Miss firing on bank 1.2.3

[CRC]

It's just suddenly struck me how the system works.

Imagine the exhaust cam fixed in place and connected by a chain to the inlet cam, which is free to rotate.

Pulling up on the chain would cause the inlet cam to rotate one way, and letting go of the chain would cause it to rotate back the other way, assuming that there is some other chain tensioner providing some tension to it.

As the solenoid must be switched by the ECU, presumably it should be possible to find that connection in the loom and check continuity to earth to determine if the coil is OK or not. It's bound to be a a digital ON/OFF signal. 

 

[CRC]

In fact, that does seem to be the case.

The wiring diagram for the early 2.5 engines show the connections to the ECU as

Bank 1 - Terminal 52, Cable colour GR/RE (Grey / Red)

Bank 2 - Terminal 25, Cable colour GR/BR (Grey / Brown)

[edc]

The Porsche testers can measure cam deviation. That might give some insight as to which one is the problem. 

[Boxstclever]

CRC is right in his explanation of how the variocam timing works.

 

The cam deviation measure is the difference between the inlet and exhaust cams and is measured by bank.

So, for example, when measuring bank 1 it may show a deviation of +27deg's which would indicate an issue in the timing of the inlet camshaft relative to the exhaust camshaft on bank 1.  I think the tolerance is +/- 9 deg's at idle (don't quote me on that).

 

As the codes are indicating mis fires on 1-2-3 cylinders here, we know it's bank 1.  What he needs to find out is the cause.  Is it the variocam solenoid or the variocam actuator.

 

I have the same issue on my car after I rebuilt the engine, (and spent way too long timing it). My cam deviations were less than 1 deg.  after a couple of hundred miles, it started to develop an erratic idle, but not all the time.  When I plugged in my hooky Durametric, with a smooth idle, the deviations were still negligible, but when plugged in when the idle was rough, the bank 1 deviation was way out.  

I also need to get it to a specialist to properly diagnose the issue, as mine is random as to whether it does it or not.  I want to know for sure that it's the solenoid before buying a new one.  Fingers crossed it's that rather than the actuator as that's even more expensive and harder to do.

 

Solenoid requires the cam cover to be removed and then it's two small screws.  Actuator requires cam cover and then camshafts to be removed!!

[CRC]

2 hours ago, Boxstclever said:

 When I plugged in my hooky Durametric, with a smooth idle, the deviations were still negligible, but when plugged in when the idle was rough, the bank 1 deviation was way out. 

Do you get random misfire error codes coming up or are they vario cam error codes, (which I've never seen but were mentioned on the invoice when mine had the parts replaced ten years ago)?

This seems such a simple system, it's hard to imagine much that could go wrong.

Judging from the diagrams, the solenoid seems to be a very straightforward pushrod that probably pushes out when the coil is energised and retracts when the coil is de-energised.  Logically, you would think that they would have it arranged so that "coil on = pushrod out = high rpm mode", as most engines would spend a lot of time in "low rpm mode", so the coil is de-energised and coil life would be extended.

Having said that, the invoice on mine when it had the problem, seemed to indicate that the solenoid fuse blew immediately on start up, so maybe it's the other way round?

It would be good to know which way it has been configured to operate.

 

 

[½cwt]

Try this for background on the VarioCam system used up to 01 model year.  This is a step change system.  A more advanced VarioCam Plus system came in from 2002 which has a range of action.  One the reasons you need to match an engine to the electronics from the same year:

How VarioCam and VarioCamPlus works - A Primer - 6SpeedOnline - Porsche Forum and Luxury Car Resource

 

[CRC]

That's brilliant, thanks for that link. It immediately cleared up something that was beginning to puzzle me as I was assuming that the piston applied force to both top and bottom chains, but this shows that it actually controls the position of the tensioner itself.

Was also surprised to learn that it cuts in at 1500 rpm, as I always thought it was higher up the rev range 

[½cwt]

16 hours ago, CRC said:

That's brilliant, thanks for that link. It immediately cleared up something that was beginning to puzzle me as I was assuming that the piston applied force to both top and bottom chains, but this shows that it actually controls the position of the tensioner itself.

