So my Chilton Manual says it needs to be timed.
Is this rubbish?

Hello go use 1999 Jimmy

Getting code @ start-up every time.
Clear it when running and it stays cleared.
Comes back on @ next start-up every time.
Starts hard when cold.
Runs and idles fine.
Dose PCM check values only at startup or is it continuously monitored by the PCM while the engine is running


Any Help

can you explain, everything needs to be timed, but also i have no idea as to what you are repairing or doing.

Was going to set the timing
No on some cars the computer times it.
You can not use a timing light like the Chilton manual says.

On this one you have to make sure the CKP to CMP outputs match within 2%.
I figured out how to do this you need a Tec 2 GM scope when you turn the distributor.

GM mechanic said if I got P1345 s the distributor gear or timing chain is probably worn and yes thus the timing is off.

Now I am wondering if you could put a standard dual trace oscilloscope scope on the outputs of the CKP and CMP and turn the distributor until they exactly overlap.

P1345 is set when camshaft retard is incorrect: either advanced or retarded ~26 degrees or more. This usually happens when the distributor is removed and not reinstalled correctly, (off one or more teeth). It can also happen if/when the distributor drive gear or bushings are worn excessively. When cam retard is incorrect, ignition timing is also incorrect causing hard starting. Some scan tools, not all, can access camshaft retard. Factory spec is zero degrees, plus or minus 2 degrees. If it's off, one tooth will correct by ~25degrees. Fine adjustments up to ~10 degrees, can be made by rotating the distributor. If the adjustment is off between 10 and 20 degrees, the distributor hold down bracket needs to be modified to make the distributor fully adjustable. First thing to check is camshaft retard, then distributor gear and bushings.

The EDI Engine Timing thread found in the Tech Article (DIY) section (index in my signature below) describes the steps to properly time the 96+ (and some 95) engines.

CMP Retard is a value that is displayed on any scan tool capable of displaying enhanced GM data and needs to be set to zero after removing or replacing any one of the timing hard parts (cam/crank gear, chain, cam, crank, distributor drive gear, or the whole distributor) as well as either the CMP or CKP sensors. Along with setting the CMP Retard to zero, when any one of those components gets replaced, the CKP to CMP correlation needs to be calibrated. That procedure is called a Crankshaft Variation Learn procedure or CASE Relearn procedure depending on your reference. Again, most scan tools capable of displaying enhanced GM data can do this.

Thanks I am going to do a tune up so I think I wil set the motor to TDC and pull the distributor and look at the gears. Chevy dealer yesterday said it was common problem. I do have a dual trace ossiliscope. I wonder if the waveforms would overlap perfectly from crank and cam sensors when the 2% tollerense is met

Do these tool cost thoudand+ dollars
Thanks I understand you

I have combined your two threads since they both deal with the timing of your engine and are related. Please try to keep to one thread per problem.

As far as the scan tools are concerned; no, they do not cost thousands of dollars. My AutoEnginuity scanner (requires a computer) with the GM enhancement currently costs $480 out the door and is a VERY valuable tool. There likely are cheaper hand held scanners out there. My next purchase will be either EFI Live or HPTuners and I'll sell my AE scanner to recoup some of the cost.

Even the act of removing & reinstalling the distributor can result in CMP Retard being off which will, over time, cause deposits in the cap leading to cross-firing as well as premature distributor drive gear wear. It pays to set the CMP Retard whenever the distributor is removed.

Just to let you know I just checked the VMC Scanner Forum and they were complaining it won't do Cam retard Offset, but I know people often don't know what they are talking about. I did find one on amazon the apparently dose Gm enhanced package.

Some info:
http://www.amazon.com/OBDLink-Blueto...9249681&sr=8-2

Go near the bottom to of the thread for info.

I am thinking about getting this one with GM software
http://www.scantool.net/scan-tools/obdlink.html
OBD Link Scan Tool about 350 with gm and it's software ScanX Professional.

I am starting to buy newer cars I need to make the jump.
No more computer-less Chevys with carbs.

Anyway thank you i completely understand this now.
I even saw a GM mechanic doing adjustment on a Tec 2 scanner on youtube