Thread: 3.9v8 not starting then not drivable

so have replaced the pump with a known running pump.

Guy, can I suggest you buy a NEW pump before going to the trouble of installing a second pump.
You can get Chinese ones for 30 bucks on ebay or a ridgy didge Brazilian Bosch for $100.
And make sure you use the new filter sock even though its a bugger to fit in the fuel sump.
Regards Philip A

So what pressure should the fuel be at, at idle and also under load? or what should the minimum be.

Most system including 14CUX run on 2.5 bar 36PSI above inlet manifold pressure.
That means that at full throttle it is 2.5 bar but at idle is around 2bar or 29PSI. disconnecting the vacuum line on the regulator should cause the pressure to rise on idle.
I read this from the BoschFuel Injection and fuel Management book.

To test fuel delivery from the pump , pinch off the return line and pressure should rise to about 4bar.
Regards Philip A

We put a t piece in just before where it goes into the fuel rail - there was already a connector there so I am assuming this is where it was previously checked. At idle its about 29psi, but drops away under load, and dies about the same point in the street with a reading of 20psi, well below the required 36psi.

Time for a new pump, think I'll just get another in-tank pump and keep it standard. The last one lasted around 3 years, but it was an aftermarket one - don't know if thats good or bad.

Originally Posted by GuyG

We put a t piece in just before where it goes into the fuel rail - there was already a connector there so I am assuming this is where it was previously checked. At idle its about 29psi, but drops away under load, and dies about the same point in the street with a reading of 20psi, well below the required 36psi.

Time for a new pump, think I'll just get another in-tank pump and keep it standard. The last one lasted around 3 years, but it was an aftermarket one - don't know if thats good or bad.

Think you might find the fuel pressure reg is cactus. The drop in load is due to more fuel demand. As vacuum drops in the manifold the regulator closes to maintain the set pressure in the rail.
The fact it continues to drop indicates it's stuck or has something stuck under the seat like oooh let's say a chunk of rust from the fuel rail.
It's the same result as running out of fuel and pump starts sucking air basically.

As long as the pump isn't sucking air, the fuel reg will maintain a set pressure in the rail unless demand starts outstripping supply, which, in a 3.9 is unlikely to ever happen.

Cheers

Andrew


I am not a moderator, I am a human being!!!

What other symptoms would a cactus regulator give?

The original pump that was in the car had to be replaced as it couldn't supply enough fuel for the motor after it was rebuilt.

Originally Posted by GuyG

What other symptoms would a cactus regulator give?

The original pump that was in the car had to be replaced as it couldn't supply enough fuel for the motor after it was rebuilt.

High fuel return flow. Stuck regs from a rusting fuel rail is fairly common. I've had to clean mine on a couple of occasions, the second one being a quick removal in a lunch break at my former diesel engineering employ. Ran the sandblast gun thru it and got a shock how much loose crud was actually in there.
Along with this the injector filter cups will also be full crap. injector tip pressure will be a lot lower again.

Pull the fuel rail and injectors and check it out. Pretty easy job and being finnicky, you could still have it knocked over in 2 hours.


I am not a moderator, I am a human being!!!

I might suggest that before you do any more messing around,that you actually do a fuel volume test,and check that the fuel pump is actually supplying the correct amount of fuel,and not just fuel at a specified pressure.
Take a fuel line off and put the end into a container,and check how much fuel the pump actually pumps whist cranking for 30 seconds at least.Normally it is fuel delivery volume that fail,and not pressure.Have seen too many mechanics caught out by this over many years.Always one of the first tests I carried out,when I was working in the industry.
Just another thought,you never mentioned whether you actually checked the fuel in the tank for contamination,seeing that the problem occurred just after you had refueled.

Wayne