High vacuum in TB's rough running?
 

Well, I been chasing a small issue I been having that seems to be a little like a vacuum leak but cant find one, and I have checked everything a million times.

I have been looking into vacuum and things and can remember that the last time I synch'd my TB's my vacuum was about 26 in-hg, now from what I read this should be 22 in-hg tops. Also from what I have found is that a high vacuum means that the ECU reads this as high load so it will richen the mixture and advance the ignition, which might explain why this is happening.

Course ill see if I can reduce down the Tickover vacuum and see what it does, if I can.

The problem I been having is a bit of a poor bottom end that surges a little and a searching tickover. What you think, likely be the high vacuum?

cheers

Re: High vacuum in TB's rough running?
 

Good morning.


When you say that you've checked everything, does that include the valve clearances? If they're not within tolerance, you can get all sorts of running issues, from a lumpy tickover onwards.


Cheers.

Re: High vacuum in TB's rough running?
 

It is due its major service at 31K miles so its a fair possibility they are out. Ill get this done as soon as I get paid (already paid insurance and other costly stuff this year).

Cheers for the heads up. Ill let you know.

Oh and as a side question, recently when in top gear if I give it full throttle then shut off a little it seems to pickup, valve clearance cause this? I checked Vacuum sensor, TPS etc etc. infact replaced both as I have one of each spare for some reason...

Re: High vacuum in TB's rough running?
 

The lower the pressure (i.e. higher vacuum) the lower the load.
Full load = wide open throttles = no vacuum (ish)

Re: High vacuum in TB's rough running?
 

Its ok, the high vacuum thing was rubbish lol. Just checked the mercury tubes and they are in cm-hg not in-hg...

I think Spanner man could well be bang on with the Valves, its at 30mph at 3000rpm in 3rd that the engine feels VERY slightly out of balance, so could well be valves, im sure it cant be anything else with all the checks I done!!!

You any idea on the full throttle not feeling quite as good as say 6/8 throttle? Fuelling?

Re: High vacuum in TB's rough running?
 

Good morning all.


One would expect a tight inlet valve clearance to cause the vacuum readings to be on the low side. However, theoretically a tight exhaust clearance could cause a high vacuum reading, due to a slight increase in timing overlap.

As I said, many strange running symptoms are caused by the clearances being out of tolerance.
You're best bet will be to have the clearances checked & adjusted, & see how it feels afterwards.


Cheers.

Re: High vacuum in TB's rough running?
 

Will do.