Mo420

Hi all.

New member here, just bought a beautiful 2007 CLS550 earlier this month. Vehicle has 99k miles on the odo with two previous owners and have been well maintained by the local indy.

The 5.5L M273 V8 is amazing and the power seriously addictive, especially coming from my previous daily beater 2L Toyota. Anyway, on to the major issue I have been facing - I've bought the car knowing from the previous owner that there is an intermittent power loss issue.

After 3 weeks of driving the car, I've now managed to isolate the scenario when the loss of power happens/will happen. It will happen independent of speed, throttle position, engine temp, RPM. So the issue goes whenever I maintain steady constant throttle position, say cruising along the motorway, and keep the throttle constant for more than 10 seconds or so, the engine will immediately feel like its loosing power and drop RPMs slightly, and wont accelerate no matter how far I push the gas pedal - it will downshift however and the RPMs will raise, but it wont gain speed/ barely gain speed (not sure if this is limp mode?). No CEL comes up. The common factor is it will happen after around 10 seconds of maintaining constant throttle, doesn't matter if its just feathering the throttle or full WOT. I can try to avoid the problem arising by regulating and just playing with the throttle all the time i.e. avoid constant throttle input for more that 2-3 seconds.

Some of the parts I've changed/have been serviced are as follows:
- New plugs
- New air filters
- New fuel pump
- New fuel filter
- Swapped new CPS to no avail
- Mechanic swapped throttle assembly also to no avail.

P/O has previously did airmatic conversion with Arnott's parts and also not long ago did a transmission rebuilt.

Strangely no error codes pop up using the scanner at 3 different local indy places. Running out of ideas now and any suggestions are very much appreciated.

unlukky

That could very well be the trans causing issues. Itd probably be worth looking at the MAF, but typically that will code misfires or 02 issues along with it (but doesnt trip the CEL).

Mo420

Thanks for the suggestions Unlukky Anything specific to the transmission to look at? This was one of my suspects and have sent it back to recheck the transmission work, mechanic assured me the trans is in order, fluids at right level etc. Shifts are silky smooth too and when the issue occurs, car does downshift and will even kickdown, just that the power is not there. But then again it does feel perhaps as if the torque conver is not fully locking up. Dunno if thats possible?

Will also look at the MAF, might consider driving with MAF unplugged. I did remember an O2 sensor code previously showed up in one of my quick scans but never came back once deleted.

Mo420

Hi all, just thought would post an update on the situation. So today I replaced my MAF with a similar part with identical part numbers from my W211 E250. Unfortunately problem is still there and car still hesitates. So I guess that means MAF is out of the question now.

One more thing I noticed, my idle is always constantly fluctuating. It stays at around 400rpm when warm but fluctuates plus or minus 20-30rpm always, and never stays stable. Any other ideas guys? Would vacuum leaks or the intake manifold flappy mechanism be causing this?

VII

I would go for some live data with DAS or similar. If no codes are being set you can look at actual values for anomalies.

Mo420

Hi VII, thanks for the great suggestion. Will try to do this so I'm now looking to get my hands on a good code/live data reader. I know there's loads of discussions on this already (I'm about to start my search) however do kindly feel free to suggest any good scanners that I should consider.

Just to update the other items that I've looked into over the past weekends:

1) Throttle body - cleaned the throttle body butterfly with TB cleaner. Car idles smoothly and stable now (yay!). However one thing I noticed, there's a lot of play on the throttle body butterfly - I can freely move the plate around 10-15 degrees without resistance, dont know if this is normal?

2) New 12V starting battery installed. The old battery just decides to quit one day without warning At least this rules out the battery being culprit to the power loss.

3) Sometimes car randomly (regardless of cold or warm starts, etc) hesitates to start. By hesitating I mean it takes longer to crank like 3-5 seconds. Most times it cranks and starts almost instantly. Any ideas? Perhaps dirty/leaking fuel injectors?

Other possibilities are now I think:
- O2 sensors
- Fuel injectors
- Throttle pedal & position sensor

The saga continues....

Mo420

Took the car to an indy yesterday who specialises in Euro cars. Their scanner brought up a number of "stored" codes, two of which have gathered my attention:

P0040 - O2 sensors upstream TWC [KAT] wrongly connected
P2237 - O2 sensor G3/3 left bank - voltage too high

I am thinking the P2237 code is causing the car to (wrongly) readjust to a lean fuel trim hence causing the car to lose power. Not sure how this relates to the P0040 code though

Cleaned the o2 sensor connectors today with electrical contact cleaners, one of them was quite drenched by engine oil due to a leak at the oil sump gasket (this is my next project). Took car for a test drive and still no improvements. Thinking of driving the car with the sensors unplugged next, is this safe? Any thoughts gents?

Mo420

Went ahead and unplugged the suspect O2 sensor (primary O2 sensor on passenger side of my RHD CLS) and took car for a drive. I was expecting bright CEL upon startup but to my surprise no CEL lights up at all and car drives 100% same as before. no changes what so ever. Any comments on this much appreciated gents.