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Discussion Starter · #1 · (Edited)
So I've had a P0305 for a couple years now. It only occurs on initial cold start. The computer is shutting down Cylinder 5, which I've verified by unplugging the coil to Cyl 5 and there is no change to the already rough idle, however there is dramatic change if I unplug any other coils. The only way to get Cyl 5 going again is to shut off the car and restart. Also, if I don't let it idle upon initial cold start, and just start driving right away, Cyl 5 usually does NOT shut down. I've replaced all the spark plugs and coils - no change. I just did a compression test on all cylinders and got the following results:

Cyl 1 - 152
Cyl 2 - 150
Cyl 3 - 147
Cyl 4 - 148
Cyl 5 - 109 on the first try, 120 on the second
Cyl 6 - 160

Based on these results, I thought I might have a blown head gasket, so I had an oil analysis done (kit purchased from NAPA for ~$15), but the results show no coolant in the oil. I think that eliminates the blown head gasket, right? Even so, the lack of compression on Cyl 5 worries me. What else could cause that, yet only throw misfire codes on cold starts? If it were a bad valve, wouldn't it throw the code all the time?

I do have one other code that is always present - P1470. I'm not sure if that could be related at all.

My next steps are going to be a Cylinder Leak Down Test (doing today) and also swapping fuel injectors to see if the code follows the injector. Do these sound like the best things to check next? Any other ideas?

Oh, I've also already done the VANOS seals swap, which did fix the "dropping idle" on cold starts, but did not fix the problem of this post.
 

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You should perform the cylinder leakage test before throwing more parts at the car. These test area easy to do, if you can change the spark plugs you can do this test. Only issue is you need a cylinder leakage test tool and compressed air.

Hopefully you do not have a problem like the guy in this thread!

http://forum.e46fanatics.com/showthread.php?t=889143&highlight=

Just need to rule out the basics before moving on.

Also look closely at the link in my signature below - Solve your misfires, lean codes, rough idle
 

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Discussion Starter · #3 ·
You should perform the cylinder leakage test before throwing more parts at the car. These test area easy to do, if you can change the spark plugs you can do this test. Only issue is you need a cylinder leakage test tool and compressed air.

Hopefully you do not have a problem like the guy in this thread!

http://forum.e46fanatics.com/showthr...ghlight=trophy

Just need to rule out the basics before moving on.

Also look closely at the link in my signature below - Solve your misfires, lean codes, rough idle
The link you gave for the guy's problem didn't take me to any specific thread. I'd be interested to read about it though, if you'd want to update it.
 

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Try this link, it may be what he was trying to show-

http://forum.e46fanatics.com/showthread.php?t=894338

you may still have a blown head gasket, it just may not have blown in an area that allows coolant into the cylinder and not between cylinders.
You could have a bad valve spring or valve lifter on cylinder 5.
Could be a broken or stuck piston ring.
Could be a bent or broken valve.
 

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that compression on cyl 5 is low, as compared to the rest. Enough that on a cold start i could see a problem. compression is an important test, but leak down will sum it all up. (milage unknown) head gaskets on these engines dont go bad often in my experience. When they are bad its not usually a one cylnder misfire on cold starts. You could post leakdown results and also put some oil into cyl 5 and manually spin the engine several times to see if it improves in compression. You may just have a weak or overly worn cylinder. Cold starts take more fuel to run properly.Also the engine tolerances are higher since the metals have contracted. Thats when a problem may surface as opposed to warmed up. Swap everything (coil, plug, injector) from 5 over to 4, and if it does not follow than your looking at mechanical engine issues. A common issue on these also was the lifters sticking in the bores of the lifter carriers in the cyl head. That could cause it to bind and not fully open the valve to allow air in when started cold..

the list can go on and on. Ive been a mechanic for 12 yrs now and often cold start and random misfires are a tough problem to figure out.
 

