well I finally have some down time due to getting my wisdom teeth out today, so I figure I can research on what my car is doing.

first of all, upon startup it seems like the car is staying in open loop for a very long time. When I start it up there is an intense "sucking" noise from the moroso intake that seems to last a very long time. The rpm's stay up high at about 1000(a4 in park) for quite a while. they never really seem to come back down for a good few minutes.

Also, I'm pretty sure the car is running rich. It pours black smoke pretty bad but only at WOT. Its fine at ever other throttle position. If I'm not mistaken the car runs at open loop at WOT so I believe thats the root of the problem.

If anybody knows what sensors would cause this, let me know. The car just doesn't feel like it used to!

Thanks
-Ryan

 

One possible scenario for the black smoke at WOT....

While the PCM does not usde the feedback from the O2 sensors at WOT, it MAY use what it learned in closed loop. If the engine was running lean, for example, and the PCM was using the long term fuel corrections to add fuel and prevent the lean condition, it would continue to use those "add fuel" corrections when it goes WOT. But your case appears to be the opposite - its running rich on closed loop, and the long terms corrections are cutting fuel to bring it back where it belongs. But when you go WOT, the PCM will not use the "cut fuel" long term corrections. It will default to "0" correction.

That means that while its possible for the long term corrections to control the rich condition in closed loop, it can't prevent them at WOT, and you get black smoke.

Hard starts and a long time to closed loop may be a function of the coolant temp sensor.

Is it possible the sucking noise from the intake on cold start is the AIR pump running?

 

What could be the cause of the fuel condition, bad 02 sensors maybe or do you think its something in the fuel system.

Is the coolant temp sensor you are referring to the one in the WP?

Ill check out the sucking noise, it hasn't always done it, Im 99% sure its the intake but I'll take a closer look and get back to you.

Thanks a lot by the way, your a big help man!

 

The coolant temp sensor in the water pump housing is the one that the PCM uses. It needs that temperature for cold start enrichment, cold start idle speed, PE mode A/F ratio, to decide when to go into closed loop, when to turn the fans on and off, etc.

If you have a "true" rich condtion, could be from too high fuel pressure, faulty MAF calibration, erratic MAP readings, erratic TPS readings, an EGR valve that is malfunctioning. Then there are "false leans" that cause rich operating conditions, because they force the long term fuel corrections to add fuel the engine doesn't really need. Exhaust leaks before the O2 sensors, misfires, and faulty O2 sensors or wires could cause a false lean condition.

 

Pulled the relay for the air pump and fired her up, still made the noise. You can definitely tell its coming from the intake. I'm going to pull the filter assembly out for the heck of it..but I'm pretty sure it has something to do with the open loop problem because it doesn't do it in closed loop.

Where is the other coolant temp sensor, in the block/head i'm guessing? Is there a way I can check this without just buying a new one? I hate just throwing parts at problems.

once again thanks a lot for the help!

 

here's another piece of info, I followed shoebox's guide for checking the coolant temp sensor on the head, the readings came out good.

When testing the sensor itself, I got a reading of 1980 ohms which seems pretty good. I tested it on a cold motor with an ambient temperature of around 85 degrees.

I also tested the harness for it and got a solid 12v reading so that can't be the problem.

Last but not least I grounded out the harness and the temp gauge maxed out so everything seems to be working properly. Now I'm not sure if these readings are fool-proof but I figure the more info the better.

Do you think this could still be a problem? I'm going to look into your other options..hopefully I can figure out how to test everything haha.

Of course...I'm also due for inspection this month do you think any of this will cause it to fail emissions? I have yet to talk to my shop to see what they say about it.

 

Why are you checking the coolant temp sensor in the head? Is your gauge not working? As I've already explained, its the one in the water pump housing that the PCM uses, and might be causing your problems. Did you not understand what I posted?

As far as the noise in the intake at cold start, it might be related to the throttle body IAC passages.

 

not sure how I read that wrong..wow haha

I went back and checked the WP sensor and everything seems good there anyway.

Something that slipped my mind is my MAF. The previous owner of the car de-screened it and really hacked it all up trying to port it I guess. Do you think it's reading incorrectly because of it? Here's some pictures:




Last but not least, I took a video of the infamous sucking noise.
http://s16.photobucket.com/albums/b4...t=MVI_2348.flv

 

any thoughts on this?

 

What do you mean checked it? Did you scan the PCM to see what temp it's reporting? Just looking at it won't mean a thing.

A modified MAF with no other changes will pass an amount of air that the PCM can't see. In other words, at the same frequency as before it was modified, there is now a different volumn of air flow. So the PCM thinks it's getting the same amount of air but it is getting a different amount. In your case it's getting more air than it thinks it's getting. Capeesh?

 

As far as the sucking noise goes, my brother has a 93 z28 that does the same thing. He has one of those throttle body air foil things that i think has something to do with it. It runs great, just makes that sucking noise really loud.

 

No, I didn't just look at the sensor. I tested the resistance across it with a multimeter and compared it to the graph on shoebox's site. I also check the wiring harness to it which read correctly as well.

Capeesh...But I'm still confused. If the MAF is passing more air than it is reading, wouldn't that cause me to run lean?

 

You are correct... if the MAF reports less air than the engine is acutally using, the PCM will not add enough fuel (lean), so it will have to rely on the long term fuel corrections to add the required fuel. If the MAF was reporting more than actual air flow, it would run rich, and the long term fuel corrections would pull the excess fuel out. The problem comes when the MAF error exceeds the limits of the PCM to control the A/F ratio using the long term fuel corrections. It can only add 25% or subtract 15% of the fuel using the long terms. In closed loop, it will then use the short terms to adjust the fuel further, but that is unstable. In open loop, on cold start, it can only use the long terms, so it may run poorly on cold start when the MAF error is excessive.