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Air at schrader valve problem

 
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Old 03-15-2019, 09:07 PM
Chris754
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Exclamation Air at schrader valve problem

I just replaced all of my o-rings on my injector lines on my 86 f250 thinking that air was getting in somewhere. The truck is not getting any fuel up to the schrader valve. I used a little ether to get it started because it wont start at all without it. That is the only way i have been able to start it. Runs perfect once it starts and runs for a while. Has anyone else had this problem? I was starting to think it could be the lift pump. The only thing is it runs fine once I give it ether. Could a bad lift pump cause this? Fuel flowing back into the tank maybe?
 
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Old 03-16-2019, 12:44 AM
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Originally Posted by Chris754 View Post
I just replaced all of my o-rings on my injector lines on my 86 f250 thinking that air was getting in somewhere. The truck is not getting any fuel up to the schrader valve. I used a little ether to get it started because it wont start at all without it. That is the only way i have been able to start it. Runs perfect once it starts and runs for a while. Has anyone else had this problem? I was starting to think it could be the lift pump. The only thing is it runs fine once I give it ether. Could a bad lift pump cause this? Fuel flowing back into the tank maybe?
If you have any fuel leaks around the lift pump it will probably need to be replaced.If cranking the engine doesn't purge the air the lift pump might not be pushing. Are you sure you are getting the schrader valve depressed? I use a short piece of old screw on fitting bike pump hose to a collection container so I can crank and have the schrader valve wide open.

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Old 03-16-2019, 01:00 AM
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Are you sure you have fuel in the tank?
 
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Old 03-16-2019, 06:32 AM
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Did you use clear acrylic hose between the lift pump and fuel filter to see if you're getting air intrusion? Air intrusion will make it hard to start and give a puff of white smoke at startup.
 
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Old 03-16-2019, 07:54 AM
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I pushed it in with a small flat screw driver. I am sure that i had it fully pressed, but I will have to try it while I am cranking the engine. I have not tried a clear hose, still has the original metal hose, I tried tightening the fittings some, I do not know where air would be getting in. I will have to try the clear hose. I do get black smoke when I start it because I have to use the ether. Some gray smoke to, not really white tho. Runs choppy the fist second you start it.
 
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Old 03-16-2019, 07:58 AM
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You still have a leak somewhere. You changed all the o-rings. This is a older truck correct? Has the water separator that came on the old trucks and was mounted on the firewall been bypassed? They are notorious for leaking air. Also look on top of the fuel filter housing. Do you have any wetness up there? Another place for a air leak is the fuel heater o-ring on top of the filter housing.

If you want to help it out till you get it fixed, find a steep hill and park it with the rearend of the truck high. This will help keep the fuel from running back to the tank.
 
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Old 03-16-2019, 08:04 AM
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yeah its older, I do have wetness around my injector lines, they have been replaced
 
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Old 03-16-2019, 08:08 AM
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Originally Posted by Chris754 View Post
yeah its older, I do have wetness around my injector lines, they have been replaced
You said you put a o-ring kit on the injectors? Did you replace the plastic caps also? I have been re-using my factory caps since they are in good shape. I have heard some of the kits that have new plastic caps can leak because the plastic caps are not made very well. Wetness means fuel is getting out, and that means air can get in.

 
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Old 03-16-2019, 04:13 PM
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Originally Posted by Chris754 View Post
I pushed it in with a small flat screw driver. I am sure that i had it fully pressed, but I will have to try it while I am cranking the engine. I have not tried a clear hose, still has the original metal hose, I tried tightening the fittings some, I do not know where air would be getting in. I will have to try the clear hose. I do get black smoke when I start it because I have to use the ether. Some gray smoke to, not really white tho. Runs choppy the fist second you start it.
Yes...the engine has to be turning over for the lift pump to work. You'll be forcing the air out the schrader valve with fuel. When you have a steady stream of fuel out the schrader the air is purged. I normally do this when changing out the fuel filter. Some people add fuel to a new filter before screwing it on...can be kind of messy that way...and the book says not to fill the filter. You can crank on it for a longer time and eventually get the air out through the injectors but purging it at the fuel filter base is best especially if your batteries are not up to snuff. Just pushing on the schrader with out cranking does nothing. I don't expect a lot of air to come out of the schrader unless you changed out the filter.

Once you get it running then look for any wetness at the injectors and keep tightening them till they stop leaking.

