Bad fuel pump? - Ford Mustang Forum
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post #1 of 54 (permalink) Old 2 Weeks Ago Thread Starter
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Bad fuel pump?

I donít own a gauge (yet) so Idk how much fuel pressure Iím getting but the little pressure gauge that is on the line reads 32. The car just started giving me some troubles at start up after itís been sitting over night or while Iím at work so Iím leaning towards a fuel problem. The engine and fuel system were replaced about 40k miles ago and I can hear the pump prime when I turn the key over but it will only start when I pump on the peddle when I turn the ignition. Yesterday it took about 10 minutes and when it finally started my low coolant light was on. What else could keep a 95 mustang from starting?

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post #2 of 54 (permalink) Old 2 Weeks Ago
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What is more likely, the fuel is draining back to the tank requiring the fuel pump to push it back up to the injectors.... with the fuel pump itself being the issue but IMHO, I would look for codes 1st...ÖÖ.. and borrow a fuel psi gauge to check and see what is really going on.

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post #3 of 54 (permalink) Old 2 Weeks Ago Thread Starter
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I didnít get any codes last week but Iíll try again this weekend. Maybe Iíll buy a harbor freight gauge to check it out. Thank you.
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post #4 of 54 (permalink) Old 2 Weeks Ago
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Originally Posted by Aye_plus View Post
I didn’t get any codes last week but I’ll try again this weekend. Maybe I’ll buy a harbor freight gauge to check it out. Thank you.
I bought a harbor fright gauge. It worked a few times before it quit working.
The motor stays running once it’s running?
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post #5 of 54 (permalink) Old 2 Weeks Ago
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I donít own a gauge (yet) so Idk how much fuel pressure Iím getting but the little pressure gauge that is on the line reads 32. The car just started giving me some troubles at start up after itís been sitting over night or while Iím at work so Iím leaning towards a fuel problem. The engine and fuel system were replaced about 40k miles ago and I can hear the pump prime when I turn the key over but it will only start when I pump on the peddle when I turn the ignition. Yesterday it took about 10 minutes and when it finally started my low coolant light was on. What else could keep a 95 mustang from starting?
When you say "the little pressure gauge on the line",you mean the Schrader Valve, correct? The next time you attempt startup & it fails to start immediately,cycle the key on for a couple seconds then off then cycle the key like this for a total of 4-5 times then attempt startup again.If it starts,thats an indication the fuel pump is weak.When you cycle the key it allows a weak pump to gradually build up pressure in the lines and fuel rail.If this cycling of the key doesn't work,try holding the pedal to the floor while turning the key to start.After a few seconds of doing this,release the pedal while you continue cranking the engine.If it starts,this indicates something is causing an engine flood condition and once you do the floored pedal routine,this clears the excess fuel out of the engine which allows it to start.A engine flood condition is normally caused by 1 of 3 things.A leaking fuel pressure regulator,a leaking injector or a defective ect sensor.If the tests above don't work,hold the pedal 1/4 to 1/3 of the way down while turning the key to start.If it starts up using this routine, this normally indicates the ect sensor is bad.A bad ect usually outputs a reading that indicates the coolant temp is too low,which triggers a fuel trim way too rich.What pressing the pedal down 1/4-1/3 of the way does (while cranking) is it allows additional air to enter the engine through the now open throttle blade and this additional air thats now combined with the rich fuel mixture allows the engine to start.Another test you should do is check residual fuel pressure once the key is turned off.So turn the koeo,record pressure,turn the key off,wait 60 seconds then record pressure again.Does pressure drop more than 5psi in that 60 second time period? If yes,you'll have to grab a rag and a pair of vice grips then use them to pinch a soft section of the fuel line closed near the passenger valve cover. Once pinched,run the same pressure test that you did above to see if the pressure still drops or not.
IF IT DOES still drop,the fuel pump check valve is bad,the S hose is leaking or the fuel pump hanger is leaking inside the tank.
IF IT DOESN'T still drop,the fuel pressure regulator is leaking or a injector is leaking.
When a regulator leaks,fuel seeps out of its vacuum port and/or the vacuum hose will be wet inside.

