Volvo 1800 ES ignition (and injection) timing

Glenn from New Mexico here.

The timing for the B20F is indicated in the Volvo manual to be set at 10° BTDC.  There is no instruction to disconnect the vacuum line when setting the timing.   The vacuum in the case of this model retards the ignition 10° at idle for cleaner emissions.

For most engines, the timing is set with the vacuum disconnected, which in this case, brings it to TDC with the vacuum connected if set at 10° disconnected.  When timed at 10° BTDC with the vacuum connected, this results in a 10° advance of ignition timing but has also advanced the injection contacts by 10°.  

Should I time the engine to 10° BTDC with the vacuum connected or disconnected?  The difference makes a significant difference in idle speed as well as having an impact on running performance.

Thank you and regards,

Glenn

Hi Glenn,

I checked Bosch workshop manual. It says 10′ before TDC without vacuum connection at idle. Second point is 32° before TDC without vaccum and air suction hose on air filter at 3500/min. Idle is said to be 900/min on manual gear and 800/min on automatic gear.

Thank you for the confirmation.  The 10° BTDC setting with vacuum connected is working perfectly.  I had originally timed it with the vacuum disconnected and there is a performance improvement now with the proper setting.

I connected a solenoid valve (from a breaker yard) in the vacuum circuit that activates when the A/C compressor is running.  The activation eliminates the retarded timing by canceling vacuum to the distributor but does not allow additional air flow to the intake manifold.  The additional 10° advance increases the idle speed instantly so that it remains at 900 r/min whether or not the compressor is engaged.  This has eliminated the characteristic rough, low idle when the A/C is cycling while allowing the compressor to operate at the higher, nominal idle speed.  In this part of the world, A/C is a must, especially in a car with so much glass exposure.

Hi Glenn,

you confuse me. I tried to write that it is 10° before TDC at idle without vacuum being connected. I understand you now did the opposite?

Hi Volker,

Your indication of 10° BTDC with vacuum connected is correct.

Only when the A/C compressor connects, vacuum to the distributor is cancelled which advances the timing beyond 10° BTDC.  Normally idle speed would increase but the compressor load keeps it exactly even at 900 RPM, with the compressor running.  When the A/C thermostat is no longer calling for cold, the solenoid deactivates and switches vacuum back to the distributor for the normal (retarded) 10° BTDC setting.  The solenoid in the circuit makes for an ideal A/C idle condition since the compressor cuts in and out without affecting the idle speed.

I only mentioned this as it was a better solution than allowing additional air into the intake manifold for idle compensation with the compressor running (Volvo did this on some carburetor versions).  Curing all of the vacuum leaks that came with my car made a huge difference in D-Jetronic performance.  I had to replace every hose before I could adjust the idle bypass properly.

I am sorry for the confusion.

Glenn

Hi Glenn,

but I never tried to mention 10° BTDC with vacuum connected. Bosch manual writes 10 BTDC without vacuum connection.

It is normal that engine will run smoother without vaccum retard. This is meant to let engine run worse but with better exhaust gases.