Air Intrusion Question

asmith

Full Access Member
Joined
Jan 28, 2012
Posts
664
Reaction score
204
Location
Atascadero, Ca
I am getting a significant amount of air intrusion all of a sudden. When I start it after sitting for a while it will start right up then die, even giving it fuel I cant keep it alive. Then it takes a bit of letting the fuel pump run and cranking to get the air out of the line so it will start. I hadn't noticed before today, but I was getting some surging going down the freeway, like I am getting air in the lines. So what would be the most likely source of this?

I need to change my return lines, because they are seeping, but I wouldn't think they would cause the surging while driving.

I swapped to one big rear fuel tank and ran new fuel lines all the way to the engine. I no longer use the fuel tank switch. All the connections are dry.

My other thought was I extended the pickup in the tank with a piece of fuel hose. maybe that has slipped and is sucking air in the tank. my fuel level was below 1/4 tank. so I filled up to 2/3 to see if that makes a difference and will report back tomorrow. Any other ideas?
 

NeverHave-I-Ether

Full Access Member
Joined
Jan 18, 2022
Posts
304
Reaction score
214
Location
Texas
I have a hard time believing that the air intrusion is that bad. If it was that bad it would most certainly be leaking fuel. Common air intrusion spots are the tank lines and fuel filter housing.

Fuel pump. Do you have verified fuel pressure? Is it an electric or stock fuel pump?

Return lines. If they are pinched somewhere it will cause it to stall out.

Last thing that would come to mind is the IP failing bit I'm not familiar with it's symptoms.
 

Farmer Rock

just a fella' without a 10mm socket
Joined
Oct 27, 2020
Posts
1,423
Reaction score
1,313
Location
Glen Rock,PA
I have a hard time believing that the air intrusion is that bad. If it was that bad it would most certainly be leaking fuel. Common air intrusion spots are the tank lines and fuel filter housing.
I bet you'll believe it when you see it......or perhaps when you don't see it....
Any diesel is extremely sensitive when the smallest amount of air enters the fuel system. That's the nature of a diesel engine.

@asmith , I agree the return lines wouldn't make that much of an impact, or much at all really...
My 88 had a terrible case of air intrusion, that drove me nuts for months. Ended up being a pinhole on top of a steel line (not leaking), and on another occasion, a pinhole on the elbow of one of the tank pickup heads. It took awhile to find that.
It is time we'll spent to just completely go over the fuel system IMHO. It will drive you crazy trying to patch it up here and there.


Rock
 

IDIBRONCO

IDIBRONCO
Joined
Feb 5, 2010
Posts
12,236
Reaction score
10,925
Location
edmond, ks
I have a hard time believing that the air intrusion is that bad. If it was that bad it would most certainly be leaking fuel.

I agree the return lines wouldn't make that much of an impact, or much at all really...
I bet you'll believe it when you see it......or perhaps when you don't see it....
Any diesel is extremely sensitive when the smallest amount of air enters the fuel system. That's the nature of a diesel engine.
Farmer Rock is right. There's a difference between air intrusion and fuel drain back. Fuel drain back happens after the engine is shut off. It can happen on either side of the injector pump, the suction side or the pressure side. It will cause the same type of starting issues that asmith mentioned, but it will not cause issues while the engine is running, once all of the sir in the fuel system had been replaced with fuel.
Air intrusion is caused by air getting into the fuel system on the suction side of the injector pump. It does cause issues while the engine is running (which asmith mentioned) and is the only way that air can get into the injector pump while the engine's running. It can, and usually does cause fuel drain back. The two are related in a way and often confused. They are separate issues though.
The leaking return lines will cause fuel drain back, but, since they are on the pressure side of the injector pump, they cannot cause air intrusion because any air that may come into the fuel system here while the engine is running will flow back to the fuel tank along with the unused fuel. In the tank, it will separate, rise above the fuel level, and not mix back into the fuel.
Asmith, your air intrusion has to be before the injector pump and probably before the lift pump as well. As Farmer Rock said, it may not be easy to find. like you said, maybe you should fill your tank up some or all the way just to see what happens. That will tell you what direction you'll have to go.
 

Old Goat

Full Access Member
Joined
Jan 14, 2021
Posts
1,581
Reaction score
1,570
Location
Northern Nevada
Air intrusion could come from your Lift Pump.
I noticed the bottom of the pump wet 6 or 8 months ago.
Picked up one but didn`t put it on, engine ran ok so didn`t bother.
About 3 weeks ago started the engine and let it run a bit to warm up along side the garage. I was over by the porch and hear this thump noise, then a rattle bang sound. Shut off the engine, check everything, start it back up and ran smooth.
One morning would start right up, next would have to turn the engine over and over to start.
Had to run 20 miles south of here to pick up some tractor parts, engine cut out, speed dropped going up hill, acted like it wanted to die. It would blow blue smoke, but not all the time. Then it would run smooth for a bit. Had doubts we were going to make it back home.
Finally hit me it was the pump.

replaced the pump, curly Q fuel hose, and replaced the steel line to the Filter with a rubber hose.
Starts right up, runs smooth.

