Mass Air Flow Sensor (MAF) going bad, again.

A few months ago when I got new tires I had the shop check and see why my service engine soon light was coming on. He said it was the MAF sensor. I had replaced it about 2 years ago when the same thing was happening. I replaced it with a NAPA rebuilt unit barely a month ago. It is back on again, and doing what it did before-runs fine, stumbles for a few seconds like it will stall, or has bad gas, and then recovers. The light has been on a week now, and later today I'm borrowing my brother's OBD II tester. If the meter shows again that it is what's faulty, is there some event that would cause it to go bad? I've checked, and rechecked, to make sure all connections are tight. The air cleaner element is new. If NAPA hassles me on the return of the part (who knows, I'll see later today) I am at my wits end. This has been a recurring problem since I bought the car. I may have to give up and go to the dealer, which I sure don't want to do, for further testing if I can't resolve this myself.

A recurring sensor (of any kind) problem which reoccurs after part replacement, points to wiring (ground, connectors, etc.) or to the PCM. You have checked the wiring path thoroughly. The PCM could have a bad input channel, or the reference voltage supplied could be fluctuating. PCM's are pretty good at detecting an internal fault by themselves, but they are not foolproof.  Multiple failures of the same factory part, especially ones certified for emission control, are rare.

Pardon my ignorance, but what part is the PCM? On my way to my brother's house today the light went off, after being on for a solid week, with a combination of city and a 150 mile highway trip. The tester again pointed to the MAF sensor. I can live with the occasional erratic behavior, but it is mostly my wife's car, and she is getting sick of the light, and the occasional weird chugging/almost stalling stuff that it does when the light is on.

Ok, just got back home after a 300 mile or so trip this weekend. The sensor went on again about 20 miles into the trip (on the highway) and stayed on, and is still on. Atlantadan, where is the PCM? Does anyone think the dealer would have a more sophisticated tester than a generic OBD II tester like the one my brother paid $100 for a few years ago? Does the dealer tester tell more than my brothers, which basically just said MAF sensor? This is getting frustrating!!!

""Does anyone think the dealer would have a more sophisticated tester than a generic OBD II""

Absolutely. The dealer has a bi-directional device that can drive outputs and simulate inputs, which most simple after market code readers cannot do.

we bought two mafs from napa,. for our 4.6 ford motor,. first one lasted a month,.it was a rebuilt/refurbished,. the second one has lasted a year now,.

You might try cleaning the maf first,..

Rev Bob wrote:

""Does anyone think the dealer would have a more sophisticated tester than a generic OBD II""

Absolutely. The dealer has a bi-directional device that can drive outputs and simulate inputs, which most simple after market code readers cannot do.

Would a place like Good Year probably have the device like you mentioned? I usually go there for service I can't do myself.

Some Goodyears are better equipped than others. None have the "Magic Phone Number" the dealer has to contact someone if they get stumped or come across something unusual.

A 20 year old Roadmaster might fall in the "unusual" category.

Mark 96 Roady wrote:

I usually go there for service I can't do myself.

You might try cleaning the maf first,..it's a simple job,..

NAPA gave me zero problem returning the unit I bought last month. When I took it out of the car it looked still brand new, with no visible broken wires or other problems. Maybe some internal problem? The light is off now, so let's hope that fixes the problem.

Light is still off, and that's important at least for today since I moved from PA to Ohio, and they do an e-check. I just had it done, and it passed.

Well it's back on again. I'm thinking at this point the chance of 2 MAF units failing is near zero. This one lasted 2 days until the light came back on. What is frustrating is that the problem presents the same way each time. The new part is put in, and for a few days the car runs perfectly. Then, like what happened yesterday, I noticed a slight loss of power upon acceleration. When I push the pedal a little harder (say to go up a grade) the car stumbles a bit, rattles for a few seconds like it has bad gas, then the light comes on. Then, the weird part; immediately after the episode the car runs fine again, with the light on! The light went out briefly yesterday, and came on an hour later. Today we came back from a weekend trip (about 300 miles) and it was on the whole way, and is still on. To recap-southern no rust car, tight air cleaner and hose connection, new filter element, tight undamaged connection to the MAF. I may need to say uncle and go to the dealer.

