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Old 05-13-2002, 11:19 AM
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Join Date: Mar 2000
Posts: 576
'94 C280 - Intermittent No-Start & Uncommanded Engine Shutdown

'94 C280 with 57K miles... with increasing frequency vehicle fails to start.... engine cranks but fails to fire.... or will experience an uncommanded shutdown...as though the ignition system quit.
When running, however, the engine is asymptomatic.

Cylinder head gasket and main engine wiring harness were replaced by M-B in 2000, at 42K miles. Vehicle has run fine, until now.

HHT revealed the following fault codes:

a) Gasoline Engine - failed Quick Check test

Engine management
P1340 CMP sensor
P1335 Engine speed (TNA signal)

Cruise Control
009 Control module CC (N4/3; replace control module)
080 Stop lamp switch (S9/1)
182 Safety fuel shutoff switch signal to HFM (N3/4)

b) Chassis/Drive - no fault codes

c) Body/Access. - no fault codes

d) Climate Control - failed Quick Check test
028 Refrigerant presure sensor
062 Electromagnetic clutch
060 Electromagnetic clutch


(Although codes are listed for climate and cruise control, both systems appear to be working without fault.)

Inspection of engine compartment wiring revealed complete loss of insulation on the air pump's ground wire and partial insulation loss on the pump's power line; no shorting was apparent and the harness has been disconnected from the engine harness.

Inspection of the camshaft position sensor revealed cracks in the sensor's housing; on the basis of this and fault code P1340 the sensor was replaced.

Fuel pump relay was replaced, on principle, and a new air mass sensor was installed. However, the engine still occasionally fails to start or spontaneously shuts down. The shut down is very smooth... one moment the engine is running and the next its not. By contrast, pulling the fuel pump relay results in the engine stumbling and running for a few seconds after the pump stops and the fuel pressure falls.

Any idea as to whats going on here? A "Check Engine" light has not been displayed.

The dealer missed the air pump's harness... are there other specific harnesses within the engine compartment that are prone to failure and should be inspected?

Or is this likely a failing HFM control unit? Any way to definitively diagnosis a bad unit? Will it eventually throw a fault code? Replacement units have to be coded before installation and at $1500 its a must that the diagnosis is correct. TIA.
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