Did some research that suggests benefits of using full manifold vacuum at idle vs ported vacuum to the vacuum advance module on the distributor. So, I changed the vacuum source to manifold vacuum. Benefits described include cooler running engine during idle, better fuel economy, and a bit more punch from zero speed.

Base timing is at 12 deg BTDC, with vac advance goes to 22 deg. Manifold vacuum increased from 16.7 inHG to 18. Driveability is excellent. Will run a couple tanks to check fuel economy. It's winter now, so no problem with high coolant temperature, but will check to see if that improves in the summer.

Any thoughts or experiences from the Forum?

 

Following this closely ... What manifold vacuum source did you spice into (for awareness only).

 

Tapped into the PVC vacuum line at the moment, but plan to transfer over to the fuel pressure regulator vacuum source when I get the correct Tee fitting. Still mulling it over, I need to consider failure scenarios of the advance diaphram and fuel regulator. It's running great so far.

 

Nice thanks. Interested to hear more. I think there is at least one extra port that is blocked on the passenger side (LHD) of the plenum?

 

Here's a photo of the vacuum connection. Engine and response definitely are happier with manifold vacuum connection (capped the ported vacuum). Used 5/16 inch fuel line and brass tee with 3/16 inch tap. Filled the tap with solder and drilled 1/16 inch to limit flow in event of VA diaphragm failure.


1994 Disco 1 manifold vacuum advance

 

Very professional looking. Keep us updated a few miles down the road?

 

I like to hear the updates too!

Have you had to adjust your base idle down?

Theoretically, your idle speed should be higher now. It might be a good idea to block the idle valve connections and rest the base idle to 500 to 550 RPM, then reconnect the valve. Better economy while idling too, but shouldn't make any difference above idle.

Manifold vacuum should give you higher idle and less delay as the throttle opens, to increase vacuum advance. After that, it should be about the same as ported.

You should get cooler idling temperatures too.

 

AlWorms "Have you had to adjust your base idle down?"

Good point. I did not think about base idle until you mentioned it. The IACV automatically corrected idle speed to normal. The initial RPMs at start up have been noticeably higher (about 1750+ vs 1500 or less previously).

So, I checked base idle today and it was still OK around 550 rpm (dash tach). Closed down the base idle screw 1 1/4 turns CW. Base idle now about 520 rpm, and start up rpms are lower. 2 turns dropped idle to 500 even. A bit surprised by how much it needed to turn.

First 1/2 tank of around town driving gave me 140 miles vs 125 previously typical. That is more than 10% better. Engine running great with smooth acceleration. My digital temperature display reads lower, but weather has been cool, so summer time will be the real test.

I ordered a new Pertronix distributor and coil, but shipping has been delayed. That will be my next ignition upgrade, even though I am happy with the stock unit, I'll have me a known good spare dizzy for my trail bag.

 

New dizzy has arrived, along with a new 1.5 ohm coil. Bought a 0.8 ohm external resistor to use with the now spare Bosch coil, so it can be used with the Pertronix dizzy.

Upper plenum is off for an injector swap. I bought a refurbished set of 4-hole Mustang injectors, same 19#/hr rating. Also replacing the fuel rail with one that has a schrader valve (from a '96 on Ebay). Will try the 3.0 Bar fuel pressure regulator (7 psi over stock), then get to the new dizzy and coil after the top get buttoned back up. Probably in a week or so.

 

You could end up with quite a bit more fuel going in at 3.0 bar. The lambdas will try to trim it back, but they don't have a huge adjustment range.

You can burn a new EEPROM with a reduced fuelling multiplier though.