My 91 pickup is putting out super high CO and HC (runnin really ritch). Its got roughly 10k on rebuild. Lce headers, big bore throttle body, intake and stage 1 cam. New cat, tried 2 maf's. Where should I start going? O2 sensors, timing, egr???Im stumped

 

O2 sensor would be a good place to start. It is the thing that monitors the air/fuel mixture and adjusts the fuel to keep it in an optimal range.

 

Mine failed recently but was high on NO. Turned out to be that the vacuum hoses were not hooked up right with the EGR (among other things).

Here's what I'd recommend:

- Make sure hoses are correct - check FSM / also check for vacuum leaks
- timing/check idle
- new plugs/wires/cap/rotor
- clean EGR (get a new gasket for like $10)....it's a PITA to get to but doable
- replace CAT if clogged

Not sure how many "free re tests" you get, but but do things in that order (Cheapest to most expensive). I had to do 3 tests....

Good luck!

 

Make sure the valves are adjusted towards the loose end of their range- minimizes influences from overlap and lift.
Adjust the idle to the higher end of the spec- maximizes vacuum.
Put it on a sniffer and adjust the idle fuel mixture- there's a screw on the AFM (under a "blank") for letting air bypass the metering plate.
Make sure you have a good converter before the test.

 

huge +1 on the converter. also, if it really comes down to it you can adjust the AFM down a couple teeth.. but you better seal that thisg up real good, the refs in cali are gettin' pretty wise..

 

no real need to jump the AFM teeth if you can find the bypass screw on the meter which lets air bypass the meter thus changing the idle air/fuel mix, unless you adjust it leaner there and run rich at the high RPM tests.

 

if you drill the plug a picky ref will fail you..

 

If you have to drill the plug to pass, you were going to fail anyways.

 

Adjusted the valves today. They were tight... Like.004 intake and '00i exhaust. Now set to '00i intake and .012 exhause. Gonna get a new front 02 put in this week and put her on the sniffer

 

.008 exhaust *

 

When cold, 0.007 intake and 0.010-0.011 (think a "tight" 0.011- takes a little effort to get the 010 in there but 011 slides in easily) is about where you want to be.
If you're too tight on the valves, particularly the exhaust, it'll start letting gasses out before they're "done" combusting, and you'll have high HC and CO in the exhaust and the converter will have problems with that, maybe even overheat. Not to mention it's bad for the exhaust valve too since it won't spend enough time on the valve seat to cool, which can lead to warping the valve and/or seat, leading to burnt valves.

 

So. I think she is ready to re test. I have- installed correct MAF, adjusted valves, re set timing....( was at 0. Now at 7 ish) new cat, cleaned the egr. Ran a bottle of techron concentrate thru thru. ˟˟˟˟er who rebuilt my motor must not have jumped the obd1 Ports when setting the timing >( gonna post results tomorro

 

Went in to the smog shop and my bad luck followed. Had it on the machine and the machine broke down. this truck does not like getting smogged

 

Broke down and took it to a shop, fixed!

 

What was the problem they anded up fixing?

 

Have installed new o2 sensors, coolant temp sensor, high temp thermostat (180°} and had a couple ground issues

 

I was suprized how much just grounding the battery to the motor mount and to various spots of the frame effected the test. Crazzy