[968norway]

Been chasing a problem for a while, some hesitation under acceleration, under 5000 rpm and only noticeable in 2nd and 3rd gear. Not long since head and cams were done, cam timing is spot on. Have also changed MAF, O2 sensor, and recently FPR & vacuum lines.
Finally decided to disconnect the variocam and there was no change in engine behavior. Though it seems to go a bit better in the higher rpm range now, go figure. But I am guessing this indicates that the variocam is not activating, so the solenoid is bad?
But I have also seen that the hall sensor can cause similar problems, is it hard to change? Is there anything else that needs to be changed with this?
Thanks for any help.

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[flash]

what fuel are you running on? is there any knocking or pinging? what chip is in there?

this sounds like perhaps an ignition timing problem, as if it were over-advanced for the fuel

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[968norway]

98 RON, as far as I can tell no pinging. Put the standard chip back in and the problem was still there, though less obvious. Probably more noticeable with the aftermarket chip because of the more aggressive timing advance. Seems odd that it's worse under lighter loading, 2nd and 3rd gears. Nothing in 1st gear, but then I have heard that the variocam doesn't activate in 1st, is that right? In higher gears, don't notice anything. As I said, I unplugged the variocam and there was no apparent difference in the low end power, 2000-5000 rpm.
It seems to wait a bit when flooring it. The power builds ok but sort of hangs a couple of times from 2500 to 5000, like steps, then nice and smooth the rest of the way. It's rather subtle, not hit your head on the steering wheel type stuff. I have had some thoughts that it could be a knock sensor, it gets pinging then retards the timing which flattens out the curve, the pinging stops and it goes a bit further before it happens again, I don't know.
But what happens if the ignition timing advances but the valves do not?, as in the case of the variocam not working.

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[Cloud9...68]

Too bad you can't do a blink test in Europe. Do you have any way to get access to a Bosch hammer?

Your problem could be caused by a lot of things, so the challene is troubleshooting it without just throwing parts at it and wasting a lot of time and money. One simple test that cured my hesitation problem a few years ago was to fully warm up the car, then pull it into my dark garage, and watch for sparks around the coil, plug wires (or anywhere else, for that matter - sparks = BAD). In my case, I was getting sparking along several of the plug wires, so a new set of wires cured my problem. Best of luck, and rest assured, a properly running 968 should show absolutely <b>no hint</b> of hesistation or roughness of any kind during acceleration. Best of luck.

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[flash]

there are so many things that can cause odd running, i'm not sure where to begin

first, never assume that anything new is working correctly - in fact, that is actually where new failures after work generally occur - it is very possible that you have a weeping head gasket - it happens more often than you would think with new work

the load is really in 2nd and 3rd, not in higher gears - this is where the engine develops the most compression per pound of resistance due to the shorter gearing and quicker revving - if there is a leak anywhere, this is where it will show up

before you go there though, do the easy stuff

check the rotor to make sure the spacers are in there
do the "in the dark" test described above to look for stray spark
check the plugs (do a compression test while they're out just for piece of mind)

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[968norway]

The plugs are new, and the old ones looked pretty good. Not long since I changes the dist. cap, the previous 'new' one had cracked. Compression is fine. The in the dark test will have to wait until it gets darker out, but the plug wires (beru) are 4 yrs old. Did the Bosch hammer and there were no errors.
Seems that if it was a general thing, the problem would not just occur under specific circumstances. But who knows. The car is 17 yrs old and has over 200 000 km on it, things do wear out.

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[flash]

age means nothing - new parts mean nothing - never presume that a new or young part is functional

regardless, you must take them out and inspect them - this is not to see if they themselves are bad, but rather to read them for indications of another problem - it's like taking your temperature to see if you're sick

here are some scenarios where plug inspection could help:

head gasket weeping - could show coolant on the plug - compression numbers might show a high cylinder

bad injector - could show lean or rich on the plug

vacuum leak - could show lean or rich on the plug

did you install the spacers on the rotor when you changed the cap? failure to do that causes misalignment which could cause misfire at advance

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[xrad]

time for the old 'elimination' game

Start with new plug wires and plugs....

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[Cloud9...68]

<!--quoteo(post=74891:date=Jul 2 2009, 12:20 PM:name=xrad)-->QUOTE (xrad @ Jul 2 2009, 12:20 PM) <{POST_SNAPBACK}><!--quotec-->time for the old 'elimination' game

Start with new plug wires and plugs....<!--QuoteEnd--><!--QuoteEEnd-->
Ugh...That could get expensive in a hurry. I would definitely do the"in the dark" test before springing for a new set of $120 spark plug wires, especially if the current ones are only four years old. Definitely a frustrating problem, though. Here's a list of what I went through when troubleshooting my hesitation problem several years ago:

Car hesitates/stumbles badly when flooring it, particularly after about 20 minutes of driving. Seems to be worse in hotter weather.

