MAF dead spot?

Crazy_pilot · #1 08-12-2008, 10:41 PM

Does anyone know if it's possible for the MAF to develop a dead spot? A certain air flow it has trouble reading? And not throw a code.

My car is almost perfect mechanically, but it has a really annoying trait that murders it's driveability in terms of nice-ness. Between 1200 and 2000 RPM, when pulling away in first, the engine puts out almost no power. It's like it starts to move, and then someone attached a 10,000 lb trailer to me. It's not revving, it just won't accelerate, it falls flat on it's face. Some days it's really bad, it will do this up to 2500 RPM. If I hit the gas a little harder it'll jump up past 2K and go just fine, but then I always have the car jumping away from stops instead of pulling away smoothly. It's just damn annoying.

The only codes I've seen are intermittent for the O2's, and even after clearing codes this happens instantly. Every so often it won't act up at all, and when that happens it feels like someone gave me a new car.

From my end it feels like the engine isn't getting fuel at those RPM's. When it gets into that spot where it's not making power, if I gently push the pedal I get no acceleration, but a different exhaust noise, like the engine is labouring.

Any thoughts?

Mensaf · #2 08-12-2008, 11:10 PM

I'd say o2 sensor or the MAF itself. Sounds like it's getting some unmetered air and running either pig rich or really lean from idle to 2000rpm (my guess would be rich, but I'm not there to look @ it) or whatever it is you see. Are you using factory O2 sensors?

kwren · #3 08-12-2008, 11:29 PM

I do have some thoughts on the matter but am unable to state them on this web site for several reasons, not the least is that upbringing from my mother.

I have been having the same problem as you described with the same things happening... Same exact thing.

I have 2 MAFs and it runs the same with either. I have replaced the 02's twice and still does the same thing.

A while back someone said they had the bosch bypass relay starter thing on their car and it ran "like crap"... took it off and that cured it. Do you have the bypass starter relay on your car?

I have done a bunch of stuff and it always comes back to the same thing. I am about at my wits end.

I would replace the engine but I am afraid that if I did, that wouldn't even fix it. Too many other things to consider besides the engine.

Any ideas...anyone?

Keith

kwren · #4 08-12-2008, 11:31 PM

I think it is too rich because when it runs the worse, the gas mileage is atrocious. If it runs better, mileage is better... a clue??

Keith

Crazy_pilot · #5 08-13-2008, 12:07 AM

Quote:

Originally Posted by Omar

I'd say o2 sensor or the MAF itself. Sounds like it's getting some unmetered air and running either pig rich or really lean from idle to 2000rpm (my guess would be rich, but I'm not there to look @ it) or whatever it is you see. Are you using factory O2 sensors?

I don't know about the O2's, the code it throws for them is intermittent, only once every couple months, and even when I've cleared codes (both by plugging in the two wires in the diagnostic port, and by leaving the battery disconnected overnight), it will happen the very first time I drive the car. I don't know what sensors are in it, factory or aftermarket. They're whatever was in the car when I bought it.

A wideband would be ideal to see what it's doing for rich/lean.

Quote:

Originally Posted by kwren

A while back someone said they had the bosch bypass relay starter thing on their car and it ran "like crap"... took it off and that cured it. Do you have the bypass starter relay on your car?

bypass relay? I don't know anything about one of those. I have a remote starter though. Same thing, or different?

I know what you mean about being frustrated. It's not a critical problem, it's just annoying as hell and ruins the experience of driving my car.

Dessertrunner · #6 08-13-2008, 02:21 AM

These are my suggestions for what they are worth. Given the age of my car 470,000 I have had every kind of problem. The most likely issues are:-
- Cam angle sensor, sysptoms are are lack of power down low and engine can't rev to red line. The engine is capiable of running with a bad cam angle sensor and not showing a code.
- Fuel pump, if you can borrow a fuel pressure guage measure the fuel pressure. The other way to tell is to run the car out of fuel then measure how much fuel it takes to fill up again. You will find that the tank will only take 50 to 54 litres as oppossed to the 65 to 70litre it should take.

Both of these problems cause the car to lack power. Both will stuff you fuel ecomny.
Tony

dcarrb · #7 08-13-2008, 05:47 AM

My silver has symptoms similar to this (and kwren, no bypass relay... not yet, anyway).

In winter, on cold days, I have to let it idle for a few minutes on startup or she'll be dragging a battleship anchor 'til she warms-up. In summer, turning off the AC until I get rolling always seems to help, and it's never as bad when the car's at full operating temp.

Feels like my old Mustang did when once when the timing was off: Idles fine, but stumbles badly with throttle*, as if it's out of time. And it's intermittent. I've always figured some sensor is sending bad info. My one experience with a Subaru fuel pump failure was sudden and complete, so I (perhaps foolishly) tend not to suspect fuel supply.

