Timing Belt Problems

[SlowPro48]

Anyway, I guess in my instructions the reference mark and the timing mark are backwards. I suppose this would not be the case had I turned the crankshaft one more full revolution.

Wha? If you had turned the crank one more revolution you'd be right back where you started - i.e., still 180 degrees off. Turning the crank is not the problem. If you want to avoid confusion, the problem is telling people to align the dotted line on the belt WITH the TDC notch - when instructions from Isuzu say align the dotted line on the belt "180 DEGREES FROM TDC timing notch".

Note it's only a problem if you want to avoid confusion - it's not a problem from a practical/operational standpoint. As you well know, the VX runs just fine with the crank aligned 180 degrees off. All you're doing is making it fire the #5 cylinder when it thinks it's firing #2. Like I said in a previous post - just one of the advantages of a wasted spark ignition!

If you leave the instructions and pics as-is then, like the OP, people are going to continue to be confused during timing belt installs. And if they end up ignoring Isuzu's instructions and doing it as depicted in your how-to, it might even cause confusion well after the install. I can imagine the frustration of a future owner or his/her unfortunate mechanic when he discovers the high misfire count DTC he's been chasing on #4 is actually due to a bad plug wire on #1 and a confused PCM that thinks #1 is #4, #2 is #5, #3 is #6, etc!

Bart, I really appreciate the time and effort you put into your timing belt how-to. It helps all of us a great deal to have picture-rich start to finish instructions all in one place. If you truly want to eliminate future confusion though, modifying the instructions for that one step (installation of the belt on the crank pulley) to reflect what's in the manual and the TSB would take care of it - no further explainations/annotations/discussion needed ever again.

[SlowPro48]

OK term117, sorry for the TJ, let's see if we can get your prob figured out.

When you say it "didnt turn over at all" do you mean when you engaged the starter absolutely nothing happened i.e., the engine did not spin at all? Or do you mean it turned but didn't start?

Did you spin it by hand for a couple rotations to make sure there was no interference after you put the belt on?

And what do you mean when you say you "tried to start the car without putting it back together"?

[nfpgasmask]

Note it's only a problem if you want to avoid confusion - it's not a problem from a practical/operational standpoint. As you well know, the VX runs just fine with the crank aligned 180 degrees off. All you're doing is making it fire the #5 cylinder when it thinks it's firing #2. Like I said in a previous post - just one of the advantages of a wasted spark ignition!

So, are you saying that because of the way I did my timing belt swap, I must be misfiring now? Or are you saying because of the mistake in my write-up, people could get confused and then their VX would misfire after they do it wrong? If I was misfiring, wouldn't my VX run like crap, throw a CEL or whatever?

To me, my install worked fine because essentially I am just taking the old belt off, and installing a new one without disrupting anything. Technically, like you said, that would work regardless of where your pulleys are, as long as the new belt goes on in exactly the same way the old one was on.

Of course, I would love to fix my instructions, but I am not about to tear into my VX just to snap 2 or 3 pictures of this the right way. So, if there is someone out there who is doing this and would like to provide correct photos, I would gladly update my instructions, but for now, I have removed the write-up from my old website and I currently have no link to it up on my new website. As for the how-to section on this forum, the pdf probably should be taken down until the error is corrected.

Anyway, I appreciate you taking the time to spell this out, honestly, it wasn't until I studied the pictures, the videos and the diagram again and again before I realized where the mistake is.

Now I am just concerned that my VX could be screwed up somehow??!?!?

Bart

[SlowPro48]

So, are you saying that because of the way I did my timing belt swap, I must be misfiring now?

No, dude, it's not screwed up! It's all good! And everybody that followed your how-to is all good too. I wasn't saying it would cause a misfire I was saying if there's a misfire it would be attributed to the wrong cylinder which might cause some confusion when it came time to diagnose the problem. But in no way was I saying installing the timing belt according to your instructions will cause misfire or poor running.

Background info: These engines are even fire V6s so there's a power stroke every 120 degrees. Firing order is 123456 with 1 & 4 paired, 2 & 5 paired and 3 & 6 paired and by that I mean rising and falling together so that while one is at TDC at end of compression stroke, its mate is at TDC at end of exhaust stroke. The ignition system is set up so that the pairs share spark. The one that's on the compression stroke goes bang when it gets spark. (and a few degrees later will be into the power stroke) Since the other one is on exhaust stroke the spark does nothing - it's wasted.

The PCM uses two sensors to determine which cylinder is firing - one to determine crank position (that narrows it down to two) and one to determine camshaft position (that tells it which one of the two is on power stroke and which one is on intake). When the PCM senses sudden drop in crank speed (i.e., a misfire) it assigns it to a particular cylinder, keeps a count of the misfires and if there are too many, throws a DTC implicating the bad cylinder.

The belt change TSB has you align the valves and crank for #2 at TDC on compression stroke which means it's mate # 5's valves are positioned for end of exhaust stroke.

Here's why I said the PCM could get the cylinders confused: I know from working on bikes with wasted spark ignitions that as long as you've got the crank right, you can set the valves up 180 degrees off and since there's a spark every time the piston is near TDC, the bike will fire and run perfectly because the with the next turn everything will line up properly for compression stroke. If the VX runs with crank 180 degrees off like in your pictures then the PCM would be sensing that #2 is firing when in reality #5 is firing and thus if there were misfire it would assign the "blame" to the wrong cylinder. I was thinking it actually would run like that because when you set up the valves like the TSB says with #2 at TDC on the compression stroke then #5 is at TDC on exhaust so the exhaust valve is open and intake is closed. Then if the crank is positioned as per your pics, with the next turn I think both valves would be closed in #5 and what used to be a wasted spark during the exhaust stroke is now happening in the compression stroke - so it fires up and runs fine - but the sensors are telling the PCM that #2 is firing when #5 is firing and vice versa.

I'm thinking more clearly now than at 2AM last night though and am now doubting it will run with the crank 180 degrees off. The problem is I mostly work on singles and when you throw in multiple cylinders and DOHC it warps my mind! Or what little is left of it. I totally suck at visualization in 3D. I'm gonna have to draw some pictures I guess!

To be continued...