Hey guys,

Some of you may remember I had some fuel economy issues last year and I thought my car was running rich. Most of that was sorted out with a replaced head and new o2 sensor.

While driving through the mountains this past week, I threw code P0172 which is system too rich. At first, I chalked it up to a 7,000 ft elevation change in an hour so I just cleared the code. Same thing happened the next day - coming down from mountains and threw code. Cleared. Then all was well for a few days and on my 15 hour drive home, it finally threw it again after ~14 hours.

I averaged ~25-29mpg through the trip depending on conditions and it ran great. As far as I can tell, this would really only be caused by the FPR. I think it's been running rich for a long time, but I've never gotten a code - let alone 3 in a week. I suppose it's possible that the PO flashed some new map in conjunction with the sprintex, but I'd have imagined it would've thrown a code sooner.

I see a lot of people saying check for vacuum leaks, but I don't think a vacuum leak would cause a too rich condition? Typically that's unmetered air entering the system and the map on the intake manifold should really account for any pre-manifold leak anyway, right? Possibly the vacuum line to the FPR is split? If I'm thinking about this wrong, please let me know.

Is FPR a common failure? I've never had one go out on me before, but I've heard of it. Someone talk through this with me.

 

I know you inherited a highly modified Mini from PO. With a Sprintex chances is it has a tune. Can it be a over rich tune? Who knows. I am not trying to tell everyone to get a A/F gauge, but as soon as I changed the SC pulley I wanted to know if the motor is running lean, just right, or rich at different load conditions. I could not find anyone had shared their successful installation of a WB sensor onto the stock header while preserving the upstream NB, which was the most challenging task and I succeeded. If you have one you will see exactly what is going on.

Have you read the spark plugs? I would do that. Look for sign of differences between cylinders which might suggest an injector problem.

Mini has a non-return fuel supply system, and I think because of it making the fuel regulator job much more difficult. I have no idea if you will get too much pressure or too little when it becomes flaky. I would definite check the vacuum lines that supplies it including all in the same branch. It is very easy to inspect these once you remove the intercooler.

You can check if the diaphragm in the FPR is leaking by sucking on the vacuum port. I have diagnosed failed vacuum chamber like this. I would not count on it being likely in your case.

 

I'd love to get an A/F gauge set up. I was talking to a shop about installing one when I actually get it tuned.

The guy I bought it from explicitly said it didn't have a tune, but I'm not sure I believe him.

I haven't read the plugs yet, just got back at 2 AM last night and naturally it's raining in Chicago again. I'll pull them whenever the weather clears up and also inspect the vacuum line while in there.

Likely very naive, but I was thinking it wasn't an individual injector problem simply because my fuel economy was still pretty close to where it should be. Thought was that they only hard fail, not soft. This will be sorted when I look at the plugs, though.

Is the diaphragm what typically fails in FPR?

 

What mountains/elevation were you at? I know almost nothing about aftermarket tuning, but is it possible that it was tuned for Chicago elevation, and didn't adapt to the lower barometric pressure/oxygen at higher elevations?

If it was delivering sea level fuel amounts but only getting leadville, co amounts of oxygen, I think that could cause a rich condition.

 

That was my initial thought. We were up at 10,000-11,000 feet. But then it happened again at sea level...

 

https://www.northamericanmotoring.co...ml#post4397684

Just posted that for those who are having issues with the more complicated CELs

 

I have a bluetooth reader and have posted LT/ST fuel trims previously, before I ever threw a code. I'm going to just run through all the normal troubleshooting for this... pull/inspect plugs, inspect vacuum line to fpr, pull/check fpr and pressure with gauge.

If none of those show anything wrong, I'll just be taking it to the shop for them to do the pre-tune inspection which would presumably go over all of this, as well as plug it into the computer and see if it was flashed with something else. I'm HOPING it's a tune problem.