1987 K100RT
How do I test/troubleshoot the FPR? I’m on this quest to resolve a bit of rough acceleration and sub-par fuel consumption (35-38 mpg US driving like the old man I am). Thus far:
Temperature sensor tests good (2.5k ohms at 66°F)
FPR holds vacuum (ie vacuum line and FPR diaphragm function as expected)
No visible fuel leaks at FRP
Fuel filter good, no restrictions
Fuel pressure: 32 psi (low)
Fuel pressure with fuel hose between FPR and fuel rail (return line?) clamped: 80 psi

What else should I be checking before throwing money at the problem?

Dave

with guage connected , t piece, in line with fuel rail 
observe if pressure holds after turning off the motor .

if it dissipates quickly ie in under a minute to near zero then one would have to consider the seat - valve in the fpr is worn or injectors actually leaking  .

pressure should be around 2.1 - 2.5 bar   although i have seen lower , but under 2 bar is dodgy 

if this is all ok ...one would have to consider 3 things 

atomisation at injectors ...ie dirty 

airflow meter bypass may need resetting  after doing injectors and valve clearances 

air leaks through induction path ....(zpipe cracked ?) 

just some thoughts

charlie99 wrote:with guage connected , t piece, in line with fuel rail 
observe if pressure holds after turning off the motor .

if it dissipates quickly ie in under a minute to near zero then one would have to consider the seat - valve in the fpr is worn or injectors actually leaking  .

pressure should be around 2.1 - 2.5 bar   although i have seen lower , but under 2 bar is dodgy 

if this is all ok ...one would have to consider 3 things 

atomisation at injectors ...ie dirty 

airflow meter bypass may need resetting  after doing injectors and valve clearances 

air leaks through induction path ....(zpipe cracked ?) 

just some thoughts

Many thanks for your comments. I cannot determine if the fuel pressure bleeds off over some period of time since the tester holds the max pressure. For example I just checked the tester and it still reads 32 psi and I had done the test four hours ago.

I have not checked the atomized pattern of the injectors given they would be working with below specified operating pressure. No injector is leaking.

I am clueless on the AFM bypass and how one would go about resetting it. Please forward me info on this process.

I used starting fluid and found no air leaks. FWIW, z-pipe was replaced maybe a year ago.

Dave

davemadsen wrote:(...) I cannot determine if the fuel pressure bleeds off over some period of time since the tester holds the max pressure (...)

Use a cabletie to hold the pressure release button down? Just as long as it's not a white one

Fuel pressure goes nowhere with the pressure relief button pressed, the fuel just sprays out the relief valve.

Oh well. I thought it might be similar to a cylinder pressure gauge where you can hold the relief button down. It doesn't give you a good reading like that mind

I replaced the FPR (with a Standard PR134 - OEM substitute I read about on the forum) and the old girl was back to idling, accelerating, and cruising like the old days.

good result ..
ride on !!