Recurring P0102 even after replacing MAF

[Stefan]

My car is a 1999 Boxster 5-speed with 85k miles.

I replaced the air intake with an EVO high flow air intake. About 6-700 miles later my CEL came on. I checked the code and it was P0102 (MAF Sensor voltage low). I removed the MAF and carefully cleaned it with electrical contact cleaner. And I cleared the code.

The code came back almost immediately so I ordered and installed a new MAF. The new part is the identical part as the old one (Bosch Part # 0 280 217 007, Porsche Part # 996 606 123 00). The problem went away for several hundred miles then came back.

I checked the electrical connections to the MAF and they seem good. I cleaned them with electrical contact cleaner to be sure. I checked the signal voltage on pin 4 and it correctly reads 5V. I used a OBD-II reader and determined that the signal the ECU is seeing from the MAF is constant at 0.0 cu-ft/min or sometimes 0.1 cu-ft/min. It doesn't change when I step on the gas.

I checked for air leaks in the intake and couldn't find any.

I assume that there is some wiring problem.

Please, does someone have a strategy for tracking this problem down?

[Loren]

Put the stock intake back on - clear the code and see if it comes back.

My guess is that it won't - and you will want your money back from EVO.

I went through this 3 years ago and they could never make it work on my car with a CEL. I returned mine.

[Stefan]

Ok, fair enough.

I don't think I understand though how the EVO can cause that particular fault other than by damaging the MAF. Is this the same error code you saw?

Do you think that the MAF might be damaged and that I would have to replace it (again!?!?)

[Loren]

I doubt that the MAF is damaged - it wasn't in my case. The real test is to go back to the stock intake - clear the code and see if it comes back.

[Stefan]

Ok, I will try that.

It's too bad because I really liked the sound of the EVO intake, especially on full throttle.

(It's also a non-trivial amount of work to get the stock intake back in)

[Rom]

Hm, I'm also interested to know how the EVO intake is triggering the fault - especially as a real-time scan is showing no airflow! Sounds like a damaged MAF, or something else in the electrical path (unless the EVO is literally diverting air past the MAF). You could monitor the output of the MAF with a high impedence meter (or DSO if you have one) and rev the engine... If you see a logical change in voltage then the MAF is probably working fine but for some reason the ECU isn't seeing it... You could also test the voltage at the ECU and see if there is a corresponding voltage there too.

Not saying that you're mistaken Loren, just from an engineering point of view a mechanical airflow "tube" shouldn't really make an ECU behave like that... Also, the fact that replacing the other MAF made the problem go away for a while kinda points to another faulty MAF. Now, if the EVO is somehow damaging the MAF's, that's entirely logical...

Thanks!

Shash

[Stefan]

I'm not quite sure how to get directly at the output signal for the MAF because the wire doesn't have any exposed metal. I tried wiggling the wire and plug while the car was running thinking that the wire might be defective but the ECU didn't pick up a voltage change.

I suppose it is possible that the EVO makes the air flow in a strange pattern but then I would expect a lower voltage, not a 0 voltage.

What is a DSO?

[Rom]

DSO == Digital Storage Oscilloscope.

It would let you analyze the output in real-time far more accurately than a multimeter.

You would have to fabricate some kind of probe that could touch the contact while it was still connected. I have used light gauge flexible wire in the past (remove the connector, place the wire so that the bare wire is touching the contact, and gently push the connector back on).

If you are not confident about doing this, I suggest swapping everything back like Loren suggested, or taking the car to a dealer!

Thanks!

Shash

[Stefan]

I am quite confident about experimenting with this. I thought about using a light gauge wire. Ideally I should also check the impedance of the wire running from the MAF plug to the ECU to make sure there isn't a discontinuity.

I may even an oscilloscope lying around. I'll have to check. I don't have a lot of experience with oscilloscopes but it should be easy enough to learn. If you have any specific words of advice, I'm all ears.

[Rom]

Well, a DSO is easier (compared to a traditional CRT oscilloscope) as it can store your data for later analysis (so you don't need to analyse it in real time, and you don't need to have a second person helping you press the gas!).

Let us know how it goes...

Thanks!

Shash

Edited July 6, 2006 by Rom

[Stefan]

I connected a volt meter to pin 5 on the MAF while the car was running and the ECU was connected to the MAF. It measures 0.1 volts at idle and 0.2 volts when I hit the throttle (no matter how much throttle I give). I'm not sure what it should be but that doesn't sound right.

