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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. Thanks
Old 09-29-2008, 12:49 PM
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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
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Old 09-29-2008, 01:41 PM
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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)
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Last edited by jmj996; 09-29-2008 at 07:42 PM..
Old 09-29-2008, 07:35 PM
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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
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Old 09-30-2008, 07:35 AM
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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
Old 09-30-2008, 07:48 AM
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I am sure the gas is good Nize. How do you do the blink codes? Also, what is a knock counter? Thanks
Old 09-30-2008, 07:52 AM
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updated my post. re-read please.
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Old 09-30-2008, 08:00 AM
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you might also want to check clark's garage for the info on blink codes.
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Old 09-30-2008, 08:01 AM
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Quote:
Originally Posted by 1986 944 Turbo View Post
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
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.
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Old 09-30-2008, 08:54 AM
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Thanks Guys
Old 09-30-2008, 09:17 AM
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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
Old 10-03-2008, 10:26 AM
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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
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Old 10-03-2008, 10:56 AM
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Old 10-03-2008, 11:01 AM
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Thanks, I will try it tonight. I'll let you know what happens.
Old 10-03-2008, 11:23 AM
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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!
Old 10-04-2008, 10:16 AM
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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.
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Old 10-04-2008, 07:15 PM
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Thanks Nize.
Old 10-05-2008, 04:41 AM
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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
Old 10-05-2008, 12:10 PM
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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.
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Old 10-05-2008, 12:40 PM
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the metal dme/klr frame does have to be fastened to the body to be grounded.
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Old 10-05-2008, 06:35 PM
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