vettemanc486

Hello,

First a little about the car:
early 86 y body
383ci 9.5cr, dart iron eagle 215cc heads, xfi280 retrofit, victor JR with sheet metal elbow, 58mm tb, long tubes w/ true dual 3" exhaust, heated O2 sensor (4wire) installed just behind the driver's side collector.

The car has a blowerworks 4" maf with their bin, ostrich, tunerpro, etc. The problem is, at idle my blm goes to 160 FAST, with the O2 reading close to 0. This is backed up by the wideband I have installed in the x-pipe (borderline too lean for it to read it seams...) I am 99.999999999999 percent sure there are no vacuum leaks. There is no exhaust leak around the collector or the O2 bung I just welded in. I do not hear a leak around the flanges against the engine, which I am using some kind of multi layered metal gasket so a leak there is not likely... The car has a walbro 255 pump and a fresh filter, new braided lines from the filter forward so fuel flow should not be an issue.

The strangest part to all of this, I tried playing with the MAF tables to see if I could get the idle fueling better and nothing I did made any difference. After this I suspected that the ECM was not using the MAF input. I shut the car down, unpluged the MAF, cranked it, it idled, barely, with the check engine light on, the wideband reading ~9.5, I had the injector constant set lower than was in it trying to bring the fueling in line, I changed it back to the correct value, loaded the bin (while running), walah! no more check engine line, idle smoothed out, car ran EXACTLY like it did with the MAF plugged in. The datalog gauge layout that I got from blowerworks was reporting a MAF reading during this time. I assume that was from some look up table for some kind of alpha-n mode??? I am pretty lost. I repinned my ECM exactly as documented in the installation manual I got the sensor, so that shouldn't be the issue...

Is there a way to look at the raw voltage input from the MAF in tunerpro?

tequilaboy

Yes, it is possible to log the MAF voltage, however some programming changes are required in order to do so. First, the bin must read and put the appropriate signal into the datastream and the adx must be edited to display the new signal.

I typically redirect the fuel pump voltage read (since this signal is already in the datastream) and correct the injector voltage offset table to instead use battery voltage as an input.

While MAF voltage is an interesting signal to log, it doesn't contain much more useful information that can't already be obtained from the two existing MAF sensor signals, assuming that you have access to the MAF transfer function (tables).

Some background info:

In your initial bin, the Code 34A and 34B thresholds (which are both 2 byte values located at 215 and and 21C in $6E) were not adjusted from the default settings. As result, the MAF voltage may fall below these thresholds due to the large housing and changes in the bin, making a Code 34 more likely to occur even with a valid signal. Instead of 140 mv, the thresholds were effectively 240 mv.

As a first step, both of these thresholds should be corrected from 0049 to 0028 or even lower, depending upon the actual signal behavior. Final values will need to be determined and adjusted accordingly depending upon the typical signal level while cranking.

Code 34 should have already been masked out as a temporary measure, but it would be a good idea to correct the thresholds and re-enable Code 34 again to protect for an open circuit failure.

Compare the 16 bit Mass Air Flow signal to the 8 bit Unlimited Airflow signal (sometimes referred to as MAF raw input in the adx file). These signals should track each other and reflect the MAF voltage, if no MAF error is present, despite the different scaling, resolution and effects of filtering.

When the Mass Air Flow signal is being driven by the default airflow calculation which occurs during a MAF error condition, it will deviate from the unlimited airflow value and appear to be more digital in nature as a function of tps, rpm and IAC position as compared to the actual analog signal. Your log confirms this behavior. The unlimited airflow value is always zero, while the Mass Air Flow signal is displaying the result of the default airflow calculation. A few unrelated codes were also present.

Clear the codes first to start fresh and verify the Mass Air Flow signal with respect to the unlimited airflow signal with the system in an error free state, if possible. You should be receiving an updated bin to correct the Code 34 error thresholds asap, or you can edit them yourself as previously described.

Check MAF power, ground and signal wiring and be sure that the sensor is oriented properly with respect to the airflow.

Please follow up through normal channels.

JP86SS

iTrader: (1)

So is this another "pay tune" using the forums for answers?
No wonder nobody here shares ANYTHING anymore.
Good job!