Hi All and thanks for all the wonderful tips and help. I have been reading through most of the post here and have learned so much about my car, both good and bad. I have had a bad run with my 850 GLE (b5252) and having owned it for 3 years it has only seen about 10 months as drivable. I have replaced the engine and just recently the auto trans as the previous owner was apparantly not nice to it and liked towing a huge heavy trailer on the freeway with her. That however is not my problem now. I have been working towards getting it back on the road and one of the reasons it was retired around 18 months ago was the fact that I was losing top end power. I have done the usual plugs, leads, cap and rotor. I have run a couple of doses of injector cleaner through the fuel tank. I have a service manual that explains all the codes but this is of no use as the ECU is reporting no faults with the fuel or electrical system. I cannot get the engine to exceed around 4200 rpm. Before I replaced the ignition parts it was around 3700 rpm. While driving it runs OK but once the revs reach 4200 RPM the engine power drops away radically and the car begins to decelerate. While sitting in P or N the engine does the same thing. Strangely it will pull up a steep hill even accelerate up the hill (this is a long hill) and if I hold the car at 4000 RPM it runs fine, as soon as I try to accelerate further it will do the same thing again. Any suggestions would be great. I need to get this sorted so I an get it roadworthy, registered and back on the road.
Many thanks
Andrew

 

My guess is camshaft sensor has a problem. I'm sure Tech has a better idea though - AB

 

Check timing
Fuel pressure. (while it is doing it if you can)
Anything else happen at the same time?

 

Hello Andrew,

Greetings from Chicagoland.

In addition to Mr. B1mmer & Mr. Tech's advice, it wouldn't hurt to check for restricted exhaust system, as well as having the injectors removed & power-cleaned. Has the fuel filter ever been replaced? Is the tranny fluid at correct level? Also, double-checkforrestricted induction system.

Engine troubles are complicated and sometimes it is impossible to tell what's wrong, unless we can actually take a look at it and do some tests.

I'm sorry I couldn't give you better ideas at the moment.

Best wishes,


JPN

 

I have had a chance to investigate a little further. While in N or P the engine will still max out at 4200 but when it settles back to idle it idles rough. I have replaced a few vacuum hoses that looked old, the fuel filter and air filter with no benefit. I seem to have good fuel flow and I am not losing fuel pressure from the fuel rail even overnight, also if it was a fuel delivery problem would it not lose power at lower revs while pulling up a long steep hill placing a higher fuel demand here than at rest in park? Transmission was giving an S1 solenoid fault and a slipping error prior to being "stored" but the slipping was obvious when you drove it, it now pulls beautifully.
if any of the sensors were at fault would it be normal to get an error code?
I have just removed the airbox and ran the engine for a few minutes during which time I did not have the airbox sensor connected ( Fenix 5.1 ) which I think is the air temp sensor. The ECU did not report any errors and the engine ran just the same but I did notice that at high revs the engine noise did sound "restricted" (hard to explain what restricted sounds like). Would it be OK to run the engine with the exhaust pipe disconnected just before the catalytic converter so I can test JPN's suggestion RE the exhaust restriction.

Thanks in advance
Andrew

 

Absolutely. It will be pretty loud, but will be fine. If you have downstream catalytic converter (after the cat) then you will likely throw a CEL. - AB

 

Yes you can run it with out the pipe on for a short time.

 

Somewhat belated reply but a resolution none the less. JPN was absolutely correct. The catalytic converter had become blocked. So the good news is that for a truly ludicrous amount of money I was going again. Sadly My first 850 has now been retired. 320000+ km and a very inconsiderate first owner has seen it die, what I believe to be, quite early for one of these. I so loved the beast that I now have 2 more, one for driving and the other as a project. The future is looking bright.

 

Glad it is fixed now!!!

 

Bright future is always welcomed!


Happy New Year,


JPN