What next - injector straws?

[Shelbynut]

I've been away as I sold my Dodge, and this is for a friend. He has a 98 12v that has been driving him nuts for 6 months. It all started with hard cold starts. If it sat overnight, he had to give some go pedal to start. It got worse to where he had to pump the crud out of it and keep cranking. He took it to a dsl shop that builds a lot of these for street to all out pulling. To make this as short as possible this is what all they've done: Airdog, 2 different injector pumps, found a cracked head and replaced including studs, and replaced pressure relief valve on pump. It acts like it ran out of fuel on cold start, but once started it runs great. If turned off and restarted right away, no problem. Sits an hour and it cranks a little before starting. Sits overnight and wont start. He's bringing it over and told me to do "whatever I think it needs" and don't bring it back til fixed. I warned him it might come back with twins and anything else good I can think of!:-laf He just called and said they put new injectors in also. The guy wants him to try another fuel line check valve, but I don't see it helping. Its been replaced once and swapped out with another known working truck and made no difference. The only thing my meager mind can think off is injector straws are leaking down. Is there something else anyone can think of or am I thinking in the right direction?



Thanks, Dave

 

[Shadrach]

By inj straws do you mean the connector tubes between the inj line and the inj? If so 12 valves don't have them. Has the fuel shut off solenoid been looked at? Is it being pulled up properly when cold or is it sticking? It's a 2 man job but real easy to check. Shad

 

[Missouri Mule]

If they replaced the overflow valve it could be lift pump or air is getting into the system ( rubber fuel lines/especially return line, fuel heater, metal lines... )

Need to do fuel pressure test to check out lift pump and overflow valve. 20 psi on up to 25 at idle 2000rpm 30 ish. if fuel pressure is low sqeeze rubber retrun line if pressure goes up overflow valve,pressure goes up slowly or not at all lift pump.

But I think air is your problem.

 

[mwilson]

Another vote for air in the lines. I truly hope that shop did not spend all that time and money for a simple suction leak.



If it were me, and you have the luxury of tying this truck up for a few days my very first step would be this. .



After you have had it running one day the next morning I would try to prime the system before starting.



What I would do the next morning is loosen the bleed screw (plug that takes a 10mm wrench on the forward line of the fuel filter housing) and pump the primer on the lift pump. If you don't get a steady stream of fuel until you have pumped for several strokes or more then you have a suction leak somewhere.

Then if that is true I would remove the factory fitting from the lift pump and go to town to purchase a barbed pipe thread fitting and some clear tubing to fit the barb. Install the fitting on the pump and securely clamp one end of the clear line to the barb. Take a 5 gallon can of Diesel and assuming the trucks tank is not full (the return fuel is going to the tank and not the 5 gallon can in this test scenario) place the other end of the clear line into the fuel, all the way to the bottom. once in place zip tie the tubing to the handle of the can so the line can't float up and get out of the fuel. Prime the system again, run the engine for a few minutes and then leave it until the next morning. The next day go out and see if the line is still full of fuel. Then start the engine.

If it starts as it should you know then that the problem is lines, tank pick-up unit or the troublesome fuel screen/heater assembly.

If the line is empty I would then attach another line to the fuel return in behind the pump and submerge that in the fuel can. Then repeat the test above.



You have to go one step at a time, it takes time but saves a lot of money from being thrown at the truck. You have to establish if the problem is on the engine side or the truck side.

Until you figure that out you're not going to get anywhere.



This assumes that you have already checked the fuel shutdown solenoid.



Keep us posted, we will help you figure it out and give you the cheapest, best fix for the buck.



Mike.

 

[Shelbynut]

The stock lift pump is gone and replaced with an electric AIRDOG. I haven't seen the install yet, so I don't know how much stock line they have left. He did say he hears it run as soon as key is on. I've only had a 24v so I didn't know 12v didn't have the connector tubes. I learn something new every month! Not saying I'm that smart, just can't do that much anymore. I can have the thing as long as needed, he has 3 old beaters. I don't think they put a fuel pressure gauge on so I'll do that first as he wants one. Are you saying that if the shutdown solenoid doesn't close all the way it allows the P7100 to bleed down? I wasn't sure on these how they kept the fuel from bleeding out.



Thanks guys, he's bringing it over tomorrow and now I know where to start.



Dave

(I still think a set of twins would help!)

 

[Flinty]

I made this mickey mouse contraption to pressurize the tank. I put about 5psi in it and then wait to see where the fuel comes out, usually the fuel heater. The Airdog introduces more connections and therefor more opportunity to suck air. If you don't want to fab a tool up you can get a friend to stuff a rag in the tank filler neck and add compressed air that way. My way is a sure thing and you can leave it set for a while to see what develops, though. This test will not indicate a hole in the dipper tube (draw straw).



Good luck, let us know what the issue ends up to be.

 

[Missouri Mule]

No the fss will not cause fuel to leak back. The fss can disengage while going down the road or only allow some fuel in. Actually it moves the rack in p7100.

 

[Missouri Mule]

No the fss will not cause fuel to leak back. The fss can disengage while going down the road or only allow some fuel in. Actually it moves the rack in p7100.

 

[rebar]

I made this mickey mouse contraption to pressurize the tank. I put about 5psi in it and then wait to see where the fuel comes out, usually the fuel heater. The Airdog introduces more connections and therefor more opportunity to suck air. If you don't want to fab a tool up you can get a friend to stuff a rag in the tank filler neck and add compressed air that way. My way is a sure thing and you can leave it set for a while to see what develops, though. This test will not indicate a hole in the dipper tube (draw straw).

I know old thread, but I really could use your "contraption to pressurize the tank." Except Iv read to get a second cap and drill tap a 1/4" fitting and use a regulator. But my plastic cap has a raised "handle" to grab and doesn't look like enough space to drill and tap..

What cap are you using Flinty, and does anyone market and sell such a contraption?

Thanks!

 

[Joe Mc]

I found the supply line on tank module had a pin hole on the bend which caused loss of prime and was a PIA to start after sitting a few days. My fix was to install the Vulcan draw straw. That was almost 12 years back... Check top of tank/module lines with flashlight and inspection mirror for moisture on the metal lines.

 

[fal308]

I have a 24v but have a similar problem. After searching here on TDR it appears that the AirDog fuel lines tend to crack and leak. That is what has happened to mine (I hope). A temporary solution TDR suggested is to park facing downhill. That keeps the fuel from draining back and allowing easier starts. Until you can get the blue AirDog fuel lines swapped out. They are 1/2" fuel lines.

 

[rebar]

On top of finding leaks, his tank pressurizer would come in handy for us mechanical fuel pump folks when we change fuel filters to. No more pumping the primer a million times and you don't need a regulator.. This video is great..

I dont know which fuel cap this guy modified though.. He said he "cant remember" if it was a dodge.