On COLD starts the motor fires up immediately with no stumbles or breakups. This year did not come with a tachometer so, I am assuming it jumps up to around 2k RPMs, and then drops around 800 after about 10 seconds. However, once the engine is up to operating temps, it has a hard time firing back up, it stumbles for a few seconds and then runs normal. No issues what so ever while driving or operating at speed, only on startup. No check engine lights or codes on the dash.

Possibly related: After the IAC swap (AutoZone) intermittently the transmission will hard downshift. Assuming it's something RPM related as it never did this before the IAC valve change.

2000 Ranger XLT - Automatic - 71,000k miles

Replaced:
IAC
Plugs
Wires
Ignition Coils

Picking up OBD scanner today to monitor the RPM activity.

 

Welcome to the forum

Automatics rarely came with tachometers, manuals usually did, so any year Ranger can have a tach, in 1996-2003 its a plug and play swap, tach wire is there in all years just no gauge on cluster, just FYI

Hows the MPG?
Cold engines need extra fuel to start, called Choke Mode with fuel injection
Warm engines can flood out with too much fuel

Choke Mode is run by the computer(PCM) based on the engine temp it gets from the 5 volt ECT sensor, this is a different device than the 12volt Temp Sender used for dash board temp gauge
A code reader may show you a code for ECT sensor
Ford code list here: https://www.therangerstation.com/tec...trouble_codes/

Never Google a code, look it up on a full list, first, as each sensor or control will have several codes and the ones the PCM doesn't use are as important as the one it did use


Yes, on any startup the engine should REV and then come down to "target idle" that PCM has in its memory, based on engine temp from ECT sensor
Cold engine should idle higher as its in Choke Mode, usually 1,000-1,100rpms based on outside temp, colder the engine the higher the idle
As engine/coolant warms up the idle will slowly come down to warm engine "target idle", on an 4cyl automatic 800rpms


O2 sensor
These are the ONLY sensors that have a time limit, 12 years or 100k miles, they don't set codes until they are completely DEAD, lol, but they will start costing you money in wasted gas after 12years or 100k miles, period
When they are past their limit they cause False Lean data to PCM so it runs the engine Richer than needed, a little at first but over the years more and more wasted fuel
But here's what also happens, PCM has a memory of Fuel Trims it has been using, called LTFT, long term fuel trims
As an O2 wears out the LTFT goes up, so engine runs richer and richer based on the False data from O2
On warm start, especially if air is hotter(less dense), it can be too Rich and flood out engine on start up

 

Thanks Ron!

I appreciate the response and welcome.

MPG's are sitting as expected 20-23MPG. I do mostly highway. Granted my gas gauge likes to float around, so this is just a well educated guess based on fuel consumption and mileage. That being said, I dont see a huge issue there.
No "check engine" lights on the dash so I am assuming no fault codes either. But, I will verify that this evening.

I had not given much thought to the o2 sensor being a fault. I guess I assumed, to your point, "no fault light no issues". I guess that would make some senes being that this is now a 23 yr old car and at only 71k miles, I doubt those have ever been serviced. I will look into changing that the o2 this week.

Would fuel pressure be a cause for concern? I have not pressure tested, however I dont have any issues under load or driving around town. Only on startup. Previous owner also replaced the fuel pump.

Thanks again!

 

New O2 should push you closer to 25mpg or above

Fuel pressure, in 1998 and up Ranger, should be 60psi
under 45 will set lean code, over 75 rich code, so most likely OK

Just a heads up and not related
You have dual spark plugs in each cylinder for better power
That's the benefit
Downside is you can never tell when one or two spark plugs are failing or bad
So once a year after engine is warmed up, shut it off and unplug the 3 wire connector on one of the coil packs
Start engine
Should run smooth no misfires
Shut it off and test other coil pack and other 4 spark plugs

This 4cyl Lima engine ran on 4 spark plugs from 1974 thru 1988 so you can even drive that way, one coil pack/4 spark plugs, not that you would want to, less power, lol

 

So quick update.

I have since replaced both the upstream and downstream 02 sensors. Still having the same issues on hot starts. However, now when sitting after initial start-up, the engine stumbles from 800 to 750 RPM. It feels like it wants to die, then catches itself repeatedly until I shift into gear. This also happens when I put the truck into park. I have not tested the fuel pressure yet. However, I reason that I do not have fuel pressure issues since under normal driving conditions, I have no RPM stumbles or cuts. Only at idle after initial startup ONLY or shifting between Drive and Park.

No dash codes. I did have a BANK 1 Code after trying and failing to remove the upstream o2 in my driveway. I think I damaged the components. No CEL codes after replacing the o2 and resetting the ECM.

Any thoughts??

Replaced:
IAC
Plugs
Wires
Ignition Coils
TPS
Down/Upstream 02 Sensors

 

What does it idle at in Drive or Reverse?

On cold start what is the idle in PARK?

How did the dual spark plug test come out?

 

Idle by gear:
P after initial startup = 800 but drops between 650/700 approx. every 10 seconds
R = Idle stays consistent
From D to P = Idle drops to 650/700 and then slowly pick backup to 800. Feels like it wants to die.
Cold Start = Idle jumps to 2000 then backs down slowly to 800. Thats when the idle starts to bounce between 650 and 800.

