Last weekend, I performed an engine wash on my 1985 300D turbo using standard garden hose pressure and car washing detergent. The next morning, the engine started normally, but as I accelerated (around 2500 rpm) I could feel the turbo boost intermittently and rapidly kicking in and out. Simultaneously, I heard what sounded like a relay under the dash rapidly toggling and the clicking sound was synchronized with the turbo boost kicking in and out. I continued to accelerate to approximately 70 mph and the intermittent boost failure continued.

I suspected that moisture had gotten into an electrical connector in the engine bay resulting in an electrical short that was causing the boost problem. I continued to drive the car for approximately 30 minutes in the hope of drying out the moisture. Upon returning home, I checked the engine bay and all was dry. I proceeded to further dry all electrical connectors with compressed air and disassembled and inspected several connectors that I thought were associated with either the EGR circuit or ALDA circuit.

Since the initial boost failure and my attempt to dry out the electrical connectors, the engine has not returned to normal operation. There appears to be zero turbo boost whereas prior to the engine wash, engine power and acceleration was excellent. The car has approximately 285,000 miles and has been carefully maintained with normal fuel filter changes, valve adjustment, etc.

I would like to start a systematic troubleshooting effort and would appreciate some guidance on where I should start.

Thanks in advance for your advice.

Aeromechanix

Check your wastegate hose for damage.

I agree, sounds like you're overboosting and the overboost protection solenoid is clicking on and off to protect the engine.

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could also be a dirty or clogged boost line going to the IP and/or over boost valve in between the intake manifold and the IP

good luck

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ForcedInduction,

Please clarify what I should be looking for on the wastegate hose. Could the hose have collapsed as a result of rapid cooling from washing the engine thus preventing venting of the wastegate? Presumably this would lead to an overboost condition.

I agree that the symptoms appear to support that idea that the "engine protection circuit" is energized by the manifold pressure switch and thus the ALDA is not receiving a signal to enrich the fuel mixture as the turbo spoils up.

I will check the turbo and wastegate and report back. Thanks for the advice.

Check the over boost solenoid also. Is in the upper left hand area of the brake booster on the w123.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

I troubleshot the turbo boost loss by first assuming that the failure was in the engine protection circuit since it is electropneumatic system and potentially prone to moisture problems. I bypassed the over boost protection solenoid by directly connecting the manifold pressure sense line to the ALDA capsule with a short length of tubing. I then drove the car to see if I had turbo boost. The car accelerated well and performance was identical to that prior to the engine wash.

Based upon this test, I then had to determine if the engine protection circuit had failed or, if in fact, there was an overboost condition and the ciricuit was behaving correctly. A review of the schematic for the protection circuit indicated that the solenoid receives + voltage directly from fuse # 14, and the manifold pressure switch serves as the gound path. A check of voltage at the solenoid showed a + 13.5 VDC with the engine idling indicating that the circuit was energized with zero turbo boost. I pulled the connector off the manifold pressure switch to eliminate the ground path and the voltage dropped to zero and the solenoid opened.

This test indicated a failed manifold pressure switch (failed closed to an overboost condition). I replaced the switch ($56.00) and all is well. I suspect that water may have pentrated the sensor and shorted it internally causing the failure. Thanks to the group for your recommendations.

I had the same problem but I just removed it. My greatest concern is that I believe that the functionality of the fuel cut below 7psi for RPM > 2000 is driven by the CCU and I removed the CCU. I am fairly certain the default behavior of the solenoid is to vent.

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