The OBD-II reader shows 0.0 lb/min (constant, even when on the gas) for the MAF sensor.

I tried my OBD-II reader on a 2003 and that reads 0.6 lb/min at idle and it goes up when you step on the gas. That is what I would expect.

So my guesses are:

(1) Some other wire connecting the ECU to the MAF is faulty. I have verified that pin 4 (the 5v input line) is correct. I don't know what the other pins are.

(2) EVO intake causes a strange airflow pattern that doesn't send air past the MAF

(3) Air leak somewhere downstream from the MAF

(4) EVO intake damaged the MAF

Any ideas at this point would be welcome. The MAF signal wire (pin 5) is a voltage, right (not resistance to ground)?

[Stefan]

Update:

I put the stock air filter and housing back in and cleared the code. The code came back.

I subscribed to AllData and tried their (probably really Porsche's) diagnostic tips. I

- Checked the resistance between MAF pin 5 and ECU pin 17

It was within spec (0.7 ohms, spec says 0-5 ohms)

- Check the continuity between ECU pin 15 and ground

It was within spec (Infinity ohms, spec says infinity ohms)

(Not in the list but seemed obvious)

- Checked the continuity between MAF pin 4 and ECU pin 47

It was continuous (0.2 ohms resistance)

-----

One thing that struck me as strange is that the MAF description says "The operating voltage range [of the MAF] is 9-17 volts"

Yet everything I have read says that the input voltage of the MAF is 5 volts, which is clearly not in the 9-17 volts range. And I measured the voltage to pin 4 as 5v.

Does anyone know whether there is some pin on the MAF plug that should be in the 9-17 volt range or if my previous assumption that pin 4 should be 5v is incorrect?

If that fails I may have to get _another_ MAF on the assumption that the EVO intake somehow messed up my MAF. If the inputs to the MAF are correct and the air intake is stock then I don't see how the problem could be anything but the MAF.

[Richard Hamilton]

Looks like there should be a supply voltage to Pin 2. Maybe this might help.

MAF_Circuit.pdf

[Stefan]

Good point. I will check that. Thank you.

[cr8on]

Good point. I will check that. Thank you.

Hey Stefan! Anything further on this? I'm curious to know if you found a faulty MAF, or if maybe the intake was "fouling" it somehow?

[986Jim]

I'm sorry but I have to say it. I just can not see how changing from a flat panel filter in a box to a round filter is going to make any difference. The rest of the car doens't know if it's the stock plastic tubing or aftermarket plastic tubing. It's just plastic tubing.

THe only difference is a flat filter in a box vs. a round filter is a housing with a shield (which is a box once the top is back on the motor...

Seriously, the intake is not causing the problem, something else is. It's not like your running an aftermarket intake manifold with sensors unpluged or something. It's a plastic tube with a round filter vs. a platic tube with a square filter... As long as the air entering the engine is going past the maf, the computer has no idea what the intake is made of, where it is place or how it works. You could make it from stainless steel, run it out the top of the engine like a mack truck smoke stack with a triangle filter on it and as long as the air is passing by the maf, it wont triger an CE light. Quite simply, automotive computers don't work that way. CHanging the filter and plastic tubing will not make the maf change what it is seeing. If the intake is leaking past the maf or something like that then yeah, you'll have a problem but otherwise, no not gonna happen.

Not to sound/act rude, however anybody who had a CE light, pulled off the intake and it went away, had another problem that was fixed during the changing of the intake. Either there was a leak in the intake getting past the maf, the intake was installed incorrectly or something else caused it. Pastic and filter material and shape do not cause faults in electrical equipment.

I have an EVO intake and got a CE light about 500miles after installing it. I pulled the maf it was really dirty, and not 500miles of driving dirty, like 6 years old dirty. I cleaned it and no problems since. No problems in rain, hot weather nothing, and my car is the same as yours.

Edited September 23, 2006 by 986Jim

[Stefan]

Your responses is not at all rude. I agree with your reasoning except that if a different air intake gave a non-uniform airflow, the amount of air going past the MAF could be different. In my case, I don't think that is the problem because the output voltage of the MAF is usually 0v, when it should be higher, even at idle.

