2005 C6

Long story short, after some fuel system issues, I am on my third pump (walbro kit from Racetronix). Now my car runs fine, but it seems that the regulator will not hold pressure. Once the pump shuts off, the pressure at the rail decays rapidly. Before this swap it would pressure hold like it's supposed to.

What's the long term problem with this situation? I really don't feel like taking the whole tank out a fourth time...

 

Check the anti drain back valve.....if that pump has it.

Some of the aftermarket pumps don't have it, so once the pump shuts off it will not hold pressure after the pump.

The other issue could be a leaky injector and it is draining because it possibly doesn't close all the way.

Don't think it is a regulator issue from what it sounds like.

 

Thanks. I am pretty sure it held pressure before with the same model pump, but perhaps my memory is incorrect. I'll do an injector test and see if a leaky one is my problem.

 

FYI, the car does a fuel pump prime cycle to bring the pressure back up before it starts.

 

If an injector was leaking down there would be a misfire on start up. I suggest you contact walbro to see if the pump has a check valve. With a one line fuel system, there will be air trapped if the fuel bleeds back. The air can only be purged by the injectors resulting in extended cranking.

 

@ScaryFast curious if you ever found the cause? I have the same year and same issue, also with racetronix pump. Pressure builds and then immediately drops off. Switch back to a stock pump and performs fine. Swap back to racetronix and same issues.

my gut says the regulator is fubar (but this is my second pump from them) or that the pump itself does not have a check valve like a production pump, despite being marketed as a “drop in” replacement.

for note - I also installed a DW400 pump into a spare stock module and it had the same issues - again swap back to a OEM pump and system is flawless.

what gives 🤷🏼‍♂️

 

All Racetronix C6 TU475 and TU476 modules utilize a Walbro 274 or 285 pump with integral anti-drain back valve (aka check-valve).
These modules are all bench tested to ensure they meet the proper specifications for flow and electrical.
If diagnosing the problem proves to be a challenge then installing an in-line check-valve on non-return (dead-head) systems such as the one below can help.

Alternatively, tuning software may be used to increase the pump prime time to reduce crank-to-run time.
Systems with aftermarket front-mount regulators will always bleed down and can't be corrected with an in-line check-valve.
Diagnostic procedures are available to Racetronix customers via our support forum.

Thank you.

 

@Racetronix thank you for chiming in. I have no doubt that the pumps are checked for function and pressure before shipping, but they seem to behave differently in a service environment vs a bench test.

As stated - I have installed two Racetonix pumps and one Deatschworks pump, all with the same result. I started with the DW400 pump into my stock module, but given the poor prime performance I presumed my installation was flawed. Thus I replaced that setup with a Racetronix full pump module. Each time I swapped back to a stock pump due to the behaviors I was seeing with the prime and drain back, and both times the stock perfomed normally.

Admittedly - both of these pump swaps were from three years ago, and I read online that the earlier model pumps didn’t have internal drain back valves. With the time that had passed I figured I would order a new pump last month hoping it would be a later generation and have a more updated design.

With my most recent Racetronix pump I received one week ago the problem still persists. At shutdown the pressure drains back through either the regulator or the anti-drain back valve (uncertain which just yet).

As suggested, I tried adding an external inline check valve from Fuel Lab to hold line pressure during shutdown but the results were very poor; adding the external valve between the pump/regulator and rail caused the pressure to skyrocket after a warm engine shutdown. So high that the injectors could not fire until the engine cooled quite some time later - unless I manually bled the valve on the rail to relieve pressure.

My guess is the non-return system needs a check valve between the pump and regulator (internal) so it can bleed off the expanding hot fuel/pressure from the rail/line to a given dwell point (54-58psi) through said regulator. Hence why there should be a valve at the output of the pump body (like OEM) - which you claim the Racetronix pump has. However I’m not seeing it perform in that manner, leading me to doubt whether there is one present. Again - when I swap back in a OEM pump the system works as intended.

I have dabbled with changing the prime time in the ecm from 2 to 5 seconds but that doesn’t really change the issue - as soon as the prime cycle stops all the fuel drains back. So unless you fire the car immediately you are out of luck and stuck with a long crank until the pressure builds after a few long cycles of cranking. To add - the E40 ECM does not send a prime signal on every ignition on cycle - only after a given time since the last cycle which is hard coded and not adjustable in tuning software. The only parameter that can be adjusted is the prime time duration, not frequency.

 

No true. All TI/Walbro modules both factory and Racetronix have always had Walbro DCSS pumps with check-valves.
Something is being overlooked.

With my most recent Racetronix pump I received one week ago the problem still persists. At shutdown the pressure drains back through either the regulator or the anti-drain back valve (uncertain which just yet).

A check-valve can only be used between the module with internal regulation and the fuel rails. Adding an aftermarket external regulator regardless of the brand will leak down.

All one has to do is look at the 274 and 285 Walbro pumps to confirm this.

Set the pump prime time to the maximum allowed. All customers with upgraded lines and regulator take this approach. It's simple and effective.

 

@Racetronix I appreciate you taking the time to respond and thankful for the insight. However I think you may have quoted me wrong or misunderstood my prior response.

I did add a check valve (not a secondary regulator) between the output of the pump module @ tank and the fuel rail connection as you have advised. It does not leak down with the check valve there as you cited - it spikes terribly. The results were abysmal as I stated - when the engine is warm it causes a vapor lock type of condition preventing hot restart.

Seemingly this is because the rising pressure (due to heat soak in rails) which cannot escape past the in-line check valve and return back to the tank where it can be bled off via the internal regulator.

So clearly the source of the bleed down is inside the module - so if the pump does indeed have an integral check valve (like OEM) then the only other port for leakage would be the siphon line for the passenger jet pump. Perhaps there is the culprit? Does the upgraded volume of your pump somehow overwhelm the secondary regulator allowing the fuel to bleed off there after shutdown?

If the Racetronix pumps have the same configuration as the stock pump as far as an integral check valve on the output of the pump, do you have any other insight why then they behave differently than the stock pump?

Every time I swap back the OEM module the system performs as intended. So what is it that I am missing? And by the way - my experience is not unique, there are many threads in this forum alone citing the same performance issues? 🤷🏼‍♂️ there must be a common cause ?

Lastly - if your suggestion of a fix is to increase the prime time in the PCM settings as a band-aide solution, then why don’t you add that to the advertising listing as a known adjustment required for installation rather than leaving customers to problem solve the issues on their own? I think we would all appreciate the heads up ahead of time rather than the hours of frustration from diagnosing it after the fact.

 

Interesting thread that came to an abrupt stop

I have the exact same issue with the same pump. We're you able to nail down the issue and/or find a suitable solution?

While priming the system works, it only works sometimes as pump won't prime at all when hot. Very annoying

Any input would be great

Rob

 

Racetronix fuel module?

If so, check the large Oring in the fuel bucket.
I dropped my tanks twice because of a pinched r
o ring on a brand new fuel module from them. They didn't even bother to return my phone call. I threw it out and went Fore w a dual pump and never looked back.

 

Yes, Racetronix Fuel Pump. Man, I really don't wanna drop the tank again unless last resort. But good to confirm that it only seems to be a issue with Racetronix Fuel module. I didn't see anything pinched on install.