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Possible Vacuum Leak

jrobinson004

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I have a 1998 Ranger 4.0 (OHV)

I hear a hissing sound when I accelerate ...
-Similar sound to air coming out of a tire
-Seems to be coming from somewhere near the gas pedal (not sure which side of the firewall
-It definitely gets louder as I accelerate more and makes no sound when idling
-I am not sure if the issues are related, but the truck also seems to be running a little on the hot side

Other than the noise, the truck seems to be running fine (no hesitation or rough idling).

Any thoughts?

Thank you,

-Justin
 


kimcrwbr1

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does the noise change if you tap on the brake pedal?
 

enjr44

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does the noise change if you tap on the brake pedal?
Yep, sounds like the power brake booster is leaking.

In a safe place, on a slight downhill, stop, turn engine off, wait about two minutes, take foot off brake, let it roll, apply brakes. You should have power brakes for about two stops. If not booster is leaking down and bad.
 

jrobinson004

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The noise stops as soon as I left off the gas pedal - braking does not seem to affect the noise.

-Justin
 

jrobinson004

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Just did another test drive - I have no loss in braking power at any time.
 

RonD

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If you have cruise control there will be a valve where the brake pedal's push rod goes into the power booster(in the cab).
It will have a vacuum hose attached, that hose goes to the cruise control's cable actuator in the engine bay, it uses vacuum to control speed, when you press on the brake pedal vacuum is lost and actuator is disabled, it is a backup safety measure to prevent run away cruise control.

This valve can leak and make noise.

Then there is the Atmosphere valve in the power booster, it is also at the end of the brake pedal's push rod, when you press the brake pedal the push rod pushes open Atmosphere valve, letting in the 15psi air pressure at sea level, the engine vacuum pressure, -18 to -22psi, in the power booster "assists" you in pressing down the pedal.
Atmosphere valve could be leaking but as above post suggests a noise would indicate the diaphragm in the power booster would have to be leaking and would lose "assist" pretty fast after engine was shut off.
Just to be clear the loss of "assist" would be AFTER engine is shut off.
Power booster has a Check Valve on the engine hose, if diaphragm in the booster is "air tight" then AFTER engine is shut down you should be able to "feel" the assist on the brake pedal for 2 or 3 pushes on the pedal then pedal will become increasingly hard to push down(vacuum pressure is gone).
If you shut off the engine and press down the brake pedal once and then it gets hard to push on the 2nd time, your diaphragm and Atmosphere valve are leaking.




And just as a "heads up", 4.0l OHV engine does not react well to overheating, if you ever see temp gauge getting up to 3/4 pull over and shut down engine quickly.
The heads WILL crack when over heated, no do overs it WILL happen the first time and every time, they have a thin casting between valve seats, but they will run forever, UNLESS you over heat them.
So a $50 water pump repair or bad thermostat can cost you over $1,000 if you try to "make it home" or otherwise ignore temp gauge.
Pull over let it cool off and figure out what is wrong, you can drive it again a short distance then shut it off again.
If it takes you 3 hours to get home, but you saved the heads then that's $333 dollars an hour you just made/saved :)

Engine running slightly warmer can also mean a Lean fuel mix, but you should get a CEL(check engine light) if that was happening.
Does your CEL work?
Does it come on with the key and then go out after a few seconds?
 
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jrobinson004

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I think I found the culprit ... I assume the EGR pressure sensor is supposed to have vacuum hoses connected to it? Both of the fittings are missing hoses.

Am I also correct to assume that each connects to a fitting in the exhaust manifold (as that seems to have two similar fittings, also without hoses connected)?

Sounds like a cheap fix ... hopefully.
 

jrobinson004

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An update ...

I replace the hoses connecting the EGR pressure sensor to the exhaust and no more hissing sound. However, now my truck has no power (especially in the low end and mid range). It feels as though I am towing something.

The transmission is fine, but power has decreased - gas mileage has also gone down about 20%.

Could the EGR sensor be bad?

Thank you,

Justin
 

RonD

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EGR sensor(DPFE) usually lasts about 100k miles, but you would get a Trouble code and CEL(check engine light) would come on, if it was failing.

And you should have had that already if hoses were unhooked????
Someone may have done a DPFE "work around" to stop the codes from coming up.


Those are not vacuum lines, as you said they both hook to exhaust manifold/EGR pipe.
Vacuum is in the intake manifold.
One hose hooks up to a fitting close to EGR valve, the other hose hooks up farther away from EGR valve.
And the hoses are not interchangeable, one is larger that the other and one fitting on DPFE is larger than the other
DPFE = differential pressure feedback, sensor
It measures the pressure difference in the two hoses
When EGR valve is closed both hoses will have the same exhaust pressure, as EGR valve is opened the pressure in the closest hose will go down, the difference in the pressure between the two hoses is what the DPFE sensor sends to the computer to tell the computer how far open the EGR valve is.

To test EGR valve
start engine
unplug EGR valves vacuum hose, there should be NO vacuum present on that hose, it is not used at idle, if there is then that would be a problem.
Next, put another vacuum hose on EGR valve and suck on the other end of that hose, engine should start to stall out as EGR valve opens, if it does then EGR valve should be good.

If the DPFE hose were not hooked up and they were not capped, then air was being sucked in to that exhaust manifold.
O2 sensors detect Oxygen(air) in the exhaust, not fuel
Too much oxygen in the exhaust means Lean, too little Rich
With an exhaust manifold "leak"(the two hoses) O2 would "see" too much oxygen so Lean would be sent to computer
So that bank of the engine should have been running rich the whole time those hoses were unhooked, if not capped.

If EGR valve is opening at the wrong time or opening too much that will also cause O2 sensors to see a False Lean, you would only notice this AFTER engine had warmed up a few minutes, because EGR valve and O2 sensors are disabled until engine coolant reaches a preset minimum temp.
So if engine seems to run OK cold and then starts to falter after warming up a bit this could be the issue
 
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jrobinson004

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I appreciate your reply.

I purchased the correct hoses (not simply vacuum line) and did notice the difference in inner diameter between the two.

During all of this the check engine light has not come on once.

It also makes no difference (performance wise) if the truck is warm or not - the best way I can describe it is that it feels restrictive (I checked an there are no bananas in my tailpipe, however).

I will do that test tomorrow and let you know how it goes.
 

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