clk320 power loss at kick down or WOT = limp mode
 

Hi Guys,

First off I wanted to say thanks for a great site, with a really helpful community.

I aquired a CLK convertible a week ago with a few niggles that I have been working through, and some of the threads on this site have been a real help.

I'm pretty much at the end of my list now, and I need to try and diagnose a power loss issue.

I'd really appreciate some help before I send it off to spend more money and have the codes pulled and a full diagnostic check done (it's a 1999 EU car and does not have ODBII so my scanner will not work).

- Car at 89k, I just changed all 12 plugs with premiun NGK plats, dropped oil and changed out filters (the problem was present before the service as well)
- Car appears to run and respond fine, a slight 'lumpy' tickover though
- Car smells rich, the vapour from the exhaust smells like it is permanently in 'cold start' even when it's been running for some time and is at running temp
- When car is warm (I wouldn't tell if it does this from cold as I do not want to destroy my engine :)), if I am travelling at speed and try to use kickdown or full throttle the car will start to pull and as the revs increase it will then go into limp mode
- Throttle response is then terrible, power is seriously down, car will linger around 2-3k and will not pull above this.
- Pulling over and checking in neutral reveals terrible throttle response, as much as 50% to three quarters to get the car to rev or respond
- Stamping the throttle in neutral has no effect, the car nearly stalls
- Turn key off and on immediately and problem is solved, until you try to kick down or give full throttle at speed to overtake something
- Ran the car without the MAF connected, throttle response etc seemed identical, it had the same 'limp mode' issue when dumping the throttle at speed.

Now the induction pipe and connections seem perfect, I connected my trusty volt meter to ground (pin 3) and the output to the ECU (pin 5). Readings were erratic, in that at idle they would sit at 1.41 steady then drop to 0.8 and bounce around for a few seconds all over the place between there and 1.7.

After a while it would settle again, then it would fluctuate from 1.2-1.4.

Holding revs the voltage would go between being steady but have moments of severe bouncing up and down by some margin.

Turning off the car and burning off the wire then turning on ignition (without starting the car) the MAF would read around 1.01 steady. Other times it would read 1.01 and then bounce around from as low as 0.3 back up.

Tonight it sits constant at 1.11 without starting, a little high??

Anyhow, I am a little confused, at this point - perhaps I have over thought it. If the ECU is getting a reading from the MAF, even if it is out, at which point would it decide to throw the car in limp mode at high RPM? Will it recognize a massive fluctuation in the voltage to the ECU compared to the RPM and shut down to protect the engine?

Someone told me it could be transmission, but there is absolutely no lag in gear changes, all gears remain and it works completely fine until WOT and the car hits limp mode.


Any advice appreciated. My local Indy wants the same to pull the codes as it would cost me to get a new Bosch MAF (as I can get it at cost). So I am tempted to get a new MAF and then at least I know that the car should be fueling right?

Advice, experience and opinions appreciated.

Thanks,

I have power loss problems, it will be running fine then after i kick down and boot it, it then takes ages for the revs to catch up with the throttle position, as soon as ive got time im going to change the crank position sensor, im not mechanic but this is a weak part of our engine, many threads with this subject, hope it helps good luck.
Jim

The symptoms you stated do not indicate a problem with the CPS. Did you possibly mean TPS?

thats the one !

Hi Guys, thought I would report back as this may be use to someone.

It was the pedal value sensor, I replaced it and all is now good.

Yes crank sensor normally occurs when the car doesn't want to fire or stalls when warm until it cools down - had that on the porsche.

So, my list of symptoms and perhaps how you can narrow it down if it fails like mine did:

- Car drives fine unless you depress throttle to WOT for a few seconds
- Accelerator responds fine unless the above OR you stamp the throttle fully to the floor and let off (simulating a kick down situation in neutral, but letting off so you do not rev the balls off of the car)
- Throttle will only respond once error occurs by holding it down for several seconds and then it is a sluggish / poor response at bests
- If this occurs while driving, you have hardly any acceleration at all
- Turn off and back on cures problem straight away
- Fault does not tally with kick-down being pressed (you can click the kick down with your hand if you like then press accelerator and it's fine only until you put it all the way to the floor)
- Will do it whether the car is cold or warm (again way to test is quickly stamp your foot fully and let off in neutral, the car will not get chance to rev up and will not damage the engine)

A few more observations and important points. I originally mistook this fault for a faulty MAF. Reason being, the car only did it when I was cruising and went to overtake on a duel carriageway, then I had severe lack of power and throttle response - assumed car was going into limp mode, although no CEL or warning on dash.

Volt checking the Bosch MAF is unreliable, I did this and there was some spiking but after replacing even the brand new functioning Bosch MAF did this DON'T RELY on simply checking the voltage (unless I guess it is totally burnt out and doesn't give an output at all).

After hastily changing the MAF I discovered the fault was not to do with being at speed, the power output of the engine nor the gearbox, nor the temperature of the car, as it could be done in neutral simply by stamping the accelerator fully and quickly to the floor.

A key point here is the car WOULD rev above 3k RPM, indicating it wasn't in limp mode, however, when moving you would not know this as power and throttle response is so down the car would barely make 3k rpm. On further testing after discovering it was not the MAF given the accelerator pedal was depressed long enough at low speed the car would accelerate beyond 3k rpm.

The two voltage circuits and the 5v feed to the pedal value sensor were perfect when testing and actuating from the engine bay, so again you can't go on this, the fault must occur when the pedal is quickly depressed then the signal recovers. For some reason once the error occurs, even though the two output circuits show the correct voltage the ECU doesn't seem to recover until a restart.

Pedal Value Sensor in my case DID show on a code read.

PVS was my second guess, and I could have saved the code read money, but in hindsight it was good to get it done to check the car was otherwise healthy and to help pinpoint the issue.

I have heard however that not all TPS or PVS issues are logged.

I hope this is of use to someone.


Thanks,

Good to hear you figured it out -- thanks for the final diagnosis and logging your troubleshooting process.

Thanks for such a clear and descriptive article. I have the same issue with same symptoms and you probably saved me a lot of time figuring out what it can be.

Thanks mate