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Old 03-16-2019, 06:09 PM
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Yeah when I start cranking the truck I have fuel right away at the valve. Just trying to figure out why its starting so hard. I am wondering if the fuel pump is draining back into the tank. Or a faulty fuel shut off solenoid.
 
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Old 03-16-2019, 06:26 PM
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Originally Posted by Chris754 View Post
Yeah when I start cranking the truck I have fuel right away at the valve. Just trying to figure out why its starting so hard. I am wondering if the fuel pump is draining back into the tank. Or a faulty fuel shut off solenoid.
If you're getting a good burst of fuel at the schrader that probably eliminates the lift pump as your problem. When you get it running let it run for a while. if not driveable then rev the engine a few times until the air is purged and it smooths out. Then keep checking the plumbing on the injectors for wetness and keep tightening them little by little. Don't strip anything just a bit of pressure to snug em up. Then check again daily till dry.

As for fuel running back to the tank I haven't had that issue. Perhaps there is a check valve that is hung open? Were you having this issue before you worked on the injectors?

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Old 03-16-2019, 06:30 PM
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Yeah, that is why I started working on them. I did tighten everything. Looks like there is a little wetness on the return lines... all the injector lines look fine though.
 
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Old 03-16-2019, 06:58 PM
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Also if you are not getting air at the schrader that pretty much eliminates the possibility of fuel running back to the tank. Cause that would put air in the line to do that.

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Old 03-16-2019, 07:26 PM
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The wetness at the injectors is usually not caused by the injector leaking. Tightening the injector will do no good.

The wetness comes from the injector return system leaking. These are the two o-rings under the plastic fitting around the injector, and the little rubber lines that go from injector to injector and then back to the tank down the return line.

How this system works; The lift pump sucks the fuel from the tank, and pushes it up to the top of the engine through the fuel filter. You will notice there is a return line coming off the fuel filter head. There are also the return lines coming off the injectors and I think there is even one coming from the injector pump somewhere.

When the engine is stopped and the fuel pump stops pushing fuel, the fuel is supposed to hang up there on top of the engine. It's just like taking a straw and putting it down in a drink, putting your finger over the straw, and pulling the straw up out of the drink. The drink will stay in the straw as long as you keep the top of the straw sealed with your finger. This is how the fuel system works on these engines. When it's totally air tight, the fuel is trapped on top of the engine and is there ready for the next time you start it. Any little leak will let air into the system and let the fuel run back to the tank down the return line.

The air entering the system does not let the fuel between the injectors and the injector pump leak back. This is the fuel in the hard metal injector lines. The reason I mention this, the classic example of air intrusion goes like this; You heat the plugs, start the engine, and it starts right up runs for a second and then quits. After that it's a bunch of cranking till it will start. It runs on the fuel in the injection lines at first, but when all that air from the rest of the fuel system hits the pump, then it quits. If this is what your engine is doing, then for sure it's air intrusion, you have air leaking in letting the fuel run back to the tank.
 
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Old 03-16-2019, 08:03 PM
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How old are the injectors and the IP pump ? When injectors wear and IP wears they will leak back causing the fuel to drain out of the injector feed line and cause hard starting.

This is very basic thing gets overlooked when trying to diagnose hard start in the IDI's.

Leaking at the return lines will not affect starting at all as this is the injector leak off and has no impact on the injector feed. With brand new injectors this line may have little to no fuel in the return line
You could take the return feed lines off completely and the caps and it would not affect starting at all. Even if the check valve in the lift completely failed fuel should still not drain back to the tank. The most usual culprits are the injectors or the IP pump and on occasion the fuel filter housing If there is any wetness around the fuel heater heater connection on the fuel filter housing the O-ring sealing this has failed and it will allow fuel to drain back through it's return line creating a harder start

The IP has a high pressure side and a low pressure side the low pressure side is sealed to the crank case through the input shaft. if this seal fails Common on high mileage IP pumps fuel can leak in to the crank case draining the IP's low pressure side of fuel this will require cranking to refill the low pressure side of the IP (much like a carb) and building enough pressure for the IP to operate. The usual symptom if this is normal start engine run for a second or two, quit, then, and then a hard start.

If the injectors are leaking they will leak down the residual pressure in the feed lines creating a situation where the IP will have to fire each cylinder a time or 2 too get enough fuel in the line to build enough pressure to pop the injector. Add in a leaking low pressure side IP pump and it will result in extended cranking to get the engine to fire. Throw in a leaking fuel filter housing and forget it you pretty much are going need a boost to crank it over enough to fire.
 

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