This car's fuel economy is just a tad worse than the teal's, but not by much. Spirited runner on the highway with no drivability problems at speed. One brief flicker of the CEL several months ago (O2 sensor—no corrective action taken). Used to have an occasional near-stall burble at low/warm idle but that has actually cleared-up. I replaced the TPS some time back to correct an AWD-binding/goofy shift condition (100% cured), but can't recall if this stumbling business got worse afterward; have wondered if the TPS needs a proper adjustment. Has really been noticeable this summer.

I, too, will be interested in ideas anyone may have.

dcb

*Edit: I should say it stumbles under load; won't pull.

dromano · #8 08-13-2008, 07:01 AM

Everyone using the proper octane? The times I have used 87 octane I experienced a cold engine stumble, like miss firing, erratic power. High octane on the next fill up made the issue go away.

I had a maf problem when some copper loving critter ate a wire on the male plug to the maf. The only thing that made the strange engine performance go away was to solder the wire back together and wrap the wires at the plug with a large amount of electrical tape.

dcarrb · #9 08-13-2008, 07:34 AM

I went from alternating between 87 and 93 octane (always filling up at >one-half tank) to straight premium for a few weeks, wondering if the old gal wanted an octane boost. No discernible difference in drivability of fuel economy.

I use the same fuel/mix/brand/pump with the other car without a problem, which in my case would seem to rule-out a fuel quality issue.

dcb

RojoRocket · #10 08-13-2008, 07:51 AM

Quote:

Originally Posted by Crazy_pilot

Does anyone know if it's possible for the MAF to develop a dead spot? A certain air flow it has trouble reading? And not throw a code.

My car is almost perfect mechanically, but it has a really annoying trait that murders it's driveability in terms of nice-ness. Between 1200 and 2000 RPM, when pulling away in first, the engine puts out almost no power. It's like it starts to move, and then someone attached a 10,000 lb trailer to me. It's not revving, it just won't accelerate, it falls flat on it's face. Some days it's really bad, it will do this up to 2500 RPM. If I hit the gas a little harder it'll jump up past 2K and go just fine, but then I always have the car jumping away from stops instead of pulling away smoothly. It's just damn annoying.

The only codes I've seen are intermittent for the O2's, and even after clearing codes this happens instantly. Every so often it won't act up at all, and when that happens it feels like someone gave me a new car.

From my end it feels like the engine isn't getting fuel at those RPM's. When it gets into that spot where it's not making power, if I gently push the pedal I get no acceleration, but a different exhaust noise, like the engine is labouring.

Any thoughts?

Chris,
I've not heard of flat/dead spot developing in the MAF, but have you thought about the Throttle Position Sensor, which can? There has been quite a bit of info out on this if I recall correctly. Check in How To Documents; Engine; TPS. Good luck with this.

Glenn

Crazy_pilot · #11 08-13-2008, 08:37 AM

Tony: I'll see if I can grab a fuel pressure guage from someone. I've actually never put more than 55L in the tank, but I've also never had the low fuel light come on. I go according to the guage, which like many may be a tad on the pessimistic side. The car revs to 6500 with the pedal down, no problem up top, which would not lead me to suspect the cam sensor.

Everyone else: The car has always run on 91 or higher octane, except for one time I needed a reciept for $20 of regular, which I then topped off with 94. I also suspected the TPS, so there's a new one in there, properly adjusted (had OT check with the Select Monitor at Reading).

Thanks for the suggestions so far folks, I'm off to my cottage for a week and a half tonight, so I'll check again when I get back.

Manarius · #12 08-13-2008, 10:59 AM

I'm having a similar problem and Tom mentioned the IRIS Check Valve (missing or broken otherwise) as one of the potential problem causes. When I get it later this week or next, I'll let you know if that clears up some of my hesitation issues.

Crazy_pilot · #13 09-09-2008, 05:43 PM

Any luck yet Jason?

And in the event the cam sensor is the culprit here, I just found out it's actually right beside the crank angle sensor. Does that mean that the timing cover has to come off to change it? Cause I don't really want to do that again three weeks after I just had the whole engine bay in little bits. *grumble*

Oh, wait, seems there are TWO cam sensors. groovy. So changing one without the ECU throwing a code would only be a $168+shipping shot in the dark.

genzzel · #14 09-09-2008, 06:05 PM

Hmmmm--I have to agree to check TPS and IRIS valve. Another thought is the 92 bead crush fix in ECU---my son's 92 acted like that and after the bead crush it seems fine---just my 2 cents http://www.subaru-svx.net/photos/files/How-To/14363.pdf

Crazy_pilot · #15 09-09-2008, 06:10 PM

The TPS is brand new and set exactly to spec. I'll have a look at the IRIS when I pull the intake off in a while to replace all the vaccuum lines. I've thought about the bead crush mod, but I'm rather nervous about squashing bits of my car's computer with pliers, even if it is something Subaru recommends.