Help w/ 98 5.7 Vortech. Misfire Cyl 3
05-19-2007, 09:36 PM
#11
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I pulled the upper intake manifold off today. The #3 injector had so much carbon on the tip it looked like it was welded closed. I have not taken it out on the road yet to see if it corrected the problem. I shall see tomorrow.
05-19-2007, 11:05 PM
#12
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^ it was still running rough even at idle.
I lent him a set of new TR6 plugs I was saving for my N20 dry 150 (no more) or now my future Turbo Project. I need tr55's anyways.. He gapped them @ .055
So it has a fresh set of plugs in it. He was running platinums before. I have allways had bad experiences with the platinums. GM motors don't seem to like them at all.
I'm thinking ignition module now.. .Usually BAD sputtering when the engine is loaded is ignition issues. .
I lent him a set of new TR6 plugs I was saving for my N20 dry 150 (no more) or now my future Turbo Project. I need tr55's anyways.. He gapped them @ .055
So it has a fresh set of plugs in it. He was running platinums before. I have allways had bad experiences with the platinums. GM motors don't seem to like them at all.
I'm thinking ignition module now.. .Usually BAD sputtering when the engine is loaded is ignition issues. .
05-21-2007, 12:58 AM
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^ Any ideas on the ignition module?? How to diagnose a bad injector/Injection system? I don't think NOID lights will work on this one.
Diag isn't one of my strong points if it isn't an LSx based engine.
Diag isn't one of my strong points if it isn't an LSx based engine.
05-21-2007, 01:36 AM
#14
Some of the things prone to fail on L31 Vortec engines have already been mentioned. These things can produce sympton like you describe:
1. Failed intake manifold gaskets. This is notorious L31 problem #1. Basically, they get crushed from manifold bolt torque and the plastic frame no longer retains the silicon gasket ring. Coolant seapage after shutdown is common. There is an improved GM gasket available that has metal inserts to prevent crushing.
2. Failed or clogged fuel injector poppet. This is the most likely cause given it sat for a while. The spider injection assembly in these engines has all 8 injectors located in the center of the manifold. At each port there is spring-loaded checkball called a "poppet valve". These are prone to clog and become bound up with fuel additive deposits. There is a GM Multec-II injector assembly replacement for this setup. It eliminates the poppet valves and locates eight tiny Multec-II injectors around the manifold at each port. Cost of this is about $200, which is a bargain for 8 injectors.
3. The "Crab" distrubtor cap. You will notice in looking at one of these that the #3 electrode crosses over the cap internally very close to the center electrode. Breakdown internally can cause #3 to fire four times per revolution. You said the cap was already replaced but I can tell you from experience that most aftermarket caps are jnk. They only one built right is made by Borg-Warner and has brass terminals inside.
Part number 93441235
Part number 89017465
1. Failed intake manifold gaskets. This is notorious L31 problem #1. Basically, they get crushed from manifold bolt torque and the plastic frame no longer retains the silicon gasket ring. Coolant seapage after shutdown is common. There is an improved GM gasket available that has metal inserts to prevent crushing.
2. Failed or clogged fuel injector poppet. This is the most likely cause given it sat for a while. The spider injection assembly in these engines has all 8 injectors located in the center of the manifold. At each port there is spring-loaded checkball called a "poppet valve". These are prone to clog and become bound up with fuel additive deposits. There is a GM Multec-II injector assembly replacement for this setup. It eliminates the poppet valves and locates eight tiny Multec-II injectors around the manifold at each port. Cost of this is about $200, which is a bargain for 8 injectors.
3. The "Crab" distrubtor cap. You will notice in looking at one of these that the #3 electrode crosses over the cap internally very close to the center electrode. Breakdown internally can cause #3 to fire four times per revolution. You said the cap was already replaced but I can tell you from experience that most aftermarket caps are jnk. They only one built right is made by Borg-Warner and has brass terminals inside.
Part number 93441235
Part number 89017465
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