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2.5L ('98-'01) Weird misfire


Kiyp

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So i have a 1999 ford ranger with a 2.5l engine, a while ago i went to flush the heater core, while doing that i messed up a vacuum line to the heater control valve, since then the poor girl runs like dog crap for the first hour to 4 hours, its like a tractor, sounds like a misfire but no codes for it, i plugged the vacuum line because i deleted the heater core control valve buuuuut it still runs like crap, had it sitting for a while cause the clutch is starting to slip so ive been using my saturn but the tranny in her sounds like a coffee grinder if its moving but not accelerating so im going to have to use the ranger again, so id quite like to get this issue fixed, to be clear she runs like a dream still after running for a while so i would think the engine is still fine, so im really stumped
 


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RonD

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The vacuum line for heater hose valve only has vacuum when cab switch is in OFF position or MAX AC, and its NOT a vacuum leak even when its disconnected because vacuum is coming from the cab switch and then the Vacuum Reservoir, not directly from the engine/intake like most other vacuum hoses
So that's off the list of why its running poorly, for sure

And yes that control valve is not needed, it might make cab 2deg cooler in MAX AC setting, maybe

During the heater flush what else could have happened?
Since that's the timing you associate with the rough running
Did water get into the computer connector just above heater hoses in firewall, so you had a short and now corrosion?

I assume there is no CEL(check engine light), so no codes?
And CEL is working, comes on with key on?
So that would eliminate most electrical issues as far as sensors


Since you have a dual spark plug setup you can run the engine on just one coil pack(4 spark plugs) at a time to see if its a spark plug issue.
Unplug one coil pack and start engine
Then do the same using only the other coil pack

Could be low fuel pressure but long shot if it starts to run better, but worth testing fuel pressure, should be 55psi at idle and then holding it at 2,500rpm, no dropping
Rangers have no fuel pressure sensor, so have to rely on owner to test it now and then

How old is the timing belt?
They need to be replaced every 100k miles, they can slip and cause rough running, but usually doesn't return to running well
 

Kiyp

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The vacuum line for heater hose valve only has vacuum when cab switch is in OFF position or MAX AC, and its NOT a vacuum leak even when its disconnected because vacuum is coming from the cab switch and then the Vacuum Reservoir, not directly from the engine/intake like most other vacuum hoses
So that's off the list of why its running poorly, for sure

And yes that control valve is not needed, it might make cab 2deg cooler in MAX AC setting, maybe

During the heater flush what else could have happened?
Since that's the timing you associate with the rough running
Did water get into the computer connector just above heater hoses in firewall, so you had a short and now corrosion?

I assume there is no CEL(check engine light), so no codes?
And CEL is working, comes on with key on?
So that would eliminate most electrical issues as far as sensors


Since you have a dual spark plug setup you can run the engine on just one coil pack(4 spark plugs) at a time to see if its a spark plug issue.
Unplug one coil pack and start engine
Then do the same using only the other coil pack

Could be low fuel pressure but long shot if it starts to run better, but worth testing fuel pressure, should be 55psi at idle and then holding it at 2,500rpm, no dropping
Rangers have no fuel pressure sensor, so have to rely on owner to test it now and then

How old is the timing belt?
They need to be replaced every 100k miles, they can slip and cause rough running, but usually doesn't return to running well
So no corrosion on the ecu, all the pins were nice and shiny, just found the check engine light is busted but i check for codes regularly and the only 1 there is is for the idle air control valve which i unplugged a few months prior to this issue cause it caused poor idle and that doesnt seem to be the cause, timing belt age is a mystery, could use replacement soon but i doubt its slipping since the engine goes back to running fine after a seemingly random long period of time, runs with either coil pack unplugged although it does affect the engine a little which is to be expected as they do spark at different times, and im unable to check the fuel pressure at this moment as i do not have a gauge
 

RonD

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The spark plugs all fire at the same time, at every TDC for all 4 cylinders, there is no alternating, just FYI

