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Timing Chain on 93 s10 4.3 v6

Old 08-04-2015, 12:02 PM
Thread Starter
Join Date: Jan 2015
Posts: 11
Default Timing Chain on 93 s10 4.3 v6

I have been having some driving, performance, and hard starting issues with my truck. Replaced IAC valve and connector, fuel injectors, and MAP sensor and connectors. Still having issues, so I decided to change the distributor, cap, and rotor since the ones on there were original (or at least very old). Once I got the timing set other issues arose. Rough idle; idle fluctuating up and down, sometimes over short intervals and sometimes over long intervals; audible vacuum leak (intermittent), and stalling after some time. I hooked up a vacuum gauge to try and find the leak. What I found is that the needle was hovering where it should be around 17 mmHg, but it was not steady, it was very shaky. At regular intervals of about 5 seconds or so it would drop about 10 mmHg then go back up to 17. According to the gauge's manual this could indicate a bad valve (but I felt like the interval of drop should be very quick not very long like it was), so I did a compression test which came out fine. Everything between 150 and 180, though cylinder 5 was consistently about 10% less than the others.

At this point decided to have a mechanic come diagnose. He quickly said the engine was misfiring, and when he fully retarded or advanced the distributor there was no change in engine idle. After plugging in a scanner and listening some more he decided it was the timing chain. He said it has jumped one or two teeth. According to the computer scanner, timing advance was 65%. It is important to note here that the engine idle was very rough, rougher than it had been before. It was obviously not running on all cylinders.

I decided to get a second opinion. I had another guy come out and look at it. He also confirmed that it was the timing chain. However, this time it was not such a rough idle as it was before. It was back to acting the way it was before.

I even talked to a third mechanic about it and he confirmed it sounded like the timing chain, even though he didn't actually look at it.

I decided to jump in and do it myself because I don't have the money to pay for this. I had worked on the truck a lot. I actually did a full engine swap on this thing a couple years ago with a buddy who is a mechanic. Yesterday I got down to the timing chain, then turned the engine by hand until cylinder 4 was at TDC on compression stroke--according to the Haynes manual. At this position the timing marks should be lined up on the timing sprockets. As I'm coming up on the end of the compression stroke I notice the marks are not lined up. In fact they were close but off exactly as the first mechanic said they would be. I checked the distributor and the rotor was close to but not quite pointing at the cylinder 4 spark wire. So I rotated the engine a little more. The marks lined up and the rotor was pointing at the #4 spark wire.

So, my questions are as follows:

Is it possible that the distributor is in the wrong position and the timing marks are actually misaligned? Is it possible that the timing marks are actually lined up and the chain is not the issue? Is it possible that when I turned the engine just a little more I actually started coming off of the compression stroke, or did turning the engine a little more actually put me at TDC? How can I tell for sure?

Thanks in advance for all replies and advice!
Old 08-08-2015, 02:34 PM
Thread Starter
Join Date: Jan 2015
Posts: 11

I took some pictures of the marks.

Here is cylinder 1 at TDC:

Here is cylinder 4 at TDC:

In both TDC positions it looks like the marks are not lined up. I'm going off of the mark on the balancer for each cylinder being at 12 o'clock, and the fact that the rotor pointing at cylinder 1 terminal is lined up with the mark I made on the base of the distributor when I changed it.

So judging by these images, is it safe to say that the timing chain has jumped teeth? Can I remove and realign the existing chain set? Or do I have to replace it with a new one?
Old 08-17-2015, 09:11 AM
GMCSierraFan's Avatar
Join Date: Feb 2009
Location: Midwest
Posts: 1,559

Man I hope someone chimes in... this gets a little too down and dirty for what my feeble mind can come up with...

Are timing chains expensive, I don't even know... If it's less than $50 I would probably just put a new one on
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