Was also surprised to learn that it cuts in at 1500 rpm, as I always thought it was higher up the rev range 

Looks like it was lifted from the Story of the Boxster by Paul Frere, out of print but I got a 2nd hand copy, good book.

The second 'kick' at about 3000 rpm is the butterfly in the induction system opening to lengthen the intakes.and improve torque with the faster air flow.

[Boxstclever]

On 9/9/2021 at 5:23 PM, ½cwt said:

Try this for background on the VarioCam system used up to 01 model year.  This is a step change system.  A more advanced VarioCam Plus system came in from 2002 which has a range of action.  One the reasons you need to match an engine to the electronics from the same year:

How VarioCam and VarioCamPlus works - A Primer - 6SpeedOnline - Porsche Forum and Luxury Car Resource

Interestingly, This mentions that oil temperature is used...

"the system in the 968 and Boxster are similar in operation, the only added sensor is an oil temperature sensor, which is required so the actuation RPM can be raised when oil temperature raises to the point that oil pressure drops off."

My car is also throwing an Oil temp sensor code.  I wonder if it could be the issue.  Worth checking it on yours too.

 

[Kay Pee]

I had misfire issues that appeared on my 1998 2.5 at around 100k with persistent misfire codes like P0300, 0301, 0302, 0303.

In my case it turned out to be a faulty variocam solenoid, the actuator was okay. I was able to remove the cam cover, remove cams and tensioner (variocam) with the engine in-situ. Little bit tight, but easy enough as my car was on a lift.

Without disassembly, check the resistance of the 2 variocams at the 2 pin connector (unplugged from loom). The open circuit (not plugged in) resistance of the variocam solenoids should be around 13 ohms. My bank 1 was a dead short, bank2 fine.

Other things to check are the chain tensioner (plastic) pads which are known to disintegrate. Mine looked well worn, so I replaced with new ones from design911 for around 20 quid. These pads are chain guides which are attached to the variocam actuator and move up and down to achieve the desired inlet cam timing variation.

[Kay Pee]

On 8/26/2021 at 12:33 PM, Steve Laming said:

...

Geoff took the car to a local garage with an ex OPC technician yesterday and he read and reset the codes. Again same codes, pointing to one bank miss fire. Possible variocam sensor issue (as Trooper88) said.

This time EML stayed off.

Geoff drove home and car is still good.

I have suggested doing about 40-50 miles today and refilling with V Power again to dilute whats in the tank.

So, is it a co-incidence that the EML light came on, or as research on Supermarket fuels shows, they have different additives when compared to BP, Shell etc.

...

@Steve Laming@Geoffcollyer I noticed after clearing the CEL (specialist did this for me using Durametric) it stayed off for a certain mileage/duration before coming back on despite the misfire (variocam bank1 issue) persisting. I don't think this is related to the fuel here.

[Steve Laming]

On 4/21/2022 at 1:20 PM, Kay Pee said:

@Steve Laming@Geoffcollyer I noticed after clearing the CEL (specialist did this for me using Durametric) it stayed off for a certain mileage/duration before coming back on despite the misfire (variocam bank1 issue) persisting. I don't think this is related to the fuel here.

Update. Sorry I don't think either Geoff or me updated this feed.

Variocam issue, diagnosed and fixed by eporsch.

The first mechanic said it might be this......however he changed all 6 plugs and coils packs. After about a day the CEL came back on, so was booked into eporsch. They had a long waiting list, so I think we both forgot about this topic !

Steve.

[TROOPER88]

20 hours ago, Steve Laming said:

Update. Sorry I don't think either Geoff or me updated this feed.

Variocam issue, diagnosed and fixed by eporsch.

The first mechanic said it might be this......however he changed all 6 plugs and coils packs. After about a day the CEL came back on, so was booked into eporsch. They had a long waiting list, so I think we both forgot about this topic !

Steve.

Do  I get a medal for being correct  

Glad it is sorted