98 5.7 Timing all over and misfires

[LastOne]

98 Silverado 5.7 still misses under load. Recent ride with Autoxray 6000 scanner reveals misfire on 3, 6, and 8. Timing varies from -8 to +33 depending on acceleration and declaration during the drive cycle. wires, plugs,rotor cap, dist cap all replace with AC/Delco within the last few months, no change. Also replaced the cam sensor.

Any Ideas

[enginebooster]

How many miles in on your truck? It could be your timing chain could be worn causing it to stretch. Also check if your dist. holddown is tight.

[2000CAYukon]

How is the dist drive gear?

//2000CAYukon

[LastOne]

125K on the truck. Rotor has a few degrees 3-5 of movement. Shaft rises a tad as you turn it like it is riding up the gear.

[enginebooster]

It will rise up a little, but that shouldn't cause what your describing.

[enginebooster]

Pull the dist. and check that gear.

[LastOne]

Am I looking for worn teeth or missing tooth??? Is the gear replaceable by itself?

[2000CAYukon]

Originally Posted by LastOne

Am I looking for worn teeth or missing tooth??? Is the gear replaceable by itself?

You are looking for worn teeth (i.e. will allow dist shaft to move without cam moving). Yes gear can be replaced by itself.

//2000CAYukon

[Jeremy-WI]

Hook it up to the autoxray again and check the cam retard while the engine is running. It should be +2 - -2 degrees and it shouldn't change, not more than a degree anyhow. Post results

[LastOne]

Originally Posted by Jeremy-WI

Hook it up to the autoxray again and check the cam retard while the engine is running. It should be +2 - -2 degrees and it shouldn't change, not more than a degree anyhow. Post results

Sad to say my AutoXray 6000 " Top of the Line" will not show cam retard.
Steve

[Bob B]

Hi,
A 98 has basically nothing inside the distributor. it shouldn't cause what you are having.
Also a thought, the computer can vary the timing so your timng may be acting normal.
Bob B

[LastOne]

I have captured a few seconds of the problem. I rerouted spark plug wires this past weekend. No misfire or codes yet but still shakes when under load going up a hill.
Here is the link to the graph.
http://i4.photobucket.com/albums/y14...rradoEZ-PC.jpg
You may need to save the jpg file and magnify it.
Bring on the brains as I have lost mine....

[MT-2500]

As said the pcm takes care of timing.
The timing is not adjustable but you need to have the camshaft retard setting check or adjusted as needed.
If it is missing under a load a good scanner should show engine misfires past or present and what cylinders are missing..
Does the engine light blink when it shakes or misfires?

Always make sure you have good fuel pressure?
What are the fuel trim readings from scanner?
Got good ac delco plugs in it?
Good hot blue spark from coil and to plugs?

What code no is it setting?

[LastOne]

Fuel Trim
Short term trim1 1.50%
Long term trim1 3.10%
Short term trim2 3.90%
Long term trim2 1.50%

When it does set a code, it is p0300 or p0306. Normal driving with it skipping just sets a p0430, cat efficiency due to the missing problem. I used a vacuum gage Plugs, wires, coil, dist cap and rotor changed within last 4 months, none changed the symptom. Ran Seafoam via brake booster hose, in oil and gas, no change. If you get on the accelerator hard from a stop it will run like it was new, however if you get part way up a hill, back off the pedal and then get back on it it will miss, skip, and usually set the 0300 or 0306.
Good AC Plugs, Fuel pressure good

[MT-2500]

The 306 is no 6 cylinder miss.
Switch plugs and wire with another cylinder and see if miss changes to another cylinder.
Also check TPS sensor.
Where it changes when you let up and mash down on it the tps sensor is moving.