Camber

For the past few weeks, I've noticed a slight hesitation at around 4,000-4,500 RPM when in third or fourth gear and under full throttle.

The dealer recently did the 30,000 service (even though the car only has 16,000 miles - I wanted the plugs changed), and then spent a couple of hours diagnosing the problem. They said the obvious causes have been eliminated, and that they determined the hesitation was caused by boost going up to 1.3 bar and the computer backing it off to .6, with the pattern of 1.3-0.6-1.3 continuing until the RPMs got to 4,500 (or so), where the hesitation would stop, presumably since boost wouldn't get up to 1.3.

If the car is driven at 90% throttle, there is no such hesitation in this range. If the car is driven at full throttle above 4,500 RPM, there is no hesitation.

I bought the car in January, so don't know if its ECU has been changed - I am going to check mounting screws to see if they're different. I have driven the car 5,000 miles this summer (yee ha), and have not seen these symptoms before.

I presume that if the dealer can't figure this out with all of their monitors, it's going to be difficult for a Rennlister to diagnose it remotely, but I'm curious if anyone has witnessed this, and if so, what the root causes were.

Thanks for your help.

Jim

PS - the oil change and installation of Porsche vs. Mahle filter, corrected all smoking and oil dripping problems!

911/Q45

Mine did that after I changed the plugs at 60K, Andial suspected a loose plug. Another possibility was a separated lifter. It didn't do it after they completed their project.

Kevin Ross

Jim,

I have exactly the same hesitation, in the mid revs in third or fourth and under full throttle.

My car is in for a service as we speak, and I did post a question in another thread about getting some feedback from Rennlisters. I have other (maybe related?) issues like a ticking sound, my belts gave up, etc...

Tell you what - I will ask Porsche to check this out and give me some insight, and I'll post what I discovered... if you can wait I should have my car back mid next week. I'll let you know if the problem is solved and what it was...

No sense in both of us spending money

Kevin

Cap, rotor, plugs, plug wires, MAF, O2 sensors, Check your bypass valves and wastegate actuators..

Kevin

PS - the oil change and installation of Porsche vs. Mahle filter, corrected all smoking and oil dripping problems!

That should be a "Sticky" With a poll attached to it... Heck we need to get one of the moderators to set it up for us..

Poll: How many had oil flowing out of there turbochargers and got it cured by the installation of new Porsche filters from the dealer..

Jim, if you are handy with a wrench.. Grab two 10mm wrenches and back your wastegate adjustment nuts backwards 2 turns.. This will cure your overboost. This condition happens if someone has installed a ECU OR has cranked up the wastegates a few turns and ARE running freeflow cat-bypasses/100 cell cats and freeflow mufflers.. The they sell the car and put everything stock back on.. Being that your gates are still adjusted, with more backpressure you will see the boost spikes..

I have written a DIY about wastegate adjustment 1-2 years ago.. Do a search...

mdd

Kevin Ross, I just posted this to your other thread also.

Check to see that the pressure hoses between the turbo and the intercooler are tight at each end and not damaged. Mine had an engine sputter at about 3500-4000 RPM and was slow building boost. Having the same problem after changing plugs, rotor, cap, etc, I found a loose clamp on the turbo end of one of the hoses. It was leaking only when the boost would start to build. It hadn't sputtered since tightening the hose (many months ago) and the boost builds very quickly.

Kevin Ross

Ahhh, mdd

now that you mention it... I do remember the dealer saying something about one of the turbo hoses having a small split!

D'oh... it really could be that simple, I remember the 964T being the same... once there was the smallest leak in the system everything would go off a tad....

... I'll sleep much better tonight

I'll post this to the other thread too....

Woodster

kevin,
Replace your turbo/intercooler hoses with upgraded ones (with orange ends).
the old ones are junk!
mk

LAT

Kevin, just to make certain I have it right, it is the Mahle filters that eliminate the problem, correct?

Thanks

Kevin

NO.. You need the Porsche filter from a dealership. Not a Mahle filter.. Mahle=leaks

Camber

Kevin:

Thanks for your suggestions on the wastegate actuator. I checked mine and they were set at 33mm each.

I adjusted them two turns as you suggested, which brought them to 30.5mm, drove the car, and still had some hesitation, but not as much. It was more like a plateau in the power curve than the hesitation I was feeling before which felt more like hitting the rev limit. I let the engine cool, and then set them back to 30mm each (about 1/2 turn). Test drove again, and less hesitation but still some.

I noticed on my last drive that I could hear excess boost coming out of the wastegates (or at least that's what I think I heard). I am set just above the low end of stock according to your earlier posts.

Two questions if you don't mind. First, does the ECU take some time to adjust to the change in actuator setting or is this all simply mechanical? Second, do I keep adjusting down, including below factory spec, until hesitation stops at full throttle, or do I stop where I am.

I doubt the problem is rotor, cap, or plug wires since everything works fine at 95% throttle, and clears up at highest revs.

I really appreciate your help on this, Kevin.

Jim

PS - still free of oil leaks and smoke. Never going back to Mahle.

Kevin

Jim;

If your 10 year old plug wires are old and have a miss under load.. The ECU YANKS your TIMING.. CHANGE THE WIRES on these engines!!! Folks listen to me, the coils need uprated, the wires need changed.. If I told you that your engine when pulling timing is robbing 35HP.. Is it worth it. Now you are making less boost to lower the combustion pressure, due to crappy spark output.

If you told me I changed the coil and wires two years ago, I'd look at other issues. However, there are very few 993TT engines that have received new plug wires..

The ECU doesn't care about the mechanical adjustment, it keys off of fuel and temp, with air metered across the MAF.. If it senses a miss, it translates it as knock!!!! Maximum torque is where your engine is missing!!! You don't have maximum torque at Redline..

When it comes to some of these posts, it might appear that I lose my patients.. You guys work hard to acquire these cars, and then problems arrise. It does take monies to repair them and to keep them running. It isn't like a Honda where you can just add gas and drive. Another point.. It is difficult to change the plugs in these cars.. I have recently changed plugs on two different 993TT, where 2 of the 6 plugs were left and the customer was charged for a complete set. And on top of that 3-6 average plugs were loose in the heads.. So you might have had new plugs installed, but did you??? 20 years ago we would stick almost every car on a scope and check the engine operation. It's hardly done these days. We just rely on reading the OBD2 codes.. Then it is to late and you are chasing problems like this..

Personally, I'd check to see how much oil has been pumped into your intercooler and plenum. Oil instantly reduces the ability to have a good clean combustion. Detonation occurs at a higher rate. The bump you feel is timing and boost being pulled.. You are masking the problem, not curing it..

Camber

Several people have reported the same problem, with causes being electrical or turbo hoses.

Mine has now been repaired and is running strong. The cause of my hesitation was a failed valve spring in the turbo wastegate actuation system. The failed spring was collapsing under boost, and allowing boost to go to the intake rather than route to the wastegate. The result - boost peaking to as much as 1.6 bar, and then backing to .5 bar as the DME backed off timing.

Once the bad valve was identified and replaced yesterday morning, everything ran according to specs.

Thought you'd like to know how this one resolved too.

Jim

Kevin

Thanks for the update Jim.

I highly doubt that it was a bad spring. It most likely was a punctured diaphram.. Infact you mentioned that you could hear a noise? The ECU was definately pulling boost and timing.

Woodster

Jim,
the "good doctor" just replaced his plugs, wires, coil, maf and reset his boost pressure
(greddy profec) and he says it runs better than ever!! This is a very well running car to
begin with (black one in picture I sent you).btw I hope you put in billet diverter valves
and not those silly plastic ones.
marty