1995 525i odd running issues

[BlackSpeed66]

Been a long time since I've had to post here since the Touring's been a champ the past few years. Over the past months, I've noticed some odd engine issues while driving and have been struggling to pin them down without simply throwing parts at it. I'll attempt to be as concise as possible:


-Car always starts and idles well regardless of engine or ambient temp

-idle to about 2k on the tach is fine

-around 2k-3k on the tach the car hesitates noticeably, lack of power, etc etc...

-3k to about 4.5k the car pulls amazing, like nothing is wrong.

- hits a wall at about 5k with heavy bucking/jerking and the CEL while come on until the revs drop down below 4k again.

-smoke tested the intake tract and crank case for any vacuum leaks - none found


Car was manual-swapped a few years ago, so no auto trans issues that would cause this. I swapped out the plugs (NGK) and fuel filter since they were about due. No change. I have a Peak tool that i've attempted to scan any codes with. Those initially came up as: 0d (oxygen sensor, 10 (crank sensor), 19 (cyl#5 coil), 33 (cyl#2 coil), and 45 (knock sensor for cyl 4-6). I attempted to swap the #2 and #5 coils from a parts motor. Still no change in performance really, the symptoms persist however the only codes that seem to show up any more are the Crank sensor and the cyl #2 and #5 coil codes. Ambient temp and operating temp do not seem to make a difference.

Was considering throwing an O2 sensor at it since there's just one and I've never touched it since i bought the car in 2015. She's getting ready to cross 200k miles so I'm thinking it wouldn't hurt. I just don't want to foul a new sensor if there's some other issue going on. I'm hesitant to throw a crank sensor at it because from my searches, those seem to manifest as a no-start issue, which I'm not having. I wanted to try and test the fuel pressure but there's no test valve on the rail. Despite there not being any code - should I consider looking at the VANOS as well? Like the O2 sensor, I've never touched it - and I assume it's never been serviced before.

Appreciate the help folks!

[TGreene]

Does it feel like the power is cutting off completely and then coming back full on? Like somebody is toggling an on/off switch while you're driving? I have had that happen on two E34s and both were dying fuel pumps.

Fuel pumps are cheap enough and contribute to a majority of dead E34s that I have seen, so good preventative maintenance in any case if you are unsure of yours.

This reminds me that I need to replace my fuel pump again =p

[BlackSpeed66]

Yeah the fuel pump was another possibility i was considering in the back of my mind. I presume it too is original -- and now I'm kicking myself for junking the '91 sedan i had for the manual swap since i assumed the fuel tank and all was different from sedan to wagon. Been battling fuel tank leaks around the seam as well for the past year. Both that spare pump and tank would have been real handy about now.

The hesitation and roughness i feel between 2-3k on the tach is somewhat mild but you can definitely tell it's there. Hitting 5k is extremely rough - the car jerks and bucks heavily like it hit a wall. I'm wondering if the codes being triggered are more of a symptom from a possible fueling issue.

[TGreene]

Figure it out?

[BlackSpeed66]

Well I ordered a Bosch pump from RockAuto and installed a few days ago. Unfortunately that does not appear to have resolved the issue.


Not entirely sure what to proceed with next... I hate to throw parts at the car, however I have to imagine a lot of the sensors and other components are more or less original.

Really wish i was able to get a live data read off this car like i can with my others that are OBDII - would be super helpful now!

Any thoughts if a failing VANOS system could contribute? Even without throwing a code? From what I've gathered on the single VANOS systems on these cars, it is more or less "off" from about 3k-5k RPMS. Is that correct? It seems that's where the car runs fine at but outside of that range is where it seems to have rev or power issues. Just thinking out loud....

[BlackSpeed66]

I picked up a seal and rattle repair kit from Beisan for the VANOS. Figure it can't hurt to do since the car has almost 200k miles on it anyway. Got it all buttoned up yesterday and went for a spin. Unfortunately, still did not resolve the running issues. Front end of the engine is a lot quieter now so I guess I was rocking some pretty good VANOS rattle.

Considering an O2 sensor next since it's cheap-ish and I've no idea when it was last replaced.

Anyone else have any thoughts?

[circuit.heart]

Failed Vanos would more likely manifest as hesitation from 2000-4500 ish. From what I could tell off my car (rigged an AFR wideband for live readings) the loss of Vanos causes the engine to run lean in the midrange, and the ECU pulls timing to keep it alive.

If it refuses to go over 5k I would think it's a timing sensor (crank and/or cam) issue or an extreme AFR/detonation issue.

[TGreene]

If it is having a really hard time above 5k, maybe it is a clogged cat issue? From what I have gathered, higher end power loss usually seems to have been fuel issues (commonly pump) or in rare instances clogged cats not letting the engine to breath over a certain RPM. Maybe roll underneath and gently tap the cats and listen for loose material?

[TallSexyJesus]

Did you ever figure it out? My 95 is doing the exact same thing and its frustrating to say the least. From what I can tell its lean symptoms. (backfire on stabbing throttle, hesitation under acceleration, jolting). What is weird to me though is its not persistent. it randomly acts normal and quickly accelerates. Thinking fuel injectors or fuel pump.

[BlackSpeed66]

So yeah… car’s been sitting for 10 months or so. Had to walk away for a bit. O2 sensor broke off at the bung trying to break it loose and one of the fuel lines started leaking. Finally hacked off the cat converter yesterday to get to the O2 sensor. Took a plumbers wrench and a 4’ iron pipe to break it loose in the vise. Worst. O2 sensor job. Ever.

Once I patch the exhaust back up with the new sensor and patch up the fuel line, will take it for a spin and see if any changes. The tip of the existing sensor looked pretty gnarly…. Not sure if it’s the problem or a symptom. Will report back…