inlaws 2002 f-150 with 4.6 cranks over but will not fire. been to the dealer and they could find no problem with it. said they tuned ignition system for $170.00. possible fuel pump relay??? starts more times than not, not knowing when it will start is a big problem , it is her only vehical.

 

Next time this problem crops up, try pressing and holding the accelerator slightly while cranking the engine. If it starts, then stalls once the accelerator is released, I would bet on a bad IAC (Idle Air Control) valve. Bad IAC's, often jammed due to carbon buildup, seem to show up more often in colder weather.

 

Yeah, and get in the habit of listening for the fuel pump when you turn the key on. Some are quieter than others, you may have to have someone listen for it while someone else turns the key to run. Should run about a minute after OFF to RUN.

 

Watch out for the pedal pressing b/c most newer vehicles will actually trip the relay if you floor the gas pedal while trying to start so that it won't flood. Then you'll be sitting there waiting for the relay to go back to normal. Try getting a fuel pressure guage on the rail and see how much pressure you have . You can rento one of these at a local parts store. If you are getting fuel then try checking for spark. They also have a spark plug and wire tester at your local parts store. Good luck.

 

"trip the relay"?? You're kidding, right?

Seriously, pressing the pedal to the floor simply tells the computer NOT to fire the injectors. This is how to clear any flooded fuel-injected engine.

The suggestion was to press the pedal "slightly". This is the correct diagnostic step to check for a stuck IAC valve. PaulC's advice was accurate and should be followed as a troubleshooting step.

Steve

 

Here is how you check your IAC valve.

1.The first thing to do (because it's easiest) is to make sure that the IAC is not electrically faulty. To do this, disconnect the harness connector from the IAC:

2. Now check the resistance across the two terminals. You should get a value between 7 and 11 ohms. If you do not, you need to replace the valve.

3.If that was OK (it probably was), you should clean and lubricate the valve. To do this, remove the bolts that hold the valve on to the throttle body(might be a torx head), and gently pry the valve off.. Be careful not to lose the gasket. Then visually inspect the sliding part of the valve (pintle) for signs of scoring or scratching.

4. If there is excessive scratching, you might need to replace the valve; in any case you should try lubricating the valve first. Take your favorite cleaner/lubricant (i.e. WD-40) and spray a lot in the two large holes. Let it sit for a bit, then shake it a bit and drain the lubricant. Repeat once or twice until the valve looks clean inside, then re-attach the valve. Tighten the bolts to 10Nm (7 ft lb).

5. If that does not work, you can check to see if the ECU is activating the valve. To do this, push back the rubber boot from the harness connector (leave the connector on the valve):

6. Probe the two connections with a multimeter while the car is running; at idle you should see a little activity. If you don't see anything, try switching the air conditioner off and then on -- the engine should lag a little bit, and then the IAC should activate to bring the idle speed back up. REMEMBER: The IAC relys on engine load mostly to operate.

The moral of the story: In NO way does "pressing the pedal slightly" truly check the valve. Thats some backyard crap. Very unprofessional.

 

my F150 does that also. I disconnect the negative cable and reconnect and it is good to go. of course that erases any codes. now I carry a scan tools in the truck to pull the code the next time it won't start. the scan tools is cheaper than having towed and paying a shop $65 to plug in thier scanner.

 

MY 2 CENTS.
How many miles on the truck?
Most electrical sensor and valve problems will give a light and a code. So I wouldn't get the ohm meter out quite yet.
I would troubleshoot it the same way as mentioned previously.
If it doesn't start turn the key off and then back to just on and listen for the fuel pump. You should hear a short hum if not proceed to test the for pressure at the rail.

The IAC valve is what allows air into the intake manifold when the throttle plate is completely closed. It is controlled by the computer system that adjust for the different sensor inputs, ie Coolant temp. intake air temp, etc.I also would crack the throttle slightly and try a restart. If the IAC is sticking or the passage is blocked this will allow air into the engine effectively bypassing the IAC. If the engine fires, this tells you one of three things, that the passage is blocked, the IAC is sticking, or it is not functioning. My truck has 112,000 and the IAC functions perfectly. I would start with a simple cleaning especially if you have higher miles.

If the engine does not start I would then proceed to check for spark.
No spark is a whole nother issue. Let us know your results.

A floored pedal is the appopriate way to clear a flooded engine.The throttle position sensor will tell the computer not to fire the injectors as previously mentioned.

On a side note "pressing the pedal slightly" will not truly check the valve however it is a valid test for a clogged passage or simply a sticking vavle that otherwise works perfectly. I learned about pressing the pedal slightly from a factory trained tech. To them tme is money and they won' break out the meter without a code.
Belittling someone that gives their time and experience freely simply because you either don't understand what they are saying or you disagree with them is simply not what this forum is about.

 

Question for mshaheedk. Your item #6. Are you checking for resistance (ohms) or volts at this point? I would think it is volts. If so, what range of volts? I'm keeping your suggestion for my files. Thanks for the input.

 

This reminds me of a situation that cropped up when Volkswagen began equipping their late Seventie's Rabbit sedans with fuel injection. Great system, unless the driver had the temerity to press the accelerator and turn the ignition key to "start" at the same time (often the drill on the driver's previously-owned carbed car). If the driver did this, a fuse governing the fuel injection system would blow, disabling the car. VW ate a lot of sheet on that one.

 

My '03 5.4L SCREW is starting to do the same thing. I is getting harder to start. Most times it cranks right up but occasionally it will crank and crank before starting. Today after work it almost did not start. When it finally did, it blew out a LOT of black smoke. The check engine light is not on so I assume no codes are stored. Still on warranty but the dealer said that until the problem was repeatable, they probably could not find anything. Sounds lame to me. Any ideas? Thanx.

p.s. I start it the same way each time and do not touch the gas pedal.

 

Given the beating that I took on my suggestion from my Chilton manual-bearing friend, I'm no longer suggesting that anyone press the accelerator on a Ford vehicle at ANY time.

BTW, use ANY lubricant to douse the IAC? No. Wrong. Very backyard. Use throttle body cleaner that is labeled as safe for oxygen sensors. Anyone care to venture a guess why?

 

HMMM.
Good catch on lubricating electrical componenets. Definitely not .

 

Same Problem I had with my 02 F-150 - Extended Cranking/No Start at times.

I replaced my crank sensor and fixed it. Only cost about $20 @ the dealer.

Just my $.02 and it fixed my truck.

Good Luck

 

Another thing to try, is the other Key, a friend of mine had a 2001 that would not start with one of his keys but would start everytime with the other, the chip in the 1 key went bad.