Fuel pressure not holding

[Creomod]

Ok I have an issue I believe it’s fuel pressure. I turn key on gauge jumps up to 40 and drops all the way slowly within 10 to 20 sec. Guys what could it be? I bought new fp,fp filters both , fp relay,I even bought a new regulator. Can turns on, dies sounds extremely ragged.I have 12 v black pink wire, orange blue wire and I know I have 12v on injectors connector all of them. Checked every injector with 9v battery all soloinds clicking (did not check to see if they were clicking car on screwdriver)I also changed the fuel harness. I am getting code 31,66,85 but 66 I think I’m getting from removing air flitter maf to pull plugs. Ecu was done last year thou eBay ecu exhange so don’t think something wrong in there any way to test the ecu fuel pump. What wire would cause me to loose fuel pressure?where should I look . O I also bought ignition switch I’m had car down 2 weeks tomorrow

 

[Blown88GT]

ECU will turn fuel pump off after 5 sec if engine does not start. Turn key on & off several times & then see if gauge will hold pressure.

 

[Creomod]

ECU will turn fuel pump off after 5 sec if engine does not start. Turn key on & off several times & then see if gauge will hold pressure.

yes I can barley hear it come on for few sec. I used a test light on the Inertia switch (bypassed straight wire to wire) and when I cycle key on yes light turns on and off but no it will not hold pressure. It jumps right up to 40 something and drops to 20
And lower and lower to zero within like 10 sec total

 

[General karthief]

Can turns on, dies sounds extremely ragged.

Does the fuel pressure stay up the few seconds it runs raggedy?

 

[rednotch]

What fuel pump did you buy... Most China and counterfeit walbro's almost never hold line pressure when powered off.... Ran a few in the past, just had a cheapy kemso die after about 5 years in a beater that would drop to zero seconds after shutting it off. Its dying now, cutting off when it gets hot. If the pump and regulator are holding pressure only other place is the injectors or a line bleeding off. Majority of those codes will pop up when a car stalls out, might need to reset the idle l if the only issue is the pump not holding line pressure after its shut off.

 

[Creomod]

What fuel pump did you buy... Most China and counterfeit walbro's almost never hold line pressure when powered off.... Ran a few in the past, just had a cheapy kemso die after about 5 years in a beater that would drop to zero seconds after shutting it off. Its dying now, cutting off when it gets hot. If the pump and regulator are holding pressure only other place is the injectors or a line bleeding off. Majority of those codes will pop up when a car stalls out, might need to reset the idle l if the only issue is the pump not holding line pressure after its shut off.

Running stock autozone pump. It’s worked fine with one so got a new one turns on but super ragged shaking turns off.O and right from the jump when you turn the key on the fuel just drops down on the gauge

 

[Creomod]

Does the fuel pressure stay up the few seconds it runs raggedy?

I’m not sure but I know I have to hold the pedal down to keep it on . I know the fuel is going somewhere. I did a oil change it looked normal but then again the problem just happened. I just installed new regulator ect sensor , checked tps only key on,.98 ,went over vacuum lines ,pvc, new spark plugs,I have 2 mustangs so swapped everything! Lol cap, wires, had tfi and alternator tested,swapped coil,not sure if this had anything to do with it but I did find a yellowish substance looked like Dijon mustard in lower and upper intake. Was assuming it’s fuel mixed with oil adding pics . Never seen this before but I do have a vacuum leak at brake booster but have been running car like that no issues but this won’t let me drive. Sputters as if I had plug wires swapped or something but I keep thinking fuel pressure cuz my other car holds pressure for hours this one seconds

 

[rednotch]

That's oil and condensation or water... Gets forthy like that until its cooked off see it alot on oil caps when ppl only drive short trips.. You have coolant running to an egr spacer still or a catch can on the pcv lines? Might be a small leak or its sucking that from the pcv and your getting water some how, possibly gas from the regulator but you said its new and gas doesn't tend to froth like that when it mixes with oil..


So this was doing the same thing before you replaced the pump and all those parts? I'd start with basics. Compression and leak down,see if oil smells like gas or looks frothy, check if the plugs are wet or one is fouling out might show a leaking injector, not holding pressure when off isn't a concern unless its a leaking line or injector, most parts store pumps these days are the cheapest China stuff they can get and its hit or miss if the anti drain back inside the pump is worth a damn as long as it primes and holds pressure running it shouldn't be an issue.. Like I said I ran a $30 kemso, China 340 pump for 5 years, it would bleed to 0 in 20 seconds if that when you shut it off and its finally starting to die..... Not holding pressure in spec with it running would be a concern but your just throwing parts at it at this point. You can test the pump threw the eec test port and watch the gauge while its forced on and the car isn't running to see if it holds pressure or not.

 

[90sickfox]

My car goes to zero as soon as I turn the car off. It's because of my aftermarket FPR. Been like that for 7 years. It's a long crank to start but runs great and fuel pressure at 42psi. You need to check the fuel pressure reading when the car is running. Make sure you have the correct injector harness. People used to re-pin the harness to run non HO engines. Made the injectors fire with the cylinder order.

