996 running lumpy

[911mark911]

hi I have just fitted a carbon eurocup gt twin k&n filter, to my 02 996, purely for sound rather than power, but the car is now lumpy on tick over and low speeds but gets a bit better further up the rev range, any ideas on why this is?
thanks

[EvoSlayer]

It's probably borked your MAF sensor, unplug sensor and see if there's any difference at tickover, alternatively replace stock intake and see what happens, but if sensor is already contaminated then that probably won't make much difference. You could attempt to clean MAF with IPA but tbh I've tried this in the past and generally found it a waste of time.

Just to add, I've been using a BMC panel filter in the stock airbox in the turbo now for a few years without any issues having had experience of various contraptions in the past which were nothing but a headache.

Edited by EvoSlayer on Monday 21st October 11:07

[Ian_UK1]

911mark911 said:

hi I have just fitted a carbon eurocup gt twin k&n filter, to my 02 996, purely for sound rather than power, but the car is now lumpy on tick over and low speeds but gets a bit better further up the rev range, any ideas on why this is?
thanks

Fitting any aftermarket filter housing / intake tract that replaces your MAF sensor housing can have unforeseen consequences.

1) Unless the replacement MAF housing is EXACTLY the same diameter as the original housing and
2) The MAF sits in EXACTLY the same place relative to the housing's sidewalls and
3) There are appropriate flow straighteners pre-MAF

then the air mass the MAF detects will have little or nothing to do with the actual weight of air going into the engine. The ECU will be getting false measurements and the engine will run like a bag of nails - especially if the MAF readings are beyond the corrective ability of the closed-loop system. It's also potentially very harmful to your engine at high throttle openings as the ECU goes open-loop (i.e. there's no correction applied to the mixture based on the Lambda probe signal as there is at part throttle.) This can allow the engine to run mad lean (great for melted pistons) or mad rich (great for scored bores as the oil is washed off them).

If you replace the original filter and all's well again, then the above applies. If you replace the original filter and the car still runs like cr*p, the it could just be the MAF died as you were replacing the filter housing.

If you want to run with a bigger diameter MAF housing, the car's ECU will need a complete recalibration to make sense of the altered MAF readings and/or a different MAF will be required that is designed to work in a larger diameter housing.

There's definitely a lot more to this airbox sh*t than people think!


ETA - Have you put the MAF in the new housing the right way round?

Edited by Ian_UK1 on Monday 21st October 16:31

[911mark911]

hi thanks for the info, I have now put the original box back in and all is normal a few answers are yes the sensor only goes in 1 way,
it is the same size hole, and sits roughly the same distance thanks will inc pic

[911mark911]

this is what I fitted purchased from the Porsche shop, thanks

[anonymous-user]

Send it back! :-)

[ooral]

Sorry to hi-jack the thread, I have similar lumpy/cold tick over on C987S, I fitted a K+N panel filter at the last service.... Any chance?

[Ian_UK1]

911mark911 said:

hi thanks for the info, I have now put the original box back in and all is normal a few answers are yes the sensor only goes in 1 way, it is the same size hole, and sits roughly the same distance thanks will inc pic

If we assume, for now, that the new intake part has been appropriately engineered and the MAF is therefore capable of sending meaningful signalling to the ECU from its new location; it would mean there's something else causing the ECU to have issues.

Some items we could consider:

1) Air leaks - When refitting the new intake, check carefully that the flexible connector between the intake and throttle body is properly seated and the hose clamps are seated correctly all the way round. Unfortunately, I can't remember if the standard 996 airbox has any vacuum connections to open/close the Helmholz resonator. If there is a vacuum pipe, it's essential it is blocked-off or you'll get an air leak directly into the inlet manifold.

2) You could try an ECU reset. This will clear any adaptation values stored in the ECU and let it adapt to the new setup. To do this, you simply remove the battery negative terminal for a couple of hours. Why 2 hours? When I owned a 996 a few years ago, I noticed that it seems to take a while before the old settings disappear from the ECU and a 10-minute disconnect just didn't reset everything the way we need.

Things to be aware of with a battery disconnect are: a) Don't close the bonnet whilst the battery's disconnected - the latch is electrically operated and a PITA to open again without juice! b) After you reconnect the battery and start the car for the first time, you'll get a dashboard full of warning lights. Don't worry about these, they'll go out after you've driven a hundred yards or so. c) One-touch window operation won't work until you've run the windows from top to bottom manually a couple of times. d) Any customised settings in the dashboard computer and PCM will need to be re-done as they'll have reset to defaults.

3) Before refitting the new intake, or doing the ECU reset, it would certainly be worth having a good specialist with either a Durametric or PIWIS check the condition of your lambda sensors and MAF. If either aren't within tolerance, it could prevent the whole system from working correctly. Having a proper diagnostic done is less expensive than just changing everything in the hope it will resolve the problem.

Be good to hear how you get on.

Edited by Ian_UK1 on Tuesday 22 October 09:58

[911mark911]

hi thanks for the advice, might try to do a reset the weekend and re-fit induction kit, just worried about codes etc, will have a word with an auto elec friend of mine about checking lambda's etc thanks

[Richard Hamilton]

No need to disconnect the battery to reset the adaption values on an '02 996. Just switch on the ignition for 60 seconds without touching the throttle pedal. Then switch off for at least 10 seconds. Job done.



edit - image added.

Edited by Richard Hamilton on Tuesday 22 October 19:49

[Rockster]

911mark911 said:

hi I have just fitted a carbon eurocup gt twin k&n filter, to my 02 996, purely for sound rather than power, but the car is now lumpy on tick over and low speeds but gets a bit better further up the rev range, any ideas on why this is?
thanks

No CEL?

