98 rodeo w/ engine knock

I recenlty purchased a 98 rodeo, 3.2 v6 w/ 88,000 miles. Everything is great except an engine knock/rattle between 2500-3000 RPM. The sound, and the RPM that it appears varies depending on how hard I am accelerating. Sometimes it sounds like valve "clatter", leading me to think it is related to ignition timing, and sometimes it sound like a "knock". CEL has not come on.

I have:
changed to NKG spark plugs (sound changed somewhat)
cleaned the EGR valve
replaced PCV valve
cleaned top end w/ sea foam (sound changed again)
I am planning to put a real oil pressure guage on it to check the oil pressure, but have not yet.

Questions:
should I get a CEL if: knock sensor, or EGR valve, etc. is bad or if timing is not being advanced/retarded correctly?
What else should I check? timing belt?

Boy do I miss distributors with a set of points.
Thanks,
David

what if it's not your engine..but the exhuast that is the problem? at certain rpm's it could rattle the heat shield under there. just a thought.

it is one of two things.

1. bad timing belt tensor (I think the FAQ's covers this)

2. Spun bearing (commonly happens when you run low on oil; if it is this you will need to rebuild the engine

what if it's not your engine..but the exhuast that is the problem? at certain rpm's it could rattle the heat shield under there. just a thought.

I had read that this could be a possibility and a heat sheild rattle would be GREAT! Is there an easy way to check short of removing them? I failed to mention in my initial post that I had crawled under the vehicle and tried to rattle, shake, tap the heat sheilds, but I really couldn't tell anything.

it is one of two things.

1. bad timing belt tensor (I think the FAQ's covers this)

2. Spun bearing (commonly happens when you run low on oil; if it is this you will need to rebuild the engine

Yeah, both of these have crossed my mind, but hoping for an easier solution. Never hurts to hope. LOL It looks like I have to take everything off the front of the engine to even check the timing belt tensioner, and am certainly hoping it is not the bearing. Guess I'll check the timing belt first.
THANKS!

good luck with that. hopefully it won't be the bearing--that would be a killer.

as far as the heat sheild. i believe it's a plate sandwiched inside between the heat shield and cat. you would see it if it was.

I had a similar knock, was the tensioner. I did notice rough engine betweein 2000 and 3000 thousand at first. Then, the knock started to develop, usually when cold and then it would go away, then it was constant. Undid all of my belts, still had the noise. Then I looked at the timing belt pulleys, they were ok. Changed the water pump... Probably was good. But, while apart I did notice that the tensioner was not stiff, but springy. It should come out and hold, not bounce in and out. Started up engine, no sound, then after a few minutes tensioner must have got loose again, noise came back. Picking up new tensioner today, can't wait. I miss my Rodeo!:)

Now ya got ME worried Amigo2k... I also sometimes get a small ticking knocking sound in my 00 Rodeo ... have had it since purchase @ 100,000 miles.
How would you know if it were a spun bearing? How long would it run before croaking the engine?
I think it is probably the belt tensioner but I am waiting till 120 or 130,000 to change it out.

I had a similar knock, was the tensioner. I did notice rough engine betweein 2000 and 3000 thousand at first. Then, the knock started to develop, usually when cold and then it would go away, then it was constant. Undid all of my belts, still had the noise. Then I looked at the timing belt pulleys, they were ok. Changed the water pump... Probably was good. But, while apart I did notice that the tensioner was not stiff, but springy. It should come out and hold, not bounce in and out. Started up engine, no sound, then after a few minutes tensioner must have got loose again, noise came back. Picking up new tensioner today, can't wait. I miss my Rodeo!:)

I pulled most of the front of the motor (not crank pulley) off to check the tensioner. I could get to the tensioner pulley, but not the spring. the belt seemed tight, but I could not move the tensioner at all. Should it be THIS stiff?:screwy:

I also removed the heat shields , but no luck.
David

bishop, your ticking could be engine PING too.

It must not be the Timing Belt or Tensioner. I finally had a chance to replace both of them, and it still does the same thing. I also removed the heat shields from the exhaust pipes, but no luck. It still "feels" and sounds like it could be a timing isssue, b/c sometimes I hear "valve clatter" and sometimes I hear the knock.

Also, in my limited experience, a spun bearing would also make noise at startup.

Well, back to the drawing board..... :banghead:

Can you tell where the sound is coming from?

Can you tell where the sound is coming from?

When sitting in the driver's seat, it sounds like it is coming from the right (passenger) side of the engine. It seems louder when I am in the car than when I stand with the hood open and rev the engine. When standing there, I can't really tell where it is coming from. I think when I get a chance, next week, I am gonna try to remove the heat shields off of the exhaust manifolds and see if that makes any difference.

Try this, stand beside your front passanger wheel-well with your truck running, keep your hood closed, and bend down putting your ear between the tire and the wheel-well, see if you can hear it better.

This sounds like the same sound I've been hearing in mine for years, though I can only hear mine inside the truck if I'm running real thin oil - seems like it gets softer if I use slightly thicker oil, but not too thick.

I know it sounds weird, but this sound, on my truck is one I've been trying to chase for the last year especially, it's always somewhat been there, but it slowly got louder at the end of last year. I too thought for sure that it was a rod knocking, however, there are 2 oils my truck does magnificient on, totally eliminating the sound.

Havoline Blend 5w-30 & Rotella synthetic 5w-40 with the OEM oil filter.

I've had this truck into 3 different mechanics, they all say that the sound is friction and not a rod knocking. I too have changed out all plugs, belt, tensioner, etc. sound is still there, though very slight in mine now, I actually have to literally have my head IN the wheel-well to hear it now.

But, if I use straight Havoline oil, it comes back louder. I really believe this 3.2L engine likes an oil with higher anti-wear additives.

Try this, stand beside your front passanger wheel-well with your truck running, keep your hood closed, and bend down putting your ear between the tire and the wheel-well, see if you can hear it better.

This sounds like the same sound I've been hearing in mine for years, though I can only hear mine inside the truck if I'm running real thin oil - seems like it gets softer if I use slightly thicker oil, but not too thick.

I know it sounds weird, but this sound, on my truck is one I've been trying to chase for the last year especially, it's always somewhat been there, but it slowly got louder at the end of last year. I too thought for sure that it was a rod knocking, however, there are 2 oils my truck does magnificient on, totally eliminating the sound.

Havoline Blend 5w-30 & Rotella synthetic 5w-40 with the OEM oil filter.

I've had this truck into 3 different mechanics, they all say that the sound is friction and not a rod knocking. I too have changed out all plugs, belt, tensioner, etc. sound is still there, though very slight in mine now, I actually have to literally have my head IN the wheel-well to hear it now.

But, if I use straight Havoline oil, it comes back louder. I really believe this 3.2L engine likes an oil with higher anti-wear additives.

I have been using Havoline 10W40. I am about due for an oil change, so I'll try a different oil. This thing has just baffled me since it only shows up at certain RPM.
THANKS

..Also, in my limited experience, a spun bearing would also make noise at startup.

Well, back to the drawing board..... :banghead:

If a con rod or main bearing was spun right out of it's journal, the engine would knock so badly you'd be affraid to be in the drivers seat.:uhoh: Under those circumstances, the engine will only run a few minutes until a rod (or rods) break. You can diagnose a worn bearing by measuring oil press. You will have very low oil press if you have a worn bearing. You'd have to measure oil press at the oil filter press tap. Worn bearing 'knock' usually happens on a hot engine / thin oil.

Joel