Sudden loss of engine power at 60 mph - 1995 E36 Automatic

[bobARC]

Greetings,

I have a 1995 E36 325i Automatic (GM 4L30E transmission) with 181k miles. The car drives completely normally: engine + gearbox + diff all smooth.
However, at around 60 mph (+/- 3 mph), the engine feels as if it's stuttering. Anywhere above or below this, all is good.
The "stuttering" also is independent of throttle applied or gas tank level.

The problem first came about 4 weeks ago, intermittently. Since last 2 weeks it is more frequent.

Could it be my transmission? I last changed tranny fluid and filter at 120k miles. Perhaps at this speed, as the auto tranny is shifting into overdrive it's clutches are worn. (I dont know how overdrive works)
Could it be engine? Perhaps caused by either fuel cut-off by MAF + Speed sensor malfunction.

I couldn't find anything through a search of this forum or internet in general. Any places to start searching, fellas?

[scooper]

when did you last change the fuel filter? If always around 60mph then it's probably a bad or clogged sensor in the trans, crankshaft, vacuum perhaps?

[66 6]

when did you last change the fuel filter? If always around 60mph then it's probably a bad or clogged sensor in the trans, crankshaft, vacuum perhaps?

I'd start with the fuel filter as well.

[bobARC]

when did you last change the fuel filter? If always around 60mph then it's probably a bad or clogged sensor in the trans, crankshaft, vacuum perhaps?

I didn't think it would be a vacuum line, as the Tranny & engine is completely electronically controlled.
Trans sensor could be something but it's the engine that feels it's running outta juice ("stuttering").

I'd start with the fuel filter as well.

I never changed the Fuel Filter during my ownership. Will do ASAP and report

[Nanniepoo]

My old E36 was an auto and ~55 seemed to be the speed threshold between 3rd and 4th gear. It would do weird things, just above 55 in 4th gear, if I came up on a hill it felt like it had no power until I gave it enough gas that it would downshift.

[Nanniepoo]

My old E36 was an auto and ~55 seemed to be the speed threshold between 3rd and 4th gear. It would do weird things, just above 55 in 4th gear, if I came up on a hill it felt like it had no power until I gave it enough gas that it would downshift.

[bobARC]

My old E36 was an auto and ~55 seemed to be the speed threshold between 3rd and 4th gear. It would do weird things, just above 55 in 4th gear, if I came up on a hill it felt like it had no power until I gave it enough gas that it would downshift.

Interesting. How many miles on the trans? Was it a M50tu as well?
In my driving, I am guessing that it shifts ~60 mph from 3rd to overdrive. Could it be that there's something up with the sensors (in trans or ECU) that it cuts off power around that time?

[Nanniepoo]

Interesting. How many miles on the trans? Was it a M50tu as well?
In my driving, I am guessing that it shifts ~60 mph from 3rd to overdrive. Could it be that there's something up with the sensors (in trans or ECU) that it cuts off power around that time?

I had the car from ~130k to 207k. It was a '94.

I wouldn't really call mine a power loss so you may have something else going on, mine was more of an annoyance really when trying to drive steadily at those speeds.

Sent from the dark side of the Moon

[ed323i]

Can you check the RPM while driving at stable speed at 60 mph?
Can you double check if the problem exists in other gears at the same RPM (both lower and higher speeds)?
So, at 80 mph, no problem at all? If that's the case, then the odds of it being the fuel filter or fuel pump get quite low, as the car probably uses 20-30% more fuel at that speed compared to 60 mph.

Can you read the error codes? Connect a laptop with INPA?
I don't if it's possible, but perhaps the crank or cam sensor has trouble reading the teeth correctly at a certain RPM..

Does the problem persist with the MAF sensor disconnected? The M52 can run surprisingly well without the MAF connected, but I think the M50 should do an OK job at it too.

