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'97 Astro cam/timing data #4633992
01/13/18 09:08 PM
01/13/18 09:08 PM
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Alex_V Offline OP
Alex_V  Offline OP
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
A customer with a '97 Astro (4.3, AWD) is trying to rule out a stretched timing chain as the cause of some problems: mainly, when placed under load it intermittently stumbles and then will run awful (missing and carrying on) until it's shut off and restarted.

Codes:
P0337 "CKP sensor A signal low frequency"
P0339 "CKP sensor A signal intermittent"
P0341 "CMP sensor circuit out of range"

Watching the live data as it idled in my shop, ignition timing was running right around 20 while "cam retard" was showing -6 or -7. How exactly do these two numbers correlate? Is the cam retard number comparing crank sensor to cam sensor, saying that it sees the cam (and therefore, distributor shaft) running 6 degrees behind the crank?

I had no time to do any physical checks, and the weather was going downhill fast so I didn't take it for a drive at the time - we agreed I'd do some homework on the codes and follow up later. He has changed the cam and crank sensors but says he's not moved or removed the distributor. Are the 4.3 dizzy's prone to excess wear on the driven gear like the Vortec V8's are?

Last edited by Alex_V; 01/13/18 09:10 PM.

I like Chevy and Valvoline.

'13 Cruze, 1.4T, 113K
'85 GMC C3500, 454, 130K
'82 Mercedes 300CD, OM617 turbo, 169K
'67 Suburban, 350, 331K
Re: '97 Astro cam/timing data [Re: Alex_V] #4634006
01/13/18 09:23 PM
01/13/18 09:23 PM
Joined: Dec 2013
Posts: 2,190
Fort Worth, Texas
clinebarger Offline
clinebarger  Offline
Joined: Dec 2013
Posts: 2,190
Fort Worth, Texas
I would ignore the P0341 for the time being.

Check the CKP wiring, Especially right at the CKP Connector as oil leakage/seepage can rot away the wiring insulation.

Cam Retard Offset readings are not accurate at idle, You have to rev the engine to 1200-1500 RPM.


2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/Auto
Re: '97 Astro cam/timing data [Re: Alex_V] #4634008
01/13/18 09:28 PM
01/13/18 09:28 PM
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Alex_V Offline OP
Alex_V  Offline OP
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
I did, up to maybe 3,000 RPM. I didn't make great note of any of the readings but if memory serves, cam retard stayed about the same with ignition timing climbing up to about 30 degrees.


I like Chevy and Valvoline.

'13 Cruze, 1.4T, 113K
'85 GMC C3500, 454, 130K
'82 Mercedes 300CD, OM617 turbo, 169K
'67 Suburban, 350, 331K
Re: '97 Astro cam/timing data [Re: Alex_V] #4634014
01/13/18 09:38 PM
01/13/18 09:38 PM
Joined: Dec 2013
Posts: 2,190
Fort Worth, Texas
clinebarger Offline
clinebarger  Offline
Joined: Dec 2013
Posts: 2,190
Fort Worth, Texas
Cam Retard in the single digits will not cause performance issues, And you don't have a P1345?


2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/Auto
Re: '97 Astro cam/timing data [Re: Alex_V] #4634143
01/14/18 01:01 AM
01/14/18 01:01 AM
Joined: Jun 2012
Posts: 1,703
USA
oldhp Offline
oldhp  Offline
Joined: Jun 2012
Posts: 1,703
USA
We always would put the timing mark on TDC. Now turn the crankshaft backward while watching the distributor. If you can go more than 10 before the rotor starts to turn, change the chain.



Re: '97 Astro cam/timing data [Re: clinebarger] #4634306
01/14/18 09:28 AM
01/14/18 09:28 AM
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Alex_V Offline OP
Alex_V  Offline OP
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Originally Posted By: clinebarger
Cam Retard in the single digits will not cause performance issues, And you don't have a P1345?


Nope, no 1345 - only those three. The first thing I'm doing if it comes back in is inspect the wiring to the sensors.


I like Chevy and Valvoline.

'13 Cruze, 1.4T, 113K
'85 GMC C3500, 454, 130K
'82 Mercedes 300CD, OM617 turbo, 169K
'67 Suburban, 350, 331K
Re: '97 Astro cam/timing data [Re: oldhp] #4634307
01/14/18 09:28 AM
01/14/18 09:28 AM
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Alex_V Offline OP
Alex_V  Offline OP
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Originally Posted By: oldhp
We always would put the timing mark on TDC. Now turn the crankshaft backward while watching the distributor. If you can go more than 10 before the rotor starts to turn, change the chain.


Good idea.


I like Chevy and Valvoline.

'13 Cruze, 1.4T, 113K
'85 GMC C3500, 454, 130K
'82 Mercedes 300CD, OM617 turbo, 169K
'67 Suburban, 350, 331K
Re: '97 Astro cam/timing data [Re: Alex_V] #4634490
01/14/18 11:45 AM
01/14/18 11:45 AM
Joined: Aug 2017
Posts: 559
MN
14Accent Offline
14Accent  Offline
Joined: Aug 2017
Posts: 559
MN
Sounds like a failing crank sensor.

Can't recall seeing a timing chain stretch on any 4.3, not that it's impossible. But I would doubt it.


2013 Chevrolet Volt - Saves enough in fuel to pay for itself!

2003 Cadillac Seville STS - The winter "beater", it uses the Volt's fuel
Re: '97 Astro cam/timing data [Re: oldhp] #4634501
01/14/18 11:55 AM
01/14/18 11:55 AM
Joined: Dec 2016
Posts: 6,241
Waco, TX
Linctex Offline
Linctex  Offline
Joined: Dec 2016
Posts: 6,241
Waco, TX
Originally Posted By: oldhp
We always would put the timing mark on TDC. Now turn the crankshaft backward while watching the distributor. If you can go more than 10 before the rotor starts to turn, change the chain.


REALLY? I would think that's about normal.

I wonder what a new one does.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: '97 Astro cam/timing data [Re: 14Accent] #4634949
01/14/18 06:56 PM
01/14/18 06:56 PM
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Alex_V Offline OP
Alex_V  Offline OP
Joined: Apr 2016
Posts: 1,185
Campbellsville, KY
Originally Posted By: 14Accent
Sounds like a failing crank sensor.

Can't recall seeing a timing chain stretch on any 4.3, not that it's impossible. But I would doubt it.


I'm also skeptical it's the chain, even with 230K on it. "Bad timing chain" gets thrown around a lot in recent years because of all the OHC engines, but a lot of people don't understand how rare it is for these short OHV chains to ever become a problem.


I like Chevy and Valvoline.

'13 Cruze, 1.4T, 113K
'85 GMC C3500, 454, 130K
'82 Mercedes 300CD, OM617 turbo, 169K
'67 Suburban, 350, 331K
Re: '97 Astro cam/timing data [Re: Linctex] #4635301
01/15/18 02:07 AM
01/15/18 02:07 AM
Joined: Jun 2012
Posts: 1,703
USA
oldhp Offline
oldhp  Offline
Joined: Jun 2012
Posts: 1,703
USA
Originally Posted By: Linctex
Originally Posted By: oldhp
We always would put the timing mark on TDC. Now turn the crankshaft backward while watching the distributor. If you can go more than 10 before the rotor starts to turn, change the chain.


REALLY? I would think that's about normal.

I wonder what a new one does.


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