I'm fed up with working on the MINI for today so I am going to ask some stupid questions to hopefully think through it.
Background: 04 Mini Cooper S. Runs very rough and applying the throttle doesn't do anything (mostly). Spraying starting fluid in the throttle body or vacuum leaks (fixed) will get it to run well.
There were vacuum leaks at the bypass valve and supercharger inlet duct. Those have both been fixed and I haven't found any other vacuum leaks by spraying starting fluid while it is running. After replacing the gasket for the supercharger inlet today it was doing the same thing and I let it warm up. Occasionally it would clear up and idle ok for a couple seconds then go back to a low rough idle. Feathering the throttle lightly can get it to rev. It runs and revs fine for a couple seconds after startup no matter what.
Codes are P0036 (o2 heater control circuit B1S2), P0031 (o2 heater circuit b1s1), P0123 (TPS A circuit high), P0222 (TPS B circuit low).
When looking at the live data that my scanner will show the front o2 sensor is steady, 0.4V at first and drops slowly to 0.1V. Rear o2 is at 0.4V steady. When I was first looking at it while it was running it was switching between open and closed loop fairly quickly. When I started it up to check again after 10 minutes or so it was stuck in open loop due to system malfunction.
Both o2 sensors have been replaced recently, (no mileage record but seemingly soon before it was parked. The front o2 sensor wire has a burn mark on the loom where it apparently contacted the exhaust but the insulation on the wires does not appear to be affected.
What additional diagnosis should I be doing to verify that the front o2 is bad before replacing it?
forget the O2's check the TPS reading. Did you plug it back in?
In reply to bobzilla :
The TPS is integrated in the throttle body which is plugged in. It has crossed my mind quite a few times that the throttle body could be the issue but haven't wanted to buy a new one yet without knowing.
Can a bad front o2 sensor cause issues this extreme?
Maybe if the sensor was the part that was bad. Those codes are for the heater element. If they were not sending signals you'd see 0.97V IIRC. The two codes you're getting on the TPS would be more likely the culprit. THat's kinda what you get when you don't have something plugged in (too high and too low means its really not getting a signal).
Since you can see data, watch the TPS % when running and you push the accelerator.
From what you describe, it sounds like the O2 is functioning. I'm with bobzilla. I've never had a failing O2 sensor cause issues other than a CEL.
If the O2 reads down towards zero, that means it thinks things are very lean. If the car runs badly, and isn't chugging huge globs of black smoke out the tailpipe, it's probably lean, and the sensors are correct.
Throttle position codes shouldn't make it lean, but the could make it not accelerate properly, because the ecu doesn't know for sure what is happening, and it may not allow the throttle to open.
Is there a pid for fuel pressure?
Was it running like this before you started fooling with it? If so, you didn't fix the right thing. If not, you broke it.
In reply to Streetwiseguy :
Fuel pressure measures in spec with a pressure gauge on the rail. My code reader won't display fuel pressure or fuel trims for it.
It was running like this when purchased. I fixed the large vacuum leaks and it still runs the same. I did the reset procedure for the ecu to clear the learned memory, I have not let it sit with the battery disconnected yet to see if that resets anything.
TPS percent changes when pressing the throttle pedal (7%ish at idle and up to 96% or so at full throttle). The throttle percent also changes when the engine idles up while spraying starting fluid in the throttle body. (decreases as the throttle closes to stabilize the idle).
well.... I'm out of ideas.
This is a BMW, which means it has a Bosch system on it- and somewhere in that era, a steady .4V meant that the O2 sensor was dead. Not hot enough to do anything.
And you have heater circuit codes.
If you are sure that the sensors are good, then I would very much look at the heater wire circuit to make sure it's good- there could be a short somewhere. That system would be outside of the sensor circuit, meaning the TPS issue isn't related to it. The heater system will be a 12V duty cycle system (depending on how much the ECU thinks that the heater needs warmed up). The sensor circuit is the 0-5V system.
BTW, I would look into those codes again- a MINI is a 4 cylinder car, so it would probably only have one bank- B1S1 and B1S2 should be the only ones there.
Back to the heater codes- it's really odd that BOTH sensors are having heater problems. It's almost if the heater power supply isn't supplying power. There may be a fuse or relay that's not working that should be supplying 12V to the heater.
Thinking about it more- the injectors also run of the 12V power supply..... It very much seems that the systems that need 12V are not gettting it.
is there a stand alone o2 sensor bench tester where you can test an o2 sensor to see if it is good ?
Check for power and ground at the chassis side of heater circuit wires (white, on a Bosch narrowband) Then check the resistance between the heater circuit wires themselves, should be single digit ohms on a cold sensor.
If it's a narrow band O2, check for any continuity between the ground (gray) wire and the heater circuit wires on the sensor, the sensor output (black) wire and the heater circuit wires on the sensor. Usually only common on Chryslers.
