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Discussion Starter · #1 ·
Hello,

I just finished changing out the intake gaskets on my 96'. The car runs much smoother now, but my main issue has not gone away.
It runs fine under light load, like cruising or even WOT if I ease into throttle. But accelerating faster from a stop, quick revs in neutral, and heavier throttle in a higher gear all make it run rough and miss, sometimes badly.
I'm thinking it's the cap and rotor, but I want to be more sure about it. I've got one picked out already (that was a different thread) but I'd like this forum's opinion before I spend $100 and a day replacing it.
I can take a video too if it helps, but that might take awhile.
Thanks.
 

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While it may be your cap & rotor, one easy check you can do before going to the trouble of replacing the cap is feel the coil wire that runs from the coil to the opti. If it feels kind of "crunchy" under the insulation, it's shot and needs replacing.
 

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Discussion Starter · #3 ·
My coil wire looks and feels fine. I replaced my plugs and wires a few thousand miles ago (but not the C&R, don't know why).
I guess it could be the coil, but I don't have another one to test.
 

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My coil wire looks and feels fine. I replaced my plugs and wires a few thousand miles ago (but not the C&R, don't know why).
Maybe because GM made it a pain in the ass to maintain? ;)
 
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Coils are cheap, and much easier to remove and replace than a cap'n'rotor.
Same goes for:
Opti- Vent & Vacuum Harness
Opti- electrical Harness
Coil Driver Module

IFF I were aiming the Parts Derringer, I'd replace those before removing the H2Opump.
 
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while a misfire under load can be a few reasons...one is plug arc. If you are using the stock heat shields on plug wire boots the arc can be "inside" them making it very hard to see, hear, find. With car securely raised and engine running in dark carefully look from under, and on top for any signs of arc. If you have not viewed each plug boot entirely around it...you didn't do enough

"Sometimes" when installing new plugs, you crack a porcelain which will cause a misfire/arc
 

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Discussion Starter · #7 ·
Coils are cheap, and much easier to remove and replace than a cap'n'rotor.
Same goes for:
Opti- Vent & Vacuum Harness
Opti- electrical Harness
Coil Driver Module

IFF I were aiming the Parts Derringer, I'd replace those before removing the H2Opump.
My opti harness is in good shape, though my harness is looking a bit old. I have another I can swap in.
I actually replaced a spark plug with my intake job because I cracked it on accident.

Lol, I'm trying to find an excuse other than the C&R, but last time I had my opti off the contacts inside looked pretty worn. I'm sure that's it, I just wanted to make sure my symptoms fit.
I'd hate to do all that work and find my injectors in need of replacing (knock on wood, they're on borrowed time). I've never replaced anything in the dizzy since I've had the car, so I think it's a neglected maintenance item.
 

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Discussion Starter · #9 ·
Fuel filter?

Vac leak?
I can take a drive with a fuel pressure gauge hooked up.
I replaced the fuel filter pretty recently.
I'm pretty confident that I've eliminated nearly all my vacuum leaks, for now at least.
 

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Discussion Starter · #12 ·
vacuum leaks, valves could need adjusting too.
Vacuum leaks would do it.

Yes, unless your rockers are seriously out of spec, the hydraulic lifters in most street small blocks nearly eliminate the need for valve adjustments. That's not to say it's impossible, just less common. Loose/ tight rockers typically make the engine run bad always.
Hence the puzzlement from @Caddylack .
 
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You could leave potentially good parts on the car by finding someone who knows how to use a oscilloscope. They would check that the coil has good output, the cap and rotor are good, ICM works, and the plugs and wires are good without disturbing any of the wires.

The oscilloscope may show a issue and a specific part OR 25 year old connector needs replacing. IE: problem shows until connector is unplugged then reseated.

The OPTI signal plugs can be back probed (for the oscilloscope) and may show these signals are marginal or failing BUT the PCM does not set a code.

If you find the right shop a hour or two of their time may be less frustrating than parts swapping.

The hard part is finding someone who has more than a scan tool, and understands how to use a scope for diagnostics.

Technicians started using scopes in the 1940-1950s. Then parts got cheap and it was new plugs, wire, and cap and rotor every time. Now new expensive parts do not guarantee to be working parts and parts swapping can cause more problems than it solves.


 

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Discussion Starter · #14 ·
I wish I had an oscilloscope right now. We used to have a portable fluke meter, but that's long gone. I'm not qualified to use one yet anyway lol.

I ordered the C&R off Amazon, slightly cheaper than Rockauto and it'll be here tomorrow. Amazon also has a great return system if I need it. Standard Motor Products DR473 Cap & Rotor Kit https://a.co/d/86K1hDr

I'll get a loaner fuel pressure tester from AZ today and go for a spirited drive later. Just to rule out fuel issues before I touch anything.
 

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Discussion Starter · #15 ·
Went for a drive with a gauge hooked up, 38psi at idle and around 40si while cruising. If I hit the throttle and make the car stumble and miss, the pressure goes up to about 43psi and holds. So, I think I can safely rule out the fuel system today.
I'll update when I get my new C&R on, I'm thinking I'll start it with the WP off to make sure it's healed before I dump water back in the system.
 

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Discussion Starter · #16 ·
Got my parts today,
Wood Gas Auto part Metal Circle

Seems like it's good quality, comes with the seals and screws too.
And yes, it does have brass terminals,
Watch Clock Analog watch Auto part Circle

It also came with a neat little instruction booklet, written by somebody who's native language isn't Chinese.
Handwriting Font Paper product Writing Paper
 

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Before you pull it apart, might want to try the night time, water mist test at the coil. Really needs to be pitch black. Had a nice little dazzling light show on both 91 and 95. This was back in 2016 and 95 only had 72K then.
 

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yes the water mist in dark test is always a good diagnostic step to trace arc source

on a cap install use a skin coat of dialectic grease on the cap O ring. Also around rubber boot of the 4 pin plug that goes in top of Opti
 

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It was mentioned before but I will re-iterate. Check or replace the Opti Vent Harness!

When that clogs (the tiny pinhole filter), it will cause the symptoms you describe as moisture and other gasses build up.

Tire Automotive tire Automotive fuel system Motor vehicle Bicycle tire


Make sure you can see light through it:

Gas Electric blue Window Circle Ball
 

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Discussion Starter · #20 ·
I got it all off this morning, this is what it looks like,
Automotive tire Hubcap Wood Alloy wheel Rim

It's much worse in person, it's hard to see how worn the terminals are on camera. The coil button is worn flat also.
Automotive tire Motor vehicle Rim Automotive design Automotive wheel system

All together
Tints and shades Gas Auto part Composite material Fashion accessory

Old cap,
Wood Gas Automotive exterior Auto part Metal


I started it after I put the Opti on, without the WP, and though it's a bit too early to tell for sure, I think this fixed it.
 
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