Vacuum leak diagnosis suggestions

[O'Rattlecan]

Hi guys,

1994 F150, all the accessories on it are still pretty stock, just FYI. I'm pretty sure I'm fighting a vacuum leak and it's resulting in a high idle and poor fuel mileage.

I think O'Reilly's sells a little pack of various sized rubber vacuum port boots to seal things off for diagnosis. Is there anything I absolutely can't plug while I'm diagnosing? The only thing that comes to mind is the fuel pressure regulator. Can you all think of anything else?

I'm not exactly an expert on the PCV system either. I'm wondering if maybe it's possible that the valve is stuck open. The seal on that booger in my valve cover is abysmal.

Ryan

 

[blacksnapon]

get some carb cleaner with a "straw" to direct the spray. while its running use the spray, when you spray the leak the engine noise will change.

 

[O'Rattlecan]

good idea, Vince. thanks. I'll give that a try before I try the vacuum sealers.

Ryan

 

[Mil1ion]

I prefer using an unlit propane torch.
Slightly open the valve and hold near possible leak areas.
Nothing spraying around the area.

Sent from my SM-G900W8 using Tapatalk

 

[blacksnapon]

I prefer using an unlit propane torch.
Slightly open the valve and hold near possible leak areas.
Nothing spraying around the area.

Sent from my SM-G900W8 using Tapatalk

The propane torch will work but I get nervous with a propane "leak" around all of the sparking in a running engine.

 

[Mil1ion]

It's only a minute amount of propane coming out the tip is basically right close to any leak.

There's no build up of gas as the fan is blowing air back.

Are your spark plug wires all worn out ?
There's really no danger.
I did it on my Mustang when i bought and the wires were 19 years old and cross sparking.

I just find the spraying of carb cleaner not as precise and causes mind to do 2 things at the same time.
Trying to concentrate on the engine running change and holding the can and aiming it to the right spot.


Sent from my SM-G900W8 using Tapatalk

 

[O'Rattlecan]

No disrespect but I'm not intentionally leaking propane under the hood. I am risk averse and this seems like an unnecessary risk.

Ryan

 

[dustybumpers]

I can bet it's the black hard line that goes behind the upper plenum, and feeds everything on your emissions.
It also feeds your heater controls, and runs to your vacuum reserve can on the fender

Does the A/c ever switch from the center vents to defrost when you step on the gas?

 

[O'Rattlecan]

I gave the carb cleaner trick a try. I couldn't really isolate any particular vacuum line. Next up I think I'll try the vacuum plugging boots.

Ryan

 

[johny89]

i have a black sensor mounted on the firewall which i can't unplug or the engine stalls. (i think its the maf or map sensor.)
spraying carb cleaner is more dangerous then the propane trick tough: the cleaner is more dense when sprayed but get bigger surface (burnable surface) then the propane. once there is not enough propane/air mixture it won't ignite, propane is also more ventilated away with the wind then the carb cleaner, and if by any spark right in front of the propane torch it ignites you have more control over it.
So if you want the safest of two i would go propane, but getting a vacuumleak to be found can be done by hearing first.
does your car have an auto or manual trans? automatic transmission as like the C6 uses vacuum to shift and the line going to the transmission is prone to be damaged trough again or even because your modulator is broke and it can leak some oil in the line.
I have a link where you can find some diagrams to know the routing of your vacuum; http://www.supermotors.net/registry/2742/12671

 

[smokey]

I also use propane. I modified torch head ,took the head off and replaced it with a long section of hose. This was I can pin point where it is directed.
Never had a flash or a flare-up over the years. I just open the vavle a little bit so only a little propane is coming out.

 

[CowboyBilly9Mile]

Hi guys,

1994 F150, all the accessories on it are still pretty stock, just FYI. I'm pretty sure I'm fighting a vacuum leak and it's resulting in a high idle and poor fuel mileage.

I think O'Reilly's sells a little pack of various sized rubber vacuum port boots to seal things off for diagnosis. Is there anything I absolutely can't plug while I'm diagnosing? The only thing that comes to mind is the fuel pressure regulator. Can you all think of anything else?

I'm not exactly an expert on the PCV system either. I'm wondering if maybe it's possible that the valve is stuck open. The seal on that booger in my valve cover is abysmal.

Ryan

^^^ It is possible that carbon is not allowing the EGR valve to fully close.

 

[smokey]

Good call Bill that could very well be the problem.

 

[O'Rattlecan]

I have the EGR deleted... But that doesn't fully excuse the possibility of that block-plate might be the culprit. I'll check that.

PS I failed my safety/emissions inspection. They don't have an emissions breather, just a visual inspection. My headers were leaking like a sieve and my tail pipe broke off at the muffler, so I didn't pass.

I've had the misfortune to now need new stainless steel long tube headers, a high flow cat converter, fresh muffler, and a 3" system all around. What terrible luck. Vroom vroom.

Ryan

 

[kiwi f150]

If you are sure that it's a vacuum leak Ryan , you could try one of these http://www.ebay.com/itm/EVAP-Smoke-...k-Detection-Tester-Detector-NEW-/231685942809 . Not too pricey over there compared to here and while i don't have one a neighboring 'shop does and it's pretty good at diagnosing leaks on these older machines where the rubber and plastic lines are getting brittle and cracking with age.

 

[jebadiah04]

CHECK YOUR CODES.

I would bet a Shiney nickel that if you don't have a vacuum leak then it's your TPS. <---They fail all the time, especially on the duel inlet throttle bodies.

After TPS....then check your timing, (check procedure for your year and smog set up)

Timing then EGR

After EGR then FPR, less likely, but possible.

 

[jebadiah04]

I also am speaking in general here as i dont know what engine you have. I don't know what Trans either. If it's auto does it have a vacuum like attached to it? If so, did you check that?

Also, propane is way better than starting fluid..... You can run your BBQ for how long before igniting it and it doesn't instantly explode into a ball of fire.

 

[blacksnapon]

if you can look at data. look a lft1 and lft2 (long fuel trim bank 1 and 2). ideally you want both as close to 0 as possible. if closer to 30 it's definitely a vacuum leak.

 

[O'Rattlecan]

It's funny you guys mentioned TPS. It might be the throttle body itself. It doesn't totally seat every time I rev it and let it back down. Maybe that's my problem.......

Ryan

 

[blacksnapon]

It's funny you guys mentioned TPS. It might be the throttle body itself. It doesn't totally seat every time I rev it and let it back down. Maybe that's my problem.......

Ryan

f your truck cam into my bay, fuel trims are the first thing ] look at. sft (short fuel trim) is the adjustment that the pcm makes fir immediate "repairs" LFT is the adjustment made for larger problems.