No change with the plug test.

I ordered an Motorcraft IAC yesterday to see if that resolves some of the issues. I noticed more issues after replacing the IAC with a Durlast one from Autozone. However, these idle issues only started after the failed o2 removal.

 

replaced the IAC with a Motorcraft OEM piece. No change.

The motor still wants to die when put into DRIVE from PARK. It also fluctuates idle still on cold start up and occasionally after being driven, then sat at idle at a red light.

I have not tested the fuel pressure. However the previous owner did confirm he replaced the entire fuel pump assembly already. So, I’m taking his word that this is not an issue.

Now I am leaning more towards a MAF issue. I have not tested the voltages yet. However, based on my symptoms, I can reasonably conclude that the MAF might be the issue. On cold start, the motor is using the IAC to open and force more air into the intake. Once that closes is when I have issues with idle stumble and when hot (IAC does not open).

Does that sound correct?

 

I would invest $15 in a Bluetooth OBD2 reader, like an ELM327, APPs are free or $5

Then you can "see" what the computer sees for each sensor or control(IAC is a control)
If temp sensor is telling computer its at 70deg then 140deg then 70deg computer will raise and lower idle
Or if RPMs are 800 then 1,500 then 500(crank/cam sensors) it will also raise and lower RPMs to try and make them stable and maybe stall the engine

Or as you said, MAF sensor could be sending computer higher and lower AIR WEIGHT erroneously
MAF sensor "weighs" the in coming air, computer already KNOWS how much air is coming in, 2.5 liters at Wide Open Throttle(WOT), the rest is just Match, i.e. at 1,500RPMs the engine is pulling in XXX liters of air every minute, its just Math
Air weigh changes alot, cold air is heavy, warm air is lighter(hot air rises), sea level air is heavier than air in Denver(5,000ft elevation)
So MAF sensor is important
Seeing what MAF sensor is telling computer and if its stable would be good to "see"

 

Thanks Ron.

I do have an OBD scanner. I have a fairly basic version that does allow me to monitor things like MAF speed, Bank fuel % etc. What exactly should I be monitoring? I cycled through a few options as I rev'd the motor up and down. Nothing seemed "out of the ordinary" but I feel as if I am not qualified to answer that fully.

I also picked up a new Duralast MAF from Autozone and hooked it up to see if the starting/idle issues were resolved. They were not. The idle issue persists.

I am not sure what to track down now. Going to get a fuel pressure gauge and test off the Schrader valve on the fuel rail. I am also now leaning towards a potential vacuumn leak? On cold starts the engine revs up and starts fine, once warm the idle stumbles. Im not sure that points to a vacuum leak though since the leak would be both when its hot and cold.

This has become a hassle!

 

UPDATE:
Replaced the entire fuel pump assembly a few weeks ago. No more bogging issues and engine fires immediately on COLD start. The engine also fires immediately if I turn it off and then back on. However, if I let it sit after approx. 5 minutes, it struggles to start. Motor turns over for about 5-10 seconds, fires roughly and hesitates to level-out. As soon as I shift into D or R it levels out. Could this still be associated with the aftermarket IAC? Finding an OEM IAC has been damn near impossible.

I have also recently replaced the coolant temp sensor and sending unit. No change.

Any help is appreciated!!

 

Good work, glad you got it working better

The 5 min thing reads like heat soak issue if it only happens after warmed up engine is shut off
Try it with cold engine, shut it off after cold start and wait 5 min to restart

When you shut off a warm engine coolant stops circulating and cooling fan stops, so engine bay starts to heat up
This extra heat can effect electrics in engine bay
You could pop open the hood, after you get home, then as a test wait for 5min, then see if re-start is better
If not then not a heat soak issue
If it starts better then it is


Wrecking yards are the best place to find factory IAC Valves

 

Thanks Ron!

I struggle with this because, if it was a heat soak issue wouldn't the engine hesitate to start again after I immediately turn it off? Meaning, I can drive home (45-60 min), shut it off and immediately start again with zero issues. However, if I walk away for 5-10 minutes and then come back, it will hesitate/bog and then level out after 10-15 seconds. Very strange. Almost like its loosing pressure over time. However, when I let it sit overnight, it fires immediately.

Could this potentially be a fuel delivery issue aside from pump and filter?

Its very confusing.

 

Heat soak comes after cooling fan is off and heat from the engine radiates out heating up the engine bay, so takes a few minutes for that to happen, so has to sit a few minutes

No, probably not losing fuel pressure, you are correct that would also effect cold start

 

Still dealing with these issues unfortunately. I’ve tested multiple items. Seems like good spark on both coils and and all wires. IAC drops rpm when unplugged then stalls. I unplugged the new o2 and drove around to test. Still have major issues. I also went ahead and found a OEM IAC extended the wire to accommodate (3.0 version) no change.

I do get a strong fuel smell when having hot start issues. Not sure why.

possible fuel dampener issue? I’m truly at a loss. Any advice would be extremely helpful.

