I have an 03 with a 5.4 with 47k on it that I bought used about 6 months ago. Recently I've noticed that when accelerating from a stop or slowing down to a stop, there's a vibration I can feel that seems to be coming from the engine compartment somewhere between 10-15 mph. I can't really hear anything that might give a hint as to what it is, only feel it throughout the truck. It also vibrates and has a slight rpm fluctuation when sitting idle at a light. I replaced the IAC & PCV valve and that seemed to help for about 2 days then I noticed it again. Whether it's related or not I don't know, but I think the A/C is short on refrigerant. The compressor seems like it's short-cycling and I can see the rpm jump when the compressor kicks on and off. For that reason I've had the HVAC controls on 'panel' to keep the compressor from coming on. And yes I've checked the elbow on the back of the TB, no issues there that I can see. The only PCV related line that looks a bit suspect is the line that runs from the top of the elbow to the firewall on the driver's side. The outside is dried and has basically crumbled away. I'll replace it once I can figure out what it's called. Any help steering me in the right direction would be greatly appreciated.

Forgot to mention that it will not start once in a while when the engine is warm. It will crank over and try to catch, but usually won't start unless I give it a little gas. It's possible I might need to change the fuel filter, but I may have already done that when I bought the truck (of course, that doesn't mean it shouldn't be done again). I'll have to check my spreadsheet when I get home.

 

Anyone have any ideas at all? Even if they seem far fetched....

 

Tough to diagnose, is it vibrating or hesitating like it is trying to keep from dying when you stop? THe short cycling on the compressor can mean that you might have a regrigerant leak and there is very little if any refrigerant in the system, does the AC work?(I know it isn't AC weather in IL right now) It sounds as if you might have a vacuum leak. It really could be a multitude of things. No check engine lights? Does this only happen when the truck is cold, or it is colder outside(below freezing)? A fuel filter wouldn't be a bad thing to change out as well. Cheap insurance....

 

My first thought is a vacum leak. I would scour the engine and try to find where something that my be bad. Change the fuel filter and see what kinda reaction you getthen from the truck. HAs this been going on long??

 

Clean the MAF sensor.

Regards

Jean Marc Chartier

 

I agree - Then ZAP the PRAM !! FREAKIN A!!- Oops pardon me , In other words, reboot after the KAM is cleared.

 

R1Jester - I checked my spreadhseet and I changed the fuel filter in September. I would hope it's not dirty enough to be a problem after only 5000 miles, but you never know. The A/C does work as far as I know (like you said, it's not exactly A/C weather in IL).

david - I'm thinking a vacuum leak also. It's been going on for about 6-8 weeks so it could be one of those things and is completely normal for my truck. My wife noticed it more than I did and pointed it out.

JMC - The MAF was cleaned about a month ago when I installed the K&N FIPK. That doesn't mean it didn't get dirty or oily from the new filter, but I would hope that's not the cause. I'll definitely give that a shot when I get some time.

Does anyone know what the vacuum line is called that runs from the top of the TB elbow over to the firewall on the driver's side? It attaches to a green fitting that has some sort of special clip on the end. I just want to know what I'm talking about when I go to get one. And thanks for the ideas.

 

It is called the Evaporative Emissions Return Tube. Your last post mentioned a FIPK was installed. That may be the culprit. Usually the Filters come pre-oiled and do not cause any problems for the MAF as the amount of oil is not excessive. Oil contamination on the MAF can reek havoc with engine controls. I would go over the install of this unit to be sure that no hose has come loose or worked it way off a fitting. Pay close attention to the joints and fittings after the MAF as they will allow unmetered air to enter the system and could cause your symptoms.

Regards

Jean Marc Chartier

 

Yea that's a fuel vapor hose for the EVAP - it should say that right on the hose if it hasn't worn off.

Listen to what your being told - I use to run a K&N - When you run an oiled filter, you have to service the MAF more often. That's why I don't run them anymore. Oil - will mist the MAF , SPECIALLY after a fresh oiling , whether done correctly or not and if your running a 3" intake , your suction is maxed to what the TB will allow, thus contaminating the MAF even quicker. When you clean the MAF disconnect the battery first - Clean the sensor and reconnect the battery - Pos. first then neg. - The MAF is an air metering sensor and needs to reset trims and tables correctly in order for your vehicle to run right.