Which Is Failing, Fuel Pump, Or Pressure Regulator?

[humanz 3]

Ok, my car has been giving trouble to start of late. I've got a standard pump fitted (I believe) along with one of those rising rate pressure regulators and an inline fuel gauge. I just happened to notice one of those times I had trouble starting (had left the ignition on with the fuel pump priming) that the fuel pressure was reading around 20psi, instead of the 40+ psi it usually reads when the engine is running. While I was staring at the gauge, the pressure built up to around 45 (or 50) psi in a few seconds. I hopped in the car and gave it a swing. It started up with no problems.

 

So why is the pressure not what it should be straight away? Is the fuel pump faulty? Is the regulator faulty? Or is it something else relating to the delivery of fuel across the injectors?

[Anton green 12 1 Cars]

Ok, my car has been giving trouble to start of late. I've got a standard pump fitted (I believe) along with one of those rising rate pressure regulators and an inline fuel gauge. I just happened to notice one of those times I had trouble starting (had left the ignition on with the fuel pump priming) that the fuel pressure was reading around 20psi, instead of the 40+ psi it usually reads when the engine is running. While I was staring at the gauge, the pressure built up to around 45 (or 50) psi in a few seconds. I hopped in the car and gave it a swing. It started up with no problems.

 

So why is the pressure not what it should be straight away? Is the fuel pump faulty? Is the regulator faulty? Or is it something else relating to the delivery of fuel across the injectors?

 

Possibly check by sueezing the return fuel line betwen some locking pliers a little to see if it runs any better?

[kyepan 291]

is the gauge before the regulator, on the regulator or after the regulator.

 

if before then it's the pump, if after then it's either the pump or regulator.

 

Does it get any higher than 20 when priming, as when i was having similar issues it was taking an age to pump up to pressure on cranking(which is when the mi fuel pump starts) , but that turned out to be dodgy connections when hot on the fuel pump relay.

 

hope this helps.

[humanz 3]

is the gauge before the regulator, on the regulator or after the regulator.

 

if before then it's the pump, if after then it's either the pump or regulator.

 

How does the fuel flow? From regulator then across the injectors? Or across the injectors to the regulator? The gauge is inline, attached to the hose coming from the end of the fuel rail opposite the regulator. Would this hose be the return line?

 

I thought 'priming' was when the pump starts up, before u swing the key all the way over to start. Have no idea what the gauge reads when u swing the key to start, because of where the gauge is, and i'm usually the one turning the key. Will get someone to turn the key and check to see exactly what the gauge reads when u try to start the car.

Edited September 13, 2009 by humanz

[kyepan 291]

How does the fuel flow? From regulator then across the injectors? Or across the injectors to the regulator? The gauge is inline, attached to the hose coming from the end of the fuel rail opposite the regulator. Would this hose be the return line?

 

I thought 'priming' was when the pump starts up, before u swing the key all the way over to start. Have no idea what the gauge reads when u swing the key to start, because of where the gauge is, and i'm usually the one turning the key. Will get someone to turn the key and check to see exactly what the gauge reads when u try to start the car.

 

i'm fairly sure it should be pump, regulator, rail, return, my thinking is that there would be little point regulating the pressure after the injectors.

 

the 8v's prime when you turn the ignition on, the mi's only activate the pump when the ecu see's a signal from the crank angle sensor (ie you're cranking the engine over).

 

Yes it's worth trying with an assistant, and also when the car is cold, and then hot, as many electrical gremlins will only manifest themselves when things are fully heat soaked, as this is when high resistance tends to rear it's head.

 

Cheers

 

J

[welshpug 1,627]

pump-filter-rail-reg-tank.

 

Don't forget to disconnect the vacuum takeoff to check the fuel pressure, else you'll get a low reading.

Edited September 14, 2009 by welshpug

[humanz 3]

pump-filter-rail-reg-tank.

Don't forget to disconnect the vacuum takeoff to check the fuel pressure, else you'll get a low reading.

 

According to this, the gauge is before the regulator. If the vacuum take off is the little hose connected at the bottom of the FPR, I'm not going to trouble it. I've been wondering how it's managed to stay on for so long.

 

Well, just did some more reading about leaks thru the vacuum take-off. But I'm still not anxious to remove that little line.

 

Kyepan, if the key is turned to ON, the pressure doesn't reach 20psi (when the engine is cold). After the first attempt to swing the engine, the pressure slowly builds up to between 45 and 50 psi. At that point u can swing the engine and the car starts, although it struggles to stay on (more so than usual), but usually does if u depress the peddle.

