Low compression / rough idle - E53 X5 4.6is
 

Hi there,

I'm quite new here on this forum - thanks much for any tips, comments or advice in advance.

Timing chain and guides have been replaced on our 2002 X5 4.6is less than 100 miles ago. When starting the car in the morning last week, it had a very rough idle, but engine was running sort of fine at higher rpms. We spent significant time searching for the problem and checked all vacuum hoses connections, sensors, ignition components, etc. but couldn't find a problem. We then checked compression and found that bank 2 (driver side) had low compression in all 4 cylinders. We are suspecting a problem with the variable valve timing system (valves off cycle / not closing completely), since it's quite unusual for all four cylinders on just one side of the engine to have low compression from wear & tear.

Did anyone experience a similar problem in the past and can confirm that a problem with the VANOS system might be causing this?

Any other ideas?

Thanks much in advance.

Yeah vanos could definitely be a problem, but it would also throw codes for timing related issues, but since all cylinders on bank 2 show low compression I would assume maybe even a loose chain gear sprocket since there is no pin to guide them gears with the cams there isn't anything that can hold them other but the pressure of the torqued bolt that holds it.


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You can get your hands dirty and check for a loose gear, remove the valve covers, set the crank pulley to TDC and compare cams, if one gear spun a little out of place you'll notice it and you can set the timing back if you get the tools from ebay


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Thanks much for this info.

So, it seems possible that the cam gear bolt did not get tightened enough by the shop who did the timing chain / guides replacement?

Also, do you have to take the whole timing cover off in order to get to the cam gear bolt / or for doing the adjustment? That would be a major pita since it's like 20 hours to get that removed and reinstalled.

But if a shop did the work they should honor their labor. Should be no additional expense to you, just an inconvenience of having the vehicle down for a day or so.

Yes, but I'm wondering if they might just say this is unrelated to the work they did.

If it was less than 100 miles ago... I'd definitely take it back to them.

Good day!

If they did the chain and guides correctly, the loose gear is NOT unrelated... I'd take it back and not indicate you know anything except it is not quite right... Let them figure it out and correct the issue...

"It ran great 110 miles ago before you did the work! Now, it should run better, not worse! Ready GO!"

and see what they say!

Good luck!!

Cheers!!

Yeah, I will definitely take it back to them.

Thanks everyone for the input, comments and advice!

On a lighter note, what is last 7 of vin so I can add you to the registry :thumbup:

Yes I have see two cases where the cam blot has backed off even with the prescribed level of torque applied. Weird. A little loctite on the bolt takes care of this. loctite that you can remove of course.

Thanks for the confirmation!

Quick follow up question ... if the cam gear slipped (as indicated by several folks), wouldn't that problem result in getting a fault code thrown? The only code we see is P0492 (Secondary Air Injection System Insufficient Flow), which seems unrelated to the timing / low compression situation.

Thanks much in advance.

It should definetly throw a timing related code, such as p0011,0021,0012,0022


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I'll double check, but there definitely was no such code after the rough idle condition started, no CEL either ... only P0492. Wondering what might be the reason ... ?

For problems like this I think it is be to start with-- there are no coincidences when working on a vehicle.

I agree with both of your conclusions.

Secondary air injection system adds air for about a minute or less for cold starts. Purpose is to heat the cats faster so engine goes to closed loop faster. Malfunction would not impact compression.

Haven't been exposed to one cam off timing but I would be shocked if there were no bank and/or individual cylinder codes and check engine light.

A failing/failed vanos makes noise that you haven't mentioned.

Seems to me if timing gear is loose enough to jump timing there would be chain slop noise. Assuming that is incorrect, if bolt has come loose it could get looser as the engine runs. I wouldn't run the engine or only for brief troubleshooting necessity. Reference is to catastrophic engine damage caused by breaking a timing chain.

How much difference in bank to bank compression?
After you got different reading from one bank did you go back to the other bank to see if it might be a problem with tester?
Have you check vanos solenoid connection?
What were individual cylinder compression readings?

Thanks. Couldn't hear any specific timing chain noises, just very rough idle and sometimes some knocking-like sounds. If a VANOS is failing, could that produce the "low compression in one bank" condition? The bank (driver side) with low compression shows between 45-60psi in all 4 cylinders. The other side was around 160 I think.

Yes, failing/failed vanos can cause loss of compression and spark knock.

Do you know what actually fails on a vanos? Is it mostly the solenoid or is there any mechanical failure in the vanos unit?

^All of that would have been touched by the shop who did your guides. Just curious why you are diagnosing it instead of just dropping it off with them?

The seals fail. The result is that timing does not advance/retard based on DME signals.

I just want to learn and be prepped with info as best as possible before going back to them.

Thanks
Conny

Do you have to take the timing cover off to replace the vanos unit?

Yes, timing chain cover and all the stuff in the way to get there. Vanos can be rebuilt.

Ok - thanks!

Fair enough. Hope it gets sorted. :thumbup:

As far as timing being off, it can be off and not throw any kind of fault codes. Period. How do I know? My 4.6is had the timing off and caused a crank no start scenario. Zero fault codes were stored when the dealer, who last timed the engine 1400 miles ago, checked for fault codes. Idiots assumed I needed a new engine.

A more educated shop named Integrity First Automotive concluded that after running a wet and dry compression test and then a leak down test that the engine timing was retarded. The shop owners friend that teachers auto mechanics said it is possibly as well to get a BMW engine out of time and not throw codes.

The dealer said no way because " there are not any codes stored" lol. Amateurs.

I had to pay said shop to time the engine and while they were taking it apart they discovered my oil passages or something like that were not tightened down. They think it caused a camshaft to run dry and threw the engine out of time. I only had slight damage to the left camshaft and am quite lucky the inept dealer did not blow up my engine.

They told me to pound sand when it came to reimbursing me the 1700.00 it took to get the engine retimed. BMW NA is hopefully going to reimburse me for it.

Hi everyone, I'm still battling with the repair shop over the low compression condition in all bank 2 cylinders of my 4.6is after they redid timing chain guides and chain. They are claiming the low compression in all bank 2 cylinders is caused by a faulty cam actuator and not a slipped gear. Is there an easy way to find out if the low compression is caused by a slipped cam gear or a defective cam actuator?

Thanks much for any input/feedback in advance :-)