'97 dakota V6 with ~76000 miles.

The truck is in great shape except once it warms up it knocks at idle only. Off-idle it's fine, when you first start it it's fine, just it seems that once it goes into closed-loop mode it leans out too much. Because of this I'm suspecting it's the O2 sensors, but before I drop $100 I don't have I wanted to check and see if anyone else has experience with this.
My dad gave me this truck a month or two ago, he wasn't the original owner but the original only put a couple thousand miles on it. I have all the service records and it is due for an O2 sensor swap but I'm not in a financial situation to do preventative manintenance unless it actually solves a problem. What do you all think - O2 sensors or something else? IAC motor?
Thanks,
Darel

 

nah....i wouldn't think it is the IAC. My money is on the O2. Just outta curiosity, what kinda plugs are you running??

Oh BTW, not to be an *** (ok, maybe just a little bit) only fixing problems that arise is pro-active maintenance, not preventative. LOL

 

Not sure on the plugs, my father just gave me the truck a month ago. Thing is it's done this for several years now which is the only thing that makes me think it's not o2 - it's done it since maybe 40000 miles or so.

 

Detonation in a fuel injected vehicle is usually fuel quality, since A/F ratio and spark timing are all computer controlled. Are you sure it's detonation and not mechanical noise that only presents after the oil has warmed (thinned out)? Detonation usually gets worse under load, but lifter ticks often go away when oil pressure builds.

 

switch to a 180 degree t-stat. you may also have a bad plenum gasket. look down into your throttle body, and if you see like a puddle of oil or anything more than just a thin film, your plenum gasket is bad. that is also a major cause for knocking in a 3.9

 

Thin film, no puddles. The first thing I thought of too was fuel quality, but the truck has made this noise for so long I'm quite certain it's been subjected to every type of fuel out there, and if the damn thing needs to run premium, then screw it.

I'll try the stat but the noise begins before the engine has reached full operating temp - it just has to be running for about ten minutes, long before it reaches the operating temp of any stat. Assuming the O2 sensors are heated, it does seem like it would take about that long for the sensors to warm up and send the computer into closed-loop mode.

Any chance it's got a bad injector? I've been looking all over for one of those fuel-injector cleaner cans that screws right on to the fuel rail schraeder valve after you pull the fuel pump relay but i can't seem to find one anywhere.

Thansk guys.
Darel

 

Well, it wasn't the o2 sensors. Replaced them both and the knock is still there. What about a loose timing chain?

 

Oh, and if it helps any, when they went to do my PA emissions inspection it kept coming up "not ready to test", which both the shop and the Dodge dealer had never heard of in a truck <9000 GVW. There were three monitors not ready to test when they tried to inspect it, both before and after the o2 swap.

Not sure if the two are related but you never know. This one has me stumped, especially the computer stuff.

Thoughts?
Darel

 

welcome to DF...

I would have suggested you could try cleaning the o2's 1st... done by getting a can of CRC electronic components cleaner, yank them out and spray the exhaust stream openings real good, let them dry and reinstall them. this works to help bring them back to peak performance and i recommend doing it about every 20k miles or so.

another thing you can try is to reset the TPS... if you drill out the rivets on it you can have a little bit of adjustablity on it... measure the voltage on the signal line and shoot for .7~.75 volts. it could be that your tps is too far to one end of the acceptable limits causing a lean condition.

 

So if I measure the voltage at the signal line right now, it should be .7-.75v, correct? Is this at hot idle? If it measures correctly there's no point in drilling out the rivets, correct?

Which is the signal line?

Thanks,
Darel