help needed - Engine Hesitation & Rear end noise-

[conzi_dv8]

I am experiencing a noticeable amount of gear noise
from the rear diff. The noise makes a stuttering type
sound as speed increases and is really noticeable with
a lift-off the throttle. The fluid I'm using is Ams
Oil 75W-90 Synthetic, from about 165K and normal BMW
gear lube prior. Can anybody break down what the
problem could be and if it's something I should be
concerned about.

My last problem is an engine hesitation @ 2300rpm.
Sometimes its subtle and other times it just falls on
its face - the colder the the engine the worse it
"trips". It seems like a bunch of E36 325i owners have
been experiencing a similar problem as well. Some
call it a shudder/bucking. I've had the following
parts replaced and the problem still persists: Fuel
pump(140k), fuel filter, spark plugs & O2 sensor. It
feels either fuel related or electrical and I was
wondering if it could be one of the coil(s) or maybe
just a tired motor? The engine has had a compression
test @ 127K and the results were: #1-160 #2-160
#3-165 #4-155 #5-145 #6-100. Could the low
compression in #6 be a cause of this hesitation?
Should I consider a head/valve rebuild? Lastly, is
there any way to have the coils checked to see if they
are okay - just-for-grins?

Thanks in advance,

czi
(oo[]oo)

[Dave at Pelican Parts]

Ouch. I don't know what the specs for the 325 motor are, but a 65 PSI difference from highest to lowest is not a good sign! And 100 PSI is pretty low in anyone's book, let alone an engine with a decently high compression ratio like the 325. (Unless you're in Denver or higher, in which case it's not quite so awful, but the 40% difference between highest and lowest is still a Bad Sign.)

Time for a top-end overhaul at the very least. I don't know that it will do anything for your hesitation issues, and it will not help your differential, but it will likely restore a fair amount of power and longevity to the engine. A leak-down test will tell you if the valves or the rings are what is leaking. Renewing the rings is a little more involved, and if they are the culprits then it is at least worth thinking about a full overhaul or possibly even a swap. (Not sure how available the 2.8 or 3.0 motors are nor how easily they swap in.)

If the compression is that low at only 127K miles, the engine was likely abused or recieved extensive "deferred maintenance" at some point in its life.

How attached are you to this particular car? Depending on exactly what is wrong with it, you may come off ahead in $$ if you get out of it and find another one in better shape. If the DME has issues, the engine needs internal work, and the differential is hurting, it may cost more to fix everything than upgrading to a newer or less "well-loved" car.

I'm not saying that the DME definitely does have problems, nor that the differntial needs replacement, but those are possibilities.

For the hesitation, I would first check all of the vacuum lines and the wiring and connectors. Hoses should be pliable and not brittle, obviously they should be hooked up (to the right parts!), and cracks or holes are a sign that you need to replace that hose. Wires should also be pliable and show no cracks in the insulation. Connections should be reasonably tight and the metal contacts should be clean.

...After that, I'm not sure where you go. Perhaps a shop that has a dyno with a wideband O2 sensor? That could at least show you if your mixture is going lean or rich when you have the hesitation. They will probably have some way to check for misfires of the ignition system as well.

A timing light might help you check for spark on your own. But the problem is geting that hooked up when the car is doing its hesitation dance...

--DD

[blkongry]

Yep, Dave is right on the money on all accounts. It may be time to move on to bigger and better, unless you've got access to cheap repair capabilities (like your brother owns a shop or something).

As for the shutter, I would lean toward the air/fuel/spark delivery system. The low pressure on various cylinders just takes away from engine power and responsiveness... it shouldn't cause the shuddering/hesitation. It really sounds like a vacuum line. The vacuum in the lines is generated by the engine intake... different levels of vacuum at different RPMs. With a missing vacuum line you get high flow, and with high flow you can get turbulence. At certain RPMs you can hit just the right vacuum flow to create turbulence in the system, and then you get this whacky shudder of 'engine confusion'.

[Wayne 962]

You're shooting in the dark if you don't have a method of reading the codes:

http://www.pelicanparts.com/bmw/techarticles/Mult-Code_Reading/Mult-Code_Reading.htm

This should be your first step in trying to figure out what is wrong...

-Wayne

[Dave at Pelican Parts]

Oh, another thing. Since the overhaul (if actually needed) is so expensive, it is worthwhile to eliminate every other possible cause of low compression if you can reasonably. So make sure the battery is in good shape with plenty of charge, make sure the engine is warmed up when you do the compression test, pull all the plugs, crank the same number of cranks on each cylinder, and have the throttle wide open.

Check for any possible blockage in the intake system and the exhaust system. (As well as you can, at least.) Check that the valve clearance is within spec. (Not sure how you do this on these engines; I'm used to solid lifters with relatively easy adjustment.) Verify that the hydraulic lifters are functioning correctly. And so on.

--DD