Negative Multiplicative Values

[Bengineer330]

My Bank 1 (Passenger) Multiplicative Values are consistently around -13%, Bank 2 hovers around 2%. Zero Codes no issues, as far as I know the car runs fine but I have nothing to compare it to. Pulls like a freight train all the way to redline.

Background on the car; car had the engine replaced at 125k when I bought it used. However nothing but the block was updated everything old was put back so when I received the car I invested some money and put in all new Index 12 injectors, CCV piping, boost solenoids, Plugs, Coils, and a new Bank 1 (passenger side) boost pressure sensor, changed all fluids. Oil changes every 5k miles and I lose almost a quart in that time.

The first things I replaced on the car was the Boost Solenoids and the Passenger side boost sensor because I was getting over boost codes for Bank 1. Since then I have learned a lot about the car and even more about ISTA+

So now I am chasing this Negative Multiplicative value and after logging values with Test-O my two suspicions are: 1) The boost between banks is unbalanced by about 1-2PSI which doesn’t seem too bad. 2) The Temperature on Bank #1 is 6-degrees less than Bank #2 constantly, it’s a hella brand sensor from Bimmerworld that they said would work but its always at least 6 degrees less.

Trying to figure out the root cause, My question is would the less boost in bank 1 cause the temperature to be that much less and I need to adjust the waste gates. Or is the sensor out of spec and reporting back cooler air than normal causing the fuel quantity to be more causing the negative multiplicative values.

Any insight would be appreciated

[Sophisticated Redneck]

Your still within tolerance and why you haven't thrown a code but it's getting up there at 13 percent, indicating a rich condition on that bank I would replace your pre-cat oxygen sensor first if you have not already and then your MAF sensor next.

1-2 psi on n63/s63 is pretty normal, I installed new turbos and regulators and still had the variance. Might be able to tighten wastegate to tweak it but have never tried. BMW added bank to bank balance tube to the Intercoolers in the TU2 and up n63/s63 to deal with issue once and for all.

Temp difference between bank one and two is normal once engine is at operating temp. Reason is drivers side intercooler coolant feed pipe runs across engine compartment, normal for 5-6 degree winter and 10-20 degree summer difference. You can cover with pipe insulation to limit it. Kinda of cheap design. I believe the M gets an extra pump and radiator to help with this issue.

However If you see a temp difference when engine is cold between any of the 4 MAP sensors, that is a problem and should replace

[Sophisticated Redneck]

Also going to add, before replacing your oxygen sensor or MAF sensor, you might want to borescope your valves, n63 is notorious for burning oil due to bad valve stem seals, your intake valves on bank 1 could be so caked with carbon that's reduced airflow enough to start messing with the long term fuel trim a and causing your rich condition.

Amazon has a dual camera borescope with one camera at 90 degrees, you can see valves with it and rotate crank until intakes are open to see condition. No real easy way to clean however (pull engine or pull heads)

[Thecastle]

Unmetered air entering/exiting the engine also causes long term fuel trims to change. In this case with the engine pulling fuel may mean an intake leak post maf. Make sure your intercooler hoses are tight, and without cracks. Also make sure the ccv isn’t leaking as this is another source of unmetered air. Usually it’s unmetered air, bad maf, bad 02, bad injector (leaking), bad ignition, bad exhaust 02 sensors, or even an exhaust leak. Easiest is to do a smoke test. Typically if it was coking, you’d see a reduction in maf which the computer would automatically pull fuel. The long term fuel trends are the measured by exhaust 02 sensors sensing too much unburnt fuel and pulling fuel from the engine aka leaning it out.

Of course it could also mean the engine is worn or leaking internally.... if the rebuild wasn’t good. My bet is an air leak.

[Bengineer330]

Wow! Thank you Sophisticated Redneck and Thecastle I'll check on the unmetered air since that has plagued me from the beginning. Just not sure how to check an exhaust leak, any suggestions?

For clarification the block was a brand crate block from BMW they showed me the receipt and I was able to verify the serial# on the block matched. So hopefully no carbon buildup yet but just for curiosity I might just Boroscope them. Are you viewing through the spark plug opening?

I changed the MAF's out last week mainly because FCP has genuine BMW on sale for $37. Couldn't pass that up. Did before and after trending and the old ones were under-reporting by 2-3% so nothing dramatic but piece of mind.

I'm planning on swapping MAP Intercooler sensors from Bank1 to Bank2 this weekend and see if the problem follows.

Thanks again, always hard troubleshooting when you don't have any baseline data to compare so all your suggestions are greatly appreciated!

[Sophisticated Redneck]

Originally Posted by Bengineer330

Wow! Thank you Sophisticated Redneck and Thecastle I'll check on the unmetered air since that has plagued me from the beginning. Just not sure how to check an exhaust leak, any suggestions?

For clarification the block was a brand crate block from BMW they showed me the receipt and I was able to verify the serial# on the block matched. So hopefully no carbon buildup yet but just for curiosity I might just Boroscope them. Are you viewing through the spark plug opening?

I changed the MAF's out last week mainly because FCP has genuine BMW on sale for $37. Couldn't pass that up. Did before and after trending and the old ones were under-reporting by 2-3% so nothing dramatic but piece of mind.

I'm planning on swapping MAP Intercooler sensors from Bank1 to Bank2 this weekend and see if the problem follows.

Thanks again, always hard troubleshooting when you don't have any baseline data to compare so all your suggestions are greatly appreciated!

No problem happy to help (hopefully). If your block came with new heads then doubt its carbon build up, I missed that part that you had a new block.

Since it's a negative value, that indicates a rich condition which means either blocked airflow or something funky going on with your fuel delivery. Would normally suspect a sticky injector but if you have new index 12's that eliminates that. Possibly issue with passenger side fuel rail pressure sensor reading lower then actual fuel pressure is causing it to run higher and rich condition.

But I would still just start with the pre cat oxygen sensors, if they are not new you should replace them anyway just for the miles that are on them. By far one of the most critical sensor your engine has and if it's off, it's sending you on a wild goose chase.

Yep down the spark plugs hole, turn on side facing camera, allows you to see valves and cylinder wall conditions.

[Bengineer330]

Well, I swapped the Charge Pipe intercooler MAP sensors and the Temperature difference was still there so I believe its just inherent in the cooling routing like you suggested.

Since I was already under the hood with a couple beers and time on my hands I decided to swap the CCV valves on top since ordered them as "just incase" spares. That seems to have done the trick. My Multiplicative values are ~6-9% when idling but when I monitor it while driving the values go closer to zero while cruising on the highway. I never thought it was an air leak since the value I was fighting was a Rich Condition, so there must be more to those vent valves than I know of. Anyways, my knowledge of Multiplicative values is still limited but I feel better now that there Normalish?

On to the next error....A72F