Correct fuel pressure?

blue94sc

blue94sc

Registered User
I am trying to figure out why my SC all of a sudden is hard to start. I get good vacuum 18-20 Hg at idle. Once I do get it running I get a code 335 DPFE sensor. I thought that my fuel pump is ok but with 150k miles the original pump may be getting weak. With the fuel system at 0 psi, I turn on the key and the fuel presure rises to 10 psi. As I am cranking the motor the pressure slowly rises until it's around 30 and then the car fires up.
At idle the fuel pressure is around 33 psi. A cylinder balance test comes up clean (99).
Does anyone know if the fuel pump is operating correcly? Is 33 psi at idle acceptable? Lastly is it typical that when the key is initially turned on the fuel pressure rises to 10 psi until it begins cranking?
:(
 
Bill,

That fuel pressure sounds awfully low. When you turn the key on, it should pressure up to 38 - 40 psi without cranking. I'm not sure what the idle pressure is supposed to be, and will have to check my service manual, but I've just recently verified the "key on" pressure. If you cycle the switch several times to run the fuel pump (without cranking), will the pressure build up to something close to 40 psi? How long does it take for the pressure to "leak down" to zero after you turn off the engine?

I don't know whether this could be a pump issue or a fuel regulator issue. How old is the regulator? How old is the fuel filter? I will take a look at my Helms Powertrain manual to see what it says about the code you're getting.

Good luck. I send another post if I find anything.

David
'95 SC - 5-speed


blue94sc said:
I am trying to figure out why my SC all of a sudden is hard to start. I get good vacuum 18-20 Hg at idle. Once I do get it running I get a code 335 DPFE sensor. I thought that my fuel pump is ok but with 150k miles the original pump may be getting weak. With the fuel system at 0 psi, I turn on the key and the fuel presure rises to 10 psi. As I am cranking the motor the pressure slowly rises until it's around 30 and then the car fires up.
At idle the fuel pressure is around 33 psi. A cylinder balance test comes up clean (99).
Does anyone know if the fuel pump is operating correcly? Is 33 psi at idle acceptable? Lastly is it typical that when the key is initially turned on the fuel pressure rises to 10 psi until it begins cranking?
:(
Click to expand...
 
kendall221 said:
Bill,

That fuel pressure sounds awfully low. When you turn the key on, it should pressure up to 38 - 40 psi without cranking. I'm not sure what the idle pressure is supposed to be, and will have to check my service manual, but I've just recently verified the "key on" pressure. If you cycle the switch several times to run the fuel pump (without cranking), will the pressure build up to something close to 40 psi? How long does it take for the pressure to "leak down" to zero after you turn off the engine?

I don't know whether this could be a pump issue or a fuel regulator issue. How old is the regulator? How old is the fuel filter? I will take a look at my Helms Powertrain manual to see what it says about the code you're getting.

Good luck. I send another post if I find anything.

David
'95 SC - 5-speed
Click to expand...



Bill,

The Helms service manual says the key on engine off pressure should be 35 - 40 psi. the engine running pressure should be between 30 - 40 psi.

Also, (from the '95 Ford Powertrain Control / Emissions Diagnosis Manual) the 335 code indicates the EGR differential pressure feedback electronic (DPFE) EGR sensor is out of self taest range. Possible causes could be:

1) Damaged DPFE sensor
2) Obstructed pressure inlet hose (to DPFE sensor)

I am not sure that this is the problem, but the manual indicates that a malfunctioning EGR system can cause a hard to start condition.

Let me know if I can possibly help anymore.

David
'95 SC
5-speed
 
Fuel pressure should rise very quickly to 40psi before cranking the engine and should stay high during crank. Only after the engine starts and vacuum builds should the pressure drop back to 35. You have an obstruction or weak pump. Change the filter and inspect the lines for damage where they pass under the car. If all is well there and it is still sluggish then a new fuel pump is in order.

The EGR stuff has nothing to do with starting or fuel pressure.

{edit} Well, perhaps I shouldn't say that. If the EGR is stuck open then it would act like a big vacuum leak at idle especially during start.
 
Probably pump

Thanx guys.
The filter was recently replaced. I did check to see if the EGR valve was sticking and it is operating correctly.
I did get a couple of other codes when I did a KOER test.
When I get home tonight I'll do some other tests to help isolate the problem.
I was wondering if I have a bad DPFE sensor would it cause a hard start?
Would an MN12 Performance 190 lph pump be ok for a few bolt on's? (Exhaust, raised top, 5% pulley).
Again thanx guys. I REALLY appreciate your help.
Bill
 
Stumped!!

Alright. I went out this evening to try to get some more hints to why my SC is hard to start at times.
It has been sitting since Sunday evening. There was no pressure in the fuel system. When I turned on the ignition the fuel pressure went up to about 10-15 lbs (hard to see gauge from inside the car). While cranking it rised up to around 30 psi in about 5 seconds and the car started right up. I let it idle for around 10 minutes to warm it up. The fuel pressure at idle was 33 psi. I then shut off the engine and watched the fuel pressure. It actually rose a little to around 38 psi with the engine off. ??? I would guess that it was due to heat of the engine causing the fuel to warm up.

