Kris Roberts

I have an ‘89 5.0 with a manual transmission. I get no response from the gas pedal at all. It starts but immediately dies. The pedal does move the throttle which in turn does move the throttle valve so no issues with the linkage there. I have gas at the Schrader valve down behind the alternator so I don’t believe there is an issue with the fuel pump or fuel filter. The mass air flow sensor is new. I checked the throttle position sensor and seems to be working fine. There are no hesitations in the reading as I move the throttle, seems smooth. What should I check next?

05stangkc

In a Round About Way I Found This Here on TMS!

See If You Can Find Some Answers Here!

https://themustangsource.com/forums/...-start-391712/

Need To Narrow Down To Fuel Delivery, Spark and Air.

Then You Can Chase The One!

A Quick Check By Unplugging IAC and See if It {Makes any Difference} Would Not Hurt!

Just My 2 Cents!

Mgb,

KC

Rather B.Blown

What about a weak fuel pump? Might be strong enough to pressurize the line to injectors to crank it, but can't keep up enough volume to keep it running when the injectors are firing.

Kris Roberts

Thanks for the suggestions! I think I have tried everything on the forum article that was mentioned now and no luck.

I haven’t heard of a weak fuel pump so I will check that next.

Rather B.Blown

​​​​​​Over the years, especially back in that era, if they were driven a lot with low fuel levels (like driving a lot on a quarter tank and just putting in a few more gallons to keep going) it would cause the pump to overheat because it is cooled by the fuel in the tank it was submerged in. Over time the pump would start to get weak and couldn't provide enough PSI to run right. Might even start off slowly, never notice it until you got on it under high demand and start stumbling on the top end. Eventually get weaker. Might make enough PSI to have plenty of pressure at the fuel rail and Schrader Valve to start and run, but once you wicked it open couldn't supply enough volume at pressure for the injectors.

Just a thought, I'm no expert but I've had a lot of Mustangs and fox bodies ones and have seen some weird stuff that was hard to find.

Maybe KC can help here but find out what the fuel pressure should be at the rail and check that with the switch on and see if it drops when it fires up

Hope you find it out easily, I love fox bodies. Wish I had several of mine back now.

05stangkc

Here You Go I Could Only Go Back to 92 As Far As Factory Shop Manual But Should Be Same Specs.


FUEL PRESSURE SPECIFICATIONS
Description kPa (psi)
Engine Running 210-310 (30-45)
Ignition On Engine Off 240-310 (35-45)
SMALLER NUMBER PSI / LARGER Number kPa

KC

Kris Roberts

Thanks for the specs. Yes the ‘89 shows the same.

Kris Roberts

Would the fuel pump get weak over time or could it happen suddenly? The car was running fine on Thursday but Saturday when I went to start it, the gas pedal was unresponsive.

05stangkc

Any Mechanical Component Can Fail in an Instant or Over time. When it Fails over Time You Simply Have a Better trail to Follow.



kc

Kris Roberts

So I finally got a fuel pressure gauge and the fuel pressure is good at the Schrader valve. Any ideas what to check next?