question on fuel pressure regulator

[jcasey007]

I'm diagnosing a rough running on petrol, I took off the vacuum tube from the fuel pressure regulator (on the end of the fuel rail) to suck on it.

I got a strong taste and smell of petrol from the vacuum tube. No petrol ran out but am I right i thinking there should not be a trace of petrol smell.

I'm waiting for my vacuum tester to arrive from ebay when I can test the regulator properly.

cheers

jim

 

[Opera House]

There is a problem that can occur in the fuel pressure regulator due to a spring that is not centered. I had this problem with my 92 and it resulted in occasional stalling at stop lights. The engine would go into a death shudder and then recover. It also would start to die when taking high speed right exit ramp turns. Eventually I cut open the regulator and found seat wear was only on one side. This allowed the valve plate to slip to one side and stick open and have very low fuel pressure. High manifold vacuum opens the valve wider and lateral force would also start the problem. This wear will also allow leak down with enough wear. Try tapping the regulator when there is a problem.

An amp meter can also be connected in place of the pump fuse. Current should be above 3.5A and vary no more than a quarter amp. Looking at the current will at least verify it is a fuel problem.

 

[jcasey007]

thanks Operahouse

With respect to reading the amps being drawn by the fuel pump, I assume a low current reading means that the regulator is letting too much fuel back to the tank resulting in low presure?

cheers

jim

 

[Opera House]

The regulator normally returns about 80% of the fuel to the tank. Current is related to pressure. Vacuum line removed is the highest pressure. Voltage to pump due to resistance of bad connections can drop down to almost 6V and the engine will still run. At about 2 1/2 amps the engine will start to stall. I had a cab mounted meter to diagnose my problem. When I saw the current dropping, I knew it was about to stall. Do you have any trouble starting with engine warm and it has been turned off for about 10 minutes?

 

[jcasey007]

no trouble starting but when it is hot and has been idling for 5 minuites it runs rough until I rev it and it clears then runs fine.

a short time at idle will not cause it to run rough (i.e when at a junction)

I also have a realtime O2 sensor in the cab which when idling on Petrol it swings between Optimum (steady for 8 seconds) and then goes very Lean for 3 seconds like a metronome!

i'm sure it is petrol related as on LPG it idles fine with mixture steady (both petrol and LPG use the same Lambda sensor)

I will set up my ammeter and test the pump current

cheers

Jim

 

[mbruffey]

Do you have any trouble starting with engine warm and it has been turned off for about 10 minutes?

Opera: I am having the kind of problem you describe above. No codes. Replaced fuel filter and performance improved, but today I had start-stall, start-stall, start-stall (immediate stalls) after being in a store for about 1/2 hour. It's done that on me about 4 times in the past 4-5 months. Other symptoms are intermittent rough idle (warm or cold), "death shakes" intermittently (pretty rare), overspeed on shift (fairly mild now that I changed fuel filter), thrummy character to exhaust sound (intermittent).I figure I will know where the problem lies when it finally dies, but, um, where were those fuel pump connections that went bad? Hopefully not in the tank! Thx, LMark

 

[jcasey007]

Might sound like a daft question but what have any of you used to measure the fuel pressure?

I can't find anything on the web for less than £80.

as the valve on the test port is a standard tyre fitting has anybody used a car tyre pressure gauge ? (mine will read up to 75 PSI)

Sorry if I'm coming off as tight but tis the week after christmas...

cheers

Jim

 

[2000StreetRod]

Fuel pressure gauge

Haven't bought this one but plan to in the near future:
Fuel Injection Pump Tester

 

[Opera House]

I made one from an old tire pump. It was a screw on end and piped to a gauge. I would avoid anything that does not screw on because of potential leaks. Another reason is I always remove the schraeder valve on the port to get the real pressure. Be aware that most gauges can be 5# off. Should be able to build one for about £8.

 

[manaen]

One nice thing about a "real" gauges is they have a bleeder assembly built into the pressure gauge where the gas can be safely vented into a catch pan. If your home made model does not have some device to vent the pressure you will be spraying gas all over your potentially hot engine. Just be sure to use extra care to wrap the connector with a rag before you disconnect it to catch all the excess fuel.

 

[SB98UKexplorer]

my cheap solution to that is to pull the plug on the fuel pump cut off swith under the passanger footwell carpet, then let it run till it dies and start afew times just to make sure before removing the plug off the rail

 

[neon tony]

fuel pressure at idle
30-45 psi (vac. on)
40-50 psi (vac. off)
hold pressure after 5 min. 30-65 psi
fuel pump max. 65 psi

mine is the opposite, it's off the chain with 60+ at idle. anyone know a "cheap" source of a new reg.? napa is the only one who lists the new style, at $152!! they changed the reg. when they went to the Al. fuel rail.
BTW, there is NO FUEL RETURN on late systems.

 

[SB98UKexplorer]

i take it yours is returnless?

 

[jcasey007]

I managed to rig up my old foot pump to the test port yesterday,

tested ok I think with 32psi vac off , 44 psi vac on,

I guess it could benefit from a filter change as it must be 50k miles since last done


thanks for all the advice

jim

 

[manaen]

I managed to rig up my old foot pump to the test port yesterday,

tested ok I think with 32psi vac off , 44 psi vac on,

I guess it could benefit from a filter change as it must be 50k miles since last done


thanks for all the advice

jim

for a 95, 44psi is high, you should be around 35psi with the vacuum on at idle.

 

[manaen]

fuel pressure at idle
30-45 psi (vac. on)
40-50 psi (vac. off)
hold pressure after 5 min. 30-65 psi
fuel pump max. 65 psi

mine is the opposite, it's off the chain with 60+ at idle. anyone know a "cheap" source of a new reg.? napa is the only one who lists the new style, at $152!! they changed the reg. when they went to the Al. fuel rail.
BTW, there is NO FUEL RETURN on late systems.

what year and engine do you have?

if you have the returnless fuel system then you should be around 60psi. The regulator on these model is part of the fuel pump in the tank so that would explain the high cost.

 

[jcasey007]

for some reason my profile said 1995 but my truck is a 4.0 SOHC 1997.

 

[manaen]

for some reason my profile said 1995 but my truck is a 4.0 SOHC 1997.

OK then you need to figure out if you have a return-less system which runs at 60psi or a return (2 lines from tank) system that runs at 35psi.

The big difference other than psi is that the return-less system does not have a FPR on the fuel rail. The FPR is located with the pump in the gas tank. There is an FPR looking device on the fuel rail however it only serves as a pulse modulator to even out the psi surges from the pump.

 

[neon tony]

'00, OHV 4.0. same specs for returnless. has a reg. on the rail.
there was some rumor of a recall on this part. any info?

 

[manaen]

'00, OHV 4.0. same specs for returnless. has a reg. on the rail.
there was some rumor of a recall on this part. any info?

on the recall or the FPR, didn't hear about a recall, but the FPR is not expensive if you need to replace it.