Multiple misfires 1,2and 3
 

Hi. My car is a 1997 986 boxster 2.5. I have recently had the variocam solenoid on bank 1 replaced at my local Porsche main dealer. When I picked it up, I was told that I have a code for the pre cat oxygen sensor on bank 1 cylinders 1 to 3.have done probably less than 50 miles since I got it back and haven't changed the sensor yet. After a decent run, 60 miles or so, yesterday and after getting home, I got a CEL. After plugging in my obd2, diagnostic in I got the codes p0300, p0301, p0302 and p0303 multiple misfires, cylinders 1,2&3.
Is this because the sensor hasn't been changed yet or am I looking at an IMS problem.
The car has done 94440 miles but the IMS main seal was changed approx 6000 miles ago but is now out of warranty.
Many thanks

Man I expect someone to jump from headlight washers not working to the IMS. LOL.... The precat 02 sensor output adjusts the injectors fuel pulse attempting a stoichiometric AFR. If reading incorrectly this can cause a lean/rich condition. A lean mixture can cause misfires as well as holes in piston from detonation if severe enough. I'd say the pre cat 02 sensor bank 1 is a likely culprit.

Thanks. Job for the weekend. Fingers crossed.

Unless the other O2 sensors have been replaced ,it is prudent to replace all at the same time.
Make sure you get the correct part number - your Boxster uses different O2 Sensor to later M96.The Pelican Parts Catalog is correct.
While you are in there, check the coils for cracks(Search), oil in the spark plug tubes, old plugs and vacuum leaks.All potential/likely sources of misfire codes.

Thank you. I will check everything.

Hi 911monty. Thanks for your reply. I have changed the bank 1 sensor, total bugger to get out, cleared the faults but now I have misfires on bank 2 cylinders 4,5 and 6. Is this likely as I have changed bank 1 sensor with a bosch and it is not matched to the original and has thrown that one out. Not really sure how these things work.

Hey Walshie: Did you disconnect the battery to reset the ECU? The learned values from bank 2 will still be stored and need to be reset. Disconnecting the battery will reset to base map.

Hi 911 monty
No I didn't disconnect the battery. Will this have caused any harm. If it's not too late, how long should I disconnect for.

No harm. Takes about 5 minutes for residual voltage to drop off.

Thanks, job for tomorrow.. Will post results. Thanks again

Battery disconnected and left for 20 mains. When started I had no cel but tick over was still rough. It was like this for bank 1 before I had cel. I have ordered another matching oxygen sensor. Hopefully all will be good after this. If not then I will look elsewhere for the cause.

A bad O2 sensor should throw a bad O2 sensor code. Additional codes are thrown for trying to control too rich or too lean. I had misfire codes when the electrical connector fell off my variocam and the engine ran scary rough at times. I do have a different DME than you, but all the same I'd look seriously at the variocam.

Hi jamesp
I have ordered another matching oxygen sensor. This weekends job and have booked in with Porsche for a diagnostic test and check over as they fitted the variocam solenoid. This is being done next Friday
I will post results.
Thanks for your help

Why?
 

I first got a Lazy Sensor code on the front right sensor and replaced it. Maybe a year and 6k later and just for symmetry, I replaced the front left. 30k later and 5 years the original rear sensors are still there with no codes or issue.

So why should they all be replaced at once? Is this replacing 3 sensors that aren't throwing codes the smartest $375 you should spend maintaining a Boxster?

Hi, yes I agree. In the UK we only have 1 sensor for each bank so it's not too bad for piece of mind.

I am as frugal as anyone but ...
To decide on replacing an old sensor - first check the voltage pattern with Durametric or similar. That is more proactive than waiting for a code.
Once you replace the sensors you have eliminated that issue from future problem/code chasing. New sensors may last 10+years of normal driving.
There is the advantage of time saved from "while you are in there and have the tools/time off."
On my 2001 S Bosch sensors are $70 each x 4 .The older 97 .2,5 cars may be cheaper than that and they have only 2. Same reasoning for doing the coils/spark plug tubes also.
Getting a CEL while enjoying a drive is something I'll spend a little to prevent.I agree , it is a hobby not a financially logical issue.Ymev

I decided to put this here, rather than start yet another thread.

I'm chasing a hodgepodge of codes I'm popping since putting the car in for some "upgrades". Most of the upgrades were suspension related, others were maintenance, and still others were purely cosmetic. The few that I think could impact this:

Replaced MAF sensor
New catless Headers & high-flow-cat-midpipes.
Extended the wires on the O2 sensors so they'd work with the new headers / midpipes.

I cleared the codes and took it for a 10-minute drive. Here are the codes it popped for me in that time:
http://986forum.com/forums/uploads02...1582327111.jpg

So, focusing on the bank-1 misfires, I took a look at Camshaft deviation numbers, which are both sitting steady in the 1.3 and 2.1 range. So then I went and took a look at the O2 sensor voltages. I think maybe I have a problem there. Watch this short video:

https://photos.app.goo.gl/ZuMjwX6F1XhhYhQM8

You can see that the "After Cat" O2 on Bank 1 is acting quite differently from the other 3. I don't have enough experience in these parts to know which is correct and expected behavior, but I'm seeing 3 acting similarly and one outlier. We do have an O2 sensor code (P0130) but that's for "Before Cat" on the same side. I'm not sure what to make of all of this.
I did have to extend the wires on my O2 sensors to work with the new headers & midpipes I installed, And it's also possible one was bad to begin with.

Now the other thing I'm thinking: the misfiring cylinders (1, 2 & 3) are on the same side as the coolant pipe that I had spring a leak. I guess it's theoretically possible I've saturated the coils? possible... but how likely? I have some spare coils & plugs I could swap, but I'd rather not chase squirrels here.

Does anyone know what I should expect to see for O2 sensor voltages or resistance?

Any other place y'all would look?

The sensor before the cat should be cycling in a rapid sine wave fashion, while the one after the cat should be almost a steady voltage.

Thanks JFP! Should I see those values change commensurate with rpm, or temperature, idle versus under load, or do they cycle in the same range regardless?

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On doing some additional reading, I think it's reasonable to suspect both sensors on bank 1. Easy enough to swap sides and see if the problems follow.

I'll report back.

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