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1996 GMC 1500 Sierra 5.0 V-8 245,000 mi.- Engine cranks eratically


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donniew6
New User

Nov 3, 2012, 2:23 PM

Post #1 of 5 (2387 views)
post icon 1996 GMC 1500 Sierra 5.0 V-8 245,000 mi.- Engine cranks eratically Sign In

When starting cold, Engine cranks normally once or twice then it acts like something grabs the fly wheel and almost stops rotation, Then will crank normal maybe once or twice then it might start or repeats. I had the battery, Starter checked. They both checked out ok.


(This post was edited by donniew6 on Nov 3, 2012, 2:33 PM)


nickwarner
Veteran / Moderator
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Nov 3, 2012, 2:26 PM

Post #2 of 5 (2383 views)
Re: 1996 GMC 1500 Sierra 5.0 V-8 245,000 mi. Sign In

Do a voltage drop test on the power and ground sides of the starter circuit. Do you have a multimeter? Are you familiar with this test? If not I can explain it to you. Its actually quite simple.


donniew6
New User

Nov 3, 2012, 2:37 PM

Post #3 of 5 (2365 views)
Re: 1996 GMC 1500 Sierra 5.0 V-8 245,000 mi. Sign In

I do have the multimeter, However I am not familiar with this test. Please continue!


Discretesignals
Ultimate Carjunky / Moderator
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Nov 3, 2012, 3:48 PM

Post #4 of 5 (2324 views)
Re: 1996 GMC 1500 Sierra 5.0 V-8 245,000 mi. Sign In

I would replace the crankshaft position sensor. Sounds like the symptoms of one over advancing the timing during cranking. There was a TSB out for that. That can cause damage to the flywheel or even blow the starter nose apart. They can also cause a backfire up through the intake blowing the back of the plastic intake off or blowing the upper intake gasket out.



Found the TSB:

Engine - No/Hard/Slow Start/Backfire/Kickback


File In Section: 06 - Engine/Propulsion System

Bulletin No.: 00-06-04-014

Date: April, 2000

TECHNICAL
Subject:
No, Hard, or Slow Start, Backfire or "Kickback" During
Crank/Start, "Grinding" or Unusual Noises During Crank, DTC P0338
(Replace Crankshaft Position Sensor)

Models:
1999-2000 Cadillac Escalade
1995-2000 Chevrolet and GMC SIT Models
1996-2000 Chevrolet and GMC C/K, M/L, G, P Models
1996-2000 Oldsmobile Bravada
with 4.3 L, 5.0 L, 5.7 L or 7.4 L Engine
(VINs W, X, M, R, J RPOs L35, LF6, L30, L31, L29)

Condition:
Some customers may comment on one or more of the following conditions:

^ Backfire during crank/start
^ "Kickback" during crank/start
^ "No" start
^ "Slow" or "hard" start/crank
^ "Grinding" or unusual noises during crank/start
^ Cracked or broken engine block at the starter boss
^ Broken starter drive housing
^ Broken starter ring gear on flywheel
^ Any combination of the above

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.

Correction:
Inspect for a stored powertrain DTC code P0338. This DTC will NOT illuminate the "Service Engine Soon" light. If this code is stored, the Crankshaft Position Sensor, P/N 10456607, MUST be replaced and the remaining components inspected for damage (engine block at the starter boss, the starter drive housing, and the engine flywheel starter ring gear).

Notice : When DTC code P0338 is set, failure to replace the Crankshaft Position Sensor could result in repeated inoperative conditions of the starter or flywheel.

Important : Some flywheel wear is normal; broken or missing teeth and/or cracks, are not normal.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Nov 3, 2012, 3:54 PM)


nickwarner
Veteran / Moderator
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Nov 3, 2012, 5:29 PM

Post #5 of 5 (2309 views)
Re: 1996 GMC 1500 Sierra 5.0 V-8 245,000 mi. Sign In

I really need to finda database for TSBs. I would follow DS's suggestion first, as it seems quite likely this is the issue. If not, what you do for a voltage drop test is simple. Realize that a multimeter on the DC voltage setting is simply telling you the difference between its two probes. If you test the battery voltage, the reading you get between the positive and negative terminals is your charge. For voltage drop, place one lead on the battery positive and the other on the battery cable end of the starter. Crank the starter and watch the meter reading. This test only works on a circuit which is under load. The reading you get is the difference between the two ends of the same cable, which shows you how much was lost between the two points during transfer, called voltage drop. Anything over .3v is cause for concern and needs investigation. You do the same test to the main ground wire in the same manner, with one meter lead on one end of the cable and the other at the battery terminal. This shows the actual conditions of your cables while under load, as a continuity test uses just a few milliamps and won't show the issue to you on something like a battery cable.

You can use this test on all electrical circuits both big and small. Its fast and easy. A cable that looks good to you visually could have a small puncture on the back of its insulation that has let in water and caused corrosion inside the insulation out of view. You could have perfectly clean ends, good battery, good starter, and still won't work. The voltage drop test would show you that issue without takinbg anything apart. I do them on undercharging alternators as the first tests before condemning the alternator. Seen a few that had perfectly good ones get replaced and still no charge due to high resistance in the cable which my multimeter confirmed fast.

If you need this demonstrated to you, go to ericthecarguy.com and check out his videos. He has one specifically about voltage drop testing that could be of use to you and its good knowledge to have.

But first follow that TSB up. You don't want to wreck expensive parts over what could be a $60 sensor.






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