Or is there more? Do ignition modules go bad?

The reason I ask is that my MPG seems low, and there seems to be some missing or hesitation occurring. It's very minor though, but I already changed the spark plugs.

Thoughts?

 

Yes, modules may go bad. You can have them checked at an auto parts store such as Autozone. Tell us more about your truck - what year; what engine.

 

It's a 2003, with the V6 and a 5-speed. It's a base model work truck (looks like it should have a yellow light on top hehe). It's got around 96k miles. I bought it at an auction for $1900.

I can feel hesitation all through the rpm range. I already changed the spark plugs but that didn't really do anything. I will get plug wires, but I was hoping that would be the only other thing that could cause the hesitation. I figured that ignition modules are probably expensive.

 

Is it an ignition module that gets replaced, or is it a coil?

 

Take apart the MAF, using 'security torkx' bits. Clean the little bitty wires inside. Or, you can test to see if it is the MAF by disconnecting it [will throw a code..]. If driveability improves, that points to the MAF sending a bum signal, so you can try cleaning it or, getting a replacement.
The other thing to check is your fuel pressure and volume. Lack of fuel or low pressure can cause misses.
The ignition module can be tested at most parts stores, and the coil packs should be testable also, but generally you just measure for shorts and opens.
tom

 

these misses are so subtle that most people wouldnt even notice them. The only reason im concerned is because im hoping ill get better MPG if i find the problem

 

I'd bet more on the wires, but if you already have changed the plugs, at least you should be able to eliminate them being problematic. Do you have the miss at idle, or just under load? If you get missing at idle, you can do a visual on the plug wires in the dark. If you get arcing from the plug wires to the engine, you will see them in the dark.
Another thing to check is the EGR. Make sure that it opens and closes properly. With your year, the OBD should note its malfunction and turn on the SES/CEL light. Some V6 Vulcans did not have EGR.
tom

 

I actually ended up changing the wires the other day. It seemed to improve about 70%. I can still sense a minor stumble at idle.. its very very subtle. I can drive it to red line and its smooth, but when its under load there is still a miss now and then.

 

If it is the 4.0, you could check the upper and lower intake manifold gaskets. Depending on year, the O-ring style diameter was a smidge too small, and would allow extra air to pass until the engine warmed up. Caused a lot of cold driveability problems.
tom

 

Ok maybe I should rephrase my question :

If I have a slight miss under loan, and have already changed the plugs and wires on my 2003 3.0 V6, what would be the next most likely suspect?

Gracias!

 

Valves, rings, injectors and coils. An engine misses because it is missing fuel, air or spark. Take your pick. Fuel is injectors, fuel pressure, or leanness caused by extra air the computer does not take into account, or richness because it thinks it is getting more air than it is.
Air is the condition of the valves, rings, and intake manifold, additionally, the throttle body and the air filter enter the picture. The flow, from outside the air cleaner to going out the exhaust... You could also add in the EGR and ECT and ACT sensors.
Spark is plugs, wires, rotor, condenser, points, coil, battery, grounds, etc.
Off the top of my head.
Which do you want it to be? What is your compression? Does your intake leak? Does your throttle body have bad bushings? Does your intake system, air cleaner onward, have any leaks? Is your PCV valve mucked up with goo? Do you have any vacuum leaks on all the hoses under the hood? Do your injectors have a good, solid power supply? Is the connector to the ECM tight? Do you have corrosion on the wires under the hood?
I can't answer any of these questions. Especially from behind the keyboard. I have to imagine, from description, what is wrong.
I just wanted to point out how many things I can think of as I type to emphasize how complex a problem is presented. Give me more information, and I'll give my best guess.
Check some of the things mentioned...
tom

 

I would suspect you have an upper intake manifold leak or some other type of vacuum leak or a bad MAF at this point. A faulty cam sensor will also cause a miss, though you should in theory have a code if that is the case. One more thing, what grade fuel are you running?

 

Well you bring up a good point, and now I realize that it could be many things. Troubleshooting all of those things would be beyond my skill level. Maybe I should just take it to a mechanic.

 

I always run 87, it's all that the manual calls for.

 

When you replaced the spark plugs, what brand of plug did you install? Ranger engines seem to be partial to Motorcraft/Autolite plugs.