I'm sick of this farking truck. I finally solved my stalling, sputtering idle problem with a new O2 sensor, and it was running great for about 3 days. Then I get a CEL yesterday, but it went away on its own today. Ran fine all along, I'm happy.

Today, on my way to work, it starts knocking like crazy, mostly when it shifts into 4th gear at about 35 MPH. Backing off the throttle helps, but any throttle makes it come back. I can also induce it in lower gears if I'm aggressive.

I looked down the throttle body, knowing this was probably the cause. The intake is a little oily, but there are no pools of oil or anything I would call unusual. But something I did check was the coolant level, because as I was stopped at a light, it heated up beyond what it usually runs (I thought the gauge was broken because it never went above about 190, but it hit 212 or more this one time). Once underway, it cooled right off and stayed cool from then on. Since my heater has been gurgling, I figured I'd add some coolant. It took about 3/4 of a gallon. On the drive home, it seemed better, but still knocked slightly in OD.

One other thing: it went from 65 degrees yesterday to 36 degrees today.

So here are my thoughts and see if you concur:

Bad coolant temp sensor?
Bad intake air temp sensor?
Tank of bad gas (filled it up yesterday)?
It's a crappy truck?

I'm sick of fixing this thing all the time. It's the most fragile vehicle I've ever owned--it's never gone more than 2 or 3 days without a CEL and every time I get it running right, something else goes to hell almost immediately. I'm sure the transmission is merely biding its time for a really inconvenient moment to take a dump. On a completely unrelated note, what's a loaded 1998 2500 SLT 4x4 extended cab, long bed with a 5.9 V8 and 68,000 miles worth?

 

what cels is your truck throwing?
wheres your coolant going? do you have a visible leak? how does your oil and tranny fluid look?
my truck will throw a code and the light will go off... but the code is still there.
some trucks will tell you what your codes are when you turn the key to the on position to the off position 3 times and leave it in the on position. it will come up on the odometer.
theres also this diagnostic thing that i can do on my truck... if you hold the trip button in and turn the key to the on position (dont let go of the trip button yet, wait) i think that the truck scans for codes when you do that. but im not too sure.

this is assuming that you have a digital odometer

 

its ok to see a little bit of crap in your intake manifold. your pcv valve will pull some oil out of your valve cover and spit it in there. you just dont want any pooling

 

My guess is that the CEL yesterday was related to a bad transmission shift--it hiccuped on the 1-2 shift and the light came on shortly thereafter. My truck is one that you can't read codes via the dashboard and AutoZone says they can't pull codes unless the CEL is on (WTF?), and it isn't on.

Oil and transmission fluid full and in good condition. Heater has been gurgling for a few months, but I knew what it was and knew it was common. I opened the cap up the other day and it puked some coolant. The recovery bottle was also empty. I don't think the coolant is going anywhere--not a blown head gasket or anything like that and there's no milkshake in the oil pan. It was just low on coolant.

Thanks for the advice!

 

Can you explain the sound of the knocking? I've been hearing about this a lot lately and actually it seems like we are having the same symptoms. My rattle (or maybe its not a rattle) starts up when I hit OD. Starts when it goes in and is pretty much constant the whole time in OD. It also does it when I'm going up hills with lot of throttle, or when I floor it. Could this be a knocking that I thought all along was some rattle? I've been listening more carefully recently and it sounds like its coming from in front of my while I'm driving, hard to tell when facing fowards but when I turn my head side ways both ways it sounds like its coming from the front of the truck. Are there any other signs of knocking other than this noise? Do you mean by adding more coolant it solved your problem? (Sorry to overtake your thread).

 

No question about it--mine is definitely pinging. It's a very distinctive sound, like marbles in a can. I'm sure you've heard other cars, usually crappy FWD GM products from the 80s, make the noise. You probably won't feel it, but you'll hear it, and your conditions suggest that you're having the same problem as I am--knocking and pinging mostly in OD, but can be induced in lower gears if you go to wide throttle openings at relatively low speed/RPM. In my case, adding coolant might have slightly reduced it, but certainly didn't eliminate it. The fact that it seems temperature related makes me suspect a temperature sensor, especially since my intake is dry.

I'm guessing this is the complaint that causes the dealer to give the ECM the "death flash" but I'm not going that route. Any other suggestions? IAT? CTS?

 

Are you going through any oil, i would check your plenum gasket.

 

That's what I meant by "no, it's not that." Checked intake first, it's dry, oil consumption is 0.

 

Check your plugs to see if they are white like it is running lean. That is what my guess is if your truck doesn't have the Death Flash. I don't know what grade gas you are running but if you are just running regular try a tank of premium to see if that helps any.

 

Yeah last night after seeing this thread/posting, I did quite a bit of research about it and the more I read the more it seemed like this could be my problem. So i have a couple of things to do, check plenum, check plugs, fill up with some 93 (any best way to do this? I read you shouldn't do it when your tank is almost empty, mixing two different octanes, creates a weak some where they might not have mixed all the way, best would be do to it half tank a couple times to get a higher percentage of higher octane fuel right?). Today on the way to school I really heard it, probably the loudest/most frequent to date. I was trying to listen carefully to see if it was simple a physical rattle, like metal on metal, or if it was inside the engine. It seems to be more in front of me (eliminating most possibilities of rattling from exhaust system) but its really hard to tell the difference if its a knocking of the engine or a rattleing. But yeah it does somewhat sound like the way matt described it, as a bunch of marbles in a tin can. This coming tuesday a guy from the shop is going to ride with me to listen to it. I dropped it off once before for them to test drive it but they said they didn't hear anything. I'm going to mention knocking and see what he thinks.