This is ODD (305 Vortec issue)

[Tom400CFI]

This was odd:

160K mile, clean, box stock '98 305/5 speed. Generally runs and drives flawlessly (if not gutlessly). Yesterday, driving home from work, I notice some bucking at light throttle. "Huh. Distributor must be out of alignment", I thought. Weird that it would come out of alignment, but the symptom was identical to when the dist isn't "timed" to the crank p/u. Any way, I come up the 13 mile climb to my neighborhood no prob, get off, drive through the neighborhood no prob, come to a stop sign, it dies. Huh? I crank it and I get that not-so-good sounding crank when the cam or dist is out of time where it cranks, "kicks" back against the starter cranks more, repeat. No fire.

Since I'm on a hill, I decide to roll start, so I get it rolling, llet clutch out, engine spins, I get some lurching and back firing....and that's weird....why is there no oil pressure!? I push in the clutch, pull over call my wife for a tow. Get out, check oil, plenty. Hmmm.


Not looking for help, more so sharing an odd one. I'll update. Figured that some might enjoy theorizing, bench diag'ing.

 

[Nad_Yvalhosert]

Vortec distributors are not the distributors of old. The lower half is just a Cam position sensor. There is no ignition advance mechanism.
The advance is applied electronically by the PCM. If the "timing" is out, you would get a cam-crank sensor correlation error code.
You've got other problems. Keep us informed.

 

[Tom400CFI]

Yep, I know. No, not necessarily. A previous Vortec truck I had did the "bucking" thing at part throttle, it was the distributor housing positioning (relative to crank sensor). It COULD give the code you mentioned (if far enough out), but in this case, it didn't. It just bucked at part throttle cruising. Anyway, I never got a code, but adjusted the distributor "timing" (positioning of the body) and it eliminated the problem. That truck was high miles (over 200k) and I suspect timing chain stretch retarded the rotor timing enough to cause the issue.

I'm thinking this one is a stripped distributor drive gear. Probably won't get to it until Sunday or Monday, as we're getting a lot of snow here, but will see...and for sure, I'll post up what I find. :thumbs:

 

[L31MaxExpress]

Probably a torched cap and rotor.

As for no oil pressure, the distributor would have to be turning for the engine to run. Plastic coupler on the oil pump could have broken from all the jarring it recieved?

I have also discovered that even new GM distributors are coming with 2x the desired shaft end play now. Too much end play can cause spark scatter.

 

[Tom400CFI]

Good initial brain storms, but....
Cap and rotor won't likely cause it to go from running fine, to....nothing. Combined with no oil pressure at the same time? Incredibly unlikely to be a cap/rotor.

Plastic coupler on oil pump drive, not too likely, but possible, to cause no oil pressure....but that wouldn't cause it to stall and not start.

Spark scatter? Developing on a 160k mile dist? Not likely....and how would that kill oil pressure?


Those are all good initial thoughts, but when you combine all of the symptoms, they no longer "fit" or work. The problem, was just as I thought:

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^Dog Poo^. Why'd that happen at such low miles? Not sure, but that's the problem. Off to get a new gear.


.

 

[clutterhead]

Good initial brain storms, but....
Cap and rotor won't likely cause it to go from running fine, to....nothing. Combined with no oil pressure at the same time? Incredibly unlikely to be a cap/rotor.

Plastic coupler on oil pump drive, not too likely, but possible, to cause no oil pressure....but that wouldn't cause it to stall and not start.

Spark scatter? Developing on a 160k mile dist? Not likely....and how would that kill oil pressure?


Those are all good initial thoughts, but when you combine all of the symptoms, they no longer "fit" or work. The problem, was just as I thought:

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^Dog Poo^. Why'd that happen at such low miles? Not sure, but that's the problem. Off to get a new gear.


.

In a situation like this, are you worried about metal shavings in the engine before they get caught by the filter? Is this just a "fingers crossed" moment?

I have an older 350 and always heard of the non melonized gear problem, but I've heard conflicting info on whether or not you can even find that on the market today. I assume its not used in a vortec either. I had flat tappet lifters but converted to roller a while back, so I had to watch out for that when researching.

Anyways, rockauto has an all aluminum dizzy by the brand united motor products. I can at least attest its good stuff. Bought mine back in 2019 and still going.

 

[L31MaxExpress]

Good initial brain storms, but....
Cap and rotor won't likely cause it to go from running fine, to....nothing. Combined with no oil pressure at the same time? Incredibly unlikely to be a cap/rotor.

