1994 530i rough idle, cylinder miss?

[Kalevera]

15% on the leakdown, according to Brett. Not sure on the compression spec. The nik block I pulled out was down to ~ 92 on one cylinder and the thing didn't start (some of the others were lower, too).


best, whit

[callen]

I've got a 530 with about 160K miles and the the valve cover is deteriorating....metal turning to mush and crumbling away. Did paint and it looked better but just for a short while......point is, hope your powder coating isn't costing you too much ....it may flake off real soon.

[Bill R.]

deviation between cylinders.. I wouldn't get concerned at 160 if they were all pretty close to equal.. The normally allowed variation between cylinders is 10% max.. but i wouldn't worry about yours, I'm almost postive if you repeated the test a couple of times the cylinders would come out more equal. As Whit said 15% is the max leakdown but with your compression numbers i see no reason to run a leakdown test. Did you do a wet and dry compression test?

I'm quite pleased with the results.
A little concerned with the #1 cylinder, though...

Does anybody know the BMW acceptable tolerances for compression?
(I did look online, but have not found any technical specs yet and the Bentley is on order..)

[Been-Jammin]

deviation between cylinders.. I wouldn't get concerned at 160 if they were all pretty close to equal.. The normally allowed variation between cylinders is 10% max.. but i wouldn't worry about yours, I'm almost postive if you repeated the test a couple of times the cylinders would come out more equal. As Whit said 15% is the max leakdown but with your compression numbers i see no reason to run a leakdown test. Did you do a wet and dry compression test?

I did a "with fuel" test. I left the fuel pump hooked up and took out all of the spark plugs. I ran through 1-8 turning over each 15 revolutions. Started over, ran the test again. I re-ran the test on the #1 cyl about 4 times and each time was the same with the lowest reading at 185. 10% tells me that a reading of 190 is marginally acceptable and well within overall compression tolerance.

Typically with V8 engines the front cylinders get the most wear as they operate at an angle with less oil than the rear cylinders. This seems to have held true with this model.

[Bill R.]

don't check it with the throttle open you'll get a lower reading. And i would do a dry compression test and a wet one with a tablespoon or so of oil squirted down the plug hole.. if you get a big variation from dry to wet then it indicates rings rather than valve sealing.. Edit, fuel sprayed into the engine without it firing will tend to wash the oil off the cylinder walls changing your compression reading also..

I did a "with fuel" test. I left the fuel pump hooked up and took out all of the spark plugs. I ran through 1-8 turning over each 15 revolutions. Started over, ran the test again. I re-ran the test on the #1 cyl about 4 times and each time was the same with the lowest reading at 185. 10% tells me that a reading of 190 is marginally acceptable and well within overall compression tolerance.

Typically with V8 engines the front cylinders get the most wear as they operate at an angle with less oil than the rear cylinders. This seems to have held true with this model.

[Been-Jammin]

don't check it with the throttle open you'll get a lower reading. And i would do a dry compression test and a wet one with a tablespoon or so of oil squirted down the plug hole.. if you get a big variation from dry to wet then it indicates rings rather than valve sealing.. Edit, fuel sprayed into the engine without it firing will tend to wash the oil off the cylinder walls changing your compression reading also..

I agree, that is a much more accurate method. I'll put it to use.

Is there a simple way of disabling the fuel pump? (like a fuse or relay?)
Would simply disconnecting the fuel injection harness stop fuel flow to the cylinders?

Thanks

[Bill R.]

passenger side you'll find all the modules, the fuel pump module will be there in a row with 3 others, these are the small square modules.. closest to the passenger side fender is the o2 sensor relay, then comes the engine module relay, then comes the secondary air pump relay and the closest to the engine is the fuel pump relay. You can unplug all 4 if you want to if your not sure which is which ,just keep track of the color and put them back in the correct order.

I agree, that is a much more accurate method. I'll put it to use.

Is there a simple way of disabling the fuel pump? (like a fuse or relay?)
Would simply disconnecting the fuel injection harness stop fuel flow to the cylinders?

Thanks

[Been-Jammin]

Valve covers are done and look nice. A textured semi satin black.
Does anybody have the torque specs for the valve cover and intake?

I started with 10ft lbs on the valve covers. Went around with every other bolt until they were all snug, then torqued them to 10...

I'll be pulling the intake here shortly. That harness is a mess.

Thanks!

[Bill R.]

this translates to 10nm =7.37 ft.lbs 15nm=11.06
On the intake manifold any m8 bolts take 22nm=16.2ft.lbs and the other bolt, such as the 6 and 7mm are the same values as listed above

Valve covers are done and look nice. A textured semi satin black.
Does anybody have the torque specs for the valve cover and intake?

I started with 10ft lbs on the valve covers. Went around with every other bolt until they were all snug, then torqued them to 10...

I'll be pulling the intake here shortly. That harness is a mess.

Thanks!

[Been-Jammin]

I found a cracked vacuum hose that goes to the brake booster, a cracked vacuum hose cap that goes to the PCV and the fuel injectors are AFU, covered with crap. One of them was really clogged. The intake is soaked with oil, infact when I pulled the PCV, oil leaked out. YUCK. Nothing too on the tear down, just lot's of little things to be unhooked and pulled out of the way. The aluminum tube underneath was pretty sneaky. No "horns" in the intake on this model.

Time to pull out the parts washer and go to town on the intake... Meanwhile, lunch, it's 90+ outside and I just lost my shade for the day, so may have to wait till the late afternoon to start the re-asembly. I wish I had a two car garage again...