The low coolant light just means the coolant level in the reservoir bottle is low and needs to be filled to the appropriate line on the bottle.If the coolant level is fine,this usually indicates the low coolant sensor is bad.
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post #6 of 54 (permalink) Old 2 Weeks Ago Thread Starter
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Awesome advice! Thank you!
Yess, the car stays running but I have to hold the rpm for a while that it doesnít turn off. After that, itís good to go until parked and the engine gets cold again.

Yes, Iím taking about schrader valve. Iíll definitely try those techniques, if itís not too late. The car sat for 2 days and wouldnít start this morning. I tuned the key about 10 times and even pumped the pedal a few and got nothing. The pump did sound a little different after I primed it the fifth time. Iíll check for codes once I get the car back into my garage. It rolled out the garage and I couldnít roll it back in
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post #7 of 54 (permalink) Old 2 Weeks Ago Thread Starter
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Awesome advice! Thank you!
Yess, the car stays running but I have to hold the rpm for a while that it doesnít turn off. After that, itís good to go until parked and the engine gets cold again.

Yes, Iím taking about schrader valve. Iíll definitely try those techniques, if itís not too late. The car sat for 2 days and wouldnít start this morning. I tuned the key about 10 times and even pumped the pedal a few and got nothing. The pump did sound a little different after I primed it the fifth time. Iíll check for codes once I get the car back into my garage. It rolled out the garage and I couldnít roll it back in
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post #8 of 54 (permalink) Old 2 Weeks Ago
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Just curious, what did you use, a tire gauge?
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post #9 of 54 (permalink) Old 2 Weeks Ago Thread Starter
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There is a small gauge that already came attached to the fuel line. Maybe a 225 lph fuel pump is not good for a daily. That spec clutch didnít last for crap.
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post #10 of 54 (permalink) Old 2 Weeks Ago
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It sounds like youve already got a fuel pressure gauge attached to the Schrader valve,so dont worry about buying a gauge.
If the engine is mainly stock,a 255lph pump is more than you need,but it shouldn't cause startup or running issues & it definitely shouldn't cause 32psi of pressure,unless something is wrong with it.It would be much more likely to create a rich condition & high pressure vs the opposite.To make sure the pump or another component isnt causing a flooding condition,hold the pedal to the floor while you try to start it & see if that allows it to start.If crank speed seems to increase after a few seconds of cranking,let up on the pedal while you continue cranking.Using this method should allow it to start,if a engine flood condition is occurring.
KOEO= 35-45psi
KOER= 30-40psi

To verify if its fuel related only,pull the small breather tube off the throttle body (the tube that runs between the oil filler neck on the valve cover & the little elbow port on the throttle body) spray starting fluid or carb cleaner directly into the port on the throttle body,reconnect the tube then attempt to do a startup.If it starts & runs for a few seconds then dies or continues to run without issue once started,its fuel related.If it doesn't start at all,its spark related.If you find that you're lacking both fuel and spark,the pip sensor is the most likely cause.It supplies the pulse to the ecu that triggers spark & injector pulse. To verify its presence,you can disconnect one of the harness plugs from any injector, plug a noid light or test light (use a paperclip inserted into one of the plug terminals to attach the test light clip to) into the plug terminals then crank the engine while observing the light.It should flash repetitively

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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post #11 of 54 (permalink) Old 2 Weeks Ago Thread Starter
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Bad fuel pump?

Geez! Who are you and how do you know so much?! No Offense to anyone else but you have provided me with so much valuable information, more than anyone ever has in all my years of surfing the web for mustang advice. I post on several forums and have never received responses like yours. Thank you!
That being said, I sprayed some carb cleaner in the TB and it started right up (the 2nd time) the previous owner wanted to make this a turbo car but didnít go all the way but he did manage to up grade the pump and switched to #24 injectors. Iím not sure If it runs rich as he gave it to me with an OR pipe but there are times where I smell like exhaust, a little more than others. I guess the aftermarket pump is going out. Iím not sure how much it cost but Iím sure it cost more than a factory unit and to have it go out after 40k miles, it seems like a waste of money. Will I be ok if I replace it with a factory unit?

