2008 Mack Mp7 fuel delivery problem.

Hi I have a 2008 Mack mp7 GU. I’m having a fuel delivery problem. We’ve replace the fuel filters. The fuel filter housing the fuel lines to and from the tank. The lines to and from the ecm cooler. The lines to and from the fuel pump. The lines to and from the 7th injector and after treatment fuel shut off valve. The overflow valve. The deaeration valve. The fuel pump. The 7th injector. The aftertreatment shut off valve. And the #1 injector. With all this replaced the truck hardly starts. We have the hand prime it atleast 30 pumps to get a good prime and then the truck cranks for a while. Starts hard and when the engine picks up it idles at 1000rpms for a second with no throttle response. Then after it runs for a few seconds it goes back to idle and there’s throttle response. Then the engine starts stumbling and eventually dies. We have blown out the ecm cooler. If we run a fuel line from a bucket to the suction side of the fuel pump the engine starts and runs perfectly fine. So we’ve determined the problem is on the suction side. And that it’s not the injectors or cups. We’re also not making oil or coolant. The only codes we’re getting are a mechanical failure for the after treatment shut off valve mechanical failure. The shop manager at our local Mack said this codes is coming up because the ecm sees low fuel pressure at the aftertreatment system and that’s what throws the code. We’re also getting a code for the idle validation switch. I’m not too sure what this does as a lot of our trucks throw the same code from time to time and it never seems to effect anything. Any ideas?

 

Not the pickup tube. We took the supply line off the tank and put it in a bucket with fuel it didn’t make a difference.

 

I agree with the small air suction part. But the rest I doubt. They’re napa gold spin on filters. We’ve changed filters twice. And we’ve put on 3 filter heads so far. The one that was originally on the truck, and another we had laying around, and we bought a new one. I doubt all 3 were cracked

 

Update. I’ve been sitting here thinking about it. Is it possible that it’s the fuel water separator bowl? I’ve heard of them leaking before but never seen it. It’s on the suction line so it’s possible that it would suck air. Also it’s the only think we haven’t replaced and it’s also left out of the system when we run the fuel pump out of a bucket

 

Old school water separator bowl