NEED HELP on Boxster S Odd Running Problem
 

Hello everyone. I am new to the site and I am also a new Porsche owner and picked up a 2005 Boxster S (3.2L) that has a very odd running issue that I need some directional help with. I have been looking for others that had the same problem, but have found anything like this. Just an FYI, I have worked on German cars (Mercedes and BMW Master Cert) for over 10 years, but I do not sling wrenches full time anymore. With that being said, this is the problem and what I have tested.
The car is very hard. When it starts, I can get the revs to climb, but not very fast. Then when it gets to around 3000 RPMs, the will engine will cut off for about 0.5 seconds and then light back up. It keeps doing this the whole time that it runs, but I have to pedal it to keep it alive. While it is lit, I am getting a MIL light and also the green light for the soft top being open.
When the car does this surge thing, both of those lights cluster lights are lit, but while the car is cutting out, those lights will both turn off and the other lights around the car will dim as well. After the RMPs fall for that half second, the MIL and top light will come back on and the car will come back alive. Also, when the car cuts off, it is very abrupt. Not like it is losing fuel pressure from a fuel pump cutting out, but more like it is shutting down. Also, there is not shutter when it cuts out, it just turns off.
FYI: The previous owner installed a new cam sensor and I think that it was on the driver’s side but am not 100% sure.
So what I have checked and has been done so far is this:
With an OBD2 scanner (Bosch Blue Tooth with cell phone App), I was able to pull 3 codes from the system. All fault codes have been cleared and they will keep coming back.
1. P0335 – Crank Position Sensor A Circuit Range / Performance (Hard Fault)
a. Crank sensor has been swapped and the problem has not changed.
2. P0341 – Cam Position Sensor A Circuit Range / Performance B1
3. P1502 - Throttle Jacking Unit, Spring Test – Above Limit

Other Diag work done:
I figured that the sensors with circuit range faults could be related to the power surge, but am not sure. I have checked and replaced the DME relay because I thought that the relay may have faulty contacts and the amp load was too much for the relay to handle causing the system to drop out. (No Change)
1. I used a Snap-On graphing meter (Vantage) and scoped all of the powers and grounds that are running through the ECU. There were no drops or flux
2. Checked car voltage while it was running and I think I was getting around 13.8v – 14.0v DC and 0.12v - 0.08v AC
3. At the ECU, I checked injector pulse, coil pulse. I found that I am not dropping ignition, but I am dropping injector output.
4. I tried to pull the OBD2 live data, but can only do so when the car is not running. While it is trying to run, the scanner will say that it can’t pull the PID data from the ECU. But when it is not running, all of the data looks to be ok.
5. I also checked for vacuum leaks and was unable to find any that I noticed.
Also, I don’t know if this matters, but the boot seems like it was dry, but from looking at the carpet, it looks like the top leaked a little because the carpet has that looks like it was wet before look and feel. More so on the pass side, but a little on the drivers.

Thank you anyone for your help and direction on this.

P0335 says you have an open circuit (read no signal) from the crank position sensor; the car will not run until this is fixed.

P0341 indicates that bank 1 cam sensor has an alternating signal, probably because it needs the CPS signal for reference.

P1502 says the egas throttle is not seeing the CPS.

Thank you JFP for your response. I have checked the crank sensor and I am getting a crank signal from the sensor directly at the ECU. I tested by back pinning it at the ECU.
I can understand that the cam sensor could be thrown off because of the crank sensor not being correct.
What are you thoughts on the surge. Plus, the MIL cutting off at the same time that the car cuts off and then lights back up when the car comes back to life?
I am starting to think that there is a short inside of the ECU and that may be the cause of the problem.

If the crank sensor is working, but the DME is throwing the P0335 code, it is not seeing the signal for some internal reason.

I would agree with that. That is why I am thinking that the problem may be inside of the ECU. I am looking for a place that I can send it to so that I can have it tested.

Or get a known good used one from Woody ? "itsnotanova"

You say you have a light dimming issue. If that's the case you either have a bad battery or an alternator or voltage regulator issue. Have you checked the voltage off the battery terminals when shut off and when idling/running. The first needs to be around 12.5V and the second in excess of 14V.

If power is low all kinds of weird symptoms will arise.

I would like to do that, or at least send mine off to get tested. I have been looking for a place to send it to, but no luck so far. Also, I can't just run up the road and grab another computer. They don't have many Bosxters in the junk yard. LOL

I have checked all of the power regulations. I get the same readings at the battery and at the ECU.
At rest = 12.5v DC
Running = 13.8v - 14.1v DC / 0.05v - 0.08v AC

Voltage at idle should be constant at 13.8 volts DC with all consumpters off. Do you have fluctuations?

Regards, Markus

Clean the battery terminals and post leads, then then reattach them. Check the ground strap connection to the chassis. If it is corroded, clean it and make sure you have a good electrical connection. Is there any chance the serpentine belt is slipping? There should be no dimming of lights, ever, when the engine is running.

The infamous (Search) "Y connector" corrosion ?

Or maybe a shot voltage regulator that shot the ecu.

Regards, Markus

I am not getting any real voltage flux when I check it. I am even getting a very low A/C voltage flux of around 0.05v - 0.08v. When I say that the lights dim, it's not by much, just something that I noticed.
I checked the connectors at the ECU and also checked to see if any of the magic smoke had come out of the ECU, but I didn't smell anything.

As for this "Y Connector" you are talking about, I don't know about this one. Can you share some more info on this please?

My big wonder is why the ECU seems like it keeps shorting or resetting while the car is running. It seems like the ECU goes into a engine startup mode and the car will fire, but then switches to a run mode and then it blanks out. Kind of like going from Open Loop to Closed Loop, but it never gets hot enough to go Closed Loop, so that couldn't be it.