The truck generally runs well but exhibits two issues which I belive to both be related to a vacumm leak and both are only at highway speed. Around town everything is great, no problems At highway speeds (65mph+) the air vents will change from the dash to the defrost. If you let off the accelerator the air will change back to the dash vents Also at highway speeds if you step ******* the brakes it takes several seconds before the brakes really work. Note that both the brakes and the change in air vents happen at the same time while the truck is decelerating. I tried changing the brake vacumm booster thinking the diaphram had a crack in it, to no avail. So it appears that at engine load it loses its vacumm storage, but where to look (other than all the hoses)
Most vehicles have a check valve (one way valve) in the small vacuum line that supplies vacuum to the dash heat/air controls. If this fails (and quite common to do so) the vacuum operated controls act as you describe. Might try hooking up a vacuum gauge to see what is happening as you drive. Brake issue may be unrelated but if it is happening at the exact same time that is very strange. The brake booster has its own check valve, but a failure there would act just the opposite, as you might have some vacuum to make brakes work at first, but would quickly get worse. Color me stumped on that one.
Testimonial: "Thanks David! Since originally posting, I spent some time just chasing the vacuum lines around the engine compartment. I found a cluster of small vacuum lines on the right side near the battery that had three tees. One of them goes around the battery and heads forward (though to what I have no idea). This line had been rubbing against the battery frame and had apparently cracked some time ago and someone had wrapped a little bit of electrical tape around it. For the moment, I've disconnected that line from the tee and plugged the tee. Now I suppose I need to start pulling the batter and windshield washer tank and see where that hose is going. Or I suppose I might be able to cut it back and splice it, but there's not much to work with, and the rest of the line is probably also aged and hard. I'm in Saudi so heat is always an issue."
Yes heat will cause vacuum hoses (and all other hoses and belts) to age faster than normal. Combine that with the fact that modern engines tend to run hotter than older ones, and that the hoses used for vacuum lines from the factory are thin and not reinforced and you can have rapid failure. I like to replace these lines with better quality fuel type hose, if I can get the correct sizes, Good luck.
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SOURCE: no acceleration,audi 1.8t,runs like no boost
have you tried cleaning out the throttle body as i had a similar problem and this worked
SOURCE: My 2002 Hyundai Elantra Gt (2.0L)engine runs rough
The Hyundai online shop manual and my newly arrived Hyundai shop manual kept pointing to the coil as a possible problem. While preparing to check coil continuity I discovered the pigtail connected to the bottom of one of the coils was loose and the contacts were burned. This is the coil that supplies spark to plugs 1 & 4, the same ones that kept showing up each time the check engine light illuminated. After cleaning the contacts and making sure the pigtail was securely attached to the base of the coil I have had no further problems.
SOURCE: AC will not come out the dash vents all the time.
my ac vent only comes out of the defroster and the floor i replaced the vent door accuator but that didnt work what could be the problem 2004 gand marquise
SOURCE: 2001 Ford Escape runs rough on acceleration and at
escape 2001 runs rough, but after a certain speed ( 50 mph ) runs smooth.
SOURCE: i have problems with my 98 chevy k1500 pickup on
If it is running bad enough to be backfiring, the Check Engine light should be on. I would start with scanning the engine computer for fault codes.
1.Fuel injectors, related wiring, sensors, computer issues
2. Running out of gas, or poor fuel quality
3. Evaporative emissions system (EVAP) concerns: fuel vapors leaking into engine
4. Incorrect Fuel Pressure
5. EGR system concerns: leaking EGR valve or restricted ports
6.Base engine concerns: low compression, valve train problems and timing issues
7. Ignition system concerns including, but not limited to:
Faulty spark plugs
Faulty coil or related wiring
Ignition module or related wiring issues
Ignition related sensor faults or wiring issues
You will have diagnose each element until you find root cause.
And it could be more than one element faulting out.
You
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Thanks David! Since originally posting, I spent some time just chasing the vacuum lines around the engine compartment. I found a cluster of small vacuum lines on the right side near the battery that had three tees. One of them goes around the battery and heads forward (though to what I have no idea). This line had been rubbing against the battery frame and had apparently cracked some time ago and someone had wrapped a little bit of electrical tape around it. For the moment, I've disconnected that line from the tee and plugged the tee. Now I suppose I need to start pulling the batter and windshield washer tank and see where that hose is going. Or I suppose I might be able to cut it back and splice it, but there's not much to work with, and the rest of the line is probably also aged and hard. I'm in Saudi so heat is always an issue.
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