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LC22E: FCB 3 ; 0.3 Second Dly prior to Burn off check, (sec * 10)
LC22F: FCB 6 ; 6 fails req for ERR #36
LC230: FCB 95 ; Fail Burnoff test if HLM A/D > 95
LC231: FCB 20 ; Fail Burnoff test if HLM A/D < 20
The above got cut off when I added to my original post.
Hardware is just a USB ALDL cable from Moates. Software is TunerproRT with my own adx file for logging/displaying data. Nothing special really.
Thanks for that, I have the Moates cable and used datamaster, but it seems I lose data when I turn the key off....
Perhaps I'll change to tunerproRT, to see if can see what the ECM sees..
Can you see what the ECM "sees" during burn off.?
Yes. See posts #64 and #79 in this thread, which show data still coming out of the ALDL port as burnoff occurs.
Cliff,
thanks, but that data (which was mine lol)...doesn't seem to show the maf burn off happening it just goes to 23 g/sec after approx 1 second (the 23 g/sec looking like its a correct number according to Cliffs table) but it seems to stay that number before the burn off takes place and doesn't change to anything else even when I can see the burn off happening.
Perhaps I'm looking at the wrong data stream?
Otherwise the maf #'s should've changed to "something else" as the wire glowed red etc??
Any suggestion what I should look at, log etc to see some change in maf values as burn off takes place?
I'll have another go this weekend....but not confident I'll see anything different unless I'm looking for/at something new.
Last edited by puzzigully; Aug 21, 2015 at 09:23 AM.
Looking at the data in post #79, it looks like you didn't log long enough. The time stamp shows the ignition voltage going to zero at 41:64. Burnoff should happen 5 seconds later at 46:64, but nothing appears in the log at that time. I don't understand that one. The ECM should finally shut off at 41:64 + 11.3, or about 52.xx, but the log stops before it gets to that point.
My recollection is that my log of the burnoff did show the MAF flow rate changing during the burnoff time. Also note that the fuel pump relay powers the MAF burnoff relay starting in 1986, so the fuel pump voltage should show that. I don't know how the MAF burnoff module gets powered in 1985 cars (probably also through the fuel pump relay, as a guess).
I'm in Pennsylvania right now so I don't have access to my home computer that has my data logs on it...
Here's a csv export of the log displayed in my previous post.
You can def see the burn off happening there!
the "23" is obviously the correct number....
Since logging the last data, ive had to get a new laptop.....
What a pain!!!
Lost Datamaster...
Kinda got it back on....then lost it again!!
Tried reinstalling Datamaster software = Fail!!
with new windows, cant allocate usb ports
Tried updating =fail!
Cant find the original files....
Damn frustrating!
thinking I'll go turnerpro RT, downloaded that, but whole new learning curve
Where do I get a "BIN" and a "XDF" to suit a 1987 corvette?
which shows the MAF goes to 23 g/sec after approx 1 second, then never changes...even after 10 seconds..
Did not log data all the way to ECM power off.
The FP volts also go to zero after 1 sec...
The Burn off DOES happen (I can see it)....can you help with what you think is going on based on this data?
Just so all info is in one place:
After ign off: wait 5 secs, then 1 second burn-off
(wait 0.3 from start of burn off, then take 6 readings at 0.1 secs interval - need to be between 0.4 and 1.9V)
ECM off after 11.3 secs from ign off
Here's a csv export of the log displayed in my previous post.
I noticed something strange in your data...
There's two columns....one with "MAF Raw" and the other with "Mass Air Flow"
From 794-795 secs:
MAF Raw was between 3-7, but Mass Air flow was between 4-8
From 795-799 secs:
MAF Raw was around 57, but Mass Air flow was approx 23
From 799-800 secs:
MAF Raw was between 30-38, but Mass Air flow was approx 23 I think this is where the burn off happened?
From 800-805 secs:
MAF Raw was approx 57, but Mas Air flow was approx 23
I'm a little confused as the the difference between the MAF Raw and Mass Air Flow? What is very confusing is why the MAF Raw number changes, but the Mas Air flow doesn't from 795-805 secs
Your MAF Air flow is the same as my MAF numbers - in that it doesn't change from the 23 after approx 1 sec after ign off.
BUT your MAF Raw DOES change - I need to find that in my data files somehow..
This is what I have been attempting to explain all along.
There are 2 maf signals present in the 8192 baud datastream.
The 8 bit unlimited airflow value or "MAF Raw Input" as labelled in this adx file is what you need to monitor in order to see the burnoff.