 

[AeroCoupe]

When you swapped pumps did you change the “S” hose between the pump and the fuel pump hanger? These can develop cracks over time especially with the ethanol based fuels.

 

[Creomod]

That's oil and condensation or water... Gets forthy like that until its cooked off see it alot on oil caps when ppl only drive short trips.. You have coolant running to an egr spacer still or a catch can on the pcv lines? Might be a small leak or its sucking that from the pcv and your getting water some how, possibly gas from the regulator but you said its new and gas doesn't tend to froth like that when it mixes with oil..


So this was doing the same thing before you replaced the pump and all those parts? I'd start with basics. Compression and leak down,see if oil smells like gas or looks frothy, check if the plugs are wet or one is fouling out might show a leaking injector, not holding pressure when off isn't a concern unless its a leaking line or injector, most parts store pumps these days are the cheapest China stuff they can get and its hit or miss if the anti drain back inside the pump is worth a damn as long as it primes and holds pressure running it shouldn't be an issue.. Like I said I ran a $30 kemso, China 340 pump for 5 years, it would bleed to 0 in 20 seconds if that when you shut it off and its finally starting to die..... Not holding pressure in spec with it running would be a concern but your just throwing parts at it at this point. You can test the pump threw the eec test port and watch the gauge while its forced on and the car isn't running to see if it holds pressure or not.

Damm I sure hope it’s condensation. The oil didn’t look frothy. No catch can on pvc,and no coolant to egr. Trying to read fuel gauge with car on but scince car wants to die the gauge going up and down with the rpm of car diying

 

[Creomod]

When you swapped pumps did you change the “S” hose between the pump and the fuel pump hanger? These can develop cracks over time especially with the ethanol based fuels.

Just swapped the whole pump it was already set up with s hose

 

[rednotch]

Damm I sure hope it’s condensation. The oil didn’t look frothy. No catch can on pvc,and no coolant to egr. Trying to read fuel gauge with car on but scince car wants to die the gauge going up and down with the rpm of car diying

You can see what it does, forcing the pump to run threw the test connector with the engine off.... If its bleeding down while doing that an injector is stuck or big fuel leak, pressure when the pump isnt running is of little concern other then an extended crack issue some times. but I don't think fuel pressure is your issue if you can't get it to idle. Can you keep it running long enough for the idle to some what stablise modulating the throttle?

How did this issue start, was it running fine then something just happend and you started changing parts, what was the symptoms then, same as now after new pump and regulator?

 

[Creomod]

You can see what it does, forcing the pump to run threw the test connector with the engine off.... If its bleeding down while doing that an injector is stuck or big fuel leak, pressure when the pump isnt running is of little concern other then an extended crack issue some times. but I don't think fuel pressure is your issue if you can't get it to idle. Can you keep it running long enough for the idle to some what stablise modulating the throttle?

How did this issue start, was it running fine then something just happend and you started changing parts, what was the symptoms then, same as now after new pump and regulator?

It’s a 92 stock,hmm I was cruising Hadent had problems at all. It was running fine but on that day I picked up car to work on the vss sensor connector. The previous owner wired the aftermarket tachometer someway somehow throu the vss wiring so if the vss connector isn’t connected the tach light won’t come on and rpm’s won’t move sooo I wanted to get it to work again. I picked car up removed front seat and removed the transmission harness to but connect the vss harness cuz I barely had wire coming thro groumet so I pulled harness to fix it right. Installed it back and and 2 hours later cruising good no racing driving 40 mph no power shifting nothing and all of a sudden car sounded different lack of power engine shaking wanted to shut off.Also same symptoms with new regulator

 

[Creomod]

anyone ever seen this before under driver dash?Has 2 relays? I’m thinking it was part of the alarm but maybe tied into fuel?

 

[Mustang5L5]

My previous pump went to zero immediately. My current walbro takes maybe 10-15 seconds to bleed off. Some pumps just have better check valves than others.

What matters is maintaining presssure with the pump running. I drove 10 years on that pump that didn’t hold pressure at all. Just needed two key primes to start it cold.

 

[AeroCoupe]

You need to chase those relays down and make sure they are not part of the problem. We would put an interrupt on the fuel pump trigger wire on cars back in the 90's when we installed an alarm so that the car was inoperable when it was triggered (not snowflake triggered).

 

[dcm0123]

You may want to pull the plugs to see if one is running excessive rich which would be a sign of a leaking injector.

I read you replaced the regulator- did you verify on the new regulator there is no fuel in the vacuum line?

 

[Creomod]

You need to chase those relays down and make sure they are not part of the problem. We would put an interrupt on the fuel pump trigger wire on cars back in the 90's when we installed an alarm so that the car was inoperable when it was triggered (not snowflake triggered).

Lol there was corrosion on those relays,probably going to replace them and see what happens if it fixs the problem then I’ll eliminate them .

 

[Creomod]

You may want to pull the plugs to see if one is running excessive rich which would be a sign of a leaking injector.

I read you replaced the regulator- did you verify on the new regulator there is no fuel in the vacuum line?

It’s weird no fuel but the other end at the intake port did have a little bit of black that smelled like fuel.This issue started 15 days ago I bought another regulator last week is it possible it’s bad as well straight out the box? It’s from lmr