My ,91 944 S3 (S2 with variocam head/DME) just got smog checked... no visible smoke comin' out the tailpipe but, as I watched a diesel locomotive across the street spew brown smoke from its stacks, the tech informed me that my car was a "gross polluter". Gimme a break!

Anyway, anyone know of a local (SF Bay Area) smog tester that can test without sending data to the DMV.
I'm not tryin' to cheat, I just want to be sure that, after tuning the thing, it will pass before I take to get the 2nd official test.

The car was running rough under load so I replaced the TPS and now it runs smoother. I still want to be certain it will pass before I get the official test done.

 

got any friends in Ely/Reno, NV ??

 

You should be able to 'pre-test' anywhere, but if it passes then you might as well have done the actual smog test.

 

Could this have resulted from using '91 S2 injectors (fresh rebuild) in place of 968 ones? (see my other post).

 

What were the results? Then results are needed to point to the cause.

 

Oh.. heh heh... here are the results... The highlighted numbers are the maximum acceptable, mine are the circled numbers.

 

The cat seems to be working. You need someone to adjust your AFM spring to get your Hydrocarbons in line.

 

No AFM... It's a 968 head/DME/MAF. Any suggestions?

 

Your engine is running rich. It is dumping a ton of unburnt fuel out of the exhaust. I'm going to guess your O2 sensor is bad.

Either you have a bad temp sensor, leaking injectors, fuel pressure problem (too high), O2 sensor is bad, air filter is clogged/dirty, or something else in the fuel management system.

How old is your O2 sensor? Is it the original factory cat or is it aftermarket? Factory cats are leagues better than aftermarket ones, even a 15 year old factory cat should still be good. Don't forget to drive long enough to get that cat hot. Drive hard if you need to; get that cat really hot! The engine should be at operating temperature too.

I'd start by doing the resistance checks on your temp sensor, and voltage checks on your O2 sensor, and replace if needed. Remember that your DME is expecting 968 temp signals, maybe your S2 signals are wrong? Check your fuel pressure with a gauge. Clean your MAF (they make a MAF cleaner spray...). If your spark plugs are old, replace them with the proper recommended plugs in the correct heat range. Replace your air filter.

Another thought I'm having is that MAYBE the S2 injectors have different impedance than the 968 injectors, so maybe they're confusing the DME and so the DME is running them at the wrong duty cycle? Just a thought. I don't know how to check, so maybe someone else can help.



I just had my own struggle trying to get my latest mercedes to pass smog. It was going to be a gross polluter as well but my boss lets me use his smog machine to do my own pretesting. I had high HC... 330. I put in a clean air filter, and manually leaned the fuel mixture (CIS-E) which got the HC down to 120. Noticed it had the wrong plugs. New (correct) plugs and HC went down to 25.

Unfortunately my work is in Pismo Beach even though I live in the bay area. If you need help with your car, I'm home on weekends and I can lend a hand. But most places should offer a pretest. Even a good number of mechanics have smog machines (not hooked up to the state computer network) and can give you a pretest.

 

Arash: since his NOx is in line, I think the cat is fine - his problem lies somewhere in fuel mixture.

 

Your engine is running rich. It is dumping a ton of unburnt fuel out of the exhaust. I'm going to guess your O2 sensor is bad.
Possible.. will check that.

Either you have a bad temp sensor, leaking injectors, fuel pressure problem (too high), O2 sensor is bad, air filter is clogged/dirty, or something else in the fuel management system.
Temp sensor is new, injectors are newly rebuilt, Air filter is newly cleaned K&N, fuel pressure (?) I don't have a gauge, possibly a bad DME?

How old is your O2 sensor? Is it the original factory cat or is it aftermarket? Factory cats are leagues better than aftermarket ones, even a 15 year old factory cat should still be good. Don't forget to drive long enough to get that cat hot. Drive hard if you need to; get that cat really hot! The engine should be at operating temperature too.
O2 Sensor is unknown age. Cat is a factory. Engine temp was fine, shop was not the first stop. I always drive hard .

I'd start by doing the resistance checks on your temp sensor, and voltage checks on your O2 sensor, and replace if needed. Remember that your DME is expecting 968 temp signals, maybe your S2 signals are wrong? Check your fuel pressure with a gauge. Clean your MAF (they make a MAF cleaner spray...). If your spark plugs are old, replace them with the proper recommended plugs in the correct heat range. Replace your air filter.
I'l probably just replace the O2 sensor anyway. Which temp sensors are we talking about? Where do I get MAF cleaner? Spark plugs I can change .


Another thought I'm having is that MAYBE the S2 injectors have different impedance than the 968 injectors, so maybe they're confusing the DME and so the DME is running them at the wrong duty cycle? Just a thought. I don't know how to check, so maybe someone else can help.
Well, that's why I'm waiting to hear back from Marren... to tell me what the functional differences are between the '91 S2 spec injectors and the 968 ones... the most obvious difference being a couple hundred bucks each.

Unfortunately my work is in Pismo Beach even though I live in the bay area. If you need help with your car, I'm home on weekends and I can lend a hand. But most places should offer a pretest. Even a good number of mechanics have smog machines (not hooked up to the state computer network) and can give you a pretest.
Pismo Beach? Do you work for John Milledge? Hmmm. I'll let you know if I need your help. (I probably will).
Another consideration is... could I have mis-indexed the cam drive gear. I know it's adjustable for a couple of degrees. Could this be a possible culprit?

Thanks in advance for all your input.

 

I found this on the web... the differences between '91 S2 injectors and 968 ones:
Bosch top feed fuel injectors
Bosch Part Numbers OHM's CC/Min Lb/hr
0280 150 811 ('91 S2) 2.2 264 25
0280 155 010 (968) 15.2 296 28

For more examples: http://injectorrx.com/boschtf.html

Could this be the culprit?

 

Yes, that can be a problem. If that info is correct, you have the wrong impedance: 2.2 ohm injectors when your computer is expecting 15.2 ohm injectors. Try incorporating 13 ohm resistors onto each injector. That should be cheaper than buying new injectors.

The fact that their flow rates are slightly different shouldn't matter too much I think. But if you find a good deal and you can afford it, buying 968 injectors would solve a lot of issues and probably make the engine run better.

No, I don't work for Milledge, I wish! I go to Cal Poly and I have a part time job down there at a German auto shop. The fringe benefits are sweet.

The cam timing will have an affect on power and emissions, but not enough to fail smog. GL!

 

That info is consistent with two different web sites. So... rather jury rigging the existing injectors, Mister Scott, I think I'll try to find some ... Pelican Parts has them priced at $602 EACH. Highway robbery.

 

Ask around, someone has to have used injectors. You are looking for S2 or 968 injectors?
Raj