2002 sputtering occasionally

[endmile]

Hi all,

I just inherited a 2002 Ranger step side with the 4.0 SOHC, about 179k miles, well taken care of. The previous owner was having an intermittent issue that he was trying to fix, but ultimately decided to give up and get a new vehicle, so he ended up giving it to me for free. I am trying to pick up where he left off.

The problem: It usually runs like a dream, but every once in a while it starts running really rough and sort of sputtering. I drove it for maybe a hundred miles over a few weeks before I finally experienced the issue on startup yesterday. When I did, it started but seemed to want to die. If I kept my foot on the gas, it would stay running, and I was able to drive it slowly. There was a lot of exhaust. It seems like maybe the fuel-air mixture is wrong. The check engine light did not come on. The next day it started perfectly with no issues. The previous owner did quite a bit to try and solve this problem, but nothing he tried solved it. One big issue is that it is so intermittent that when he put it in the shop, they never actually experienced the problem first hand, so they had a hard time diagnosing it. Like I said, it usually runs perfectly, but then it pops up occasionally, making it unreliable.

What's been done already: Full tune-up, spark plugs and wires replaced, throttle position sensor replaced, mass air flow (MAF) sensor replaced, ignition coil replaced, computer replaced.

Any ideas on where to start? The previous owner mentioned the fuel pump driver module as something he wanted to check next. Maybe a bad connection somewhere?

 

[RonD]

Welcome to the forum

The sensors and controls are all monitored, and if out of range or not connected will set 1 of several codes computer has for EACH sensor or control, depending on what was detected
Full list here: https://therangerstation.com/tech_library/OBD-II_codes.shtml
You can see each sensor has several codes that mean different things

So with no codes and a running issue the sensors must be OK and its a mechanical issue, or is it?

There are a few sensors that the computer can't compare to anything else
ECT(engine coolant temp) sensor is one of those
On startup computer looks at engine temp and will set the CHOKE if it shows under 140deF
If engine was already warmed up, it would run poorly, Rich Fuel Mix, and computer would ignore O2 sensors because it thinks its a "cold start"

The computer also can't compare upstream O2 sensors to anything else, but to have both O2 sensors fail at the same time would be very very long odds, and it wouldn't be intermittent

Its possible the fuel pump/pressure regulator(fuel pump assembly) is going out but that would be Lean running not Rich, and would be hard to be intermittent, so long shot

Plugged exhaust, Cats and muffler can break apart inside, and the pieces shift around to block flow
This causes False Lean at BOTH O2s which means computer runs engine richer than needed, and low power
Over the long term this would set codes but not when intermittent


If you haven't switched it I would do the ECT sensor because its cheap
There are two temp units on the 4.0l thermostat housing
ECT sensor, grey/red stripe wire, 5volt sensor, only used by the computer
ECT sender, red/white wire, 12volt sender, only used by dash board temp gauge

You can get a Bluetooth OBD2 reader, under $40 with extension cable, get the cable
It uses your smartphone or tablet as the display, APPS are free or $5
Works on ANY vehicle sold after 1996, any vehicle, not a Ford thing
This would allow you to view LIVE data when vehicle acts up, you can see what the computer sees and what the computer is running for a mix, and maybe why

And its not a bad investment if you plan on owning and driving vehicles, one of the better universal tools to have in the box

Intermittent is just a guessing game until you find the problem
And you think its running Rich at that time, but don't know for sure, so....................hard to pin down even a good guess, lol

 

[Dirtman]

To add to what ron said there are things called pending codes. The computer sees an issue BUT the issue requires a certain timeframe or amount of fails before it sets a permanent code (check engine light). If it's very intermittent it could keep throwing and clearing a pending code and never set off the check engine light. BUT a code reader will still pull the pending code (depending on the scanner).

I agree. Get a scanner. Best investment for an obd2 vehicle. If you have a laptop you can buy an elm327 adapter for 20-30 bucks and download forscan for free which is better than any scanner you can buy short of a professional tool costing over a grand.

 

[sheep herder]

@PetroleumJunkie412 has probably been peeing on your motor.

 

[Dirtman]

I think he only pees on the 4.0 OHV motors.

 

[PetroleumJunkie412]

I think he only pees on the 4.0 OHV motors.

Correct. The 4.0 SOHC was based on the success of the 2.9 DOHC, so I give them a pass.

 

[PetroleumJunkie412]

@PetroleumJunkie412 has probably been peeing on your motor.

Also. I like your style.

4.0 Ohv is sitting here, free to pee on for all passers-by. Invite your border collie; mine has peed on it several times.

 

[endmile]

To add to what ron said there are things called pending codes. The computer sees an issue BUT the issue requires a certain timeframe or amount of fails before it sets a permanent code (check engine light). If it's very intermittent it could keep throwing and clearing a pending code and never set off the check engine light. BUT a code reader will still pull the pending code (depending on the scanner).

I agree. Get a scanner. Best investment for an obd2 vehicle. If you have a laptop you can buy an elm327 adapter for 20-30 bucks and download forscan for free which is better than any scanner you can buy short of a professional tool costing over a grand.

I took everyone's advice and got a bluetooth ODB2 reader. It took a while to experience the problem again, but it finally happened. It's been really cold here (10-15 degrees), and the the other time it happened to me it was also very cold. There was a pending code, as Dirtman suggested.

P1121 - Throttle Position Sensor Inconsistent with Mass Air Flow Sensor

As I said in my original post, both the TPS and the MAF were replaced when trying to diagnose the problem originally. Maybe one of the new ones is bad? Maybe the wiring for one of them? Any ideas?