Walbro255#342 won't run in hi flow. Normal ops?
 

I installed a walbro fuel pump last summer and before I put the cover and seat back on I drove around for a little ops check. I noticed three things:

1. The fuel pump had two modes - high and low
2. Runs in high exactly 2 minutes after car is started then switches to low mode
3. Runs in high flow mode with accelerator to the floor

Keep in mind, at that time, the the car was untuned for the pump.

Since then the car has been tuned and is running better than ever, but anyways, out of curiosity, I decided to lift the seat and cover and listen just for a general ops check and I noticed this:

1. Fuel pump only runs in high mode for 1 second (was 2 min every time before).
2. Stays in low flow mode no matter how hard I push.

The question I have for the experts is "Is this normal ops due to the cars tune for the new higher flowing pump and the demands aren't great enough for high flow operation?"

Or is this a problem and I currently run risk of fuel starvation under loads?

Thanks everyone for the input.

Steve

What afr are you running wot?

I have no idear, whatever setting the tune used.

Here are some more variables which may help:
Stock 9.8 turbo, ecu, injectors, IM, TBody, & IC; no wide band at hand and no safc.

I suspect that all this is normal operation - that the fuel pump just doesn't need to go into high flow at wot. However I won't be at ease until I know for sure from the experts.

The car seems to run great as is - fp running in "low flow" at wot.


How does the ecu sense a demand for extra fuel thereby sending extra current to the FP?

not sure if you'll get an accurate representation of what mode the fuel pump is in by listening. You stated you installed the pump in the summer. If the engine was warm when you did your test, some of the fuel in the return line may have vaporized and what you may have heard was gas bubbles making extra noise going back in the tank. In the winter time, with less under hood temperature or a cold engine, there will be less fuel vaporization and things may quiet down.

the fuel pump will switch between hi/lo mode based on engine load. With the mods you made and even the tune, the pump should still switch hi/lo just like it did on the stock setup. Nothing would have changed in relation to the fuel pump mode.

You'll need to either put a volt meter or an amp meter on the pump to get an accurate view of if/when it is switching modes, and if you have a problem.

Remove the seat and the fp access panel, turn the car on and you can clearly hear two distinct modes of operation.

Right after I installed the pump (untuned) the pump would run for exactly two minutes ( via stopwatch) after starting car hot or cold every time. It would also kick in to high mode at WOT.

Now I've been custom tuned for the pump and cams, car runs great but pump will only run in high mode for one second (vs 2 min) after starting car, and furthermore will stay in the low mode @ WOT in any condition.

I just want to know if this is normal.

I don't need to read current drawn accross the pump because with the seat and access panel off you can clearly hear the two modes of operation

no, it is not normal for your pump to run in a reduced voltage state at WOT at all conditions.

Thanks, thats what I wanted to know.

I will now troubleshoot

I guess I now need to find out if it really is flowing in low flow @ wot, this time without using my ears. I'll have to use a meter with long leads and check for either 12vdc or hopefully 14vdc at wot.

I got to get a good evo tech manual. I dont know where to tap off for a voltage check except at the connector. I guess I could check for current (unknown) at the fuse or check the voltage at the pump connector ( without damaging the connector)

the voltage difference will be more like 5 v in low mode, and 12.5 v in high mode. Forget the leads, find a friend and stick them in the back seat (lol, or on the transmission hump since the backseat will be out of the car) and tap in at the plug going into the fuel tank. I don't have the service manual or wiring schematic, but most wires capable of carrying high amps (like a fuel pump will pull when maxed out) will be a bit thicker than the rest of the wires (like the wires for the sending unit for fuel tank level). A power lead will be 10-12 gauge wire instead of 14-16 gauge for something like the fuel tank level indication. The power wire will usually have either a red base color or a red stripe. Usually that is. Find a good ground anywhere, and all you have to do now is find the power supply wire to the pump.

Thanks for the help Ugly, I will be doing the test this weekend after I buy a meter. This is what I'll do:

1. Disconnect battery
2. Find the two larger wires in the harness, check for ground at respective pins and assume the other is power and connect a thin wire to it to then to meter lead.
3. Reconnect plug
4. Connect battery, put meter on dash and start car and take readings.

I will post results here since probably few have done this and would be good science to go on record in the threads.

I did a study on my fuel pump voltage at idle/normal driving and WOT. The meter I used was a cheap $30 unit so the actual reading may have been off slightly. However the differences between high and low mode should be fairly accurate, just not precise. The reason I did this test was in fear of the pump not going into high mode properly. Turns out to be paranoia.

Idle/normal driving - 8vdc
WOT - 12 -13vdc

The strange thing that leaves me scratching my head is that at WOT voltage went (didn't really jump there) to 12v and as the rpms increased it steadily increased to 13vdc. This is 0.5 to 1vdc beyond voltage normally generated from the cars elect power system - I think ( I did another test at the cigarette lighter were it stayed at 12vdc idle or WOT). The fact that there is only two modes of operation leaves me cluless with this part - It's like high flow is a variable operation mode depending on demand/supply (not voltage generated either).

Conclusion: Although this study may be useless to others and a waste of thread space, furthermore, despite unexpected readings, I can finally be at ease because before I thought there was a possibility of fuel starvation in low mode at WOT.