[bobARC]

Can you check the RPM while driving at stable speed at 60 mph?
Can you double check if the problem exists in other gears at the same RPM (both lower and higher speeds)?
So, at 80 mph, no problem at all? If that's the case, then the odds of it being the fuel filter or fuel pump get quite low, as the car probably uses 20-30% more fuel at that speed compared to 60 mph.

RPM at 60 mph are anywhere from 2,000 to 3,500 depending on how I'm driving. Problem look to be independent of RPM

Yes, it's completely fine all the way upto 90 mph. Only at 60 mph (+/- 3 mph) does it "stutter" intermittently
That's why I myself suspected that it was something in the trans rather than the fuel system. But regardless I'm ordering a $10 fuel filter

Can you read the error codes? Connect a laptop with INPA?
I don't if it's possible, but perhaps the crank or cam sensor has trouble reading the teeth correctly at a certain RPM..

OBD1 so can't run the more elaborate diagnostics. But using the brake pedal technique, no codes came up.

Does the problem persist with the MAF sensor disconnected? The M52 can run surprisingly well without the MAF connected, but I think the M50 should do an OK job at it too.

Could try that over the weekend, MAF sensor was cleaned just 65k miles ago. Air filter is super clean.

[Eric93se]

So one thing to check is to see if torque converter lock-up is working properly. When cruising at 60mph, watch the rpm needle, it should hold steady and not jump up or down (~200rpm), that would indicate that lock-up is slipping out (loosing lockup and then re-engaging). My converter did this and it was due to a cut o-ring on the input shaft seal going into the converter.

Second, while at 60mph (steady), give a small amount of gas, the rpm should stay the same, if it jumps then the torque converter is not locking up.

I would agree to do the fuel filter. Also if the ignition coils are very old or original they should get replaced. I just replaced my aftermarket coils and the car has better acceleration. The coils that I took out had "treeing" (dielectric breakdown) on the plastic.

[bobARC]

So one thing to check is to see if torque converter lock-up is working properly. When cruising at 60mph, watch the rpm needle, it should hold steady and not jump up or down (~200rpm), that would indicate that lock-up is slipping out (loosing lockup and then re-engaging). My converter did this and it was due to a cut o-ring on the input shaft seal going into the converter.

Second, while at 60mph (steady), give a small amount of gas, the rpm should stay the same, if it jumps then the torque converter is not locking up.

I would agree to do the fuel filter. Also if the ignition coils are very old or original they should get replaced. I just replaced my aftermarket coils and the car has better acceleration. The coils that I took out had "treeing" (dielectric breakdown) on the plastic.

Can confirm that Torque Converter is locking up correctly after 60 mph. Not sure if it occurs when the "stuttering" situation occurs.

Further, I cleaned my MAF. Occurrences of "stuttering" have gone down.

Now waiting on fuel filter to arrive.

[bobARC]

2 weeks ago: replaced Transmission fluid & filter. Problem persisted

1 week ago: replaced Fuel Filter. It doesn't stutter nearly as much at ~60mph, but there is clearly some faint "stuttering".

Time to look at my injectors, I guess?

[bobARC]

2 weeks ago: replaced Transmission fluid & filter. Problem persisted

1 week ago: replaced Fuel Filter. It doesn't stutter nearly as much at ~60mph, but there is clearly some faint "stuttering".

Time to look at my injectors, I guess?

Alright, used Lucas Oil and Chevron Techron injector cleaner. Still no luck.
So in conclusion: I guess my tranny is going to die soon? Welp!

EDIT: Shifting from 1-2 and 2-3 has been smoother (most likely thx to fuel injector cleaner). Better fuel consumption as well. Shuttering ~60mph still occurs, but I think I understand why:

So one thing to check is to see if torque converter lock-up is working properly. When cruising at 60mph, watch the rpm needle, it should hold steady and not jump up or down (~200rpm), that would indicate that lock-up is slipping out (loosing lockup and then re-engaging). My converter did this and it was due to a cut o-ring on the input shaft seal going into the converter.

And that explains (most liekly) what's going on. That O-ring is finally giving out after 185k mi