Been working on a lean issue.

My tuner tells me the injectors are commanding max flow. Told me to check fuel pressure and that he thinks the fuel pump is weak.

Well I checked today and fuel pressure is at 78 at idle and holds between 65-78 psi between 2500rpm to redline. To my understanding this is totally normal. AFR ranges about 12.4 then trends lean to about 13.0 near redline.

Also on a side note, I received the tune for longtubes and the car ran LEANER than the stock ECU tune…okay, no big deal….I asked for a revision and was told “the injectors are already tuned for max since it’s a stock injector”

Starting to think this might be in the tune and not mechanical. Am I wrong to think this way? Just hard to believe the injectors are maxed out on a exhaust only setup when my old car was fine with 77 and headers etc

 

Try a different tuner. Your paying again but might be your only option.
Or....give Troy a call from MK Ultra he is very knowledgeable on scaling fuel injector flow rates.
He will have you send the tune to him to open it and see what's is going on if anything.

 

I’m thinking that is what it’s coming down to. I really don’t want to pay for another tune with the hopes it fixes it. If a tuner wants to look at the tune and can fix it based on the tune I don’t mind paying however.

 

Fuel pressure is supposed to be at 5.5bar/ 80psi when starting the car and then sits at 5.3bar/ 76psi. Yours is too low, I suspect one pump is dying in your case.

Did you measure the pressure when the car is standing or under driving conditions?

 

did you read anything I wrote? LOL

 

I'm not sure if I misunderstood something, but you said your fuel pressure drops as low as 65psi. The fuel pressure should stay stable at around 80psi, even under load and when driving. If it doesn't it's either an issue with your pump, pump wiring, fuel damper or everything. The fuel system on these cars is a weak spot and has been revised by Mercedes on the 2006 models. There's enough information out there documenting this.

 

So I did 2 pulls with the gauge hooked up. The 1st pull it dropped to 65 briefly toward redline.

the 2nd pull it stayed solid at 78 all the way to redline.

BOTH pulls the AFR was lean and didn’t fluctuate