Plastic coupler on oil pump drive, not too likely, but possible, to cause no oil pressure....but that wouldn't cause it to stall and not start.

Spark scatter? Developing on a 160k mile dist? Not likely....and how would that kill oil pressure?


Those are all good initial thoughts, but when you combine all of the symptoms, they no longer "fit" or work. The problem, was just as I thought:

You must be registered for see images attach

You must be registered for see images attach

^Dog Poo^. Why'd that happen at such low miles? Not sure, but that's the problem. Off to get a new gear.

The gear on my 97 wore down in under 70K to the point it was causing a misfire and shudder at light load and highway speeds. It is a well known issue, failing even before 100K on some of these. The distributor gear is much softer than the cam and the excessive shaft endplay does not help things.

Yes cap and rotor will cause it to go from running fine to not running in flight. Just had that issue on my 97 a while back. Started spitting and sputtering when it went into passing gear on the highway, then stalled out, coasted to a stop. Backfiring while cranking. The cap and rotor both burned through and the spark was grounding out completely to the distributor shaft. I have also had both large cap and small cap HEIs do the same burning through the rotor. When you get the new gear on it and still does not run or run correctly which is probably a 90% certainty, look at the cap and rotor. My rotor burned through in a spot that was not visible from the top as well.

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[rebelyell]

Good initial brain storms, but....
Cap and rotor won't likely cause it to go from running fine, to....nothing. Combined with no oil pressure at the same time? Incredibly unlikely to be a cap/rotor.

Plastic coupler on oil pump drive, not too likely, but possible, to cause no oil pressure....but that wouldn't cause it to stall and not start.

Spark scatter? Developing on a 160k mile dist? Not likely....and how would that kill oil pressure?


Those are all good initial thoughts, but when you combine all of the symptoms, they no longer "fit" or work. The problem, was just as I thought:

You must be registered for see images attach

You must be registered for see images attach

^Dog Poo^. Why'd that happen at such low miles? Not sure, but that's the problem. Off to get a new gear.

Good initial brain storms, but....
Cap and rotor won't likely cause it to go from running fine, to....nothing. Combined with no oil pressure at the same time? Incredibly unlikely to be a cap/rotor.

Plastic coupler on oil pump drive, not too likely, but possible, to cause no oil pressure....but that wouldn't cause it to stall and not start.

Spark scatter? Developing on a 160k mile dist? Not likely....and how would that kill oil pressure?


Those are all good initial thoughts, but when you combine all of the symptoms, they no longer "fit" or work. The problem, was just as I thought:

You must be registered for see images attach

You must be registered for see images attach

^Dog Poo^. Why'd that happen at such low miles? Not sure, but that's the problem. Off to get a new gear.


.

How do the teeth on its Cam gear appear ? ... almost as bad as above ?

Do you think 160K miles is Low ? that ain't chickenfeed ! ... or what am I missing? ... sarcasm ?

FWIW: 1998 L30 Vortec 305 should have OE billet 5150 steel core camshaft & OE Melonized steel distributor gear. If replacement gear has a dimple (as in above pics), do align dimple with rotor tip.

 

[L31MaxExpress]

Here was my distributor findings. Tightening up the shaft endplay made the CMR reading stop dancing around and it became a near rock solid reading.

Distributor shaft end play fail!

I noticed my distributor making some weird noises. The rotor tip was contacting the cap electrodes, causing a clicking/tapping sound. I pulled it out and discovered I had 0.055" end play and cracked distributor cap mounting bolt holes despite the thing being aluminum. The gear had some wear...

www.gmt400.com

 

[Tom400CFI]

How do the teeth on its Cam gear appear ? ... almost as bad as above ?

Do you think 160K miles is Low ? that ain't chickenfeed ! ... or what am I missing? ... sarcasm ?

I don't think 160k is "low"?...but on a SBC, it's not "high", either. Last Vortec truck I had, sold it with 300k. That's "high" to me, although it still ran and performed like new. I haven't looked at the cam gear teeth, but will before I put the distributor back in. Not much I can do about the cam though; I'd run it until it fails (if it ever does), then change the cam.

Yes cap and rotor will cause it to go from running fine to not running in flight.

And no oil pressure at the same time? Like I said; when you consider ALL the symptoms....
Glad you got yours fixed. Mine's not the cap and rotor, though.