I've recently bought a 2002 Ranger with a 3.0 L engine with 70,800 miles. No check engine lite. Engine runs noticeably rough. It's more so at idle and when engine is cold. To clarify, the rough engine is not bad. Just very noticeable to me. I've had the following replaced: coil, plugs, coil to plugs wiring, 1st(?) O2 sensor and fuel injectors cleaned. The mechanic agrees that after all of these repairs (about $625.00) there is still the noticeable roughness. He suggests the next thing is to replace the inlet manifold gasket. But he won't guarantee that that will fix the problem. He says if I want to wait for cold weather (Houston area) the roughness will become more severe if it is an intake gasket. I'm a stickler for a smooth running engine but I feel like there may be something that is being overlooked. PLEASE: Any suggestions will be appreciated. I would rather not change mechanics just yet.

 

Welcome to the forum

Buy a $20 vacuum gauge and you won't have to guess.

Read here on tests and what they mean: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

It's almost like mechanics have forgotten what they are dealing with and think things have changed since Nikolaus Otto invented the 4-stroke engine in 1876.
They haven't

Don't let the Vacuum test wording make you think its for old engine, where it says "points" think ignition module, Carburetor think injectors/fuel pressure

They can add what ever they want to the outside, but a 4-stroke engine is an air pump, self powered, but still just a simple air pump.
And the best way to test a pump is pressure, in this case Vacuum pressure is more telling than exhaust pressure.


After engine is warmed up.............and idling
Unplug the two wire connector on IAC Valve, it will close all the way
RPMs should drop down to 500 or engine may even stall, either is good, no vacuum leak
If RPMs do not drop then there is a leak

Get a spray bottle and fill it with soapy water, while engine is running spray it around intake seals, should get a drop in RPM if you find a leak

What did the old spark plug tips tell you about each cylinder?
They live inside each one so can tell you if any are lean or rich or seeing some oil

Computers are a wonderful addition to making engines much much more reliable, but they are not "smart", they don't "know" what an engine is or if it is running rough, they don't "know" what "rough" even means, lol.
So don't assign a vehicle computer more brains that an Idiot Light for oil pressure, because that is what it is, dozens of Idiot Lights in one box, computer is a bit of a misnomer, calculator is closer to what it is but not as "sexy" as computer, lol. .

They see "numbers" and nothing else, and they have acceptable "ranges" for those numbers, if a "number" is out of a preset "range" they will "set a code"(turn on the Idiot Light), the code is in Binary Language, and CAN NOT BE translated into English, so if you see a code like P0171 and it translates to English as "Bank 1 too Lean", this is NOT what it means, in Binary Language it actually means "I am opening the fuel injectors on Bank 1 too long so open time is out of preset range for RPMs, thank you for listening, The Computer", computers are very polite
So even if you do get a code do not buy anything to fix it, post it in a forum and get CORRECT translation

 

First off $625 dollars for six spark plugs six plug wires, one O2 sensor and a fuel injection cleaning? I have been out of the trade for some time but this seems very expensive to me.

If I were you I would call around to a few other shops that you may have heard good things about and price out the exact job you just paid all this money for.

Make sure to go by the receipt so you get a apples to apples comparison.

Was part of this expensive service encounter due to diagnostic charges?


Regardless of the financial aspect of the last service, lets step back and see what we are dealing with.

You have a 2002 truck with 70,000 miles on it which is well below average use for a vehicle. this is under 5000 miles a year.

Things can go south when a vehicle is not used enough.

If this was my truck I would do some keep it simple old fashion diagnostics on it.

First as always I would perform a compression test ( mainly to get that warm fuzzy feeling to know each cylinder is within specifications )

Then I would do as RonD suggest and connect a vacuum gauge to the engine for diagnostic purposes.

Because the truck has been used so little, I would suspect a few things.

First and foremost I would suspect excessive carbon build up in the combustion chamber.


To take the guess work out of it, I suggest purchasing a Wireless Endoscope, or a Borescope.

Make sure to get one with the mirror attachment and make sure it is designed to penetrate your spark plug hole size.

Remove a few the spark plugs and inspect the top of the pistons then attach the mirror and inspect the upper combustion area.

The link I provided is just an example of what I am talking about, not the tool I suggest purchasing. ( do your due diligence and research what will work for your truck )


Fuel system may have and may still have complications from old stale fuel.

