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Assistance with troubleshooting MAF

1652 Views 41 Replies 6 Participants Last post by  PeterDuerr
Hey guys,

I have an issue with my mass airflow sensor. I have just received my tunercat cable and I'm reading data via $eehack (thanks for the tip @Marky Dissod)

I have also received my PCM back from a mail in tune.

My mass air flow reads 0.00g/s. I do have 12v and ground at the connector. I couldn't check the signal wire. (Its plugged in).

I have trouble codes/ CEL : "MALF 43c active" and ERR43(esc failure). I'm assuming this is the same as DTC 43 (knock sensor)?

Why am I reading nothing on the MAF but not getting DTC 48? Is this part of the tune?
The knock retard is at 0 deg. And a think im not receiving knocks.

Also oil temp is all red failled low.

Is this as simple as needing a new MAF sensor?
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Oil temp pic attached
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The easy one first. B-body cars do not have PCM oil temperature sensors. That is a Corvette thing.

As to the MAF you really need to do some diagnostics. If you back probe the MAF signal at the MAF plug you may find voltage which means you have a wiring problem.

You really need a meter with frequency measurement or a oscilloscope to check the MAF sensor output. Parts swapping is expensive if the part was good and the wiring was bad.

You could unplug the PCM and check the wire between the MAF and the PCM.
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It could be a bad tune.

Did you have drivability problems with the old tune?

Have you flashed the "old tune" back in to check if Eehack shows MAF reading with the old one?
Ok, thanks. Oil temp ignored. I do have access to occiliscopes or fluke meter with frequency reading.
Wouldn't the DTC 48 chime in if it was MAF?

I had a rock auto order lined up already. A budjet MAF was $60 after shipping. I may have droped the air box with MAF if I do recall.
I sent it to a reputable tunner, they have an free 60 day adjustment policy. I will contact them after I confirm a few things. I don't want to blame them right off the hop.

I didn't have laptop capabilities untill after I received the PCM back. So I do not have original tune.. hindsight is 20/20....
It would be worth the back probing of the MAF plug to at least check for voltage.

Rock Auto only does what they call "customer service" by email. I do not buy anything from them I can not afford to loose the full cost on.

Ask the "reputable tunner" for a free stock tune so you can check something. There are also online sites with stock tunes or someone may have one for you.

I have returned parts and they pay for shipping, but it has to be with 30 days and probly a few more requirements.
I will ask for the stock tune, good idea. Thats a good start for troubleshooting.

I did have an CEL but i couldn't check. I assumed it was because of the AIRpump delete.
I will ask for the stock tune, good idea. Thats a good start for troubleshooting.
No tuner wants to work with a car with preexisting problems.

Get permission before you swap any tune.

The reason you need to do physical measurements is you have to locate the source of the issue.
Could be a MAF, connector, wiring, bad PCM, or a real odd programming problem.

RE: RA Things can get more problematic when they send the wrong part in the right box or a old dead part in a new box because they do not check returned boxes. I like their prices but buy with caution. When a order comes in I check every parts box and bag for the correct part and the little accessory parts bags that come with some parts. I also double check with another vendor to confirm the RA part is the correct part number. Do not get me wrong they can be cheaper than the local "wholesale" account a friend lets me use.
Agreed, I have had flat out wrong parts shipped. There is more risk with rock auto.

Do you know what kind of reading i should get? Frequency, voltage peak. If I were to receive any voltage signal, I would think that would give something better than zero on the laptop reading.

On another note, I'm definatly not understanding the mis-match if error codes. There is something I'm missing here.
Do you know what kind of reading i should get? Frequency, voltage peak.
Read the link in post #7 even if you will not go to the link.

If I were to receive any voltage signal, I would think that would give something better than zero on the laptop reading.
That is why Eehack can not tell you what part of the system has failed.
Think of a sensor for the PCM as a chain. The PCM can not know which link is broken, or if the PCM is damaged.

