98 er34 gtt replace fuel pump

[JC71]

1998 er34 gtt....

If I replace the current stock fuel pump with a 255lph Walbro Fuel Pump, will it require a remap or any other things, or will it run no different and fine?

Edited January 8, 2024 by JC71

[Duncan]

It will run fine, as the fuel pressure regulator makes sure the injectors get the right pressure, not the pump.

You should check the maximum current draw of the 255 is within the standard wiring's fuse (and therefore wire size), and if not you may want to take the opportunity to replace the factory wiring with a properly fused direct battery feed

[GTSBoy]

There are some caveats to Duncan's advice for cases where the old fuel pump has been losing pressure capability at high flow (as they do when they get old) and the thing was tuned with lower than reg pressure in the high load cells. Then it could go pig rich with the new pump. Better than scary lean though.

[tylink720]

When I did my walbro swap, my base fuel pressure increased by about 10psi, which could affect fueling a bit. I had to get an aftermarket fpr bring it back to normal pressures

[joshuaho96]

On 1/8/2024 at 6:17 AM, JC71 said:

1998 er34 gtt....

If I replace the current stock fuel pump with a 255lph Walbro Fuel Pump, will it require a remap or any other things, or will it run no different and fine?

Depends on what the interaction is with FPCM and the FPR. If the FPCM can take the higher amp draw (up to 16.5A when stalled) and the pump can handle being run at the voltages provided by the FPCM + it doesn't lose voltage at full speed then it can be a drop-in replacement. If you can't use the FPCM then most likely running the pump at 100% speed will cause the stock FPR to be overwhelmed as tylink mentions and you will need a new FPR.

[Duncan]

8 hours ago, tylink720 said:

When I did my walbro swap, my base fuel pressure increased by about 10psi, which could affect fueling a bit. I had to get an aftermarket fpr bring it back to normal pressures

That is unusual (noting you didn't say what size Walbro it is).  What was the pre and post fuel pump fuel pressure.

I have Bosch 044 in the race car and Walbro 525 in the Stagea, both with the stock fuel regulator, not issues.

BTW Josh good point about the FPCM, I assume that people bypass it when changing the fuel pump by running the fuel pump negative straight to the chassis.....the standard FPCM is calibrated to a good condition standard fuel pump so it might give unreliable results with an aftermarket pump.

[GTSBoy]

9 minutes ago, Duncan said:

the standard FPCM is calibrated to a good condition standard fuel pump so it might give unreliable results with an aftermarket pump.

My 040 is wired up to the FPCM. Was done at least 20 years ago when the stock pump died, and when the car was making barely more than stock power. Fuel pressure was fine at the low end and the high end back then.

Has stayed that way through boost ups, 25 transplants, etc. And sure, the ECU has been tuned as a result of most of the big changes, but regardless, the FPCM has worked just fine running an 040. No meltdowns, no pressure problems, etc.

[GTSBoy]

I must stipulate though, that I haven't been able to turn the boost up on my new highflow because the car was pinging and the ECU was going to panic mode, and it is quite possible that the 040 is low on pressure from great age and needs to be replaced. Maybe. Haven't had a chance to get it onto the dyno with the fuel pressure gauge etc etc, and so just dribbling it around on low low boost.

So, likely Walbro replacement might be a different story. Shouldn't be, but might be. Only going to need a 255 (341? 342? Whatever they are), and I think they pull the circa same current as the 040.

[Kinkstaah]

You should totally buy my 460 and/or 525 and do whatever Duncan has figured out so it doesn't melt

(or you may consider rewiring it to run at 14V, which is one of the most oldschooly mods in all of SAU, right up there with running 7psi all the time :D)

[tylink720]

On 1/14/2024 at 6:16 PM, Duncan said:

That is unusual (noting you didn't say what size Walbro it is).  What was the pre and post fuel pump fuel pressure.

I have Bosch 044 in the race car and Walbro 525 in the Stagea, both with the stock fuel regulator, not issues.

BTW Josh good point about the FPCM, I assume that people bypass it when changing the fuel pump by running the fuel pump negative straight to the chassis.....the standard FPCM is calibrated to a good condition standard fuel pump so it might give unreliable results with an aftermarket pump.

