sancho

I pulled my car out for the first time after a very long rebuild today, and I noticed that the Service Engine Soon light came on. I had a code scanner put on it, and it said that the MAF sensor was bad.

I'm just curious: what would be the consequences of driving around with a bad MAF sensor?

I'm a tapped-out high-school student, and I don't have the money for a new MAF sensor ($145.00) right now...

Thanks

rezinn

It told you the MAF was bad? Wow! That's pretty impressive. All I get is a flashing bulb.

There are only a few ways to tell if the MAF is bad. You can either take voltage readings from it and compare to what they should be, watch for bad readings using a computer, or see that it's physically broken.

If you got a MAF code, the problem could very well be remedied by cleaning the sensor and replacing the MAF relays.

If you have a bad MAF, you may face difficult starting, bad gas mileage, and stalling.

sancho

Thanks for the reply, rezinn!

I was actually told by my mechanic that it was bad. I took my car in because I saw that it flashed the SES light when I was driving, he put his scanner on it, and he told me that it was the MAF sensor. He's got one of those expensive portable scanners, too--he wasn't just reading Moorse code off of the SES light.

As far as seeing if the MAF was actually bad, my mechanic said that if tapping on the MAF sensor casing makes the idle fluctuate, then it's a bad MAF. He tapped it a few times with the handle of a breakover bar, and I didn't notice any changes direcly from him tapping it.

I would like to know about the other ways of testing it. I have some experience from doing this on my V6 car (i.e. changing the MAF burnoff relay), but I don't know where the relay is located on this car, and this MAF sensor has more leads comming out of it than on my V6 car. What leads specifically do I need to test, and where can I find tables with normal values? Is it true that disconnecting the MAF sensor with the battery still connected will ruin the sensor? Also, how could I go about cleaning the sensor?

Thanks

rezinn

Unless he told you the sensor was bad while the car was running, he was just guessing.

The relays should be on the drivers side firewall, near the fuel pump relay(they're all the same, the two MAF and the fuel pump relay). As far as testing it, I really can't tell you what the voltage scale should be. Perhaps you could find out on the DIY board or elsewhere. Taking readings while the car is running would allow you to monitor the flow rate in grams/sec, and you would be able to tell, based on how many grams/sec in relation to rpm, if the sensor is reading accurately.

If the MAF burnoff relay is failing, the hot wire inside the sensor could become too dirty and cause the sensor to not read correctly or malfunction. You can remove it and clean it with some throttle body cleaner or something similar. Something that will not leave much residue and that wont harm electronics. If the burnoff relay is bad, though, you may need to clean the sensor to get the car to start sometimes. This was the case for me, once.

The sensor will be fine if you disconnect it with the battery connected or with the car running. The car should run worse with the sensor disconnected. Relays are cheaper than a new sensor, so it's always good to try those first.

You can check the code using a paper clip with the ignition on. Count the flashing lights, code 12 or one flash, a pause, then two flashes, is normal. Just do like this picture illustrates:

DH1987TA

One thing to consider, make sure the mechanic isn't a
"code popper"...someone who hooks up a scan tool, pulls codes and says "it's setting a MAF code, it need a MAF" or it's setting an oxygen sensor code, it needs an oxygen sensor"...this is the what differentiates a "mechanic" from a "technician".

Truth is, a diagnostic trouble code only tells you which sensor or circuit is having the problem,whether you have a $3,000 scan tool, or if you simply jump across the ALDL.Although the high dollar scan tool will ASSIST in diagnosing the problem, it alone won't diagnose the problem (if anyone finds a scanner that DOES diagnose the problem, let me know,I will pay any amount of money for it!!)My T/A was setting a MAF code, but only took a $9.00 MAF power relay to fix it...not to say your MAF isn't bad, but just questioning whether the mechanic is diagnosing the problem, or just reading codes.

sancho

Thanks for the replies.

rezinn: For the record, he did check the computer while the car was running. I didn't actually look at it when he did it--I don't know if that computer just says explicitly that there's something up with the MAF sensor or if he got real-time readings of the values from the MAF sensor and decided they were bad.

