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91 f250 460 efi not starting


overtheedge472

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91 F250 460 efi not starting at all.
The truck has started this all of sudden 2 weeks ago.
Then it started once and then back to not starting.
The truck has good fuel pressure, spark, signaling injectors
to fire. But won't start at all even if you shoot starting fluid into
the intake.
Any suggestions or ideas.
 


RonD

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If you put gas or staring fluid into the intake and it still won't fire then you have no or weak spark or no or weak compression.

Good read here on TFI system: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

Also try just running a jumper wire from "+" on battery to "+" on coil, worn ignition switch can reduce or cut power to coil/TFI system
 

overtheedge472

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I do have spark clear out at the plugs. It is okay spark
but I will try that jumper out just to see. Thanks for the link as well.
 

RonD

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I would also pull out a spark plug and see if it has too much fuel(wet), and it's general condition.
Then crank engine with it out and listen for the loud whoosh of air coming out spark plug hole on compression stroke, or if you have a compression gauge use it to get a PSI number.

IF spark plug is wet with fuel, all EFI systems have a "Clear Flooded Engine" routine.
Turn key on
Press gas pedal to the floor and hold it there(this tells computer to turn OFF fuel injectors but leave spark on)
Crank engine(hold gas pedal down, as soon as you release it injectors will start again.)

If engine fires(assuming you haven't added fuel yourself recently), then you have fuel leaking into the intake, could be injector or Fuel Pressure Regulator(FPR).
FPR is on the fuel rail and has a vacuum line attached, remove the vacuum line and check it for fuel or fuel smell, if found replace FPR it is leaking.
 
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marauderx

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Repeat after me while repeating, "check the grounds"
 

marauderx

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Also, check to make sure your power wires are good.
 

overtheedge472

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I will check the grounds. They look ok so far though.
The motor seems to have good compression. The plugs were not wet. Still fighting this thing. It stumbled to life again on Thursday and then immediately would not restart. This is annoying.
 

RonD

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Compression should be OK if it starts cold, even if it doesn't do it reliably, compression is not a "come and go" thing.

That's the first of the big 3 for a running gas engine
1. compression
2. spark
3. fuel

If you add fuel to the intake and engine doesn't start then spark would be lacking.

If you think there is spark then spark can be weak so cold engine start would be marginal, or spark could be at the wrong time.
A timing light used while cranking can tell you if spark is timed correctly.
'91 should have a TFI spark system these do had their problems after 20 years of operation, good read here on testing for a problem: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

Fuel, as said above, can be manually added to the intake, if engine starts up and then dies fuel would be the problem.
Listen for fuel pump when key is turned on, it runs for 2 seconds each time key is turned on.
Turn key on then off a few times, this builds up pressure in the fuel rail.
Fuel pressure regulator(FPR) on the fuel rail can fail, it gets stuck open, so fuel system pressure is lost after a few seconds, engine starts then dies.
FPR is connected to the fuel return line, remove this line and turn key on, no fuel should come out of FPR, if it does then replace FPR, it is leaking.
Fuel pressure on '91 should be 35-40psi, that more pressure than most tires, on the fuel rail is a schrader valve(tire air valve), press on the center pin and fuel should squirt out 30ft, 35psi is alot of pressure.
 

overtheedge472

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FYI
This truck has started and has continued to start who knows why.
I have at the beginning tested 38 PSI on the rail the fuel pumps would cycle on like they are suppose to. When it started I took the time to check timing and it is on, checked spark out of the coil with timing light it is good. Signal was and is good to injectors per noid light.
Who knows why it started and has continued to but till next time I guess we are going.
 

Maggie may

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Ignition switch! Get a new one. MCU/edis not getting signal to energise coil packs.
 

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