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A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 4585
Experience:  ASE Master Certified, ASE Advanced Gasoline Engine Performance
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I have a 97 lincoln Mark VIII I have fuel pressure of 28 PSI

Customer Question

I have a 97 lincoln Mark VIII I have fuel pressure of 28 PSI at idle and when I rev the engine I hit a maximum of 34 psi. I have changed the fuel filter prior to this test. the vehicle has a lack of power when at low rpm and putting a load on the enigine and feels like it is misfiring. There appears to be no vaccum leaks and no DTCs.
Submitted: 4 years ago.
Category: Ford
Expert:  A. Penland replied 4 years ago.

HelloCustomer

From the fuel pressure readings you have listed, your fuel pressure is too low. It should be about 35 psi at idle. 28 is too low and it can cause misfire and lack of power under load. Since you already replaced the fuel filter, your fuel pump will need to be replaced. The 4.6L engine in your Mark VIII requires the proper fuel pressure to give you the performance it was designed for.

A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 4585
Experience: ASE Master Certified, ASE Advanced Gasoline Engine Performance
A. Penland and 4 other Ford Specialists are ready to help you
Customer: replied 4 years ago.

I would like to see if you have any further areas I should look. I changed my fuel pump and fuel filter. I still have the same readings.

 

If I remove the vaccum line from my fuel pressure regulator I start receieving about 40psi at idle. When I replace the vaccum line the pressure returns to 28psi?

 

Please let me know of what I should check next.

 

Bobby

Expert:  A. Penland replied 4 years ago.
Unplug the Mass Air Flow sensor and see if the problem is still present.
Customer: replied 4 years ago.
<p>Sorry for the long delay haven't been out to the garage lately.</p><p> </p><p>I unplugged the mass airflow and the situation did not change. </p><p> </p>
Expert:  A. Penland replied 4 years ago.
Leave the vacuum line off the regulator and plug the vacuum line with a bolt to stop the vacuum leak. Drive the vehicle and see if the lack of power is still present.
Customer: replied 4 years ago.
with the regulators vacuum hose remove the performance was much better.
Expert:  A. Penland replied 4 years ago.
You may want to remove the regulator and see if there is anything in the fuel rails clogging them up causing the low fuel pressure. If nothing can be seen, replace the fuel pressure regulator.
Customer: replied 4 years ago.

Thank will try tomorrow

Expert:  A. Penland replied 4 years ago.
Keep me informed. Just don't wait another month please!! JK!!
Customer: replied 4 years ago.

Ok I changed the fuel presure regulator and there is no change. Fuel pressure at idle remains at 28 PSI.

 

Could clogged catalytic converotrs cause something like this?

Expert:  A. Penland replied 4 years ago.
I will OPT OUT. I will see if another expert has any info to help you. Do not respond back to me or it will lock the question back to me again.

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