I got a PO171 code (system lean bank 1) the other day. I changed the fuel filter and check fuel pressure, here is what I got...

96 4.9L

engine running 42 psi on both tanks
key on engine off 42 psi rear tank, 30 psi front tank.

Why do you think I get the same pressure from both tanks while running?

Before I buy a expensive fuel pump is there anything else I should check?

Am I correct in assuming that my fuel pressure regulator is OK?

If I remember right, the code came on after I changed tanks.

Thanks for the help!!

 

System lean bank one is refering to one specific side of engine- exhaust/O2 readings(4.9L only has one bank exhaust readings- a 5.0L has two banks).

42 psi is good for eng on. 30 is a little low for engine off, but ok. I don't think the fuel running psi is causing your code.

Can you do a vacuum test

 

Check your vacuum lines.....I've had to replace all of them on my 96 4.9L..I think it was Macgyver you said to spray the lines with wd-40
and if your idle goes higher then you have a vacuum leak.

 

ya or starter fluid . also good for checking for intake leaks.

 

those pressures are VERY low for a 4.9. You should see approx 55 PSI key on engine off and it should maintain that pressure within 5 PSI for at least one minute after you shut the key off. There could be a regulator problem or a problem with the fuel pump in the front tank or both.

Pull the vacuum line from your regulator, is it dry or is there gas present?

 

Vac line dry. I also checked vacume , OK

Ran fuel pressure test with vac line disconnected

running 50PSI both tanks

KOEO 50psi rear tank (steady w/ throttle)
32psi front (varied w/ throttle)

pressure maintained for 5 min.

 

I talked to a guy at the part store and he said if the pump is working and the engine runs, it is most likley the fuel tank selector valve. He said fuel pumps usally either work ,or they don't. Said this is a very common problem on these Fords and most people who replace the $150+ pumps usally come back for the valve anyway.

Anyone know how to test the selector valve?

Any input is greatly appreciated.

Thanks!

 

The good news is that one tank functions perfectly, so it's not the regulator or a leaking injector. Since the front pump module holds pressure, even though it is low, it's not the check valve in the pump module, another common problem. The failure to build enough pressure has me stumped though. I need to run through the step-by-steps in the PCED manual, I'll get back to you if I find anything on testing the selector valve or another likely problem.

 

OK I checked through the manuals. As nearly as I can tell, Ford discontinued the selector valve on or before the 96 model year. The selector switch on the instrument panel doesn't position a valve, it selects which of the 2 in- tank fuel pump modules is operational.

Following the sysptoms you gave me, it seems very likely that the problem is related to the front tank module, but it may not be the module. Check the supply voltage to the front pump. It is supposed to be 10.5 volts or gearter. If it is not then you need to trace the wiring to find the problem. If it is 10.5 or greater, the problem is likely to be the fuel pump. If you can get your hands on a 96 PCED (Powertrain & Emissions Control Diagnosis Manual) look in section HC for the step-by-step procedure for diagnosis

 

Well that makes is easier if there is no selector valve on '96. I will check voltage, if OK I will replace pump. Will post results.

Thanks for all the help!!!!