84 318I Surging - BMW Forum

prosavage2600 · 08-21-2009, 02:38 PM

Just started a few hundred miles ago. When I am on the freeway for longer than about 15 to 20 minutes, the car will start to surge every second or so. The engine seems to stop producing power for very short bursts. Then it continues in town until I let the car rest for about an hour. Then the cycle repeats.

I believe it to be a fuel system issue by the nature of the symptoms. I did however check the dist cap and rotor and ignition leads.

I took the fuel line off the fuel rail and ran the fuel pump. It flowed very freely out, so I would assume that rules out a clogged filter.

My next idea is to swap out the fuel pump for a known good one. (I have another 84 318I)

I am also going to check the fuel pickup screen inside the tank.

Let me know if you have any ideas. If the fuel pump does not fix it I will be completely out of ideas to try.

Thanks!!!

marti5 · 08-22-2009, 03:59 AM

Maybe its the AFM playing up swop that from your other one.

FCPGroton · 08-24-2009, 08:41 PM

Or the fuel pump relay is overheating and cutting out. I definitely sounds fuel related.

prosavage2600 · 08-25-2009, 04:33 PM

Alright guys. Thanks for the suggestions. I swapped the fuel pump out and it made a world of difference. The pump was dying a slow death. Now everything runs smooth, and it fixed the hard starting issue as well. I guess after the pump was running for an extended period of time, it could not maintain proper pressure.

FCPGroton · 08-26-2009, 07:58 PM

Nice, i knew it had to be fuel related. Glad you got her all fixed up.

darkhorse737 · 08-27-2009, 01:16 PM

Quote:

Originally Posted by prosavage2600

Alright guys. Thanks for the suggestions. I swapped the fuel pump out and it made a world of difference. The pump was dying a slow death. Now everything runs smooth, and it fixed the hard starting issue as well. I guess after the pump was running for an extended period of time, it could not maintain proper pressure.

GREAT DIAGNOSTICS... Good Job!

prosavage2600 · 09-03-2009, 02:43 PM

Ok guys, sorry to get your hopes up (mine too) but the problem has resurfaced. It seems the dying fuel pump was only one problem.

The original symptoms have resurfaced with a vengeance. On the way home from work, it was the first cool night in a while, which could be coincidence, the symptoms occurred right when I first fired up the car and lasted the entire drive home. I parked and checked for loose wires while the car was still acting up. I checked the wires on the MAF, the ECU, and the coolant temperature sensor.

The surging is very quickly paced, and very sharp bursts. When it is acting up, the surging is very evenly spaced and non sporadic. It happens everywhere on the rpm range although it is more noticeable at low rpm with low engine load.

The only things I can think of that are left are the MAF and the ECU. Maybe old solder joints?

Sorry to bring this back up but it seems to be happening more often. When it is not happening the car runs like a champ.

Thank you for your continued input.

FCPGroton · 09-03-2009, 02:57 PM

I would give the MAF a good cleaning and see if that helps. You can test the MAF by disconnecting it and starting the car. If the car runs and drives better, it is the MAF.

k.sidlosky · 09-04-2009, 11:18 AM

Is it consistant or random?

prosavage2600 · 09-04-2009, 03:17 PM

The problem itself seemingly is random. However, when it happens, it is a constant surging, almost digital in nature. Like little pieces of power are being taken out for very short periods of time.

prosavage2600 · 09-05-2009, 12:20 AM

Ok. Im edging closer to a solution. On the way home from work. It started its usual business. I got home. It was still doing it, so I took this chance to try some ideas.

The one that got me a result was with the temperature sensor. I unplugged the wire from the sensor on the car, and i plugged it into a spare I had, which was at room temperature. The problem disappeared. I went back to the sensor on the car, problem resurfaced immediately. I went back and fourth a few times to be sure. So today I replaced the sensor with the spare.

I am going to test this for about a week or so before I am convinced I fixed it, due to the trickery of this problem. If it continues at least I have a start and can start tracing back to the problem. Which I would think is the ECU the sensor feeds.

I will keep you posted as to the results. Thanks for all of your help.

k.sidlosky · 09-05-2009, 12:28 PM

Hopefull it stays away.

prosavage2600 · 09-07-2009, 12:47 AM

No such luck for me. With the new sensor installed, the problem again resurfaced. This has me now tracing the issue back down the line. The ecu is what the sensor connects to. It seems the problem happens when the car reaches running temperature.

My best theory is (without expert knowledge) is that when the car reaches running temperature, the circuit that controls the mixture for that range is malfunctioning. (bad solder joint maybe?) I will now swap out the ECU from the other bmw and see where that leads me. only thing left is wiring after that.

prosavage2600 · 09-08-2009, 04:06 PM

*Update* Ecu is now swapped out. Knocking on old one would initiate the problem. And it would not go away. So i switched it out for the known good ecu. Problem went away. I shall test the car some more and see what happens. I am also going to start the other car and see if the symptoms have been transferred to it.

I will get to the bottom of this! And yes I plan on opening up the old unit and checking the circuits.

Thanks again.

witeshark · 09-08-2009, 04:10 PM

Best of luck with it!