crazy question of the day perhaps...where can I look for a vacuum leak on this engine? Uninitiated old-timer here used to working on cars that you could almost get in the engine bay and THEN look for troubles. Feels like a vacuum leak or fuel/air problem of some kind...cleaned MAF, changed PCV valve, cannot hear a bad leak, seems to come and go, but I honestly cannot spot any problems by examining what I can get to from above (because of course I want to check the easy stuff first). Truck runs fine almost all of the time, but can get a little hesitant at times or slight shake/vibration at other times, and I will change the fuel filter as soon as I can get a disconnect tool that actually works. Thanks to anybody that can offer any advice of where potential vacuum leaks might occur that I am unaware of (which would probably be about anywhere).

 

Has the CEL come on? Have you scanned the OBD2 for codes?

The most common source of a vacuum leak on these engines is a rotten PCV elbow behind the intake.

How many miles are on the spark plugs and plug wires?

 

Double post, please delete

 

The CEL was on at one point. I cleaned the MAF and reset it and it stayed off, though the truck still seemed a little hesitant. It came back on one day when I had to quickly accelerate while on the highway from about 65 mph to 80 mph...it didn't want to go there and the CEL came back on. When I did scan for codes when the light was on I got the 0174 code...left bank too lean? Plugs and wires are about 3 years old, but with my driving that equates to less than 10,000 miles. I do not like the way the PCV valve 'sits' in there that I bought and the little plastic piece that came with it to make the connection turn 45 degrees...maybe I can upgrade it...thanks for the reply.

 

Replace the PCV valve with a Motorcraft, aftermarket valves don't meter correctly.

The lean code is a BIG clue to a vacuum leak, check the elbow behind the intake, NOT the one at the valve.

 

Thanks GLC for trying to help...I will get the Motocraft PCV valve and check what you suggested....when you say "check the elbow behind the intake, NOT the one at the valve" do you mean just follow the hose back from the PCV valve and check it there?

 

Yes, the hose goes around the back of the engine and connects to the intake or throttle body - the rubber elbow where it connects rots out. It's not that difficult to get at if you remove the plastic doghouse on top of the engine.

 

Replaced the PCV valve with motocraft and cleaned the MAF sensor again (with the MAF cleaner)...definitely smoothed things out, but still a little roughness and then 24 hours later, the dreaded PO174 code popped up again...cannot see a problem with the PCV valve hose to the intake, but will replace it today or tomorrow.

 

Do you have an exhaust leak? That can throw lean codes if it's upstream from the O2.

 

Actually, now that you mention it....it occurred to me the other day that I may have an exhaust leak when I heard my son drive the truck away...just a slight difference in sound that wasn't there before and I have not had a chance to look for it yet...do you know where it is most likely to occur? On another note, I did get a chance to remove the PVC hose that connect to the back of the intake. It is relatively new, as obviously been replaced in the past few years, before I bought the truck, and has no defect. As with many such hard-to-determine problems, the removal of this hose and just putting it back on seems to have made things better and after I cleared the CEL, it has not come back on for 3 days now (though I have not had the truck on the freeways yet). Thanks again for the idea about the exhaust leak.

 

The first place to look for a bank 2 exhaust leak is the EGR pipe. It goes from the manifold to the EGR valve.

 

Thanks again! As soon as the weather permits, I will check that out. I will say, the truck performs much better in cold weather...maybe that points me right back to the MAF sensor again....but I will check for the exhaust leak.