Need advice on driving without Vacuum Advance working

I'm very curious to know how he set up average timing, as you mentioned. Please ask him if you can.


"But it could be a long time before I find a new (used) Microplex ECU, so
will have to live without advance until then."

Obviously you still have advance or the car would not be driveable. You just don't have advance that is modified for different vacuum levels (loads).

There are plenty of people, myself included, that have installed the Electromotive XDI system and our cars run very well with no vacuum-based adjustment/advance at all. Having said that, I have the vacuum module to connect to the XDI and plan to install it some time in the future. It will allow some fine tuning.

I'm not sure why you're associating possible valve wear with incorrect timing. Anyway, I would be listening for any pinging or knocking (hopefully there won't be any). Make sure oil/water temps. do not exceed normal indications for your car. Of course you should avoid "lugging" the engine and I would use the highest octane gas available just to add a small safety margin.

I suspect there are a number of 328's driving around with failed vacuum transducers with no ill effects or the owners even being aware of a change in running behavior.

 

My understanding is that the vacuum advances the timing under light throttle (when there is vacuum) and this gives better fuel economy. At wide open throttle there is no vacuum and no ignition advance. So you don't have to worry about giving it full throttle.
My Lancia Montecarlo has no vacuum advance timing while other Lancias/Fiats with the same engine do have it.
How could your mechanic set the elctronic controlled timing, other than repositioning the flywheelsensors?

 

Read your new post: inginition timing is about when the sparkplugs fire and has nothing to do with the valves or valve-timing. Valve timing is controlled and fixed by the cambelts. Some modern cars do have variable valve timing but not the older Ferraris.

 

I don't think you'll have any problems. If you trust your mechanic he is the guy to ask (if you don't trust him find another mechanic

As you increase rpm's the spark must occur sooner because it takes a fixed amount of time for the mixture to burn in the cylinder. Because things are happening faster you have to start the burn earlier (advance the timing). With light load (small throttle openings) you can also have more advanced timing.

You're absolutely correct that there is also valve timing and it is no less important but it is not directly related to ignition timing. In any event, incorrect ignition timing or valve timing can cause a power loss and engine damage.

Like Bert, I also have a Lancia Montecarlo that had no vacuum advance from the factory although the same engine in other car bodies did. We do have centrifugal advance on our distributors but I defeated mine when I installed an MSD ignition system.

Generally speaking the more a car is geared toward performance/racing the less the need for vacuum adjusted timing. A big truck, for example, that has greatly varying loads (sometimes only a driver, other times full and pulling a boat) and that is used in "hill country" definitely has a greater need for vacuum compensated ignition timing.

 

I don't know of a way he could have adjusted timing on your car. Maybe he just plugged the vacuum line so you have no vacuum leak (if there was one). It would appear that there is a default timing curve used when there is no vacuum signal and if your car is running really nicely like you mention then things cannot be too far off. Either that or your car was running REALLY poorly before that.

 

Plugging the line makes the unit think the car is always at WOT . . . so it just uses that particular advance curve . .. PO of one of my cars had done the same thing . . . it's my understanding fuel economy and emissions will suffer 'cause you're not getting the extra advance at part throttle and coasting.

edit: from memory I think the car's seem to idle better doing this 'cause you end up with way more advance at idle with the line plugged

 

lets see, based on the 328 ign maps. with a functioning vacuum you'd have a 3* retard at idle, with out it would be 6* adv. so you'll have a faster idle. the difference will be at the top, WOT from 5k on is 32* adv, if your vacuum was reading then any cruising speed above 5k would adv out to 40* not a real big problem. the majority of the map shows the vacuum timing to be retarded by about 5* from WOT and around 4k the two values switch places.

there is no way for your mechanic to adjust the timing of the maps as those are programed into the ECU. more than likely he adjusted the cam timing by tweaking the LSA (lobe separation angle).