Hello, a friend of mine has been having this problem with his Merc and we're looking for info. He has a constant check engine light that is under powering the car.this is how it started

The car was not used for a couple of weeks after doing some tune up (new crank pulley/cylinder gaskets). Then the rims were modified to a wide staggered set-up 245-19 front 275-19 rear, it felt a bit slower maybe due to bigger rims. When he tried to open throttle a bit more it felt slower at about 4500 rpm(Kinda getting stuck) and the Check engine light came on between 5500-6000, the car started to misfire/hesitate. So he parked, switched off and on again and it ran normally no hesitation/misfire but felt very underpowered. I think this might be limp mode but am not sure

So we took it to the indy to check codes. We got error that..cylinder no. 4 is shut..crank pully sensor shut..and misfiring in cylinder no. 4..right cylinder bank shut. The tech thought it was just a trouble shoot and reseted the codes, the car ran great for a while. However, once you push it to wide open throttle you get the check engine light again.
Went back to the indy, changed both the coil and injector on cylinder 4 but we still have a check engine, however this time it's cylinder 2. So we did the same procedure for cylinder 2 but still the check engine was on.

The indy thought it must be the ECU, but after further inspection he believes it's the Multi point injection fuel system!!!

Well i think its either the Mass Air Sensor..or the Crank Position Sensor as it was the last thing i touched in the car?

 

did you touch timing in the car>? if you changed the cylinder head gasket you must have taken the chain off. if you did that make sure the timing is right. mis fire means that it misses the timing. and maybe a cam position sensor is going bad. did you remember to put all sensors in? My theory is that if you did somehitng to the timing the engine has less room to spark// if the timing is off and detonation at higher rpm's is likely.