Still I am at a lack to explain the problem. I put in a new MAF on a car with the proper voltage and grounding and no (detectable) leaks. Yet the output of the MAF is incorrect. I haven't yet checked the voltage on pin 2 and that is the remaining check. If that isn't getting the 12v then that would completely explain the problem.

There is a possibility that the first MAF was worn out and that the second is just defective. But it is a $300 experiment to see if that is the problem. I'm thinking of finding another pre-2000 Boxster to put my MAF into and see if the output voltage is correct. That would immediately tell me if there is some problem with my configureation.

Now, to find a pre-2000 Boxster in the Boston area with an owner who is willing to have me try my MAF in their car... :-)

[Stefan]

I just checked pin 2 and found that it is 12v (engine off) and 14v (engine running). So that is correct and a bad MAF is my only remaining explanation.

[986Jim]

Your responses is not at all rude. I agree with your reasoning except that if a different air intake gave a non-uniform airflow, the amount of air going past the MAF could be different. In my case, I don't think that is the problem because the output voltage of the MAF is usually 0v, when it should be higher, even at idle.

Air from the engine is pulled in through the intake in pulses. It's not a steady stream like one would think, the exhaust is the same way. This effect is demonstrated best on muscle cars with huge lift cams that burp at idle and you can see the exhaust puffin out the back in pulses... It will be pulled through the intake in exactly the same way from the evo vs. the stock. THe evo has a higher flowing filter, and less restrictive tube, but thats the only real difference, they are essentially the same.

Once the air is inside the intake tube it will act no differently than when the stock air box was on the car. As it flows past the maf the effect will be the same. The smoother the pipe the higher the velocity entering the engine. That would happen after the maf though as the stock rippled pipe is downstream from the maf where it would cause turbulance.

There is just no way that it would cause a CE light.

[GoodVibeGroove]

I've been through hell and back with this issue. Worked with EVO and two dealers one independent mechanic, and Bosh directly. Between them and myself and 5 new MAF sensors, we never proved but one thing for sure, anything but the stock FILTER and air box will work with out causing the MAF to fail. Now weather this be due to the air flow not hitting the sensor properly, which was my theory (remember it used a hot spot and the sir across it to cool it off and the temp difference is used to calculate airflow) thus not letting it cool down low enough causing it to overheat and "burn" out. Or the fact that the cotton filter let it get contaminated (this is what everybody else thought) was the case, the end result was always a new MAF. I also tried using the stock airbox and new stock Mann filter with just an aftermarket tube, thus leaving the stock MAF in it's original housing, and still killed a MAF. So...I think that pretty much confirms my theory. This has taken place over a span of two years, lots of work, 7 trips to different dealers, dozens of hour long phone calls and many tears.

[Stefan]

Wow, that sounds like a lot of pain. I'm getting ready to purchase my second replacement (third MAF overall). Were you able to determine that the MAF was actually bad? It would be a shame if the configuration somehow prevented the MAF from giving the correct signal but that the MAF would work fine in the correct configuration.

I'm still looking for another non-egas car to test my MAF in to verify that it is bad.

[tatios]

I am wondering if this saga ever came to a final conclusion. Did you convert back to stock? What was the final outcome a year and a half later.

Ed

Edited July 8, 2008 by tatios

[Stefan]

Yes, I converted back to stock and had no further MAF problems for many tens of thousands of miles.

But apparently I didn't learn my lesson because when I did a 3.4L engine swap, I put the EVO intake back in.

Lo and behold, I got the same P0102 error after a few hundred miles.

I purchased yet another MAF and put the stock 986 intake back in. Now more than 15k miles later, absolutely no MAF issues.

I am convinced that the problem was related to the EVO intake. Note that the MAF on the early Boxsters is much less robust than the newer (2000+ MY) ones which might explain why not everyone with EVO intakes has this problem.

[JeTexas]

I wonder what tests EVO did in determining the placement of the MAF on their intake. I'd hope some kind of science went into it, but I'd like to see what thought process/measurements/testing their developers used. I also wonder what would happen if you cut out the Porsche stock MAF receptacle and epoxied it into the EVO in place of the EVO receptacle.

[Stefan]

The EVO intake has the MAF in the same place as stock. The pipe is metal, not plastic but other than that they are largely the same. The difference as far as I can tell is that the stock intake has a mesh that I have heard is there to make the air flow patterns more regular.

The EVO intake air is probably more turbulent.