car_ramrod

Hey all,
I was posting in another members thread about being stuck in cells 16,17,18 and I got that sorted by reloading the factory tune, but I'm still having issues with high BLM's.

5.uni

7.csv

The Idle (cell 16) seems to be the worst (155-ish), but they all are pretty high (135-148ish). They seem somewhat balanced when I look at the averages in the DM Histogram so I don't think I have any nasty splits to worry about.

I'm kind of a noob at this BLM thing. My tuning experience thus far has been limited to fan temps, timing, stuff like that. I've read Solomons page and understand the principals behind adjusting the MAF tables, but I'm unsure if I should be doing that yet with BLMs this high, does it indicate something else is going on that should be resolved before changing the MAF tables?

Thanks in advance for any insight that can be offered.

bobdec

Looked at 5.uni .. Your ST BLM's look a lot better than the LT's and you have a Air Pump DTC 29. I ran a historgram selected options 'view enhanced' and compared left/right ST and LT BLM's. Your LT's all show lean, and ST's show lean at 50-100 AFGS (higher end). Your MAP (35) at idle is a tad high and Baro is 103 also a little high. But the Pcm should adjust for that. I would reset the PCM to get all LT and St BLM reset back to 128. Then monitor LT BLMs after running a while. As everything else looks OK you may want to tweak the MAF tables (increase values a percent at a time) at the above 50 AFGS ranges to richen the mix. Are your O2's in good shape or are they old (or Bosch), Also make sure you don't have any exhaust or intake leaks prior to messing with the tune. Nothing looked abnormal, pointing to any major leaks and your BLM's were not really out of balance, (indicates a leak). PS always save the stock tune to go back to..before to loading a new one....

car_ramrod

Bob,
That log, 5.uni, was taken shortly after reloading the stock tune, so the LT values all started out at 128. I was monitoring with freescan before I used one of my datamaster trial runs and every cell I went into LT started out at 128 and then slowly incremented. Maybe if I had taken the log earlier in the drive, we would have seen the ST numbers more on the lean side before the LT's started incrementing, could that explain why the LT's on that log were all so high, and the ST's, at least in the lower cells, were not too far off?

The O2's are in fact old...possibly the original ones, and I'm at 130k miles, they seemed to be swinging through the right mV values so I took it for granted that they were ok, could they be part of the problem?

How can I best check for the leaks? I don't hear any of the ticking that I'd normally associate with an exhaust leak. The intake system wouldn't surprise me if there may be some cracks in the plastic or something though, can I just spray starting fluid around it and see if the idle jumps up, or is there a better way to find those pesky post-MAF vacuum leaks?

bobdec

Remember BLM's are sort of a misconception on running rich/lean. In closed loop the O2's are the final decision maker. If the BLM for a specific BLM cell reads 140 then (140-128)/128=0.09 says your engine sensor (temp/MAP/MAF), injector size fueling calculation is 9% lean according to the O2 readings. The PCM then adds 9% more fuel to keep the AFR at stoich (14.7 AFR). So in essence the engine should be running OK. However an air leak prior to the O2's will generate a FALSE O2 lean and the PCM will add fuel causing a rich engine mix that can foul things up. So you will have lean BLM indications , but a rich running engine. This gets confusing, proper tuining assumed no air leaks. The PCM can correct up to 10-15% errors from the sensors. Getting BLM's at 128 indicates a perfect running engine and is import in cells 14 and 15 prior to going WOT as the BLM in that cell is used in PE fueling calculations. So we always try for perfection at 128 at all cells or operating ranges. I saw your O2 voltage swings and they look good , correct levels and steady switching. Since O2's are the final arbitrator to the PCM, and the only way to verify good O2 readings is with a wideband, lots of tuners will recommend replacing them prior to tuning an engine. It's a crap-shoot as they may not have any problems , but 130K is stretching their life span. If you do go for O2's get Delco or Densco for some reason our OBD1 PCM does not get along with the Bosch switching speeds and a few posters have had problems with them.

car_ramrod

Bob, I appreciate all the info. Just thinking out loud here, would a wideband O2 also read a false lean if there was an exhaust leak prior to its location? How can one really verify if there are no leaks, or that the engine is actually running at whatever A/F ratio the O2's report? Should a person go old-school and try reading the plugs just to make sure that 9% extra fuel the PCM is adding should actually be going in there, or if its a false lean and that extra fuel is fouling the plugs?

Injuneer

At idle, with a 158, your adding 23.4% extra fuel via the BLM. If that is due to a false lean, it should show up as dirty plugs.

At idle the MAP is 45kPa. That's too high if you have a stock cam, and may indicate a vacuum leak, incorrectly adjusted valves or misfires. The 103.3kPA barometer simply indicates you had a fairly decent weather day, at the near sea-level elevations of central NJ.

And I assume you realize you have a code for a faulty AIR pump circuit.

car_ramrod

If the high MAP is indicating a vacuum leak, could that vacuum leak be causing the false lean condition?

Injuneer

A vacuum leak would be a true lean, requiring the BLM's to add the fuel for the air that was bypassing the MAF sensor. In that case, the plugs would look normal.

Incorrect valve adjustment or misfires would put air into the exhaust, causing a false lean.

car_ramrod

Ahhh, yeah that makes sense when you put it that way Fred. Thanks for the help while I try to learn what all this stuff means. I was hoping to learn the tuning skills and try to get my tune perfect on all the stock equipment before I went changing hardware and getting things farther out of spec...I didn't really think it would be this hard, but I guess with mileage this high, there's no telling what hoses might have pinhole leaks in them or if the valves are maladjusted after all this time. I'll poke around this weekend and see if I can find any leaks and maybe pull a couple plugs to see how they look and report back in.

Injuneer

That's why you shouldn't jump into playing with the MAF calibration to get the BLM's back to 128. Figure out why they are so far off first.

car_ramrod

Just got done troubleshooting, and I pinpointed the (a) vacuum leak to the underside of the throttle body. Turns out the intake elbow was torn, cracked, and leaking right at/before the throttle body. Hopefully this is the only one, its the only one I could find with a length of fuel line stuck in my ear or by spraying starting fluid over all the vacuum line connections. I have a new CAI and new elbow on the way so I'll report back after I have a chance to install it and say if it cures my high BLM's. Thanks for the advice to look for a vacuum leak.

bobdec

Ramrod, will be watching for update.. your log sort of highlighted what I have been thinking about BLM operation. That LT BLM's are not an average of the ST BLM's as many posts indicate. But are actually a PCM adjusted number used for fueling calculation while the PCM observes the ST BLM's to verify the results. Basically the PCM bumps the LT number up/down till the ST's look good. Your log showed the LT numbers were as reading lean across the board (PCM was adding fuel) while the ST's were closer to normal. An indication that the PCM was correcting AFR for the un-metered air entering from the snorkel leak. By the way I say your MAp at 39 Kpa at idle in gear on the log can you verify what it is at idle in N/P ?

car_ramrod

Until I can get my new elbow installed, I did my best to re-seat the factory one and I took another log. This one seems much better in the lower RPM ranges, but still showing high BLM's in the upper, maybe the leak is fixed at lower airflow, but starts to let in air at higher airflow. This does give me some confidence that once I take care of the leaking elbow, things should be pretty normal.

6.uni