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Hard to start when warm

Brian1973

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Previously had a thread titled Fuel Pump because was thinking it was a fuel pump issue... Previous posters suggested getting fuel pump pressure, replace IAC, replace fuel filter.

1991 Ford Ranger with 1992 3.0L engine. Seems to start fine in the morning but the rest of the day, I find pushing accelerator down to the floor helps turn her over faster.

Recently changed fuel filter. Swapped IAC from swapped engine's throttle body. No difference with either.

Mechanic suggested maybe Crankshaft Positioning sensor? or Electronic Module... but would either explain why it's easier to start with accelerator pressed down?
 


RonD

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On fuel injected engines when you press the gas pedal to the floor and hold it down(key on, engine off) that is a signal to the computer to shut off the fuel injectors, this is called "Clear Flooded Engine mode".
As soon as you release gas pedal or gas pedal comes up a bit injectors will start.

So if you hold the gas pedal down all the way engine should NOT start, it will have spark but no fuel.
If you try this test and engine fires then you have fuel leaking into intake, could be from an injector or Fuel Pressure Regulator(FPR).
FPR is on the fuel rail, the Return fuel line is connected to it and a Vacuum Hose, remove the vacuum hose and check it for fuel, if FPRs diaphragm is leaking, fuel will be sucked into intake.

IAC valve was not a bad guess.
When you turn on the key to start a fuel injected engine the computer opens the IAC Valve all the way.
Without touching the gas pedal, when you crank the engine, and it starts, RPMs should go up to 1,500+ because IAC Valve is open all the way, then computer will close IAC Valve to set idle according to coolant temp, cold engine idle should be 1,100(approx), warm idle 650(manual), 750(auto), slightly higher for both if AC is on.

If you disconnect IAC Valves wires after engine is warmed up, RPMs should drop to 500 or engine may even stall, either is good, it means no vacuum leaks, just FYI.

1991 3.0l will have a distributor and TFI module so no CKP(crank position) sensor.
The TFI modules are well known for becoming heat sensitive, causing no starts when warm.
Good read here on this system: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml
 

Brian1973

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Great info!!! Thank you for explaining. I will have to take more time than I currently have to really dive into it all. Just replaced TPS from an extra intake manifold... because yes, sorta thought it didn't have a crank position sensor as mechanic and I both looked under the hood for one previously. Possible TPS issue? Figured an easy swap so will see... Will look at TFI issues but from just scanning VERY quickly, not having any shorting out or stalling issues... ??? I believe when I press accelerator, I am doing so after turning key... Did not realize there is an issue if done in a wrong order... very interesting... Thanks!
 

Brian1973

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and FYI, I've already had a hydrolocked engine due to a faulty FPR... I'm very familiar with that little booger!!! Cost me engine as well as all the time swapping in another one... grrrr
 

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