You could fire the parts cannon and get lucky with a new MAF being the problem, but if the car is new to you and you have not driven it much on the road I would suggest diagnostics not parts.

This is a example of back probing. In this picture the TPS.

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Ok, i'll read up on that post. "Parts pistol" will get a few shots.
Car is new to me and I will have to learn all the in's and out's.
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Ok, I was able to measure frequency and voltage off the yellow wire at the sensor.

With the meter on frequency, I had 3.3khz at idle and increases at higher RPM.

I then put the meter in min/max DC and measured 4.2vdc and it went down as increased RPM's.

FSM shows B19 on the PCM. I can't find how to determine what connector/pin that would be.

I'm thinking this sensor is fine...
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PCM pinouts and connector ID: 4th Gen LT1 F-body Tech Articles (shbox.com)
Thanks,

I have confirmed continuity on the wire to the PCM. I'll contact the PCM tunner.
One thing you could do is download TunerPro and the $EE XDF and see if speed density is enabled. It's been awhile since I've played with speed density mode, but it's a possibility if the MAF is feeding the PCM but the PCM isn't reporting. I'm not sure what the PCM does if it's in SD mode but the MAF is active, if eehack will report MAF data or not.
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Ok, thanks. Thats quite a bit out side of my comfort level at this point. We'll see what the pcm tuner comes back with.
Great that you looked at the MAF sensor circuit. In a pinch I would have been happy to see the slight voltage change on the sensor output, but the frequency check suggests that the PCM should be showing something other than 0g/s.

As a non expert with engine tuning I have suggestions/questions.

g/s is a calculated value. My point is that a bad table in the tune will result in bad or no calculations which would explain what Eehack is showing you.

The FSM suggests that the OBD1 PCM only will output the calculated g/s so the frequency is not available.

If things start pointing towards the PCM being bad take the extra time to double check that the MAF sensor signal at the PCM.

With all PCM connectors unplugged you can verify that the MAF sensor voltage is on the PCM pin with key on.
The definitive check would be to back probe at the PCM and view the waveform on a scope.

I do not want to get into details but under some weird conditions checking "continuity" may give a false result.

The forum can at times save you a lot of time by other's experience pointing to a specific test. Suggestions of swapping parts without testing can be detrimental in some cases.
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Thanks, I do have a set of FSM manuals. I could not find a similar diagram to what sherloc9c1 posted. I will print that out and keep it in the FSM.

The programmer responded, all is fine with the MAF reading, it has to do with speed density that sherloc9c1 mentioned. And also why no MAF code was coming in. So ill be returning the MAF(-$30) I ordered. Stimulating the courier industry.

I will troubleshoot the knock sensor circuit this weekend. I'm sure its a bad connection/sensor.

Usually I would prefer to work on one thing at a time, then move to the next. But the way it went with this was "its easier to do it all while its apart". So I replaced and changed many things, which makes toubleshooting more challenging.

My digital dash also started to cut out on top of it all which added to the confusion. My current speculation is that with the call for both fans to run because of the MIL code, it creats a high current draw which somehow cuts out the dash. But thats another issue thats TBD or will be a mystery forever.
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Thanks, I do have a set of FSM manuals. I could not find a similar diagram to what sherloc9c1 posted. I will print that out and keep it in the FSM.
I always try to use copies when working on the car. At worst I take a picture of the FSM then print it.

The diagrams are available in both drivability and emissions and in electrical diagnosis. 94 FSM 6E-A13 or 8A-20-10.

The programmer responded, all is fine with the MAF reading, it has to do with speed density that sherloc9c1 mentioned. And also why no MAF code was coming in.
Maybe I am not understanding you.

Did you make a special request for a tune that ignores the MAF?

If the tune ignores the MAF it works off tables and the PCM will not be able to make fine tuning calculations.

It is my understanding that the MAF is the only way a PCM can know and correct for the different densities of air due to the change of humidity in the air.
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