LS5 engine miss
I have a LS5 that has a pretty bad miss. I changed the points out to an electric limited electronic ignition module and that took care of the miss, but then it wouldn't get spark (and not start) when hot. So I went back to points and my miss came back (but at least it started when hot). Thinking that the module was overheating, I tried a new Accel electronic module and that caused the motor to run even more rougher. I then installed a matching Mallory coil, the one they recommend with the module, and that didn't help at all. I am at a lose, please help if you can.
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Re: LS5 engine miss
Bad spark plug wires?Rob.
NCRS Dutch Chapter Founder & Board Member
NCRS Software Developer
C1, C2 and C3 Registry Developer -
Re: LS5 engine miss
Vacuum leak? Does it just miss at idle, or going down the highway??Dick WhittingtonComment
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Re: LS5 engine miss
They only have 5K on them. But I guess anything is possible. ThanksComment
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Re: LS5 engine miss
It's very obvious at idle and she "floats" at high RPM so I have to assume it's happening then as well. I put a vacuum guage on it and it shows no leaks, but that's a good one to check. It just seems distributor related due to the performance difference in the modules/points. It's driving crazy......Comment
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Re: LS5 engine miss
If your car has repro plug wires, they would be my #1 suspect. A vacuum leak cannot be detected with a vacuum guage. You need to use something like carb cleaner to find one. You use the nozzle on the can and direct the spray toward anywhere that could possibly leak. If you spray it on a leak, the idle speed will pick up. It does not take a lot of spray to accomplish this. Intake, carb mounting gasket, vacuum hoses, etc. You can eliminate the hoses real quick by clamping/plugging the main feed hose behind the carburetor.Dick WhittingtonComment
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Re: LS5 engine miss
And how much time is on them? Deterioration is not just from miles.TerryComment
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Re: LS5 engine miss
I remember that trick now that you mention it. Great suggestion I will definately try that. I have read a lot about repro wires being issues today and I do have them on my car. I like the shielding look, do you know if there are any good wires with the sheilding available? Thanks again, excellent suggestions, I will let you know if either takes care of the problem.Comment
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Re: LS5 engine miss
These seem to be an ongoing issue with many engine problems. I think it's time I changed them out....Thanks!Comment
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Re: LS5 engine miss
Ok, so over the weekend I replaced the wires with a set of ACCEL 8 MM (look like crap compared to my shielded OEM set) and replaced the sparkplugs, checked for vacuum leaks as you suggested and it came up tight but still idleing rough. Rough may be a stretch, it just "pops" every now and then out of the right bank and I am a perfectionist. The good news is I have much better power at higher RPM and the "float" is gone. Now I have to decide if the increase power is worth the look and an occasional pop out of the exhaust. I have tried to tune the idle mixture but just can't get rid of that dang pop!Comment
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Re: LS5 engine miss
Set up Ebay to alert you when an NOS set of shielded plug wires come up for a sale. Eventually they will show up and at a reasonable price.Comment
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Re: LS5 engine miss
An update to the miss. I changed out the plug wires as suggested and sure enough the miss almost all but went away. It is now just a little "Pop" every now and then versus "Popcorn" all the time. I can live with that! Thank you for all the help, once again the Technical Board keeps another Vette on the road!!Comment
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Re: LS5 engine miss
Tom,
A well tuned LS5 should be silky smooth from idle to redline and pull like a freight train. If you have a "pop" at steady throttle or under acceleration, that's a misfire. If you have a pop during deceleration, that's an exhaust leak.1969 Riverside Gold Coupe, L71, 14,000 miles. Top Flight, 2 Star Bowtie.Comment
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Re: LS5 engine miss
I suspect there is a problem with distributor assembly (dimple orientation), plug wire indexing, or distributor installation indexing.
...suggest you set the engine at the proper initial timing point BTDC #1, remove the distributor, check drive gear orientation, plug wire indexing, and properly install the dist IAW the appropriate CSM. As long as the distributor is out you might as well do a "blueprint overhaul". I'd bet even odds it's never received any service other than points, condenser, and maybe a cap and rotor, and bubba has probably worked on it and "fixed" it by reindexing wires and installing not IAW the service manual and the way it was originally done at Tonawanda.
This is not an uncommon problem!
DukeComment
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