NON-Z/OffTopic: Mazda v6 blowing black smoke after timing be

[Guest Anonymous]

Hey, sorry for the off topic post.. I changed the valve cover gaskets, plugs, and timing belt on a '91 DOHC V6 Mazda 929. When I put it all back together, it idles low and very rough, and blows black smoke (actually, if you look by the tailpipe, the smoke looks white for about 4" then turns black..?...)

Messing with the electrical timing (turning dist.) makes little to no difference. I took the timing covers back off and looked at the timing marks again. I turned it to where they all line up, and it looks like they do. The only thing is it looks like the driver side bank cams are a tiny bit off when everything else is lined up... But not enough to be a whole tooth.

The belt is new, and the sealed HYDRAULIC tensioner is also brand new.

Oh! Almost forgot! I had to take the upper intake plenum off to get to the valve covers! So.. what do you guys think? Timing? Vacuum leak?

 

Thanks!

 

- Rob

[Mike kZ]

Any error codes comming up? Maybe it's just a bad oxygen sensor.

[DAW]

Take a good close look at your vacuum hose hook-ups and sensor connections that you may have disturbed during dissasenbly, especially temp sensors (intake air, water, cyl head temps) and AFM connections. An unplugged temp sensor will send a signal of infinite resistance to the ECU which thinks the engine is being run at the North Pole and maximally richens the mixture. Is the fuel pressure regulator vacuum line connected? If not, this might make it load up rich at idle. DAW

[Guest Anonymous]

Cool. Thanks for the info. I will check everything this week. Can you tell me the basic procedure for checking for vacuum leaks? I have a vacuum guage but am not sure what to watch for. I suppose the Hanes manual I have will tell me what levels of vacuum to expect, but to I just tee the guage into a line coming off the intake manifold?

[DAW]

That won't tell you where the leak is though. Sometimes you can listen closely and hear and sometimes you can find one by spraying a little carb/f.i. cleaner around a suspicious area and if the engine speed increases, you've found your leak. I think you might need to rule out crossed up vacuum hoses as much as an unplugged one. If you had a big vacuum leak like an intake gasket the result wouldn't be an overrich condition, it would be too lean due to "false air" that wasn't metered for by the MAS. DAW

[DAW]

BTW the reason I mentioned the vacuum line to the fuel pressure regulator is that it has to have vacuum at idle to lower the pressure otherwise it will be too rich at idle. DAW