Backroads Posted February 23, 2010 Share Posted February 23, 2010 I have an 86 with 2.5L I noticed theres an extra 'tube' Under the intake mani tube. Looks like its going to the header, and after seeing this pic It looks like it does. What and why?! Its that old rotten coily plastic like the intake tube, shouldnt that be melted and on fire? Maybe I'm just trying to understand it all wrong. Link to comment Share on other sites More sharing options...
Joop Posted February 23, 2010 Share Posted February 23, 2010 There should be a vacuum operated valve in the intake tube that is controlled by some sort of temperature sensor, its function is to draw fresh outside air trough the intake at hot days and on cold days it redirects the air to be drawn from around the hot exhaust headers. They often fail, making your engine suck hot air all the time = poor performance and gas milage, or cold air all the time = carb freeze over during extreme winter, makes your engine stall or even worse it gets stuck at full throttle :eek: Link to comment Share on other sites More sharing options...
Geonovast Posted February 23, 2010 Share Posted February 23, 2010 He doesn't have a carb. 86 2.5 is TBI. Also, there's no way that valve failing can cause it to be stuck at WOT. All that does is allow warm air that's heated from the exhaust enter the airbox. It has NOTHING to do with the butterfly, which is solely controlled by the gas pedal. All 3 of my Renix Jeeps were missing that little tube at some point, and I never had any problems. Of course... they were all 4.0s, therefore MPFI, not TBI. Link to comment Share on other sites More sharing options...
Joop Posted February 23, 2010 Share Posted February 23, 2010 It CAN and WILL happend on fuel injected engines as well. Happend just a few hours ago when i was out with the volvo. -20*C, moist coastal climate and open air filter makes this a usual problem. Yeah, I know, stupid me for hacking up that intake tube, definetly not worth it :nuts: It has also happend a few times with my 4.0L. Funny thing is, theyre both MPI engines... I guess its just pure fysics, air can only hold a certain amount of water at a certain temperature. That amount drops as the temperature drops. A the air passes trought the carb, or throttle body in this certain scenario, the pressure in the air drops, making the temperature of the air to drop as well. Wich again leads to water drops being formed since the air can't hold as much water as it did before. These water drops freeze to the cold metal surfaces, and might cause the throttle flap to get stuck in whatever position it might be in. But I have to admit, didnt know he had a TBI engine, I just read 86 and my mind automaticly went into 2.8-rochester- :ack: mode. Link to comment Share on other sites More sharing options...
Backroads Posted February 24, 2010 Author Share Posted February 24, 2010 right, its TBI. From what I know and understand all comanche 4 bangers are TBI, whereas in a cherokee it could be either until 86-87. But still not really clear on the purpose. My throttle cable is only to the throttle, so nothings getting stuck anywhere unless another something fails. But if some of that is right, then that tube is just to bring cool air from the grill area and route it to the exhaust header to cool it down? I mean makes sense in a 1986 kinda way...Not really looking to eliminate anything I like my jeeps original! But that tube can definately be improved on if thats its sole mission. Link to comment Share on other sites More sharing options...
Geonovast Posted February 24, 2010 Share Posted February 24, 2010 right, its TBI. From what I know and understand all comanche 4 bangers are TBI, whereas in a cherokee it could be either until 86-87. 84-85 XJs were carburated. 86+ was TBI. But still not really clear on the purpose. My throttle cable is only to the throttle, so nothings getting stuck anywhere unless another something fails. There should be a vacuum controller valve on the bottom front of your airbox. But if some of that is right, then that tube is just to bring cool air from the grill area and route it to the exhaust header to cool it down?. Other way. It's to bring hot air from around the header into the airbox to get sucked into the motor. Link to comment Share on other sites More sharing options...
Backroads Posted February 24, 2010 Author Share Posted February 24, 2010 So does that conclude that TBI needs warmer air as opposed to cooler air? Link to comment Share on other sites More sharing options...
Geonovast Posted February 24, 2010 Share Posted February 24, 2010 It's usually only open until the motor warms up. The MPFI motors have them too. Link to comment Share on other sites More sharing options...
Backroads Posted February 24, 2010 Author Share Posted February 24, 2010 Well I will have to do some poking around then. I already replaced a couple vacuum lines that were dry rotted pretty good so I'll have a better look at it then. Also, when I put my key in the accessory position, I hear something opening/closing clicking/turning....in the engine compartment. Could that be part of this? or something entirely different. Link to comment Share on other sites More sharing options...
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