hey there people.

ok for about 3 months i have had a going lean under boost issue issue, turns out my fuel pressure is going to base at 0 vaccume and falling under base pressure when in boost. This causes a lean condition.

Im stumped... i searched and found lots of good info about fuel pressure and went through my fuel system.

I replaced:

Pump (walbro hi psi one)
Pump strainer / filter sock
Fuel filter.
Fpr to a known good aeromotive 1:1
Changed the fpr vac source to the top front of UIM.
Put new clamps on short hose that connects pump to pump holder thing.
New clamps on the feed and return on top of the pump holder thing.

What its doing:

base is set to 40, vaccume pulls it down to 30
When i turn the key and build base pressure and then turn the key off the pressure bleeds down about 1psi per sec from 40 down to about 33 and holds there.
When i rev the car in neutral i can get 7psi boost on my boost gauge, but the frp gauge shows it goes to base when at 0 vaccume and as soon as i get into boost it falls off some to 38 or so. The new fpr does the same thing.

Whats left? im sooo lost.

Could the stock PD have failed and cause a restriction? No hoses are crimped.

 

I'd be asking myself another more important question. That would be: Why on God's green earth am I getting boost pressure when I'm in neutral????? Mom always told me that was not quite right.

If it were not for that important question above, I'd get me a Mitty Vac from the auto store. I'd connect it to the fpr and then start the engine. Then I'd look at the fuel pressure. While looking, I'd pump the Mitty Vac to supply pressure to the fpr. The fuel pressure should go up.

As I wrote the above, it became apparent to me that you have the fpr vacuum hose going to something other than vacuum. Tell us EXACTLY to a TEE , where is the vacuum hose connected on your engine? That is your problem (plus you don't get boost when in neutral unless there is something amiss.

 

So did you take the FPR vac. source from the single, turbo-side UIM nipple and move it to one of the 'front 3' UIM nipples? If you did so, I assume it's because you have about 5 million other things split off from turbo-side UIM nipple, lol.

 

yep, those are the most stable vacuum sources and where i hooked up my FPR and standalone MAP sensor lines to.

you did rewire the fuel pump correct?

 

I switched the source for the vac/boost line for testing purposes. To make sure that was not the cause. I dont have any thing T'd in my vacuum lines. my setup is very simple.

Tonight we tested things.

we took my hood off and ran a hose up to my windshield with a gauge on it to see fuel pressure when in boost.
The pressure falls off when i get into boost just like i saw when reving and getting boost in neutral.

We tested to make sure the falling fuel pressure was not from the FPR by pulling the vac hose and driving. the pressure was steady at 40 till i boosted it some. When i get into boost the pressure falls from base. So its doing it regardless of signal.

The pump was getting crazy loud tonight so we switched out to another walbro and it does the same thing. It starts quiet and gets LOUD gradually.

When we pulled the PD to check it out, the fuel pressure bled down and the fuel ran out (normal). well about 2 minutes later while we were messing with the PD we hear a "PSSSsst" and the feed line shot fuel out. FTW? we thought... soo there has to be a clog between the PD and the pump.

Between the PD and the pump there is: a rubber fuel line <> a filter <> rubber hose <> the hard line <> rubber hose <> pump

There is a blockage somewhere. There has to be. This blockage go so bad on the way home the pump was screaming and the a/f under even slight load was lean like 16s 17s.

Tomorrow we plan to replace the filter with a short piece of hard line (temp) and blow out / test the lines for a clog using compressed air. These cars are old... maybe its just a clogged line.

Will update as i find out more.

yes using a relay and powered straight off the battery which is relocated back there by the pump anyway.

 

you mom is wrong
True, and i bet it would
This is not the problem. Your logic is not based on fact.

 

where exactly are you tapping in to check the fuel pressure?

 

Have you taken the outlet from the fuel pump and put that straight into the gauge....just for testing...did it make FSM Psi?

Also, in your fuel mod list I noticed you left out fuel pump rewire...

Have you done this?

Edit - Just for reference I did what you did on your car... ran a fuel pressure tester thru my hood scoop...

I was seeing 40 psi at idle...on boost 45psi...and on heavy vacuum during decel 38 or so. That with 720/1600cc, walboro pump, rewired, stock s5 pd.

James

 

I have a aftermarket FPR. it sits over by the brake booster.
The gauge is about 3 inches before the FPR.



The only peak testing i did on the pump was to crimp the return line after the FPR. The pressure maxed out the gauge to over 100psi.

I rewired my pump. I did it when i changed the got a new pump the first time.

 

Does anybody else other than the thread starter actually believe that you should get boost when in neutral and reving the engine?

Why are you so reluctant to tell where your fpr vacuum source is?

What FACT are you talking about?

And (B) TRUE I BET IT WOULD. Well then why won't your pressure rise IF you had the fpr going to the right place?

 

Hum... I though it was not possible to get boost just by reving the engine in neutral. I though the engine would not create enough exhaust energy to spin the turbine then to create boost.

 

make your own thread asking how much boost people get in neutral revving the motor.

We did hook up a gauge and drive it and the gauge showed the exact same drop. (already said that in a my last post.)

Im not reluctant. WTH are you talking about. I stated in the FIRST post where it is. top frot of UIM. Its a commonly used source.

Have you read any of my posts or just breased through them?

After all the tinkering we did last night we narrowed down that its a clog or some sort of restriction between the pump and the PD on the rail.


Go do your homework about the boost in neutral thing and vaccume/boost sources, ya might learn something.

 

Whoo.. This could take a bit, so lets get started:

Stock turbos have been known to make a little boost on free revs. I used to be able to make about 5 or so PSI on a stocker. I wouldnt consider that to be a SOLID 5 PSI though, because it was generated with little or no load.

I couldnt agree with this statement more. Free revving to get boost and watching your FPR is the LAST method I would use to test your fuel pressure.

Thats about standard for a Whinebro..

Be nice to Hailers! He is just asking a question.

Anyways, free revving is not the best way to test for FPR operation. HOWEVER, in the interest of science, I will go warm up my FC and perform the same test in my car (I will only get about 1-2 PSI of boost though, Hybrids dont like free revving). I will post results back.

Rat

*edit* I see it does the same thing while driving.. That changes things a little.

 

We ran another gauge and watched it while driving. The gauge showed the same thing while driving.

There is a clog, the car barley made it home lastnight.

I will post my findings as i test the fuel lines that i think are hiding the block.

 

Check the in line fuel filter, although you replaced it, perhaps the filter on the fuel pump got messed up and maybe isn't filtering how it should? If that's the case, the pump might be working a little harder, which would make it more noisy, to push dirty fuel through the system. I would also check your FPR again, it should hold pressure with the key on engine off.

When you turn the key on, for two seconds the pump should turn on, to build pressure in the system. After that check to see if you still have pressure at the fuel rail, with a gauge, tap into it. If it's falling off, it's likely your FPR is skewed. It should hold the steady pressure, with the key on, engine OFF.

Good luck,
James