W124 Plug gap-Haynes wrong? / Economy gauge indicator of vacuum leak

[crammy69]

Went to see a fella whose breaking a 300CE 24V, & whilst looking at my car & chatting he said he reckoned I must have the plug gaps wrong (rough idling). I told him that I had followed the 0.8mm detailed in the Haynes manual, and explained that the plugs in fact came pre-gapped at 0.8mm anyway. He said he had his set at 0.025 and suggested I do the same to mine!

Edit: Just read on Benzworld an argument over plug gaps and there may be some confusion over metric!/imperial perhaps this guy means 0.025 Inches which would be 0.635 mm...

Is he right? does it even make sense that it would make much difference to the running?

Also, he noticed that my economy guage was about a quarter the way across whilst the car was at idle (500/600 rpm) and said he thought this was a sure indication of a vacuum leak (which many here have suspected on my car anyway).

Does that seem fair as well?

Cheers
Simon

 

[LastMinute]

I had followed the 0.8mm detailed in the Haynes manual

Brooklands book specifies 0.8 mm as well.

he thought this was a sure indication of a vacuum leak

Sounds plausible. Does the economy gauge work normally when you're driving?

 

[jaymanek]

Also, he noticed that my economy guage was about a quarter the way across whilst the car was at idle (500/600 rpm) and said he thought this was a sure indication of a vacuum leak (which many here have suspected on my car anyway).

Does that seem fair as well?

Cheers
Simon

yes thats true, but it may not be worth worrying about...

 

[crammy69]

Brooklands book specifies 0.8 mm as well.


Sounds plausible. Does the economy gauge work normally when you're driving?

Yeah I though it seemed a bit 'old wives tale', but on the assumption hes talking Imperial (0.025") then hes only talking of a difference if 0.0165mm - would that conceivably improve anything?


The economy guage moves up and down in line with my foots position on the throttle, so if that normal then yes. Seems a fairly pointless annoyance to me, I drive a 3 litre car weighing nearly 2000kg, i KNOW its not economical, I dont want to be reminded constantly

 

[LastMinute]

I drive a 3 litre car weighing nearly 2000kg

Car's 1480 kg empty. You been on the pies lately?

 

[crammy69]

Car's 1480 kg empty. You been on the pies lately?

Chinese takeaways actually!

 

[Dieselman]

The position of the vacuum gauge is an issue at idle as if there is a vacuum leak then it will have the greatest effect then and will upset the fuel mixture over the rest of the rev range.

The gauge will still show a relative vacuum when driving but not the what it should be.

 

[crammy69]

The position of the vacuum gauge is an issue at idle as if there is a vacuum leak then it will have the greatest effect then and will upset the fuel mixture over the rest of the rev range.

The gauge will still show a relative vacuum when driving but not the what it should be.

Sorry Dieselman, not sure that I 100% understand , do you mean that this fluctuating at Idle "Economy Guage" is in fact further proof I have a vacuum leak? Im going to spend some more time on the car tommorrow (oops, today now in fact) so interested to know. Going to do the Carb cleaner in throttle body thing and try out a spare EHA I bought as well. Also going to try and look at whatever I can see of the vacuum pipes.

Cheers

 

[Dieselman]

IF the reading is low then it indicates you have a vacuum leak.

With a proper vacuum gauge the engine should suck about 16" of water height at idle.
With vacuum, more is better.

You can make a gauge out of a clear plastic tube in a U shape filled with water. Alternatively buy one, they are cheap.

 

[Number_Cruncher]

>>suck about 16" of water height at idle.

So little?

 

[crammy69]

IF the reading is low then it indicates you have a vacuum leak.

With a proper vacuum gauge the engine should suck about 16" of water height at idle.
With vacuum, more is better.

You can make a gauge out of a clear plastic tube in a U shape filled with water. Alternatively buy one, they are cheap.

Not sure if I am at cross purposes here, I was referring to the guage below the Oil pressure guage in the instrument binnacle inside the car that swings between white & red with the legend ECONOMY underneath it.

 

[Dieselman]

Not sure if I am at cross purposes here, I was referring to the guage below the Oil pressure guage in the instrument binnacle inside the car that swings between white & red with the legend ECONOMY underneath it.

That is a vacuum gauge but has no scale.

 

[Dieselman]

>>suck about 16" of water height at idle.

So little?

Oops, no got the wrong scale. Try 17"-22" of mercury. It's a while since I've used mine..

Here is some advice on use.
http://autospeed.com/cms/A_2393/article.html

 

[crammy69]

Aaah starting to understand now. Had a quick scan of that article, very helpfull indeed (I like the bit where he said theres a reason its called a throttle, when its closed your choking the engine! -never heard that analogy before, makes perfect sense).

Cheers