’t get hooked on the little hole. I ordered a different one and wait for it.
To the point now…
I’m not 100% sure but I think that the previous owner mentioned to me that he had the computer replaced while the car was still on warranty. I thought that it may be the computer that for some reason can’t calculate fuel trims but no. The computer adjusts the fuel trims when the car is moving and everything is fine. Then when the car idles, it’s adjusting to the high fuel trims that I mentioned before. An air leak would explain everything. There isn’t one though based on smoke tests.
Moreover, all the times I got CEL was on very low rpm when driving locally on eco mode. Never an issue on high rpm. Actually the longest I’ve been without CEL was about 4k miles that I was always on sport mode.
My next move is to replace the crank case ventilation valve located on the back of passenger’s side valve. It is what WRC has mentioned before as pcv, Mercedes came up with a different name. Mercedes software says to replace from underneath but I think it is doable from up too. Waiting for the part before I take it out. After taking it out, it will be easy to check if the diaphragm is gone.
I have a link here with Tasos explaining how the diaphragm breaks on these. It is from the 6.3 engine but the idea is the same. If the diaphragm has gone bad, then it sucks unmetered air and oil on idle which explains the fuel trims. It also explains the fouled spark plugs I had a year ago. It should also explain the boost loss from 0.9 to 0.6 bars.
I think the manual says every 70-80k miles to be replaced. It is a wear item.
WRC I should have read your comments more carefully, you mentioned pcv time and again. I couldn’t find anything though because Benz calls it crank case ventilation cover or sth like that.
Anyway… thank you all for your help. I’ll keep you posted.
Did you ever try changing the cat or o2 sensor? I think you said that was recommended by your mechanic. I’ve been following this because I was having similar issue with my 2010 but it ended up being a collapsed motor mount. Obviously with your codes it’s not that but I’m a betting man and I feel strongly about the cats or o2 sensors 😂.
I'm in to see what actually is identified as causng these issues. Love the hard work everyone does. If it is the crankcase ventilation system, then that may explain much issues like Chevota has had for a long time. It is painful on these cars isnt it? To my mind it explains the trims being off . I dont know if the vacuum issue might explain the lack of proper boost since the turbos are vacuum controlled, but im sure you guys will figure it out.,
@Chevota, look up Acta_Verba on here he apparently know HP tuners for his Merc.:-)
Thanks for your message Chevota. I feel like we are dealing with the same problem.
Before I get into it, I want to say that yes, the little diaphragm on the vaccum pump that sucks air for the turbos isn’t the problem. Worst case you will get oil in the turbo lines because of it, which hasn’t happened in my case. Also, you can buy the diaphragm alone on eBay and Amazon. BMW, Ford and Volvo have the same vacuum pump. I bought it, it fits in the plastic but the nipple doesn’t get hooked on the little hole. I ordered a different one and wait for it.
To the point now…
I’m not 100% sure but I think that the previous owner mentioned to me that he had the computer replaced while the car was still on warranty. I thought that it may be the computer that for some reason can’t calculate fuel trims but no. The computer adjusts the fuel trims when the car is moving and everything is fine. Then when the car idles, it’s adjusting to the high fuel trims that I mentioned before. An air leak would explain everything. There isn’t one though based on smoke tests.
Moreover, all the times I got CEL was on very low rpm when driving locally on eco mode. Never an issue on high rpm. Actually the longest I’ve been without CEL was about 4k miles that I was always on sport mode.
My next move is to replace the crank case ventilation valve located on the back of passenger’s side valve. It is what WRC has mentioned before as pcv, Mercedes came up with a different name. Mercedes software says to replace from underneath but I think it is doable from up too. Waiting for the part before I take it out. After taking it out, it will be easy to check if the diaphragm is gone.
I have a link here with Tasos explaining how the diaphragm breaks on these. It is from the 6.3 engine but the idea is the same. If the diaphragm has gone bad, then it sucks unmetered air and oil on idle which explains the fuel trims. It also explains the fouled spark plugs I had a year ago. It should also explain the boost loss from 0.9 to 0.6 bars.
I think the manual says every 70-80k miles to be replaced. It is a wear item.
WRC I should have read your comments more carefully, you mentioned pcv time and again. I couldn’t find anything though because Benz calls it crank case ventilation cover or sth like that.
Anyway… thank you all for your help. I’ll keep you posted.
