Fuel Pressure Drops after shut off

[LiquidX]

I won't be able to do that until tomorrow but I will get that log up. I'm assuming the car needs to be cold for this long?

 

[boostNmetal]

Here is what you want to do:

I noticed from the mods in your profile that your Walbro 255 is not re-wired. I did this mod on my car and it causes the fuel pump to run as soon as the ignition is turned to "ON". The trick is in selecting a +12 volt power source for the relay coil (that you will add).

Grab this stuff from your local automotive store:

- 10 AWG braided wire that will reach from battery to trunk

- inline fuseholder (if it has wire attached to either end, ensure the wire is at least 10 AWG)

-30 amp fuse for that fuseholder

- 12 volt (coil) relay

- 16 AWG wire to connect relay coil

- connectors for battery, ground, and connectors for the relay prongs.

- a few self-tapping screws

Run the new wire from the battery to the trunk. Install the inline fuseholder and fuse within 10 inches of the battery. Find a +12 volt positive source from the factory fuel pump/fuel level sensor plug which is on when the ignition is selected "ON".

Once you have found your +12volt source, splice into the wire with 16 AWG wire and connect it to the relay positive COIL terminal. Connect the Negative coil terminal to a solid chassis ground.

Now connect the 10 AWG wire coming from the battery to one terminal of a NORMALLY OPEN contact on the relay (a contact which is open circuit when the ignition is OFF and has continuity when the ignition is ON.) Connect a piece of 10 AWG wire from the other side of the contact to the POSITIVE wire of the fuel pump. Connect another 10 AWG wire from the NEGATIVE wire of the fuel pump to a solid chassis ground.

I used crimp-on 'spade' type connectors, they work nice. Use a self-tapping screw to secure the relay to something in the trunk. It doesnt hurt to tape the terminals with electrical tape to avoid shorts if something happens to come in contact with the relay.

Congrats! You have just re-wired your fuel pump!

Your problem is gone, since you can select your ignition 'on' for a second or two before cranking... Basically what you've been doin by quick-cranking but this will save your starter and flywheel wear and tear.

Hope this helps... PM me if you have any questions, I did this on a 1G but it will all be the same for you except for maybe +12 volt relay coil tap-in.

 

[LiquidX]

A fuel pump rewire is something in my future but tapping it so it turns on with the key in the "on" position is only masking a problem which is not what I'm wanting to do. I prefer to find and fix problems. Props on the install write up however and I will keep note of that as well.

I honestly have a choice if I want to fuel pump to turn on when I have the key turned to "on" with just a button click but I want to figure out what the problem is

 

[boostNmetal]

I would be clicking that button right away then. Your starter and flywheel were not designed to get "bumped" a few times before every start-up. At least its a temporary fix in the meantime.

 

[LiquidX]

It's a little hard to do without a lap top all the time especially when trying to diagnose the issue when you need the fuel pump off

I'll be turning it on tomorrow though after I get some logs done.

 

[LiquidX]

Well I got my ICS and Lrndidleadj taken care of. Just needed to screw out the BISS and let the ICS adjust itself closed.

I'm still having hard starts now even with the fuel pump turned on. I have 2 logs for you all to look at. The second one is where the first one left off so you can see the full 600 or so seconds.

 

[BIRDCLAWTSi]

I dont know if you still have the stock feed line or not , If you do you can build pressure in the system, Then pinch off the feed line and see if it still drops.

 

[Calan]

Looking at the second log, your idle is still off. It's a bit on the high side, and your low fuel trim and ISCPosition is off. By the end of the log, ISCPosition finally drops to 39, but RPM's are increasing to 1500.

I think the fact that the car is still a bit hard to start even with the pump on shows that the pressure drop-off in the rail isn't an issue. With that said, it also looks like you were only cranking for about 1-1/2 seconds before it fired up, which I would call a borderline "hard start" for a heavily modded DSM.

To maybe get it a bit closer...

I would zero out the MAFComp and fuel trims, and then observe the LTFTs and see if the deadtime looks reasonable. (Here is an excerpt from the old link manual...not sure if it's in the new one or not):

"1. Car must be fully warmed up then must be operated at cruise for about 10 minutes followed by idle for 5 minutes to get stable LTFT values.
2. Compare the LTFT at idle and cruise. You want both to be right about zero (+/- 5% or so).
3. If the two are about the same, dead time setting is good.
4. If they are equal but non-zero, adjust the global setting.
5. If idle LTFT is more positive than cruise LTFT, increase the dead time, less, decrease."

Note: The only part I'm not sure I agree with is step #4. I would always set global to correctly model the fuel delivery, and assume that any errors are due to a modified air intake system.