I did notice that the engine was low on power, and just wrote it off as IP or Injectors as they have been in since...who knows?
With the new lift pump, the acceleration is smoother, and the pick up speed is faster, like a new truck.


Goat
 
Last edited:

Cubey

Van dweller
Joined
Oct 18, 2017
Posts
4,066
Reaction score
1,580
Location
USA
Air intrusion could come from your Lift Pump.

I kept having air intrusion but an obvious leak too from the short hose with clamps at both ends that the mechanical pump when it was still on my RV. Turned out to be a bad clamp after i fixed it the first time. Fixed it again with a new clamp and the hose didn't leak again.
 

asmith

Full Access Member
Joined
Jan 28, 2012
Posts
664
Reaction score
204
Location
Atascadero, Ca
Thanks for the replies. Farmer rock i have replaced the entire fuel system. new tank, pick up, electric pump, filters and lines all the way to the engine. Thats part of why this kinda caught me off guard, with it dying like that. All my connections are dry, from tank to Ip.

I dont have a pressure gauge on the truck yet, which is on my short list of things to do, that keeps getting put on the back burner:frustrate but I dont think the pump is the issue.

I filled it up 2/3 of the way yesterday, and after sitting over night this morning started no issue, didn't stumble one bit. drove to the job, which is so close the temp gauge doesn't move, sat all day, went to leave and didn't stumble at all again, drove a quick 5 minutes on the freeway home and didn't feel any surging. I will need to give it some more time, but it is leading me to believe there is something wrong with the pickup in the tank. a hole or it has slipped or something. not sure what else it could be.
 

Cubey

Van dweller
Joined
Oct 18, 2017
Posts
4,066
Reaction score
1,580
Location
USA
If you're close to a HFT, they sell a cheap dual purpose low pressure fuel/vacuum gauge. I zip tied it to my cowl when i was troubleshooting the fuel pressure.
 

IDIBRONCO

IDIBRONCO
Joined
Feb 5, 2010
Posts
12,236
Reaction score
10,925
Location
edmond, ks
I filled it up 2/3 of the way yesterday, and after sitting over night this morning started no issue, didn't stumble one bit. drove to the job, which is so close the temp gauge doesn't move, sat all day, went to leave and didn't stumble at all again, drove a quick 5 minutes on the freeway home and didn't feel any surging. I will need to give it some more time, but it is leading me to believe there is something wrong with the pickup in the tank. a hole or it has slipped or something. not sure what else it could be.
I think you've found your issue. In the mean time, it doesn't cost any more to run it on the top half of the tank than it does on the bottom half.
 

Farmer Rock

just a fella' without a 10mm socket
Joined
Oct 27, 2020
Posts
1,423
Reaction score
1,313
Location
Glen Rock,PA
it doesn't cost any more to run it on the top half of the tank than it does on the bottom half.
Boy, I can't tell you how many times I've had to tell folks that. I know too many people who are always running around town on empty, drives me crazy.


Rock
 

steve phillips

Registered User
Joined
May 6, 2009
Posts
97
Reaction score
49
Location
burnwell/ky
have you checked drain valve on bottom of fuel filter. it is a likely suspect. if you have a leak around fuel heater in top of filter base, bingo, fuel drain back. there is a connection between return lines and supply side fuel, the rubber line from filter base to return cap. supposed to be a check valve in filter head, i eliminate this line,unnecessary. when new these trucks had check valve in shower head, it is flapper, most have rotted off by now. have you changed hard line olives? hope this helps. steve
 

asmith

Full Access Member
Joined
Jan 28, 2012
Posts
664
Reaction score
204
Location
Atascadero, Ca
I think you've found your issue. In the mean time, it doesn't cost any more to run it on the top half of the tank than it does on the bottom half.
I think so too. I am going to run it down and see if i can recreate the symptoms. If I can then I will just keep it full, until I can get a free weekend to drop the tank and take a look inside.
10-4 on that. I just run on my 38 gal rear tank, when I get to 1/2 I fill her up.
Costs as much to fill the top 1/2 now as it did to fill the whole tank when Trump was in office. :frustrate


Goat
Is that the truth?!! The pump shuts off at $100, and I get about 3/4 of a tank now. We pay right about $5 a gallon here now.:cry:
have you checked drain valve on bottom of fuel filter. it is a likely suspect. if you have a leak around fuel heater in top of filter base, bingo, fuel drain back. there is a connection between return lines and supply side fuel, the rubber line from filter base to return cap. supposed to be a check valve in filter head, i eliminate this line,unnecessary. when new these trucks had check valve in shower head, it is flapper, most have rotted off by now. have you changed hard line olives? hope this helps. steve
Thanks for the reply. I have deleted all that stuff. I have a homemade setup of an electric fuel pump and two filters down of the frame close to the tank. No more olives or fuel heaters creating problems.
 
Top