O2 heater circuit code generally means the computer is seeing no evidence of a proper load on the circuit. It sees and controls the ground, power is supplied by... somewhere. This will have nothing to do with the drivability issues, though. It's screaming "vacuum leak" and the first thing I'd do is a smoke test.
Could be completely unrelated but I remember my 2004 having serious issues when things in the hatch got wet....which was all the time on mine. I had to make sure to dry out the area under the hatch floor whenever it rained. I never figured out where the leak came from before trading the car in.
If you want to eliminate the O2 sensors as a source of your running issue, unplug them. Clear the adaptive memory, and fire it up. If it runs like E36 M3e, the sensors were reading correctly. If it runs well, the sensors were driving it lean.
O2's are a tuning tool for the ecu, not a primary signal. It will run on the base map quite nicely with them unplugged.
Cam timing ok?
In reply to Pete. (l33t FS) :
2004 would be narrow band. WB didn't come around for a few more model years after that. Not many, but they would have been phased in on the higher end models, too- so figure the 8 series before the 5 and 3 and then MINI in the BMW world. But that happened really fast- as the benefit to WB for control was pretty dramatic.
Can you see anything like a fuel trim? What does the car think it's doing? It's very rare but not impossible for an upstream o2 that's completely wrong to cause significant drivability problems, but you'll likely see pegged out fuel trims.
One thing to add- if you have to ADD fuel to make it run, the engine is running lean, right? And when the sensor actually got to be something other than ~.4v, it went close to 0V, which is the lean side.
So IF the O2 sensor had any input, it would be adding fuel- which does not sound like it's happening if you can get it to run better by spraying in fuel.
Still, if it sees a steady ~.4 (I think it's .54 on ours, for some reason- when we changed to a Bosch circuit on the board), the system should know to totally ignore it.
Thanks for the responses so far. I was sure the o2 sensors weren't causing the issues but after fixing the two obvious vacuum leaks I was second guessing it. The #3 fuse in the engine bay is for the o2 heater circuit. I checked the fuse and it looked good, I put in a new one anyway and no change.
Another thing I forgot, if I cover the throttle body with my hand it runs smooth which also leads to being very lean/vacuum leaks. I'll do some more investigating and maybe it's time to finally build a smoke machine.
Also may need to invest in a better code reader since I have multiple OBD2 vehicles in the fleet for the first time in a while. Mine is not showing anything on fuel trims but I don't know if that is from the car or the reader. It's a bluetooth adapter and Torque lite.
No idea if this will help, since it was not on a Mini, but the TPS High and TPS Low was an issue on one of my nephew's cars (Ford Focus), and I think all indications are that that the TPS needed to be replaced and of course it was integrated into the throttle body. Went through a replacement throttle body, including making it relearn, and there would be a very short period when the car started up that everything was fine, but the codes would come back, and the car would run rough and stall. In the end, I think it turned out to be damaged wiring, so it may be time to trace the wiring from the TPS to the ECM.
Last night I built a smoke tester. By the time I got done around 9pm and did an initial test I was only able to conclude that there is smoke coming from everywhere, including the smoke tester itself and where I blocked off the throttle body. There is a significant leak somewhere near the supercharger inlet though that I couldn't pinpoint. Sometime today when I feel like going out to fire up the heater to let the garage warm up I'll seal the smoke tester better and try to find out where the largest leaks are first.
Also yesterday before I did that I took another look at the scanner and this time it showed me the long term fuel trim of -100.7%. I got a INPA diagnostic cable today so I can try to load the bmw diagnostic software on a spare laptop and hopefully have better data.
Update: smoke tested it and found some vacuum leaks on the supercharger inlet duct. One was a vacuum line not seated all the way. It was also leaking from the plastic welded seams on the duct so I took it off again and covered all seams with RTV. After that I smoke tested it again and did not see any leaks.
Started it up and it does the same thing. Starts fine and idles ok for 4-5 seconds then drops down and runs rough around 500-600rpm. Sometimes playing with the throttle (pressing it a few times) can get it to idle smoothly around 1k rpm before it drops down again.
EvanB (Forum Supporter) said:
Started it up and it does the same thing. Starts fine and idles ok for 4-5 seconds then drops down and runs rough around 500-600rpm. Sometimes playing with the throttle (pressing it a few times) can get it to idle smoothly around 1k rpm before it drops down again.
That sounds very much like my nephew’s Focus, only it would end up stalling after running rough for a few seconds.
I should check the wiring on it. The TPS codes were gone when I checked today and the only codes were for the O2 heater circuit.
In reply to EvanB (Forum Supporter) :
I can’t remember if codes turned up immediately after doing a relearn or not. Different manufacturer, though, so who knows? I hope it is something more obvious, pulling the wiring harness apart is tedious.
