97 yukon p306 issue ??

[97blueyuk]

97 Yukon vortex 5.7, 160,ish miles. Random cylinder 6 misfire. By random I mean sometimes the light is on and it runs rough, sometimes the light is flashing, sometimes the light is off and it runs great. The truck takes turns doing these. The flashing doesn't happen very often. I have changed plugs,wires,cap,rotor. I have swapped wires between cylinders nothing changes. Compression numbers on that side (dry test) are cylinders 2,4 195. Cylinders 6,8 165.

My question is what can I do to pinpoint these issues. Are compression numbers bad?

Truck does not overheat or run hot either.

Thanks

 

[ccapehartusarmyINF.(ret)]

a 30 psi difference would indicate there is a problem
yer possibly lookin at valves or piston rings

 

[SunlitComet]

Pressure differential you stated is just fine. about 16-17% not great but not means for chucking it either. If misfire is intermittent then rings or springs are on the highly unlikely side. Please list names and #'s of parts used. Has An injector balance test/fuel pressure test been performed? Either your fuel or ignition is dropping out. Can you extract the misfire history count off the pcm after driving a bit to set off the issue? For your knowledge banks a steady light indicate a problem which effects emissions but not necessarily performance all the time. A flashing light indicates the pcm is tracking a live misfire. Trust me data is being recorded in the pcm on it. Oh btw fix the numbers you posted. #4 has two pressures listed and I assume #8 is missing by accident.

 

[ccapehartusarmyINF.(ret)]

i guess i shoulda said possibly but not likely
listen to what he says
sunlit comet is more like yoda and im more like obi wan in episode 1

 

[97blueyuk]

I will get the injector balance and fuel pressure tests done. Parts used were delco except plugs. I've tried spotlight,Bosch and ngk. I fixed the numbers. 8 wasn't missing, I mistyped. 2 and 4 were 195. 6 and 8 were 165

 

[SunlitComet]

use delco 41-993 plugs.

 

[Junior8677]

Check our distributor for play in the shaft, both vertically (front-back/left-right) and for rotation play. There should not be any play at all vertically and only a few thousandths play of rotation if at all! These distributors are known to have the bushings wear out inside the shaft itself and slowly gets worse and worse until the distributor gear starts to wear out on the camshaft... If you find any play in the distributor shaft, mark the orientation of the body and the rotor. Pull the distributor and check that gear (it will be worn and maybe not evenly either). You can get a brand new distributor for about $120 or you can try to find a good one at a junk yard! Good luck.
Let us know how you make out with it.


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[SunlitComet]

there can be a lot of play but the engine still runs normally. it is the dizzy gear itself that can wear and create the rotate play but even then it can still run normally because friction keeps the dizzy gear pushed toward the camshaft gear drive face. like the same effect on a rear end accelerating and slowing except the computer can compensate timing. but after a certain point in all hat wear it will just start farting. the bushing wear is not as bad because you can have 1/4"+ mote in vertical travel and the rotor still clears the upper wall of inside the cap. have yet to see a dizzy gear destroy a cam on the l31 yet. the dizzy is quite sacrificial.

 

[Junior8677]

I've had this happen to me on 2 different truck now and there wasn't much more than a few thousandths of an inch of play and the truck would barely run and had some major trouble starting. Now I'm not saying that's what the problem is for "97blueyuk" but it's very common, and it does not take much play at all! If I still had the old distributor I would make a video for you!


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[SunlitComet]

http://s1222.photobucket.com/user/Sunlitcomet/library/1996 Chevy Tahoe 4X4/Engine?sort=3&page=5

232k on it at the time original block and parts. dizzy had 1/4"+ vertical play and several degrees rotational. would slide up or down. depending which way turned by riding on tooth face. yet ran smooth and hauled ass. Eventually a msd unit took its place. Now the msd one i had an issue with. Second one was fine but the first, oh was i pissed about how it failed. thought you might the interested in the pics. gear looked good considering the wear it had. msd had much tighter tolerances.

 

[Harlech]

Which MSD did you install, Sunlit?

 

[SunlitComet]

http://www.amazon.com/MSD-Ignition-5592-Street-Distributor/dp/B004A6679S

direct replacement for any 5.0 +5.7l vortec engine no matter the model of vehicle. cap, rotor and cam sensor included.

seemed fitting as i already had wires, control box, coil and adapter harness. isn't it beautiful?

---------- Post added at 08:17 PM ---------- Previous post was at 08:09 PM ----------

and rotor attachment screws should lightly loc-tited before cap install. factory forgot that on mine and i forgot to check. one day massive pinging and stall on the freeway when rotor lifted and contacted cap and spun the assembly right of the shaft. http://s1222.photobucket.com/user/S...Tahoe 4X4/MSD Dizzy 1?sort=3&start=all&page=1

 

[Harlech]

Nice, added to my wishlist.

Thanks!

 

[SunlitComet]

welcome. should be on a vortecs upgrade or rebuild parts list.

 

[97blueyuk]

Going to do fuel pressure test, change the plugs, and check the distributor today or tomorrow. I'll do some research on the injector balance test and how to do it.

Thanks for the answers so far

 

[SunlitComet]

need a pressure test unit and a scanner with gm bi-directional controls to tell the pcm to fire the injector while watching the gauge. you fire it twice and record your pressure loss. re-prime pressure and then another injector and so forth.