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Old 02-11-2016
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Ranger misfires after high RPM

Hey guys,
my 1997 ford ranger 2.3L I4 is having a bit of an issue when it it cold out more so than when it is warm out. when i have to merge onto the highway from a stoplight or or am just trying to pass some slower traffic it seems to misfire when i shift from say first to second at any RPM over 2500 or so. if i then have to stop the truck will shake and misfire for a few seconds then level out. it has new plugs and wires all motocraft and autolite products, new coil packs, new timing belt, a cold air intake cause my stock one cracked, a high flow cat cause when i got the truck it was cheaper than the OEM one, and a thrush turbo muffler because i was looking for some more tone and had a hole in the muffler after a year or so of owning it. the check engine light came on and began to blink and has stayed on for about 3 days have not had the chance to get it to get scanned. i was wondering if anyone had the same or similar issues if so how did u fix them and how much did it cost. i don't wanna get rid of my baby but i do alot of driving and cant afford to have ant major issues. truck has approx 167k on it odometer looks to have been messed with but not entirely sure and dont wanna pull dash to find out.
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Old 02-12-2016
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Flashing CEL means "danger" possible engine damage may occur, this is usually from a bad misfire detected by computer.
While there are no "good" misfires, there are ones that are worse.

Computer reads the crankshafts spinning by a "tone wheel" on the crank behind main pulley.
A circle has 360deg, tone wheel has 36 teeth, so 1 tooth = 10deg, one tooth is removed, this missing tooth passes by the CKP(crank position) sensor when #1 piston is at TDC.
Computer watches crank speed by timing the 10deg teeth as they pass by.

Computer has two ways to see misfires.
1. spark feed back, when coil fires there is an electrical feed back in the circuit if the spark plug doesn't fire, a miss but not a very bad miss.
Unless there are several feed backs in a row.

2. crank speed, computer watches crank speed, when a cylinder fires it adds spin to the crank, when it misfires it doesn't, this doesn't slow the crank down but doesn't speed it up either, so a miss but not a bad one.
Spark always happens AFTER piston passes top dead center, even though spark timing may be 10deg BEFORE TDC, by the time the spark plug ignites the air/fuel mix enough to push against the piston it is passed TDC, if it wasn't then it would SLOW the piston down and the crank, this would be a bad misfire.
And you would get flashing CEL.

I would check coil pack firing order, and make sure spark plug wires go to the intended cylinders.

Then unplug the Intake side coil, the 3 wire connector.

Now start engine, if it has a miss then firing order is wrong or bad plug or wire.

On the 4clyl Lima engines only the exhaust side coil and spark plugs work when starting.
Intake side will start to work after engine RPMs are above 400.

If engine starts and seems to run OK with just the exhaust side connected then problem is most likely on the intake side spark.
CEL will come on with coil pack unhooked, that is normal.

You do need to have the codes checked, it could be the cam sensor and crank sensor are not in sync.
The Flashing CEL is a "get it looked at right away" thing, CEL just being on means "have a look when you can".
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Old 02-12-2016
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Thanks Ron that was alot of insight! the CEL went out this morning when i started the truck and let it sit for a minute or two. the only time it seems to miss or have a code is after i need to accelerate hard to merge into traffic. the tune up and coils are both brand new because it was having a similar issue more constantly when it needed a tune up. i will have the crank position sensor checked if not replaced. im not sure if my 97 is a LIMA motor or not all i know is its a SOHC 2.3L I4. i checked the wires and plugs they are all in good shape and ran to the correct spots on the coils. im thinking maybe Timing issue or valve issue because when i had the timing belt replaced it had snapped that morning with the truck running where i took it replaced everything and said there was no sign of value issue or timing issue. it does this much more when it is cold out and even more if its cold and the motor is cold.
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Old 02-12-2016
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i should also probably mention when it does it most of the time its in first gear and second gear (the bulk of misfire and hesitation) and will usually level out once i hit 5th gear and let it cruse. Its been doing this on and off for years even before the timing belt issue and before it needed a tune up. i have kept good fuel in the truck and replaced the fuel filter and whatnot. the truck get driven between 100 and 300 miles a week between school and work and going out to see people. im just tired of not being able to find the issue and dont wanna pay a mechanic to look it over "with a fine tooth comb" and have them test everything under the sun since the CEL goes off so quickly. i have cleared all codes in the truck before and there was only the cyl 3 misfire which lead me to go get a tune up. I love my truck and dont want to screw something up by not getting it fixed but dont know where to start.
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Old 02-12-2016
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i would run several cans of seafoam mixed in with the fuel , it could just be partially clogged injectors causing the mis-fire
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Old 02-12-2016
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You have a 2.3l SOHC Lima engine, the 2.3l Duratec DOHC was first used in Rangers in late 2001 model year.
The Lima is a non-interference engine, this means the valves and pistons do not share any space in the head dome, so even if valves are open fully they can not come into contact with the top of a piston when it is at TDC.
With an interference engine the valves and pistons do share space in the head dome, so valves can be bent if they are open when piston gets to TDC.

Whats the MPG like?

Has it always been the same or do you notice it changing now and then?

So the only code in memory was P0303, misfire #3

Couple of easy tests:

All fuel injection computers have a "Clear flooded engine" routine.
Turn the key on
Press gas pedal all the way to the floor and hold it down(this will turn OFF fuel injectors)
Now try to start engine

It should not start or even fire a little

With key on computer is on, if computer sees above 4.5volts from throttle position sensor(TPS), foot to the floor, and 0 RPMs, it will enter Clear Flooded Engine routine and shut of fuel injectors but leave spark on.

If engine starts then TPS could be failing, or throttle cable has stretched(very likely) so you can't get full throttle.
If engine fires a little then you could have a leaky injector or Fuel Pressure regulator.

But try the test, it is best to do it with warmed up engine since it will react better with just a little fuel if there is a leak.
As soon as you let off the gas pedal, even while cranking engine, computer will restart injectors.


With engine warmed up and idling, unplug the IAC(idle air control) valve, RPMs should drop to 500 or engine may even stall, either is good, it means no vacuum leak.
If idle stays up around 700 then there is an air leak.
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