Let me preface by saying I'm not a novice at working on cars- I'm a certified BMW master tech and have several ASE certs and I'm stumped: The engine is a 383, forged eagle rotating assembly, probe pistons, plasma moly file fit rings. Heads are Trick Flow units stage II from Nevarez Racing aka: combination motorsports, long tube jet hots and Ignition: Dynaspark opti w/Delteq and finally tuning by Tony Bishop (tuned on the dyno). SYMPTOM / issue: the car will sputter and throw entirely too much gas on the plugs under 2k rpms, with throttle and high RPM it clears up until you go back to idle, I have a datamaster scan on it and it does go into closed loop like it's supposed to. Where I see a problem is with LTerm counts are going to 160 which is telling the PCM I'm running lean and obviously it's not. I have change 3 diff set's of plugs experimenting with heat ranges, new GM 02's, new MAF, and I have checked every last opening in the intake track checking for unmetered air getting in - it all check's out like it's supposed to. So before I go and buy a grand worth of software and do some dyno testing would someone who has run into this similar issue please shed some light in the problem? I'm going to go and do a compression test and check for a dead cylinder. BTW- I have also verified ignition is working properly the engine has about 3800 miles on it and this has just surfaced but I don't think I'm having a component failure ie: valve or lifter etc. But like I said it's stumped me.

 

WHat does your IAT read? Mine had a similar problem it did not code but was reading neg-40 degrees, had an open wire.

ALso what is your timing at idle?

WHat is MAP reading at idle?


David

 

In which Cells are the long terms going to 160?

How big is the cam? Enough overlap to allow significant amounts of air to blow through into the exhaust under 2,000 RPM?

 

Has it always done this or did it just start doing it?

 

...

 

Timing at idle is 30.0
IAT is reading 86.9
Map is reading 58.7

 

The Cam is not a huge monster specs are: Comp Cams TN233XL 233/239 duration @.050 .569/.576 with 1.6 rockers, 112 lsa

I can email the datamaster file to you if you wouldn't mind taking a look at it.

 

You know a header gasket leak will allow in fresh air for the O2s to read.

 

I'm sure a header leak would let in air, but my stage 8 locking bolts don't really back off. I do appreciate any input.

 

Still going through this huh?. You purchased the software or did i send you ther datamaster file and you figured out how to open it?.

 

You sent it to me and I downloaded the free program to read it. I also got a new laptop and a ALDL cable with the USB port attachment. I have to pay for the software so I can change the settings to use the USB cord - go figure.

 

Im off tomarro and can stop by with my serial port cable if you want to use it?.

 

Header bolts can only back off because they lose torque, they lose torque when gaskets compress.

Very BIG difference between knowing how to bolt things together and truely understanding what is going on.

Not saying header gaskets ar ethe issue but they could be a contributing detail.

 

I appreciate your input, but I'm willing to bet that you don't even know what a stage 8 "locking bolt" is by that remark. I never realized that the gasket thickness would change when pancaked between a header and a head That's why I use copper gaskets to minimize the amount clearance between the two and THEN I "LOCK" the bolts in place with the afore mentioned Stage 8 bolts and they cannot back out. As far as knowing what's going on I would say that with as many M engines I have put together and changed heads on, I pretty much understand what's going on to the point the BMW trust me to do it, sooooo - You might want to refrain from insulting someone who definitely understands it better than you.

 

I looked at your data log. Its of limited value, because its just a few minutes of idling and a blip of the throttle at one point. You need to drive it to generate more meaningful data.

What does appear:

PCM is not able to hold idle. Programmed target is 900rpm, but its idling at 1000-1100rpm. That's because there's a glitch in the TPS reading. Its showing a non-"0" value, so the PCM is elevating the idle. You may need to adjust the TPS voltage down a bit, and check the linkage and the blades to insure they close consistantly. The PCM successfully baselines 0.75V as 0% TPP, but later in the log is running 0.8%, then 1.2%, while the sensor is still reading 0.75V. But at one point in between, the TPS volts drop to 0.73V and to 0.71V, possibly causing the PCM to rebaseline incorrectly.

System voltage appears very high, peaking at 14.9V. The scanned voltage, coming from the power supply to the PCM, generally shows about 1V lower than actual alternator voltage. Are you possibly running a 16V battery? I usually see about 13V at idle on most logs I review. Maybe the PCM is having a problem stabilizing its reference voltage output with the excessive system voltage. Shouldn't be a problem at that level, but it may be affecting some of the sensor readings.

O2 sensors look "lazy". They move very little and very slowly. Normally in closed loop, the sensor voltages, and the short term counts (which are the PCM's response to the O2 voltage) are swinging over a wide range of volts. The system reads the O2 sensor volts and adjusts the short term corrections about 9 times per second. Normally, you would see O2 readings swigning over the range of 1xx-9xx millivolts. Yours aren't.... they sort of get "stuck" in the 300 or 400 or 500 mV range and don't seem to respond.

MAP appears normal for that cam, seeming to confirm solid tuning.

The obvious problem is the long term fuel corrections, which start out at 160L/140R, then eventually start to drift and switch to 151L/160R at the end of the log. Again, may be the result of lazy sensors. Is there any possibility the sensors have been exposed to large amounts of leaded fuel? ...possibly contaminated with silicone from RTV or coolant?

You need to find out more about the O2 sensor behaviour and the long term fuel corrections. You need to log the system while actually driving the car, trying to get it to operate in as many of the 16 fuel correction cells as possible. With your ASE background, I assume you are aware of the basic operation of the A/F control system, but if you need to check the boundaries for the LT correction cells, they are shown in my online scanner guide. These would be the stock programming boundaries. Your tuner may have changed them.

http://members.aol.com/InjuneerZZ/ScanMast.htm