96 GMC K1500 - P1345 code - No scanner

[IMV8N]

Hey all. I was just wondering if I can use a timing light to fix the P1345 code? I see that it’s very easy to adjust the CMP retard with a decent scanner but I don’t have one. I was wondering if I could use a timing light to adjust the timing to resolve this code? Both methods require you to turn the distributor. Is CMP retard the same as timing? If I use a timing light to adjust my distributor so that I’m between +- 2 degrees of TDC, is this the same thing as using a scanner to set CMP retard to +- 2 degrees.

 

[termite]

Hey all. I was just wondering if I can use a timing light to fix the P1345 code? I see that it’s very easy to adjust the CMP retard with a decent scanner but I don’t have one. I was wondering if I could use a timing light to adjust the timing to resolve this code? Both methods require you to turn the distributor. Is CMP retard the same as timing? If I use a timing light to adjust my distributor so that I’m between +- 2 degrees of TDC, is this the same thing as using a scanner to set CMP retard to +- 2 degrees.

Let's start with providing some basic info regarding what you're working on. Year, make, model, engine, transmission. Given you're asking about CMP retard, I'm guessing 1996 later vortec engine.

CMP adjustment is different than the traditional timing setting. Yes, they both require turning the distributor but CMP is the correlation of the cam sensor with the crank sensor. I think the ignition timing on the vortecs is controlled fully electronically (if I'm off here, i trust others will chime in and correct me)

CMP retard adjustment REQUIRES a scan tool of some sort to adjust it to within spec. Some on here have had luck with bluetooth OBD2 adapters and an app (I have no experience here). Dashcommand with the appropriate in app extension for additional PIDs, if memory serves me well. Do a sesrch on the forum for CMP. Others opt for the used professional scan tool route via ebay or elsewhere. Of course, you could always take it to a shop you trust, pay an hour of labor and have them set it.

 

[1998_K1500_Sub]

I’ve actually cleared that code by installing the distributor following the method in the service manual (see "Malfunction Indicator Lamp turns on, and a DTC code P1345 sets" in the attached .pdf)

But to get the setting absolutely correct, you need to use a scanner.

I've attached relevant sections from a 1998 FSM for installing the distributor, including the part describing the use of the scan tool.

I ran into the P1345 code issue after replacing the intake manifold gaskets. I followed the FSM instructions for "Procedure 2" and it cleared the code, but I later used my scan tool to set it to spec.

 

[SableSlayer]

Buy a Bluetooth scanner on Amazon for around $20 then get Dashcommand from the app store and purchase the extra pids for your truck from Dashcommand. There's an option in there for cmp correlation so you can set the distributor.
The engine has to be warm and idling at 1000 rpm the the distributor needs to be working 2 degrees of 0 positive or negative.

 

[Schurkey]

Ignition timing is totally independent of distributor position, until the distributor position is so far off that the spark jumps to the wrong plug wire terminal inside the cap.

Ignition timing is non-adjustable, set via the crank sensor and sensor reluctor, then processed through the computer and ignition module.

The issue with that code is that the crank sensor signal, and the cam sensor (inside the distributor) signal aren't in synch. The distributor is turned to align the sensor signals, then the spark gap from rotor to distributor terminal is as small as practical, and the computer can determine which cylinder is misfiring.