yet another smog thread!

i have a 93 xj, 4.0, auto trans. i had a cracked exhaust manifold so i swapped it out for the apn header. while i was there i also swapped out my stock fuel injectors for the ford 19lb injectors. took it to get smogged and got this.

15MPH %CO2=14.6 %O2=0.0 HC=41 (max=62) CO=.07 (max=0.66) NO=0321 (max=517)

25MPH %CO2=14.6 %O2=0.0 HC=39 (max=38) CO=.07 (max=0.80) NO=0317 (max=539)

so i did an oil change, new spark plugs(basic autolite), and a new cap and rotor. the spark plug wires looked ok so i didnt swap those. went back and got these numbers

15MPH %CO2=14.7 %O2=0.0 HC=46 (max=62) CO=.06 (max=.66) NO=0383 (max=517)

25MPH %CO2=14.7 %O2=.26 HC=41 (max=38) CO=.06 (max=.80) NO=0266 (max=539)

as far as i know the cat, O2 sensor, and assorted other sensors are the same ones. 200k miles on the engine. i just dont want to throw parts at it, and im lost. has a new air filter, i had the rock-it intake tube but the smog guy told me to take it off cause he didnt like the way the vacuum hoses were ran. so i threw the stock box back on.

based on the numbers im a bit rich, but thats as far as ive come as far as diagnosing the issue. :helpme: it did run for about a year and a half with the cracked exhaust manifold, wasnt bad at first but got worse as time went by...if that helps at all?

for a possible simple fix, how old are those spark plug wires? if the old ones are breaking down internally, or were "cheap" wires to begin with, a new set can make a surprising difference in smog readings. especially under a load. pretty cheap too.

Elevated HC means you aren't burning the fuel all the way. If it were accompanied by elevated CO levels, I'd say to check your plugs, wires, and catalytic converter (they can "run cold" - which will elevate HC and CO. "HC" means "HydroCarbons," and is unburned fuel. "CO" is the chemical symbol for Carbon Monoxide, and is a product of partially-burned fuel.)

However, since you've only got elevated HC, look at sensors that have to do with fuel metering:

- HEGO sensor (if OEM, it's shot. Spec life on an oxygen sensor is 60-80Kmiles.)
- MAP sensor
- IAT sensor (The IAT and MAP generate the basic signal for fuel metering, by determining how much air is going into the engine. The HEGO provides a feedback loop for fuel trim afterwards, and a failed/failing HEGO will "fail rich" to prevent engine damage - it goes to about a fixed 13.0:1, which is rich enough to not cause ping but not so rich as to make cylinder washdown a problem.)
- CTS (this one can bumfoozle the PCM into thinking that the engine isn't warmed up sufficiently, which will keep it in "Warm Up" mode and let it run slightly rich.)

Yes, OBD-I is supposed to throw a code when any or all of these go out of whack. The catch is, they're typically failing for a while before they go far enough out of whack to throw a code at you. Test them individually, and see what's not working. Chances are, you're about to get a code (but just haven't gotten one yet...)

I'd check the HEGO first. Hell - if you've got 200K on the OEM sensor, just replace the wretched thing. The OEM sensor is probably Bosch, and I will say to buy Bosch or ACDelco (which is pretty much rebranded Bosch anyhow.)