The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1988 - 1998 GMT400 Chevy & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 06-04-2018, 12:02 AM   #1
wildwilly
Registered User
 
Join Date: Mar 2008
Location: Bellvue, CO
Posts: 7
Distributor CMP Offset Issue

I hope someone has a similar issue that can help with a timing the camshaft retard offset (CMP) and aP1345 issue.

I have a 96 K1500 5.7 ... 280000 total miles. It has about 700000 miles on a replacement GM engine. After about 50000 miles there was a slight ping under load or higher RPM. At 60000 miles I was getting random misfire codes under load. Eventually after throwing parts at it with no change ... I did a full tune up. It did get better but still pinging a bit ... but finally read about the Distributor CMP offset and decided to check it with my scanner and it was at -10. I rotated the distributor, but could only get to -4 before it hit the intake manifold. At the same time I did a compression test and all cylinders were sound. It ran a good bit better, ping gone and no more error codes ... well I decided to see if I could move the distributor clockwise a tooth and reset CMP offset closer to zero.

Since I was pulling the stock plastic distributor I sprung for a Summit Racing billet replacement. I set it back one tooth from the original and reset the CMP and now got it to +1 degree ... within the +/- 2 degree window. It started back up straight away and sounded good, but P1345 is set right at start up. It resets and comes back immediately on restart.

I read you need to re-learn the crank/cam, but another place said this is only on 98 an newer. Do I need to take it in and have this done? ... or do I need to move it back a tooth and live with the -4? I am not sure how it got to -10 to begin with ... maybe being off a bit initially and wear over time?

Thanks in advance if anyone can help.
wildwilly is offline   Reply With Quote
Old 06-12-2018, 01:03 PM   #2
speedygonzales
Registered User
 
speedygonzales's Avatar
 
Join Date: Jan 2006
Location: Smithfield, VA
Posts: 1,345
Been there........

If you have the ability to do cam offset, you can do the relearn also.

These engines do not like to be positive and mine doesn't like being 0. Always make sure it's negative.

Also this is not causing your ping issue. If you have the OEM plastic intake gaskets, I'll put a month's wages on a bet they are leaking oil. I had that issue once and it pinged like you would not believe. The only thing that helped reduce it until I replaced them was using premium grade fuel.

Once I changed the gasket to the new steel core ones, problem was solved.
__________________
99 Z71 (98 body style)
Pride and joy
speedygonzales is offline   Reply With Quote
Old 08-07-2018, 05:43 PM   #3
wildwilly
Registered User
 
Join Date: Mar 2008
Location: Bellvue, CO
Posts: 7
Re: Distributor CMP Offset Issue

Sorry guys for not posting and update sooner ... Life gets in the way sometimes. I moved the distributor back to the stock location. I could set the CMP to zero and had room for up to +4 before hitting the intake. Initially it was +2 within spec. I drove it a bit and it was happier, no ping I then dialed it back to zero per advice and it was a bit better. When I have a chance I may try -2 just to see. I inspected the original distributor a bit more closely and the gears are worn pretty good.

I used my FAST flash programmer that reads error codes and CMP. I had the programmer mainly for tire size adjustment, but the tunes are decent. The first thing I did was back to stock when I had the pinging so I elliminated that. There are some phone apps that work with OBD 2 Bluetooth adapters that read CMP. You have to pay a few bucks for them to get the CMP, but reasonably cheep.

I have a cheep Amazon blue tooth OBD 2 and the trial versions worked. I had to try them to see if CMP was included for free before I discovered the FAST programmer had it. I tried dash command and car gauge for the CMP offset, but ended up not needing to purchase it. I have used the free Torque app for a long time for the basics, but I could not find specifically if the paid version had CMP.

Anyway check your distibutor gears and replace it if worn ... The summit racing billet distributor is super nice and at a better price than the big name brands ... Upgrades the stock plastic ... Time will tell on the gear. Before my engine install that came with a new distributor I never has an issue in the stocker after over 200k, the second one did not make half that so we will see on this summit version.
wildwilly is offline   Reply With Quote
Old 08-07-2018, 05:46 PM   #4
wildwilly
Registered User
 
Join Date: Mar 2008
Location: Bellvue, CO
Posts: 7
Re: Distributor CMP Offset Issue

Thanks for the help speedy g ... You pointed me in the right direction ... Hope this may help someone else.
wildwilly is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 04:04 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Copyright 1997-2013 67-72chevytrucks.com