that-son Posted August 23, 2014 Report Share Posted August 23, 2014 manual says there should be suction when you release the accelerator. mine has suction the whole time but much stronger pull when the accelerator is released. good or bad? Quote Link to comment
bonvo Posted August 23, 2014 Report Share Posted August 23, 2014 start a build thread and put all your questions there Quote Link to comment
datzenmike Posted August 23, 2014 Report Share Posted August 23, 2014 manual says there should be suction when you release the accelerator. mine has suction the whole time but much stronger pull when the accelerator is released. good or bad? During sudden deceleration the air fuel mixture goes rich and will pop in the exhaust pipe. Not only annoying but it expels hydrocarbons into the air wasting fuel. To reduce this, the AB valve receives a vacuum signal from the intake and opens and allows air into the intake to lean it out. It should not be sucking all the time as this is basically a vacuum leak that will cause a lean mixture. Pull the very small hose off the AB valve and plug the end. Does it still suck? IF so the AB is probably defective. 1 Quote Link to comment
that-son Posted August 23, 2014 Author Report Share Posted August 23, 2014 will do it later today. thanks! Quote Link to comment
that-son Posted August 25, 2014 Author Report Share Posted August 25, 2014 did what you suggested and i think i need a replacement. i even tried installing it the other way but could not get any suction at all. not even when i rev the engine and release it quickly. bummer. could that be why i'm only getting 15mpg? too much air in the system so i turn the gas screw more than i have to to get it to run smoothly? Quote Link to comment
xsdg Posted August 25, 2014 Report Share Posted August 25, 2014 I had a leaky AB valve. Basically, above a certain vacuum, the control line is _supposed_ to actuate a diaphragm which lets air pass from the air cleaner to the intake manifold. In mine, there was a leak so that air would always pass straight from the air cleaner into the control line, and the valve itself would never open because of the vacuum leak. I actually passed smog with the valve removed (and capped off with purpose-made vacuum caps), but I plan on putting it back in place after I figure out an EGR issue that I've got going on right now. But the easy way to check for the problem I had: apply vacuum to the control line. If it doesn't hold a vacuum (that is, if you can suck without encountering any resistance), the valve needs to be replaced. Nissan actually still sells them, but they're $80, so if you can find one in a JY or elsewhere, you'll probably be better off. 1 Quote Link to comment
xsdg Posted August 25, 2014 Report Share Posted August 25, 2014 that-son: To clarify, my test is a stand-alone test, with the valve off the vehicle. Also, you should get your hands on a FSM. It explains all this stuff, and gives suggestions for how to test every component to make sure it's working. 1 Quote Link to comment
that-son Posted August 27, 2014 Author Report Share Posted August 27, 2014 just ordered another from rockauto. they've got it listed for $60. i just bought an aftermarket closeout ab valve from them for $30... no wonder it's half price- only half of it works. been looking for a fsm for an '81 kc 4x4. i've only found one for an '82 and without the 4x4. will keep checking the bay. thanks. Quote Link to comment
xsdg Posted September 5, 2014 Report Share Posted September 5, 2014 I dunno about '81, but the '86 FSM covers both RWD and 4WD. Quote Link to comment
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