Idles great, but stumbles when driving

rwordenjr · Oct 30, 2025

Stang9050 said:
That was my thought, but when I took the gauge off there was fuel. The kit requires using adapters (included) to attach to the shrader valve and I used a wrench to tighten it before attaching the gauge to the adapter. I even come in the house to watch YouTube to make sure I doing it right.

Seems unlikely fuel is your issue but proceed with your process.

AeroCoupe · Oct 30, 2025

Have you checked for codes? Check engine light only comes on for emissions related codes so there can be codes and no CEL.

rwordenjr · Oct 30, 2025

AeroCoupe said:
Have you checked for codes? Check engine light only comes on for emissions related codes so there can be codes and no CEL.

Sounds like egr/egr sensor related but he said no codes besides 11.

Stang9050 · Oct 30, 2025

rwordenjr said:
Sounds like egr/egr sensor related but he said no codes besides 11.

66 is the only code that shows up when using an OBD1 code scanner. Engine off, or running, that's the only code.

Stang9050 · Oct 30, 2025

Stang9050 said:
66 is the only code that shows up when using an OBD1 code scanner. Engine off, or running, that's the only code.

I'll try again tomorrow to get the fuel pressure gauge to work.

AeroCoupe · Oct 31, 2025

Well Code 66 is MAF voltage low so that is a problem that needs to be corrected.

Post in thread 'Code 66 Help!!!'

Oct 6, 2017

What codes other than the 66 are you getting?
What are you getting for MAF readings when you measure the MAF output voltages at the computer?

Code 66 or 157 MAF below minimum test voltage.

Revised 10-Feb-2014 to add 95-95 Mustang code 157 and 94-95 ECC diagram

Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires...

Blown88GT · Nov 8, 2025

Stang9050 said:
...Car runs well until it starts to warm up, then it jerks, bucks and stumbles...

Fuel Pump. They can run perfectly at idle, but when under load (car in gear on the road, not on lift), they will do exactly what you say. You will see the mechanical fuel pressure gauge drop to zero & then recover, over & over again. In my case, the pump sock had come apart & a bit of plastic was covering & uncovering the pump inlet.

Mcmahst · Nov 8, 2025

Just to eliminate it as an issue, I would go to another auto parts store and rent their fuel pressure tester and try that process again. And if you get it to work, leave it on and have somebody rev the engine so you can see the effect on fuel pressure. Also, make sure you test the pressure regulator by removed the vacuum hose at idle. Good luck.

Idles great, but stumbles when driving

rwordenjr

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AeroCoupe

lube between the nut and the face. I know my lubes

rwordenjr

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Stang9050

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Stang9050

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AeroCoupe

lube between the nut and the face. I know my lubes

Post in thread 'Code 66 Help!!!'

Blown88GT

Mcmahst

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Idles great, but stumbles when driving

Advanced Member

lube between the nut and the face. I know my lubes

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lube between the nut and the face. I know my lubes

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