968 Shudder on Acceleration - Page 2

flash968 · 02-10-2009, 07:17 PM

220 is torsen type lsd - so, not much of a chance of that being the problem

rickharrison · 02-11-2009, 07:15 AM

fuel filter?

flash968 · 02-11-2009, 07:51 AM

yeah - there are a couple of things like that which could create "shudders" of sorts, but any of them should feel more like a misfire or a stumble than a shudder or vibration - that's why i don't like speculating and trying to diagnose things like this online - it's like that joke about the four blind men and the elephant

that's why i suggested he take it to the best guy on 968s - it won't take him long to figure out where it is

rickharrison · 02-11-2009, 08:00 AM

flash...you are very right. It would be nice to diagnose online tho....

flash968 · 02-11-2009, 08:29 AM

absolutely - sometimes it works too - stuff like this though is really hard

Jamie '92 968 · 02-11-2009, 10:03 AM

Trying to describe this thing is not easy. This "shudder" could be a misfire/stumble.

I hope you are right Rick. I am about 10k overdue for the fuel filter, and have one in transit from Pelican that should be here the day after tomorrow.

Still seems like a strange coincidence that this thing showed up on the way home from service where the timing belt was removed/reinstalled (lower balance shaft cover seal). I also had the valve cover seal replaced. Any chance there could be something out of place or loose that the tech would have disconnected during these jobs? I also had a heater valve replaced and a high pressure steering line. My car has a lot of leaks...

I was experimenting on the way home from work yesterday. I could pretty reliably reproduce the problem if I pushed the gas pedal more than about 3/4 to the floor when the RPMs were between 2000 and 2500. If it was 3000 RPM or above, it wouldn't happen. This seemed to work in any gear, though I mostly experimented in 4th, 5th, and 6th. Not sure if this would tend to invalidate the fuel filter/pump theory.

Even if we don't get a conclusive answer until next week when I go to see Pete, I really appreciate all the info. I'm learning a lot!

flash968 · 02-11-2009, 10:10 AM

just for giggles, do a "blink test" - see what codes pop up

Jamie '92 968 · 02-11-2009, 05:14 PM

OK.
Have not done this before, but I had printed out a procedure a while ago.
I turned the ignition to ON.
Then pushed in the accelerator to the floor for about 3 seconds.
When the Chech Engine light started to blink I let go of the accelerator

OK, here's what I got...
1 short , 5 short, and then 1 long light.

After it did this sequence a bunch of times, I pushed the accelerator back in for about 3 seconds until it started to blink.

Then it gave 1 short followed by 1 long light.
I think this is the signal that it is done with the codes.
Pushing in the accelerator again only brought me back to the one short, one long sequence.

I turned the ignition off and was able to repeat the sequence again... twice.

Since I don't have a list of diagnostic codes, I'm dying to know what this means!

flash968 · 02-11-2009, 06:55 PM

you did it right - no faults - that's good - rules out all the dumb little things

968 GUY · 968 GUY's Garage

Would like to find out more about "blink test'?

