E30 battery change and now poor running

[speedyg 16]

Hi Guys,

As you may know I am trying to sell my E30 325i, so it has been getting little use lately. Battery is not holding it's charge and has gone flat a couple of times. So today I fitted a new battery, exactly the same as the old one, fitted correctly etc etc.

Turned the key on and there was a bit of a power surge before I turned it over. ie the car kinda moved as the power reached the engine.

Anyhow started it and it started straight away but the idle was surging from 1000-1500rpm, it's never done that before. Gave it a rev and it settled down. So I proceeded to go for a drive but as soon as you approach 2500rpm the car almost feels like it dies and then goes again, so you end up bunny hopping down the street. Kind of feels like you have hit the rev limiter @2500rpm.

Not a good look!

Any ideas?

Drove it last weekend with a different battery and it went flawlessly.

Great timing as someone wants to come a take it for a test drive tonight. Murphys Law!

Edited October 27, 2010 by speedyg

[speedyg 16]

Ok, disconnected battery and left for half and hour, no change but idles fine on start up. Changed back to original battery, no change. Checked intake boot , only 1 year old and all connected correctly. changed idle control valve, still no change. Still cutting out at exactly 2500rpm whether driving or sitting on driveway revving. Any other suggestions?

[cliffdunedin 8]

Sounds like it may be the alternator as opposed to the battery...maybe pull the multimeter out and check it, or get it tested.

[speedyg 16]

Yeah, not really too interested in what happened to the battery, not the alternator causing the rough running.

Battery was 7 years old and has been replaced.

Talking to someone else who had a similar problem when he changed the battery. Fixed it by setting the clock on obc! So I will be trying that when I get home.

Edited October 29, 2010 by speedyg

[speedyg 16]

Update, set the clock etc no change, knew it couldn't be that easy! (Fixed the guy's e30 twice that trick.)

Changed the coil, no change.

So thinking it could be the ECU or even DME relay or speed sensor.

Other than changing the battery I haven't had to touch the car in months, so thinking it has to be electrical.

Another clue is when the revs cut out the fuel economy gauge cuts out too.

Anyone else had a similar problem?

[oscar90 0]

put the old battery in, jump it and see if it hits false limiter or runs fine yet again?

The clock thing had new in tears haha! anything could work though I guess!

[speedyg 16]

put the old battery in, jump it and see if it hits false limiter or runs fine yet again?

The clock thing had new in tears haha! anything could work though I guess!

Yeah tried the old battery still doing the same.

The clock thing was too good to be true, but it worked twice after replacing the battery on his e30, so worth a shot. haha probably coincidence.

[cliffdunedin 8]

Yeah the not really too interested in what happened to the battery, not the alternator causing the rough running.

Battery was 7 years old and has been replaced.

Talking to someone else who had a similar problem when he changed the battery. Fixed it by setting the clock! So I will be trying that when I get home.

Sorry mate. couldnt really work that one out

Just because the battery was old and has been replaced, does not mean it may not be the alternator...those symptoms sound like an intermittent alternator.

At the clock fix - he had to be pulling your leg...you could always try using a left handed screwdriver

[speedyg 16]

Sorry mate. couldnt really work that one out

Just because the battery was old and has been replaced, does not mean it may not be the alternator...those symptoms sound like an intermittent alternator.

At the clock fix - he had to be pulling your leg...you could always try using a left handed screwdriver

Ok will check alternator, this guy was dead serious that setting the obc clock had fixed his E30, but I certainly wasn't holding out much hope!

[speedyg 16]

notice the fuel economy gauge moving as it cuts out.

[cliffdunedin 8]

notice the fuel economy gauge moving as it cuts out.

That looks like it may be a fuel supply prob. injectors/carby??

[speedyg 16]

Any other suggestions on what to check?

[speedyg 16]

Ok, problem solved, new ecu and it runs fine.

Pulled old ecu apart and it has a aftermarket 2.7 chip in it, so swapped 2.7 chip into new ecu and it runs like crap. So put new ecu chip into old ecu and it runs fine.

Sooo... looks like the 2.7 chip is stuffed.

Car runs ok with new chip but is a little jerky cruising at constant speed and doesn't quite have the go that the old chip had. Glad it's fixed though!

[djguranga 0]

Ok, problem solved, new ecu and it runs fine.

Pulled old ecu apart and it has a aftermarket 2.7 chip in it, so swapped 2.7 chip into new ecu and it runs like crap. So put new ecu chip into old ecu and it runs fine.

Sooo... looks like the 2.7 chip is stuffed.

Car runs ok with new chip but is a little jerky cruising at constant speed and doesn't quite have the go that the old chip had. Glad it's fixed though!

Hey mate, after seeing your video it reminded me of a very similar problem my 91 320i e30 had, the chugging idle with the rev meter going up and down (and the consumption meeter moving like it did), turned out to be the alternator for me! Glad you managed to fix it with an ECU swap out

[speedyg 16]

Hey mate, after seeing your video it reminded me of a very similar problem my 91 320i e30 had, the chugging idle with the rev meter going up and down (and the consumption meeter moving like it did), turned out to be the alternator for me! Glad you managed to fix it with an ECU swap out

Hi, it was the ecu, must have fried it when putting a brand new battery in it. Apparently it is best to turn on your lights, fan etc to disperse the power surge. Lesson learnt!