Boost/Acceleration Problems
 

Hi Everyone:

I am having problems with my acceleration. I think it is vacuum related but I can't find anything wrong. When I accelerate sometimes the car: (1.) pulls strong and the turbo boosts to 1.8 bar, (2.) only boosts to 1.2 bar, (3.) boosts to 1.6 bar but the engine stutters, (4.) hesitates and stutters all the way through the rpm range. It does seem to do it more when the engine is warm. I have inspected the vacuum lines as much as possible, put a gage on some of the lines (they all read good at idle), and tested the cycling valve. All seem good so I am having a hard time figuring out what is going on because the performance is so inconsistent. Any suggestions would be appreciated. ThanksSmileWavy

Check the connectors to the hardpipes by the intercooler. You will have to pull them off to really see but they tend to deteriorate underneath and depending on how cold it is the turbo can still make pressure but when warm it is more noticable.

The connection at the turbo to the hardpipe can also split

You may also want to check the ISV

You'll need to provide more detail to work with. You will need to continue the troubleshooting/diagnostic path you already began, i.e. confirm that all vacuum-connected devices (FPR,Damper,BOV,etc.) will hold vacuum in order to ensure there are no torn diaphragms. Do you hear any hissing only under boost? Are you sure your FPR and Damper are good? When those are bad, they can display a wide range of symptoms. The significant stuttering you described makes me think the problem is possibly more significant than a vacuum leak. The TPS switch is also suspect. If you can sometimes boost and run just fine when warmed up, and stumble at other times, I don't think the problem is vacuum, possibly electrical.

From Clarks Garage

Fuel Pressure Regulator Failure Symptoms:
Engine runs rough
Engine stumbles or sputters
Engine runs very rich - black smoke from the exhaust
Engine will not start
Engine starts but stalls shortly after startup
Noisy fuel pump
Noticeable decrease in fuel mileage

The following lists some of the symptoms that MAY indicate a problem with the throttle position switch:
Poor idle - particularly a high idle condition
Engine cuts out to an idle condition during acceleration
Poor power at various RPMs (various throttle positions)
Surging idle
Misfire
Stumble during acceleration
Intermittent boost problems (turbocharged cars)

bad gas?

water in the gas tank?

have you checked the blink codes yet? what does it show?

do you have a knock counter? it would make diagnosing knock quick and easy. counter info can be found here;
http://forums.pelicanparts.com/porsche-944-turbo-turbo-s/433157-knock-counter.html#post4210398

I believe the BOV is good, I tried to clean the TPS with carb cleaner (no change), and I have no idea about the FPR or the damper. How do you check those items?

Thanks

I am sure the gas is good Nize. How do you do the blink codes? Also, what is a knock counter? Thanks

updated my post. re-read please. :)

you might also want to check clark's garage for the info on blink codes.

The only thing I know of that you can do is hook up a Mity-Vac to the line that goes into each of those, and confirm that they will hold vacuum.

Thanks Guys

Nize-I got info for the blink codes from another thread. Do you make the LED or is that something that you can buy?

Thanks

you make the LED using parts from radio shack. :) it's very simple. details on lindsey;

http://www.lindseyracing.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=LR&Category_Co de=BLINKCODE

http://www.lindseyracing.com/pics/blincode.jpg

http://www.lindseyracing.com/pics/blincod2.jpg

Thanks, I will try it tonight. I'll let you know what happens.

ok Nize, I I'm getting a blink code of 3-3 so either the KLR is bad or the TPS. Do you know how to test the TPS? Thanks. PS. that blink code test is awesome. I had no idea you could do that!

here's info on how to test the tps;
http://clarks-garage.com/shop-manual/fuel-06.htm

be warned, i had an intermittent problem and the tps tested okay. i later found out that when the tps gets hot it tests faulty. so i think the only real way to 'test' the tps is to replace it with a known good one and see if the problem goes away.

