91 eco not making boost or revs. need help

[TylerDurden]

With your bottle of fuel 70% full, start the engine and warm it up to operating temp. Note what max rpm it will reach. Pour in 30% virgin corn oil and shake it up. Now see what max rpm it will reach. If rpm is higher, it affirms the worn pump theory.

That's interesting... might that also indicate low internal pressure regulation?

Internal pressure is detrmined by the regulator bolt adjustment (w hammer) by the fuel inlet. I don' think that changed with the bad fuel. If there was accelerated wear and pressure loss from fuel diluted with water, i.e. vane pump, plunger, delivery valve, injector nozzles etc. the thicker viscosity fuel will restore some of that lost pressure.

AIUI, increased viscosity would raise internal pressure even if the internal wear was minimal, advancing timing that was retarded due to low pressure setting. The advanced timing would reduce injector lag and raise top rpm.

So, I'm not confident it would be a definitive diagnosis of internal wear, without a gauge to validate internal pressure is to spec.

[8v-of-fury]

This summer I will be doing the wax in the diesel for this very thing. To thicken the fuel WAY up.

[jboogie13]

so heres where im at; when i run fuel lines from a can to the filter then to the pump, everything works as advertised. When i hook everything back up to the tank plumbing, pump looses its prime and drains the fuel filter within minutes of starting. tons of air bubbles in the lines. A friend and myself think the tee fitting on the fuel filter may be the culprit? all the fuel lines that i can see look alright and when i shut the car off i can hear air being sucked into the filter.

[92EcoDiesel Jetta]

so heres where im at; when i run fuel lines from a can to the filter then to the pump, everything works as advertised. When i hook everything back up to the tank plumbing, pump looses its prime and drains the fuel filter within minutes of starting. tons of air bubbles in the lines. A friend and myself think the tee fitting on the fuel filter may be the culprit? all the fuel lines that i can see look alright and when i shut the car off i can hear air being sucked into the filter.

 I don't follow your logic  since everything was dandy from can to filter, the filter is okay. the problem is in everything back to the tank starting from the fillter.

[92EcoDiesel Jetta]

This summer I will be doing the wax in the diesel for this very thing. To thicken the fuel WAY up.

 why are you doing that? what's the matter with your fuel system?

[TylerDurden]

so heres where im at; when i run fuel lines from a can to the filter then to the pump, everything works as advertised. When i hook everything back up to the tank plumbing, pump looses its prime and drains the fuel filter within minutes of starting. tons of air bubbles in the lines. A friend and myself think the tee fitting on the fuel filter may be the culprit? all the fuel lines that i can see look alright and when i shut the car off i can hear air being sucked into the filter.

Those tee fittings crack easily and the o-rings tend to leak.

Unfortunately, you can't just bypass the tee; you need to replace the filter with the old style, to eliminate that potential for air leaking.

[92EcoDiesel Jetta]

With your bottle of fuel 70% full, start the engine and warm it up to operating temp. Note what max rpm it will reach. Pour in 30% virgin corn oil and shake it up. Now see what max rpm it will reach. If rpm is higher, it affirms the worn pump theory.

That's interesting... might that also indicate low internal pressure regulation?

Internal pressure is detrmined by the regulator bolt adjustment (w hammer) by the fuel inlet. I don' think that changed with the bad fuel. If there was accelerated wear and pressure loss from fuel diluted with water, i.e. vane pump, plunger, delivery valve, injector nozzles etc. the thicker viscosity fuel will restore some of that lost pressure.

AIUI, increased viscosity would raise internal pressure even if the internal wear was minimal, advancing timing that was retarded due to low pressure setting. The advanced timing would reduce injector lag and raise top rpm.

So, I'm not confident it would be a definitive diagnosis of internal wear, without a gauge to validate internal pressure is to spec.

 we don't know if his fuel pressure setting was low on not. I would think the setting remained the same after the bad fuel.

[jboogie13]

 I don't follow your logic  since everything was dandy from can to filter, the filter is okay. the problem is in everything back to the tank starting from the fillter.

when running from the can to the filter, the return line was routed into the can rather than into the tee fitting. once hooked back up to the tee fitting i could hear air sucking back into the filter. seeing as the other lines were all clamped (trust me, they were sealing) I have a new fuel filter to put in it anyways to eliminate any remaining contamination, and a tee is not hard to obtain. I hate the idea of shotgunning parts at problems, but im going to replace the cheap/wear items just in case.

[92EcoDiesel Jetta]

 I don't follow your logic  since everything was dandy from can to filter, the filter is okay. the problem is in everything back to the tank starting from the fillter.

when running from the can to the filter, the return line was routed into the can rather than into the tee fitting. once hooked back up to the tee fitting i could hear air sucking back into the filter. seeing as the other lines were all clamped (trust me, they were sealing) I have a new fuel filter to put in it anyways to eliminate any remaining contamination, and a tee is not hard to obtain. I hate the idea of shotgunning parts at problems, but im going to replace the cheap/wear items just in case.

 ok I see. sounds like  a leak at the tee.  those tees are expensive. I would try a new oring first if the tee has no cracks. or get rid of it all together as suggested and use a different filter.

[TylerDurden]

we don't know if his fuel pressure setting was low or not. ...

Precisely... since we don't know if his IP internal pressure was low to begin with, the test will not be able distinguish between wear or if the regulator is maladjusted.


@jboogie13:
The fuel recirculation feature doesn't provide enough benefit compared to the potential for trouble (IMO). They can also leak fuel all over the place.

[jboogie13]

If you use a filter without the recirculation fitting, where does the pump return dump fuel?

[TylerDurden]

If you use a filter without the recirculation fitting, where does the pump return dump fuel?

It goes back to the tank.

I just put a barbed union where the tee fitting was and use the older style filter.

[92EcoDiesel Jetta]

If you use a filter without the recirculation fitting, where does the pump return dump fuel?

 back to the tank. did you call the gas station to tell them about the bad fuel so they don't sell it to anyone else?

[jboogie13]

not yet, i may do that today, things have been kind of busy, getting my car back has been priority over dealing with the fuel station.

[jboogie13]

replaced the tee fitting and everything is just andy now. thanks for all the help guys!