My Chevy Truck Failed the Emission Test HELP?

Hi guys I just joined this forum and this is my first post and I really need some HELP.

I have a problem and would like come suggestion on how to fix it.

I have a 1988 Chevy truck with a 4.3 motor and I swaped it out for another 4.3 motor because the other one was no good . I had to take it for a emission test but before I did I changed the oil 'oil filter replaced the plugs' rotor and cap and then took it for the test and it failed.

Here's the reading of the test.



ASM 2525 Curb Idle

Limit Reading Result Limit Reading Result

HC ppm 83 190 FAIL 200 419 FAIL

CO% 0.46 0.95 FAIL 1.00 1.99 FAIL

NO ppm 893 203 PASS N/A N/A N/A

RPM 1296 VALID RPM 582 VALID

Dilution 14.8 VALID Dilution 14.8 VALID



OVERALL TEST RESULTS : FAIL



IT FAILED : So I brought it back home and I took of the EGR valve and checked the ports to make sure they where not cloged and they where clean and I cleaned the EGR valve put it back on. I checked the vacuum line on the EGR valve to make sure it was opening right after idle and checked all other vacuum lines for leaks.I dumped some good throttle body ' valve and combustion chanber cleaner down it and let it site . Then I started it and boy did it ever smoke. I changed the plug wires air filter and pcv valve and took it for another test.



ASM 2525 Curb Idle

Limit Reading Result Limit Reading Result

HC ppm 83 191 FAIL 200 313 FAIL

CO% 0.47 0.58 FAIL 1.00 0.52 PASS

NO ppm 893 172 PASS N/A N/A N/A

RPM 1321 VALID RPM 563 VALID

Dilution 13.4 VALID Dilution 13.2 VALID

OVERALL TEST RESULTS : FAIL

Can anyone give me a suggestion on what to do next.

I checked the timing but I wasn't sure what the timing is suppose to be. I looked in my book but it did not say and I looked on my truck but nothing.

Anyhow I read in the book that the ignition timing cannot be abjusted on 1996 and later SFI engines on a 4.3L v6 engines because it is electronic controled. So what can I do to bring the HC and CO down to make it pass.

Thanks in advance for any HELP.

PS: and I changed the catalytic converter 2 years ago ' I put a universal cat on it and now someone told me that they only last one to two years ' Is that true.My Chevy Truck Failed the Emission Test HELP?
LOL, (not at you),

everybody always says replace yhe O2 sensor,

well in this case they would be correct,

if you had a scan tool available you would note the high block learn and integrator numbers,

simply replace the O2 sensor and go pass your test

your welcome in advance,



if you do as I say you will pass!!!!!



change only the O2 sensor, not the cat.,

the egr valve only works to reduce NOX emissions by lowering combustion temperature, the cat helps burn excess hydrocarbon but only to an extent, a good running fuel injected vehicle could pass a HC and CO emission test without a cat, however it would fail in the nitrogen oxide area!!My Chevy Truck Failed the Emission Test HELP?
If both HC and CO are high, the vehicle may have a bad catalytic converter or an air pump problem. if you put a new catalytic converter on it prior to swapping motors, the old one probably plugged it up.



Also, you need to make sure that the truck is good and hot prior to the test. The cat is only effective when it's hot.My Chevy Truck Failed the Emission Test HELP?
Is running rich, check for loose and/or dirty connectors and like mentioned, the O2 sensor can be reading wrong. By the way... is all stock? Did you changed anything like High Performance? Such as, Exhaust Headers, Performance Chip or any other toy that can throw off the sensor readings?My Chevy Truck Failed the Emission Test HELP?
my trust in bustas here he has bailed me out beforeMy Chevy Truck Failed the Emission Test HELP?
Did you say the timing hasn't been set?

On these it must be set.

There is a wire you disconnect, then a timing light will work.

I am not sure where it is, but I would get the timing set first.

This will cause your emission problems.