Porsche Enthusiasts Club Forum

Hi all,

I have an issue with my 944 turbo and hoping someone can help. I've run a number of diagnostics which I'll list below.

Symptom:
Low boost about 1.1/1.2. (test drive link below). Boost was working perfectly, then took it to the bodyshop and it didn't work when I picked it up. The car wasn't driven for about 3 weeks, although the bonnet and badge panel was removed.
https://www.youtube.com/watch?v=ylKTfgR65kI&list=UU-Yq4t2RDTtzDSijGNa6Zeg


Tests:
1/ Removed CV to WG line and drove car --> boosts fine. This most likely means CV, line to WG or sensor / computer are at fault
2/ Replaced CV with brand new one --> no change
3/ Tested all vacuum lines. Replaced some rubber connections but all connections hold vacuum
4/ Took off air cut off valve --> operates perfectly. Cleaned and replaced.
5/ Made up a fault tester --> no codes. Breaking the circuit somewhere throws up a code.
6/ Tested if WG stuck open --> xover pipe doesn't warm up quickly so appears sprung shut. Does warm up slowly but not as quick as exhaust section
7/ Pressure tested WG --> opens fine and I can hear the valve closing against the seat afterwards. Appears fine

Now I've come to the conclusion (not saying this is correct) that it is the control of the CV so the computer or KLR, or perhaps exhaust leaks / clogged cat.
Given the symtom occurred suddenly after lack of use i don't think its the latter. The exhaust is blowing a little but it was before.

One piece of information that might help someone identify my problem - I started the car with the WG to CV line detatched and used a hand vacuum pump to test the vacuum. Initially it didn't hold vacuum but after 3 or 4 attempts it got better then finally held vacuum. After this I drove the car and I got 1.6 boost. This only lasted one day.
Any ideas guys??

My next test is to hear if the CV is working as I rev the car. Any ideas what readings I should get on the multimeter as I rev the car on the connection to the CV?

Hello,

Apply 12V on the CV connections and make sure it clicks.

Check then that current flows correctly between the KLR output to the wiring connector to the CV.
Had a case recently were the pins of the connector were loose and allowing max boost erratically.

Hello thanks for the advice.
How do I check the klr to CV? Would this only show volts when I rev it past 3/4k rpm?

I'll check CV clicks but almost ruled that out since I fitted a new one already.

I was suggesting checking the wiring, with the KLR box unplugged.
Send current from the KLR plug pin controlling the CV, it should show if the wiring is faulty.

Are you really sure your vacuum lines are correctly connected and you have no leak anywhere? Is the black/blue one-way valve working correctly? A broken J-boot, between the AFM and compressor inlet, can also cause a loss of boost, and can be difficult to diagnose.

Do you mean from inside the car, or from the unit under the bonnet near the fuse box?

I haven't 100% ruled out vacuum leaks, no. I've used a hand vaccum pump to test a lot of the individual connections, but need to do a static test to make sure there are no leaks, and the intercooler isn't damaged.

I spoke to a porsche specialist, they said this is the first test I should do, by connecting up the output of the turbo, near the air box, with a pressure tester. I've got a compressed and a guage, but i'm unsure which hose to connect to. Any one know which one I should use?

I mean checking the wiring from inside the car, with the engine not running.

Use a 3" adapter to the J-boot (pre turbo inlet) to pressure test the inlet tract.

It is of major importance that none of the vacuum lines are leaking, otherwise the engine will run in default mode (with an maximum inlet absolute pressure of 1.4 bar). This is the first thing to check, then pressure test the inlet.

Thanks that is extremely helpful.
Could you help me figure out how to check the KLR wiring? Do i have to remove the KLR to do this?

You have to find which pin from the KLR plug controls the cycling valve. Send current through it and see if it makes its way to the plug on the side of the cycling valve.

Hi all,

I've done a few jobs to my turbo recently, and had a small update for this thread. I've fixed the exhaust leak where it was blowing badly before the wastegate and in a couple of other places but changing the gaskets and refitting.

Just before doing this, for one drive, the turbo was working, and to 1.75 bar boost, the full effect. This was fairly short lived as I quickly ran out of fuel and after stopping at the petrol station, the turbo wasn't working again.

I've made my own boost tester (pictures to follow in case they are of any use) and can confirm there are no leaks. I replaced the hose from the CV to WG as it was old while I was underneath doing the exhaust. I don't want to lead any thoughts, but does this indicate a particular problem to anyone? Perhaps this could be ECU related? If it is somewhat intermittent i'm thinking it could be electronic.

I'll inspect further this weekend, the wiring is all a bit untidy underneath as there is an aftermarket alarm housed in the same area.

Is it possible that the body shop flattened the battery? and use a Booster to start it?

I did the same once and gave one of out forecourt cars a misfire under load - which turned out to be the KLR.
We always use a battery and leads to jump them now!

Where are you based? the next easy thing would be to swap ECUs with someone to see if it is that.

Thanks, they may well have they had the car over 3 weeks.
Is the ECU located under the passenger floor?

Yes, its located under passenger floor board, the KLR is the smaller ECU with the pipe attached.