Bringing the Champ back to fighting condition

[bmarcum]

Ok. I have been driving my 90 Z VIN1965 and it has not been a driven car for 24 years. Not sure the history and why it wasn't driven but for all signs (oil tags, and condition) it not been a sports car for 24 years.

I have a miss that is weird. It only misses when the secondary are on. It seems to only miss when warm. Still trying to confirm warm only miss.

Thoughts on what I am chasing. I don't have a scope for LT5 waste space, so I can't tell if it is a cylinder or a bank that is missing. I have not pulled the plugs yet. But it is very intriguing that it does not miss with secondary off. Thoughts? I am a big one for diagnosing then fixing vs just changing plugs and wires especially pulling the intake. Thanks to all my LT5 friends!

[Starman]

You probably have one or more bad secondary injectors. There is a way detailed in this forum to check them at the ECM harness. If bad, replace them all. The original injectors are not ethanol resistant and short out. About 93 on did not have this problem.


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[Starman]

As I recall you are looking for around 14 ohms resistance.


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[Mystic ZR-1]

Replace the coils while you're in there....

[bmarcum]

The buyer I purchased it from said injectors had been replaced, but I have no documentation. It really feels like ignition, but it is strange that it will only miss on the secondaries. Just curious if the fuel mixture could be such that it would not miss on primary but miss under a load on secondaries with a full cycle charge needing more voltage. I am thinking maybe wires when the motor get heat soaked. I really like the OEM coils and have run them for a long time with no issues. I have had problems with MSD etc Chinese coils that were new.

Thoughts on wires being the problem? I will replace unless someone scope suggestions.

Other injector problems I have had on previous car would have bad misses at idle. This feels like ignition, but so weird it only on secondaries.

Anyone have a scope for wasted spark they like for LT5?

[A26B]

You probably have weak spark on 1 or more cylinders. It can occur on a single cylinder. The weak spark condition is not noticed during low RPM driving but will be noticeable under load as a misfire. It is most likely a coil, not plug wires.

There are 2 simple tests to determine if this is the case. I suggest conducting both to verify and isolate the cylinder(s) affected.

1. Load test in 6th gear at 35-40 mph, lug the engine. When you accelerate, not pedal to the floor, but 1/4 to 1/2 pedal, it chugs. If all is right, the LT5 will accelerate smoothly during this test.

2. Best done in shade or low light. Test spark by pulling one wire, attach a spare spark plug & lay it on the plenum to ground. Start the engine, hold the boot & observe the spark as you raise the plug. You should see a 1/2" long bright blue spark. An orange spark denotes weak spark. Repeat for all cylinders.

There are a few reasons for a single cylinder weak spark. The solution is to replace the coil. Your option whether to replace one or all four.

When replacing the coil(s), I recommend cleaning all the spade contacts on the coil base. Apply a light coat of dielectric silicone grease to the contacts before installing coils. Likewise, lightly lube the coil terminals & inside the wire boots.