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George
George, BMW Technician
Category: BMW
Satisfied Customers: 1861
Experience:  BMW Master Technician over 20 years BMW Dealership Experience. BMW Auto Repair Shop Business Owner
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BMW 318i: erratic compression readings..one cylinder..misfire

Resolved Question:

Hi,
Does anyone know why a BMW 318CI might give erratic compression readings on one cylinder?
Sometimes there is no compression at all, then if I re-check it there could be anything from 20psi to 150psi or 200psi (hot). The problem is with no 4cylinder and the sparkplug is very white in colour. Also a misfire on no 4 Cylinder is recorded in the ECU. The other 3 cylinders seem to be fine and consistently record 150psi cold and 200psi hot. It seems to be worse when the engine is cold and it smoothes out once revs are increased above about 1500 rpm and it drives well enough on the road apart from a rough/lumpy idle at traffic lights. I was thinking about a sticking valve, but I was assured that the cylinder head was removed recently and sent to an engineering shop for checking. I did remove the rocker cover and observe the electric motor move the essentric shaft to full lift while the engine was cranking and return again when the key was let go.
Any ideas?
Submitted: 3 years ago.
Category: BMW
Expert:  George replied 3 years ago.

George :

Did you perform a cylinder leakdown test?

George :

Also can I have the last 7 digits of your VIN #

Customer:

Yes, I did one today, but I couldn't hear anything.

Customer:

It's not my car, but I could get the vin tomorrow if it's of any help.

George :

What was the percentage of leakdown in each cylinder?

Customer:

I can tell you it's a 2002 car.

Customer:

I didn't check all the cylinders, I was just hoping to hear air leaking past the valves in no 4 cyl.

George :

What was the percentage of leakdown then in cylinder # XXXXX?

Customer:

I don't have a figure but the only leak I could hear was into the sump.

George :

What did you use to perform the leakdown test?

Customer:

Just a tool used to keep the valves in place by compressing a cylinder while removing the cotters and springs on an engine in place.

Customer:

The compressor was running at 150psi

George :

What were the "P" codes that were stored in the ECU?

Customer:

What are they?... where would I find them?

George :

You said you had faults stored for misfiring in # XXXXX was stored, what was the actual fault code # XXXXX what type of code reader did you use to read the fault codes?

Customer:

I think it's called an Autoboss( I think it's made in China). I have deleted the codes over the last few days, but it will return after a short drive around the block.

George :

Ok in order for me to help I will need some of the items.

George :

1st I will need to know what fault codes are stored & what the "P" codes are. Example P0301 Misfire cylinder # XXXXX

George :

You will need to perform a cylinder leakdown test with the proper tool and let me know what the percentage of leakdown is in each cylinder.

George :

Also I need to know what the STFT (short term fuel trim) readings are.

Customer:

I won't be able to get the fault code untill tomorrow morning, is there anything else you would like me to take note of while I'm at the car??

George :

What has lead you to believe it is an internal cylinder problem?

Customer:

That's a hard question George, a few guy have pulled this car apart before me and they had to give it back the same way they got it! I suppose I'm stuck on the fact that 1 cylinder is not compressing like the other 3 and I got fixed with the idea of an internal problem. I did think about sticking hydrolic lash adjusters or maybe the valves no opening at all on no 4 cylinder.

George :

OK depending on the results you have from the tests I have asked you to perform will give me the answers I will need to give you a better idea if this is an internal engine problem or possibly something else.

George :

So once you have the results just post them and we will go from that point on.

George :

Please don't forget the last 7 digits of the VIN # XXXXX I know exactly what I am dealing with instead of guessing.

Customer:

Ok George, I'm new to Just Answer, how do I contact you tomorrow??

George :

You will just continue to post to this same question, and if I am not on line at the time once I am it will be waiting in my mailbox and I will respond to you.

Customer:

Ok, Good night.

George :

Have a good night.

Customer:

Hi George,

Customer:

Hi George, sorry for the delay in getting back to you. I was waiting untill I have all the information you require to make a diagnoses. At the moment all I have is the VIN: WBABV72070JZ76705. The build date is June 2002. Yesterday I had an 'interesting' conversation with a guy and I decided to replace the 4 lash adjusters in no 4 cylinder. It was not an easy job with the head and cams in place, but I managed to get them fitted, I suppose I should really have fitted an entire set, but I got the last 4 in Dublin!!. Today I changed the oil and filter and I brought the car to a guy with an exhaust gas analyzer. He says the CO emissions are perfect for the car and year: 0.00. I am going to keep the car at home and drive it during the weekend and see how it behaves. I canceled any stored error codes and I'll keep a list of any recuring or new ones. It feels a bit better to drive, but there is still a slight hesitation at low revs and it's a bit lumpy when I back off the throttle, but it smooths out quickly. I also had a look at a few Youtube videos on Leak Down Testers after talking to you and I can see the value of the readings. I am going to check around to buy one and I'll let you know when I have the readings.

George :

Ok thank you for the update.

Customer:

Hi George, Just another update. Friday, This is the first time I've started this car early in the morning. I didn't touch the throttle and it started first go, it was very lumpy like it was only running on 3 cylinders and there was an occasional poping sound. I think the poping was comming from the exhaust manifold, but I can't swear to that at the moment. The error code today is P1349, there were no error codes stored yesterday before I headed for home (about10 miles in city traffic). These are the old symptoms that have plagued the owner for several months now. I was also told that he wasn't the type of guy who would change the oil and filter on a regular basis, he'd just top it up as needed!!

George :

OK

Customer:

Friday update: Now 3 Error codes. P1341, P1347, P1349.

George :

OK

Customer:

Hi George, This week I did a few more compression tests on no4 cylinder and I got consistant readings of 200psi, I'm taking this as a good sign after fitting the hydrolic lash adjusters last week. I also fitted new rubber gaskets to the inlet manifold even though they 'never sell them' at the local BMW dealers. I've also discovered that if the car runs and revs a lot smoothly when the MAF sensor is disconnected!.. I did try replacing it with one from a similar car that was not displaying any problems but it went back to a rough idle and hesitation when the throttle was pressed. So I guess it's back to the drawing board. The only new thing I've learned is that Valvetronic system goes into 'limp home' mode and increases the valve lift when the MAF is disconnected so maybe the problem is with the Valvetronic system??

George :

What fault codes is it storing now?

George, BMW Technician
Category: BMW
Satisfied Customers: 1861
Experience: BMW Master Technician over 20 years BMW Dealership Experience. BMW Auto Repair Shop Business Owner
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George
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BMW Master Technician over 20 years BMW Dealership Experience. BMW Auto Repair Shop Business Owner