Did you try wiggling the connector to check for internal continuity? Do an ohm check on the wires, and wiggle all wires at connectors.

The dealer may be able to put "tap" connectors between the wiring and sensor to verify the output of the sensor. You may be able to make a tap as well, if you want to do it yourself.

Fred Kiehl wrote:

Did you try wiggling the connector to check for internal continuity? Do an ohm check on the wires, and wiggle all wires at connectors.

The dealer may be able to put "tap" connectors between the wiring and sensor to verify the output of the sensor. You may be able to make a tap as well, if you want to do it yourself.

My brother is pretty sharp at electrical stuff-not me. I'll mention this to him and see if he can help. Thanks Fred.

I stopped at the local Buick dealer today to see about the problem, and i think I'm going to let them take a look at it. For $95 they will do an hour of electrical diagnosis. If they find the problem, and I let them fix it, the $95 is applied to the job. A factory MAF sensor is almost $300 vs. the $100 or so from NAPA. The parts guy was very upfront with me. He said they use aftermarket parts to save their customers money, but some parts (like the MAF) are problematic. We're leaving for Florida in about 3 weeks, and I want to get to the bottom of this before a 1200 mile trip. My appointment is next Wednesday, so I'll let you guys know what happens.

A lot of us on here probably have 2-5 OEM B-car MAF sensors sitting around. I'm pretty sure I left all mine back in BC but I can check. I'm sure people here can get you one for uner $50. If no one here has one, ISSF probably has dozens of folks that replaced their maf with an F-car maf.

How does the car run when you unplug the MAF ?

It is extremely unlikely the PCM itself is faulty. Also, statistically not super likely you've had that many MAFs go bad, but I have had NAPA mafs go bad on the T-type before.

Personally I would take the following steps:
0) Yes step zero. ALWAYS scan and post your DTC before attempting anything. This will allow you to follow the flowchart in the 96 FSM.
1) check to see how car runs with no maf
2) obtain an OEM MAF (not necessarily a new maf)
3) obtain PCM pinout form 96 FSM (I don't have the 96, but someone here should have it)
4) remove PCM and clean the 4 sets of contacts with contact clearner. I would also check and clean the MAF harness terminal. I would also check the MAF harness AND PCM harness for yawning terminals. Pay special attention to the MAF terminal at the PCM.

If you have a kinked wire in the MAF harness then the PCM will have an erroneous reading. I have had to run new wires from the PCM to an 02 sensor for this reason. It's not difficult.

I got the car back today with some interesting results. As I stated earlier, I gave up and took the car to a local Buick dealer. They did a diagnosis, and sure enough, still showed the MAF sensor acting up. The mechanic I worked with is probably in his 50's, and remembered working on the Roady's when they were new. His idea was for me to get a GM part for several reasons. First, obviously, the re built part could be bad. Secondly, he said over the years they have experienced problems with re build 02 and MAF sensors. By putting in the factory part, if it threw a code again they at least knew the GM part would be good. He said many things could cause the OBD 11 to put out a code for the sensor- a clogged cat converter, vacuum leaks at the intake manifold, and many more things. So with the new sensor on, I went for a 40 drive today. First, no light! Secondly, it idles very smoothly now, not that it was bad before, but it is better. And, I swear it has more power. Of course the bucking and stumbling are not happening. We are leaving tomorrow for a 300 mile trip, so I will report back in a few days once we get home. Hopefully problem solved!!

Well, it came back on again. But the weird chugging episodes were much shorter, the car ran better, and the light stayed on for shorter periods of time. Today, however, I discovered something that may, or may not, help figure this problem out. The car is now in the shop getting the body damage fixed from when the tree branches fell on it last month. The shop took off the front cover today, and several of the lines to the vacuum canister had dry rotted, and were no longer connected. Is this the culprit? I don't know, but the shop is certainly replacing the damaged lines, and will clear the codes once the repair is done. Car will be done end of this week, or beginning of next week, so I guess we'll see.