This may be long...but I want to spill out all the symptoms so you guys have a better idea of what I am looking at. It may all be related, it may not...

Truck has over 217,000 on it. With fresh engine oil and fresh ATF+4.

Towed a light boat stuffed with camping gear and the bed of the truck was full of camping gear. On the way to camping about 1.5hrs into the trip, I would loose all horsepower in the top gear (overdrive). If I didn't get out of the throttle, it would slowly decrease in speed and eventually some slight bucking would occur. When the bucking occurs, I could hear a popping under the hood. Hard to truly describe the popping sound...but is was like a valve slapping something. It wasn't constant, but it would be once or possibly 2-3 quick pops and then it wouldn't do it...but still with loss of horsepower.

If I stopped on the throttle to make it downshift, it would fire right back up to speed, but when it shifted up into OD it would loose all horsepower again. I pulled over and shut her down. Waited a couple of minutes and started it up and took off. It did it a couple more times, but then the problem went away. The entire episode lasted about 15 min.

On the way home....about an 1.5 into the trip, the same thing happened. This time I pulled off the road to give it a rest and even trying to excellerate at the stop sign caused it to bog down. Shut her down and let her rest for a few min and then off I went. When it happened again, I pulled over and shut her down again. When I started her up and wanted to leave the shoulder to get into traffic flow, she wouldn't go. So I rode slowly on the shoulder with flashers on hoping to limp to an exit. I decided to try getting up to speed one last time, and she did.

Now here is where it gets weird. For the last 6 months or so, when ever I got on the throttle at all (up just about any grade) the heat/AC flow in the cab would go from blowing on us, to defrost. It had a mind of its own.

Well with the last push towards home I decided to turn off the A/C and just run the air from the outside into the cab. I didn't experience another problem on the trip!!

Since the time that I bought this truck in the fall of 2009, it has not liked having to drop itself out of OD into a downshift. It would do it if I forced the issue, but never did it like to do it automatically.

IS this all realted? Or are they seperate issues? More importantly than the air in the cab...why won't my baby go when I hit the go pedal?

Thanks.

 

you have a vacuum leak.. the air shifting to defrost is indicative of this.. you won't be able to generate the power you need with a leak like that.. it's either that or your hopelessly loading the engine and in it's despair, it's kicking your defrost on.. but it's most likely a vacuum leak somewhere..

you're also describing 'pre-detonation'.. or 'pinging'.. a problem caused when the a/f load in the cylinder(s) is ignited BEFORE it reaches the top of it's travel (TDC)- and the force of the explosion is pushing down on a piston that has no choice but to continue rising.. you're hearing the piston slap against the piston rod, or the piston rod against the bearing cap.. none is good.. it is a good way to trash an engine..

Your ping sounds more as if it is from a hot engine (which means it takes FAR less fuel to ignite the a/f load), and the temperature is capable of igniting it all by itself.. this could easily be caused by running the snot out of it trying to keep up w/ overdrive on... if you have a vacuum gauge (and no vacuum leak) you could see how much load the engine is under.. (the trick is to find the speed/load that is most comfortable for the weight)..

running with the o/d on and weight anything over 1500# will cause the tranny to 'hunt' most often, which makes the engine lug, which makes the tranny hot, which causes you to respond by punching it- which causes excessive fuel consumption and engine load..

the best thing you can do is NOT use o/d while hauling anything more than 1500#.. you'll likely see an INCREASE in mpg's, and a lot more responsive an engine.. adjust your TV cable, and track down any vacuum links.

 

by the way, I'll likely get slammed for this by the board elders, but a can of ether goes a long way in finding a vacuum leak.. the general idea is to spray a little at a time around the engine while it's idling.. when you hear the increase in engine speed, you've located the area where the leak exists.. then it is just a matter of finding the broken/cracked/loose or popped off hose itself.. there is a snake pit worth of vacuum hoses behind your engine and in front of the firewall.. they can be a pain to locate when there is a leak.. it could be all the way down to your CAD, or your charcoal canister.. anywhere actually.. this is why ether is your friend..

also, you may want to consider new dizzy cap, wires and plugs too..

I hope you the best dude.. it doesn't sound like there is anything majorly wrong with your ride- it's just little things.. they can be a real PITA though.

 

I was wondering if it had something to do with the transmission getting hot, because the first time it happened on the trip, I had run with the OD off after entering a construction zone and forgetting that I had turned off the OD. What I was pulling never caused the tranny to search for gears back and forth.

So, are you saying that if I find where the vacuum leak is on the engine it could possibly fix the cab heat/AC issue as well as the loss of horsepower in OD?

What is my TV cable? And how would you adjust it/look to see that it needs to be adjusted?

 

there is a how-to in the faq section on adjusting the tv cable.. the basic concept is for the cable to be taught, and start moving at precisely the same time the throttle cables do..

if the o/d was overheating, it would have kicked off all by itself. I doubt it was overheating, but that doesn't mean the engine wasn't over-working itself when it was just to try to keep up.. you can hear and feel this, but it is easier to quantify with a vacuum gauge.

the vacuum issue can absolutely rob you of power and responsiveness.. if it isn't responsive it will hesitate to kick down to third unless you really romp it..

all of this can lead to a hotter than normal engine, which can cause pinging.. but the pinging may be a separate issue all together too..

and.. I hate to suggest this- but a loss of vacuum AND pinging is indicative of a blown plenum gasket.. have you peaked down the throttle body and looked for pooling oil in your intake manifold?

 

Oh, yeh. When I first got the truck and found this forum, I peaked. I see oil down there. Have put off tearing into that because it looks like one of those "simple" jobs that you have to take on 10 other jobs just to get to the gasket. Then walk backwards just perfectly to get humpty dumpty back together.

Is it possibly this could all be a Plenum Gasket issue? I hate to be the cause of yet another Plenum Gasket thread.

 

I'm going to say it absolutely is.. it will cause, with ease, everything you've described.

I have a '02 keg with a hughes plate installed I'll sell you if you're interested.. it only has one bung for temperature sensors.. I think your truck requires two..

sorry to be the bearer of bad news dude.. the job isn't that hard- it just takes a while to do...

edited to add: just like any other gasket- once it's compromised, it's downhill from there.. it may not have been capable of doing what you're describing slightly blown, but an all out 'sucker' and oil guzzler? It can cause it real easy like..

 

ahhhh. Thanks.

 

sorry dude.. on a parting shot: check your oil dude.. chances are once it sucked up a bunch of that it ran low and started sucking air instead, which caused the shift of your vents (loss of vacuum)- and you're low now..

 

When pulled over on the shoulder of the road, I checked the oil (new synthetic prior to the trip), and the ATF+4 (new when I changed the tranny pan gasket prior to the trip). Both were at the top of the MAX fill line.