'91 4Runner Air Flow Sensor/Meter

I recently purchased a 1991 Toyota 4Runner V6 4x4 with 75k miles. I've been attempting to diagnose a problem I'm having (running too rich) and, in doing so, I decided to test the MAF Sensor with the help of my Chilton's manual.

To make a long story short, I removed the screws on the side of the housing that attach the terminal receiver to the housing INSTEAD of just disconnecting the terminal wire (there wasn't a picture in the Chilton's and I got confused... I'm an idiot... etc). When I did, lots of wires sprung forth which I quickly crammed back in and re-attached the screws. Then I unattached it at the CORRECT location and tested with an Ohm-Meter. Everything was within spec.

The next day, the engine stumbled and coughed and almost stalled once while driving. Check Engine light came on and then went off again. I pulled the codes to find 24 and 32 (Air Flow Meter and Air Temperature Sensor). 4 days later, the truck stumbled again... but this time, no code was thrown.

Is there a way I can fix whatever damage I did to the internals of this component? I didn't pull too hard before realizing I was doing the wrong thing. So hopefully... there isn't too much broken.

If not, I've called my local auto parts store. The part is just under $200 and they can get it to me in a couple of days. But, since it's not on the shelf, they can't confirm for me that it is the entire item including the housing and any other sensors that might have been in there with it. I don't need JUST the sensor... I'm sure the sensor is fine. It's the wiring in the housing of the sensor that may have gotten ripped apart.

Also, as best as I can tell, I have a heated wire Mass Air Flow Sensor. That's what the Chilton's leads me to believe anyway. But, I found some information online that leads me to believe I might have a Vane Air Flow Meter (based on the shape of component that I have). Can anyone tell me what I've got and/or how to tell for sure?

Thanks, Jim

Reply to
Jim
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Good luck getting an answer here. This is more of a "what kind of oil should I use" news group. Try

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Reply to
PC User

Well, you had it apart once. Wanna try again? Carefully open it but don't put any stress on any connections and do not touch the MAF meter elements themselves. Make sure no internal connections are loose (if that's possible). You said you tested the resistance of the meter. Only the MAF part or did you ohm out across E2 & THA to test the IAT and match it to the chart? How about hitting it with a blow drier? Did the resistance drop? If all is well in resistance land, then I would concentrate on connections. Once that's ruled out it would be time to try to find a used one some where or try to find a kind soul that would let you borrow their know good one. Now about running rich. Are you just chasing bad gas mileage or do you know you're running rich? What kind of mileage are you seeing? I had a 93 X-cab V6 4x4 that got 17 mpg no matter what I did. I could easily see a heaver (probably an auto) 4Runner getting 13-15. There could be other reasons for poor mileage. One that comes to mind besides a basic tune up is O2 sensors. It's not uncommon to need O2 sensors after 75k miles. Might not even trip a code. Depends on if they are just malfunctioning or if they totally died. A dead O2 sensor looks like a lean condition to the computer so it will add fuel up to its max setting. I don't know a lot about Toyota's EEC programming but I guess it could trip a MAF sensor error if the O2 sensor input doesn't jive with the MAF sensor inputs. Like I said, I don't know the Toyota EEC strategy so this is pure speculation of a possibility. Hopefully one of the more knowledgeable guys will post up to add some real experience for you!

Good luck!

"Jim" wrote in message news: snipped-for-privacy@kilgore.homeip.net...

Reply to
Bard

I will probably do this once my local parts store gets the part in. That way, if I really screw it up I can just go buy a new one.

But I have a question... should I expect to see a Vane type Air Flow Meter or a heated element Mass Air Flow Sensor once I open it up?

I tested only the MAF because I don't have a blow dryer to test the IAT. However, I don't think it's faulty as it never did this BEFORE I tested it. So, if it is troublesome in any way, it isn't what's causing the stumble, because that didn't start happening until after I opened it up.

I'm pretty sure I'm running rich. When I first bought it, I sensed a general lack of power, and a bit of "stinky car smell" especially under idle and open throttle. I also have a rough idle AFTER the truck warms up past the cold idle stage but before the engine really has a chance to heat up (maybe 2-3 minutes after starting). And, while I don't see any black smoke, there is quite a bit of black soot collecting at the end of the tailpipe. An online source suggested it might be a clogged cat, so I took it to a muffler shop (Midas) to get it tested. They said that the cat was fine but that my exhaust was running hotter than it should be, pointing to a possibly rich mixture. They suggested taking it to FireStone to have it hooked up to an engine analyzer for $90, but... I'd rather not... which is why I started testing everything.