Did you end up replacing the crankcase valve? I may need to do this also.
Did you end up replacing the crankcase valve? I may need to do this also.
Hi all,
I replaced the vent valve cover but nothing changed. The fuel trims are still the same. Pics of the old vs.new vent valve cover below
Membrane was worn out but not cut.
It was pretty hard to be replaced from the top but it is possible. Merc book says to raise the car and take out the cat. I replaced it from the top by removing the HPP protector. I left the pumps there but if I had removed them it would be much easier. Point is, nothing changed.
No, wait. Almost nothing. Because I found a leak that I would like you guys to help me figure out where it is from and if it can anyhow be what is messing with my fuel trims. Video below
any idea if it is oil or coolant and where it comes from?
Last thing I thought is, can it be that some previous owner flashed some tune on the computer that doesn’t work well? How can I check if my computer is stock?
I'm in the same position with low vacuum. I make a video addressing the check valve issue; but it did not resolve my low vacuum issue. I'm FBO and tuned on E50 on HPTuner.
I recently replaced the check valve membrane shown above and also the short hose pieces that connect the boost controller lines to the wastegates (they were slightly dried out and easy to rotate on the WG fitting, so I figured there may be a leak there):
I also tightened the charge pipe hose clamps on the turbo compressor outlets. For what it's worth, my car runs a lot stronger now and wasn't holding boost well at higher RPM before.
Fyi I bought one of those check valves on ebay to have on hand. Different seller than the link Brian posted but the exact same pictures showing the nice orange valve you want. It arrived with a crappy excuse of a stiffer black rubber valve, which doesn't work.... So if anyone here gets one, be sure it's a good one. The oem unit is orange like the picture in that link, or my pix posted earlier. I also have a good one from a new vac pump that is green. The good ones are dished and very flexible. The cheap chinese one is flat faced, much thicker and stiffer, and doesn't actually work. I hate ripoffs, which are almost always from china. The little cage cover just pops right off so you can pull it out for a look-c. Or, like my oem one, the cage falls out.
As for the fuel trim problem, I checked my Evap Purge and it has nothing to do with my trims. I was wrong earlier when I said 12%, I added 10.8% fuel across the board.
The idle trims are still appear to be the fuel pressure, but why I don't know. It makes sense pressure would drop at idle, because why not take a load off the pump when not needed. So it seems the ecu isn't adjusting for that so trims have to do it.
i dunno about the M278 in the E550 but many cars with turbos have a relay that sends a nominal voltage to the fuel pump for no boost conditions, then a hgher voltage to the pump when under boost to allow more fuel to be delivered. If it is the same on the M278, and you have to add fuel trims, then it might be possible the relay is not up to snuff or the wiring is shaky to the pump.
WRC; I didn't see your PM until just now.
I don't see any difference in fuel psi between boost vs no boost, just idle vs not idle. So when I come to a stop it drops psi from the normal 2450 to 1750psi, then I touch the gas and it's 2450. It doesn't always drop immediately, so it could take maybe 5sec after, but it always does. Sometimes it starts dropping before I stop, but the eng was in the idle zone leading up the stop. So maybe it always takes x seconds once in the idle zone and it's confusing since I don't know when the timer starts?
I have no idea why I have to add fuel. It's baffled me since day one. I think it was more like 4-5% off when I first checked two years ago, now it's ~10. It also varies a lot even when psi is steady at 2450. So it may read -5 or +5 or more at various conditions. Basically I have it set so I'll be fine under full load if it faults out and doesn't trim at all. It makes sense to me that it'll never be 0 all the time, or even most of the time, but to listen to other people it's as if 0 is all they see. Maybe I need to swap out my O2's, which I admit I'm lazy and they're still sitting in the box, but note it was doing this with 28K on the odo, and the O2's seem to be responding very quickly. It seems to me it's not so much an O2 issue, but the ECU's ability to respond to it. Eg; I might be idling at an avg of ~.970 lambda with a command of 1.00, but the fuel doesn't adjust. I mean it's adjusting many times a second but it doesn't bring it to the 1.00 per the command. I blip the throttle and it may or not bring it to an average of 1.00, it may settle on a different #. It's hard to tell the avg O2 reading because it's all over the place, so I just have to watch it and avg in my mind. Cruising it seems to stay on target better, but again both the O2's and actual fuel delivery are constantly moving, yet not always dialing it to match commanded 1.00.
