I'm REALLY, REALLY desperate folks, need to crack this one - please help!


First the specs: 1984 Mazda 626 LX 2.0 Carborator
Manual choke
It's run 273.000 Km


I've searched quite alot through the forums and can't really say I've found any posts matching my problem
in particular. I live in Norway and have already tried to speak to several mechanics about this, but haven't been successful with their help. So now I'm pointing towards you for some insightful assistance.

When the engine is just above idle rpm cylinder nr 2 stops igniting. This I know because when I pull the the cable from the spark plug there's no drop in rpm. But there are sparks coming from the plug and from the cable when I check them. When I put my hand near the exhaust behind the car i can feel it pulses as if one cylinder won't ignite. If i rev up the engine a bit the cylinder in quiestion starts to ignite, also checked this by pulling the cable. But if i compare it to other cylinders the engine doesn't drop as much in rpm as on the other cylinders when I pull the cable. If I let the enging reach idle rpm it coughs for a little while struggling to remain on and then dies. The other 3 cylinders seems to be running fine.

The engine starts up ok, sometimes if I've pulled the choke full out when starting it starts and then dies. Then I have to turn off the choke to be able to start the engine again. This applies to when the engine is cold.
Don't need the choke when it's warm to start it. But I use the choke to boost the rpm's a bit over idle rpm so the engine won't stall when stopping at lights etc.

This I have done:

I've tried to check for vacuum leaks, but maybe I haven't checked thorough enough, any ideas?
Have checked the time glass (afterburn, I think?) filter underneath the air filter to see if it shuts when
dropping in rpm, and it does.
I've done a compression test on the cylinders and they're all equal in pressure.
I've recently changed the ignition regulator (half moon piece inside the distributor), distributor cap, rotor, ignition cable for cylinder 2 and to the coil and all the spark plugs to original NGK.
I've checked if there are sparks from the cables and the plugs.

If you need any more information, just say what and you'll get it.

Please, I really want my good old mazda to run som more km before I put it to rest on the green pastures.

/Pappa T

 

EUVREKA!

I found out what was wrong with my engine and ofcourse it was a vacuum leak. I removed the air filter
housing to have a closer look around the intake manifold. At first glance I couldn't see any loose hoses
so I started to use some carby cleaning gas around the manifold to see if there were any leaks. I sprayed
on some parts and the engine reved in rpm, so at this stage I understood that there were indeed a leak
somewhere. But the engine reved in rpm on several places around the manifold, so at first I thought it
could be the gasket, so I tried another trick I learned from other posts on this forum. I took a piece of
garden hose and used it as a stethoscope to pinpoint the leak. Eventually after som minutes of carefully
listening around the manifold i located a pipe on top of the manifold that seemed to be missing either a
plug or a hose.

When I plugged the hole on the pipe the engine reved in rpm and when I then tried to pull the sparkplug
cable off sylinder 2 the engine whent down in rpm. Finally there it was, sylinder 2 fired again on idle!

What I'm wondering now though is what function does this little pipe have? Is it only to be plugged or is there
supposed to be a hose connected to it? Trying to add som picture to my post, so you can have a look for
yourself.

The red arrow shows the pipe where the vacuum leak is. The green arrow shows a similiar pipe next to it
with a black rubber plug onto it. The first picture is taken from the right side (from the front of the car) of
the engine. The other two picures are fom the front of the engine.

Hope for a speedy reply, thank you in advance!

/Pappa T

 

I would think it is a vacuum hose that would connect to the air cleaner from this port. Maybe the hose is missing due to age and where it's been worked on before. If it is it would be a short jumper hose. I was going by what hose diagrams I have for US models. Let's hope babyhuey will check this topic soon!

 

Thanks for the input, I'll take a little walk to the garage and check out the air cleaner to see if there is a
intake on it missing a hose. Took a rough look when I found the vacuum leak but couldn't find any intake
then, but I'll be more thorough this time around, so I'm a 100% sure.

I'll return with an answer soon...

 

Yep bkey71 you sure were right about that one. From what I could see there was a hose coming from a vacuum
mechanism on top of the intake of the air cleaner. I think it's an open and closing mechanism for the hot air
coming from the exhaust manifold. Really stupid of me since I should have checked this better, but bailed on
that part when I removed it

I didn't really think about the hose since it was not hanging loose from the air cleaner when I removed it. The
hose went through a clip underneath the air cleaner. So there you go...

Popped on the hose and everything seems to be allright with my trusty old servant.

Thanks for the tip, led me right to the source!

/Pappa T