The 16 bit Mass airflow (control) signal is being limited by the max maf vs rpm table, so it displays 23 gm/sec at zero rpm whenever the MAF voltage is above approx. 1.46 volts.
Since the MAF sensor voltage during burnoff is typically above this (1.46 volt) value, as evidenced in the log showing 30-31 gm/sec, the unlimited airflow value is the better indicator of the MAF sensor output during the burnoff.
This is what I have been attempting to explain all along.
There are 2 maf signals present in the 8192 baud datastream.
The 8 bit unlimited airflow value or "MAF Raw Input" as labelled in this adx file is what you need to monitor in order to see the burnoff.
The 16 bit Mass airflow (control) signal is being limited by the max maf vs rpm table, so it displays 23 gm/sec at zero rpm whenever the MAF voltage is above approx. 1.46 volts.
Since the MAF sensor voltage during burnoff is typically above this (1.46 volt) value, as evidenced in the log showing 30-31 gm/sec, the unlimited airflow value is the better indicator of the MAF sensor output during the burnoff.
Thanks,
i'm pretty new to this and the terminology, so thanks for your patience!
Prior to your reply, I was tyrying to "dig out" the 8 bit values from the data I have using Datamaster, but I don't seem to be able to find a parameter that matches it..
I may be able to post the original data, if that will help?
Cliff posted a table that referenced volts to g/sec.... and it was approx 1.46 volts to equal 23 g/sec.
BUT am I correct in assuming that at 0 rpm, the maximum the maf can show is 23? (from its max maf vs rpm table)?
Sorry for the size, but on the Datamaster screen, right hand side half way up is a cell "Burn Active".
This is just before I turn the engine off....note that the "Burn Active" is
green, which means, not active.
Then after ign off, "Burn Active" is yellow, which means ON.
This where there may be a hint of some sort...."Burn Active" is yellow (ON) all the way until the ECM turns off.
This maybe what the "experts" were saying...that the ECM doesn't see the end of the burn off?
Another interesting observation is that the cell "Burn test" never turns yellow (or goes ON)
I haven't been following this thread, just came across it today , but I went through 3 rebuilt maf sensors and never did get one that worked properly..The rebuilt mafs are complete junk, one of them wouldn't even allow my car to start....I ended up going to " Blowerworks" and installing one of there maf sensors into my 89, best move I ever made..There maf sensors don't even use a burn off system, I just clean it once a year with maf sensor cleaner..Tequilaboy is the one who told me about the Blowerworks maf sensor and he helped me through the installation process...Gregg Carol is the owner of Blowerworks, he was very happy to explain everything to me , go to their website and check them out.........WW
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But not sure how a MAF without burn off would fix the code 36 problem? (Burn off fail)
Car runs absolutely fine with existing MAF.
I'll talk to blower works, thanks for the recommendation.
My car ran fine with a few of the rebuilt maf units also, but when I looked at Datamaster I saw they were throwing my (air/fuel ) ratio way off from normal...The problem with the rebuilt maf sensors is that they don't recalibrate them after the rebuild , so they're not back to spec which throws off your tune...With my Blowerworks maf unit they eliminated the burn off sequence and the burn off code from the chip..My 383 motor is now running a "maf stick" from a Ford Mustang which is a much better maf system then the Corvette maf sensor...Below is my thread ( with pictures) on the Blowerworks maf unit...WW
The trick here is to determine what voltage the ecm is seeing during the burnoff to better understand why it is failing.
What we do know is that the MAF voltage is greater than 1.46 volts since the signal is being limited to 23 gm/sec by the max maf vs rpm table in the log data.
We also know that a voltage greater than 95 A/D counts will set the code 36 failure. Since 95 A/D counts is approx. 1.9 volts, we can safely assume that your MAF voltage during burnoff is exceeding 1.9 volts.
Now if you would log the same event using TunerPro with an appropriate adx file and monitor the unlimited airflow signal during the burnoff and relate the value back to the appropriate MAF flow vs voltage table (likely the #2 MAF table), we could indirectly estimate the MAF voltage during burn off.
Once the actual voltage is known, we could then adjust the upper limit (95 A/D) threshold accordingly in the bin to avoid setting the code. I would only consider this in the event that the voltage is exceeding the expected 1.9 volts by a small margin.
This method does not address why the voltage is greater than what is expected, but it will avoid setting the dtc assuming that the behavior is repeatable for your specific hardware.
The Blowerworks MAF will also work since the burnoff delay, burnoff time and code 36 are all disabled in the programming and the MAF itself does not physically support the burnoff signal.
....WW