MTBSully

Bought my 2006 E55 bone stock with 128k on it. At 133k I installed longtube headers with catless X pipe, 77mm pulley, DTK belt wrap kit, PLM heat exchanger and Bosch 010 pump, and a DTK ECU and TCU tune to wrap it all up. Car ran great. About 500 miles after install i got a CEL and a slight stumble under partial throttle. Pulled the codes and it was both upstream o2 sensors "Slow to respond". I thought it was strange that this happened right after install of headers, but alas it is a 130k mile car and o2s are wear items, so I replaced both upstream o2 sensors with Bosch units from FCP euro along with 16 new NGK iridium spark plugs. Codes went away and car ran beautifully.....until yesterday when the car stumbled pulling out of the work parking lot, and threw the CEL, same o2 sensor codes AGAIN. So clearly, something is up.

Any ideas? Possible vacuum leak causing the car to run rich? Anyone else have this issue? Maybe the tune from DTK is just garbage? Thankfully i ordered the sensors from FCP euro so they will be warranteed but i'd like to get to the bottom of the issue.

JohnLane

OP How are the O2 sensors 'fouled?' You mention both sensors are fouled which rules out an injector or coil issue.

Exhaust leaks on both banks of cylinders? Seems unlikely.

Oil? Fuel? If they are fuel fouled and all spark plugs are black I'd be inclined to point a finger at the software running the engine.

MTBSully

Well I assume that they are fouled in that they are both throwing the "slow to respond" code. No exhaust leaks that I can find at all.

coupesedan

remove and inspect

if it’s fouling that fast the engine’s probably running rich, warren buffett rich

jmb614

Are you datalogging with a wideband, or perhaps logging narrowband 0-1 volts on the primary O2's? If you vary RPM rapidly and watch the primary O2 voltages, they should switch accordingly in relation to variation of throttle input. Compare that to how quickly the wideband sensor switches, if they both show voltage changes roughly the same, in relation to changes in AFR, I would say the problem lies elsewhere than the sensors themselves.

MTBSully

Thinking about buying a wideband although I swore this would be a nice daily driver and here I am buying gauges for it lol

Bankroll

Check your fuel trims. That should tell you everything. Have you run any "leaded" fuel, like race, or Avgas?

E55Greasemonkey

Strangely after installing my long tube headers (had Kleemann's prior) my 50k mile front O2 sensors also fouled. I think it was either the high temp copper sealant that I used to seal the slip connectors on the exhaust, or the fuel rail dampener going bad. Check your fuel pressure at idle, if the needle rapidly fluctuates by 10 psi but smooths out with increased RPM's you'll need to replace it.

JohnLane

O2 sensors that throw a 'Lazy O2 sensor code' after giving it headers can usually be made to wake back up via the Italian tune-up.

When you give the car headers there is a lot more volume in the exhaust ahead of the front O2 sensors. That is a lot of tube to get up to temperature before heating up the O2 sensor enough that it is happily sending a reliable signal to the ECU. Think the 'Heater circuit' in the O2 sensor can get it done? Guess again. Drive the car like the Octogenarian and you can reasonably expect it to set the crybaby code.

In short.... You made a hotrod. Drive it like you hate it for best results.

MTBSully

Lol i'll give it a shot i typically do baby it around town most days haha.

jmb614

I've had to replace that fuel dampener before too. Having the primary O2 as close to the collector is preferable.

Also, using dielectric grease on the O2 connectors was a no-go for me. Car switched to a rich fuel map as it did not know how to fuel itself, subsequently chugging black smoke out of the exhaust. Pulled the neg. batt term., cleansed the connectors, hooked everything back up and she ran perfect. I dunno man, this car is really finicky with regards to LTH and O2 sensors.

AMG__POWER

I would take it to a dyno see how your tune is running