Ridin Dirty

May I ask has anyone ever experienced this? Just started today. 993tt hesitates in 3rd and 4th gears above 4000 rpm. Couldn't test 5th or 6th really due to speed of course. But no evidence of the hesitation in first or second gears, in fact she pulls very hard/normal in lower gears.

I had noticed a slight vibration, a rough idol recently. Not anything too bad that even anyone would notice but I know it's there and it never had a rough idol; to reiterate it is very slight.
She's at 55k miles.

Plugs, rotor, (these have a cap and rotor?, really?....I know our air cooled engines are vintage but no electronic ignition system? Am I reading that right?) Plus, cap, and wires too. Plugs and wires also kinda old...25k on them.

And i think this is the best possible scenario, right? If Its not ignition related I think need a leak down right? But why is first and second A-okay? If it was bad compression on a cylinder it would be all gears...right?

She is throwing no fault codes either (she doesn't like to complain) And she has a protomotive ecu for a year now w/o event.

Any ideas would be appreciated.

Thanks

Joe

ca993twin

I would suggest plugs, but usually a misfire is accompanied by a misfire code (but not sure what the Protomotive ECU does). Its about plug time anyway, so change them first.

Droops83

When the hesitation occurs in the higher gears, does the engine momentarily hiccup and then continue to pull, or does it simply not accelerate well past a certain RPM range?

The hesitation, combined with a rough idle makes a vacuum/boost leak my initial suspicion. A large enough vacuum leak will cause a rough idle, but its effect will be diminished at higher RPM. However, if said vacuum leak is on the boost/pressurized side of the intake, it will become a boost leak and cause a lack of power past a certain boost pressure, depending on the location and size of the leak. Boost leaks can often be heard as a hissing/whistling if they are large enough. A boost leak may not show up in lower gears as these cars accelerate so rapidly that the engine often does not have time to build up full boost pressure in the first two gears. A long pull in 3rd or 4th will build full boost pressure and could expose a boost leak. Check the turbo to intercooler hoses, and have the intake system smoke tested as a first step.

The problem could be ignition related, but I would expect that to show up in the lower gears as well if that were the case. If the rough idle and hesitation are related, I would expect a scope test of the ignition to show which cylinder(s) is causing the issue. That said, a weak ignition component will first show up under sustained heavy load conditions and gradually get worse.

On that note, the 993 does have an "electronic" ignition in that the primary side of the ignition is transistorized, and the ignition timing map is electronically controlled via the DME control unit. It does use an older style single coil and distributor versus individual coils per cylinder like the 996 and newer Porsches do. This is the reason that I do not always trust the misfire detection system on 993s; it is relying on the correlation between the crankshaft position sensor and the Hall sensor in the distributor to extrapolate which cylinder is misfiring (the DME is looking for minute changes on crankshaft speed to detect misfires). Mechanical lash between the engine and distributor can affect the accuracy of the misfire detection system, and 993s can set "phantom" misfire faults because of loose/non-factory drive belts or a worn out dampener in the dual-mass flywheel. Modern coil-on-plug equipped engines use camshaft position sensors along with the crank sensor to precisely monitor engine running conditions and are much more accurate.

I would also check with Protomotive to see if their DMEs alter any fault detection thresholds, thus preventing the DME from setting a code that otherwise might be set with your symptoms.

Good luck.

Mike J

Hi Joe,

I am with Chris, you need to provide more info on the characteristics of the hesitation. Provide as much detail as possible.

Service details would be good to - when was the cap/rotor replaced, etc. I do not replace plug wires unless its called for due to misfires or failures, but some people do it as regular maintenance.

The load characteristics on the engine is different in 3rd than 1st - it;s a more sustained load, less rapid increase in RPM, and often the quick blip-blip of 1st and 2nd masks issues, and it becomes more pronounced in higher gears.

cheers,

Mike

LexVan

Zaammm, when you say it hesitates, what do you mean exactly? Maybe your clutch is going out?? If your in 3rd and 4th gear, and get strongly on the throttle, does the car hesitate it's momentum forward, and the RPM's slightly blip up, once you get past that 4,000 mark?

Just another thought.

Ridin Dirty

Ill try a better description forgive the analogies. Okay at idol there is a vibration present that again someone sitting in the car as a passenger would not notice. But a glass of water on the dash would have appreciable ripples.

First and second gear fly and pull extremely hard; you are pinned in the seat. Impossible to ask for anything better. 3rd and 4th sputter a lil. And the hiccup/hesitation is only observed on these "long pulls" of those higher gears that first and second don't usually encounter. she still pulls all the way through it and keeps pulling higher in the rpm range.

A passenger in the car may not even notice this hiccup unless u point it out to them. But After u do they would easily appreciate that hesistation and consider it abnormal. We are talking split second multiple hiccups like 20 rapid fire hiccups going from 4000 rpm to 5500 rpm in 3rd gear. We know thats only a matter of a couple of seconds and in that time we have the hiccups.....they do rob power I'm certain. She still pulls through it though. I didn't go over 5500 rpm. I guess I should?

Raining here today. Supposed to clear later. Will take her out and observe a lil more. Anything else anyone would like me to observe?

And sincere thanks again

Joe

Joe

LexVan

OK, then it's not the clutch.

You have good advice above from Droops and Mike.

Hope you have good quality, fresh fuel, good fuel filter, and MAF sensor. Surprised there are no codes or CEL.

ScottMellor

I used to experience something similar in Frank, my FVD modded car. The car would kind of flutter going through 4500 rpm, but only if I mashed the gas from low rpm in 3rd or 4th gear. Since it was able to build max boost and torque at 4500 it appeared to be in a bit of an overboost situation and releasing pressure. It would not happen if I was thrapping it through the gears to redline in first and second before changing into 3rd which sounds different to your situation.

rinlv1

I had similar problem and a new MAF sensor cured it.

pstoppani

I think a new MAF is the first step. If you want to take things a step at a time. Or, just give the car a nice tuneup with new distributor, plug wires, and plugs...

dbf73

New distributor or just cap and rotor?

Felix

It's only in third and higher gears that the car is able to generate full boost for any meaningful time; in the lower gears the revs just climb too fast. Can you hook up a boost gauge and get a passenger to watch it to see what the boost behaviour is and if there's any correlation to the hesitation?

WingChun

Been experiencing similar symptoms with mine but occurs higher up in rev range between 4500 and 6000, almost seems like you lifting off slightly when it happens.

Pulls cleanly in the lower gears (1 & 2) through to redline, no probs.

So far I changed Dist Cap, rotor arm, plugs, diverter valves, TP Sensor, boost control valve, wastegate actuators, rebuilt the turbos and cleaned the MAF. I even plugged an external boost gauge into the test port and all was ok at 0.8 bar.

All Made no difference really.

I think I will follow the advice of others and buy a new MAF next.

r993

Iam having the same issue with my car hesitation ocure between 4000 rpm and 5500 rpm , after that the car pull slightly harder. I didn't try any fix yet waiting to see what you guys do.thx

ACEparts_com

I had this issue ongoing in different ways for a couple of years. I ended up just changing ALL the sensors, wires, plugs & injectors. Cured it!