jeblevins

I have a 1986 porsche 944 late edition. The boost gauge moves from 0 to 1 when i turn the ignition on and does not move when the engine starts and stays regardless of rpms. I replaced the gauge no change and had the klr reconditioned one with vaccum hose no change. Can the problem be in the DME?

Tom M'Guinn

Probably not. The KLR has a pressure sensor that reads the pressure in the vacuum hose from the engine. Based on that, the KLR itself sends a variable voltage of 0-5v (PWM smoothed by resistors/cap) directly to the cluster to drive the gauge. When you say you had the KLR reconditioned, what do you mean? Was the pressure sensor tested, and did you confirm the vacuum hose/connection INSIDE the KLR is not leaking? You can bench test the KLR by giving it power, and checking the voltage on pin 5 with a multimeter as you pull a vacuum and/or apply regulated pressure to the vacuum port. It should sweep smoothly from near-0 volts up to 5 volts as you go from max vacuum up to 14 psi or so...

rlm328

The engine normally needs to be underload to build boost.

Tedro951

rlm has a point. To the OP, are you saying the gauge never moves at all when driving the car?

Tom M'Guinn

The OP said... "The boost gauge moves from 0 to 1 when i turn the ignition on and does not move when the engine starts and stays regardless of rpms." I understood that to mean it is stuck on 1 all the time. If I understand that correctly, and if the OP has tried a new gauge, seems like the mostly likely thing to cause that is a bad vacuum line (internal or external) to/in the KLR. To get 1 on the gauge, it needs to get 2.5 (ish) volts from the KLR (which will read as about .45v with the gauge connected) -- that's what the sensor produces at atmospheric pressure. It's possible a failed sensor or circuit in the KLR could produce 2.5v, or some freak/partial short is acting as a voltage divider, but the odds would seem to point to the sensor not getting a good vacuum signal.

rlm328

Hook a boost gauge up straight from the manifold and see what it says. At least that way you would have a starting point.

jeblevins

I sent the klr to ecu doctor to be checked and refurbished. They returned it stating nothing was wrong and I reinstalled it. Not sure about vaccum inside the klr

jeblevins

Yes just stays on 1 and back to 0 when igniyion is off

jeblevins

I will check vaccum again

jeblevins

Good idea

GPA951s

Nothing is very clear . with the engine off and key on it should read one. Meaning one atmosphere, as soon as the car starts and is idle it should read less than one ( normal vacuum) and under load make boost over one. Its cycling valve is most likely . pinch the wastegate hose shut and take the car for a short drive. Hit the gas and see if it makes boost. If it does more than likely you need to spend 80 bucks on a new valve.

jeblevins

GPA951s

Nope, follow the left intercooler pipe then find the 17 mm head banjo bolt. Follow that line to the hard pipepipe,keep following (under intake) by injectors and it connects to the cycling valve almost direct on top of cyl #3. It has three ports for the vacuum lines and one connector on top that has spade lugs 90 degrees to each other.