540i Hesitation / Stumble

[Andrew]

Hello

I purchased a '95 540i 6 Speed (Nikasil with 125K miles!) a few months ago. Recently, it has developed a hesitation during acceleration at the same point in my commute which will dissapear within a mile or two.

When I start the car (cold), the engine idles very smoothely and drives perfectly for about 2 miles. Then, all of a sudden, when I give it gas (doing around 35mph in 4th gear) the car bucks / hesitates. I will upshift and down shift and feel the same vibrations. I get a strong smell of sulfur from the exhaust too ONLY when this hesitation occurs. Then, the problem disappears within a mile or two OR when I shut the engine down and restart. The check engine light never comes on and there are no faults recorded in memory.

I know from the archives that there are dozens of things that can cause hesitation (coils, plugs, intake gaskets, etc.) However, I am just wondering if any of you guys had a similar problem and could suggest where to start. I just find it strange that it happens at the same point every day and clears itself.

Thanks
Andrew

[632 Regal]

probably during the transition of cold to warm mode when the O2 sensors and everything relies in sensors. Did you start by rebooting the computer? After you do that wait for the stumble and after you get to your destination do the stomp test to see what codes were thrown, most likely the O2 sensor code which can be from a multitude of reasons where vacum leaks are mostly the culprit. If you dont know if the intake gaskets and the front and rear intake panel gaskets were changed, you should spend an afternoon and do them before cold weather. Once it's cold you will certainly have a lot of problems.

Good luck and congrats on your new purchase!

Hello

I purchased a '95 540i 6 Speed (Nikasil with 125K miles!) a few months ago. Recently, it has developed a hesitation during acceleration at the same point in my commute which will dissapear within a mile or two.

When I start the car (cold), the engine idles very smoothely and drives perfectly for about 2 miles. Then, all of a sudden, when I give it gas (doing around 35mph in 4th gear) the car bucks / hesitates. I will upshift and down shift and feel the same vibrations. I get a strong smell of sulfur from the exhaust too ONLY when this hesitation occurs. Then, the problem disappears within a mile or two OR when I shut the engine down and restart. The check engine light never comes on and there are no faults recorded in memory.

I know from the archives that there are dozens of things that can cause hesitation (coils, plugs, intake gaskets, etc.) However, I am just wondering if any of you guys had a similar problem and could suggest where to start. I just find it strange that it happens at the same point every day and clears itself.

Thanks
Andrew

[tim]

[edit- damn- jeff beat me to it]

I don't know if I have a solution, but I think I can diagnose that symptom. When the car is started, the engine uses the "sports mode" programming in the DME. It's sort of like a choke- the mixture is rich and idle runs a little higher until the o2 sensor is warm enough to start signalling. When it finally happens (which can take awhile on the big block v8), the lambda feedback loop takes over, and the car runs in "normal" mode. The coolant temp has nothing to do with how long it takes the o2 sensors to warm up.

Sounds like your car is bogging down right when it crosses over. Perhaps one of the sensors is warming faster than the other. The other bank runs like **** until it's sensor catches up (it just went from super rich to lean). That why it happens at the same place every day- that's how long the sensor takes to warm up. I don't know about the sulphur smell. The first thing I'd do is get both sensors checked out. If that's not the cause, it will help to eliminate that as a possibility.

Ok, heres what it could be if it's beyond that easy fix (IMHO of course).
A) You may have some blockage on your cat causing unequal exhaust pressure/temperature. The sulphur smell? When I smell suphur I think "cat".
b) You may need a new pcv if you're blowing by enough gasses to throw off the o2 sensors. Every m60 needs it done, and it's a good excuse for doing all the other crap these things need. Probably not it if it idles ok and runs perfect except for this little glitch.

There are other possibilities. Everything Jeff said is true, and will need to be done eventually. There are others but they aren't as cheap as the ones I've mentioned. Others will chime in I'm sure. I'm not even bringing up the subject of a leakdown test. I'm pretty sure you need a couple o2 sensors and you'll be good to go. Small prices to pay for having a car with as much balls as yours.

Best,

[gmannino]

Try to do your basic tune up with new plugs before troubleshooting more advanced components. My M20 used to do pretty much the same thing when I first bought it. I replaced the old worn plugs with new ones and it ran like a dream.

[Andrew]

Thanks Jeff! Interestingly, however, the Oxygen sensor code is not stored in memory. Just 1444 is displayed. I have checked a few times and tried performing the "shogun reset."

The previous owner said the O2 sensors were changed, but I cannot beleive him. I got a fairly good deal on the car, but at the cost of concrete service records. So I think I will just replace them. You are right about the hesitation occuring just about when the 02 sensors kick in...

I might also try replacing the MAF. I remember one of my first posts to this forum occured after my AFM in my 535i died. The symptoms were similar but not exactly the same. (Car would buck and hesitate until fully warmed up.)

I have seen your posts regarding the intake gaskets many times so I think I will take your advice and spend a Saturday replacing them before I regret it!

I'll let you know what I find.

Andrew

probably during the transition of cold to warm mode when the O2 sensors and everything relies in sensors. Did you start by rebooting the computer? After you do that wait for the stumble and after you get to your destination do the stomp test to see what codes were thrown, most likely the O2 sensor code which can be from a multitude of reasons where vacum leaks are mostly the culprit. If you dont know if the intake gaskets and the front and rear intake panel gaskets were changed, you should spend an afternoon and do them before cold weather. Once it's cold you will certainly have a lot of problems.

Good luck and congrats on your new purchase!

[Andrew]

Thanks Greg and Tim as well. A complete tune up is not a bad idea since I hope to keep this car for a long time. I wish my previous owner actually supplied maintenance records. The only think I knew he had replaced was the clutch.

I think I was just spoiled having the car run perfectly for a few months. My 535i (as much as I love it) always had something that needed my attention.

Andrew

[ThoreauHD]

02 sensors and Mass AirFlow meter do that. I had the same stall after about a mile, and that damn MAF failed. One damned expensive part too.

[tim]

At 125k mi I'd do radiator, belts, waterpump, PCV, intake manifold gaskets, valve cover gaskets, plugs, o2 sensors, AFM boot replace, and take off the front cover and pan to make sure your oil pump bolts are still there.

But that's me.

You could do all that yourself plus do rotors and pads for about a grand if you go cheap.

Meantime get the Bosch o2 sensors. Expensive but necessary. Call BMA and get a discount if you mention the site.

[Traian]

Yo, it's the Nikasil man, your car is f--ed!!!!!!!!!!!! Just sell it to me for a couple hundred, and I'll turn it into a nice couch or something....damn, good thing there's ppl like me around.

[Andrew]

LOL

Yo, it's the Nikasil man, your car is f--ed!!!!!!!!!!!! Just sell it to me for a couple hundred, and I'll turn it into a nice couch or something....damn, good thing there's ppl like me around.