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Discussion Starter · #7 ·
Ok, I just got done with the cylinder leak-down test. Went ahead and did all cylinders, since I was doing it. Here are the results:

Cyl 1 - 7%
Cyl 2 - 15%
Cyl 3 - 9%
Cyl 4 - 17%
Cyl 5 - 8%
Cyl 6 - 14%

Ok, so now of course I'm wondering how can my cylinder 5 results be that good when its compression test showed much less compression than the other cylinders? Any thoughts or ideas on what I should do next? I'm guessing swapping fuel injectors would be the next step in diagnosis?
 

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Leakdown looks good, lower compression might be valvetrain issue, but before I would worry about throwing hard parts at the car, suggest you look over the link in my signature closely - Solve your misfires, lean codes, rough idle

Then I would probably swap or pull injectors for cleaning, look at coils and coil boots?
 

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Hopefully you do not have a problem like the guy in this thread!
Haha well I'm the guy in that thread and yeah, hopefully you don't have a problem like me! It wasn't cheap. I don't get why your leak down test has better results then your compression test so that's a little weird.
On mine, the leak was big enough that you could hear the air coming out the exhaust on the compressed air test. Your problem is a little different from mine but its got to be either head gasket (which it doesn't really look like it) valves or piston rings.
 

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Swapping injectors isn't going to fix your compression problem. A passed leakdown but failed compression means something in the valves isn't closing or opening at the right time, but manages to close by the time you get it at TDC for the leakdown test.
 

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Discussion Starter · #11 · (Edited)
Just read this on a site:

"One problem that might not lie inside the cylinder itself is a worn camshaft. If a lobe is badly enough rounded off then that valve won't open fully, or at all, and if no air can get into the cylinder then of course it's not going to generate much of a cranking pressure... If the leakdown test shows no fault but the cranking pressures are low then it must be a cam lobe or cam timing type of issue."

BTW, I do have 184,000 miles on her. How often are e46 camshafts replaced due to "wearing lobes"?

Also, if it were a camshaft timing issue, wouldn't I get other codes thrown besides cyl 5 misfire?
 

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After some thought, your compression problem MAY?? be caused by a broken compression piston ring??

A broken ring might give you the problems you are running into, lower compression with a good leakage test??

If I suspected a broken piston ring and only had a cold start issue, I would live with the cold start issue and drive the car into the ground!

But I will still check the link in my signature below regarding misfires as most of the systems are cold start problems.
 

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i dont feel these leakdow numbers look good. At the shop were looking for under 10% all cylinders. Your numbers are all over. Assuming its being done correclty with a decent tool. those numbers are higher than what youd want to see. Leakdown is tricky to do properly if you dont do it often. top dead center must be found, and sometimes the air pressure applied to measure leakdown rolls the piston back down giving a false result. I always do it 2 times, per cyl or mainly the troubled cylinder. Ill do a check, than cut the air off and roll the engine back counter clockwise, find tdc again and recheck the numbers. They should be smilar.

If you swaped inj/coil/plug over from one good cyl to another and still had an issue, than your pointing to mechanical engine issues. At that point you would know its either begin to decide to repair furthur or maybe its out of your skill level to do anything else with it.
 

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Discussion Starter · #14 ·
Well, I feel confident I could remove the head if need be. I've got The Bentley and TIS, plus a couple DIY's from this site. Read them about 5 times. I've already done most of what I'd need to do before. I've got the specialty tools available to rent. Obviously I don't WANT to do it unless its absolutely necessary. I am gonna have my intake manifold off in the next couple days so I can replace my heater inlet hose and whatever else needs replaced while I'm under there (I've got a couple pretty bad coolant leaks), so it would be a good time to do it if I needed to. I'm gonna swap injectors today and will post the results.
 

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Yest, the leakage results could be better, but I was only focused on cylinder #5 which did not have bad leakage. Before you take the intake off, you may want to pull the top engine cover and try the brake cleaner trick with the engine running. Spray around all intake ports and vacuum connections.

But again read my link in my signature below very carefully. You will find a lot of simple solutions to many cold start problems.

