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7 Posts
Discussion Starter · #2 ·
I am hearing a loud knocking from my engine (1999 isuzu trooper 3.4L automatic)... scary sound. Can anyone tell me how to check it out to see if it is the timing belt tensioner? I had a mechanic tell me that it threw an arm(he didn't really do much diagnostic work other than listen to it). I have had others here tell me that it is probably just the timing belt tensioner. If you can help me it could save me a lot of money and I would be grateful!!![/b]

2,334 Posts
Heh, sfellows, so you're still polling for answers. :)

I've been hoping someone else would jump in here, but…….

I'm the one who suggested to you on your original post ( which was about replacing your engine, that your problem might actually be a defective timing belt tensioner and not a rod.

I said, from the info you've given , which wasn't much.

I suggested you do a SEARCH here at planetisuzoo (LINK and at 4x4 wire, and i even gave you their link (LINK ), AND i gave you a couple of search term entries to try.

I expected you to get back with more specific info about your vehicle -- what preceded the knocking sound? what conditions? what you yourself have done so far to check it out? what, if any, other symptoms? what, if any, other conditions? -did you run low on oil? Oil light came on? Oil pressure gauge read ok? Has the timing belt been replaced? ETC!
>>> Diagnosis is as much to do with the recent past as with the current&#8230;it helps point us in the right direction without spinning our wheels needlessly. <<< help us help you.

And I expected you to get back with the results from your search, and then go from there.
I see no indication you've done any of this.
Come on - you want help, but you don't seem willing to put in any effort yourself?

My own searches here and at 4x4wire yielded a wealth of material. At this site's search engine i used the search terms AND tensioner AND noise. At 4x4wire isuzu i used +tensioner +noise. Set the time period for 5 years or so. Wade through them, and you'll get a pretty good handle on what's going on if that's your problem. I think you'll find it's worth it, whether you decide to do the work yourself or in talking to service reps and/or techs. I only read a few now, but two jumped out at me - see below.

It's one thing to be "dumb" about these things (which is why we're all here, really), it's another expecting everything presented to you on a silver platter, with no effort on your part&#8230;&#8230;&#8230;

------- Well, that's the lecture&#8230;and i can only hope you'll follow up&#8230; ------

My own experience with the tensioner knock preceded my knowing about this site and the 4x4wire site. If I *had* known, i would have saved many days of car rental and anguish about whether rebuilding the engine was a good idea.
In my case, i opted for a second opinion, and had the car towed to the dealer, who correctly diagnosed and fixed the problem. I was so relieved it wasn't a rod or whatever, i didn't even mind the high dealer $$$.

Since then, i had not-so-good experiences at the dealer (no independent shops around here work on these engines), so i decided to do my own work whenever possible. I have since changed by own timing belt and tensioner and water pump, etc. so that's my personal knowledge base about this.

My knock sound was gawd awful, and i thought it was a rod, but at the same time something didn't quite compute right; i didn't know about the tensioner as a likely culprit. a problem is pinpointing the noise - it's so loud and pervasive, that just about anywhere you check, it seems to be there. And the whole time the sound is so yelling $$$$$$$$$ that i found it hard to concentrate through my wincing.

I suggest you use a mechanics stethoscope or a length of vacuum or fuel hose stuck in an ear, with the other end placed up against different surfaces.

According to two posts i scanned from the above searches (i think in 4x4wire)
1. '&#8230;if it's the tensioner, the noise will stop at about 2300 rpm&#8230;'. I really don't remember in my case, and can't verify this. I'm quite sure that wouldn't be the case if it were a rod, though.

2. '&#8230;.the noise is caused by the timing belt flapping against the timing belt covers&#8230;'. More than likely, i'd say the noise is from the pulley 'arm' whacking against the tensioner and/or against the stop, metal against metal.

Here's an illustration of the timing belt setup.

[[[ DOHC stands for Duel OverHead Cam engine. SOHC stands for Single OverHead Cam engine.
You can see they're pretty much the same as far as this is concerned; the timing/alignment marks for installing the timing belt are different. ]]]

so, concentrate your listening efforts on the timing belt cover area, especially the passenger side about midway and down. WATCH THAT FAN AND BELTS. Feel the cover with your hand. WATCH THAT FAN AND BELTS. Use your stethoscope/vacuum line. Listen. Feel. WATCH THAT FAN AND BELTS.

Oddly, this illustration doesn't call out the timing belt tensioner - it's that cylinder-looking thing with two tabs (for the installation bolts). You can see how it keeps tension on the tension pulley(6), which keeps tension on the belt.

If you're still not sure - take the timing belt cover off and inspect - you're not losing much. If it's the engine (rod), and you rebuild what you've got, you'd be doing that anyway.

Hope this helps. And if it is the tensioner, plan on replacing the tensioner, the timing belt AND the water pump ( it sits back behind all this, and your mileage means your due for that too, and you don't want to do, or pay to have done, all this again). Some say the tension pulley, too; but i don't see the need unless it's obviously damaged in some way, and/or its bearing seems to be in bad shape.

And, IMHO, if you take it to a mechanic that doesn't work on these engines, make bloody well sure that they have the info and will take the time to install the timing belt correctly.

So, that's my info. HTH.

Please, follow up here, not a new thread, and let us know the outcome
good luck

(so there, now maybe i won't feel so guilty about getting so much from these sites without contributing some, at least) 8)

7 Posts
Discussion Starter · #4 ·
I will check it out today and post a follow-up. I have spent hours and hours searching, but I must be doing it wrong because I couldn't find anything on anyway, thanks for the help... I didn't mean to piss anyone off.

As for the addtn'l info, here goes:

The only thing that preceded the knocking was the oil light came on and went off intermittently over a 15 minute drive to get breakfast. When i came out to the trooper after breakfast, it started up and the knocking began. It was quiet at first and then became very loud over the 1/2 milethat I drove it to a mechanic 9who subsequently told me it was a rod). Checked the oil: low, but there was still oil in it. Oil pressure is ok. Just bought it at 85K and don't know if the timing belt was replaced before.

Thanks again for your help!!!!!

2,334 Posts
sfellows said:
...I didn't mean to piss anyone off. ...
not at all, although the written tone might have given you that idea. just want you to avoid unnecesary $$$, and not getting enough info to help. BUT...

The only thing that preceded the knocking was the oil light came on and went off intermittently over a 15 minute drive to get breakfast. When i came out to the trooper after breakfast, it started up and the knocking began.
well that's not good... :cry: most anytime the oil light comes on in these vehicles, it's too late.

so, 'nevermind' the previous post -- more than likely it's not the timing belt tensioner, it probably is the rod.

an oil pressure test ought to *help* you decide for sure, but probably not necessary, 'cause it's such a sure thing. but if mine, i'd like to know....

good luck :cry: sorry to give you any false hope. that's why all the info is needed when trying to give advice, especially sight unseen.
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