Bosch LH-Jet 2 /'84 Volvo troubles

[Clare Snyder]

>     Help!
>     
>     Does anyone out there know what the LH-Jet 2 test port signal means 
>     _before_ the 02 sensor kicks in and closed-loop mode begins?
>     
>     Here's my problem; I don't think it's all that uncommon on LH-Jet 2 
>     Volvos.  Once the car reaches closed-loop mode, it runs fine.  When 
>     first starting the car in the morning (about 60 deg F outside), the 
>     car will fire right up, run for about 30 seconds (or less) and quit as 
>     if all fuel were cut off, and is very difficult to start thereafter.  
>     I'm attempting to diagnose the problem using the LH-Jet 2 test port 
>     (located near the ignition coil and air mass meter on my 240 Volvo).  
>     
>     When the car is warm and closed-loop mode is functioning properly, the 
>     signal at the test port is a time-varying voltage related to the 
>     signal produced by the O2 sensor.  The air-mass-meter mixture screw 
>     can be set so that the test point voltage bounces back and forth 
>     regularly between approx 0 volts and approx 4 volts.  
>     
>     When the car is cold, the test port signal behaves differently.  When 
>     the car is first cranked, the signal pops up to the "high" value ( 
>     approx 4 volts as in closed loop mode) and remains there until the car 
>     starts.  After 15-30 seconds the signal falls back to zero; within 
>     five seconds the car will stall.  The car seems to restart only when 
>     the signal pops back up to "high", which for some reason does not 
>     happen every time the motor is cranked.  
>     
>     I just installed new plugs, plug wires, cap, rotor, air filter 
>     thermostat, timing belt, etc.  I'm about to change the fuel pump 
>     relays.  The air mass meter isn't very old, though this doesn't 
>     necessarily mean anything.  Since the car runs great once it starts, I 
>     don't think the air mass meter is at fault.
>     
>     
>     As a second question, does anyone know how to test the air mass meter, 
>     other than the classic "unplug it" strategy?  
>     
>     Third, would a faulty block temperature sensor prevent the car from 
>     running?  
>     
>     Thanks
>     
>     Mike Skolones
>
 If the block temp sensor says the engine is hot, and it is not, the engine,
in open loop, will run lean. If it says it is -60, and it is not, an open
loop engine will run rich. Both can cause stalling and hard restart, so the
answer to your question is a (qualified) yes.