Hello I just bought my first ranger and it's an automatic 2003 4.0 edge model with 135k miles. It runs fine but the engine idles poorly as if it's trying not to die and sometimes when i pop it into reverse it knocks back pretty hard. Are these issues of concern or normal? Also are there any common problems that should be checked out?

 

Welcome to the forum.


No, none of those are normal operation.

2003 4.0l will have the 5R55E automatic, good transmission but at 135k will be on the backside of the time to rebuild hill, 120k is the top of the hill, lol

All automatics run on Pressure, Fords are no different, Reverse requires the highest pressure, so any pressure issues will usually show up first in Reverse.
That's why when an automatic starts to fail common thing is that it is slow to engage and then looses Reverse.
Hard clunk into Reverse could be sticking solenoid, or leaking valve body gasket, these can be checked and changed without removing transmission.

What does the transmission fluid look like?
When was it last changed?

Lucas Transmission fix can be good for high mile transmissions, it swells gaskets and seals in the trans so keeps pressure up, not a "fix" as claimed but can be a "extender" so trans lasts a few more miles.

And ALL automatics need two transmission coolers, the one in the radiator is fine for 100k miles if you never tow or carry any loads to speak of, or drive when outside temp is above 90degF, 2nd air cooler will add 50K plus miles to that.
You want trans fluid to stay between 175 and 200degF
Engine runs best at 200degF, so radiator is 180degF at best, if climbing a hill engine heats up, trans heats up and rads is at 200degF, so 0 cooling to stay below 200degF for trans fluid, lol.
Best money you will ever spend is on a 2nd trans cooler.
You may have one already so check first.


Is the idle rough only when cold or only when warmed up, or all the time?

Could need new spark plugs, gap is .054 on this engine so they need to be gapped before installing, out of the box they are often .035-.040 so wouldn't idle very well.

Fuel injected engines use an air valve to set idle, Ford calls theirs an IAC(idle air control) Valve.
The computer opens this valve all the way for starting, so without touching the gas pedal, when you start the engine RPMs should go up above 1,500 then drop back down to 1,100 for cold engine, or about 750 for warmed up engine.
When you put trans into gear idle should bump up 50-100rpm, this part can cause the clunk in reverse if trans solenoid is sticking, normally the trans eases into reverse as soon as you shift it, and then computer bumps up the idle, so no clunk, if reverse is delayed then RPMs are higher and you get the clunk.

If idle is not changing with cold and warm engine temps then could be IAC Valve needs to be cleaned.

Also the MAF(mass air flow) sensor(on air filter box) should be cleaned every 5 years or so, and fuel filter replaced at the same time, under cab, drivers seat area, in frame rail.

 

In addition to what RonD said about transmission fluid: a visual aid + more info.


There's something you can try if you want. The PCM has a base line for the engine's habits and transmission's behavior. As you drive, it makes adaptations to suit your driving style. This can cause it to pick up some unsettling habits.

Get yourself a rag and a wrench that fits your battery post nuts, as well as a jumper wire. Remove the ground post first and move it out of the way, then repeat for the positive post. With both posts disconnected, lay the rag on top of the battery to keep the terminals from touching the battery. Now, take your jumper wire and connect both of the terminals together, and leave it that way for about 20 minutes for all voltage to be 'used up' in a sense.

What this is doing is draining the capacitors inside the PCM, forcing it to 'forget' any and all adaptions it may have made and revert back to the factory settings. If you don't feel comfortable just straight up connecting positive to negative, you could also use a light bulb to do the same thing.

And, no, just pulling the negative doesn't do the same thing.

I've done this on my truck and my father's truck (both Rangers) and the difference is INCREDIBLE.

 

Wow, thanks for such helpful and in depth replies! I'll look into all those fixes. also I've read that the timing belt on the 4.0 is crap, is this true? Should i replace it?

 

4.0 SOHC doesn't use a timing belt. It uses timing chains. I know for a fact 02 and older SOHCs on the ranger had a problem with them rattling, which a set of guides, new chain, etc would fix. Not sure if the 03 has this problem. 04 for sure doesn't. Certainly not a bad idea to go in and replace if you fancy to do so.

 

+1^^^

Rangers used the 4.0l OHV engine from 1990 to 2000, very reliable engine but only 160 horsepower.
Ford built another engine, the 4.0l SOHC(over head cam) in 1996, and started installing them in Explorers in 1997, it has 205 horse power.
And in 2001 Rangers got the 4.0l SOHC engine instead of the 4.0l OHV.

But..............as said above there was a design and material flaw in the timing chains and guides used.
These were redesigned and different materials used starting around 2004/5.
2003 and earlier may have the older design or it may have been changed out already, quite a few were change under warranty, once changed there were no more issues with this.
It does require the engine to be pulled out as there is a timing chain in the rear of the engine along with 2 up front, 3 on a 4WD.

This timing chain issue wasn't 100% failure so there was no recall, but it was a known issue.

Problem often starts with a rattling noise at certain RPMs, and it is important to get it fixed sooner than later if you start to hear this noise because the 4.0l SOHC engine is an "interference engine", which means the valves and pistons share space in the cylinder.
On an interference engine if the timing belt or chain slips or breaks the pistons will hit the valves, this will for sure ruin the valves and usually cause piston and rod damage, it would be considered a catastrophic failure at that time.

You can go to a Ford dealer with your VIN and they can look up what service any Ford dealer has done on your truck, which can be informative