2002 4.3L Vortec Timing - S-10 Forum
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2002 4.3L Vortec Timing

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Old 09-01-2009, 01:08 AM   #1
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2002 4.3L Vortec Timing

Need some help here.
Just replaced the lower intake manifold gasket and the spider injectors to the updated MFI. New plugs, wires, cap and rotor. I replaced the cam sensor in the distributor as well.
I have 62+ on my fuel pressure, strong spark and running a cold air intake.

I brought the motor TDC using my compression gauge and visually watching #1 come to the top of the stroke. I pointed the rotor at the (6) mark on the distributor (this is not the #6 cylinder it is a mark that GM put on the distributor for timing.) The truck starts up and idles rough. Out of all the cylinders I can pull the #3 spark plug wire off and little to no change. All the other positions change the idle and so my question is what the HECK?

If you have a solid idea on how to set the timing since there are not timing marks on the front cover only 2 marks on the harmonic balancer. I called the dealer ship and they told me to advance the timing one tooth so I did, that did not work.

There is a crank sensor that I have bench tested to be working.

I am lost at this point.

Any suggestion would be great. Please if you have this problem let me know ASAP since I need my truck to get to work.

Thanks!
Old 09-01-2009, 01:28 AM   #2
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Re: 2002 4.3L Vortec Timing

Compression is good on all the cylinders as well.
Old 09-01-2009, 02:46 AM   #3
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Re: 2002 4.3L Vortec Timing

Let the truck run and now have a P0303 missfire on number 3, any ideas of what could cause this? Compression is good. Got spark and installed new MFI injectors. Maybe the new injectors has a bad #3?

Any help would be great, thanks!
Old 09-01-2009, 03:11 AM   #4
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Re: 2002 4.3L Vortec Timing

Pulled the plugs on 1,3,5 and they are black. #3 comes up in code as it misfires. I have read through several forums. Some pointed to the MAF some to the O2 sensors...

Help?
Old 09-01-2009, 08:49 AM   #5
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Re: 2002 4.3L Vortec Timing

are the plugs on 2, 4, and 6 clean?
also, did you make sure you got the wires on
the right side of the dist. cap correctly?
3-1-5 instaed of 1-3-5?
Old 09-01-2009, 10:33 AM   #6
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Re: 2002 4.3L Vortec Timing

Yes 3,1,5 and 2,4,6 are clean. O2 sensor left side before CAT? I am going to pull it and check. Maybe when I did the work on the intake gasket cleaner and carbon made it's way down some of the exhaust ports. The truck did not start up right away so that could have caused some fuel to make its way there too.
Has anyone had this problem? I will keep you posted later today when I pull it.
Thanks!
Old 09-01-2009, 10:59 AM   #7
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Re: 2002 4.3L Vortec Timing

it might be the left bank O2 sensor. (before cat.)
you could try swapping the O2 sensors from each bank,
or if your aft-cat O2 sensor is the same part# as the front ones,
you could try swapping them to see if that makes a difference.

i'm thinking the 01-laters might have a different part# for the
aft-cat sensor though, not sure.

does your fuel pressure hold after shutting the truck off?
if it falls quickly, it MIGHT indicate a fuel leak in the
new injector asy.
Old 09-01-2009, 09:26 PM   #8
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Re: 2002 4.3L Vortec Timing

Fuel pressure is holding. Looks like the 1,3,5 cylinders are running rich.
The O2 sensor is easy to get to as well. Maybe just gunked up from the work that was done.
Just got home so I will pull it and see what condition it is in. I bought a new one this morning to have it just in case. I will swap from right to left to see if the problem follows before installing the new one.
Thanks.
Old 09-01-2009, 09:49 PM   #9
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Re: 2002 4.3L Vortec Timing

Only one cylinder mis-firing? Bad or sticky injector. If it were O2 sensor, MAF, or almost anything else, it'd be multilple mis-fires. Just went through all this on the van I drive at work. Turned out to be a bad spark plug wire.
Old 09-02-2009, 08:58 AM   #10
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Re: 2002 4.3L Vortec Timing

cleaned up the O2 on the left side and that cleaned up the 1,3,5 plugs. They no longer have that black soot look to them.
#3 is still misfiring and idle is rough. It does start out misfiring and gets worse the longer I let it run so I know the plug is getting fouled.
I have read some things online, but have no experience, with a valve issue.
I did a compression test on it showing 150+
New ECU's no change
New Coil, no change
Swapped wires, stays on 3
Swapped plugs, stays on 3
Cap rotor all new.

The dealer said to take the distributor out and advance it 1 tooth. I did and it ran worse. He said that they just had a truck in and since these motors don't have any timing marks to line up with on the chain cover you have to bring it to TDC, align the rotor pointing at the (6) and start from there... nice, huh. Don't see how this would effect just the #3 or maybe #3 is getting the worse of it. 1 and 5 when unplugged don't seem to effect it as much if I unplug 2,4 or 6 when the motor is running. <deep in thought>

The battle continues.
Old 09-02-2009, 09:02 AM   #11
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Re: 2002 4.3L Vortec Timing

New MFI injectors installed 2 days ago. One could still be malfunctioning. The problem is with the new MFI injectors you have to remove the lower intake to remove the injectors. Simply pulling on them will not work.
That is something that I don't want to pull if I don't have too. I will check to see if the injector is clicking later today.
Old 09-15-2009, 01:05 AM   #12
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Re: 2002 4.3L Vortec Timing

Truck is going to the dealership tomorrow.
Thanks for all your help, but looks like they win on this one.
Old 09-15-2009, 01:28 AM   #13
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Re: 2002 4.3L Vortec Timing

Keep us updated.
Old 09-16-2009, 05:08 PM   #14
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Re: 2002 4.3L Vortec Timing

Shop called, VAC test was jumping around. #3 has a bad valve. I figured it was going to be mechanical at this point...
$200 for a valve job, $1500 if they do it... hmmm. Time to get busy. I am a pro at pulling the top end of this truck off. HA.
I will keep you all posted when I get the heads pulled and take a look.
Old 09-22-2009, 11:51 PM   #15
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Re: 2002 4.3L Vortec Timing

So I have Warranty Direct extended warranty on the truck so back to the shop it went.
GM service pulled the valve cover off and found a bad spring on #3 exhaust valve. This was causing the misfire.
SOOooo, if you are having a misfire problem and you have done all the things that I have on my truck then pull the valve cover, start it up and check the sping movement. That is my best advise and since I could not find anything on this forum or the web I figure now it is known and it will happen to someone's 4.3L hopefully this thread helps!
Thanks,
Old 09-24-2009, 02:07 AM   #16
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Re: 2002 4.3L Vortec Timing

Truck is back and finished. Just gave it an oil change and topped off the fluids. Sure is nice to hear it just idle with out any problems. This truck is ready for the winter.
Old 09-24-2009, 08:02 AM   #17
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Re: 2002 4.3L Vortec Timing

glad to hear you got it fixed. a bad valvespring
is a fairly rare failure.
Old 12-22-2011, 03:21 PM   #18
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Re: 2002 4.3L Vortec Timing

Just to update had another valve spring go bad... Uggg.
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