I only put in a 255. Yeah I thought it was strange too. I had seen lots of posts on here saying the stock reg was good for mild pump upgrades. Possibly the oem fpr was clapped the entire time and I only checked fuel pressure after installing a new pump

[Dose Pipe Sutututu]

19 minutes ago, tylink720 said:

I had seen lots of posts on here saying the stock reg was good for mild pump upgrades

and many of these posts don't mention anything about fuel pressure either  

I am certain if you put a fuel pressure sensor on most factory reg with bigger pumps/injector setups, you'll see unfavourable fuel pressures 

[GTSBoy]

1 hour ago, tylink720 said:

I only put in a 255

39 minutes ago, Dose Pipe Sutututu said:

I am certain if you put a fuel pressure sensor on most factory reg with bigger pumps/injector setups, you'll see unfavourable fuel pressures 

255 should have been fine. Mine worked just fine (as in, fuel pressure is/was correct) with similar sized 040.

[Dose Pipe Sutututu]

2 hours ago, GTSBoy said:

255 should have been fine. Mine worked just fine (as in, fuel pressure is/was correct) with similar sized 040.

log the fuel pressure vs. manifold pressure on a spirited drive, I believe you'll see unfavourable results.

[GTSBoy]

7 hours ago, Dose Pipe Sutututu said:

log the fuel pressure vs. manifold pressure on a spirited drive, I believe you'll see unfavourable results.

Don't need to log it. Stood next to the car holding the fuel pressure gauge in hand as it was run across the full load range. It sat where it was supposed to. Was 20+ years ago though....

[Dose Pipe Sutututu]

9 hours ago, GTSBoy said:

fuel pressure gauge in hand

liquid filled?

If so, yeah.. use a proper sensor and log fuel pressure vs. manifold pressure. I doubt you'll see a consistent 3bar delta between the two, this also applies to aftermarket regulators, albeit the issue is less evident. 

[GTSBoy]

Well, the main risk with going to a bigger fuel pump is losing control of pressure at idle or low load because the FPR isn't able to flow the juice. So, if you manage to see your normal 43ish psi when you expect to, and ~11 psi or so less than that at idle with the sense line connected, and it's not wandering too far away from 3bar + boost at the top end, then you can't really fault the stock FPR (or any other FPR) if it wanders around a little bit in between. The FPR is a mechanism after all, and it will have hysteresis and a mechanical response time, so dynamics will always result in some local non-linearity and under and overshoot behaviours. You could gather a lot of data from logging that would make your eyelashes curl looking at those details, but provided it hits the 3 main points (or really only 2 main points if you discount the sense line disconnected test point) at steady state, then the reg is doing what it is designed to do.

With a low power RB, coming onto boost in the 2300 rpm range (actually probably worse than that, given that it was still a 20 when I did this), you can see the fuel pressure gauge go from reading 3 bar + low load vacuum (so, what? About 26 psi?) up to ~43 psi when the throttle is opened up full but no boost yet, and then a few psi creep in followed by the very rapid ramp up to 3 bar + boost, which in my case was probably 12 psi at the time, so 55ish on the gauge. All of that is fairly easy to follow even without being able to see the tacho, and happens slowly enough that what happens and when it happens either makes sense, or if it doesn't then it indicates a problem. And on a typical 6 bar gauge it all happens right around the top** of the dial. On a 10 bar gauge it's a little more compressed to between about 25-40% of full scale, but that's still quite readable.

I'm used to doing pitot measurements in process ducts where I have to pinch the silicone tubes down to damp out wild 2 kPa fluctuations in total pressure while the dynamic pressure in only about 50 Pa or so. By comparison, measuring fuel pressure on a car is something I can do without even needing a coffee first!

 

**And what I meant here was like at the 12 o'clock top, not full scale over on the lower RHS.

Edited January 18, 2024 by GTSBoy

[GoHashiriya]

When I re-wired/installed my Walbro 255 the fuel supply line in the engine bay popped off. Check them all thoroughly during the first few drives.