newbie with a question.

[93firechicken]

Hey guys I am new to the f body world I converted from fox bodys, (got tired of being beat by near stock Lt1s and Ls1's My car is a 93 firebird and motor is stock, besides tb, cai. The car runs great cold and as it warms up it starts to miss between 1,000-2,000 rpms under half throttle, at WOT it runs great and at little throttle its great. I popped the hood at night and when I rev it up you can see electic flashes under the alt. Right around the plug wire or the plug. My question is this, Is it the plug wires arching (they oems) is it a plug that is grounding, or could it be the cap cracked??? any help would be great.. thanks

[Injuneer]

Welcome to the site, welcome to the F-Body and welcome to the exciting world of the LT1.......

How many miles on the engine?

If you see sparks its most likely a combination of spark plug gaps that are too wide and plug wires that are broken down. If you don't know the age of the plugs and wires, and feel that they may be "original" (= 16 years old), condsider replacement as the first step in returning your engine to top condition. The OEM AC/Delco plugs are know to lose the little platinum pucks on the electrodes, opening up the gap way too wide. The OEM Packard wires are very good, but the will get "old". The NGK TR55 Iridium plugsd are a good replacement. Lots of opinion on wires, but I like the MSD 8.5mm Superconductors - a tight fit in the stock routing, though.

A cracked distributor cap is not too common on the LT1. But the cap has wires embedded in it, that route the terminals inside the cap to the plug wire towers on the outside of the cap. The epoxy di-electric strenght can break down with age. The OptiSpark distributor (particularly the "unvented" 93-94 unit) can also be prone to problems with moisture and corrosion. The moisture will cause carbon tracking in the cap, and rust can "blind" the optical cam position sensor. The bearing is also subject to problems. The "Opti" as it is affectionally known, is expensive, and a bit of a pain to replace, so its often the last item to replace, it nothing else works. It will set trouble codes for problems with the optical cam position sensor, but noe for problems with the high voltage section (cap/rotor).

Start with a quick scan for codes. You can do that simply by shorting a couple pins in the ALDL connector under the dash near your right knee (93 is the only year this works on).

http://shbox.com/1/dlc2.jpg

After the code check, pull a couple plugs and look at the condition. Changing the plugs and wires is failry time consuming, but worth the effort.

Also consider the age of the O2 sensors. An engine that runs good cold, but starts to weaken as it heats up may indicate a problem with the O2 sensors. 93 again is unique, in that they used 1-wire unheated sensors, compared to the 94+ with the 4-wire heated sensors. If they are "old" they may need to be replaced.

Another possible problem is failure of the ignition control module (ICM) due to heat soak. Its bolted directly to the driver's side head. You can reduce the heat soak by spacing it off the head:

http://shbox.com/1/4th_gen_tech2.html#ICM_cooling

The links above come from Shoebox's website - probably the best source of LT1 info on the planet. Bookmark it - you're going to need it:

http://shbox.com/1/4th_gen_tech1.html

Good luck... and have fun!!

[93firechicken]

the motor has 160k on it. If the opti goes out will you see flashes in the engine bay?? The girl that i got the car from said that it had just had a water pump opti and opti sensor put in it. I dont know if i beleve her but that what she said. Also if the cap did go out would it arch as well???

[Joe 1320]

What you are seeing is the spark energy taking a different path to ground rather than though the spark plug. This could happen at any point along the voltage path from the coil, though the "distributer" (read: optispark), all the way to the electrodes in the plugs. If you see blue flashes you are getting voltage leak.

Here's the ignition lecture......... the factory designed the ignition system to last 100K miles. Mostly this was due to emissions requirements from the government. At 100K miles, figure that it's all used up and you'll want to replace the plugs, wires, optispark, and maybe even the coil and driver module. This way you're good for another 100K miles. Now with 160K, if you aren't the original owner you probably have no idea if anything has been replaced.

[93firechicken]

Not knowing really does suck, the girls dad owns a shop i guess and did alot of work on it. What work i dont know, wish i could of talked to him, would i see a voltage break from the distributor???? Is that common for it to arch from the distributor to the header or something? Or is it more like going to be a plug and wire???? Or a cap and rotor or should i just replace the all of them??? I would really pefer not to have to change the opti, which i was told that if it was the opti it would cut out at WOT as well which its not. All help has been great thanks guys

[ConElite]

Not exactly man. My buddy had a bad opti and would mis-fire from 1500 right when he would punch it. Then from 2000k to redline it pulled like a beast! Those damn opti sparks are trash. Replace it with a factory unit. Change plugs and call it a day. Pull a plug, if it looks bad or bad then replace them with some NGk's and should run like a top! 160k is a ton of miles. Impressive

[93firechicken]

Not exactly man. My buddy had a bad opti and would mis-fire from 1500 right when he would punch it. Then from 2000k to redline it pulled like a beast! Those damn opti sparks are trash. Replace it with a factory unit. Change plugs and call it a day. Pull a plug, if it looks bad or bad then replace them with some NGk's and should run like a top! 160k is a ton of miles. Impressive

If the opti goes out would i see electric flashes in the engine bay????