 

Try the "clear flooded engine" mode when engine is warm
All engine computers have this, not a Ford thing specifically

Key on
Press gas pedal down to the floor and hold it down all the way, this shuts off fuel injectors
Crank engine over, if was flooded, then in might fire a few times, spark is still on
But with throttle wide open while cranking it will dry the intake/cylinders out
Count to 3
Release the gas pedal, injectors will start working
See if it starts normally

Computer on, RPMs at 0, TPS(throttle sensor) showing Wide Open = Clear Flooded Engine mode, injectors OFF

 

Thank you Ron.

I tried it. Still having the same issues. Truck runs great under load. Either on the freeway or around town. As soon as I come to a stop (usually) and or put it into PARK the car idle surges and/or wants to die. This idle issue also happens when put into gear and/or reverse. Sometimes the engine will die. As soon as I drive off, no issues. Still getting a perfect start on COLD start in the mornings. When the IAC levels out the idle starts to stumble and/or surge.

This certainly reads like a IAC issue. However, I've replaced it twice now (OEM and Duralast). I read another post on this forum that it could potentially be a CPS issues. Its a cheap part that is easy to replace. I will give that a shot this weekend. Not sure that really explains all my issues though...

RonD, this is a longshot... but, is there any HOUSTON, TX area mechanics you would recommend I visit?

 

For the stalling, try a new PCV Valve
PCV Valve is a "controlled vacuum leak", if it gets old and sticky it becomes a "random vacuum leak"

No I don't, as far as a Texas mechanic, but you would probably be better off with a Mobile mechanic for this issue
Shop mechanics would have to waste their time and your money on warming up the engine to try and duplicate the issue and if it stalled and wouldn't restart have it towed back to the shop, at your cost, lol
You can setup a time for a Mobile mechanic to come to your work or home and have the engine warmed up and stalling so they can try to diagnose it on the spot, with or without a test drive with you driving or in the vehicle
If it did stall and not start they can bring their service vehicle to where it stalled, lol

Shops are great for hard fixes, engine, trans, suspension repairs
But if you want to do a shop then do a Ford Dealer, the techs have access to the Ford service database where they can look up symptoms specific to your powertrain/model years, so there may be similar issues that could help diagnose the issues without having to reproduce them

 

Thanks Ron.

PCV Valve was replaced. No change unfortunately. Looks like next steps are to send to a professional. I am out of options.

Thanks for your help

 

So I went ahead and did both a smoke test (from the IAT port in the intake) no leaks, and did a fuel pressure test with a brand new tester. (I did not trust the AutoZone rental)

Key On = reads 0
Motor Running = reads 0

it did very slowly creep up to about 5psi over the course of a few minutes running. I know the rail is getting decent pressure, it shoots out when the valve in the test port is depressed. It also leaks out very little once motor is off and I depress the valve. However, the gauge reads nothing…. Even while revving the motor. This was also the case while using the AutoZone rental equipment

what could possibly explain this?? Pump AND filter were replaced roughly 6months ago.

 

 

The week I bought the truck, I do remember it blowing Fuel Pump Relay on the highway. No real indication on what or how it blew.
it has never happened again since…

Could this be related?

I have no issues aside from hot starts and sometimes at idle. Most of the time it runs with no hiccups.

 

Engine can't run below 10psi fuel pressure so gauge is, of course, not able to read pressure, check it on a tire, same valve, schrader valve
1998 and up Ranger should run with 60psi fuel pressure, and hold above 30psi with key off for MONTHS and MONTHS

 

Appreciate the advice Ron! Turns out it was user error all along.

I was able to get some good readings and I believe a leaking fuel injector is the culprit....

1st Cycle = 15psi
2nd Cycle = 35 psi then dropped to 10-15 psi within 60 seconds
3rd Cycle = 60 psi then dropped to 10-15 psi within 60 seconds
multiple cycles = 60psi and dropping

I then tried to turn the motor over. It took a very long time then sputtered and slowly got up to idle. Which I suspect as a flooded cylinder. Running motor held steady at 68 psi with idle fluctuations.

Turned the motor off and tried the "clear flooded engine" mode. Key on. Pedal WOT. The car started on multiple attempts.

Being that the fuel pump and filter were both recently replaced, is it safe to assume then that the fuel pressure loss is due to faults with the injectors?

 

Yes, could be but there is a fairly easy test for that

Clear Flooded engine mode shuts off injector pulses, so you can use that
Unplug the coil packs 4 wire connector, so no spark
Cycle key on and off a few times to build up pressure
Crank engine over a few times with "foot to the floor", i.e. clear flooded engine mode

Start pulling out spark plugs
WET tip has the leaking injector


Just to be sure
Clear Flooded engine mode only works if TPS(throttle sensor) shows WOT, 4.5v to 4.8v to computer
Throttle cables stretch over time
Put a stick against the seat and on the gas pedal holding it down all the way, go to engine bay and see if you can manually open the throttle a bit more, if so then you were not at WOT
Easy fix, Google: Ranger throttle cable mod
Couple of wire ties and your good
Re-test for leaking injector with spark on