But, nonetheless, I just checked the codes myself by shorting pins 5 and 6 on the ALDL. I pulled the following two codes:

-- Code 34: Low voltage (high vacuum) at mass air flow sensor (or MAP sensor)
-- Code 42: Fault at electronic spark timing circuit, Fault at direct ignition system, OR Fault at fuel cutoff relay circuit

I referenced the ThirdGen.Org FAQ to get descriptions of what each code meant.

I didn't expect to pull anything but a code 34 and, based on the descriptions, it doesn't look like one code has anything to do with the other. Agree/Disagree? I'm actually starting to wonder which problem is causing the SES light to come on when I'm driving...

I'm in sort-of a unique position in that I don't really have any "reference" to compare the performance of my car to; I only noticed these codes now because I just finished up an engine rebuild. In other words, I can't really say that "the car is acting funny" or "it isn't performing like it used to" because this is really the first time that I've driven this car. I was test driving it today, and while it was running, it didn't seem to have any noticible problems.

What I will say, though, is that this car is a little bit difficult to start sometimes. Usually it takes about one or two times of cranking, then on the last time it will start right up. Also, I can tell that the computer is playing with the idle speed sometimes because the idle fluctuates every now-and-then.

I am definitely all-for saving $145.00 on a MAF sensor if I don't need one. I don't know if this new information helps to narrow-down anything, but let me know if it does. In the mean-time, I will try the suggestion about the relay (if I can figure-out which one exactly it is). Also, I'll see about cleaning the MAF sensor itself (although I'm a little-bit timid about that--seems like the film would be very delicate).

Thanks again.

BTW -- If that code 42 is another issue, let me know so that I can start another thread for that (or do a search ).

sancho

I just read this post where Vader says that the code 42 could be a result of the EST connector being disconnected. I know for sure that it wasn't disconnected when I checked my codes, but I did have it disconnected for a little while today just to check the base timing.

Could that be the reason for my code 42, in which case I don't need to worry about it?

8Mike9

Yes, code 42 will set when disconnectiong the EST bypass connector. IIRC, it takes 50 startup to clear a code from ECM memory.

Unhook the batter cable, clear the codes, see if any return, then concentrate on those codes.

Before replacing the MAF, I'd:


Check connector on underside of MAF, make sure wiring is good, no female pins opened up, etc
Trouble shoot the relays/wiring.
If no schematic, then I'd replace them (about 10 bucks each)
Then monitor for MAF codes.

And still before I replaced the MAF, I'd beg to borrow one from someone who has a known good MAF, to see if it's really the problem.

Vader

Sancho,

Your mechanic may be right, or maybe not. If he/she was reading the MAF signal from the ALDL, that is only what the ECM is reading from the MAF, not necessarily what teh MAF is reproting. The connections between the MAF and ECM are critical in getting the correct signal/data. Those connections involve the connector at the MAF, the connectors at the ECM, grounds, and the MAF power relay. You should check the power and signal directly at the MAF for a certain diagnosis. Your mechanic apparently didn't take any of that into consideration, or just presumed the 15-year old connections were still relaible. I wouldn't, especially if it involved a $160.00 part replacement without a complete diagnosis.

Check this thread for a little more detail:

https://www.thirdgen.org/techbb2/sho...hreadid=166493

sancho

Man, I post here so much that I sometimes forget that I have a manual.

I just referenced my Haynes book, and according to it the following should be my MAF relays:

-- MAF sensor burn-off relay (Labeled "A")
-- MAF sensor power relay (Labeled "C")

I am assuming that my relays are in the stock positions, for the most part, so hopefully that should be correct (although, without the manual, I would have thought that B and C were both MAF relays because they're the same).

Now, I can't really understand what would have made the previous owner have so much distain for wiring harnesses, but he obvously must have done some venting on the connections for relay "A" (you're looking at some non-insulated wires, BTW). I just disconnected it, and there's some sort of grease all over the connectors (for whatever reason). I'll definately be checking those relays.

