Rough running & miss diagnostics.
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Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Rough running & miss diagnostics.
Several days ago the LB9 in my IROC started to miss at idle and while crusing, with the tach jumping at each miss.
Diagnosis:
1) I pulled, checked and regapped all spark plugs - no clue & no difference.
2) I used a timing light to verify base timing - OK at +12deg
3) I hooked up the AutoXray and ran several scans at various speeds. - nada
4) I removed and cleaned all the MSD SuperConductor wires. - no better, but I found that the terminals had pulled out of the the dist cap at positions 3 & 4.
4) I connected the timing light to #1 and firing was rock steady even when the miss occurred. When the timing light was connected to #3 or #4 the light flash was interrupted at each miss.
Fix
1) I ordered a new HyperTech coil/cap/rotor from Summit.
2) I just pulled the dist cap - one nylon rotor bolt was nearly "out"
3) I put a touch of LockTight on each of the two nylon bolts that hold the rotor and installed the rotor.
4) I put anti-sieze on each of the (4) screws that hold the cap to the dist base and installed the dist cap.
5) Reseated all plug wires into the cap and fired her up. - smooth as silk
BTW, the original HyperTech assembly had been running fine for over 4yrs.
I thought this scenario might help those who have a rough running L98 and suspect ignition problems. Sometimes tools serve to benefit in other than their intended use.
Diagnosis:
1) I pulled, checked and regapped all spark plugs - no clue & no difference.
2) I used a timing light to verify base timing - OK at +12deg
3) I hooked up the AutoXray and ran several scans at various speeds. - nada
4) I removed and cleaned all the MSD SuperConductor wires. - no better, but I found that the terminals had pulled out of the the dist cap at positions 3 & 4.
4) I connected the timing light to #1 and firing was rock steady even when the miss occurred. When the timing light was connected to #3 or #4 the light flash was interrupted at each miss.
Fix
1) I ordered a new HyperTech coil/cap/rotor from Summit.
2) I just pulled the dist cap - one nylon rotor bolt was nearly "out"
3) I put a touch of LockTight on each of the two nylon bolts that hold the rotor and installed the rotor.
4) I put anti-sieze on each of the (4) screws that hold the cap to the dist base and installed the dist cap.
5) Reseated all plug wires into the cap and fired her up. - smooth as silk
BTW, the original HyperTech assembly had been running fine for over 4yrs.
I thought this scenario might help those who have a rough running L98 and suspect ignition problems. Sometimes tools serve to benefit in other than their intended use.
