Help me troubleshoot poor fuel economy - Page 4 - North American Motoring


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Help me troubleshoot poor fuel economy

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  #76  
Old 07-24-2017, 11:49 AM
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The presence of soot at the tail pipe does not necessarily indicate a malfunction.
When the car is cold it runs rich and will soot up the tail pipes even though everything else is in good tune. Once it warms to operating temperature it will stop producing soot at the tail pipe.
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  #77  
Old 07-24-2017, 09:09 PM
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I have a bluetooth reader, but I didn't think it did any logging. It's OBD Fusion. I wasn't aware it did logging. Sounds like I'll need to do some googling to figure out how to actually use it.
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  #78  
Old 07-29-2017, 08:43 AM
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Sorry for big pics... Just started monitoring logs and trying to figure out OBD Fusion. I can't get anything for AFR, I think because o2 sensor data isn't available. Readiness monitors aren't all okay, so maybe it's due to that and they'll be good soon? I've driven about 120 miles, though... I'd imagine that should have put me through enough paces to sort it out.

In any case, my LTFT is around -14% at idle, at cruise it drops to -9%. I also included the coolant temp reading which says 231. Seems a little high? Also IAT was reading 143... Also seems pretty high. Also -11deg timing advance seems a bit high... What gives? Are these normal?






Last edited by CSP; 07-29-2017 at 08:50 AM.
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  #79  
Old 07-30-2017, 07:53 AM
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Still running rich. I can smell it and see it on the tailpipe.

I pulled the map on the manifold and it had a little bit of oil on it. I ordered some MAP/MAF cleaner to try to fix that instead of just replacing it at $100. We'll see if that helps.

Beyond that I'm not sure what to do. Do bigger injectors fit without a problem? Like, do 440cc injectors need any rail spacers or anything? It wouldn't surprise me if the PO put big injectors on there to try to compensate for the Sprintex, but the fuel trims don't match up with that. Any suggestions beyond the MAP?
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  #80  
Old 08-06-2017, 06:52 PM
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I still think I'm running rich at times, but I just managed to get 25.7mpg to my last tank! Again, strong majority of highway driving with some suburban and city driving mixed in. I'm going to replace the MAP sensor I think. Or maybe I'll just give it a real good cleaning and see how that works. Although I read since MAP is just pressure and not airflow it doesn't make THAT much of a difference. Thought? Opinion?

I'm super stoked that I am finally starting to get proper economy. It's only a start and needs to be repeated, but it's still a start! Woot!
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  #81  
Old 08-07-2017, 11:50 AM
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Great to hear. Glad the changes have made an improvement to your car's MPG. Sounds more inline with what most get in mixed hwy/city driving now.

I used the MAF cleaner on the MAP sensors a while ago when we did the rear 02 sensor and no issues using that as it didn't cause any additional problems. Still planning to do the front 02 sensor like you since you saw such a significant improvement.
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  #82  
Old 08-07-2017, 12:42 PM
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My 02 R53 w/240,000 miles was dropping from 26 to 22 mpg. I had a "pending" code 1242 MAP sensor. Fortunately I had an idea of the issue prior to it failing so I had the new plastic vacuum line on hand . Yesterday I replaced so it will be interesting to see the mpg. I was noticing a hesitation or a lumpy feeling when I rolled out of the throttle. That has gone away with the new vacuum hose.

FYI... pending codes won't trigger the CEL until they become a real issue. And the plastic vacuum line to the MAP are a common failure point on older minis.

Quote:
Originally Posted by CSP View Post
The last 2 tanks I've averaged 18 and 19 mpg, respectively, with about 70/30 highway/city. From what I gather, it's about 7-8 mpg difference which is pretty significant with a 6 speed. I typically cruise around 75 mph on the highway and I'm not hooning around in the city.

Mods that I know of to the car are just a sprintex (69mm pulley) and CAI which wouldn't do much. I do have the torque app which I suppose could help track fuel usage, but I don't know how to read the logs because I'm a noob. I'd be willing to save some logs and post them here if someone could get anything useful out of it.

