Coolant temp sensors and emissions tests (first posted in FAQ and DIY, wrong place)

[hammer_e30]

What's the difference between part #13-62-1-709-966 and part #13-62-1-357-414? Realoem.com says my car uses 13-62-1-357-414, but the one on it now has the blue insulator like 13-62-1-709-966. Just curious because I think I need a new one. I keep failing my emissions test at idle and I think that might be the cause. I replaced my O2 sensor and that made it a little better. I also have the Miller MAF conversion and I followed the instructions to a T. The car idles and runs smooth so I don't think that's the problem. The only other thing I can think of is a bad cat or possibly a torn intake boot. I have replaced all the intake gaskets because I had a bad vacuum leak on cylinder 1. It still passed emissions with the vacuum leak last year. Also the car is a California emissions car. Anyway, here are the results for this test after the O2 sensor replacement:

2500 RPM Test
HC(ppm): 85/Standard 220
CO%: .62/Standard 1.2
CO2%: 14.2
All passed

Idle Test
HC(ppm): 395/Standard 220 FAIL
CO%: .58/Standard 1.2
CO2%: 13.8

Here are the results from before I replaced the O2 sensor:

2500 RPM Test
HC(ppm): 86/Standard 220
CO%: .48/Standard 1.2
CO2%: 14.4
All passed

Idle Test
HC(ppm): 420/Standard 220 FAIL
CO%: .74/Standard 1.2
CO2%: 13.6

And finally, the results from way back in 2006 when I first bought the car:

2500 RPM Test
HC(ppm): 34/Standard 220
CO%: .06/Standard 1.2
CO2%: 14.7
All passed

Idle Test
HC(ppm): 32/Standard 220
CO%: .03/Standard 1.2
CO2%: 14.8
All passed

So I'm not sure if the coolant temp sensor would cause it to fail emissions because it could be causing it to run rich. I do have a slight idle surge when I start it cold. It goes from 700 to 1000 for about the first 1-2 minutes and then it's smooth after that. I'm also not getting good fuel economy anymore. I used to get 27 MPG on a long trip, now I only get 20-21 MPG. The guys at Miller assured me the MAF and chip won't affect fuel economy or emissions. It's kind of frustrating, he car has passed emissions every year until now. Hopefully someone can help me figure this out.

[hammer_e30]

Anyone know the answer? I hate running around with a temp tag.

[nando]

I think they are functionally indentical, at least cross referencing those part #s leads me to that conclusion.

I would get the blue one and measure the resistance and compare it to your old one.

[jlevie]

I rather doubt that the ECT sensor is the cause of the high HC at idle. A bad ECT should have a much greater effect on the 2500rpm test than the data shows. Nor would a bad catalytic converter seem likely given the difference between idle & 2500rpm data.

There are a number of possible causes for the test results, but the presence of the Miller MAF is a wild card in the list. You may not like this idea, but what I'd do would be to revert the engine to the OE airbox, AFM, and tune and then get the engine running like it is supposed to. With the engine in Oe configuration I'd smoke test the intake, run the fuel system tests, have the injectors cleaned and flow tested, replace the plugs, ignition wires, distributor rotor & cap, and adjust the valves. Then I'd see what the idle and 2500rpm A/F rato is.

Once the engine is running right, swap back in the Miller MAF and see what the idle and 2500rpm number look like.

[Evan12]

I also failed mine with old gas and dirty injectors. I'd get some injector cleaner, fill up, run it down and put stock airbox back on. I was about 200 Pts over on mine because of bad gas and then passed with flying colors after driving it aroun and filling up again.

[hammer_e30]

I rather doubt that the ECT sensor is the cause of the high HC at idle. A bad ECT should have a much greater effect on the 2500rpm test than the data shows. Nor would a bad catalytic converter seem likely given the difference between idle & 2500rpm data.

There are a number of possible causes for the test results, but the presence of the Miller MAF is a wild card in the list. You may not like this idea, but what I'd do would be to revert the engine to the OE airbox, AFM, and tune and then get the engine running like it is supposed to. With the engine in Oe configuration I'd smoke test the intake, run the fuel system tests, have the injectors cleaned and flow tested, replace the plugs, ignition wires, distributor rotor & cap, and adjust the valves. Then I'd see what the idle and 2500rpm A/F rato is.

Once the engine is running right, swap back in the Miller MAF and see what the idle and 2500rpm number look like.

Well, the guys at Miller were confident that it would pass. You're right, I don't like that idea haha. The only reason I don't like it, is because there has been a wire that has been cut and soldered and T'd to another wire to get 12V to the MAF sensor. I may replace the intake boot and see what that does. It looks like it has a few small cracks. It's weird though, I passed with a massive vacuum leak last year. I just replaced my intake manifold gaskets, throttle body gaskets, timing belt, and all the other things you mentioned about 5K miles ago. The injectors are the new pintail design and were replaced in 07. I have a can of BG 44K that I'm going to try. I wonder if the car sits too long before the test is done, so the cat has too much time to cool down 20-30 minutes it sat both times before the test was done, even though I made sure the cat was hot. The only other thing I could think of is the ignition coil putting out weak spark at idle. That's the only original part of the ignition system and it has 277K miles on it. The car runs perfectly smooth at idle though, other than a slight surge from about 600-1000 RPM for about 1-2 minutes when it's first started cold.

[hammer_e30]

I passed! I changed the coolant temp sensor and ran a can of BG 44K through the fuel system. The old sensor fell apart when I took it out. Also made sure the cat was hot before the test. The cat had 20-30 minutes to cool on the last 2 tests because I had to wait for someone else to finish their emissions test each time. This time, I got right in. The Miller chip is still in. Here are the new readings:

2500 RPM Test
HC(ppm): 10/Standard 220
CO%: .02/Standard 1.2
CO2%: 14.7
PASS

Idle Test
HC(ppm): 22/Standard 220
CO%: .01/Standard 1.2
CO2%: 14.8
PASS