Thanks Nize.:)

OK, I tried to clean the TPS and reinstalled it. Now the only code that I have been getting today is 2-2 whch is Knock sensor monitoring- Knock sensor supplies excessivly small or no signal or K/CP control unit is deffective. 1. The K/CP control Unit is the DME right? 2. I put an ohm metter on the #11 and 13 terminals of the DME. I don't know much about electricity but on no setting on the meter (2K, 20K, or 200K) did I get 270 to 330 kohm like the service manual says so does that mean that the DME is bad or could there just be a grounding problem? 3. Also does the kick plate have to be fastened to the body to be grounded? The PO did not screw the kick plate down. Again, as you can tell I know nothing about electrical issues. Thanks:confused:

i had a similar problem with the knock sensor. turned out that the wiring had been partially cut. i had to take the intake manifold off to clean it. could also be that you have a bed knock sensor. it is possible to replace it without removing the intake manifold, but in the end it may take less time to just pull the manifold.

the metal dme/klr frame does have to be fastened to the body to be grounded.

Thanks Nize, like I said, the PO just had the frame laying there. Nynor, did you have the same boost/acceleration problems that I described when your knock sensor was bad?

Another question, do I have a knock sensor on my 86 turbo?

all 951 cars have a knock sensor, even an 86 turbo.

I'm confused. Is it the little half dome shaped sensor like in the 944S or is it the KLR box? Long question short, with an error code of 2-2 what should I be checking? Thanks

the knock sensor is sort of half-dome shaped and attached to the top of the motor block near one of the intakes.

http://www.pelicanparts.com/cgi-bin/...4460614500-M14

the K/CP referenced in the manual is the knock & charge pressure unit, which is the KLR.

if all of the wires and connections check out fine, you'll probably have to replace the knock sensor itself, for $57.25;
http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait= N&make=POR&model=944M&section=FULinj&page=3&bookma rk=13&part_number=944-606-145-00-M14

i just noticed the manual says there's two of them. hmm, i wonder where the other one is.

Thanks Nize, your advice is much appreciated.

There is only one knock sensor...


-Rogue

Nize: I have heard that this knock sensor is not needed. Porsche only used them to test the engine at the factory? Does this mean that the KLR is most likely causing my problem? Thanks again.

who told you that? i can tell you that the knock sensor is most definitely needed if you want any reliability from the motor. :)

I was not getting any reading from the knock sensor when I checked the #11 and 13 terminals on the KLR plug. I removed the knock counter and put the ohm meter on the 2 pins coming out of the knock sensor. I did not get any reading. Does the knock sensor need to be on the block in order to get a reading? If not, then it looks like I need a knock sensor. Thanks

i'm not sure if the knock sensor will give a reading when it's not detecting anything. i do remember seeing a knock sensor diagnosis how-to somewhere, but i can't seem to find it now. you might do a bit of searching around and see if you can find info on how to diagnose/test the knock sensor itself.

Sounds like you have a bad knock sensor. You should be able to get an ohm reading.


-Rogue

Thanks Rogue. I will order one.

Rogue, I pulled the knock sensor off and put the ohm meter on the 2 pins on the sensor. Should I still have got a resistence reading? Just checking before I order one. Thanks

Yes, you should have gotten a resistance. Most knock sensors are 500-1000ohms, IIRC. If you're getting an open circuit, the knock sensor is bad.


-Rogue

Thanks Rogue, everyones help on this forum is much appreciated.

did you pull the intake manifold? just curious....

Nynor, I did not. I was able to get to the sensor between the ports. Thats why I was asking about the ohm reading on the sensor itself. To make sure it was the sensor and not the wires. Like I said, I put an ohm meter on the 2 pins on the sensor, I did not get a reading so I am assuming it is the sensor and not the wires. I am also having the KLR checked as a precaution. Before this problem, I never even heard of a knock sensor. Thanks

i was able to do that, but it took me hours and i scraped the crap out of my hands. strong work.

Well I replaced the knock sensor and the KLR. I only drove the car about 4 miles last night but it seems to be working good. Hopefully I'll get to drive it more this weekend. Thanks for everyones help.