The only things I can think of are I either have a leak or bigger injectors. What other variables are there? I've never had a fuel issue like this before so how do I troubleshoot from here?
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  #83  
Old 08-07-2017, 02:52 PM
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Interesting. Is one MAP sensor more important than the other? I'd imagine the one on the manifold is more important since it has fewer connections to realize actual pressure? In any case, I'll inspect that vacuum line tonight.
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  #84  
Old 08-22-2017, 11:37 AM
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Over the weekend I took the mini on about a 1,000 mile road trip to watch the eclipse. In 95* heat, the mini took it all in stride and I managed anywhere from 26-28mpg. It's not ideal, but it's super as hell a LOT better than it was. I did replace the MAP sensor and didn't see any notable changes.

I can still smell it running rich, but I think the only thing left to change is the injectors. Negative fuel trim is lean, right?
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  #85  
Old 08-22-2017, 12:45 PM
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Was the O2 sensor the biggest positive change to gain back the mpg?
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  #86  
Old 08-22-2017, 12:49 PM
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That's the only thing that has given me a noticeable gain.
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  #87  
Old 08-26-2017, 12:21 PM
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Replaced 02 sensor

We did the deed. Super easy from below with the long 22mm wrench. Once I loosened it from the manifold, my son unscrewed and pulled the sensor up and out.

Sure looked like it wasn't optimal. Look at the crud at the base and the white powder all over the cage of the sensor. Is that coolant? It also looked like it was the original for all we know.

Now we get to see if it makes an improvement. (Sorry for the HUGE pic, but neat to see the detail.)

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  #88  
Old 08-26-2017, 12:59 PM
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Heh. That looks about like mine did. Yours may even be a bit worse. Have you monitored your fuel trims at all?
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  #89  
Old 08-26-2017, 01:14 PM
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Does all that black cake point towards running rich? I've never diagnosed that myself, but it certainly looks like a flag to me.

(been monitoring this thread with interest)
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  #90  
Old 08-26-2017, 01:18 PM
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Probably. I don't know enough about o2 sensors, though. Maybe a more experienced vendor will chime in with some input.

Also - ZSM - I believe being fouled white like that is coolant. Have you noticed any loss?
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  #91  
Old 08-26-2017, 01:58 PM
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Haven't monitored fuel trims, but last time I pulled the plugs, they all had a normal light brown color so I was happy to see that. (About 10K ago)

This sensor may likely have been original. With 225K miles, who knows when or how long it was caked with the white residue. I think you're right CSP, seems to be coolant. The car is not losing coolant, so could be an old problem prior to our ownership.

My kid left a bit ago to go to work so we will see if mpgs improve or stay the same over the next few tankfuls.

This has been a good thread to go through all of the common issues related to fuel trim and economy. 👍🏼
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  #92  
Old 09-22-2017, 06:44 AM
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Mine looked like that with age, Not that white but a little white. When i did mine the fuel economy just starting dropping, then I got a CEL for the 1 of the sensors, then a couple weeks later the other one went. I would do both at the same time. AS one goes then the other one will go when they get a lot of miles and age on them. I used this tool in the link and the sensors.

https://www.northamericanmotoring.co...om-up-top.html

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  #93  
Old 10-15-2017, 02:20 PM
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Quote:
Originally Posted by CSP View Post
Over the weekend I took the mini on about a 1,000 mile road trip to watch the eclipse. In 95* heat, the mini took it all in stride and I managed anywhere from 26-28mpg. It's not ideal, but it's super as hell a LOT better than it was. I did replace the MAP sensor and didn't see any notable changes.

I can still smell it running rich, but I think the only thing left to change is the injectors. Negative fuel trim is lean, right?
negative fuel trim means rich. Negative takes away fuel, positive adds fuel.

Did you ever end up doing an injector swap?
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  #94  
Old 10-15-2017, 02:24 PM
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Quote:
Originally Posted by MiniCooper_S View Post
negative fuel trim means rich. Negative takes away fuel, positive adds fuel.

