1998 yukon Mystery p0300 and rough idle still

[east302]

Well, yeah, it looks “off” to me. If it was my truck I’d get that scanner app (I think @exp500 mentioned another few product options) and confirm the distributor installation. But, before pulling it, check your misfire counts, fuel trims, what your current CMP offset is, etc.

Going by memory here, but that flat part of the distributor (when correctly pointed to #1 at TDC compression stroke) will be roughly parallel to the back part of the upper intake. It’s then twisted to get the CMP set and locked into place with the hold down bracket.

YouTube has videos that explain it a lot easier, but the shop manual has a nice section detailing it as well. Download those PDFs (link below) or get an alldatadiy.com subscription - it’s the exact same thing (same images from the manual) and a lot easier to navigate. Maybe $60/year.

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

 

[OilBurner2003]

Well, yeah, it looks “off” to me. If it was my truck I’d get that scanner app (I think @exp500 mentioned another few product options) and confirm the distributor installation. But, before pulling it, check your misfire counts, fuel trims, what your current CMP offset is, etc.

Going by memory here, but that flat part of the distributor (when correctly pointed to #1 at TDC compression stroke) will be roughly parallel to the back part of the upper intake. It’s then twisted to get the CMP set and locked into place with the hold down bracket.

YouTube has videos that explain it a lot easier, but the shop manual has a nice section detailing it as well. Download those PDFs (link below) or get an alldatadiy.com subscription - it’s the exact same thing (same images from the manual) and a lot easier to navigate. Maybe $60/year.

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

Looking to buy a scanner right now to see CMP offset, I can’t see that or fuel trim data right now anyway. I suppose I have to put it on hold until I can see the CMP offset

 

[east302]

Those two apps that I mentioned will read it. You have to buy the “extended” PIDs, think it’s $10 or so more. Plus your Bluetooth adapter.

Works well enough for what you need it for.

 

[OilBurner2003]

Those two apps that I mentioned will read it. You have to buy the “extended” PIDs, think it’s $10 or so more. Plus your Bluetooth adapter.

Works well enough for what you need it for.

I’ll go get a Bluetooth one, thank you sir! I’ll update you when it gets here.

 

[east302]

Grabbed you a couple pictures, 98 model, 350.

I don’t know the answer, but the question is can you be within spec on the CMP offset yet be a tooth off (rotor wasn’t at #1 cap terminal when installed). Maybe others would know for sure.







Copied your photo for comparison:

 

[OilBurner2003]

Grabbed you a couple pictures, 98 model, 350.

I don’t know the answer, but the question is can you be within spec on the CMP offset yet be a tooth off. Maybe others would know for sure.




View attachment 385260
View attachment 385261Awesome, thank you so much.

 

[east302]

Thinking more about it you can have the CMP/CKP correlation off by a good bit (think it’s 14 degrees) before it sets the code. It may have been installed/indexed correctly and just not set with a scanner, the error in degrees just looking extreme in your photo. Seems like it would run like hell, if at all, if it hadn’t been stabbed correctly.

One thing you could try (and since you can undo it if it makes it worse) is to mark the current location of the distributor cap and shaft relative to the intake, slightly loosen the hold down bolt, grab the distributor by the cap and twist counterclockwise until that screw tab hits the intake. That’s close to zero degrees - but a scanner would still be needed.

Might be worth a shot?

Edit: if you have an aftermarket distributor with a fixed clamp like this, then you’ll need to source the GM clamp in order to set the offset. Though sold as compatible with a 350, this style does not allow adjustment for the CMP.




GM part numbers in right column:

 

[exp500]

It could be that you have a P1345 and your scanner can't see it. Dist installation could be off a tooth and close enough for it to run, just not run perfect. All the dist installs I have done had to have teeth correct , even 180 out wouldn't work.
BAFX bluetooth scanner I linked before has worked well for me 5 years or so. It is in the console and gets more use on friends vehicles than mine. I'm using Torque Pro which has a steep learning curve sometimes. DashCommand and others seem recommended here alot.
For more technical analysis and TWO way comms I'm using VCX nano. The MDI is supposed to be way easier setup and about $220 if you have a laptop. Good Luck!

Please stay on this thread until you get Everything sorted out. Then we won't have to chase around for what was, only back up a page or 3 to locate. Thanks.

 

[OilBurner2003]

Thinking more about it you can have the CMP/CKP correlation off by a good bit (think it’s 14 degrees) before it sets the code. It may have been installed/indexed correctly and just not set with a scanner, the error in degrees just looking extreme in your photo. Seems like it would run like hell, if at all, if it hadn’t been stabbed correctly.

One thing you could try (and since you can undo it if it makes it worse) is to mark the current location of the distributor cap and shaft relative to the intake, slightly loosen the hold down bolt, grab the distributor by the cap and twist counterclockwise until that screw tab hits the intake. That’s close to zero degrees - but a scanner would still be needed.

Might be worth a shot?

Edit: if you have an aftermarket distributor with a fixed clamp like this, then you’ll need to source the GM clamp in order to set the offset. Though sold as compatible with a 350, this style does not allow adjustment for the CMP.

View attachment 385278

View attachment 385285
GM part numbers in right column:

View attachment 385286

Thinking more about it you can have the CMP/CKP correlation off by a good bit (think it’s 14 degrees) before it sets the code. It may have been installed/indexed correctly and just not set with a scanner, the error in degrees just looking extreme in your photo. Seems like it would run like hell, if at all, if it hadn’t been stabbed correctly.

One thing you could try (and since you can undo it if it makes it worse) is to mark the current location of the distributor cap and shaft relative to the intake, slightly loosen the hold down bolt, grab the distributor by the cap and twist counterclockwise until that screw tab hits the intake. That’s close to zero degrees - but a scanner would still be needed.

Might be worth a shot?

Edit: if you have an aftermarket distributor with a fixed clamp like this, then you’ll need to source the GM clamp in order to set the offset. Though sold as compatible with a 350, this style does not allow adjustment for the CMP.

View attachment 385278

View attachment 385285
GM part numbers in right column:

View attachment 385286

Trying to figure out what setting to use on the dash command to find CMP offset, or relearn, whatever they have it labeled as, the scanner might be here today so I want to get a reading BEFORE I mess with it to see what it’s at. Resources tell me it should be within 0 -2

 

[OR VietVet]

It could be that you have a P1345 and your scanner can't see it. Dist installation could be off a tooth and close enough for it to run, just not run perfect. All the dist installs I have done had to have teeth correct , even 180 out wouldn't work.
BAFX bluetooth scanner I linked before has worked well for me 5 years or so. It is in the console and gets more use on friends vehicles than mine. I'm using Torque Pro which has a steep learning curve sometimes. DashCommand and others seem recommended here alot.
For more technical analysis and TWO way comms I'm using VCX nano. The MDI is supposed to be way easier setup and about $220 if you have a laptop. Good Luck!

Please stay on this thread until you get Everything sorted out. Then we won't have to chase around for what was, only back up a page or 3 to locate. Thanks.

Yes, with those close quarters, you have to drop the distributor correctly with the teeth just so. Gone are the days of just dropping the distributor and running the plug wires to match the compression stroke.