Vacuum advance unit needs replacing
Discussion
Hi Guys..
Driving home tonight, 350i stalled a couple of times when stopping at lights and the revs were returning to idle. My matey suggested it could be the vacuum advance unit and that the diaphragm within the part could have perished..
Anyway, we got back to mine and he pulled off the pipe from the phelum to the thingy, checked for a vacuum and there wasnt one..
Does anyone know which one is the right one to buy..
found this link but not sure if correct one
http://www.simonbbc.com/ignition-spares/lucas-35d-...
Is there anything else worth checking whilst this part is being replaced ??
Thanks
Dom
Driving home tonight, 350i stalled a couple of times when stopping at lights and the revs were returning to idle. My matey suggested it could be the vacuum advance unit and that the diaphragm within the part could have perished..
Anyway, we got back to mine and he pulled off the pipe from the phelum to the thingy, checked for a vacuum and there wasnt one..
Does anyone know which one is the right one to buy..
found this link but not sure if correct one
http://www.simonbbc.com/ignition-spares/lucas-35d-...
Is there anything else worth checking whilst this part is being replaced ??
Thanks
Dom
How did your matey come to the conclusion that the vacum advance mechanism is faulty? If he pulled the vacum advance pipe off at the plenum end, the suction would be from the plenum end, not from the vacum advance end. When all connected up and the engine is revved, you should be able to see the mechanism move the advance lever on the side of the distributor if the diaphram is intact.
Tony. TCB.
Tony. TCB.
Hi Tony.
I'm car sharing at the mo with a matey who is a mechanic at the garage next to office.. He said it would be the first thing to check regarding the stalling at low revs.. To check the vacuum, he disconnected the pipe at the plenum end and sucked on it - in theory, replicating the vacuum from the plenum. he could not create a vacuum to the advance unit so really, his diagnoses was spot on..
with regards to checking the advance lever on the distributor - it looks like it is within the distributor housing so not sure how to see whether it's moving or not..
I'll have a look this coming weekend.
anyway, if the advance unit did need changing.. do you know if the part on the previous link is the correct one ?
Thanks.
Dom.
I'm car sharing at the mo with a matey who is a mechanic at the garage next to office.. He said it would be the first thing to check regarding the stalling at low revs.. To check the vacuum, he disconnected the pipe at the plenum end and sucked on it - in theory, replicating the vacuum from the plenum. he could not create a vacuum to the advance unit so really, his diagnoses was spot on..
with regards to checking the advance lever on the distributor - it looks like it is within the distributor housing so not sure how to see whether it's moving or not..
I'll have a look this coming weekend.
anyway, if the advance unit did need changing.. do you know if the part on the previous link is the correct one ?
Thanks.
Dom.
Hi Dom....If he is sucking on the vacuum pipe from the diaphragm then you should hear a click...Although trying to replicate the vacuum from the plenum would take a shopping trolley's worth of spinach and a girlfriend called Olive!....
What is your idle speed...ideally it should be 850-950rpm for a 3.5...Any lower then it will idle rough...Hunt and stall....The best way is to check the advance with a timing light...The diaphragms can get stuck if they have dried out or split, Remove the dizzy cap and suck on the pipe..You should see the base plate moving, If it isn't then it could be that the diaphragm has failed or the actual distributor is kaputten.
Its possible that the weights might be sticking inside the distributor...Remove the dizzy cap...Rotor arm and plastic cover and spray some electrical lube/Cleaner down the inside, Allow to dry thoroughly and test...
Normally if the advance is not working then you would get hesitation on initial acceleration...Idle shouldn't be effected by it so it shouldn't stall...
The unit looks right that you have linked but check before you buy anything....Cheers...Ziga
What is your idle speed...ideally it should be 850-950rpm for a 3.5...Any lower then it will idle rough...Hunt and stall....The best way is to check the advance with a timing light...The diaphragms can get stuck if they have dried out or split, Remove the dizzy cap and suck on the pipe..You should see the base plate moving, If it isn't then it could be that the diaphragm has failed or the actual distributor is kaputten.
Its possible that the weights might be sticking inside the distributor...Remove the dizzy cap...Rotor arm and plastic cover and spray some electrical lube/Cleaner down the inside, Allow to dry thoroughly and test...
Normally if the advance is not working then you would get hesitation on initial acceleration...Idle shouldn't be effected by it so it shouldn't stall...
The unit looks right that you have linked but check before you buy anything....Cheers...Ziga
mrzigazaga said:
What is your idle speed...ideally it should be 850-950rpm for a 3.5...Any lower then it will idle rough...Hunt and stall....
