Sudden loss of power, then normal - why??

[romus]

Happened twice in two days. First time while driving at 80-90km/h in 5th gear and second time 50km/h in 2nd. The problem is while my foot is on the accelerator, (at 80km/h it was constant pressure, at 50km/h i was accelerating slowly) the car suddenly loses breath for a second. I dont manage to react even, before everything goes back to normal.

Compare it with driving in 1st at about 2500/3000, then taking your foot quickly off and back on the accelerator. That jerk you get, that's what im having.

Is this common?? And what could it be guys??

Thanks!

[billb]

Is this common?? And what could it be guys??

Thanks!

Ignition coil? Rotor button? Bad spot on the AFM?

[romus]

Thanks for the quick response Bill. It's not AFM as it's not the same revs it happened at...Rotor cap and button were replaced just 2-3 months ago. I'll have to look into other ideas you had.

Thank you very much again

[632 Regal]

check the engine grounds and other grounds for corrosion, any electrical fault can cause this.

[emw525E34]

I got a couple of similar situations a while back. Strange to say both my occasions were similar to yours in gears and speed.

First one on 5th gear at 100 kph. Just sudden drop in power and speed falls to 60 kph. I rev furiously thinking it was"bad gas", lasted about 15-20seconds. Then it caught on, I down shifted to 3rd and push to 130kph. Did not recur for 2 weeks, then on a short local run, in 2nd gear about 45kph at a turn, same problem happens. This time it lasted about 10 seconds. That was months ago.
I kept thinking "bad gas" or water in gas. But electrical gremlins is a distinct possibility. Things like these are so hard to diagnose!.
M50TU manual Euro version.

[Jose]

Check your fuel filter, it might be clogged if it's too old, fuel pump could be defective or the suction filter at the end of it could be filthy, check your O2 sensor aswell, when this one goes crazy the engine could do strange things. Did you have a ECU error codes read out already ? If not , do the read out, it could be something very small as a crackpulley sensor.

[tnt525i]

check and clean grounds, read my post from a few days ago

[jmw.bmw]

Hi I have experienced very similar problems with my car and have spent a fortune replacing lots of parts. I have not solved the problem yet. Did you manage to fix your car and if so what was the solution.
Many thanks

[romus]

Nah Jose, fuel filter is fine. About 2-3 months old at most. Thanks.
Error codes only show "no fault".

I still have to check the grounds, i've read the post from afew days ago, tnt, thanks.

[romus]

No. Happened twice in two days, not as long lasting as emw's but still sounds like same problem. Haven't had it since. I'll check grounds like tnt suggested, other than i have no idea what the problem could be. I've changed distributor arm (button) and cap couple months ago, fuel and airfilters just recently...

I will post here what i found it out to be.

Thanks for replies everyone

[Gene in NC]

Have two '89 525s. Manual runs clean. AT has had your problem in spades for several years. Have confirmed that "stumble" is accompanied by fuel pressure drop, which in turn is caused by drop of power to the f pump. FP guage rigged to windshield and test light clearly show condition. Improving grounds has always seemed to temporarily reduce occurrence. About a year ago replaced dist cap and problem vanished.

Immediately after Katrina fuel quality or source changed and problem returned. Going to Shell 93 has greatly reduced incidence.

Original failures followed several years of Texaco 89 use as preferred fuel. "Stumble" was severe. Switched to Shell 93 and over several weeks problem resolved. To be scientific went back to Texaco. Problem returned and could not be solved by use of Shell.

Many changes made that seemed to help for a short time. Use of Stabilant contact enhancer on grounds was a big help. Then "it" came back to be resolved by the dist cap change.

Suspect that for some reason ecu may be cutting power to fuel pump. Ihave no way to verify.

My electrical engineering friend who suggested the dist cap referred to his experience (not BMW) that was with what he assumed was cross firing that, through an open intake valve, burned the fuel in the intake manifold which caused his stumble. This was counter to my finding on power to fuel pump.

However, it worked!

[emw525E34]

Actually folks, I am more convinced this is a fuel quality related issue. Lately, in the last few months, the local BMW club members are getting more of such occurances with E36 and even E46 cars. I guess the M50 engines are pretty similar. When we changed pump gas from a few selected stations of the same brand, the problem seems to have disappeared. It does appear more than a co-incidence, I think it is likely so, yes, there appears to be a brief drop in fuel pressure and it resumes very quickly after within seconds. The higher-the speed it happens, we tend to feel a longer lapse. I guess 3-5 seconds would be a good enough guess. Most of us have fairly new fuel filters and well stocked in consumerables. Surely a fuel pump going south would have died since, but it has been months since I had that in my manual. Like more than 2 years since my auto had similar symptoms, but never consecutive days!. Strange eh ?. What do you guys think ?

[Gene in NC]

Let's keep this going. Only four posters reporting the problem but 222 "peeks". If you are a peeker with the problem, please post. The more information we have the better probability of an answer developing.

[romus]

Gene, i replaced distributor cap and button for different reasons than stated here but replaced never the less. As for fuel grade, im only using Shell 98 (the best we can get here).

I'm still confused as with what it is. I haven't had the problem since however.

[632 Regal]

Im still betting on electrical, grounds, fusable links, batt terminals, alternator connections, theres not much left but there may be a common area that is the culprit and will help nail this issue down.


Let's keep this going. Only four posters reporting the problem but 222 "peeks". If you are a peeker with the problem, please post. The more information we have the better probability of an answer developing.

[Gene in NC]

Re prob following Katrrina gas, have now been through a couple tanks of Shell hi test, including 250 mi @ 80mph. Prob seems to have resolved itself.

That does not explain why the ecu drops power to the fuel pump when the stumble happens , or better said, the ecu momentarily drops powe to the fuel pump which causes the stumble.

Does the '89 m20 engine have a knock sensor?

[misfortune]

Yeah I get this semi frequently in my 89 525i as well. I'd say fuel. Maybe once a week?

[Andryuha]

I have the same problem as well. I got a bit scared today because today it lasted about 10sec, as opposed to like 5sec occurances in the past. I was accelerating from the stop in first, then switched to 2nd and felt a sudden loss of power (no stuttering or jerking) - I floored the gas, and the car just didn't do anything for about 10sec. After that everything went back to normal. I also think that it's a problem with gas, because I never had this problem when I used only Shell gas.

[Gene in NC]

Bump to connect this to tnt525i thread which may be very important or even key to this prob.

http://www.bimmer.info/forum/showthread.php?t=15605

[Gdub]

I had the same problem of sudden power loss especially right after cold starts and during harder acceleration. I also had overall powerloss at all times with excessive fuel consumption. It turned out to be my fuel pump. It had a big crack in the metal housing around it.

[Gene in NC]

Thanks for postng gdu. Your's is a different problem not related to this thread.