Weird Cranking Saprk Issue

[onegonewild]

Hopefully someone else has come across this issue. I have a problem with the PCM commanding ~80 degrees timing while cranking (verified with a timing light and the fuel shut off). Engine is very hard to start and does give my mini starter a workout. After the engine does start, it runs great! Timing is dead on to what the PCM is commanding (verified with a timing light as well). Cam/Crank correlation is withing limits. I have played with B5909 & B5915 with no luck. I have triple checked the wiring as well with no ideas.

21109


383 internal balance L31 Vortec
Mercruiser MPFI ported, 27lb injectors, ported throttle body
Iron 64cc vortec ported and polished
Comp Cams Beehive springs for 0.550 lift, Crane gold rockers 1.5 Camshaft:Comp Cams XFI 280 hydraulic roller, Comp Cams Magnum hydraulic rollers

[joecar]

Weird.

Post some logs.

[onegonewild]

I have never been able to log spark when cranking. Here is the last log trying to capture spark while cranking.

21110

This is a 2001 S-10 with a L31 V8.

[onegonewild]

Actually, one thing to note here, I could never get the CASE relearn process to properly complete. I can perform the process and rev to the ~4000 rpm and stumble, but the code never resets. Possible this issue could be tied to the CASE relearn? I know the 5.7L vin R engines had issues with hard starting when there was a bad CKP.

[onegonewild]

I think I am on the right track. Bulletin No.: 00-06-04-014

"Cause:
A condition may exist that allows the crankshaft position sensor to command up to 50 extra degrees of spark advance during engine cranking only. This in turn exposes the engine to higher than normal cylinder pressures which may result in an inoperative condition to the starter drive housing, the engine flywheel starter ring gear, or the engine block at the outside edge of the starter boss."

Now i need to figure out what is the problem. I have swapped a CKP sensor from a donor 2001 S-10 with a 4.3L but no change. Maybe I should try a new CKP sensor 10456607

[joecar]

Interesting...

good job on digging up the bulletin.

~ posted by phone ~

[onegonewild]

Are there tables that could affect cranking spark? Multipliers, etc.?
Maybe I can zero those out if there are any.

[onegonewild]

Checking a few tolerances out on the crank sensor. The block was line bored before assembling so I want to see if this could be a factor.

I measured a good working donor truck and measured the depth to the lobe of the reluctor.
Working engine: .756" from housing edge to lobe. CKP Sensor is .721" reach leaving .035" air gap
Problematic engine: .759" from housing to lobe. CKP sensor is .709" reach leaving .050" air gap

I filed the timing cover down a bit until the depth was .740". This reduced the air gap, but made no improvements.

Do i focus on the tune? Anything that could stand out causing a bunch of timing to be added when trying to start?

[joecar]

I don't see any spark tables in your tune file that could be causing that.

I do see the Cranking VE table looks weird.

What physical engine do you have...?



BTW: set B3608 to 0.010 s and set B3618 richer to be safe during PE/WOT.

BTW: set A0012,13 to in-range values (i.e. max-1).

[onegonewild]

Engine is a 5.7L Vortec stroked to 383. Using the 2002 Chevy Express tune

[onegonewild]

I logged EST PIDs and could only acquire data when the engine was running. The only PIDs that affected the timing when idling was the following:
EST - Base Spark
EST - Idle Spark
EST - Run Spark

Is there any way to log these while cranking? I can never obtain data for EST PIDs during the startup procedure.

Any ideas what i could log that would show the timing being added during startup?
This is a stock Vortec distributor with MSD wires. Any chance the distributor could be the issue? I have no misfires when the engine is running.

[onegonewild]

Little more troubleshooting here, the engine startup routine is nearly the same with the Camshaft position sensor unhooked. It still has way too much advance in timing (like before) with the sensor unhooked. I did the basic testing out of the CMP sensor, 12.7 V in and 10.8 V signal to the PCM. This does drop to 0 V and back up to 10.8 V when the engine it turning.

Ideas?

[joecar]

Where is the sensor location for the CKP and CMP sensors...?

~ posted by phone ~

[onegonewild]

CMP is in the distributor. CKP is in the front timing cover

[onegonewild]

RESOLVED:
NEVER TRUST reman distributors from local parts houses. This distributor has less than 1000 miles on it and is shot.
Luckily i had a donor vehicle to trade parts on and compare. Pulled the distributor out and noticed a good 1/2" or more vertical slop in the shaft. I swapped it out for one that had less than 1/16" vertical play. SUCCESS!! Starts perfectly!

For anyone having an issue with Vortec engines adding a crap ton of advance timing on starting, this is most likely your issue. All the slop allows the distributor to climb of the helical gears on the cam and change the timing. This most likely was attributed to the reluctor window not passing through the Camshaft Position sensor correctly.

The PCM definitely references the CPS while cranking for proper timing. This acts like an old pickup coil.

[joecar]

Good job on finding the cause.

Climbing the helical drive gear accounts for the extra 60 or so degrees of timing.

~ posted by phone ~

[onegonewild]

Distributor spec'd out perfectly when I originally installed it. Even the Camshaft position sensor reported good with proper values during hand turning.

Totally different scenario when cranking as the rotor is pushed up.