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87 Pathy V6 in limp mode. Rough idle and unable to go past 3 k rpm


jeactx
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Hi everyone,

 

I recently did head gaskets and valve job to my 87 Pathfinder V6. Broken timing belt destroyed the valves so I removed heads and took them to the shop to get new ones. Everything is assembled now, but Pathfinder can't go over 3000 rpm and has a bad rough idle. Loss of power is also present.

 

I have checked timing. I'm pretty sure I have crank and cam timing synchronized. I also checked ignition timing (distributor) and stuff.

 

I'm getting code 12, that is air flow meter. I cleaned the MAF sensor without luck.

 

 

I need serious help. Is it the MAF sensor, vacuum leaks or off timing? Thanks for your time.

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The VG30I looks like carby, but (unless it's modded) it's actually got a single injector in the throttle body. Doesn't sound like that's your issue, though.

 

Check the MAF's plug for corrosion. If that looks good, check out the wires off it and make sure they're in good shape. IIRC there's a ground wire in that harness, make sure it still goes somewhere and that its connection is good. It takes a lot for the MAF to trip the check engine light, so chances are it's disconnected one way or another.

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Do NOT replace the MAF yet, it would probably be a waste of money! If the truck ran fine before then it's more than likely the wiring is crossed, not grounded, corroded, or messed up somewhere from the removal and install.

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Try cleaning the MAF with isopropanol.

My truck ran like crap until I did this:

Remove the air cleaner: on the drivers side of the throttle body, remove the three screws and wiring harness (pull the metal clip and don't lose it!) from the MAF; clean the wire gently with a Q-tip dipped in 99% iso

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Well, I checked the wiring that goes to the MAF sensor. It seems to be fine. I also cleaned the sensor using your method ORCGuide. I remember that I removed the MAF sensor and it was hanging all the time when I was working on the heads. It might gotten damaged. How can I test it using a multimeter? Thanks for your replies guys.

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:omg: lol just replace the sensor.

No, that is not the first thing to do being as they rarely go bad and most of the time its a wiring issue. However since the OP has now said he left it dangling it probably did get damaged.

 

So every ground is hooked up on the intake plenum? That's where the MAF ground is.

 

Ohm the harness to the ECU. The green/yellow wire goes to pin 30, the black/white wire is power and should have B+ with the key on , the green/black wire goes to pin 31, and the black wire is ground.

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mine went bad recently. from what hes sayin he has checked everything and all is good. so im thinkin the sensor. when my comp said what part was bad i replaced it and all was well. so its either shorted or open. so just replace it and call it good. :lol:

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And possibly waste money for no reason. Testing the wiring is free and takes 15 minutes if that.

 

Its a crappy feeling when you drop money on a part and it doesn't fix the problem. Even crappier when the actual fix is free. Hell if the shielded casing for the signal wire isn't grounded or is missing even an inch of length the ECU will go in to limp mode and throw a code.

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The FSM should have a full test procedure for what resistance you should get through the sensor. Was the MAF dangling on its own or with the big metal housing bit on it? I can't imagine much harm coming to it if it was still in the housing.

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I know! These sensors are not easy to come by. My Pathfinder is manual, so it's even harder. I ordered one online, just in case. If that's not the issue, I can just resell it. I will check everything again. And I will test sensor. Thanks guys

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The MAF is the same whether its automatic or manual. There's no housing for it to hang out in unless the whole throttle body was dangling. They insert directly into the side of the throttle body, not in a separate housing like the MPFI trucks.

Edited by Kingman
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I've seen one or two manual TBI trucks with an actual 5-speed sensor without the POT. Most are the same sensor but the automatic uses both the POT and throttle switch while the 5-speeds only use the throttle switch, leaving the POT unplugged.

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