Just because the mechanic cleaned the fuel injectors does not mean they are functioning properly.

You may be dealing with injectors that need to be replaced, a fuel filter that should be replaced, and possibly a fuel tank that may need to be pulled and cleaned.

Not to mention a fuel pump assembly or at minimum a sock-filter that may need to get replaced.

Since you hire out your work, it is a safe bet you will not likely want to pull spark plugs and or do any diagnostic testing.

If this is the case you can try some mechanic in the bottle.

First next time you top off your fuel tank, Use premium fuel and add a bottle of fuel injection cleaner.of your choice. ( I used to like Chevron Techron I am not sure if the formula has changed )

Do this for three tanks of fuel or go by the label on the bottle for suggested use.

While the premium fuel and cleaner is in the tank, make sure to drive your truck safely and within the legal limits but spend some time at a higher engine load than normal.

You will want the drive the truck where the engine is at 4000 rpm after the engine is up to operating temperature for a extended period of time.

This does not mean go on the interstate doing 70 mph in third gear for two hours.

This means when given the opportunity to safely do so spend some time with your foot to the floor, give the engine a chance to get to 4000 rpm.

If you have a manual transmission just shift once you get to 4000 rpm.

If you have a automatic manually shift your transmission once you get to 4000 rpm.

There is no need to go full street outlaw doing smoky burnouts or abuse your truck.

Use common sense and you should see some improvement and not the police behind you.

Second if the symptoms have not improved by the third tank, clean or have cleaned the combustion chamber.

Cleaning the combustion chamber when done right and if it was really needed can dramatically improve the idle quality.

My last tip for now is to make sure the rough idle is not caused by collapsed
engine and transmission mounts.

You can get a floor jack and blocks of wood, place the jack under the oil pan and jack the engine up slightly.

If the mounts are collapsed it should be obvious with a visual inspection.

Normally jacking the engine up slightly will confirm collapsed mounts as the rough idle will smooth out and no longer be felt through the body or steering wheel.

 

Thank you EaOutlaw, I failed to mention in the description of my 2002 Ranger 3.0 engine running rough that the mechanic did do a diagnostic check, a vacuum check and "smoke test" whatever that is. On the diagnostic check he showed me a display on his computer with the engine running that strongly suggested to him that the O2 sensor was not working properly. There were intermittent spikes that should not have been there with a hot engine. I should have asked him to show me the same display after the O2 sensor was changed but I did not. I suspect the same spikes would have still been there. I will try the Chevron fuel injection cleaner. Your suggestion about the engine and transmission mounts intrigue me. I don't understand why you think that could cause an engine to run rough. I do see how it would manifest itself as a "feeling" through the steering wheel but that is not what I am feeling. I will give it a try. Thanks again for your comments about my Ranger problem.

 

Ron D, Thank you for your input on my Ranger 3.0 engine running rough. I failed to mention in my write up that a vacuum test and "smoke" tests were performed and no problem was found. I sure wish I had looked at the plugs. I would hope that if there was carbon build up that the mechanic would have let me know. Also the diagnostic test he did before the O2 sensor was changed showed spikes (hot engine) that he said should not have been there. I saw the display on his computer before the sensor was changed but not after. I suspect the spike were still there. I will try your suggestion with the IAC valve though I don't know where it is or what it looks like. Please let me know if you have a suggestion as to where I can find it. Thanks again for your reply.

 

What IAC valve is, does and looks like is seen in this thread: How to: IAC valve cleaning thread (w/pics) | Ford Explorer and Ford Ranger Forums - Serious Explorations

Mechanics, or any specialized profession, tend to over look basic things, it is often how they are trained, i.e. the old saying "if your only tool is a hammer then ALL problems look like nails"
This doesn't make him/them bad mechanics, just limited by their training method.

Not sure why someone would do a smoke test if Vacuum Test was OK?????? $$$$$$$$, lol
Almost like they were running testing procedures from a book, while that's the way you start your career in any profession, its not what YOU need as the end user of that profession.
Experience is a good teacher but NOT the best teacher, failure is, lol, so your mechanic is getting better if he failed to find the problem, hopefully a good lesson for him but you had to pay for that lesson.

 

RonD, Thanks for the link to the IAC valve. Won't disagree one iota with your observation about the mechanic. He is part owner of a well respected shop here in Alvin, TX. Thanks again.