The benefit of dual spark plugs is better power, like in the Dodge Hemi's, but it was always hard to design a dual spark distributor and also finding an open spot in the head for the extra spark plug
Distributorless ignitions made part of that easier
So both spark plugs in each cylinder fire at the same time or no benefit
Yes, you do lose a bit of power running on just 4 spark plugs, but these engines ran fine from 1974 to 1988 that way

4 valves per cylinder made for better power, and better use of space in the heads, so dual spark is not used that much any more
Except on airplane engines, lol, where reliability of two separate spark systems is a GOOD idea
 

Kiyp

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The spark plugs all fire at the same time, at every TDC for all 4 cylinders, there is no alternating, just FYI

The benefit of dual spark plugs is better power, like in the Dodge Hemi's, but it was always hard to design a dual spark distributor and also finding an open spot in the head for the extra spark plug
Distributorless ignitions made part of that easier
So both spark plugs in each cylinder fire at the same time or no benefit
Yes, you do lose a bit of power running on just 4 spark plugs, but these engines ran fine from 1974 to 1988 that way

4 valves per cylinder made for better power, and better use of space in the heads, so dual spark is not used that much any more
Except on airplane engines, lol, where reliability of two separate spark systems is a GOOD idea
Ahhhh i had always been told it was for emissions and that one goes on the exhaust stroke or something like that to burn up extra fumes but that never sounded quite right to me, in any case it loses a tiny bit of power i think but it still runs all shakey

Qfter letting her sit and run for the past 3 hours or so shes running ok again, no idea when it went away i just set it and forgot it lol but yeah still jo idea what the problem is
 

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Maybe a long shot, but I'd replace the IAC and check the O2 sensor(s)for proper operation.

-Jazzer
 

Kiyp

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Maybe a long shot, but I'd replace the IAC and check the O2 sensor(s)for proper operation.

-Jazzer
IAC hasnt been hooked uo for a loooooooong time, runs better without it, the 02 sensors are a bit grimey and old but that just makes the engine run rich not lean
 

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It’s generally a good idea to fix known problems before trying to diagnose new ones. Do you know if your IAC was operating correctly?, or why it “runs better without it”?

-Jazzer
 

Kiyp

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It’s generally a good idea to fix known problems before trying to diagnose new ones. Do you know if your IAC was operating correctly?, or why it “runs better without it”?

-Jazzer
Its just a crap IAC valve, wont bother replacing it because there's no issue with it being unplugged, im sure that if i had extreme weather changes or altitude changes id need it but i live in florida so i can manually set the throttle idle position and forget it, a bad IAC wouldn't cause the engine to run lean or have a slight misfire and it feels like it is one of those 2, bad o2 sensors could maybe cause that but it wouldn't be able to just miraculously go away after its been running for a little while, besides that when its running poorly its only doing so below 3k rpm when i get around that it will very suddenly snap back to working fine till i go below it, its not consistently ome speed it likes, and if i stay on the edge it switches between the 2, one second you will be running with hardly any power a bit shakey and engine audibly sounds like a tractor then split second you have way more power engine runs fine and everything is good, and after a seemingly random amount of run time the engine just stops having that issue unless you shut her off for a good 5 hours or so

I dont want to use up all of my money fixing issues that don't appear to be connected to this one at all
 

RonD

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IAC Valve is used on all fuel injected engines because there are no Idler Jets
All gasoline engines need to be Choked when cold, even in Florida

The computer sets a Rich Mix and high idle(IAC Valve) until engine coolant temp is 150degF or so, based on ECT sensor

So without the IAC Valve adding more air you will have a Richer mix on cold start, so sluggish engine, i.e. too much Choke
The Rich mix(choke) is based on coolant temp so no way to adjust that externally

O2 sensors can't work until they are above 650degF so need 4 to 6 minutes of run time before computer can use them

