Metro 3-cyl General Info
 

Okay, motivation for starting this thread is a few things that have been bothering me lately. Any info anyone can provide is appreciated.

1...When I installed my vaccum gauge, krousdb thought my vaccum was reading too low. This could simply be a Suzuki vs. Honda issue, but I have noticed that vacuum will only hover in the 18 in. Hg. range on hot days when the engine is warmed up. Hayne's manual says 17-22 in normal, but I think it's referring to ALL engines (a generic portion of the manual). 16.5 in. Hg. seems to be the most common number.

2...A sticker under the hood states that the idle has been factory pre-set and sealed at 850 rpm. Lately it seems that the engine is really racing when it's first started up (I need a tach). It hasn't been cold, but humidity has been high due to some storm weather.

3...I probably should change my transmission fluid. The owner's manual calls for gear oil, but the viscosity level of gear oil is like 75w-90. This seems really "sticky" and I especially noticed it during the winter. In -20?C/-4?F the shifter felt like it was moving through glue. Is there lower viscosity gear oil I can safely use? What are some options?

1. These 3-pots have relatively high compression (199 psi is spec.), and the flip-side of that would be more vacuum, if I'm not mistaken.

2. Can't help much there. Firefly #1 consistently idled too low, and I was never able to fix it.

3. I followed the manual and stuck 75w-90 synth into FF#1. Made it worse (harder to shift, more likely to grind the 2nd gear syncro) - I figure the fluid had been changed by a previous owner to something lighter.

Did some learnin' since then and went with GM Syncromesh semi-synth. It's far lighter weight than the 75/90. I personally think the 75/90 recommendation is a typo/mistake.

See my comments on it at teamswift: https://www.teamswift.net/viewtopic.php?p=148643

Do you have any crunchy syncros on your car?

according to the ScanGauge:

MAP @ idle (845 RPM), temp @ 190 F

= 4.7-5.1 PSI

multiiply by 2.036 to get in./hg

1...So my vacuum should be higher? I can't find any bad hoses. I've been wondering about the head-gasket (partly because I want to change it for the experience...:p). I should do a full leak-down test, but the stupid tool is $70 :mad:.

3...The only time I've heard anything crunch was when I accidentally let the clutch partway out while I was shifting :o. I'll check out those comments. I have to be careful with teamswift...my computer locks after surfing for a few pages there...:confused:

So the ScanGauge is only reading 10.4 in. Hg.? That doesn't seem right at all...:confused: But is that air pressure instead of vacuum? I don't really understand a lot about this. :o

I'm no rocket scientist, but I'd say any pressure below ambient is what you'd call vacuum. (Probably more correctly: partial vacuum.)

Indeed, but I dun think your car is seeing any boost, :)

My factory manual doesn't give a value (just gives MAP sensor voltages). My Chilton says 18 in. hg at idle.

Can't say why the the SG is so far off that value.

18 in. hg is only in 20°C or higher weather though :mad: - no manual specified that.

I'm looking for info involving manifold pressure vs. vacuum. I think I've found something - I just have to read it.

Ok the vacuum is not going to be very high because it is a small motor and can't create a lot of vacuum besides only three cylinders are sucking on the intake not 6 or 8. My Geo didn't show a high vacuum until I went down a hill with engine braking and even then with crank ventilation it didn't get very high - emmissions probably prevent that - engine needs to keep burning fuel to run clean.
My idle under certain conditions was so low that you could feel each cylinder fire and I never had to adjust it up or down.
Transmission oil I never changed only added some Slick50 Gear lube to it but some good Spectro or Amsoil would be the best bet and if you are going to be in cooler northern areas all the time then a lighter weight should be ok. The syncro in second is the one that takes a lot of abuse and is usually the first to go and get crunchy. Make sure your clutch is not dragging too much and then allow some time for the engine to slow down between shifts or shift at a lower RPM from first to second to reduce the speed/rpm difference between gears. Downshifting from third to second is also tough on the syncro. Too slippery an oil will also have this effect in all gears - I.E. Synlube makes all my gears crunch a little if I shift too fast.