850 T5 - Running issues post fuel-pump replacement

[Cookeh]

Good evening,

I'm rather hoping I can get some help with a recent issue. My fuel pump recently died, and I bought a Walbro GSS432 to replace it with. Firstly, it is not a fake, so there's that at least. The assumption is that the new pump is fine (it does run constantly under cranking and there is fuel supply at the rail - more on that in a moment). After fitting the pump I waited around 30-45mins or so for the disturbed debris in the tank to settle and then fired the car up. It ran with no issues, crank time was normal, and it idled for 20mins. I then turned it off and restarted it, again all fine, for another 10mins before turning it off. Roll on this morning, as I walk out the door to go to work, assuming that the car will start and run fine. Lo and behold, crank no start.

Since getting home, I have tried the following:

• Floored the accelerator whilst cranking for extended periods in case of lawnmower syndrome

• Removed spark plugs and added some oil down the cylinder heads, letting head and plugs air out a bit, for the same reason as above

• Tested for pressure at the rail by removing the 17mm nut on the fuel line and turning key to PosII - there is plenty supply there, filled a 300mL jar within a few seconds. I hence assume flow rate is good

• Tested for pressure at the rail (no fuel gauge yet, and tyre gauge proved useless), but did press the schrader valve in. Interestingly there was noticeably less flow here with the key in PosII, barely a trickle

• Unplugged the MAF to rule out MAF issue and to assess it under 'default' values, no change

• Jumpered the fuel pump relay, no change

• Fairly reproducibly, by pumping the throttle prior to cranking, and occasionally via pumping the throttle during cranking, I can get the car to fire. It will then rise to 2500-3000rpm, and steadily decrease until idle revs where it just cuts out

From the above, I have frankly no idea what the issue could be. I'm fairly confident that it is not lawnmower syndrome, as it doesn't meet the criteria per se. For a smidge more additional information, one the occasions the car does fire it will die the very second I touch the throttle. This almost suggests a fuel starvation issue, but again brand new pump rated to the correct flow rate and sufficient psi.

Now then, the elephant in the room....The words "Made in the USA"... The pump is a genuine, sourced from an approved supplier. What are the chances or indeed occurences of a DoA pump?

Things I intend to check, when I have a more spare time, are:

• The condition of the filter on the pump

• The pump in general

• Attempt to acquire a pressure gauge for the rail

Where else should I be looking? Could there be a blockage in the fuel rail (solid, vapour, or otherwise?). Am I going to have to resort to pulling the rail to asses injector flow. I had the battery disconnected when replacing the pump, might it be an ECU issue (i.e. fuel trims?).

Many thanks in advance,

[jreed]

I haven't had an issue like the one you're describing, and I bet others who have more experience will be more helpful.
It does seem unusual that you're only observing a trickle of fuel coming out of the Schrader valve on the fuel rail. It could be that there is blockage somewhere in the rail. I agree that measuring the fuel pressure at the rail will be a helpful next step.

[850oldschool]

Is there a cloud of smoke when it does run? I can't tell for sure from the parts diagrams, but the 1996 turbo cars may have the same vacuum connected fuel pressure damper as the 1996 NA models. If so, (and the damper is leaky) the higher fuel pressure of a new pump may be blowing a lot of fuel through the vacuum tree.

If you do have this style damper and it's leaking you'll see and smell liquid gasoline in the vacuum hose when you pull it off.

Here's my thread:

viewtopic.php?f=1&t=97007&start=10

[Cookeh]

Thanks, oldschool, mine has an FP regulator on the rail and return line. I'll check for petrol smell this evening. I also have a fuel pressure tester on order. There is no real cloud of smoke when it does fire, nothing notably above the ordinary anyway. That being said I have long suspected it runs a bit rich on startup.

May I ask if you found many sources for these or is it really more a case of gamble on junkyard parts?

Jreed, thanks for your reply. Weirdly yesterday when trying to cobble a pressure reader from old bits and pieces there was significantly more flow at the valve, so not sure what happened there. Still same starting issues though.

[Cookeh]

No fuel in the vacuum line of the fpr. US Pro fuel pressure tester placed on the schrader valve says 2PSI (yes, I mean PSI, it is that low) on cranking. I don't entirely trust this so I'm going to stick the pressure tester directly onto the pump outlet and see what it generates there.

Low pressure causes that aren't fpr (confirmed) and aren't a duff pump (tbc)?

[abscate]

Uh oh, 2 psi isn’t going to get you far across the Severn, even if you have your choice of bridges. It should be a lot more than that.

[misha]

You can't test fuel pressure directly on the fuel pump outlet nor on the fuel supply pipe where it enters the fuel rail,because fuel pressure is determined by fuel pressure regulator(FPR) and your's is on the rail.

There is only three options here:
-fuel pump is faulty directly from the box...(it happens)
-submersible little hose from pump to housing is leaking in the tank and fuel doesn't reach the fpr
-fpr is faulty and it is returning all fuel in the tank via return line.

I assume that you didn't mixed up fuel feed and fuel return lines on the fuel pump housing during the replacement.

[Cookeh]

Seemingly I forgot to recheck the basics before diving down the rabbit hole. The fuel hose in the assembly had ruptured - will be have a chat with the seller with regards to the appalling quality.

[misha]

This is what you need for in-tank application:
https://www.lightningmotorsports.com/pr ... r10-1-foot

Pricey...but that's the only option.
Regular fuel hoses are not designed for submersible applications.

Inside of regular fuel hose is fuelproof,but outer layer will degrade pretty fast.

[Cookeh]

Replaced the hose, starts and runs with intermittent stalling at idle and no power under boost. Stuck the pressure gauge back on and I'm getting 20psi at PosII, cranking, and idling/revving under no load. Regulator, or pump?

No smell of sight of petrol in fpr after running. Jumping the relay made no difference.