[MB968]

There are a couple of tests described in the <acronym title='factory service manual'>FSM</acronym> volume 1 under DME Diagnosis. Have never had cause to work on an <acronym title='mass air flow'>MAF</acronym>, so can't add anything. The tests described seem fairly straightforward.

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[tamathumper]

Car continues to run very, very strong today. Better than ever, which I'm happy about but which also bothers me because it ran so poorly in comparison last week with no definitive change to account for it.



The tach still does not bounce when starting, which also bothers me... so I was doing some searching today on "Porsche Tach Bounce", and I was kind of surprised to find the video I posted on YouTube (and included earlier in this thread) was being used on some other site already. I guess I didn't read the fine print about posting on YouTube.



http://howtoautorepairs.com/videos/porsc...nd-stumble

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[Cloud9...68]

Weird how that happens sometimes. My tail lights were completely nonfunctional, so I took out the headlight switch to measure the resistance across the different combinations of connectors. I didn't take the switch apart, or modify it in any way. When I put back in the car, the tail lights started working!

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[tamathumper]

Stumble is back, maybe even worse now. Interesting,...



Can anyone verify for me what their tach needle does when the car is turning over, before it starts?

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[flash]

it sounds like you've got something electrical going on there. i suspect an issue with the MAF. check all of your MAF extension connections.

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[MB968]

[quote name='tamathumper' timestamp='1371997878' post='144785']



Can anyone verify for me what their tach needle does when the car is turning over, before it starts?

[/quote]



Pulled the coil wire so it wouldn't start. Cranked as I would to start; no depression of the throttle. When I did this, the tach barely wiggled the needle. Hope this helps.



But, I'd agree with Flash, check out the wiring for the <acronym title='mass air flow'>MAF</acronym>. Stumble under throttle opening is most commonly a super lean condition.

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[tamathumper]

@MB968, that does help, thank you. Mine also barely wiggles, but earlier in this thread when I was trying to diagnose the stumble (and before I changed out the crank position sensor for a new one) the needle did actually jump to about 1,500 RPM a few times.



I will double-check all of the <acronym title='mass air flow'>MAF</acronym> connections, and try to find a way to verify the <acronym title='mass air flow'>MAF</acronym> is "good", although I suspect that would require some advanced electrical testing equipment?

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[MB968]

Don't be too discouraged by the <acronym title='mass air flow'>MAF</acronym>. Check out the simple tests indicated for the <acronym title='mass air flow'>MAF</acronym>. They aren't that difficult. As I recall you blow on the hot wire, and look for changes in the system to reheat it back to the correct temp with the added air going over it (that's basically how it works). It is a fairly simple control loop, and you should be able to at least check it's basic operation with a simple VOM.

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[tamathumper]

Have been reading up on the <acronym title='mass air flow'>MAF</acronym> a lot (and possible complications with the K&N), and I do recognize several of the symptoms, including running rich a few times at idle, the bad hesitation when cold, and also a harder-than-normal deceleration when letting off the throttle slightly. I've cut-and-pasted a bunch of tests and diagnostics and will post results back.

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[banditsc]

If you haven't cleaned and oiled your K&N filter yet, then it wouldn't have caused any issued with your <acronym title='mass air flow'>MAF</acronym>. The only time it causes issues with <acronym title='mass air flow'>MAF</acronym>'s is when someone goes to heavy when they oil the filter. If you just lightly oil it after cleaning you will have no <acronym title='mass air flow'>MAF</acronym> issues. Some people have hard opinions that a K&N filter will kill all <acronym title='mass air flow'>MAF</acronym>'s immediately, which isn't true as long as you are oiling properly..



The biggest killer of <acronym title='mass air flow'>MAF</acronym>'s is just age, I've already replaced mine at 100k miles.

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[flash]

if you don't screw with the K&N, it will not create any problems.



the only time that ever messed with anything is when some yutz over-oiled it. it got a bad rep for that, especially with the 928 crowd.



this is largely due to K&N changing their oiling bottle to a spray bottle from an aerosol. the spray bottle does not atomize as well, leading to over oiling.



also, the tendency to think that more is better is a problem. it takes a VERY light dusting of the aerosol spray to do the job.



the air cleaner came pre-oiled. it should not need oiling for a year.

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[tamathumper]

I just took it out of the box and installed it, so hopefully I'm good.

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[flash]

yup - that's right - cool

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[tamathumper]

I'm reading that if the <acronym title='mass air flow'>MAF</acronym> starts to get wonky, it can run the car very lean - and I'm also reading that running lean can cause detonation which is especially bad in supercharged engines. I'm also wondering if that is what I have happening and that is why I sometimes have a higher-than-normal heat situation? I'm not getting a CEL, but I don't know if that happens with detonation or not.



If so, I'm wondering if driving 12 hours each way to Traverse City and back this weekend is such a good idea...?

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[flash]

i don't know yet that you have a higher than normal heat condition. the laser readings are correct. i suspect you have a wonky gauge or gauge sender.



detonation is very bad. lean condition is very bad. the tuning provided is not lean anywhere it is not supposed to be. if you are running lean, you need to correct that. you will need an A/F gauge to know though.



it sounds like you need to stop driving the car, and diagnose the problem, starting at the beginning, and verifying everything along the way. don't assume anything, and certainly don't jump to the conclusion that it must be something you have touched, or not something that is new.



if you are going to attempt to do this yourself, you should probably invest in an LM-1, LM-2, or something like it, and the durametric.



then, when you have the tools needed:



check for code readings. you can also read what the temp sender is saying, as well as MAF readings.



test your mixture.



verify proper fuel supply. use the gauge. test the pressure. for you it should be 53lbs at idle with vacuum lines connected



verify the MAF, wire by wire.



check again for vacuum leaks, using the setup i showed, with the gauge where it is supposed to be, and the setup disconnected from the compressor. it should hold pressure for a couple of minutes.

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[MB968]

Just my 2 cents, but everyone who is running a boosted engine, especially if it didn't come from the factory that way should have at a minimum an air/fuel gauge (even a narrow band is better than nothing). There are quite a few items that can cause an engine to run lean, and you really should know it when it happens before it results in other issues. And, I'd also like to see an exhaust gas temp gauge as EGTs among other things are a product of both air/fuel and ignition timing, so you get a feel for how these two are playing together (for that reason, EGT gauges are very commonly used in internal combustion airplane engines).



It is really cheap insurance compared to the cost of an s/c or turbo setup, or bad results from detonation.

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[flash]

those things are nice, and certainly better than not, but they are not needed, unless you need to work on the car.



this kit is just as dependable as the stock engine, because it uses the OEM computer, and everything like that. there is no reason to suspect that there is anything to fail or cause issues. there is really nothing to watch, and those things would be distracting. i used to run a lot of gauges, and still run more than most, but i have also always pushed things a bit farther.



the only reason that i am pointing him to getting the tools is that his car has never run right, and since he wants to do this himself, rather than take it to a shop, he should have the tools to do the work, and not guess or try to diagnose over the internet.

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[tamathumper]

I'm not sure on what basis you're saying my car "never ran right" - I was quite happy with it until recently.

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[flash]

you said it always had a lower rev hesitation. it should not.

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[tamathumper]

That just started in late April, early May.

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