Shawn Stanford

I bought a set of Denso coils from Pelican.

I wouldn't worry about the footwell wires at this point. I'm still not clear on if you checked the wires running from the ECU to the coils. Those wires sit on top of a very hot and very wet motor; I could easily see them deteriorating in a near 15 year-old car. Before you buy more coils, I'd check those wires and the connectors to make sure they're still carrying a good signal from the ECU.

That doesn't sound right to me. If the timing was off, it shouldn't clear up at 3k.

MisterMisfire

I've simply ordered new connectors and I'll get them fitted next week and see how that goes. I know that three of them are brittle so you're probably right about that being a contributory factor.

I'll let you know how it goes after itsi done.

I'm still unsure about this timing chain. This independent Porsche garage was absolutely sure it was that.

I guess we'll see....

MisterMisfire

just been for a drive and hoked up my OBD reader to an app on my phone called Torque.

These are the readings from the bank 1 and bank 2 lambda/oxygen sensors behind the cat (sensor 2). Looks like the bank 2 sensor has a problem and that coincides with my cylinder 6 being the main one to show a fault.

As soon as there is a low voltage spike like this the car misfires.

Think I've found the problem?

Shawn Stanford

One way to find out. And cheaper than having the motor torn apart!

MisterMisfire

I just bought a product called Cataclean and used it as per instructions. It's meant to clean O2 sensors and catalytic converters.

Well, the O2 sensor 2 on bank 2 is awful now. Hideous permanent misfire. Loss of power. Just stuck 85 litres of fuel in to try and wash this stuff through. But there's no doubt that this O2 sensor has issues.

Time to buy a new one and get it to the shop.

Shawn Stanford

O2 sensor should be a pretty easy driveway fix.

MisterMisfire

Got it going in for analysis in the morning. Did a long drive today and took two screenshots of the sensor 2 both banks. one shot is at a steady 60mph, the other at 70mph.

Engineer thinks that it might NOT be the O2 sensor as it is simply showing that a misfire has taken place, and is not the cause of the misfire.

I just need my car to work!

Shawn Stanford

Any updates?

MisterMisfire

Hey Shawn,

I was tempted to update a few days ago but I reckoned it was best to cool down first.

Doesn't it just hack you off when you take your car to a garage, tell them what work you want doing them go back a day or two later and they've not done the work you asked but did something completely different?

That's exactly what happened.

They decided that they know best and instead of doing the O2 sensor they decided to change the spark plugs. And then code P1134 came up which is.......O2 sensor, bank 2, sensor 2!

i don't tend to go nuclear but I came close.

I've ordered the part and when it arrives I'll take it somewhere else.

They did say that when the car is revved high, if you take your foot off the accelerator there is some chain slap to be heard if you've got your head in the engine bay. So they think timing chain, but I want this O2 sensor changed first.

MisterMisfire

Car going in on Tuesday to have the O2 sensor replaced and also all of the coil pack connectors.

Will let you know if a miracle happens!

MisterMisfire

Car is back - they replaced the coil pack connectors as requested. Nothing wrong with the signal but a few of them were cracked and split.

But......the cat on bank 2 is dead. It isn't the O2 sensor. So I have ordered a twin cat replacement and have had to order the gaskets from Germany - total outlay £300 for parts. They'll fit the new cats and replace the sensor whilst they're at it.

Spoke to the engineer. After reeling off all of the parts replaced (and he is not convinced it is a timing chain issue) he thinks it might be a fuel injector problem in cylinder 6. So when they put the new cats in they'll take the top rail off and squirt some carburettor cleaner in injector 6 and then try swapping it out with another injector and see what happens.

Oh, isn't Porsche ownership fun!

nodoors

I do not believe post cat O2 sensors will have any effect on how your engine runs. They are strictly for emissions. You should be watching the primary sensors for fixing/tuning this issue. Run a graph of the readings on bank 2 sensors 1 and 2 for comparisons. A clogged cat would probably not be as intermittent as you were previously describing this issue to be, but after running your cataclean stuff, it does sound like the cats/sensors are gunked up now. Which cylinder was misfiring the most and what did the plugs look like when they pulled them?

MisterMisfire

There is a zombie thread that I resurrected on Rennlist that was a discussion about the O2 sensors. Basically, the post-cat sensor does feed into the algorithm for fuel mix. But, yes, you're right in that the major player is the pre-cat sensor.

If you look above, I posted bank 1 and 2 sensor 2 live data graphs. The bank 1 sensor 2 shows the expected trail. The bank 2 sensor is erratic - more than likely following the bank 2 sensor 1 trail. I have an iCarsoft Por II arriving this week and I'll certainly run the graphs of bank 2 sensors 1 and 2 and expect to see them following each other. The engineer today said that is what he saw when he had it hooked up in the workshop.

The Cataclean was awful and immediately caused and not cured a problem. I am running a tank of fuel through (luckily I have a lot of children who need shunting around the country at this time of year) and hope to get the crap out of the system. The plugs were slightly oily and there was some brown staining beginning to show on the insulator part of the plug. I am afraid that I did not get a photo of them, but the engineer said that this was from poor timing and that the ignition was happening beyond the top of the cycle.

The worst offender has always been cylinder 6. I've swapped coil packs and plugs all over the place but invariably cylinder 6 comes up. Mysteriously, at 3000 rpm all misfire counters go to zero. That can't be timing chain....

nodoors

You should check into a vacuum leak since the misfire goes away at higher rpms. That is a really important piece of information. I am not familiar with the VR6 engine, but can tell you from experience that a leak can make one cylinder act up much more than others. Have you done a compression test yet?

MisterMisfire

The independent Porsche garage that I initially went to told me that there were no compression issues - I don't know if they did an actual test. They did replace one of the air inlet pipes which had a slight leak but I did a basic test (I removed the oil cap whilst the car was running and it misfired like a dog) and it seemed to indicate no major air leaks.

That said, I have recently been getting an exhaust fume whiff in the cabin from time to time.

I am hoping that the injector is the culprit, but if it isn't that then I'll have to chase around and tru and find the air leak.

I took it for a drive earlier and it seems to have a second burst of acceleration after 4000 rpm. I was doing 106mph in 4th gear and only changed up because I lost my nerve!