Did you ever end up doing an injector swap?
I bought some. They're sitting in the back seat right now. I just returned last night at 2 AM from 2 weeks out of the country - wasn't trying to make any big changes right before we left since the mini is our only car and we needed it to be functional to drop our dogs off and get to the airport. I've been trying to get my suspension done for a while and think I'm going to a local DIY shop to do it. I think I'll swap injectors there.
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  #95  
Old 10-15-2017, 04:05 PM
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Quote:
Originally Posted by CSP View Post
I bought some. They're sitting in the back seat right now. I just returned last night at 2 AM from 2 weeks out of the country - wasn't trying to make any big changes right before we left since the mini is our only car and we needed it to be functional to drop our dogs off and get to the airport. I've been trying to get my suspension done for a while and think I'm going to a local DIY shop to do it. I think I'll swap injectors there.
I hope you had a nice trip! Let us know if that solves it for you!

Are te you keeping the suspension stock or going aftermarket?
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  #96  
Old 10-16-2017, 10:07 AM
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Mexico and Cuba for 9 days... Hard to NOT have a nice trip! I'm glad to be home, though.

I have KW V1's in a box ready to go on, just been dealing with some rusted bolt issues. Hopefully the aid of a lift and proper air tools makes it a smooth install. Otherwise, I'll be paying ~$400 to have these installed.
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  #97  
Old 10-18-2017, 11:12 AM
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I haven't perused the NAM forums for a while, so I'm coming very late to this party (thread). Nevertheless, I am very interested in what you have found, and would like to add my experience.

In the three years (and 50k miles) I have owned my Mini Cooper S, I have averaged 21 mpg. At first I was a little concerned with this, but the car ran really well so I eventually just accepted that low MPG was normal for my Mini.

I bought my 2003 MCS in 2014 from a friend who had it for ten years. It had 135,000 miles, and my friend had done some light mods: 15% SC pulley, widened airbox, one-ball exhaust, and tune. Apart from the #3 spark plug stripping out of the head shortly after I bought it (subsequently repaired), it has generally run great. Which is to say, it has had lots of problems (coolant tank failed, headlight washer tip broke, shock towers tore, shocks are worn out, engine mounts are bad, AC blower motor resistor failed, and it developed a major shifting problem which has only gotten worse, but is as yet undiagnosed), but the engine has always run great.

The engine purrs, idles smooth, revs nicely, and pulls better than other most MCSs I've driven (with the notable exception of a friend's track car). It has always seemingly run a bit rich, with very sooty exhaust tips. I once got 30+ MPG driving back from Yosemite, but otherwise I have almost always gotten between 19 and 23 miles per gallon in what I might call spirited, mixed daily driving.

I'm inclined to continue to accept this low mileage as normal, as I have enough headaches with this car already (and fear what I might learn if I look too deeply into the condition of the engine). However, due to a recent catastrophic failure of the original exhaust manifold (thread forthcoming), I am now rather familiar with the pain of dealing with the O2 sensors. When I replaced my broken exhaust manifold with a good used one, I simply swapped over my old O2 sensors (which looked a bit white on the outside, but not terrible). But now that I've read this thread, I'm considering installing a new upstream sensor.

Have you continued to see a four to five mile per gallon gain?
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  #98  
Old 10-18-2017, 11:25 AM
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Mixed driving has netted me around 25 mpg fairly consistently - around 350 miles per tank. It still runs a bit rich, but is definitely better and more consistent overall.
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  #99  
Old 10-18-2017, 11:50 AM
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After my son and I replaced the upstream 02 sensor in his R53, mileage improved a little. His route to school and work includes rolling terrain (SF State to San Mateo via 280), but overall, his mpg is now around 26-27 mpg. About a 15% improvement.

We did upgrade the wheels since two were bent to a used set of OZ superleggera, but that didn't make any difference on the mpg front.

Last edited by Zsm; 10-18-2017 at 12:08 PM.
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  #100  
Old 10-21-2017, 07:43 PM
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This update isn't a productive one.... I got my suspension installed, but I was at the shop for a total of about 9 hours. I had zero motivation to swap injectors. They're still on my list to do. I think I'm going to try to swap them either tomorrow if I have time/motivation, or they'll have to wait until first thing in November.
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