I have a 2003 Montero Limited, 3.8L V-6, Automatic transmission. 155,000 miles.

Have had these 2 problems for a while, not sure if the symptoms are related. I bought it with these problems.

On cooler mornings (about below 50 deg F) I have a knocking or clicking that happens for a few minutes until the engine warms up. Not sure if fatiqued metal or related to the next problem...

Also, at highway speeds above about 75 MPH I get a sudden vibration that feels like a missing cylinder. It happens as long as I have the accelerator on past about 75 MPH. As soon as as let off the gas pedal it stops. As long as I'm under about 75 MPH it doesn't happen. Sometimes over 75 MPH it's not there either...so it it doesn't always do it, but usually it does.

I have an Check Engine lite on that says "bank 1 burning lean". Also, my skid-traction control does not work (I bought it this way too). Sometimes the dash light comes on saying it's not on, and also that I've lost traction, and sometimes it isn't on.

Today I changed all the spark plugs and wires...the old ones looked fine. It ran the same for a while but then after 2 hours of highway use it began acting like it could hardly stay running and was missing very badly, like never before. I started this behavior after I had the car off for about 30 minutes while I ate lunch. It hardly wanted to start...I had to pump the gas pedal some. Almost like it was out of gas. I checked all the wires and connections and all was good. I drove it less than 60 MPH to get home for about 2 hours, then it stopped missfiring and began running normal again. I've driven it three times since in the same day and it hasn't done it again.

It still does the hi-speed stumble or missfiring, however.

What are any and all of the issues the highway speed missfiring (or something that feels like it) could be? Could a a knock-sensor or speed sensor have anything to do with the rough running? Fuel feed or filter issue (only does on acceleration, not coasting)? Timing? Timing belt may not have been replaced yet.

What are the possibilities of the cold-morning start noises? Rod knock? Bad sensor? Pully knock? The sound is almost like if I stuck a playing card in the spokes of a bike wheel...steady and about that loud. Not really loud, but noticeable for sure before it goes away (2 to 3 minutes after cold start).

 

clicking=tappets, non destructive, easy to replace/set though.
miss= check coils, compression.

 

Knocking sound is likely the tappets. They are hydraulic and auto adjusting. With age, they tend to leak some oil when the engine is not running. This caused the clicking sound when you start the engine. Since you get it only at the beginning, you should be OK. If it happens all the time - you have air trapped in one or more tappets and you need to try to bleed them. Here is how:
1. Park on the level ground.
2. Make sure your oil level is good (not below the mark).
3. start the engine and while in Park with no load slowly increase RPMs to about 3,000 in the period of 15 seconds
4. Release accelerator pedal and let the engine idle for 15 seconds.
5. Repeat the rev up/ idle cycle for 10-20 times. It should clear the noise pretty quickly.

Problem #2 - miss fire and running lean. Sounds like you may have ether an air leak, a clogged injector, or an ignition problem. If you had only a misfire code, I'd suspect the ignition problem. However, since you have a Lean condition code, I think it is the other two. It may be as simple as a broken plenum gasket that lets some air bypass into the intake, or an injector not working right. You can start by checking (re-connecting) the injector harness wires and the ignition wires. If you have to take off the plenum, check all gaskets for any kinks or breaks. Replace them with new gaskets. Check to see if all your vacuum hoses are connected and not cracked too.

 

If the sound upon cold start is tappets, and it worsens, how do i adjust them myself? What do they do? Is it bad to leave them be, making that noise?

I was starting to think the misfires or missing was unrelated but couldn't see how. When I replaced the plugs and slave wires the missing became worse, which makes me think maybe something was further disturbed (like a wire, vacuum, or gasket/seal).

Thanks!

