Misfiring 991 997.1

[brian.pilgrim]

Please can someone help!!!. My porsche 911.997.1 2007, keeps misfiring, the garage has checked for bore score, changed the timing chain, replaced a bent valve, replaced the wiring loom, spark, plugs coil pack have all been changed, it's been going on for 3 years. I'm going crazy. Please help !!!

 

[Motorhead]

Hi Brian,

Sorry to hear about your long-term problem. I suppose the first thing to ask is if your garage has run some Porsche-specific diagnostics [PIWIS or equivalent] to see if any error codes are flagged-up, since this is the most reliable and cost-effective way to track any problems?

If the misfire is associated with a particular cylinder you’d have to assume a spark plug or coil pack issue, but it seems as though your garage has taken that route without success. If a cylinder bank is involved [cylinders 1-3 or 4-6] a VarioCam solenoid usually is faulty. The problem could be fuel rather than ignition-related, in which case a dodgy fuel injector could be the cause, and you could try using one of the proprietary injector-cleaning products to see if that helps.

Jeff

 

[brian.pilgrim]

Hi Brian,

Sorry to hear about your long-term problem. I suppose the first thing to ask is if your garage has run some Porsche-specific diagnostics [PIWIS or equivalent] to see if any error codes are flagged-up, since this is the most reliable and cost-effective way to track any problems?

If the misfire is associated with a particular cylinder you’d have to assume a spark plug or coil pack issue, but it seems as though your garage has taken that route without success. If a cylinder bank is involved [cylinders 1-3 or 4-6] a VarioCam solenoid usually is faulty. The problem could be fuel rather than ignition-related, in which case a dodgy fuel injector could be the cause, and you could try using one of the proprietary injector-cleaning products to see if that helps.

Jeff

Thanks Jeff I'll check with the garage about the vario cam solenoid, all coil packs have been changed many thanks for your suggestions

 

[Motorhead]

Brian,

You mentioned that a bent valve was replaced, which is a bit of a concern … especially if the misfire is associated with that cylinder. Do you know why it was replaced?

Note that a proper Porsche diagnostic check should identify any issues with the VarioCam solenoids.

Jeff

 

[brian.pilgrim]

Brian,

You mentioned that a bent valve was replaced, which is a bit of a concern … especially if the misfire is associated with that cylinder. Do you know why it was replaced?

Note that a proper Porsche diagnostic check should identify any issues with the VarioCam solenoids.

Jeff

Jeff I'm getting a bit despondent about the independent porsche mechanic I'm using, I'm getting a second opinion on Monday and will let you know the outcome. Thanks

 

[Motorhead]

Good idea Brian, but just to say that it’s worth approaching a reputable Porsche Independent who should have the necessary experience and diagnostic tools to help you.

Note that this isn’t really the appropriate section for your post because it’s for the air-cooled 911s, and there’s a dedicated section for 997s on the forum where you should get a better response:

997 (inc. turbo)

www.porscheclubgb.com

Jeff

 

[Peter_Bull]

Thread moved to 997 area.

 

[brian.pilgrim]

Thread moved to 997 area.

Many thanks Peter!!!I'm not that computer literate!!!

 

[ianthow]

To echo Jeff's advice, "it’s worth approaching a reputable Porsche Independent who should have the necessary experience and diagnostic tools to help you".

A competent mechanic with a decent multi-manufacturer diagnostic tool will be able to read sufficient codes to determine which cylinder is misfiring and possibly also any electrical anomalies detected. If the misfire is intermittent and on all cylinders on one bank, it would point to the Variocam solenoid hydraulic valve failing.

The bent valve and timing chain replacement could be connected and be the result of an excessively worn chain and tensioners/guides or a previous IMS bearing failure. You mention that "the timing chain" (singular) was replaced. There are separate chains for both banks, were both changed?

Yours is definitely a case where taking the car to reputable, recognised, Porsche specialist is essential.

 

[jmaddox]

As others have said if it is a general misfire on one of the banks then it is likely to be the solenoid on that bank. This is quite a common fault and I am surprised this hasn’t been changed already by your mechanic. It needs proper diagnosis via a scanner and is not too expensive. Good luck on sorting.

 

[Red997C2Sport]

I can recommend a fanstastic specialist, called AMS Porsche, in Hertfordshire if you are nearby.

 

[brian.pilgrim]

Hi all I'm trying to attach the photos sent through what's app. But failing miserably. It's been on the computer. Which shows a misfire from every cylinder, apart from number 4, various sensors are giving false readings aswell. He says the next stage is to carry out a compression test when it's cold. Which I think is just a waste a money. Because everything points to a electrical problem. But I'll go with him for now he may find something

 

[brian.pilgrim]

I can recommend a fanstastic specialist, called AMS Porsche, in Hertfordshire if you are nearby.

Thanks but it's a bit of a distance. I'm in West london

 

[Motorhead]

Brian,

Although a compression and leak test will be useful in verifying that all’s well with the valves, pistons/rings and head gaskets with all the cylinders, I’m not totally convinced that it will move you forward very much with your problem given what you’ve told us about all the misfires and apparent sensor faults, all electrics related.

You’ll have noticed that we’ve been banging-on about making sure that any diagnostics used are of Porsche dealer-level [PIWIS] which provide much more detailed information compared with general diagnostic testers used by many garages. Moreover, it’s essential that whoever is conducting the test has the necessary skills to interpret the results correctly.

Jeff

 

[ianthow]

The fact that there are misfires on all but cylinder 4 and the history of a bent valve does raise a question whether other valves may be slightly bent and not closing fully. This would result in low compression.