Hey guys,

I posted a few days ago about my 95 4.9 not passing CA smog. I'd like to adjust the timing back to factory spec, but I'm a bit confused. The smog technician told me the timing was set at 13 degrees BTDC. The timing has never been adjusted since I've owned it. I bought it in 1999 with 51,000 miles on it.

The smog tech also told me the factory spec should be between 7 and 10 degrees, and that should correct my Hydrocarbon issues. He also noted a slight miss, which I can feel at steady throttle at about 40 mph. It's really minor though. I think the over advanced timing is the problem.

I went to go adjust the timing today, and the underhood emission sticker says the timing is not adjustable, that it is computer controlled. The truck has a traditional distributor, so what gives? My Haynes manual made reference to MCU controlled Duraspark II and III as well as TFI-IV setups. How do I determine which I have? If I can determine which setup I have and adjust the initial timing, will the computer do the rest? Can I hurt anything by manually making adjustments at the distributor?

Can you guys point me in the right direction on how to adjust the timing on my truck?

Its a 95 CA truck, 4.9 manual trans, OBD I with 99,000 miles. Less basic tune up stuff, everything is original. The truck runs well, no problems or strange gremlins. I even average 17 mpg.

Thanks!!

 

Vintage Blue

I just set the base timing on my 92. Your truck should be running OBD-II and EEC-V. This probably doesn't make any sense right?

Look under your hood. If you have a distributor cap, I am willing to bet that you can adjust your base timing. I know on my truck, the BASE timing is a mechanical adjustment (you grab the distributor and turn it). All other corrections above that are handled in real time by the computer as the engine is running. That is why you need to disconnect the computer when you set the base timing, so it does not advance it while you are trying to baseline. (This is refered to as disconnecting the SPOUT or "SPark OUT").

Now, if you have a dist. cap, then look down at the base of it where it meets the engine. You shold see some sort of bolt that looks like it holds it in place. On mine, the bold secures a small triangle pice of steele that sits on the base of the ditributor. Loosen that off an you can turn the cap to adjust the base timing.

Here are the base instuction I followed to do mine from 924x2150 and with some mods from me...

FIrst let step right out and say it. If you Don't own a Haynes or Chilton manual , then maybe it is time to buy one.

1. clean off the area where the timing scale is located (should be right next to the harmonic balancer pulley) you will want to see the mark for 10 degrees BTDC or whatever the spec is on your engine emissions sticker.

2. Find the 0 scratch mark on the outside edge of the balancer pulley, there should be one line, ignore cutouts notches or holes. You may have to sand (carefully!) off some rust to see em, or crawl under your truck, they may be pointed down)

3 You will need to read the directions for setting timing according to the emissions label on your hood underside . The label probabaly has instructions to disconnect the SPOUT connector before a timing test. The SPOUT is an acronym for "spark out" it is a signal sent by the computer which helps to determine when the engine will fire a spark. I don't have a 302 so I can't tell you where it is located. It will be a one or two wire connector most likely taped to the main wire harness near the PCM or TFI module. Look near the the right corner of the drivers side near the firewall. On mine it is a little black block with a grey cartridge in it. If you pull the cartridge out it should have only two connectors inside the plug portion.

4 Once the SPOUT is disconnected, start the truck and warm up the engine, wait for idle speed, check the timing as usual with a timing light, and turn the distributor a few degrees clockwise or counterclockwise until you see that the timing is set where your label specifies.
If you are supposed to be 10 degrees BTDC and the timing mark is at 18, 26, or 6 degreesBTDC, rotate the distributor a little at a time, until the correct timing is achieved.

5. Reconnect the SPOUT wires, tighten the dist bolt and test her out.

6 I hope you don't have other problems. Good Luck

Post back and let us know!

Brent
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How did it turn out? Were you able to adjust the timing?

 

Well, I disconnected the the plug on the spout connector like I was supposed to, brought the truck up to operating temp, waited for idle speed, and checked the initial timing. Here's where I got really lost... My timing light showed the timing mark to be about an inch to the right of the degree marks above the crank pulley, putting it somewhere near 15 degrees After TDC. Is this possible? Is my timing light on crack? I made sure I was looking at the correct timing mark, on the crank pulley, and not at the notch on the pulley. There is a notch in the pulley and there is a inscribed line, I was using the line, the notch was nowhere near when I put the timing light on it. I tried attaching the light to several places on the number 1 plug wire, incase there was any sort of interference issue, but nothing changed it. I went ahead and adjusted the distributor until the timing mark hit on the 10 degree BTDC mark, and although the truck still idles, it seems to miss and run poorly at that setting. I wasn't ballsy enough to drive it, fearing I might hurt something. If it stinks at idle, I figured it can't be good under load. I adjusted the timing back to where it was before, way off the timing chart above the pulley, and the truck is idling like it used to. I triple checked for vaccum leaks, and all of my lines are in good condition, no cracks, no wear through, and I even tried the hose in the ear trick, and came up empty. There is plenty of suction at every place I disconnected a vaccum line, but I must say the truck did run smoother when I had the timing set at 10 degrees and disconnected one of the vaccum lines at the intake manifold.

Whats the next step? I'm more confused than before.

Thanks.
T.J.

 

What I understand with the worn camshaft gears and stretched out timing chain is that it sets your timing to get "retarded".

So, to compensate for the worn camshaft gears and stretched out timing chain, the previous mechanic might have set the base timing to advance and that is probably why you have 15 degreess ATDC.

Original camshaft is made of aliminum and its gears is coated with a hard plastic but that hard plastic breaks down into pieces over time and messed up your base timing. The replacement one that we got on our vehicle is made of steel and it's gears is made of steel as well.

 

It could be a number of things...but what Slade just decribed is probably what happened. At any rate, it's gonna take some hands on diagnostic (read: getting at the timing chain/gears and having a look.)

It also sounds like the last mechanic may have tweaked the timing to cover a vacuum prob. Check your PCV (just pull off the PCV and shake it, it shoud make a clicking niose if it's not stuck) get a code reader on it again and see if it is throwing any error codes realted to the emissions system.

I find it weird that it idles properly at proper timing spec if you pop off a vacuum tube..

Brent

 

You sure you where looking at the right pointer?

 

The good old 4.9L doesn't have a timing chain to wear or stretch, it's gear to gear. The originals had the timing marks on the front cover and even though they changed everything else, they still use that same cover. Ignore the timing marks on the driver's side and look for the correct timing marks on the passenger's side.

 

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