CMP retard is now +0.2 at 1,000 rpm (from -8.5 to start) and fuel delivery is verified good. I'll put some miles on the truck and report back.

Torque does in fact cause bluetooth issues for Car Gauge Pro. It looks like Torque leave a service open even when the ap is closed so that may be it. I just deleted Torque because I had to get back to work. I am also now evaluating Dash Command.

Thanks.

Some observations for those new to CMP retard:

I removed the distributor, took off the stock hold down bracket and replaced it with the Mr. Gasket 1009 adjustable hold down. Note that the gasket that comes with this kit does not fit on the distributor shaft. I had to carve out the inner diameter with a knife. While I was at it I replaced the distr gear with GM part 10457356. You pound out the pin, take off the gear/washer/backing plate and do the reverse. Drifting CMP retard is apparently due to a stretching timing chain and worn distr gear. Before removal tap the starter with the distr cap off until the rotor is pointing towards the firewall and mark its position. Then mark the body of the cap to the distr body. If you lose track of these two positions you will have more work.

Note that CMP retard is very sensitive, you don't move the distr body very much so get the hold down bolt just loose enough to need some force to turn the distr so it stays put when you tweak it and more importantly when you tighten it down because its hard to tighten without bumping the cap or wires. A 10mm ratching articulating box wrench works best. CCW to make CMP retard less negative and CW to make it less positive. It does change slightly when you fully tighten the bracket so don't go for zero or you will be chasing your tail.

CMP retard - What! - who knew?

George

 

Yep, I used the Mr. Gasket 1009 adj. hold down when I replaced the worn out plastic body dist w/worn on 'one side' dist. gear in my 2000 4.3 Silv. CMP is very sensitive to as little as +/- 0.5mm adjustments (and maybe less). Just slightly loosening and then re-tightening the hold down bolt is enough to make a noticeable change in CMP.

Note: also make sure that the dist shaft doesn't bind when the dist. is fully tightened down (there should a bit of 'up and down' rotor play when all is said and done. If not, just add an extra gasket or, better yet, a nylon shim made for this purpose.

 

Took a test drive. Idle is still rough maybe worse and now I have a stumble at the beginning of acceleration. No codes and no pending codes.

Lesmyer:

What would you look at next?

Thanks,

George

 

a lot of extra work when you can just oval out the hold down bracket

 

Update:

Looks like the ECM is relearning after the CMP retard was corrected (CMPR still running less than 0.5). LTFT's have both come down averaging 2 or less, down from 9. The truck is really running lousy now, stumbling and hunting at idle and hesitating at initial acceleration but running decent at highway speeds.

Lesmyer:

All fuel pressure tests are good, CMP retard is less than 1. Where do you suggest that I go from here?

While I await your guidance I am going to test:

Catalytic converter given that I was burning coolant and diluted oil (lower intake manifold gasket)

Vacuum leaks

MAF sensor

Thanks,

George

 

George, I would like to try something with you using the OBD2 software.

Let me get some various readings on my Blazer at idle and at 2000 RPM so we can compare and see if anything sticks out with yours. Things like MAF, Coolant temp, Intake air temp, engine vacuum, TPS, IAC Counts, EGR. Also can look at cycle time for my O2 sensors at both speeds using the plot function (good indication of their condition).

 

Les

Thank you. It might also be helpful to have open loop vs closed loop as well as idle/2500 rpm.

Also if you have time perhaps you can answer my open loop question on another thread to help me with diagnosis.

Thanks for taking the time,

George

 

George, I'm going to give you a link to what I consider to be the best primer on OBD2 that I have ever come across. You strike me as a person who will appreciate it. It should cover any questions that you have about how things work and give you something to do while I collect my data.

http://www.lbcc.edu/attc/documents/OBD2.pdf

 

70 ambient temp. Hot Idle in Drive with A/C on. Oops looks like my Baro sensor is off some. 12.82 psi = 26.1 in of mercury and baro pressure outside is suppose to be 29.89 in of mercury

O2 Sensor Bank 1: Note this slow cycling past 0.5V is normal at idle



O2 sensor Bank 2

 

70 ambient temp. Somewhere around 50 MPH in OD, level road, steady speed with A/C on



O2 sensor Bank 1: Note rapid cycling past 0.5V should be observed at higher RPM. this is why numerical values for O2 sensor voltages typically tell you little (note 0.13V and 0.29V instant readings at time of snapshot). O2 sensors respond more and more slowly as they age. I think these are original 89K mile O2 sensors.



O2 sensor Bank 2