Last edited by Aye_plus; 2 Weeks Ago at 05:06 PM.
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post #12 of 54 (permalink) Old 2 Weeks Ago
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Quote:
Originally Posted by Aye_plus View Post
Geez! Who are you and how do you know so much?! No Offense to anyone else but you have provided me with so much valuable information, more than anyone ever has in all my years of surfing the web for mustang advice. I post on several forums and have never received responses like yours. Thank you!
That being said, I sprayed some carb cleaner in the TB and it started right up (the 2nd time) the previous owner wanted to make this a turbo car but didn’t go all the way but he did manage to up grade the pump and switched to #24 injectors. I’m not sure If it runs rich as he gave it to me with an OR pipe but there are times where I smell like exhaust, a little more than others. I guess the aftermarket pump is going out. I’m not sure how much it cost but I’m sure it cost more than a factory unit and to have it go out after 40k miles, it seems like a waste of money. Will I be ok if I replace it with a factory unit?
I don’t think it’s the pump. 32 psi is good. If you take the vacuum line off of the regulator while it’s running it should jump up to around 40 psi. Also, generally a car with a bad pump won’t idle or drive very long. How about the fuel pressure regulator? Pull the little vacuum line off of then regulator and see you can see any gas coming out. It should be dry.
The 255 lph pump isn’t hurting really since we have a return style fuel system. The gas that isn’t used returns to the tank. They run around $100. The 24# injectors on the other hand might be working against you if it doesn’t have an aftermarket mass air meter and or tune. For what it’s worth, 24#’ers aren’t large enough for turbo applications.
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post #13 of 54 (permalink) Old 2 Weeks Ago
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Quote:
Originally Posted by wbrockstar View Post
It sounds like youve already got a fuel pressure gauge attached to the Schrader valve,so dont worry about buying a gauge.
If the engine is mainly stock,a 255lph pump is more than you need,but it shouldn't cause startup or running issues & it definitely shouldn't cause 32psi of pressure,unless something is wrong with it.It would be much more likely to create a rich condition & high pressure vs the opposite.To make sure the pump or another component isnt causing a flooding condition,hold the pedal to the floor while you try to start it & see if that allows it to start.If crank speed seems to increase after a few seconds of cranking,let up on the pedal while you continue cranking.Using this method should allow it to start,if a engine flood condition is occurring.
KOEO= 35-45psi
KOER= 30-40psi

To verify if its fuel related only,pull the small breather tube off the throttle body (the tube that runs between the oil filler neck on the valve cover & the little elbow port on the throttle body) spray starting fluid or carb cleaner directly into the port on the throttle body,reconnect the tube then attempt to do a startup.If it starts & runs for a few seconds then dies or continues to run without issue once started,its fuel related.If it doesn't start at all,its spark related.If you find that you're lacking both fuel and spark,the pip sensor is the most likely cause.It supplies the pulse to the ecu that triggers spark & injector pulse. To verify its presence,you can disconnect one of the harness plugs from any injector, plug a noid light or test light (use a paperclip inserted into one of the plug terminals to attach the test light clip to) into the plug terminals then crank the engine while observing the light.It should flash repetitively
I thought 30+ at idle w/ the vac line connected was “good.” Or are you saying that it shouldn’t prime to 32 psi?
OP was the motor running when you saw 32 psi?

Last edited by 90lxwhite; 2 Weeks Ago at 10:53 PM.
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post #14 of 54 (permalink) Old 2 Weeks Ago
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I just had this thought. Since he has an aftermarket gauge on the rail odds are he has an aftermarket adjustable regulator. It’s also plausible that the adjustable regulator was added to try and “tune” it for the 24’s without a calibrated MAF.
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post #15 of 54 (permalink) Old 2 Weeks Ago
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Quote:
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I thought 30+ at idle w/ the vac line connected was ďgood.Ē

Yeah 30+psi KOER (key on engine running) is good & its within the range (30-40psi) I listed in post #10.Pressure is usually lower with the engine running (at idle) vs with the engine off & the key on because of the vacuum supply being sent to the regulator.As seen in the diagram at the bottom,a spring is what keeps the valve seated,to prevent fuel from returning to the tank to keep pressure normal.A vacuum hose is connected.Vacuum lowers the amount of fuel pressure needed to overcome the spring pressure that keeps the valve closed.IOW- when vacuum is present at the regulator,fuel pressure will decrease.When pressure,like boost,is present at the regulator vacuum port,fuel pressure will increase from the amount of boost being created.
IOW - if the SC is putting out 8psi,8 additional pounds of force will be applied to the valve,so fuel pressure will go up.


1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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