 

When the engine is hot, the car starts first swing.

 

Was just watching a vid on youtube about FPRs on an unrelated car, and realized I'm experiencing all the symptoms of a leaking FPR: the car's been running a little rich of late, i'm getting a pretty strong gas smell , and hard starting. If I'm going to replace the regulator, what qualities or connections should the replacement have so it fits back as standard. Don't really want to run a standard FPR.

[kyepan 291]

Kyepan, if the key is turned to ON, the pressure doesn't reach 20psi (when the engine is cold). After the first attempt to swing the engine, the pressure slowly builds up to between 45 and 50 psi. At that point u can swing the engine and the car starts, although it struggles to stay on (more so than usual), but usually does if u depress the peddle.

 

I stand corrected, thanks welshpug.

 

That sounds suspiciously like the fuel pump relay / pump problems I had... the relays them selves were fine but the connector block was giving poor connection to the terminals.. that or it's the multiplug(i've never had a multiplug but believe the fuel pump relay travels through it). Except mine would start from cold but only turn over when hot.. pressure gradually rising.

 

Try temporarily bridging the two fat wires that go into the fuel pump relay, and see how the pressure climbs... don't leave this on the car as it's not safe to leave a fuel pump permanently wired on, if you were to crash and the engine stalled it would keep pumping and pumping.. fire... bad.

 

if that gets the pressure to rise correctly, it could be the terminals on the connector block, check them for corrosion, i had rewired and insulated mine to fix this.

 

if the connectors are pristine and wiggling the relay with the engine running does not lead to it stuttering and cutting out, i vote pump.

 

although i'm not familiar with the regulator symptoms.. so perhaps you might have a link to that?

 

J

Edited September 15, 2009 by kyepan

[humanz 3]

Try temporarily bridging the two fat wires that go into the fuel pump relay, and see how the pressure climbs... don't leave this on the car as it's not safe to leave a fuel pump permanently wired on, if you were to crash and the engine stalled it would keep pumping and pumping.. fire... bad.

J

 

Er, that's how they're connected now, as my fuel pump relay kicked the bucket months ago, and haven't been able to locate a working one that matches it. I'm looking for a relay from off an early engine by the way. So it can't be the fuel pump relay. Guess I should just replace both the pump and the FPR then?

[kyepan 291]

Er, that's how they're connected now, as my fuel pump relay kicked the bucket months ago, and haven't been able to locate a working one that matches it. I'm looking for a relay from off an early engine by the way. So it can't be the fuel pump relay. Guess I should just replace both the pump and the FPR then?

how many pins does it have?

[kyepan 291]

Was just watching a vid on youtube about FPRs on an unrelated car, and realized I'm experiencing all the symptoms of a leaking FPR: the car's been running a little rich of late, i'm getting a pretty strong gas smell , and hard starting. If I'm going to replace the regulator, what qualities or connections should the replacement have so it fits back as standard. Don't really want to run a standard FPR.

 

was that the one for the american car? i was slightly concerned i had missed something after reading your post, but the symptoms of cold start issues, and general overfuelling are not what i had experienced.

[humanz 3]

was that the one for the american car? i was slightly concerned i had missed something after reading your post, but the symptoms of cold start issues, and general overfuelling are not what i had experienced.

 

Yes, can't remember the make of the car. GM I think. Update: the car's driving worse now. The pressure on the regulator keeps getting higher during normal driving and the screw to adjust it is as far out as it can go. It was running at somewhere between 45 and 50 under driving conditions, but the pressure now keeps working it's way up to 60+, and the car is backfiring when coming off the throttle, or going past 4000rpm. Will have to check the old tachy. I believe they all have the same number of pins? But mine was mounted on the inner wing of the engine bay (ph1) and has no metal tab on the end.

 

And to make things interesting, a guy in a Ford Explorer pickup decided to rearrange some of my rear end early yesterday.

[humanz 3]

Well, my mechanic swapped my FPR for a standard one. The pressure is around 40psi, where it should be, according to him. The car is starting fine now. But around 4000rpm, it stutters badly. Got a chance to have someone hold it at that rpm while I studied the pressure gauge. Apparently, at that rpm, the pressure varies rapidly anywhere between 20spi and 40+psi. Is this normal or would the low pressure explain the missing i'm getting now?