Under load it seems the command itself is slow to respond. Say I floor it and go all the way to redline, the command seems to lag behind and may only go to say .850 when I have it set to .800. The O2 readings may read ~commanded or be leaner or richer. It's different each time so I can't see a pattern, so basically none of it makes sense. The HP program recording all this is both delayed and skipping many scans, so my guess is it completely missed the command data of .800. I'm probably getting the command reading from 5k, then the next one is so late it's after it shifted and down at 4k.
And if I didn't mention it before, the turbo has nothing to do with idle. you can unplug the vac lines to the turbo and it won't change it at all. The issues with the vacuum will only cost you power, and only if vacuum is below a certain point. It only needs good vacuum at peak boost and rpm, which are not the same thing. It pulls boost at higher rpm so if you lost 10" of vacuum it may only cost you power at say 4k. It won't give you an underboost code either, unless your vacuum is really low. So in short, it would be rather difficult to know if you were 5" low, or even 10". You literally have to measure it, manually. The vacuum is supposed to be the same at idle and all rpm, more or less, but if the check valve is not working right I can't only guess what it'll do. So I not only checked mine at idle, I checked at all rpm & loads. I simply ran a vacuum gauge to the dash, which I ziptied to my defrost vent. I ran some teeny tubing in the gap between the fender & A pillar, past the door hinge and in. Redneck but it works, easy, cost nothing and no damage to anything. Otherwise the only clue to low vacuum I noticed is the rods between the wastegate and diaphragms were moving back n forth, kinda jerky, at idle. It seems there's a zone where just the right vacuum will do this. Too much, even if if the vac pump is low, and no jerking. Too much and no jerking. It also matters when because during cold starts, while in cat and O2 heating mode, it can jerk around too.
Note it can go into cat heating mode at any time when warm too, so while fully warmed up it may be fine, then start jerking. Then you have to wonder if it's jerking because of cat heating mode, or not jerking because of it? So annoying, but in the end measuring vacuum tells you so much more. I even have a chart that gives the approx vacuum needed to xx wastegate position, so you can better decipher if it's doing what it's supposed to, if anyone is into that.
Lastly, when I get low manifold pressure it's the throttle doing it. It's open further than I think it should be. So if it's cracked open a couple degrees but the timing is low and/or fuel too lean, it stays at the correct rpm. So watch your throttle position. Not pedal position, or commanded throttle, but actual throttle position.
Note the throttle position at 12.9% instead of a more normal 12.2
The fuel is lean at ~1.07
Spark is negative (Catalyst Heating mode)
Result; 5.5 MAP instead of 4.
I have my Cat retard turned down so oem would be worse, and MAP even higher
Note the comment at the bottom of each pix explaining it.
This should help to better understand and troubleshoot the turbo, and hopefully not make it more confusing.
I can't recall if an app like Torque Pro can see the turbo duty cycle or not. Xentry can see it, and of course HP Tuners, but you'd need to know that in order to compare it to what the rod on the wastegate is doing.
When idling I'm at 90%, and I think oem is 90 too but not sure if that's the normal spot or just sometimes. There's also that stupid catalyst thing that will lower duty cycle and I don't know if it only does it during cold idle, or if it's like the spark retard and does it whenever it feels like it.
The one on the far right is really all you need, but the others show what happens with exhaust flow pushing on the wastegate. How much is pushing on it at a given load/prm I don't know, but I do know it does push. If I lock the duty cycle to say 50, it'll stay closed just fine to a point, but it will open and dump my power with it. I'd imagine 60% would be enough to net full oem boost, which is why losing some vacuum won't hurt you. It would need to drop the point where 90% duty cycle isn't enough to maintain the MAP it wants to see. So if the vacuum is a little low, the ecu will see the boost is low and it'll increase the duty cycle to compensate, until it hits 90%, which despite what the carts says, is the actual max. It's range is 10-90%. So the chart on the right is only correct if the vacuum is good, and limited to 10-90. Good oem vacuum I think is ~24"? But oem boost should be good even if you're only 15", from what I recall. So the ecu shoots for the duty cycle it thinks it needs, based on these charts, then adjusts duty cycle up/down if MAP is too low/high. Make sense?
07-22-2022, 03:52 AM
