Bad MAF Sensor...ecu? Engine Died on Interstate--Need Help!

[JT95]

Hey all. I was on the interstate this morning, crusing at about 80 when my car just died with no warning or no weird noises or anything. I hadn't noticed anything blinking on the dash beforehand. Luckily, it happened right at an exit ramp, so I got pulled on there. The car would start, but then die after 5-10 seconds, or immediately if you gave it any gas. I checked all hoses. I removed the cover and made sure the timing belt was in place. Took the fuel hose off and made sure it was passing thru the fuel filter, as that is what it acted like--a starved engine. I unplugged the MAF sensor and the car started and ran okay. (Not perfectly, but good enough to drive.)

 

Now, driving with the MAF unplugged, the Check Engine light was obviously lit (not blinking), but the AT Oil Temp light was blinking. Neither was illuminated before dying and then unplugging the MAF. What in the world would be a connection between those two lights?

 

Do MAF sensors just go kaput like that with no warning? I let the car sit in the cold for 5 hrs, and the AT light still blinks as soon as I start the engine. The engine itself did not seem to happy to be running when cold w/o the sensor plugged in. Can the unplugged MAF sensor do something to make that AT light flicker? (Can moisture ruin a MAF sensor?)

 

Is it useless to have a diagnostic comp read the ecu because the sensor is unplugged and that is going to give that code, for that obvious reason. Does this sound like something replacing the MAF sensor will fix (for those who have had one go) or is something deeper awry here? Could it be an issue with my ECU? (Should a 99 and a 00 ecu from two different OBS cars be the same? I have a spare ecu if so.)

 

I really need the car to get around this week. I sure don't want to pay for a MAF sensor--damn those are expensive--if that doesn't fix the problem. Honestly, if it works, I don't care to shell out the Franklins for it.

 

Any assistance is greatly appreciated!

[98obster]

did you figured it out? did you try to plug the MAF back in with the engine cold? It would be nice to have a code with the sensor plugged in. the blinking AT light could be separate-check fluid? check AT wire harness connector under intake plenum? Actually, when you say it stalled when you gave it gas makes it sound like it's not getting air. chek the intake for blockage? check throttle body for anything loose/foreign/missing.

[heartless]

car specifics would be helpful....

 

year, model, engine, etc...

[idosubaru]

You need to rule out two things first: Vacuum leak and spark.

 

Get a spare spark plug and test for spark at each wire.

 

Vacuum leak sounds very plausible. A can of carb spray/cleaner sprayed all around the intake/engine bay will show a vacuum leak in less than 8 seconds. Give it a whirl. These engines will not start and will exhibit the issues you're experiencing with a vacuum leak.

 

Have you had any recent work done to the car?

 

MAF sensors aren't expensive and don't fail often enough to warrant buying new, so get a used one. A yard or someone on here will probably sell you one for $30 or something like that.

 

Do you use a K&N filter or other oil impregnated air filter? The oil can foul up the MAF which a cleaning will fix. Not likely since yours was such a dramatic failure, but worth a shot. Auto parts stores sell MAF specific cans of cleaner. Brake cleaner would likely be a good shot too.

 

MAF sensors have a visible failure sign too. I haven't checked out the new gen sensors since i've never seen one fail, but the older ones can be checked and I wouldn't be surprised if the new ones can as well. If you look inside of them (from the ends) you can see the hair thin wires going through the inside of the air flow. They are very fine so you'll need good lighting to see. If one strand is broke, this will cause the symptoms you're experiencing and tells you for sure the MAF is bad.

 

MAF sensors can also fail internally and show no visible signs. The FSM may have spec's on how to test yours, I can't recall.

 

Personally I wouldn't spend tons of time diagnosing the ECU and AT until I checked/replaced the MAF with a used one. With the sensor plugged in, try and read the engine codes. You are correct, reading it with the sensor unplugged probably won't tell you anything. You can clear the codes, then plug the MAF in and read them. This may show you something. But you're saying the CEL never came on, so it sounds like the ECU isn't telling you anything.

[JT95]

Sorry, the car is a 99 OBS, 2.2 engine, 84k miles

 

One of the first things I checked was the intake passage. With the throttle fully exposed the car still died a few moments after being started.

 

I didn't check spark plugs, but can't imagine that is an issue, as the car will idle and drive with the MAF sensor unplugged. It doesn't run great with the MAF unplugged, but it won't run at all with it plugged in. It just doesn't seem likely that a fouled MAF sensor would totally kill an engine, but I have no idea, as I've never dealt with the issue on a car before.

 

I had been running an aftermarket filter since July, and figured out that might be a cause to the problem. I'd never heard of that before putting it on my car or I would never have used an oil charged filter.

 

To run the diagnostic tool, does your car have to be running? I've only had that done a couple times at the parts store, and they always had me start the car. If the has to be running, then I can't have it tested with the MAF plugged in because the car will not run more than 5 or 10 seconds if the MAF is hooked up. I'll stop by the parts store after work and see.

 

The parts stores all have the MAF sensor replacement priced from $280-300. Subarus are hard to find in junkyards in my region, but I'll give it a try.

 

 

It takes a special torx bit to remove the sensor from the housing. Is it possible to clean the thing while it is still in the plastic tube?

 

Thanks so much.

[Gloyale]

More than likely, one of the small pcv hoses that hook into the intake tube. Either that or the tube itself is loose or cracked. If the MAF was *bad* it would throw a CEL for the momentary cranking and running it wil do.(you said it will run for a second or 2 with the MAF plugged in) The way you say it just died makes me think a hose popped off.

 

Check the intake tube for leaks.

 

And most code scanners can be used with the key in the on position. Good ones can scope it's output will running.

[Rich]

I had the same problem 3 weeks ago. Same symptoms - no codes thrown. It was the MAF sensor. I got another from the Junkyard and all is well now. One test I learned was that if you plug it in and start the car and it runs, tap on top of the MAF with the butt-end of a screwdriver, and if the car acts abnormal (surging, searching for idle speed, dies), then that proves the MAF is bad. The electronics can go fuzzy after a while. Check Pullapart.com and see if they will send you a MAF if there is no Pullapart in your area. MAF's sell for about $17. Good luck - its definitely the MAF.

 

Rich

[idosubaru]

i've seen failed MAF's not cause any check engine light, so it could still be that.

 

carb spray to narrow down a vaccuum leak would be wise before buying parts.

 

do not buy the $200+ parts from the auto parts store, that's ridiculous. get a used one. don't get hung up on finding one locally, there's a number of high market subaru areas, just order one from anywhere in the country. that's what i do, ends up being cheaper anyway because the cheaper prices more than make up for the shipping on small stuff like this. saves time too, no driving, waiting in line, waiting for them to pull it, etc.

 

i have a 98 OBS EJ22 MAF i could sell you, don't know if the MAF changed in 99 though, the engine did.

 

if you know huck, he's from sommerset KY and may have this part.

[Rich]

Hey JT95 - Whats the word on your solution?