If it was my car, I might pull all the injectors and send them off to Witchhunter for cleaning and flow checking, they will come back with all new O-rings as well.

http://www.witchhunter.com/

Pulling the intake may not be a bad idea anyway. Make sure you replace the SAP check valve vacuum hoses if you have a system that uses a vacuum controlled SAP check valve.
 

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Discussion Starter · #16 · (Edited)
Well, here's an interesting update... my compression test readings were bothering me, so I decided to do it again. Before doing so, I made a couple changes. First off, I rented the tester from autozone and the hose would spin freely if I grabbed the valve end. This was preventing a really good seal. So I squeezed some crazy glue in the joint that was spinning. That allowed me to really twist the hose pretty hard to get a good seal. The second thing I did differently was I made sure my wife put the gas pedal to the floor before, and during, cranking. I don't think we did this before, which means air probably wasn't getting to the cylinders as it should have been, right? The only other change was that the car was completely cold - hasn't run for a few days. The first test was done at operating temp. The results on a cold test should be slightly lower than on a warm test, right? Here are the results:

Cyl 1 - 150
Cyl 2 - 150
Cyl 3 - 150
Cyl 4 - 145
Cyl 5 - 151 (yahoooo!!!!)
Cyl 6 - 154

Is there any reason these results (being on a cold engine) would be inaccurate? Or can I assume I do NOT have any compression issues?

I'm thinking of also doing my leak-downs again, and doing it a few times for each cylinder. Maybe it's possible on the cylinders with poorer results, it wasn't completely in TDC??? Or will it always push the piston down if it's not in TDC?

On a side note, my threads were really gunky in cyl 5 - it was pretty hard to thread the hose in all the way. Is there any way to clean those out without letting all the gunk fall into the cylinder? (I assume that would be bad.)
 

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OK, so it is looking like your compression is not an issue?

Skip the leak down, skip the heavy mechanical, skip swapping injectors at this time.

Read this link in my signature below - Solve your misfires, lean codes, rough idle

Order the e-bay DISA O-ting, pull the DISA make sure the flap is not loose, make sure the vacuum actuator holds vacuum, check the intake boots for cracks, replace the lower CCV oil drain hose. Pull the engine cover, not valve cover, start car cold and use brake cleaner and spray around injectors, intake, IAT, air distribution manifold, IAC and see if you can find any vacuum leaks.

Money it you have something rather cheap and simple to resolve.
 

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I don't know how your doing your compression tests but there is a way you can have a bad cylinder but still get a good compression reading. First off, your supposed to crank the motor over at least 6 or 7 times per cylinder. A healthy cylinder will pressure straight up and level out at a psi very quickly. If a cylinder takes many revolutions of the motor to "pump" up to say 150 psi then that's an indication of bad rings.

If it takes a few revolutions more then it should to get the pressure up, you can pour a little oil in the cylinder and do the test again. If the cylinder performs better with oil in it then you know its a problem with the rings.
 

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Discussion Starter · #19 ·
I don't know how your doing your compression tests but there is a way you can have a bad cylinder but still get a good compression reading. First off, your supposed to crank the motor over at least 6 or 7 times per cylinder. A healthy cylinder will pressure straight up and level out at a psi very quickly. If a cylinder takes many revolutions of the motor to "pump" up to say 150 psi then that's an indication of bad rings.

If it takes a few revolutions more then it should to get the pressure up, you can pour a little oil in the cylinder and do the test again. If the cylinder performs better with oil in it then you know its a problem with the rings.
Ya, that's what the Bentley manual said. All the cylinders had identical results. Went about 3/4 of the way up on the first cycle, then hit 150 by cycle 4.
 

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I am having the same exact issue cold start cyl 5 miss if you give a bit of gas its fine.. hmm

killa your valve looks like that from cylinder going lean that was the weakest point. Did you happen to replace that injector

Sent from my Galaxy Nexus using Bimmer App
 
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