Please Help!! Lost Compression in 1 Cylinder

**pete92879** · 08-19-2008 09:54 PM

I bought a used 745LI from a private party a couple of months ago with 70K miles. I have driven the car only 1500 miles since and today while driving the check engine light began flashing and the car had major misfires. Took it to my mechanic who said cylinders 4,5 & 8 were misfiring. He replaced the ignition coils, but misfires continued. He then checked the compression on the cylinders, and cylinder #8 had zero compression. The car is out of warranty.

Can anyone help with this or am I out of luck.

**ROYinGA** · 08-20-2008 08:47 PM

shows up bad with any of the valve stems/springs/etc on No. 8. Wouldn't expect it to be a piston or rings but maybe.

**pete92879** · 08-20-2008 10:39 PM

Pulling out the valve cover is the next step. Not sure what really happened - the car did not overheat or anything. We'll see what happens next.

**bmwtech2003** · 08-25-2008 11:59 PM

This will pinpoint the tech in the right direction. If air comes out the intake or exhaust ports then this is the place to start. This is one of the basic tests that need to be done before removing any hardware. Could be as simple as carbon buildup on the valves.

**GeezTech** · 08-28-2008 11:47 PM

Most certainly, but, doesn't the valvetronic have to be put into a certain position by the DIS before doing a compression check?

**pete92879** · 08-31-2008 12:09 AM

My mechanic opened the valve cover today, and sure enough it was a broken spring. Hopefully there's no damage to the valves or piston. Let's see what's next.

**bmwtech2003** · 08-31-2008 01:22 AM

To get proper compression numbers yes. The vvt motors can be unplugged to get compression since they default to minimum lift. Not needed for leakdown. The valves are still closed at tdc and you should be able to pinpoint the leak by using a stethascope and plastic bags.

**wog40** · 08-31-2008 09:30 PM

Question, My 735i over heated, I fixed the leak, drove the car for about 2 miles and than while driving car came to a complete stop, and now will not turn over. Were should I start to look ?

**bmwtech2003** · 08-31-2008 11:05 PM

Sounds like the engine is hydrolocked. Remove all of the plugs and see if it turns over. Also try the e32 board.

**wog40** · 09-01-2008 02:49 AM

Thanks I'll give it a try,

**ROYinGA** · 09-05-2008 11:21 AM

**pete92879** · 09-09-2008 01:05 AM

The BMW is a 2004 745LI. Anyway, as I stated earlier, there was a broken spring when they opened the valve cover. Everything got fixed, and now the car runs like new. Dealer said it was a blown headgasket, and they recommended replacing the engine for around 10K. This repair cost $900. Go figure......

**bmwtech2003** · 09-09-2008 01:39 AM

Hence the confusion. Sounds like the dealer didn't do their homework. Leakdown would have led to checking the leaking component. If the air was leaking into the intake then they would have known it was an intake valve problem, same with exhaust. If the air was leaking into the crankcase then the cylinder or rings would be suspect. It is a way of eliminating the mechanical components of any engine. At least the problem was resolved before the valve broke and the engine was trashed.

**dbaw** · 01-11-2011 01:57 PM

Is there any known caveat that I should know about before buying a BMW 735 4 -door as compared to a Porche XK8. Which one is better? As to road ride, how smooth, safety, and the little things that make one car better than another? Thanks DBAW

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