Manifold/plenum vaccum at idle ???
Turbo Mini Forums

For any of you running a mild cam (MG Metro N/A in my case but say a Ph2 or similar) and have a vac/boost gauge installed, what vacuum do you see at say 1000RPM idle.

I'm struggling to get my idle mixture(s) right and think I may have a massive air leak somewhere as I'm only getting down to 40-50kPa and I'm sure I should be seeing 10-20kPa.

The MAP sensor is fine, I've pulled it down to 10kPa on a syringe to check.

The lack of vaccum is causing the ECU to inject too much fuel so I'm running far too rich at the moment.

Before I pull it all apart to try and find an air leak, I'd just like a sanity check on what I think the figure should be....

Schrödinger's cat - so which one am I ???

Van shows about -0.6bar on its boost gauge.

If something is worth doing, it's worth doing half of.

Thanks John, then mine isn't as bad as I thought (-0.6bar is 40kPa)

I was still expecting better though and my fuelling is way too rich at idle at the moment.

Schrödinger's cat - so which one am I ???

Van has a n/a MG cam

My cam is similar to the MG Metro and I get around 15" to 18" HG. So around 40-50kPa.

I've only ever seen 20 kPa on overun.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

OK, thanks all.

Obviously my rich mixture is not from an air leak confusing the ECU - inbetween playing with my old laptop I ran the engine for a while (with my good laptop) and openned my soldering blowlamp (just gas, not lit) all over the plenum, connections, pipework etc, and no change until I pointed it directly into the throttle body and it went off scale rich.

And it does go below 40kPa if I simulate overrun (throttle wide open then snap it shut).

So I obviously have some settings wrong as it's reasonable (not as good as yours Paul yet) once warmed up.... but during warmup it's all over the place rich.

Doesn't help that I can't get the TS gauges to read sensible units any more at the moment......

Schrödinger's cat - so which one am I ???

I've attached my warmup curve.

Attachments:

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Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Just to agree with the above mine is about 50 odd kpa on idle, but I'm running 1.5 rockers, so the overlap is more.

Thanks for the confirmation Joe, I obviously have another more fundamental problem.

The fuel pulse widths are pretty directly related to vacuum at no/low load so I would be expecting 2mS or less at tickover to give me AFRs of say 13-14.

Instead I get pulse widths of 4-6mS and AFRs of 10 or less so it won't even warmup properly and the garage (and me) stinks of partially burnt hydrocarbons.

I think my vacuum is too low because I can't get it to run evenly which just makes the fuel input worse.

My warmup curve looks about right but I can't be certain as the units have all been screwed and even the online gauge has a corrupt display.

It looks like a lot more than my basic setup was screwed when ms Tobin decided to screw me for money.

I just ran out of fuel, and that was 15 litres I put in last Thursday......

Looks like I'll have to start from scratch with a new installation but it seems my "old" laptop isn't capable of running XP + TS ("Lite") + Megatune + Winlog as it has ground to a halt during the setup......

So I'm now searching for one of my spare Laptop 2.5" HDDs and a copy of Win98SE to see if I can get it to run under that.....

Schrödinger's cat - so which one am I ???

Sounds like it is not set to "Multiply MAP".

Alternatively your MAP sensor calibration has gone astray.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Schrödinger's cat - so which one am I ???

Well it looks like the whole install got screwed by Ms Tobin's "upgrade"......

I found a few other settings that had reverted to other than I had set them but even when corrected, and the pulsewidth is now showing on the screen what it should be, the AFRs are off-scale rich one one sensor and about 11 on the other and the garage is full of black smoke again.

The injection timing part of the code still works as I can swap inners and outers between off-scale rich and 11 by biasing the injection timing but the AFRs will not respond even if I set the "req'd fuel" down to 1.0 and "openning time" to 0.2 (they should be 2.3 and 0.5 respectively but changing the values makes sod all difference, even changing them by extreme amounts).

It looks like I'm going to have to completely re-install the code to the cpu and start from scratch thanks to Ms Tobin.

And I guess a complete re-install will lose the traction control module.....

The only other possibility is that these new injectors are extremely un-responsive, stevieturbo was rather scathing of them a while ago

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=307401

so I may try putting the 680cc ones back in that ran fine last year and see if I can get control back - i't just a real pain to swap them with my fuel rail design.

Schrödinger's cat - so which one am I ???

Can the old download not be got from a cached internet site? or google? or another forum member somewhere?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Schrödinger's cat - so which one am I ???

Have you checked all the temp folders and inside your profile etc on your laptop?? Applications can hide downloaded files in lots of places.

PM me if you want a list of place to look.

Thanks for the suggestion/offer Andy but, thinking about it, even if I could revert to an earlier version, like most things software wise it would soon be out of date and un-useable.

I've taken Jean's suggestion and downloaded MegaTunix and am just in the process of configuring it - it looks a lot more sophisticated (so a bit harder to set up) - so I should have everything back to how it was before fairly soon.

Then if the vacuum is still good (like yesterday afternoon) then I just have to find out why the fuelling is wrong at low RPMs.

Schrödinger's cat - so which one am I ???