Car now running poor

I’ve just had a walbro 255 and a new adjustable fpr fitted but now the car is running really bad. Afr’s are all over the place won’t boost properly hesitate under boost. Was running fine before new bits fitted. Will it be the fpr needs adjusting or the map tweaking

Thanks

What pump was it running previously mate?

Is it a 255lph that you’ve fitted?

Hi mate it was a uk 300lph . Yeah new one is a 255

I would say the map needs tweaking to compensate for the smaller/lower flow pump.

You will also need the FPR setting up by someone with a fuel pressure tester, which any competent mapper should have

The map shouldn't need changing if you set the fpr to the same preasure as before

You need to contact the person that put your old FPR into the car to find out what base fuel pressure they set the old FPR too. This base fuel pressure is key, as it is one of the main factors that dictates how much fuel will be injected at a given point. So you will need to have a matching base fuel pressure on your new FPR or the whole map will be off.

In order to calibrate the fuel pressure on your FPR, you will typically have an extra 1/8NPT port on the FPR housing which you can screw in an electronic pressure sensor, or you can grab an analog gauge like this one.

Once you have a fuel pressure sensor/gauge plumbed in, then you can start the engine and on idle, remove the vac line which goes to the FPR. With the vacuum removed you can now adjust the dial on the FPR to calibrate the base fuel pressure.

So if you need a 3Bar(43.5psi) base fuel pressure, either rotate clockwise/anti clockwise the dial until you gauge shows you reading 3 Bar. With that done, lock the dial down if your FPR has some sort of locking nut, then re-attach the vac line. On idle you will see the fuel pressure drop as there is vacuum pressure acting on the spring inside the FPR, dropping fuel pressure below the base fuel pressure setting, this is normal.

That's all you need to do to setup the FPR.

The other situation you may be experiencing is that the new fuel pump may be struggling up top under boost to provide enough fuel against the fuel pressure in the fuel system. Assuming that the new FPR is at the same base fuel pressure as the old one. However, the car will run fine under idle/cruise conditions.

Alternatively, you can just get a remap using your new hardware and the mapper can set a new fuel base pressure to take into account the new fuel pump and your power requirements.

Thanks guys. The old fpr was a stock one . The car has been back in twice now to adjust the pressure but still not right.

No wonder the car was running like a dog. Took it out the other day and it wouldn’t boost . So had a chance today to look at it and looks like the garage didn’t fit the heat blanket properly and the hose was resting on the hot side

Always nice when it’s a cheap and easy fix !

Yeah was getting really frustrated with it. Haven’t had a chance to take it out but fingers crossed all will be fine.

That would do it , but surely you would have noticed a boost issue straight away ?

No the car was running really bad I thought due to the fueling . But wouldn’t boost up. was due in for a remap as the garage said the fuel pressure would need setting up again.