- Checked engine flash codes (came up perfect)
- Tested throttle position sensor, and installed a spare someone loaned me. No impact
- Replaced DME relay
- Cleaned throttle body with chemical flush
- Checked spark plugs (all perfect)
- Checked distributor cap and rotor (replaced 12/03. They are in good shape, but I cleaned up contacts anyway)
- Ran two tankfuls of dessicant to remove any water that may have been in gas
- Had injectors cleaned and blueprinted by Marren. Amazingly, this didn't help at all, though the car runs better than before when in its "sweet spot."
- Replaced fuel filter.
- Replaced coil with a loaner
- Added 5% toluene to tank to raise octane as a test of knock sensors.
- Replaced high performance Racer-X chip with stock chip; if anything, it made the hesitation a tiny bit worse
- Re-checked flash codes with stock chip; still indicated perfect
- Tested fuel flow volume; came out to ~900 ml in 30 sec
- Sprayed carburetor cleaner around intake manifold; no leak detected.
- Vacuum gauge reads 14.5-16” Hg, with an oscillation about a range of about 0.5”, with a period of just over 1 sec.
- Disconnected variocam solenoid – no change
- Watched engine run in the dark, and saw arcing and flashing along the plug wires, and around the coil. Ordered new plug wires.
- Cleaned MAF connector

To this I would add, "Clean MAF wire with cleaner designed for this purpose."

With all due respect to xrad (whose mechanical skills I'm utterly in awe of), there are several very inexpensive things in this list I would do before buying new parts. If you know anybody nearby with a 968, you could even potentially swap soe key parts with his to save money during the troubleshooting process.

Best of luck.

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[968norway]

thanks for all the suggestions

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[S_Cal968]

O-k I'll throw a couple of guess-timations...
Had a similar experience after installing new s/plugs. I kept telling myself, it can't be the spark-plugs. As it turned out there was a fracture in the ceramic of one of the plugs. Apparently it would only arc under load - once changed, the engine ran fine. I always cringe when I see an autoparts clerk slam a set of plugs down on the counter completely unaware that he may have damaged 1 or more plugs. I always closely inspect the ceramic section of new plugs.

By chance have you checked your coil. Stumbling/hesitation under load is often attributed to a flaking/tired coil. If you have access to a known good coil, compare the resistances. This of course may not tell the whole story - the insulation may only fail while under load.

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[flash]

yup - stuff like that happens - i had one just a little loose, and it did the same kind of thing

always check the simple stuff, no matter how new, or perfect you think it is - never take anything for granted

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[xrad]

ahhh...new plugs ...such a simple fix.......

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[Cloud9...68]

From some other discussions on the topic, I understand the car runs <i>really</i> crappy with a bad hall sensor, so this would seem to be an unlikely cause of your problem.

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[Kim]

Check that the variocam switch on the top of the motor is well seated. Take it off and push in back in firmly. Maybe do that a couple of times. And then be sure that the vanity cover is not misaligned such that it is hitting the variocam switch under load if the engine flexes a bit. Also be sure that the speed control cable is not jammed against the variocam switch. I have this problem periodically and, unless really bad, it will not throw a code but will cause hesitation under load.

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[968norway]

Thanks again for all the suggestions. Regarding plugs, the problem was there before I changed them. The head gasket is 2 years old.
To be more clear, the problem only occurs between 2500-5000 rpm and is only noticeable in 2nd and 3rd gear.
I will have to study all the components that have been mentioned.
Is there any way to check if the solenoid is working without taking it out?

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[PorscheDude]

when you pulled the plugs, how did they look?

Have you checked your valve cover gasket?
Possible small vacuum leak can be found here.

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[flash]

are you using up coolant at all?

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[968norway]

The old plugs looked fine, no indication of anything amiss. The bolts on the valve cover seems to 'sweat' a bit of oil, so there could be something to look at there.
Doesn't seem to be losing any coolant. Don't see any other symptoms of head gasket problems.
I have been trying to figure this out for a long time now, so pretty much all the obvious things have been checked and rechecked.
To describe what happens in more detail. Say I floor it at 2500 rpm, the power builds with little pauses (like a flat spot) at around 3300, 4000 and 4800 rpm, then it goes up to 7000 without a hitch, seems like the rpm gauge pauses too. I have suspicions it also happens on 1/2 throttle. Only in 2nd and 3rd gear, and not temp dependent. Since there are no error codes coming up, it is very hard to get to the bottom of it.
If it was a general fault (plugs, injectors), wouldn't it happen all the time? regardless of gear?

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[flash]

great - that helps a lot

on the presumption that there is no leak at the head, and that the ignition components all look shiny and new, and if it is a persistent problem only at full throttle, and only in the high load gears like 2nd and 3rd, i would suspect a fuel delivery problem (like dirty or clogged injectors)

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