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Discussion Starter #1
went to smog my truck but it failed
the HC measurement was too high, and it has a miss that ive noticed for a while
it has a horrible combustion smell also but no check engine light
I did a full tune up but the miss is still there
i can drive it with no problem but it idles real rough and the gas mileage is way down
I cleaned the EGR also
Im at a loss here trying to avoid a trip to the shop
so thoughts?
thanx
 

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Vacuum leak? Gummed up injector(s)?

Did your full tune up include cap, rotor, wires, plugs, pcv, air filter, and O2 sensor?

Checked the timing?

Try pulling the codes, even if the CEL is off now the ECM will store the codes that were triggered even momentarily.
 

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Discussion Starter #3
yeah i did a full tune everything except the O2 sensor
ill check the timing
the injectors looked like they sprayed fine but ill check them to make sure
 

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Boozebag
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If you have a burnt valve, this will cause the problem. Any vacuum leak will also be an issue.
Your brake booster diaphragm might be leaking - any issue with the brake pedal feel?
If you have the tools, try a compression test.
You can take carb cleaner and spray around the base of the TB, and check any connections. You're sure the firing order is correct?

Oh, and a worn camshaft can also cause this problem. Easy to tell... Pull a valve cover (one at a time) and run the engine. Look for a rocker arm that is barely moving. This is not uncommon since modern engine oils have no zinc any more. Zinc is a high pressure additive that prevents wear...
2.8s have flat tappet cams that are prone to wear.
Hope this helps...

Confucius say: Man with bad camshaft not pass smogs... :rotf:
 

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Discussion Starter #5
So I threw a timing gun on it and it looks like my timing is off...went to adjust it but couldnt see the bolts to loosen the distributor..idk maybe i missing them. Ive only adjusted the timing on fords and could see them. So this is a first for me trying to adjust the timing on a chevy. Any tips you guys?
 

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It's there, it's just a real pain to get to. Feel the shaft of the distributor and follow it down. There you'll find the clamp and bolt. Just like a Ford, only nearly impossible to get to.

Before you mess with it though, did you disconnect the wire in the cab below the glove box before you checked the timing? You need to or you won't get a proper reading.
 

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Discussion Starter #7
What wire? i need to look that up. you remember the size of the bolt holding it??
 

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overthinker extraordinar
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So I threw a timing gun on it and it looks like my timing is off...went to adjust it but couldnt see the bolts to loosen the distributor..idk maybe i missing them. Ive only adjusted the timing on fords and could see them. So this is a first for me trying to adjust the timing on a chevy. Any tips you guys?
If your timing is way off "now", and wasn't before, you have a mechanical problem. Something like a timing chain jumped a tooth, or other such calamity. Timing does not change hardly at all if the distributor is tightened down.

BTW, the bolt head for the distributor clamp is 15mm on my s10. I find the best way to get to mine is with a 15mm socket, a swivel u-joint, then an extension and then a ratchet.
My first guess would have been vacuum leak. Use some starter fluid. While the engine is running lightly spray the fluid around any hoses, hose connections, and gasket seems. It there is a leak, the RPM will surge when you hit the vacuum leak.

good luck
 

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4 Year Intermediate Tech
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Also a metric stubby wrench is a great way to get to the hold down
 

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What wire? i need to look that up. you remember the size of the bolt holding it??
Below the glove box at the fire wall is a wiring harness. It's all wrapped except one wire, brown/tan IIRC. That wire is outside the harness and has a disconnect connector in it. Your timing is controlled by the ECM and you have to disconnect this wire to stop this control so you can set your base timing. Similar to disconnecting the vacuum advance on an older rig to set the timing.
 

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Found a pic with a search:


"The ESC Electronic Spark Timing "tan wire with a black stripe" that everyone can't find when attempting to set their timing (s-series). Wire is under the carpet on the passenger side below the heater box. It is disconnected to set the timing, then reconnected."

The sticker that *was* on your fan shroud should have called out 10 degrees advanced for the timing.
 
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