Low Pressure Drop Across Fuel Injectors

EDrgr

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All,

I was datalogging a little bit last night and came across something concerning. It appears my fuel pressure is dropping at WOT to around 29-30 PSI and my AFR is creeping into a dangerous range (12.35). This is a boosted application. Also, I logged my returnless fuel pump duty cycle and it was maxed at 1.00. I have the FMS LU47 injectors and a Deatschwerks 340 pump, no BAP.

Ok, where to start? After googling, I'm going to make sure I have a fresh fuel filter in to rule that out. What would be the next step...BAP/ better fuel pump??? I've heard horror stories about Deaschwerks.
 

DSG2003Mach1

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slow down a tad

Have you logged the car before? If so was everything good then? Have any changes been made to the combo since then?

Personally I would look at alternator voltage when pressure is dropping - low voltage will send pump output off a cliff
 

EDrgr

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Thanks DSG! I have logged before and never noticed this drop. I did notice the car dragged a little to crank last night. Perhaps you're right on voltage. I logged voltage at fuel pump and it was 11.95, which I've logged before. It has never been at 12v or higher which is why I really didn't consider that. No other changes.

Eddie
 
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01yellercobra

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I would log the system voltage. Make sure the alternator is keeping up as mentioned.
 

EDrgr

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Thanks 01! I plan on logging and checking that this weekend. I tend to jump to worse case and immediately thought that the horror stories about the fuel pump were true.

Eddie
 

EDrgr

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I just checked the last log and battery voltage shows from 12.9 to 14, but actual voltage at fuel pump is showing about 11.88 when at it's highest point. At idle, it was only showing around 4.5-5 volts then as I rolled into the throttle is would slowly climb, but never over 11.88.

Eddie
 
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BigPoppa

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Voltage of the fuel pump is derived from the duty cycle. A duty cycle of 1 should be 12v. 11.88 should be ok.

How does the fuel pressure look at idle and mid rpm?
 

EDrgr

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Thanks Big! Fuel pressure at idle looks good, but starts to drop as I get into WOT around 6000 RPM. Car runs good, but I'm always afraid I'm going to hurt the motor as it's stock so I'm trying to keep the tune very conservative.
 
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EDrgr

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Ok, I just went back through LoSota's manual and it states that when pressure drop across the fuel injectors that I should look at fuel pump duty cycle as it may be maxed out. Coincidently, my FPDC does hit 1.00 as the pressure drops across the injectors.
 

03cobra#2

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Ok, I just went back through LoSota's manual and it states that when pressure drop across the fuel injectors that I should look at fuel pump duty cycle as it may be maxed out. Coincidently, my FPDC does hit 1.00 as the pressure drops across the injectors.

It's possible your fuel pressure could have always been dropping but AF is showing lean because of cooler weather this time of year.

I would look at old logs and compare.
 

EDrgr

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03, thats a really good point. I'm going back through data now to compare. I'm not sure in some of my earliest datalogging that I datalogged fuel injector pressure drop.
 

EDrgr

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I just realized that I never went back into Advantage and adjusted the fuel pump voltage table. It still has the data from a stock 2001 Cobra table.
 

decipha

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doesn't matter the kam pump voltage table will save the corrections needed to hit target delta pressure.

Only time it becomes an issue is if the ecu keep alive memory is reset and only for a short while.
 

EDrgr

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Bringing this back to the top as I just did another log yesterday.

The car runs great up until it falls over around 5000 RPMs. FPDC is maxed out around that point and fuel injector pressure begins to drop. Battery voltage is well above 13v from idle all the way to around 5800 RPM.

My plan now is to rule out mech issues first as per another thread which 01yellercobra suggested i.e. new fuel pump sock, look for internal leaks in the fuel line. I replaced the fuel filter yesterday. I plan to drill a few holes in the basket as well.

Thoughts or suggestions on anything else?

Eddie
 

EDrgr

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Just to keep this thread updated for someone doing a search, I have fixed my FPDC maxing out issues. I bought a VMP Voltage Booster and installed it. Took about an hour.

I was going to pull the tank again and dig into the basket, but thought if the VMP unit fixes my issue then it's worth a few extra dollars for the convenience.

Additionally, I went in and updated the tune as per VMPs recommendations. Adjusted the PID and lowered the FPVT by about 1.5 in each cell.

So far so good.

Eddie
 

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