When cold, it will roughly idle approx 1000 but without feathering the throttle, revs will drop and stall. Once warmed up after couple of minutes it will idle at approx 1000 all day quite happy.When warm, and after spirited driving, pull up to traffic lights and stop, again without throttle feathering, revs will drop below what should be idle and possibly stall - not everytime but it has happened more than once..
A couple of other symptoms.. not sure if related.. over the last couple of weeks, without any adjustment, there is noticeably more popping and bangs from the exhaust end and also at highish revs I have noticed a bit of pinking under heavy acceleration.
Edited to add... just a query.. if the Vacuum advance had gone, other than the low rpm idleing stability.. what would happen higher up the rev range ??
Edited by Sireatalot on Thursday 18th September 14:33
Has the vac advance tube got the orange/black non-return valve in it, because if it has you may not be able to suck enough vacuum orally. Ooer missus. If it is fitted, it could be blocked.
IIRC it's intended to stop advance being added under slow throttle opening, or something along those lines...
I'd try sucking on a length of small-bore tube direct to the vacuum capsule on the distributor and see if anything moves. It could be the advance/retard plate is stuck and no amount of sucking will shift it - or it could be the return springs have snapped and it's stuck at full advance.
IIRC it's intended to stop advance being added under slow throttle opening, or something along those lines...
I'd try sucking on a length of small-bore tube direct to the vacuum capsule on the distributor and see if anything moves. It could be the advance/retard plate is stuck and no amount of sucking will shift it - or it could be the return springs have snapped and it's stuck at full advance.
I have sucked mine and can confirm that you get measurable advance with oral.
Not huge mind - maybe 10 degrees.
You obviously need a strobe lamp on your damper while you suck the pipe.
If the diaphragm - or the pipe - is split, the sucking might not show any resistance. Which will affect your idle advance as suspected, but also will be another small source of unmetered air into the plenum, which will also affect the idle speed.
The pipes quite often split near the end and can be trimmed a bit to fix it.
If you do turn out to need a new advance unit they are quite easy to fit - 10 minutes and two screws as I recall.
Not huge mind - maybe 10 degrees.
You obviously need a strobe lamp on your damper while you suck the pipe.
If the diaphragm - or the pipe - is split, the sucking might not show any resistance. Which will affect your idle advance as suspected, but also will be another small source of unmetered air into the plenum, which will also affect the idle speed.
The pipes quite often split near the end and can be trimmed a bit to fix it.
If you do turn out to need a new advance unit they are quite easy to fit - 10 minutes and two screws as I recall.
Sireatalot said:
A couple of other symptoms.. not sure if related.. over the last couple of weeks, without any adjustment, there is noticeably more popping and bangs from the exhaust end and also at highish revs I have noticed a bit of pinking under heavy acceleration.
Pinking/Detonation is NOT good for any engine but especially the V8...Literally in seconds you can trash the engine!..I had this and thought it was cam related, Initially my timing was set to 8 degrees static idle but on heavy acceleration it pinked real bad so the timing was backed off until it stopped, It currently resides at 3 degrees..Even though this sounds low it could be a tad higher as the timing marks are not that accurate in some cases.What grade fuel are you putting in and what is your timing set to?...
Also check for the leak valve that Ian is talking about, It supposed to be similar to a one way valve but will leak back very slowly..You may not have one fitted...I haven't.
Check the vacuum hose is not blocked by removing it completely and blowing down it.
Check the condition of your plugs as well...Also check the condition of the dizzy cap contacts and the rotor arm..Hold the rotor arm firmly and see if there is any side to side movement...There shouldn't be..Turn the rotor arm to about 20 degrees and let go...It should spring back...
Didn't you have a couple of stalling moments at this years fest?...
Evening gents.
Thanks so much for the responses.. alot to investigate by the sounds of it..
in responses to you all.
Ian - It is only the tube from plenum to vac advance assy.. no one way valve is fitted.
Adam - no splits in tube, have checked that.. cant confirm the condition of diaphram untill its taken off and inspected.
Mark - normal unleaded is what i use unless there is massive queue, may go super.. Vacuum hose is not blocked, have checked. will try and check points condition etc this coming weekend.. yes i did have a couple of stalls at fest.. since then, I reckon 3 out of 10 drives it stalls if i dont catch in time with throttle.. having said that, other week when i attended the ACE - it didnt stall or want to stall once that whole trip.
Watch this space, will investigate as soon as pos.