Once DT looks good, adjust the MAFComp to get CombinedFT as close to zero as possible, and then see if you can get the idle down to around 850-900 with the BISS.

 

[LiquidX]

In the second log or maybe towards the end of the first I did reset my fuel trims in hopes the two values would just drop down. I still need to go back and adjust some stuff. I was just happy I got the numbers down though. How about the global and dead times for the 1250s? They seem very high to me.

 

[Calan]

Global is just a little lean...the calculator comes up with about -64% for a 2G with stock pressure.

The DT does look a bit high to me, but with these larger injectors, I've seen people with it all over the place over on the link forum. I have mine set to 540us, but I'm not sure it's exactly right.

 

[LiquidX]

I'll have to see what i can do about it tomorrow or saturday

 

[Spanky_DSM]

liquid, did you ever get this resolved?

 

[foxracing4500]

if having a FPR causes the car to need to crank a little more during start up why not make a primer switch? wouldn't this kinda fix the problem?

 

[PrimerPLus]

I had this issue. Turned out the o-ring on the fuel pump was the wrong size. Replaced it with a bigger thicker one and fit nice and snug. Also the white top hat thing that goes on after the O-ring was cracked. Replaced both of those and now I hold fuel pressure for well over and hour and it starts in 1 or 2 cranks now

 

[Spanky_DSM]

Will a bad sending unit gasket cause fuel pressure loss because i know mines a bit torn up.

 

[PrimerPLus]

I would replace all that is broke.
Do you have stock fuel pump?
Check it and see if the top hat is broke, maybe the o-ring has torn. It should fit nice and snug.
This may be weird but after I installed mine with new parts I blew as hard as I could into the line the takes fuel to the rail to see if air would escape. None did so I was confident there was no leakage. It now holds fuel pressure for over an hour.

Are you using an AFPR? Or stock?

 

[curt-s]

I had this issue. Turned out the o-ring on the fuel pump was the wrong size. Replaced it with a bigger thicker one and fit nice and snug. Also the white top hat thing that goes on after the O-ring was cracked. Replaced both of those and now I hold fuel pressure for well over and hour and it starts in 1 or 2 cranks now

My setup consists of the fairly typical Walbro 255 + Fuellab AFPR, and it bleeds as soon as the pump stops receiving power. 0 psi usually within about 5-7 seconds, takes a couple cranks to start up, even with priming the pump via MMCd before I start (bleed-off takes effect right away).

When it warms up, I'm going to do the same and check my pump seals and rest of the in-tank components.

 

[Spanky_DSM]

okay, i had a bad fuel pump and got one off ebay.

it was abit shorter than the oem but still fit.

3 days later i had fuel pressure loss.. i would have to crank to prime the pump and start my car.

i know my gasket for the sending unit is cracked and all but it did take 3 days for this problem to occur after the swap.

an just recently i pulled the the ebay pump and dropped in a evo 8 fuel pump and still having this problem.

so does the gasket for the sending unit affect the fuel pressure? or it all lies within the oring on the fuel pump?

Never had this problem before until i swapped my fuel pump.

 

[curt-s]

The sending unit to tank sealing gasket will not cause this problem.

 

[Spanky_DSM]

^^^^
thanks for the answer.

Will having a fuel pressure drop cause my to sputter under boost.

its real hesitant under boost.

 

[ktime]

I got to look a little more into this havin similar issues

 

[shredwin]

I'm currently having the same issue, it takes about 8 secs to start and when I shut her off the fuel pressure gauge drops to 0 in 3 secs... I have an aeromotive FPR with 1000cc pte injectors and a walboro 255hp pump... So far I have tried another FPR and it still did the same thing. I'm starting to think its the pump since it sat for a long time.

 

[Spanky_DSM]

I had this problem a while ago.

I did the fuel pump installation 3 times with same results. But what I wasn't doing was lubricating the o ring in the fuel pump to the assemble causing it to get pinched and drop pressure.

I had this problem for so long and couldn't figure it out till the last time I redid the fuel pump as my last try and lubricated the O ring with some spit and to my surprise, it now starts up first try every time.

 

[xxNocturnalxx]

I'll just add to this and say I have the same issue too. I have fic 1050cc injectors with new seals boost leak tested, wally 255 and a fuel lab fpr. My bleed off is pretty rapid, the car takes about 5-8 sec. to start. It seems the general consensus is the fuel pump o-ring, I'll give that a try.

 

[boost97gst]

I thought my afpr was causing this. Now i know. I did buy an ebay afpr but it works fine actually.
It started after the 450 install. Mine takes a day to drop to zero but it still starts right up. Dont think im going to dick with it if its working fine. Atleast this cleared the afpr for me .