1998 4.3 Misfire
 

Had a strange problem...
332 000 km.
Cylinder 5 intermitent misfire. Didn't set a code, but can see it in history and current when misfiring.using Torque Pro.
Changed plugs. Still misifiring.
Swaped out lead with good lead. Still misfiring.
Dreaded Injector issue? MFI conversion was done 15 years ago.
Checked fuel pressure 58 lbs. Holds for 5 min.
Notice windshield washer plastic hose broken. It was spraying on distributor. This must be issue...
Started to clean distributor.
Bloody distributor was loose!
Replaced distributor with new one years ago. Guess i did not tighten it up... Rotated it back where i think it should be and tightened in down.
Misfire problem solved.
Will have to reset the Camshaft Relearn.
Dont have Scan Tool to set it.
if still no misfire in couple weeks ill take her in, to to get relearn done.
From what i under stand the relearn does not effect operation. It just dectects misfire for ECM. As timing is controlled by ECM. When distributor gets too far out of adjustment the rotor and cap dont line up, causing misfire. Distributor was so far out of posistion, no doubt the cyliner 5 misfire wasn't even #5...fooling the misfire logarithm.
Learn something new every day.

This is useful! Engines sure don't like loose distributors!

Glad you got it figured out!

Are you getting a CMP/CKP correlation code?

Adjusting the distributor on its mount should not require a relearn. If you have torque pro, monitor the cmp retard value, loosen the distributor and adjust distributor position to get cmp retard value as close to zero as you can get it then tighten it back down. That will get the distributor set to it's best position to allow for the ignition system to have its full range of spark control.

The only time you should have to redo the relearn is if you replace the CMP sensor, CKP sensor, the front timing cover, or the distributor itself if I remember correctly.

is the distributor adjustable?,,i dont think mine is

There is the ability to move the distributor for a few degrees of adjustability in CMP retard value as displayed on a compatible scan tool on the 2nd gens, yes. The procedure is explained towards the bottom of the EDI Engine Timing tech article. Basically, the hole in the lower intake manifold is large enough to allow the distributor to be moved side to side, thereby adjusting the base timing which is what the PCM displays off as CMP retard. It is not adjustable in the sense that older distributors were turned on a clamp that slipped on the outside of the distributor body, I'll give you that.

My dead eye dick positioning of distributor was good.
Photo is from Torque Pro.. Ignore the RPM. Engine was off when taking screen shot. Offset is 1.5 at 1500 rpm.
https://cimg4.ibsrv.net/gimg/blazerf...1c3d64e3db.jpg

Sorry i mentioned the Relearn in error.
Crank Sensor in OK.
Didnt change crank sensor, relearn not needed.
Ment to say CMP adjustment at distributor.
Changed hold down clamp to old style. So distributor can rotate freely.
Distributor cap was do far out or range and was causing the misfiring.

Adjusted CMP Retard to 0 degrees
https://cimg3.ibsrv.net/gimg/blazerf...ddde6f62b4.jpg