Cheers
Dom
Thanks so much for the responses.. alot to investigate by the sounds of it..
in responses to you all.
Ian - It is only the tube from plenum to vac advance assy.. no one way valve is fitted.
Adam - no splits in tube, have checked that.. cant confirm the condition of diaphram untill its taken off and inspected.
Mark - normal unleaded is what i use unless there is massive queue, may go super.. Vacuum hose is not blocked, have checked. will try and check points condition etc this coming weekend.. yes i did have a couple of stalls at fest.. since then, I reckon 3 out of 10 drives it stalls if i dont catch in time with throttle.. having said that, other week when i attended the ACE - it didnt stall or want to stall once that whole trip.
Watch this space, will investigate as soon as pos.
Cheers
Dom
Be careful,it is possible that the vacuum advance has been removed and your distributor is modified to run only on mechanical advance. This is quite a comment modification and locks the advance curve, mine has been modified as such. so no matter how much sucking you do there will be no advance and is controlled entirely by mechanical advance.
Have you check the base idle is set correct and that the idle control valve is not sticking?
Pinking under load or heavy acceleration, check the ignition timing but don't trust the rover markings they vary in accuracy as the engine ages etc.
Have you check the base idle is set correct and that the idle control valve is not sticking?
Pinking under load or heavy acceleration, check the ignition timing but don't trust the rover markings they vary in accuracy as the engine ages etc.
Edited by keatsie on Friday 19th September 07:37
keatsie said:
Be careful,it is possible that the vacuum advance has been removed and your distributor is modified to run only on mechanical advance. This is quite a comment modification and locks the advance curve, mine has been modified as such. so no matter how much sucking you do there will be no advance and is controlled entirely by mechanical advance.
Thanks for the warning.. how would it be confirmed whether this mod has been done or not ???Usually the pipe is left on but where it connects into the inlet on the plenum chamber it gets plugged with a small laugh of rubber, this how mines has been done. Sometimes the vacuum advance arm is disconnected and removed or possibly the vacuum mechanism is plugged.
It's worth quickly checking, but with all these things always check the basics first - honestjohn has a bunch of web pages worth reading, some interesting helpful notes on setup and diagnosis on V8 engines.
It's worth quickly checking, but with all these things always check the basics first - honestjohn has a bunch of web pages worth reading, some interesting helpful notes on setup and diagnosis on V8 engines.
Hi Guys..
Just a quick update..
The Vacuum advance unit has been changed today by the garage along with the distributor rotor arm.
I was asked to take it round the block to see if there was a difference and also to aid the timing adjustment.
WOW.. what a difference for the better, the engine seems a lot happier returning to idle.
Following the bible, the timing has been set to 8 BTDC ( with the engine timing marks) now, I understand these markings can be in-accurate but as it stands it is now idling happily approx 900 rpm.
The trip home tonight will help determine if the timing needs further changes - my matey is going to bring his timing strobe with him to do adjustments to suit..
Fingers crossed that's now one more thing off the to do list.. Just need a good hoon now.. Bring on Saturday.
Thanks to you all for your input on this.
Cheers
Dom
Just a quick update..
The Vacuum advance unit has been changed today by the garage along with the distributor rotor arm.
I was asked to take it round the block to see if there was a difference and also to aid the timing adjustment.
WOW.. what a difference for the better, the engine seems a lot happier returning to idle.
Following the bible, the timing has been set to 8 BTDC ( with the engine timing marks) now, I understand these markings can be in-accurate but as it stands it is now idling happily approx 900 rpm.
The trip home tonight will help determine if the timing needs further changes - my matey is going to bring his timing strobe with him to do adjustments to suit..
Fingers crossed that's now one more thing off the to do list.. Just need a good hoon now.. Bring on Saturday.
Thanks to you all for your input on this.
Cheers
Dom
Hi Dom...Sounds like that was the offending item...Great news...You can do the retarding by ear..Put it into 5th whilst doing 30mph..Foot flat to the floor...If it pinks then pull over and retard..Then give it some beans in 2nd or 3rd ..Revs just over 4000rpm...(I prefer second) and if you hear any pinking again retard....Sometimes its best done this way..Its worth checking your distributor cap and rotor arm on a regular basis and cleaning with an electrical cleaner/Lube as this will also protect from any moisture ingress which can and does happen....And then..Enjoy....Cheers...Ziga
PS: I believe its clockwise for retard....
PS: I believe its clockwise for retard....
Edited by mrzigazaga on Wednesday 24th September 14:25
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