 

The tappets are hydraulic and self adjusting. They are part of the rocker arms and their job is to ensure that there is no gap between rocker arms and valves. If they are slapping around, that is because oil leaked out of them and the do not make full contact all the time (it is not extended as far as it needs to be). It can also happen if you were running low on oil and some air got sucked in and passed through the oil system. This causes an air bubble to become trapped inside one or more tappets and the they now do not have full stiffness to transfer camshaft action to the valves (air can compress easily). Try the bleeding procedure i described in the previous post. Do it few times and it should eliminate the noise. You really need to worry about this only if the noise does not go away soon after the engine start.

 

Thanks for you help so far! I’m in the middle of changing my timing belt and water pump components. I don’t think this is the problem with my sporadic idle and miss-fire problem though it needed to be done anyway. The antifreeze looks like it could be the original…it is black, and looks like used oil when in a bucket. Yet it’s not oily at all, just nasty color. And I never had any overheat issues to date. I’m wondering if the belt (that says Mits and Japan on it) and the water pump were the originals…it has 150k on the motor. But that’s just my curiosity, makes no matter now. The pump and belt looked in near-new condition, but where dirty and dusty as if on there for a few miles at least. I’d be amazed if these were the originals, but not sure too likely.

I’ve got the upper intake off and stuffed the 6 cavities with paper towels. I’ve removed all the components required off the front of engine and removed the front half of the water pump assembly and timing belt itself, and the two pulleys (all components of the timing kit from ebay). I can’t figure out why there is a freaking bolt sticking through the rear half of the pump assembly towards the front of the vehicle, which is keeping me from removing the rear pump plate so I can finish the timing component job. ??? Why did Mits design it this way? As if to force me to remove the entire intake and valve covers? So I have these 4 questions for you, one of which I hope fixes this thing:

1. The screw comes from the rear of the water pump housing (the rear half, which is still on the block). Do I have to remove the entire intake manifold (the lower part) in addition to the valve covers, to get to that screw to remove it? It looks as if I have to, but I wanted to be sure I wasn’t missing something.

2. Also, after I get the timing belt and water pump back on, I’m going to check the compression in Cyl 6 (maybe others as well) as well as test the ignition coils. What are the procedures for checking the 3.8 liter’s ignition coils? I haen’t been able to find specific bench testing or on-vehicle testing info. What should they ohm at? Or is there other better ways to check them to see if that’s the problem with the mis-fire?

3. How do I test the injectors? If I have to get that close to them anyways I thought I should test them if able.

4. Lastly, if the misfire is caused by an air leak from the manifold somewhere, I’m curious if I should change all of the gaskets on the intake manifold plenum too, even though not required for any other reason. I don’t want to cause more problems by replacing stuff that isn’t required and disturbing something else. To date that’s been my problem with this thing, lol. I have to laugh, otherwise I want to smash it! Lol

thanks!

 

here are photos of rear pump assembly and stupid bolt, lol

 

here is CL link with photos of what I'm talking about:

2003 Montero 3.8L V6 Limited with rough idle and high-speed mis-fires

 

Just a thought. Had a 99 Expedition with noisy tappets at start up and a slight tick at idle. It had 160k miles and hadn't been well maintained. Did the full seafoam treatment(1/3 can oil, 1/3 intake, 1/3 gas). I was a bit sceptical but a friend convinced me to try it. It worked. No more start-up noise or idle noise and the slight off idle hesitation was gone.

May be worth a try.

 

My guess is that the bolt shown in your photo is to help with alignment of the front half of the pump when you are assembling it.
I think you got all the bolts necessary to remove the water pump housing. According to the diagram, there should be only 5 larger bolts that hold the pump housing to the block (2 on the left, 3 on the right side looking at it from the front). There is a gasket behind the pump housing (housing to block). I wonder it if is sticking or glued. Did you try to tap the housing with a rubber mallet? On the other hand - why do you need to remove that portion of the water pump? It doesn't sound like you have a leak there and you do not need to go any further in order to replace the water pump or the timing belt. I'd stop at this point and start re-assembling.