3.9 Help needed

Hi all, new to the site, and have been told by a couple of members that you are the guys to get some answers from. From the start i will tell you that its a speed boat im talking about so i hope i dont put people off from answering. Anyway the boat is fitted with a fully marinised rover 3.9 running the 14cux and loom, bought it as a none runner, i found it needed a new fuel pump, dizzy was 180 out and the leads were any how.
The engine would not start, the plugs were wet, bought new plugs as they looked old and still the same, turns over but no start, i found if i disconnect the fuel pump after a few turns over it fires up and runs on the pressure left in the fuel rail, pump connect and back to no start, pump off and after a few turns will run again !
Has anybody had this problem ? things check out timing, both relays injectors getting the signal required, (though i havent had them out ) cleaned all the connections and to the ecu also.
Its a though its getting too much fuel pressure, can this happen ?
Regards

Sounds like flooding to me as well.
Leaky injectors being over pressured? Regulator or injectors.
don’t know the 3.9, so that’s all I can say.

I know it’s a boat but would be great to see pics.

J

marjon said:

Sounds like flooding to me as well.
Leaky injectors being over pressured? Regulator or injectors.
don’t know the 3.9, so that’s all I can say.

I know it’s a boat but would be great to see pics.

J

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Thanks for the answer, unfortunately i havent a clue how to add pictures . lol

Does it have a regulator fitted or does the fuel go directly to the fuel rail from the pump?

just wont start said:

Thanks for the answer, unfortunately i havent a clue how to add pictures . lol

Click to expand...

That's the easy bit!
On your post at the bottom right you will see 'Reply' - click that and it will take you to a quote of your post with space below it to ............. type and /or add files/pics.
Click on 'Upload a file' and follow the instructions that will come in a box. This will let you choose pics from your own albums - follow the instructions to open that and this adds it on here.
When you have finished uploading, choose 'Post a reply' and if you have done it right it will magically appear on this thread.
My pics take a while to upload but that is because I have a very, very, very slow connection.
Good luck.

steve24v said:

Does it have a regulator fitted or does the fuel go directly to the fuel rail from the pump?

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Hi steve, Now then have i got pipes the wrong way round at all ? From the pump it goes to the fuel rail then at the end of the return is the fuel acumilator or whatever its called before returning to the tank, think this is how it is plumbed, is this correct ?
Cheers

steve24v said:

Does it have a regulator fitted or does the fuel go directly to the fuel rail from the pump?

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Hi Steve, forget about me asking about if the pipes could be the wrong way round, upon thinking it must be rite as its the device that keeps the rail pressurised ! Have read loads of past posts and a few that may apply are if the sensor on the rail is acting up the ecu tells the injectors to fire at the wrong time, does this make any sense to you at all ?
if when i disconnect the pump and turn the engine over till the rail pressure drops maybe this is why it fires up then. any thoughts ?
Cheers

Do you have a gauge to measure the rail pressure when it wont start and when it does?

J

Not sure about electrics on the petrol v8s, never had one, just thought if there wasn't a regulator it would overpressure the system.
like marjon says, check the pressure on the fuel line into the fuel rail with an inline guage

marjon said:

Do you have a gauge to measure the rail pressure when it wont start and when it does?

J

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Hi, i havent but will see my mate at a local garage and ask if i can borrow one.

No electrics involved with a pressure regulator, and the fuel pump pressure should be in the 2.3 - 2.5 bar range.

The fuel pressure regulator is mounted in the fuel rail at the rear of the plenum chamber. The regulator is a mechanical device controlled by plenum chamber vacuum, it ensures that fuel rail pressure is maintained at a constant pressure difference of 2.5 bar above that of the manifold. When pressure exceeds the regulator setting excess fuel is returned to the fuel tank.

Fuel pressure of up to 2.5 bar will be present in the system, even if the engine has not been run for some time.
Just press the Schrader valve thats in the fuel rail, if petrol shoots out thats usually okay.

Wet spark plugs is an indicator that there isn’t a spark usually, the 3.9 ignition system is straight forward but you will need a workshop manual for the EFI.

discool said:

No electrics involved with a pressure regulator, and the fuel pump pressure should be in the 2.3 - 2.5 bar range.

The fuel pressure regulator is mounted in the fuel rail at the rear of the plenum chamber. The regulator is a mechanical device controlled by plenum chamber vacuum, it ensures that fuel rail pressure is maintained at a constant pressure difference of 2.5 bar above that of the manifold. When pressure exceeds the regulator setting excess fuel is returned to the fuel tank.

Fuel pressure of up to 2.5 bar will be present in the system, even if the engine has not been run for some time.
Just press the Schrader valve thats in the fuel rail, if petrol shoots out thats usually okay.

Wet spark plugs is an indicator that there isn’t a spark usually, the 3.9 ignition system is straight forward but you will need a workshop manual for the EFI.

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discool said:

No electrics involved with a pressure regulator, and the fuel pump pressure should be in the 2.3 - 2.5 bar range.

The fuel pressure regulator is mounted in the fuel rail at the rear of the plenum chamber. The regulator is a mechanical device controlled by plenum chamber vacuum, it ensures that fuel rail pressure is maintained at a constant pressure difference of 2.5 bar above that of the manifold. When pressure exceeds the regulator setting excess fuel is returned to the fuel tank.

Fuel pressure of up to 2.5 bar will be present in the system, even if the engine has not been run for some time.
Just press the Schrader valve thats in the fuel rail, if petrol shoots out thats usually okay.

