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Old 01-09-2011, 09:20 PM   #1
01bluefun
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Join Date: Jan 2011
Location: South Eastern Michigan
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My Ride: 2001 325i
Lean on Both Banks, Pesky CEL/SES light with codes

CEL problems started in November. The light popped on intially with a manufacturers MAF voltage code...cleaned the MAF with CRC spray and the CEL went away for about a week. It began coming on an off intermitantly for the next week and ultimately popped on permanently. BMW specific MAF codes have vanished, the cause on the second run was lean air conditions on both banks (P0171, P0174, P1083, P1085) and multiple misfire codes (each cylinder w/ fuel cutoff)

Ive replaced the lower intake boot, spark plugs and valve cover gasket. Cleaned the IAC, MAF, throttle body and DISA. I resealed the DISA with RTV. Also ran techtron fuel system cleaner with 12 gallons. I only use 93 octane fuel and the air filter is nice and clean. On Friday I swapped in an MAF from my buddies e46, cleared the codes and after driving for about a half hour the cel came back on.

Since doing the spark plugs/VCG all misfire codes have gone away.

My current codes are...

P1083
P1085
P0171
P0174

Car is a 2001 325i 5speed w/ 112,000 miles.

Other symptoms...

Poor gas mileage: 21-23 average city, 25ish on the e-way. I'm an easy going driver.
2000 rpm vibration, sounds similar the "chewbacka" thing, varies in loudness with throttle input
Car feels very sluggish, lacks power until 5,000 rpm...could just be the 2.5 m54!?!

So im running out of things I can check/diy. Any other suggestions? Oh yeah, its my first post! Please be gentle

Last edited by 01bluefun; 01-09-2011 at 09:27 PM.
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Old 01-09-2011, 09:35 PM   #2
jdstrickland
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Lean is an air leak.

The MAF is telling the computer how much air there is by density and temp. The computer adjusts the Fuel Map according to the air density and temp. If there is air that enters the intake without the MAF seeing it first, the result will be not enough gas, which the O2s will report back as a lean condition.

The MAF will be telling the car that there is a certain quality -- density and temp -- of air, and the injector timing is set for that quality. New air comes in that the MAF has not seen, and now the fuel map is not opening the injectors long enough.
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Old 01-09-2011, 09:48 PM   #3
01bluefun
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Quote:
Originally Posted by jdstrickland View Post
Lean is an air leak.

The MAF is telling the computer how much air there is by density and temp. The computer adjusts the Fuel Map according to the air density and temp. If there is air that enters the intake without the MAF seeing it first, the result will be not enough gas, which the O2s will report back as a lean condition.

The MAF will be telling the car that there is a certain quality -- density and temp -- of air, and the injector timing is set for that quality. New air comes in that the MAF has not seen, and now the fuel map is not opening the injectors long enough.
Yup, I definitely get all that. It seems like on this forum everyone with the lean problem has the infamous torn lower intake boot. I replaced mine but am still getting the lean codes. Any other areas to look for vacuum leaks?
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Old 01-09-2011, 10:08 PM   #4
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Originally Posted by 01bluefun View Post
Any other areas to look for vacuum leaks?
Smoke test.
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Old 01-09-2011, 10:10 PM   #5
jdstrickland
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Sorry, not any suggestions that don't start with, double check your previous work. There are not many ways for there to be a vac leak, and you have put your hands on all of them.

Well, let me regroup a little. You have MISFIRE WITH FUEL CUTOFF. Cutting the fuel off is a good way to go lean. I don't know what causes fuel cut off, whether the computer cuts it or there simply isn't enough. If the latter, then then you should be looking at fuel pump reliability issues, filter clogged, regulator reducing the fuel pressure, those sorts of things.

I'm not sure what the result of low pressure is, but a SWAG - silly wild-ass guess - is that there can be conditions that would cause the O2 to read lean, and stretch the fuel injector time, and eventually the injector time would be as long as it can be and still be lean, fuel cutoff is the description of the problem.

I have not studdied how fuel pressure regulation happens on our cars, but given your codes, I would be looking that way.

I am sent in this direction because a MISFIRE is the result of the expected work is not performed. The spark plug fires, and the crank goes to the next position, but not fast enough so the work is not done as expected and a misfire is reported. A lean condition can cause the work to be weak, so a misfire because the injector timing is as long as possible and still lean would mean to me that the fuel pressure was low.

Give it a whirl and see where it takes you.

You have _some_ pressure. I don't know the spec for fuel pressure, but let's say it is 60psi. At idle and other low load conditions, the injectors only need 45psi to do their work, but at 80mph, you need all 60psi. What if there was only 50psi of fuel pressure instead of 60psi. In this case, you could drive around town doing low-load journeys and the car would be happy. But when you get on the freeway, within a short distance, the CEL will be on because there's not enough gas at the injectors to fullfill the demand. The mixture would turn lean and misfires would result.

A fuel pressure regulator lets the extra fuel at idle be sent back to the gas tank because you only need 45psi at that time but have 60psi available. The fuel pressure regulator is often times a vacuum operated device on the fuel rail. but I don't know how BMW accomplishes this task. I'm afraid pressure regulation is actually done at the pump, but I don't know that to be a fact.

I once had a buddy with a 260Z with a failed fuel regulator, and his car would not run, the pump was sending gas up to the injector rail, but most of it was going back to the gas tank. It was too old to have codes to read.
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Old 01-09-2011, 10:15 PM   #6
TxTorqueMade
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o2 sensors
Clean ICV again
Clean MAF again
CCV R and R time?
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Old 01-09-2011, 10:39 PM   #7
01bluefun
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Thanks for the comments so far. And sorry for the long winded post. The misfire went away when I changed the plugs and VCG. What happened was my VCG was so bad it allowed oil to pool in the spark plug wells which must have caused detonation...plus the plugs were original and in terrible condition. I replaced with NGK stockers. Right now all I'm dealing with are the lean codes (p0171, p0174, p1085, p1083.) So are there any other common vacuum leak trouble spots?
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Old 01-09-2011, 10:46 PM   #8
jdstrickland
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I think you are at a point where you need to collect information from the DLC.

You can drop Ken, at Peake, a note and ask if his scan tool will give you fuel pressure information. You still have lean codes. My previous post still holds true at least for reasons of checking fuel pressure. Fuel may not be the problem, but if pressure was border line low, and you had weak plugs then a misfire could result that goes away when the plugs are fresh. You have to at least check. Otherwise, you have double back on the stuff you already did.
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Old 01-10-2011, 12:13 PM   #9
01bluefun
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Okay, well I agree I should do smoke and fuel pressure test. I will take it in for the diagnostic.

What do you guys think, dealer or indy? At least with a dealer if theres a bad sensor they will know immediately and just pop a new one in. With an Indy I think they will do more guess work.
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Old 01-10-2011, 12:15 PM   #10
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Originally Posted by 01bluefun View Post
Okay, well I agree I should do smoke and fuel pressure test. I will take it in for the diagnostic.

What do you guys think, dealer or indy? At least with a dealer if theres a bad sensor they will know immediately and just pop a new one in. With an Indy I think they will do more guess work.
Not a good, indy shop.

Surf through www.bimrs.org for BMW indy shops in your area.
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Old 01-10-2011, 12:21 PM   #11
xavi330i
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Lean codes both banks..... CCV fail.
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Old 01-22-2011, 10:21 AM   #12
SHK&BAK3
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Any updates I think I might have the same problem.
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