When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Need some help on how to diagnose my 2014 GL450 engine that is running rich. The car has around 65K miles. There is a slight vibration at idle and I am smelling a little bit of exhaust type smell from the engine, all signs of the engine running rich. Also gas mileage is not great - around 13mpg in the city. I hooked up my torque app and the stft and ltft are shown below
ltft bank 1 (idle) = ~ -6.2
ltft bank 2 (idle) = ~ -11.7
stft bank 1 (idle) = ~ -0.8
stft bank 2 (idle) = ~ - 0.8
on acceleration (around 2500 rpm)
ltft bank 1 = ~ 5.5 (not much change)
ltft bank 2 = ~7.8 (significant change)
stft bank 1 = 2.3 (not much change)
stft bank 2 = 7 (significant change)
I have changed the air filter a little less than 2 yrs ago, so I was going to do this, but I didn't think just a dirty air filter would make this much change.
I also noticed that the intake hose had a rip in it, so I taped it up real good with duct tape (I'm going to order a new one) and it look air tight now. I didn't measure the ltft/stft before I taped it up.
Any ideas? I feel there maybe 2 problems here - one problem that has both bank 1 and bank 2 with a high negative ltft at idle and then a 2nd problem which is causing only bank 2 ltft to change significantly on acceleration.
Could it be a fuel pump/filter problem? What would be the right steps to diagnose?
FYI - I have a Star Diagnostics C4 system so I can run any tests from that also.
Use your star to test the injectors as I believe you have a bad one
Would one bad injector cause both Banks to run rich?
Also do you know the exact test? I did one test called "smooth running of engine" and the values of all injectors were oscillating between about -.8 to .8, but on injector 5, it was always about above 1.5. not sure what those values mean.
Thanks, I'm definitely going to order the torn hose today. I actually replaced the drivers side one last year.
But I'm still not sure that is the issue. I do know the xentry tool pretty well and last night I was playing around more and still not exactly sure how I test the injectors. If I run the injector test under ME ECU, it just seems to actuate each injector on/off which does not real tell if the injector is running optimally.
But two things I found that I would also like to ask about. First I could not run the "test engine under load" test because the air intake temperature was always too high. Also I have a P026a00 code (the efficiency of the charge air cooler is not sufficient). This code can not be cleared. It is NOT showing as a current fault, only a stored fault, but it won't clear out.
Is it possible I have a bad air intake temperature sensor that is reporting high temperature? Would this cause the engine to run rich? I'm guessing that when I go to clear the p026a00 code it is just getting set again .
Just an update, after removing the engine covers I found that the intercooler coolant overflow tank was empty. Add coolant and the IAT came down to 125F but after stopping engine, coolant started leaking out the bottom of the car. Have taken it to my Indy to find the leak and fix it first. Then will chk the ltft and do more diagnosis if there is still an issue
More info. So since the last post, the intercooler issue is resolved and now the IAT temp is proper. However, the car was still running rough and LTFT1/2 are still negative with LTFT2 very negative. Next I took the car to a well known Mercedes tuning and repair shop. They diagnosed and told me the injectors are probably fine and that spark plugs needed to be changed. I went ahead and did those as the car has 65K miles. No change in LTFT1/2. After doing a lot of research, I noticed that the left o2 sensor (downstream) values did not look right so I went ahead and changed that. This actually has made the car run a lot better, but still there is no change in the LTFT1/2 numbers. See the screenshots from Xentry. After changing the O2 sensor, the left downstream O2 sensor waveform (blue line in the image) has gone from being a flat line around 150-200mV to being this oscillating waveform (I thought it should be flat around 500mv). So the car is running better but this waveform does not look right. Also, the right O2 sensor waveform (pink line) is completely different from the blue line which does not seem right.
Also, if you see the lamda control screenshot, you see the exhaust gas temp downstream on the left side is out of the accepted range and not in line with the right side temperature. So even the car is working better, I think there is still something wrong here. Any ideas? Catalytic converter? Still an injector problem? One thing is that after replacing the O2 sensor on the left side, I did not pull the battery terminal to reset the LTFT values. Do you think I need to do that?
Another potential item to check is the engine wiring harness for oil intrusion. My '13 GL550 with 67K miles started out with a CEL for the O2 downstream sensor. Took it the dealer and they found motor oil in the O2 wiring connection. They traced it back to oil leaking past the cam position sensor wire connections which then migrated oil through the entire engine wiring harness all the way back to the O2 sensors. Oil contamination will cause weird electrical things to happen. They replaced the entire engine harness, ecu, fuel injectors and several sensors ...all contaminated with oil. Lets hope this is not your problem!
BLK GL550, Thanks for the post. I don't think there is oil contamination, because I did not see oil on the O2 downstream sensor that I replaced and I looked at the cam position sensors and did not see any oil around there either. But having said that, I did see green grime on the side of the transmission body near the left exhaust and CAT and that looked like it was from the coolant leak I had. I don't know if any of this got into my upstream O2 sensor, so I am thinking of replacing that.
Before I replace, I had a question: Does any one know what sensor reads the "exhaust gas temperature downstream of left CAT" that is shown in my picture above from Xentry? That is showing out of range and I am wondering what sensor would give me that data. Because I don't think there is an EGT sensor in a gasoline engine. Maybe it is that sensor and not the upstread O2 that is my problem?
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