[Injuneer]

Depends how the Opti fails, but most likely, its not the cause of arcing in locations other than right at the Opti. If you have arcing along the wires, its either bad wires, or excessive gaps on the plugs. You can also get arcing at the coil if the coil is failing. If you see sparks at those location, it means the Opti is sending the spark out to the plugs, to its not likely due to the Opti. Think of the Opti like any other distributor - if the cap is damaged, or if you have excessive corrosion at the wire terminals, its going to spark.

[RAF7789]

That sounds like a coil problem... There are some troubleshooting articles on Rob's (Shoebox's) site and, as previouly stated, that is the best website in on Earth for LT1 help.

Does the arcing under the alternator speed up with rpm increase?

And like everyone else said, it could be a number of things and you can narrow down your cause by a simple investigation in the daytime. Just check the wires for gashes (the smallest cut or nick can be a big problem), (Start on the passenger side b/c that is the side that you were seeing the electric current grounding out,) check for codes, check the plugs... if all of these lead you no where, then diagnose the rest of the ignition system (coil, ICM, opti). "How-to's" can be found on that website. Welcome to the F-Brotherhood

[ConElite]

If you arte arcing somewhere under the alternator theres a high chance that your wire has a gash in it. Check that then make sure all your plug wires are smug on the plugs and on the Opti and Coil.

You simply saying you see sparks under the alternator does not make it very easy to give you more information. Best bet is to take off the alt. and see whats going on. Id change plugs and wires and eliminate the possibliliy of it being that.

Then if the problem continues then move on to the Opti.

[93firechicken]

That sounds like a coil problem... There are some troubleshooting articles on Rob's (Shoebox's) site and, as previouly stated, that is the best website in on Earth for LT1 help.

Does the arcing under the alternator speed up with rpm increase?

And like everyone else said, it could be a number of things and you can narrow down your cause by a simple investigation in the daytime. Just check the wires for gashes (the smallest cut or nick can be a big problem), (Start on the passenger side b/c that is the side that you were seeing the electric current grounding out,) check for codes, check the plugs... if all of these lead you no where, then diagnose the rest of the ignition system (coil, ICM, opti). "How-to's" can be found on that website. Welcome to the F-Brotherhood

Yes it does increase with rpm's I have not been able to take much time with the car as of my job keeps me busy, (police officer) At night you can see eletric flashes in the coil too, didn't know if that was normal for a GM or not. As for the flashes under the alt, it looks like a arching wire to me. but could be wrong

[RAF7789]

It is not normal to see any arcing anywhere within the ignition system. If it is arcing directly at the coil wire, remove the coil wire and check it. If it is flawed, replace it (i haven't been able to find a source that sells just the coil wire, so you would end up buying all 9 wires in a kit, and at that point you might as well replace them all. And AT THAT POINT, while you have access to the plugs, you might as well replace them too ) When buying plugs, go for the single ground strap + iridium. As mentioned above the NGK TR55 iridiums are a popular choice.

I know it is kinda hard to see the coil at night; could you have been seeing an arc off a possible gash in the coil wire?

Also, make sure that the coil wire is tight up to the coil upon re-connecting. Its diagnosing time!

[93firechicken]

I think maybe it is a gash in a wire or just a bad wire or plug gap, the coil wire is on top of the water pump and I have not seen it arch at all. I only see arching under the alt close to the headers. The only part that i dont understand is why would it just do it after it gets warm...? Only after driving it for 20 min or so... what do you think??? On a side note dont get me wrong I still love this car and think I made a great choice. After getting this problem fixed I am ordering a kit maybe just a 75shot. Just something for the track.

[Joe 1320]

The only part that i dont understand is why would it just do it after it gets warm...? .

Resistance increases in proportion to heat. The higher the hieat, the higher the resistance and the more likely the current will find another path of less resistance.

[93firechicken]

thanks guys all your help has been great. The car is going to a place called all out performace to get new plugs, wires, set of 4.10's and the kit hooked up.