So i bougt a 2001 Dodge ram 1500 a couple weeks ago and it ran pretty good when i got it, but on my way home the check engine light came on so i checked it and it was a misfire on cylinders 6 and 8. so i replaced those 2 plugs and it still had the code up but 4 and 5 came up, so i replaced them too and the code for 4 and 5 went away but 6 and 8 was still up so i decided to redo the rest and the code is still on and 4 and 5 came back up. The truck idles rough between 500 and 600 rpm and it doesnt stay at one rpm its always moving and it shakes the whole cab and when in gear it does the same thing and sounds like the truck is going to die. and while im driving from 60 to 80kms or 40 to 50mph it runs rough and the whole truck studders when you hold it at any speed in between there. but at every other speed it runs smooth. im redoing the wires on the weekend. i was wondering if anyone could tell me what they think is wrong

 

It does sound like the wires are out of place.

 

Yeah, well the wires on them are so weird, its so hard to do them.

 

Could be many things including your Crank Position Sensor or your Camshaft Position sensor. Now, I don't know about your year but, on mine, both control the timing. Lots of things can cause a misfire including a spent / clogged cat to a bad O2 sensor to a lean fuel mixture.

So, it may not even be your wires at all. You may even have a problem with the fuel pump where, the output is below normal operation thus providing less fuel / flow rate than what it should be getting. When that occurs, the A/F mix goes lean. When it's very lean, there's not enough fuel to burn thus causing a misfire. It's very uncommon to have a set of wires go south where, ALL the cylinders are throwing a misfire code.

This is what I believe to be your problem and the reason why the problem went away and then reappeared even after changing wires.

Check your fuel pressure first.

(1) Start engine and bring to normal operating
temperature.
(2) Observe test gauge. Normal operating pressure
should be 339 kPa +/–34 kPa (49.2 psi +/–5 psi).
(3) Shut engine off.
(4) Pressure should not fall below 30 psi for five
minutes.
(5) If pressure falls below 30 psi, it must be determined
if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking.

If at any time during the test the pressure fails to stay within the above range, remove and replace your pump. If at any time, the pressure drops below 30 psi within five minutes- you have a problem. Refer to step 5 for possibilities.

Chris

 

Okay thanks ill try that later and see what happens

 

have you changed the distributor cap and rotor?

 

doing that this weekend too. the truck sat in a garage for about 3monts

 

if it sat, maybe some debris clogged something in the fuel/fuel pump going bad

but that wouldnt explain misfir codes...

 

yeah like the truck runs fine at all other speeds its just in that one area

 

Just reread your symptoms again. You may want to check your coil. It sounds like symptoms of a bad coil. Under load, the coil may not be keeping up. Measure the primary and secondary and note whether it matches spec or not. It can create stuttering and would lead up to misfire codes for sure.

You may also want to check your TPS output through the driving range and note if there's any dead spots in the range of travel. If the TPS sensor is bad, it will feed erroneous data to the PCM which in turn has a negative affect on your A/F mix, the injector pulse width and numerous other timing functions.

That may lead to your O2 sensor putting out incorrect voltage and, during certain rmp ranges, it is causing the PCM to lean out the fuel mixture to the point of there being so little fuel that it can't burn the mix thus throwing a misfire code on one or more cylinders.