flash968 · 02-11-2009, 08:56 PM

you have a PM

Jamie '92 968 · 02-17-2009, 04:14 AM

Went to see Pete at RS Barn yesterday.
First of all... Flash, I owe you big time for directing me to Pete! WOW! What an experience!
I spent the better part of the day with Pete (and his protege, Max), going over my car and checking the condition of things I had been concerned about, as well as a bunch of things I never thought about.
Pete was certainly not following the model of most places you go for service where you only talk to a guy at a desk and never get near the car or the mechanic who does the work. This was more like a workshop class on the 968. I was under the car poking and proding and getting a thorough explanation of everything they were doing and any questions I had (and I had a lot).
These guys are clearly experts on the 968, but more importantly, they were great at explaining how things work and what needs to be done. Max, who did most of the wrench turning while I was there, did a better job of communicating technical information than a lot of the engineers I work with every day.
Great guys!!!
So... the shudder problem... well, it didn't show itself yesterday! Damn those intermittent problems!
The good news is that we replaced the fuel filter and air filter, and cleaned the MAF sensor (there was some oil in that area), and the car now hat 20% more horsepower!!! I tried and tried to get the shudder to come back on the drive home, but it didn't happen.
If it doesn't appear in the next week or so, I'm declaring victory!!!
Thanks to Pete and RS Barn, I have new found confidence in my car that comes from knowledge, from having my concerns and questions about the unknown answered, and from knowing that Pete will be there when I need him.
Before RS Barn, and before discovering the power of this forum (and others like 968forums.com) I was so frustrated that I was on the verge of selling my car, but that's all changed now.
I can't thank you enough, Flash, for helping me trouble shoot this issue, and for sending me to Pete...
RS Barn is like I made up a dream about the best car repair experience I could imagine, and it came true. (over the top? not at all. You had to be there!)
THANKS PETE! YOU'RE THE BEST!!!!!!!

rickharrison · 02-17-2009, 06:21 AM

I wish I had a guy like that near me. Sounds like you have likely solved your problem.

flash968 · 02-17-2009, 07:29 AM

pete is an immense resource - your experience is typical of the treatment that happens there - as for me, there aren't a lot of 968s around, and those of us who own them tend to help each other wherever we can - happy to have been able to do so here

see you around

StoneGrey · 02-18-2009, 02:19 AM

Could it not have been the HT leads/HT lead from Cap arcing against the Cam belt cover. I had that problem after having work done.

Jamie '92 968 · 02-20-2009, 04:01 AM

StoneGrey,
Since the problem appeared mysteriously, and then went away after we did a bunch of things to the engine including pulling the cam cover to check the Variocam pads, your theory sounds possible.
Can you tell me more about what and where the "HT leads" are?
Sorry, I have to again admit my ignorance...
I would like to check to make sure this is not the case, or it may mysteriously reappear someday.
Thanks

flash968 · 02-20-2009, 06:49 AM

HT are spark plug wires

it is my understanding that the indication of the problem on this car was the puddle of oil in the throttle body and all over the MAF

Jamie '92 968 · 02-23-2009, 04:09 AM

IT'S BACK!
You're right Flash, cleaning the MAF was a big deal, and the car runs a thousand times better now.
I did say I'd give it a week before declaring victory...
Friday on the way to work, I passed a truck on the highway, going up hill in 6th gear, and the shudder reappeared!
Strange, but once that happened, I could get it to repeat any time I pushed the accelerator down past 1/2 way when around 2K to 2.5K RPM. Just like before.
The shudder was there on the trip home from work also.
Describing the problem to a friend of mine who used to do engine control system design for GM led him to the theory that it might be an intermittent spark problem.
Would the computer pick this up and record a fault if it were the source of the problem?

I'm thinking that I just might need to learn to live with this problem, and take the car back up to Pete if it gets more consistent so he can witness it.

Ugh!

flash968 · 02-23-2009, 10:12 AM

bummer - i was really hoping that was it

ok - the shudder - i presume the following:
at 2 to 2.5 k, you are merely accelerating, and not trying to stay at that rpm

that this occurs in all gears

that there is no noise associated to it which might show a contact issues somewhere

questions:
is the exhaust stock?

is there any slipping going uphill in a tall gear?

at 135k with the original clutch, you could have the beginnings of that failure

Jamie '92 968 · 02-23-2009, 11:06 AM

Your presumptions:
Correct - Pushing the accelerator near the floor, trying to accelerate
Correct - though it seems easier to touch it off when in a taller gear (4th, 5th, 6th) where the RPMs don't change as quickly when the accelerator is down, and the shudder is therefore sustained.
Correct - no noises that I have detected

Questions:
Yes - stock
No slipping

This morning on the way to work there was no sign of it, though I tried many times. I even tried re-enacting at exactly the same place as on Friday. I think the ambient temp was even about the same both days.

I may look in the Yahoo yellow pages for an exorcist.