Tech question for an LS swap (1 Viewer)

[adman02]

I'm trying diagnose a lack of power issue and would appreciate any ideas or advice.

Vehicle - 1988 Toyota Landcruiser
Engine - 2006 LM7 (returnless fuel rail; corvette-style filter FPR at/near the tank; I also have an additional fuel filter between the fuel pump and the corvette-style filter/FPR)
Fuel pump wire is grafted into stock harness to control fuel pump; it is not connected directly from ECM to the Fuel Pump

Issue - I’m experiencing low power under load/at high RPMs; I measured fuel pressure at the rail. At idle it’s 58 PSI exactly; at high revs (~3-4K) the fuel pressure drops to 20 PSI.

I think there are three possible causes for the low fuel pressure:
1. One of the two fuel filters is clogged (could be, but why good pressure at idle and low under loads? Need to get my a$$ under the truck and check)
2. Stock fuel pump is old/weak (do fuel pumps die suddenly or just weaken over time?)
3. Stock toyota body harness wiring/relays is causing a delay in fuel pump signals/PWM (should I connect the fuel pump wire directly from ECM to Fuel pump?)

I'd appreciate any advice you LS swappers can provide.

 

[lt1fire]

Realistically it could be any of those.

With you using the stock fuel pump I wouldn't imagine the stock wiring is an issue.

Fuel filters are cheap so I'd start with replacing those as a clog can cause this.

This can also be a fuel pump starting to go bad.

Start with the filters though.

Did this start after the swap or have you been driving with the swap fine for a while and it's just starting to do this?

 

[adman02]

Did this start after the swap or have you been driving with the swap fine for a while and it's just starting to do this?

I've only been done with the swap for about a month, so probably safe to say it's always been doing this. The intermediate fuel filter is serviceable, so I'll take that apart and see if there's junk in it. If that's not it, I'll escalate efforts.

 

[NCFJ]

I agree with Al, go for the filters first.

Past that, I always hook up the fuel pump direct to the ECU. I also run a dedicated ground to the fuel pump from the battery. Get a proper in tank fuel pump. Tanks Inc. is where I get my set up, comes with an adjustable fuel tray as well.

 

[mtweller]

Is the stock pump designed for 58PSI? Obviously check the filters, but my money is on the pump / wiring / stock capacity. I'm just not sure of the stock pump's capacity, but Stan or Matt probably can tell you if the stocker SHOULD be able to support that kind of flow. I'd go with a retrofit solution like Stan recommended above either way, that's what I did when I upgraded from a Bosch external pump I had running the 2FE in my truck.

Don't keep trying to run it like that because you might burn a piston going lean!

 

[adman02]

Get a proper in tank fuel pump. Tanks Inc. is where I get my set up, comes with an adjustable fuel tray as well.

I'm running the stock tank. Does Tanks Inc have a setup that will fit it? I was also looking at a Delphi FE0486 on RockAuto as a direct replacement.

 

[NCFJ]

yes

 

[SFROMAN]

One real cool truck that I saw on YouTube was to blow out any new fuel line you use. The guy blew aur into the new fuel line he was using and blew out a bunch of rubber pieces out the other end from when it was cut.

I just thought it was smart and simple to do. I’m going to replace all the fuel lines in my truck to chase down a fuel issue with my sniper. I plan to blow out all fuel lines with air before connecting them to the Holley efi.

It’s probably not the issue in your case but worth doing.

 

[cruisermatt]

Stock pump is fine when set up correctly. You said it was running fine with the 3FE and your truck only sat for a few months.
You said on the other thread the fuel pressure is 58psi at idle and drops to 20psi as soon as throttle is touched. Did you ever double verify the lines are correct on the FPR? Did you try another FPR?

 

[mtweller]

Stock pump is fine when set up correctly. You said it was running fine with the 3FE and your truck only sat for a few months.
You said on the other thread the fuel pressure is 58psi at idle and drops to 20psi as soon as throttle is touched. Did you ever double verify the lines are correct on the FPR? Did you try another FPR?

On the Corvette filter with built in regulator, IIRC, it's all or nothing - if you connect it backwards it won't flow at all. I think I got it wrong initially and had to swap the lines. Wow, my memory is crap.

 

[NCFJ]

Wow, my memory is crap.

CRS my friend, I've had it for years Just wait until you write things down so you can remember, but can't remember where you put your note book.

 

[adman02]

Stock pump is fine when set up correctly. You said it was running fine with the 3FE and your truck only sat for a few months.
You said on the other thread the fuel pressure is 58psi at idle and drops to 20psi as soon as throttle is touched. Did you ever double verify the lines are correct on the FPR? Did you try another FPR?

I’m 99.9% sure they’re correct. I had them reversed when I tried the first start. Tried to start multiple times and nothing - no fuel to the engine. Reversed the lines and the truck started the first try. I haven’t touched them since.

EDIT: mtweller beat me to it.

Have not tried a new FPR.

 

[adman02]

Update: if you guessed clogged fuel filter, you WIN!

Started diagnosing the problem today and went with the easy stuff first. Removed and disassembled my intermediate fuel filter (between tank/pump and FPR/filter) and found some rust issues. Cleaned it out and FP is 58 at idle and 58-ish at high RPMs.

Pics

Now to address the rust in my tank...

 

[lt1fire]

What do I win

 

[adman02]

What do I win

You did call it - second post/first reply. You get a thumbs up! (I burned through all my prize funds with this build; sorry).

 

[lt1fire]

You did call it - second post/first reply. You get a thumbs up! (I burned through all my prize funds with this build; sorry).

Lol glad you got it figured out

 

[adman02]