| Author |
Message |
    
Disco94Jason
| | Posted on Saturday, February 16, 2002 - 07:28 pm: | 
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Hello All,
Doing some weekend maintenance on the disco (1994) the realized that the vacuum advance unit on the distributor has a broken seal. Therefore, the distributor is not getting vacuum to advance the timing. Anyone fix this problem? Did you see any improvement in fuel miledage>
TIA,
Disco94Jason |
Brian Jackson (Nerover)
| | Posted on Saturday, February 16, 2002 - 10:47 pm: |
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I did. I rehooked it into the dizzy, and then retapped to fit slightly larger screw to hold it on...and use a slight bit of siily-cone.
HTH,
Brian |
Disco94Jason
| | Posted on Saturday, February 16, 2002 - 11:30 pm: |
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Brian,
My vacuum unit ... the internal rubber diaphragm dry-rotted, so if you were to pull a vacuum on the nipple.. it will just suck in air. Whereas a working vacuum unit will be air tight. I was just wondering if the lack of ignition advance made a big different in fuel miledage. In theory it should make a different. My vacuum unit (on the distributor) probably has been broken for many years now (I just discover it was broken). So the ignition timing is based on TDC setting.. Anyway.. did you experience any different before and after you fix the vacuum problem?
TIA
Disco94Jason |
jp
| | Posted on Sunday, February 17, 2002 - 10:45 am: |
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The only fix is replacement, unless you want to uncrimp the outer edge, dismantle and replace the diaphragm? It will make a difference to smoothness, but not a whole lot to economy.
jp |
Randall Smith
| | Posted on Sunday, February 17, 2002 - 09:39 pm: |
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It is unlikely that you would notice any difference if the vacuum advance is working or not. The diaphram only advances it maybe two or three degrees when the throttle is barely cracked open. This distibutor based ignition system is about as good as they get, but distrbutors are limited to two timing variables, vacuum and rpms.
Unfortuantely the price is $90 in the US for a LR advance diaphram. About $30 if you order from the UK.
Randall |
pjkbrit
| | Posted on Monday, February 18, 2002 - 11:10 am: |
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NOOOOOO....under throttle load that advance unit gives about 15 degrees of extra advance....and about 25 horse power difference....fixing my 94 made a HUGE difference to the previously crappy performance.
Fix it.
Pete
94Disco |
Disco94Jason
| | Posted on Monday, February 18, 2002 - 09:11 pm: |
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Thanks all,
The vacuum advanced is 23 degrees at 3400rpm. Mine rubber dry rotted, and the little arm does not even move. So I was just running base ignition at 6 degrees BTDC all the time. I just order the vacuum unit today from LR dealer... I check all the aftermarket suppliers, and no one has a replacement. Vacuum unit for Ford or Buick is only about $25 each.. LR must be made of special UK rubber LOL!
I remember my Disco used to get 16mpg... years ago... now is it at best 14.5mpg.... Just want to see if others have similar experience :-)
Cheers
Disco94Jason |
Randall Smith
| | Posted on Tuesday, February 19, 2002 - 06:48 pm: |
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The vacuum advance is only 2 or 3 degrees at most, just like I stated above. It also gives no advance at 3400rpms. The vacuuum advance only works when your throttle is closed, or nearly closed. You probably wouldn't notice if it is working or not. You would have a real tough time finding anthing in the service manual that even mentions vacuum advance, and it certainly won't give you 25 horsepower. They don't even have vacuum advance on high performance engines.
You may be confusing total ignition advance with vacuum advance. Total advance would be base timing plus mechanical(centrifigal) advance. Above 3000rpm or under heavy throttle you need less advance, so that is the end of the advance curve at around 3000rpm.
You may get slightly better mileage idling and cruising with the unit working. Don't expect miracles.
Randall |
Disco94Jason
| | Posted on Tuesday, February 19, 2002 - 09:52 pm: |
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Randall,
You are absolutely wrong. Mechanical advance like that of my 94 Disco at idle with vacuum disconnected should be 6 degress BTDC (factory setting procedure) Vacuum advanced on igintion timing does not happen until throttle plate opens, because the nipple port is on the air filter side of the throttle plate, and not the plenum side. I guess if you hook the vacuum tube to the plenum side of the throttle plate... you will get igintion advanced at idle.
In a nutshield, the higher the RPM and load, the higher that ignition advanced. For example, in a timing curve of a Porsche 993. It idles at 10-13 degrees and at full throttle, ignition advanced is around 35 degrees. Turbo car run less timing around 24-28 degrees, but the timing curve still increase from idle. I think Porsche is consider high performance engine?no?!! Even though Porsche and Rover is completely different automobiles.. the theory is the same..
Total advance of Rover's system is mechanical plus vacuum advanced 23 degrees at 3400rpm (max engine vacuum in hg)
25 hp?? not sure as I did not dyno the engine before and after
Disco94Jason |
Randall Smith
| | Posted on Tuesday, February 19, 2002 - 11:47 pm: |
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From your first post at the top of the page to your last, it is obvious that you are confused about ignition advance. I was just trying to help you when you asked for it. My advice on what to do is replace with a new unit which can be bought for only $25. Or plug the hole in the plenum and throw it in the trash, you probably won't miss it.
Randall's last post |
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