so my 84 4cyl manual failed the Colorado emissions test. hydrocarbons at 4.55 with a 3.00 limit. it has a relatively minor miss at idle. the graph they gave me shows it spiking all over the place until it hits 50MPH then all the levels drop way down. i reset the timing and it seems a little better but it still has an occasional miss and i notice the timing mark moves around between 8 and 6, is that normal?. i switched the MAF? (the one on the side of the air cleaner) no effect. however, i did note that when i disconnected the EGR vac line nothing happens. finger on the port feels no vac at all. higher revs get a small vac but still not much. is that normal? appreciate any help.
I don't think it is normal. Is your idle speed around 900 rpm? If you pull a vacuum line does the idle go up? Is there oil in the air filter tray? There could be some carbon build up somewhere that is reducing the manifold vacuum, perhaps at the EGR valve.
idle is normal around 900ish, yes pulling a vacuum line raises the RPMs, yes it has oil in the air cleaner (some blow by but no smoke). however, pulling the vac line going to the EGR does not cause the rpms to change and a finger over the port on the throttle body does not register any vac at idle and raising the rpms only generates a very weak vacuum. pull the throttle body and check for clogged port? net search indicates non functional EGR causes high NOx reading (and it isnt good but passes with 3.42 out of 4.5 allowed)
I had the same issue in the past when I had my 84. High HC with everything else within limits. It ended up being a bad catalytic convertor. A new one dropped the HC's way down and it passed easily..........
------------------ Rod Schneider, Ball Ground, Ga. "You can't have too many toys!" 1988 Fiero GT 1987 Porsche 944S 1987 Corvette 1966 Porsche 911 2001 Chrysler 300M Van's RV-6 airplane
i found the EGR vacuum (or lack thereof) link using the pennock's search, so no worries there (thanks though) so it now has a new CAT and O2 sensor. doesnt run any different although the sound is lower (kind of Evenrude-ish) :-) i still have a random miss at idle thats driving me nuts, and worries me regarding the pending emissions re-check. ive checked for vac leaks (none). replaced plugs, wires, coil, swapped dist from my spare motor still have the same random miss. next, lets talk timing. i set it as best i can to 8ish and that bothers me cuz it really is 8ish according to the timing light #1 is firing between 12 and 4 with it constantly moving. does that give anyone any ideas? i'm fresh out :-(
Originally posted by wolf63: next, lets talk timing. i set it as best i can to 8ish and that bothers me cuz it really is 8ish according to the timing light #1 is firing between 12 and 4 with it constantly moving. does that give anyone any ideas? i'm fresh out :-(
Do you have the A-B pins on the ALDL connector jumpered when you check the timing?
next, lets talk timing. i set it as best i can to 8ish and that bothers me cuz it really is 8ish according to the timing light #1 is firing between 12 and 4 with it constantly moving.
Assuming you have the two pins on the ALDL connector properly jumpered ... A couple of degrees of timing jitter, especially at idle, isn't unusual for a worn engine. Jitter can be introduced by a worn timing chain and/or gears, by a worn distributor drive gear, and by wear in the distributor itself.