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2G Rich or lean?

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spyderdrifter

10+ Year Contributor
5,267
711
Jul 11, 2009
Somewhere in, Colorado
I keep getting the P0170 code. It's been doing this for a while now. I'm trying to figure out if my car is running rich or lean. I know I can check my spark plugs to see if it's running rich, but what can I look at to see if it's lean? What's a dead give-away sign of it? I don't have a wideband, DSMLink, afpr, or anything else to monitor A/F mix.
 
Coolant temp sensor could also be a possible cause. If you don't know the age of it, or haven't replaced it since you have owned the vehicle, I would just replace it. It's not an expensive part, easy to replace and can cause all kinds of weird fuel delivery problems if bad. Usually the sign of running lean, as far as checking spark plugs, would be kind of a reddish tint to them like they are getting hot.
 
Check and see if your o2 is cycling. Possible bad o2 sensor. Do you have a datogger or a basic dvm?
Sadly I do not have a datalogger, I do have a dvom from snap-on and a bluepoint code reader tool that does show live data while the car is running. I figured I could use this, but I've never really know how to understand the o2 readings on it.

Coolant temp sensor could also be a possible cause. If you don't know the age of it, or haven't replaced it since you have owned the vehicle, I would just replace it. It's not an expensive part, easy to replace and can cause all kinds of weird fuel delivery problems if bad. Usually the sign of running lean, as far as checking spark plugs, would be kind of a reddish tint to them like they are getting hot.

Starting this Wednesday I dropping my old 6 bolt back in since the current 7 bolt has crankwalk. I have the same temp sensor on it that I did have on the 6 bolt, since I used a 2g head for the old setup. The sensor isn't more than 2 years old at very most.
 
Well I guess we will have to wait and see if the code comes back with the 6 bolt in then. If so then it would be best to get some sort of fuel monitoring device such as a wideband or datalogger. It would be a good idea to get a wideband regairdless just to keep an eye on fuel delivery in the future. A lot of problems can be solved just by knowing for sure your a/f ratio is on point.
 
I'm reviving my old post, so that I can continue the same discussion, but for my current car. My old spyder seemed to return to normal after I swapped back to the 6 bolt, so that story is complete as the car was sadly sold last May. I now have a 96 TSI awd and have a similar issue. I'm currently getting right around 180 miles to a full tank and have averaged about 16.5 MPG. I have checked the tank to see if the gauge is reading accurately to the level, and it seems to be as accurate as it can be. I know these cars are old now, but I rebuilt the engine for it and have only put a few hundred miles on it, mostly in town, but to and from work I'm on the highway for about 10 miles each way. I've had the car back on the road for roughly a month now, minus 1 week it was down while I found a new t-case. I have had 1 trouble code, and sadly can't remember the specific number, but it indicated my IAC motor was bad. I do get some random idle surge, but have narrowed it to my throttle plate sticking. I have all the parts to rebuild the TB, but haven't had the time available yet. So in the end, could these two issues result in that bad of fuel consumption? I do have a noticeable fuel smell as well.
 
The IAC and throttle body are unlikely to be your culprit for crap fuel economy, it's most likely boost leaks as Chrysler Kid noted. Your TSi is a '96 and therefore OBD2 compliant; pick up a Bluetooth (Android) or wifi (apple) OBD2 adapter on Amazon (I use/recommend VeePeak) and Torque Pro or whatever OBD2 app apple uses. It'll cost you like $25 total and you'll be able to directly view your fuel trims with live data and instantly see if you have vacuum/boost leaks.

Don't waste your time troubleshooting things blind, it will just make you frustrated. If your Long Term Fuel Trim (LTFT) is over +5% it's time to boost leak test. If it's beyond -5% your fuel pump is likely overrunning your FPR. Both can cause fuel economy issues, and are common places to start.

Get your mod list updated and a basic logger up and running, and we'll be much more able to help you. That or you can just throw parts at it while praying to the DSM gods, but they rarely answer prayers. Let us know your fuel trims and we can start from there. Good luck man, it's likely something simple :)
 
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