Fuel pressure drops like a rock!!!

[hal keiner]

I do not have much automotive repair experience but this forum has got me motivated to troubleshoot my own automotive problems rather than taking my 2002 ST into the shop right away whenever there is a problem. My ST idles and runs fine once it starts, but there has always been a 1-3 second lag/delay in the motor starting when turning the key to START. This has been annoying me for a long time and I did some research on the forum for possible solutions. I cleaned the MAF senser and the IAC valve, with no improvement, so I next got a pressure gauge and hooked it up to the schrader valve. This is what I found:



1) I turn the key to the ON positon (motor off) and the the gauge jumps up to 68psi almost instantly (in less than a second). I turn the key to the OFF position and the pressure drops to 15 psi almost instantly (in less than a second) and then drops the rest of the way to zero psi in less than another 5 seconds.



2) I START the engine and the gauge jumps up to 68 psi instantly (in less than a second) and stays steady at 68 psi while the motor is idling. I turn the key to OFF position, and again the pressure drops to 15 psi almost instantly (in less than a second) and then drops the rest of the way to zero psi in less than another 5 seconds.



3) I did not do a road test to check the pressure gauge at various speeds, but I assume that the pressure would be OK since the motor runs fine when driving.



4) I did not yet do a test after the motor sat overnight, to see how fast the pressure jumps to 68psi when the key is turned to ON. I did not have time to do this as I use the truck every day and don't want to mess with it in the morning. I hope to try this test soon though.



Based upon the above, I have tentatively concluded that the fuel pump is OK for providing sufficient pressure for motor idling and driving purposes, but there may be a failure in the fuel pump's check valve causing the fuel to drain back to the fuel tank which might be causing the a lag when starting the motor. Does this seem like a good conclusion? I am not totally sure that it is causing the lag in starting the motor, since the pressure jumps up to 68 psi pretty quickly when the key is turned to ON.



If the fuel pump check valve is faulty and causing the problem, is it wise or unwise to install a check valve into the fuel line (between the fuel pump and the fuel rail) to see if it solves the problem? Even if this is only a temporary "fix", it might demonstrate if the motor will start better before I spend the big bucks on a new fuel pump. What do you all think of this idea? Is it crazy? If so, save me from myself.



Thanks in advance for any responses.



Below is a link to an earlier post of mine on the same subject. It got kind of long, so I thought it better to start a new thread for these new questions.

 

[scott degroot]

See what your pressure does first thing in the am. Don't turn the key and wait, just try to start it like you normally would. If it is cranking and not starting and your pressure is normal then the f/p isn't your problem, however if it is cranking and your pressure is low and it starts when the pressure hits normal then the pump is probably your issue. Your fuel pressure shouldn't be bleeding off that quick. Also make sure that you have no leaks anywhere in your gauge connections, even a little seepage will cause the pressure to rapidly decline.



As far as a check valve in line goes I would think that after all these years of pumps failing due to this concern that if it were a good idea someone in the aftermarket would have made a check valve kit already. Personally I wouldn't even mess with trying it with todays plastic fuel lines and all you are just asking for trouble.

 

[Doug Watts]

I ALWAYS wait until the ABS light goes out before trying to start my truck and have never had an issue with it starting and idling (unless the IAC was dirty). I was always told to wait a couple seconds before trying to start an engine with fuel injection to ensure the fuel pressure was up. Maybe this is old school thinking, but it's always worked for me.

 

[hal keiner]

Also make sure that you have no leaks anywhere in your gauge connections, even a little seepage will cause the pressure to rapidly decline.

You might be right on this. I only hand tightened the gauge to the schrader valve and it might have been leaking a little. The connection is kind of hidden at the end of the fuel rail near the firewall and under some vacuum hoses. Next time I do the test, I'll wrap some paper around the connection to see if it stays dry or not during the test. I sure would hate to replace the fuel pump only to find that it was only a leaky gauge connection. Thanks for the wisdom...

See what your pressure does first thing in the am. Don't turn the key and wait, just try to start it like you normally would. If it is cranking and not starting and your pressure is normal then the f/p isn't your problem, however if it is cranking and your pressure is low and it starts when the pressure hits normal then the pump is probably your issue.

This test makes a lot of sense to me and I can see how it would be pretty definitive as to whether replacing the fuel pump would be warranted. I'll do this test the next time I have a chance. Thanks for the wisdom...

As far as a check valve in line goes I would think that after all these years of pumps failing due to this concern that if it were a good idea someone in the aftermarket would have made a check valve kit already. Personally I wouldn't even mess with trying it with todays plastic fuel lines and all you are just asking for trouble.

The check valve idea came from the below linked product. You are probably right about not messing with this type of fix. If the fuel pump is confirmed to be bad, I should probably just suck it up and have it replaced rather than doing a possibly hack repair.



Does anyone one else have an opinion or experience with the "in-line check valve" solution for a failed internal check valve on the fuel pump?







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