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Probably not Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 3 Aug 2001 10:20:55
In Reply to: distributor valve check/NOx emissions problem, Marc, Fri, 3 Aug 2001 01:49:55 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I'm pretty sure that the line to the distributor is vacuum retard only. Lots of vacuum, you get retard. No vacuum or boosting, and you get whatever the distributor is set at. I don't think there is an advance function there. Yes, there is a one-way valve, but it's there to prevent boost from pressurizing the retard diaphram and possibly rupturing it. The retard diaphram on the distributor has a pretty large surface area, because it has to move the retard mechanism a significant distance. That large surface area would see some pretty major forces under boost, so they're blocked in the valve on the way there.
Also, at 25 mph, you aren't getting any boost. The test is done simulating a level road, so at 25 mph the load on the engine is minimal, and the RPM is probably so low that the turbo is nowhere near kicked in.
I think you're working too hard on the advanced timing angle. The most common reason for high NOx is high combustion chamber temperatures, and the most common reason for that is running lean. I suspect the 'pre-ignition burn' you see on the plugs is just lean burning. Look for vacuum leaks - check all the hoses. Since you've got a turbo, hoses tend to blow off. Pull the right front turn signal assembly and look in. The charcoal canister is back there, and it's common for the hoses to blow off under boost, giving you a nice big vacuum leak. Since it's buried in the fender, you can't see it. Make sure your hooter valve isn't leaking.
Tap a digital voltmeter into the O2 sensor line. The voltage should be swinging between about 0.2 and 0.9 volts, crossing 0.5 about once per second. If the voltage is stuck near 0.2 or 0.0, you're running lean. This could be due to a misadjusted AMM, or low fuel pressure (check the fuel pressure regulator), or vacuum leaks.
If the output of the O2 sensor is swinging properly,, then I'd suspect the catalytic converter has gone bad. But I really think you've got a vacuum leak/lean running issue here, not timing.
, Fri, 3 Aug 2001 10:20:55 <-- Viewing This Message
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