FP TRIP - low pressure

[TrackScotland]

2015-07-25 17-44-46 plus 0h00m00s S6#1105 FEE_SLS_Round4_final.SD

LOG1 - CAL04 Cut

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Hi, first post on here I think!

Fee is having some fuel pressure issues when her car... GC8 impreza, 2.35l

A brief history:

• Fuel pump fuse blew 1 week ago. Replaced and ran fine for 10lap race.
  Fuel pump fuse blew again this morning. Replaced twin 044's with 2x new 044s.
  On high boost (CAL03 up, so ~1.6bar up) she is now get a limp triggered - FP LIMP.

Looking at the logs shows relfp1 dipping below 3000mbar as boost (map1) climbs.

Poss a very newbie question, but can someone explain the relationship between FP1 and RELFP1 (relative FP).

Any suggestions on why the car will be struggling to make desired FP?

• FPR on the way out?
  Vac leak on line to FPR?
  Pumps not quite up to it?

I've included two log files, and a cal file.

17-44-46 - Limp mode in Cal04
17-45-03 - Does a lap in Cal01/02 then presses 05 cal and immediately trips LIMP mode.

Any help would be appreciated :S PS - I'm not there to check anything, so its a little awkward.

[RICE RACING]

Your FP LIMP is happening because you have this set the below
3000mb relative fuel pressure (this is FP - MAP)



The engines fuel pressure in inverse of MAP, so this suggest to me you have a FUEL PRESSURE REGULATOR problem.
*possibly a leak in the line/fitting* (most likely)
If it were electrical then this would be stable until very high current draw under the effect of increasing positive boost pressure, which is not the case in your car see picture below. The relative pressure is a reverse mirror image of the MAP signal virtually.



Lucky for you this is set, which is saving the engine (Lean on load limp)



On a side note the Bosch 044 draws a 'stupid' amount of current! it really needs each pump with its own separate power feed and fuse's on each battery + feed.
They really will blow any OEM power feed easily I have found, but this I believe is not your issue as what is happening is going on at trailing throttle too, the relative fuel pressure should stay flat since it remember is FP-MAP (so should always stay at your target above 3000mb) don't confuse this with you gauge reading you are setting it too, engine off power the pumps and set to 50psi gauge pressure (= ~ 3400mb) give some margin to you rel FP trip minimum 10% is normal for example.

FIRST STEP:
Make sure you rel FP is pretty much flat when you are revving you engine from trailing throttle to a full throttle blip, if so then you have a FPR (fuel pressure regulator that is working or hooked up correctly) if not then you need to solve this first.

[TrackScotland]

Thanks,


Will pass on info.

She gave a brief try of a few things lastnight.

new pumps earlier....
new earths to pumps
bypass filters for a short test

She ran SMON with relfp1 this morning, and it wasnt flat, and has since sourced a new FPR.

Will see whats what when I hear back.

[TrackScotland]

No change, still FP TRIP when significant boost is added.

New Pumps
New FPR
With/Without filter
Vac line to FPR checked - no damage

Next step re-wiring both pumps

[TrackScotland]

New Pumps, + re earthed
New FPR
Filters ruled out
Changed vac lines
Rewired pumps completly

Still hitting FP trip on boost.

Will get it into the garage next week.

Mechanically there is only the lift pumps left to change, but I cant see that being an issue. The cut happens as soon as boost is introduced, not after a while where the swirl tank could have been drained (if lifts were down on pumping rate)

[pavlo]

I think you have 2-3 problems

I believe partly the problem is caused by running 2x bosch 044 pumps at idle where you are trying to set the fuel pressure at 4 bar. At idle there is not enough flow in one FPR to regulate the pressure when 2x044 pumps are running. This means that you set your pressure at say 4 bar but when the injectors take some of the excessive flow it regulates down to more like 3.5 bar.

You may also have a lift pump problem I believe as a general loss of pressure on short bursts is accompanied by a critical loss of pressure when stringing together a a longer pull, however this coincides with an increase in boost with cal override and a loss of overall fuel pressure, so a supply issue of some sort.

A single bosch pump will do about 540hp worth of flow out the box, and about 580hp worth if you remove the original Bosch non return valve which only has a 4mm orifice through which all the fuel must flow. If you lightly pressurise the input so it's not drawing any low pressure on the suction side this rises to about 610hp worth when running 0.77 lambda.

The first step is to check the pressure with just one pump running, and the other feed blocked if a non return value is not fitted.If the actual set point is only 2 bar then you are never going to get this to work! I would also do a flow test as Andy F suggested.

fee-fp.png (97.38 KiB) Viewed 24592 times

[TrackScotland]

Thanks Paul

Will relay this info to Fee, who'll then get it checked out.

[TrackScotland]

Update:

Steven (SD Motorsport) basically changed everything with the fuel system, and complete re-wire of pumps. I think it was a host of small issues combining to give the low fuel pressure at boost.

Low voltage to pumps - pumps weren't wired individually, and earths had some flaky connections due to previous fire extinguisher corrosion.
FPR (new!) wasnt tracking map sensor/boost increases correctly.
Lift pumps were not doing anything
one 044 was a bit lazy