Author Topic: rev issue... (Read 5399 times)

nigel · « **on:** August 05, 2009, 12:05:09 PM »

I just bought a 318i as a parts car for my is. Upon closer inspection, though, the i is in better condition (the 318is is badly rotten in the wheel wells). So this morning i set out to tune up the 318i. It had a running issue - sputtery acceleration. So I pulled the plugs (4 prong) and put in some stock ones. It ran smooth and strong - right up to 4k rpm, where it acted like it was hitting the limiter. Weird. So I swapped the AFM, tested it again, and I lost 2k rpm! Now it only revs to 2.5k. Swapped back to the original AFM, and it still only goes to 2.5k. Are there bad contacts? OBC problem? did I do something really bad in a past life? any help/karma donations would be greatly appreciated.

nigel · « **Reply #1 on:** August 07, 2009, 08:37:03 AM »

update: changed plug wires, checked cam sensor - both are fine. Still won't rev past 4k

bearsbmw · « **Reply #2 on:** August 07, 2009, 10:24:49 AM »

your car is stuck in limp mode by the sound's of it .... try reseting the computer by removing your battery + terminal for a few mintues and turn the key to start and hold it for a few seconds with the battery disconnected ... good luck!

nigel · « **Reply #3 on:** August 07, 2009, 11:20:12 AM »

Ok, I'll try that. What's limp mode? and what causes it?

Edit: tried that - didn't work.

bmwman91 · « **Reply #4 on:** August 07, 2009, 05:19:38 PM »

"Limp mode" happens when you have too much whiskey in one night.

But on the car, it is a special mode the ECU goes into when the AFM stops working / is disconnected. The ECU will run solely based upon throttle position & RPM from some very conservative fuel & ignition maps, so that you can "limp" home & fix it.

You may want to look at the ignition coils. A LOT of people have had theirs go bad by now, and when they go the motor will not want to rev & cut-out a lot. It happened to me.

nigel · « **Reply #5 on:** August 11, 2009, 05:04:25 PM »

The coils are and spankin new... besides, the revs are smooth at lower rpms.
I was sure that resetting the comp would fix it, because that sounded like the perfect explanation, but I've tried several times, with no luck. I was thinking it might be a bad connection or blown fuse. Are there any fusible links in the MAF wires? And what's in that narrow black box (under the intake manifold) that the sensor wires lead to?

dwf08 · « **Reply #6 on:** August 14, 2009, 08:41:55 PM »

mine did that while i was driveing it one day then stoped and did it a few more times i had to change the fuel pump.It spitted and wouldnt go then went and acted like it was hitting the rev limitor

nigel · « **Reply #7 on:** August 16, 2009, 08:12:44 PM »

dwf08 ; did it bounce at one specific rpm all the time, or just sputter around? Mine goes to exactly 4k rpm, but like you said, it acts like it's hitting the limiter.
I'm going to try switching out the AFM again tomorrow... really don't have the money to go buying fuel pumps if that's not the problem.
Can this problem be pinpointed by an OBD?

roundel318 · « **Reply #8 on:** August 20, 2009, 10:02:13 PM »

i had that problem once, was the crank position sensor.

nigel · « **Reply #9 on:** September 01, 2009, 04:37:39 PM »

Thanks, roundel, you nailed it. Problem resolved.

After you mentioned the CPS, I noticed that the the tach had a funny little bounce right after I turned off the engine... like a small voltage spike. Maybe this would be a good indicator to anyone else with this problem.

roundel318 · « **Reply #10 on:** September 02, 2009, 06:26:36 AM »

my tach has always done that

nigel · « **Reply #11 on:** September 02, 2009, 07:11:35 PM »

even after the new CPS? With the new sensor, my tach drops dead and stays there, no bounce at all.

roundel318 · « **Reply #12 on:** September 02, 2009, 09:24:50 PM »

yeah after new CPS it still does it, who knows

Ramblin MAn · « **Reply #13 on:** September 03, 2009, 11:18:26 AM »

Good. I saw mine do that yesterday and I said oh hell here we go. Glad I can ignore it.

roundel318 · « **Reply #14 on:** September 04, 2009, 12:52:29 AM »

Hah, stranger things will happen.
I think its probably some cap or something that releases.
Glad it's working