I then tried to start the engine and it was hard to start. It would crank then try to get going then stall at 200 rpm. I connected my timing light to cylinder 5 to see if I was at least getting spark. It would light when I would crank the engine. The fuel pressure stayed around 40 psi. I then cranked the engine and did a WOT test to turn off the injectors and the engine fired up. I may be getting too much fuel during startup and it may be fouling the plugs.

I have installed a 180 degreee thermostat and the engine temp hovers around the first white line before normal while driving. The KOEO test gives me a code 335 EGR sensor voltage out of range. I get a code 542 Fuel pump circuit open; ECA to motor in the continuous memory. Could be when I stalled the car pulling out of the car wash last week (stupid rollers :-b).
The KOER test gives me a code 326 EGR circuit voltage lower that expected. The cylinder balance test passed.

I took it for a spin and really got on it. Near WOT I get spark knock slightly. It seems to fade as the rpm's increase.

I am going to replace the DFPE sensor since that's what seems to be giving me the codes (335 & 326).

I wonder about the spark knock. Would the plugs have anything to do with it? They were installed only a couple of months ago (Autolites APP764's @ .047 gap). I may get some Motorcraft AWSF34PP plugs to see if that helps.
I'm stumped. :(
 
blue94sc said:
Alright. I went out this evening to try to get some more hints to why my SC is hard to start at times.
It has been sitting since Sunday evening. There was no pressure in the fuel system. When I turned on the ignition the fuel pressure went up to about 10-15 lbs (hard to see gauge from inside the car). While cranking it rised up to around 30 psi in about 5 seconds and the car started right up. I let it idle for around 10 minutes to warm it up. The fuel pressure at idle was 33 psi. I then shut off the engine and watched the fuel pressure. It actually rose a little to around 38 psi with the engine off. ??? I would guess that it was due to heat of the engine causing the fuel to warm up.

I then tried to start the engine and it was hard to start. It would crank then try to get going then stall at 200 rpm. I connected my timing light to cylinder 5 to see if I was at least getting spark. It would light when I would crank the engine. The fuel pressure stayed around 40 psi. I then cranked the engine and did a WOT test to turn off the injectors and the engine fired up. I may be getting too much fuel during startup and it may be fouling the plugs.

I have installed a 180 degreee thermostat and the engine temp hovers around the first white line before normal while driving. The KOEO test gives me a code 335 EGR sensor voltage out of range. I get a code 542 Fuel pump circuit open; ECA to motor in the continuous memory. Could be when I stalled the car pulling out of the car wash last week (stupid rollers :-b).
The KOER test gives me a code 326 EGR circuit voltage lower that expected. The cylinder balance test passed.

I took it for a spin and really got on it. Near WOT I get spark knock slightly. It seems to fade as the rpm's increase.

I am going to replace the DFPE sensor since that's what seems to be giving me the codes (335 & 326).

I wonder about the spark knock. Would the plugs have anything to do with it? They were installed only a couple of months ago (Autolites APP764's @ .047 gap). I may get some Motorcraft AWSF34PP plugs to see if that helps.
I'm stumped. :(
Click to expand...

An improperly functioning EGR can cause spark knock.

How much fuel pressure do you see when under boost and how much boost do you get? The numbers should match.

Your plugs are NOT the problem. It IS very possible that you an injector that leaks under certain conditions. How long does fuel pressure hold after you turn off the ignition?
 
Fuel Pressure under boost

Hey Dave.
I haven't tried to check the fuel pressure under boost because the hose on the gauge I have is a little short. I may be able to tuck it under the top edge of the hood and scoot down the street ( i'll try it tonight).
I get around 10-12 psi boost pressure near WOT. When I shut off the car the fuel pressure holds pretty stable for over 5 minutes. I'm going to replace the DPFE sensor to see if the spark knock goes away. When it tries to start it idles real low and rough at 200-300 rpm. Then it suddenly jumps up to around 1200 and settles back down. Could the IAC be sticking? And is there a way to check it?
Thanx alot for your help.
Bill
 
Low fuel light?

Interesting observation. Sometimes when I turn the key on the low fuel light turns on. If I turn off the ignition and turn it back on the low fuel light goes out. Wierd. I am going to replace the pump. MN12 Performance sells a 190 lph and a 255 lph fuel pump kit. Rich states that the 190 is for stock engines with bolt-ons and the 255 is for supercharged. I'm a little confused. Which would be good for an SC with a raised top, and 5% pulley?
 
blue94sc said:
Interesting observation. Sometimes when I turn the key on the low fuel light turns on. If I turn off the ignition and turn it back on the low fuel light goes out. Wierd. I am going to replace the pump. MN12 Performance sells a 190 lph and a 255 lph fuel pump kit. Rich states that the 190 is for stock engines with bolt-ons and the 255 is for supercharged. I'm a little confused. Which would be good for an SC with a raised top, and 5% pulley?
Click to expand...

go with the 255 lph I have that in my car with everything else stock only becase I have been told our cars are fuel starved anyway.
 
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