The only way that I can think to test the relays, though, is simply to put a multimeter between the common and either of the NO or NC poles, and then to apply a current to the coil. If my multimeter gets a closed or open circuit after powering the coil, I'll know weather the relay is good or not based on which pole I'm connected to. I don't know if that's sufficient to proove a relay is "bad" or not, though... Should I instead be checking for currents at the wires with the relay connected and the car running?

I'll definately be checking those relays, and if they test out good, I'll come back see about checking the MAF sensor directly. If they test out bad, then hopefully I just saved myself some money...

Thanks again

DH1987TA

To check the relays, you need to follow a wiring diagram. There should be 4 wires to each relay. Maybe five, but follow the diagram. The wires you are concerned with are the wires for the relay field, power in, and power out to the component. You will need to apply power and ground to the relay field (closing the relay) and then measure resistance across these terminals:
the fused power terminal
the terminal that goes to the MAF

With the relay closed, resistance across these two terminals should be less than 1 ohm (though I personally like to see less than 1/2 ohm). If resistance is too high, MAF will not get full power (even though it may show 12 volts, once the component pulls an electrical load, voltage will drop). Based on the saying of "garbage in, garbage out", if the MAF is not getting a full 12 volts, it cannott send a correct siganl to the ECM, and out pops a trouble code (MAF voltage low).

firebirdchick24

i had a bad MAFS and got a new one for $80 from a company online i didnt install it for a month because of the cold weather but if you have a bad MAFS give your car time to warm up before driving it...warm it up all the way or it will drive funny, and it could possibly stall all of an sudden on ya (that sucks ***). but if you want any info on it IM me or email me anytime

87z28camaro

i have a bad maf sensor, but im buyin one on here, and i didnt notice any problems when the code 34 i think came up, it wasnt till later i noticed problems, it started flooding, blowin black smoke, which is unburnt gas because its flooding so bad, loss of power, so you do need a maf sensor immediately, also, just wait, your gasmileage will get so bad you cant keep gas in your car,

Vader

Sancho,

The grease ing the electrical connectors to the relays is there to dispel moisture and prevent corrosion. Either leave it there, or clean it out and apply fresh silicone grease to the connectors.

The relay you have labelled "A" should not just be lying there:



If you question which relays are which, you can follow the wire color coding:

89' RS/blue

The MAF can be a very troublesome sensor sometimes. and driving with the connector disconnected wont hurt anything. Also i don't know where you're getting ur MAF's but $145 sounds like someone is ripping you off. Got to kragen and they have them for like $75. Also Smothers auto parts has them for like $105. I'm just saying if u do have to replace the MAF shop around for the best price first, dont get ripped off.

87z28camaro

his price his right, 145 sounds good, cause at autozone, they can order them, and they cost 170, so...

sancho

Well, I changed plans a little bit... I decided to just go with Vader's suggestion and check the sensor directly. I got some 24 gague telephone wire, inserted it into the female plug holes (terminals A and C), and reconnected the plug to the sensor with the telephone wire sticking out. I hooked up a digital meter to the other ends of the wires, and at a ~800 RPM idle, it said that it was reading 30.1 mV. I opened up the throttle a little bit and, looking at the meter, I noticed that the voltage didn't change at all.

Based on Vader's pictures of this test, I think that pretty-much tells me that it's the sensor. Plus, that would be in line with what the computer is reporting (i.e. low voltage). At least that saves me the trouble of fooling around with the wiring...

----------------------------------------------------------------------------------

I just had a thought about why the MAF sensor might have gone bad. When I started this engine for the first time (after dropping the engine in for the second time), it would backfire through the intake very frequently when in gear. I can remember seeing a video somewhere on this site of a TPI car backfiring through the intake with the intake snorkel off--shot out a big flame that was more than a foot long. If that's what was going on inside the intake snorkel when it was backfiring, would that have fried the components of the sensor?

sancho

BTW... for those of you who think that I'm getting ripped-off because of the price. My guess is that you guys are thinking of a MAF sensor for a V6 car. I've had to replace the MAF sensor on my '88 Camaro before, and it cost about $65.00. The one for V8 cars, however, is more expensive (also has more wires comming out of it--5 as opposed to 3).