O2 sensors use a chemical reaction to read Oxygen level in exhaust, they run out of chemicals after 100k miles or 10 years
They can last to 150k or 12 years but after that they are costing you money in MPG, for sure

Motorcraft or Hitachi IAC Valves are the only brands that work reliably in Rangers(1986-2011) they are true solenoid type units
3rd party are solenoid/stepper type so don't work as well in Rangers
 

Kiyp

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IAC Valve is used on all fuel injected engines because there are no Idler Jets
All gasoline engines need to be Choked when cold, even in Florida

The computer sets a Rich Mix and high idle(IAC Valve) until engine coolant temp is 150degF or so, based on ECT sensor

So without the IAC Valve adding more air you will have a Richer mix on cold start, so sluggish engine, i.e. too much Choke
The Rich mix(choke) is based on coolant temp so no way to adjust that externally

O2 sensors can't work until they are above 650degF so need 4 to 6 minutes of run time before computer can use them

O2 sensors use a chemical reaction to read Oxygen level in exhaust, they run out of chemicals after 100k miles or 10 years
They can last to 150k or 12 years but after that they are costing you money in MPG, for sure

Motorcraft or Hitachi IAC Valves are the only brands that work reliably in Rangers(1986-2011) they are true solenoid type units
3rd party are solenoid/stepper type so don't work as well in Rangers
Well i see i was slightly misinformed but still it just further proves my point because this behavior persists long after the engine has warmed up
 

RonD

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How old are the O2s?

They take over fuel trims after warm up

Back in the day, lol, you needed to do spark plugs and wires every few years, and then tune carb and set points twice a year
Replace distributor cap and rotor every 5 years, Rebuild carb every 6 to 8 years

Now-a-days plugs and wires last longer, and you just need to replace O2s every 10-12 years
So way cheaper and way less work but it is work that needs to be done

Also in any year, replace PCV Valve every 3 to 4 oil changes, prevents valve cover and oil pan gasket leaks and generally makes engine run better
 
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Kiyp

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How old are the O2s?

They take over fuel trims after warm up

Back in the day, lol, you needed to do spark plugs and wires every few years, and then tune carb and set points twice a year
Replace distributor cap and rotor every 5 years, Rebuild carb every 6 to 8 years

Now-a-days plugs and wires last longer, and you just need to replace O2s every 10-12 years
So way cheaper and way less work but it is work that needs to be done

Also in any year, replace PCV Valve every 3 to 4 oil changes, prevents valve cover and oil pan gasket leaks and generally makes engine run better
Well if the suspension is anything to judge their age by that would mean 22 years old with almost 300k miles on them, doubt they have ever been replaced, i just wouldn't expect them to be the source of this since the issue goes away after a little while, id have done it a while ago i just cant get the upstream one loose and im broke as hell, ive got a new cat just lying around i plan on having a muffler shop put in when i have the money eventually cause i cant get the upstream bolts to it loose either so ill probably have them swap out the 02 sensors for me then but it just seems unlikely they are causing this issue
 

RonD

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Then it would be down to your computer, which costs more

The 1995 and up computers are self contained, they run both spark and fuel
And they monitor sensors and controls pretty well
You should have IAC Valve code so full time CEL(check engine light) if IAC is unplugged, its a "control"
If not then computer "sanity" is in question

What other codes have you seen?
 

Kiyp

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Then it would be down to your computer, which costs more

The 1995 and up computers are self contained, they run both spark and fuel
And they monitor sensors and controls pretty well
You should have IAC Valve code so full time CEL(check engine light) if IAC is unplugged, its a "control"
If not then computer "sanity" is in question

What other codes have you seen?
Well lately ive just seen the IAC valve cide with the obd2 app i have rn, but the one on my old phone b4 i smashed it to bits read all kinds of wacky codes popping up then disappearing, even when things were running ok, wasnt sure if it was the app or the truck but nothing else read so much insanity, that was b4 this issue tho
 


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