CO too high at idle, won't pass smog (CA)

[Eric M.]

Help!

My 87 R3500 won't pass the idle CO part of the smog test. It's a 454 with TBI.

At idel HC is 48 and CO is 1.86
at 2500 HC is 28 and CO is .88

I get 2 intermittent code errors:
#32 EGR
#13 Oxy sensor

What I've done:
Replaced EGR valve, solonoid and hoses
New180 degree thermostat
TBI rebuild, all sensor checked or replaced on TBI
rebuilt distributor
air filter
spark plugs
cap and rotor
checked timing
fuel filter
oil and filter
oxygen sensor
checked PCV valve

Took it back to the smog man, CO was even higher 2.81.

Any ideas?

Thanks,

Eric M.

 

[dyeager535]

First off dump the 180 thermostat. Colder thermostats most definitely do NOT help emissions.

You've obviously got something else going on with the EGR and O2 sensor codes, there is another thread going (FI forum?) about an O2/EGR issue.

No clue why the O2 sensor code should be thrown when EGR is bad (MAP uses vacuum difference to indicate EGR function, maybe that isn't all it uses) but that is a remedy at least a couple people have used.

O2 sensor or EGR not AC Delco may not fix any problem.

 

[Eric M.]

I'll move up to a 195 thermostat.
Would it be a good idea to swap the oxy. sensor, EGR solonoid and valve for AC Delco? I have new oxy. sensor by Bosch, is that still not a good idea?

Would any of this (other than the 195 degree ther.) help redeuce CO at idle?

Thank,

Eric

 

[dyeager535]

Well, the computer uses engine temp to "choke" itself, you'd need to see what sort of compensation the ECM uses for 180* engine operating temp (if any) but a cooler combustion chamber is not as efficient as a hotter one, and that MIGHT affect the O2 sensor operation as well. (cooler combustion chamber=cooler exhaust stream) Anything outside of stock is going to compromise some system to some extent, a whole bunch of small changes combined may equal one big problem.

I wouldn't throw the new stuff away just because it's not Bosch, but I'd make sure I was getting good operation out of them. Scanner will give you a BIT of an idea if the O2 is working correctly, switching between rich/lean, but even if it isn't doing that, it may very well be because it's constantly rich or lean from something else. But the Bosch's are known for not being good out of the box, and non-AC EGR replacements are sometimes problematic as well. (especially the "universal" replacements)

 

[badmix]

I heard something about running a lil bit of race fuel or alcohol or something like that to pass emission testing. Could research it I guess.

On a side note. They finally did away with emission testings about 5 years ago down here.

It seems everyone owned cars that were only a couple years old or brandnew and complained that they didnt need tested, once they got rid of the testing all the aftermarket companies started making a killing. Soon all the RICERS had fart cans and all kinda crap on their cars. lol.

 

[Eric M.]

Scanner will give you a BIT of an idea if the O2 is working correctly

Did the scanner, O2 is ok, but every once in a while, it drops very low. Like you said, it could be the sensor or it could be something causing it. I've got the Bosch oxy sensor, I might as well swap it.

I'll post up results.

Thanks,

Eric M.

 

[obijuan]

move to texas!

 

[dyeager535]

It ain't running good, why not fix the actual problem??

But I know what you mean.

 

[vortec]

move to texas? better be to a small town, if you feel like passing. co is what i failed for, and it wasn't much worse than yours. in and around the largest cities, pre-obd2 vehicles have to be run on a dyno and tested at two speeds. needless to say, it's a lot harder for an old borderline vehicle to pass than when it was simply run in park at two engine speeds.

 

[NoReGrEtS]

View attachment 31266

I put this stuff in and got my ford ranger to pass with flying colors.

 

[btolenti]

Definitely get the 195 thermostat....otherwise, the truck will run rich all the time......thus a high CO at idle. The stock chip is meant to run with a 195 thermostat.

If that alone doesn't help, check to make sure that the truck is going closed loop (and staying there) once it warms up. If it doesn't, a heated O2 sensor can help.

.....also, when was the last time you changed the coolant temp sensor? Is it reading correctly?

WINALDL can be a huge help at times like this....

 

[1985_K5_Silverado]

Definitely get the 195 thermostat....otherwise, the truck will run rich all the time......thus a high CO at idle.

Not to mention slightly lowered fuel economy. One might run a lower-than-stock temp thermostat in an EFI engine in order to allow a little more spark advance without ping rattle on pump gas, but the ECM has to be reprogged to see the lower coolant temp as normal (instead of "not warmed up yet, so stay rich until is is").

 

[Eric M.]

So, here's the problem and the fix. I broke down and took it to a shop. It was 5 months past due for registration and my progress was slow.

First, bad ground for computer sensors (probably caused O2 and EGR errors), Air pump was bad causing high O2 which destroyed the cat. They fixed the ground, replaced the pump and cat and it past smog with flying colors and so far, no more SES light.

Eric M.