Wet spark plugs is an indicator that there isn’t a spark usually, the 3.9 ignition system is straight forward but you will need a workshop manual for the EFI.

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The engine runs until the pressure runs out of the rail, turn on the pump and it will not, the injectors sqirt and the plugs fire ! disconnect the pump and after it turns over a few times it runs again. there isnt a schrader valve on the rail !

just wont start said:

The engine runs until the pressure runs out of the rail, turn on the pump and it will not, the injectors sqirt and the plugs fire ! disconnect the pump and after it turns over a few times it runs again. there isnt a schrader valve on the rail !

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Ok, thats good no issues with the ignition system, so its fuel supply with its ECU and a few peripheral relays/sensors.

I’m sure u know this, when the ignition switch is turned the fuel pump starts for a couple of seconds to prime the fuel rail and then stops all controlled by the EFI ECU.

You don’t say what the duration of engine is running before it stops, not for very long with a V8, so maybe that is because of a lack of petrol, and either the pump isn't now running or has a issue with as it would if told by the ECU via a single signal wire from the + terminal at the ignition coil, for the pump to carry on as the ECU had bee told the engines running

If you are able to read the system schematics in the manual you will soon find the issue.
And the Schrader valve (its purpose is to bleed the air from the fuel rail) is on the drivers side 3.9 fuel rail or was when it left the factory, and I expect the item is shown in the workshop manual.

I reckon fuel pressure regulator has had it, have you tried getting it started then quickly connecting the pump back up to see if it dies?

steve24v said:

I reckon fuel pressure regulator has had it, have you tried getting it started then quickly connecting the pump back up to see if it dies?

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Hi steve, thats the conclusion i have come to, when its running i tried the pump and it literally stopped it dead. i dont know much about rover v8s but its been a fast learning curve, im good on the spanners and quite knolagable, The schradar valve the other chap is talking about isnt on the rail, the rail looks totally stock rover to me and as i have said before the pump does run from the information given by the ECU. will take the fuel return pipe off tomorrow and see if the flow is as fast as it is pumped, this should indicate if it is faulty .
Cheers pal

I don't know much about them either never had one (although ive always wanted one).
Might be talking cr4p here, but could you rig up a fuel tank/container so the fuel is gravity fed into the fuel rail? Not sure if this will give it enough pressure to run as I don't know what they run at.
Or just get an inline guage fitted

steve24v said:

I don't know much about them either never had one (although ive always wanted one).
Might be talking cr4p here, but could you rig up a fuel tank/container so the fuel is gravity fed into the fuel rail? Not sure if this will give it enough pressure to run as I don't know what they run at.
Or just get an inline guage fitted

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Yeah i think that would be a no go, will borrow a pressure gauge this week and check the rail pressure as suggested by others.

Have a look at this thread if you have seen it already.
https://www.landyzone.co.uk/land-rover/fuel-pump-fuel-pressure-regulator-problems.347158/

discool said:

Have a look at this thread if you have seen it already.
https://www.landyzone.co.uk/land-rover/fuel-pump-fuel-pressure-regulator-problems.347158/

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Maybe a Ecu problem then

This is an interesting one.

So you have a V8 on 14CUX Hotwire injection in a boat.
First question, is it running cat or non-cat?

Your problem is the engine will fire then die unless you disconnect the fuel pump then it runs until the fuel in the rail is used.

There are a number of possibilities here. The running and stopping bit can be a symptom of an inlet air leak but as others have already said the problems you describe point at fuel pressure regulator or possibly fuel pump control. What pump is it using? As long as it can deliver the correct pressure there shouldn't be too much of an issue.

What you need to understand is how the start up sequence works. It actually starts when the engine is switched off; the ecu winds the stepper to full open so there is maximum air available in to the plenum. When you turn the ignition on again, the ecu will pulse the fuel pump, about 1 - 3 seconds which pressurises the fuel rail. When you crank the engine 12v goes to the ecu from the coil negative as the ignition amplifier switches which causes the ecu to turn on the fuel pump and then energises the fuel pump relay that provides the 12v power for the injectors. Transistors in the ecu then switch ground to fire the injectors. At start up the injector pulse is longer than normal and this longer pulse is held for 3 seconds. Hopefully this will allow the engine to start and once it does, the air flow meter then feeds the air flow signal to the ecu to control fuelling and the stepper is then wound in to stabilise the idle. The short burst of higher revs on start up is caused by the time taken for the ecu to wind the stepper in to bring the revs down.

In terms of fuel pressure, if the pressure is too high the fuelling is altered and the ECU can't compensate. If the fuelling can't be controlled the ECU will go in to fault status and essentially, this means it just throws fuel in to the engine. I suspect you don't have an EFI warning light so you won't know if there is a fault or not. Normal fuel pressure should be 37psi. I believe you don't want more than 41 psi or there will be problems on standard injectors.

I think I would be inclined to look at the following:

1: Injection system earth - check and clean the main earth points.
2: What pressure is the fuel pump delivering?
3: Is the stepper working properly?
4: Check for inlet leaks.
5: What is the ignition timing set to?
6: Is the vacuumm advance on the distributor working?
7: Check throttle potentiometer. This affects idle control.
8: How does the system compensate for speed sensor and auto transmission? (these can affect idle control switching).
9: Check air flow meter: CO trim and air flow.

Hopefully that gives you a few pointers. One other thing, have you tried starting it with a bit of throttle on?

Hope that helps.