I have a 5speed and I get about 15-17 mpg. That's with mixed city and highway driving and a pretty heavy foot.

I TRIED to test the O2 sensor... but it's fairly difficult. I don't have a way of injecting propane into the intake, as they suggest, so all I was able to do was run a Volt-Meter across it and look for the cycles as is crosses the .5 volt mark. Also, my digital meter only reads about once a second, so I couldn't get continuous information. However, I did notice that it alternated between being above .5 and below .5 fairly consistently. When I stepped on the throttle, it would show LEAN for a bit, and then even out. When I let off the throttle quickly, it would show RICH for a bit, and then even out. That seemed to be within spec. I need to get a better (perhaps graphing) Volt Meter to really test it, as, if it is just very slow but not exactly broken it could very well be the cause of my rich mixture.

I also replaced the spark plugs, and tested all of the plug wires. I tested the TPS (as best as I could without measured feeler wires) and it also seemed to be within spec.

Thanks for your help!

Jim

Reply to
Jim

Thanks. I've posted there as well.

Jim

Reply to
Jim

. . . . . '91 4Runner Air Flow Sensor/Meter Group: alt.autos.toyota.trucks Date: Wed, Oct 15, 2003, 12:10pm From: snipped-for-privacy@revjim.net (Jim) I recently purchased a 1991 Toyota 4Runner V6 4x4 with 75k miles. I've been attempting to diagnose a problem I'm having (running too rich) and, in doing so, I decided to test the MAF Sensor with the help of my Chilton's manual. To make a long story short, I removed the screws on the side of the housing that attach the terminal receiver to the housing INSTEAD of just disconnecting the terminal wire (there wasn't a picture in the Chilton's and I got confused... I'm an idiot... etc). When I did, lots of wires sprung forth which I quickly crammed back in and re-attached the screws. Then I unattached it at the CORRECT location and tested with an Ohm-Meter. Everything was within spec. The next day, the engine stumbled and coughed and almost stalled once while driving. Check Engine light came on and then went off again. I pulled the codes to find 24 and 32 (Air Flow Meter and Air Temperature Sensor). 4 days later, the truck stumbled again... but this time, no code was thrown. Is there a way I can fix whatever damage I did to the internals of this component? I didn't pull too hard before realizing I was doing the wrong thing. So hopefully... there isn't too much broken. If not, I've called my local auto parts store. The part is just under $200 and they can get it to me in a couple of days. But, since it's not on the shelf, they can't confirm for me that it is the entire item including the housing and any other sensors that might have been in there with it. I don't need JUST the sensor... I'm sure the sensor is fine. It's the wiring in the housing of the sensor that may have gotten ripped apart. Also, as best as I can tell, I have a heated wire Mass Air Flow Sensor. That's what the Chilton's leads me to believe anyway. But, I found some information online that leads me to believe I might have a Vane Air Flow Meter (based on the shape of component that I have). Can anyone tell me what I've got and/or how to tell for sure? Thanks, Jim //////////////////////////

Jim, are you fairly SURE....that you reasembled it without causing any harm?

DID YOU DISCONNECT THE BATTERY???

try'n to help

pop bunkle ~:~

Reply to
Pop Bunkle

That's just it. I'm not sure about ANYTHING. Yes, the battery was disconnected. However, I merely crammed the wires back in and put the screws back on as quickly as possible once I realized that I had done something wrong.

Jim

Reply to
Jim

(My thoughts are kind of jumbled here so bear with me. It's been a long day!)

I would assume a heated element MAF since the other is "old school". I would go ahead and test the IAT for grins. If it comes up bad, you have to replace the unit anyway so that will take some guessing out of it. If it's reporting an incorrect air temp, then your fuel tables will be off and can cause a rich or lean condition depending on which way it's off. You're gas mileage sounds in line to me but maybe I had low expectations of my 93. I've never heard of anyone testing an O2 sensor at home, but go for it if you think you can! I would just shotgun it at this point and replace it. If it doesn't help, then put the old one back in and hold onto the replacement for when it does go out. A rich condition will cause the cat to work overtime which creates more heat but I wouldn't bother with the cat. If it's running overtime then its a result of running rich, not a cause. You could take it to a performance shop and put it on a dyno with an air/fuel gauge. That will tell you if and when you're running rich. The hp/tq #s will tell you if you're down on power or if you're just hoping you are! My Chilton's says the 91 3.0 is rated at 150hp/180tq at the motor. Through the 5 speed you can expect to put ~130 hp and 165 tq to the rear wheels. Oh, what's the propane for? I've heard of using it to detect an intake leak, but not test an O2 sensor.

Reply to
Bard

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