Well, you got the sound you wanted, or thought you wanted. The stock intake is designed to deliver properly filtered air and in sufficient amounts the engine can develop its advertised HP yet all the while do so with a tolerable (and to many) a pleasurable intake sound.

You have messed with this in the quest to get some different kind of sound.

Sounds like (no pun) you were successful.

[911mark911]

hi thanks for the advice , just re-fitted the filter after cleaning the maf sensor, and letting it tick over for 20 mins then drove it for a few miles(the Porsche shop advice), seems to be a lot better now, still has a very little flat spot on initial pull away but runs smoothly now and yes sounds much better, the Porsche shop said they don't reset the ecu it will learn after the 20 mins thanks guys

[Ian_UK1]

Richard Hamilton said:

No need to disconnect the battery to reset the adaption values on an '02 996. Just switch on the ignition for 60 seconds without touching the throttle pedal. Then switch off for at least 10 seconds. Job done.



edit - image added.

Edited by Richard Hamilton on Tuesday 22 October 19:49

IIRC, this procedure just resets the throttle adaptation, not the ignition/LTFT adaptation. To reset the whole ECU to defaults, a disconnect is required

[Ian_UK1]

911mark911 said:

hi thanks for the advice , just re-fitted the filter after cleaning the maf sensor, and letting it tick over for 20 mins then drove it for a few miles(the Porsche shop advice), seems to be a lot better now, still has a very little flat spot on initial pull away but runs smoothly now and yes sounds much better, the Porsche shop said they don't reset the ecu it will learn after the 20 mins thanks guys

In theory, yes, the ECU is supposed to adapt by itself over a period of time. In practice, they don't always do so - especially the older Bosch units - so a full reset (battery disconnect) gives far better and more immediate results. I also forgot (in my earlier post) that you should indeed follow the instructions Richard posted above with regard to throttle adaptation on first restart.

The ECU reset / throttle learning procedures may get rid of the flat spot for you. I think you'll also be surprised how much better the car runs after you've driven it for a mile or two after the reset. Typically the engine will feel a lot more responsive and will have a little more torque across the rpm band.

I still recommend having your MAF and lambda sensors tested too. They don't last forever and all are critical to the proper running of the car.

[eastcoastporsche]

I fitted this mod to my 996 about 7 months ago..

When it was first fitted , say the first 200 miles , the engine was below par .. a bit drown in air.. what I mean is you put your foot down and more noise than action and a bit lumpy on tick over.

Super Plus unleaded is CRITICAL to this mod.. after I discovered running ordinary unleaded the car instantly goes off form.

Not sure how many miles you have done to allow things to settle in, ECU to work out whats going on etc etc once things settled down with my car.. its now well up power wise.. NO WAY would I put the old unit on.. Previous I was running a stock air box with K&N..

In a mag there was an article about a guy who had your trouble and fitted a MAF from a bigger engine.. But my car a 1998 C2 3.4 is on a standard MAF and runs really great.. and i mean that significantly smoother and more responsive and it was not a slouch to start with..




Note I have cut an extra intake in the engine cover.. pointless having two air intakes and then the system trying to suck air through the gap between your boot and the body.

Get some cold air in your boot.. run super unleaded and gets some miles in!

[911mark911]

hi yes will keep it on only done 20 miles so far, and yes I thought about cutting another cold feed into the boot. but for some strange reason tonight the PSM off and ABS warning lights came on? any idea's thanks

[911mark911]

eastcoastporsche said:

I fitted this mod to my 996 about 7 months ago..

When it was first fitted , say the first 200 miles , the engine was below par .. a bit drown in air.. what I mean is you put your foot down and more noise than action and a bit lumpy on tick over.

Super Plus unleaded is CRITICAL to this mod.. after I discovered running ordinary unleaded the car instantly goes off form.

Not sure how many miles you have done to allow things to settle in, ECU to work out whats going on etc etc once things settled down with my car.. its now well up power wise.. NO WAY would I put the old unit on.. Previous I was running a stock air box with K&N..

In a mag there was an article about a guy who had your trouble and fitted a MAF from a bigger engine.. But my car a 1998 C2 3.4 is on a standard MAF and runs really great.. and i mean that significantly smoother and more responsive and it was not a slouch to start with..



Note I have cut an extra intake in the engine cover.. pointless having two air intakes and then the system trying to suck air through the gap between your boot and the body.

Get some cold air in your boot.. run super unleaded and gets some miles in!

hi thanks for the advice, and did you disconnect battery and do reset ETC

[Pope]

It's likely your MAF is faulty; the fault 'torque transfer disturbed at times' will probably be present in the DME and or PSM ECU's - the ECU's rely on precise data to control the Stability Management system and any data out of tolerance (MAF signal especially) will generate an implausible result and the system shuts down. The MAF sensor can be fragile if you're unlucky / too rough with it. Get the codes read.

It may be something else but in my experience the above has been more common.

[911mark911]

hi thanks I will try to get the codes read today and see what that brings up

[nick996]

Hi Everyone. Is there a follow up to this. I have a problem with my C4S fitted with the EuroCup Y intake in that the cars failed the MOT with high CO and HC. Fitting a standard intake cures the problem. I've written to EuroCup (Porscheshop) and waiting for a reply. I think the design (positioning) of the MAF is the reason and wonder if this requires a different MAF.

Danger is running any aftermarket intake could effect the car running either too lean or too rich.

All ideas appreciated.

Ta.