Failed NJ inspection again. Ideas?

[rturbo 930]

Hey guys,

I've got an '88 325is that won't pass inspection. It has a rough idle when it's hot, but off idle, it runs well.

Here's a list of things we've checked, fixed or replaced:

Injectors
Carbon deposits on intake valves
Compression test: I don't recall the exact results, but it was something like 145, 150, 160, 160, 150, 145, from piston 1 to piston 6.
O2 sensor
Cat
Checked for closed loop
Intake manifold hoses
New spark plugs
Checked for vacuum leaks
Water temp sensor
Checked ingition with a scope
Checked the valve adjustment

Might be more I'm forgetting.

The results (cat was plenty hot):

HC ppm @ idle:
Max: 220
Reading: 1110

That's the only part it failed. Ideas?

[flyboyx]

holy shit! thats bad! i just took my ix down for the test it came back with a hc reading of 26. i didn't even know it was possible for yours to be that high. maybe the new o2 sensor is bad? thats where i would start. this is the feedback sensor that tells the ecu how to set the timing and mixture.

[Joe G]

find a shop that will inspect another car and hook you up with a pass for a $20 hand shake.

[bowtie2bimmer]

^ i like that idea

idle control valve? clogged charcoal canister? install fresh air injection?

[JeremyE30autox]

Leave NJ?

[TurboJake]

HC ppm @ idle:
Max: 220
Reading: 1110

WOW!

Checked the fuel pressure lately? High HC's generally are the result of a rich mixture. Carbon deposits second that.

I would also venture to say your cat is toast/useless now. All that raw fuel coming out probably torched it.

[lolcantturn]

High HC at idle on an M20 is directly correlated to the TPS and nothing else. Change that and you will pass definitely.

[rturbo 930]

holy shit! thats bad! i just took my ix down for the test it came back with a hc reading of 26. i didn't even know it was possible for yours to be that high. maybe the new o2 sensor is bad? thats where i would start. this is the feedback sensor that tells the ecu how to set the timing and mixture.

When we installed the new sensor, it didn't really make a difference. I think the old one was fine, but we tried it just to try it, since we were running out of ideas, and it was pretty cheap. I'll double check it to be sure.

^ i like that idea

idle control valve? clogged charcoal canister? install fresh air injection?

I'll check these things. Thanks.

Leave NJ?

I like this idea.

WOW!

Checked the fuel pressure lately? High HC's generally are the result of a rich mixture. Carbon deposits second that.

I would also venture to say your cat is toast/useless now. All that raw fuel coming out probably torched it.

I'll check the fuel pressure. I know it's running lean.. or is it rich? I don't know, my dad is doing most of the work here since he knows what he's doing. But I think he told me it was running lean.

We replaced the cat this week. The old one was toast for sure - the high idle readings the first time were just barely passing (212), but today it read around 110.

High HC at idle on an M20 is directly correlated to the TPS and nothing else. Change that and you will pass definitely.

I'll look into this as well.

Thanks guys.

[lolcantturn]

Change your TPS before anything else. I guarantee that's it- Passing at high idle and failing at idle is directly the TPS.

[TurboJake]

High HC at idle on an M20 is directly correlated to the TPS and nothing else. Change that and you will pass definitely.

This makes sense.

High HC is the hydrocarbon, raw fuel, coming out.

If the TPS is bad, the DME could be thinking that the throttle is depressed, and is constantly dumping load fuel in. Which does, and sometimes doesn't, affect the driveability/idle.


Lean mixtures causes high NOx

[lolcantturn]

This makes sense.

High HC is the hydrocarbon, raw fuel, coming out.

If the TPS is bad, the DME could be thinking that the throttle is depressed, and is constantly dumping load fuel in. Which does, and sometimes doesn't, affect the driveability/idle.


Lean mixtures causes high NOx

This is exactly what is happening. If you search into my M20 days threads, you can see a lot more information into it, but that's not necessary. Change your TPS and not only will you pass inspection, your idle will improve pretty dramatically.

[jlevie]

The engine having a rough idle means that it is misfiring, which will dump raw fuel into the exhaust and cause misfires. The cause of the misfires is what needs to be found.

The first things I'd do would be to check the rail fuel pressure and have a smoke test run on the intake. I realize you have looked at ignition with a scope, but if more than five years old I'd replace the ignition wires, distributor cap, and rotor. I don't know what plugs you used, but if not the correct Bosch or NGK plug, replace them. Check the idle switch in the TPS and make sure that it is working, by checking for continuity at the DME connector.

Were the replacement injectors new or rebuilt parts? If not send your old injectors to RC Engineering, have them rebuilt, and install those.

[long tall eta]

is the car chipped? and would that have anything to do with it?

[cunninglinguist]

High HC at idle on an M20 is directly correlated to the TPS and nothing else. Change that and you will pass definitely.

LOL I can no longer tell if people are stupid on this site or just trolls.

[Thizzelle]

check ICV, Injectors, air flow sensor (make sure plate isn't binding inside) also check coolant temp sensor (there's 2 brown goes to your gauge, blue goes to DME)