VT V6 (non-supercharged) power issues under load

[kornchief313]

Hi team,

I have an issue with a VT V6 non-supercharged. I 'think' it is the fuel pump.

When starting the car, it idles okay but when putting load on the throttle, it bogs down. It will keep bogging down and go to stall if I don't lift off the throttle.

There is also a yuck, possibly rich used fuel smell from the exhaust when revving heaps.

If I get the revs through the bogging and at high revs (>3.5k) it will run reasonably okay. It seems to bog when WOT from idle to 3.5k revs. If I pump the throttle through the idle to 3.5k revs, I can get it through the bog stage and keep the revs up. If I WOT, it will bog and look to stall.



I have checked spark plugs, leads, air, checked coils (as I have a new tester coil). All of which are good.

I am down to fuel related. I changed the fuel filter a year or so ago with an SCA, so will probably need to replace that and test again.

I noticed a small drip of fuel from the fuel inlet line to the passenger side fuel rail, so I cut the split off and reconnected the fuel line, but still having the same issues.



The other test that I have done is a Fuel Pressure Test, with the following results.

I put the fuel pressure tester on the fuel inlet rail, before the fuel rail on the passenger side of the engine.

When putting the car to ignition, it went to just under 2 BAR. Probably around 170-190kPa. (see image below)

When starting and idling, it stays around the 170-190kPa.

When putting the throttle under load and having the bogging symptoms, it reduces to 130-160kPa.

The manual specifies it should be 290-410kPa or almost 3 BAR for non-supercharged.

My question is, does this look like a fuel pump and/or filter issue?
Should the fuel pressure kPa increase or decrease when increasing the revs?
Should the kPa sit at 290-410kPa when turning on the ignition?
Should the kPa sit at 290-410kPa when idling?

Full talk of fuel in the car so not looking forward to dropping the tank to inspect the fuel pump and fuel pump lead

 

[Immortality]

If I remember correctly the VT V6 FPR is rated at 3.5bar, with the engine under full vacuum of idle that pressure will drop some.

The simplest way to test is to start the engine, remove the vacuum hose on the back of the FPR and you should see 3.5 bar (or close to) fuel pressure, than reconnect the vacuum hose and the fuel pressure should drop maybe .5 bar .

 

[Vin999]

Hi team,

I have an issue with a VT V6 non-supercharged. I 'think' it is the fuel pump.

When starting the car, it idles okay but when putting load on the throttle, it bogs down. It will keep bogging down and go to stall if I don't lift off the throttle.

There is also a yuck, possibly rich used fuel smell from the exhaust when revving heaps.

If I get the revs through the bogging and at high revs (>3.5k) it will run reasonably okay. It seems to bog when WOT from idle to 3.5k revs. If I pump the throttle through the idle to 3.5k revs, I can get it through the bog stage and keep the revs up. If I WOT, it will bog and look to stall.



I have checked spark plugs, leads, air, checked coils (as I have a new tester coil). All of which are good.

I am down to fuel related. I changed the fuel filter a year or so ago with an SCA, so will probably need to replace that and test again.

I noticed a small drip of fuel from the fuel inlet line to the passenger side fuel rail, so I cut the split off and reconnected the fuel line, but still having the same issues.



The other test that I have done is a Fuel Pressure Test, with the following results.

I put the fuel pressure tester on the fuel inlet rail, before the fuel rail on the passenger side of the engine.

When putting the car to ignition, it went to just under 2 BAR. Probably around 170-190kPa. (see image below)

View attachment 212201

When starting and idling, it stays around the 170-190kPa.

When putting the throttle under load and having the bogging symptoms, it reduces to 130-160kPa.

The manual specifies it should be 290-410kPa or almost 3 BAR for non-supercharged.

My question is, does this look like a fuel pump and/or filter issue?
Should the fuel pressure kPa increase or decrease when increasing the revs?
Should the kPa sit at 290-410kPa when turning on the ignition?
Should the kPa sit at 290-410kPa when idling?

Full talk of fuel in the car so not looking forward to dropping the tank to inspect the fuel pump and fuel pump lead

that kpa pressure of 290-410 is for the supercharged, standard pressure at ignition on is 270-350kpa.
anything lower would indicate a possible restriction somewhere along the fuel system, even pump is on its last legs

 

[mechanic]

Do a fuel flow test to check for restrictions.
Take the fuel line off at the engine and put it into a jar or bucket. Turn on the ignition and fuel should flow out solidly for a second or two. If it dribbles or changes flow quickly there is a restriction.
The manual will have flow specs if you want to look it up.

 

[kornchief313]

that kpa pressure of 290-410 is for the supercharged, standard pressure at ignition on is 270-350kpa.
anything lower would indicate a possible restriction somewhere along the fuel system, even pump is on its last legs

Hi Vin,

When looking at the VT manual, the 270-350 is for the supercharger

 

[kornchief313]

Do a fuel flow test to check for restrictions.
Take the fuel line off at the engine and put it into a jar or bucket. Turn on the ignition and fuel should flow out solidly for a second or two. If it dribbles or changes flow quickly there is a restriction.
The manual will have flow specs if you want to look it up.

The only test i can find for the fuel is....

Wondering if anyone knows roughly how much (in a bucket in milliliters) that should be pumped out when turning on the ignition?

 

[Immortality]

That manual is wrong. The supercharged engines run more fuel pressure as it is boost referenced.

Take a good look on the pressure reg, I'm certain it will be stamped with 3.5 bar somewhere on the body.

 

[kornchief313]

That manual is wrong. The supercharged engines run more fuel pressure as it is boost referenced.

Take a good look on the pressure reg, I'm certain it will be stamped with 3.5 bar somewhere on the body.

Ill check it out and see what i can find