Coil Pack primary resistance?

Anyone know if there is a specification for the primary resistance of the coil packs? I see a secondary resistance spec in the FSM, but not for the primary. Reason I ask is because I am going back and forth with this poster on another Buick Board. He claims that all 3 of his coils are reading low on the primary side, .3-.5 ohms, when the specs call for .5-.9 ohms. He claims his SC Regal GS used to get 33 MPG, and now his mileage is down to 25 MPG. He feels a weak spark may be responsible. I feel if his ignition was weak, he would have misfires, especially under boost, but he doesn't seem to have any performance issues. Here's the thread if anyone is interested.

http://www.buickforums.com/forums/showthread.php?t=23100

LARRY70GS wrote:

Anyone know if there is a specification for the primary resistance of the coil packs? I see a secondary resistance spec in the FSM, but not for the primary. Reason I ask is because I am going back and forth with this poster on another Buick Board. He claims that all 3 of his coils are reading low on the primary side, .3-.5 ohms, when the specs call for .5-.9 ohms. He claims his SC Regal GS used to get 33 MPG, and now his mileage is down to 25 MPG. He feels a weak spark may be responsible. I feel if his ignition was weak, he would have misfires, especially under boost, but he doesn't seem to have any performance issues. Here's the thread if anyone is interested.

http://www.buickforums.com/forums/showthread.php?t=23100

Did you try asking him if the coils were ever replaced? There are different spec coils for the SC versus NA engines and for later vs earlier 3800s, and it sounds like your fellow poster just has a pack of coils different from what he expected.

Albertj

albertj wrote:

LARRY70GS wrote:

Anyone know if there is a specification for the primary resistance of the coil packs? I see a secondary resistance spec in the FSM, but not for the primary. Reason I ask is because I am going back and forth with this poster on another Buick Board. He claims that all 3 of his coils are reading low on the primary side, .3-.5 ohms, when the specs call for .5-.9 ohms. He claims his SC Regal GS used to get 33 MPG, and now his mileage is down to 25 MPG. He feels a weak spark may be responsible. I feel if his ignition was weak, he would have misfires, especially under boost, but he doesn't seem to have any performance issues. Here's the thread if anyone is interested.

http://www.buickforums.com/forums/showthread.php?t=23100

Did you try asking him if the coils were ever replaced? There are different spec coils for the SC versus NA engines and for later vs earlier 3800s, and it sounds like your fellow poster just ahs a pack of coils different from what he expected.

Albertj

I asked him on that thread.

I am thinking that like the rest of us he's just getting his mileage pwned by Winter Reformulated Gasoline.

Albertj

Of all the things that can cause bad mileage what made him think coil packs? Especially since there are no other issues with the car.

They rarely go bad, and when they do its normally just one of them at a time.
If all are reading the same ohm values, assuming that value isnt right, then he may want to look into the ICM, ICM ground and if the coils are the right ones for the car.

I don't know. He seems to think that a weak spark is responsible for his lowered gas mileage, and I was trying to tell him that it would misfire first, and he would notice that. I've just never seen a spec for ohming out the primary side of the coils, just the secondary side. I don't see anything in the FSM.

Imo, the idea that ignition spark can impact fuel economy, at least in our engines, is mostly theoretical marketing hype (a way to sell multiple electrode plugs, or exotic wires). There might be a slight impact, but it's not 5-10 MPG like your buddy is claiming.

I once decided to let my spark plugs go until I detected a symptom. I was using AutoLite 104 copper plugs. Normally, I set the gaps to .058" and take them out at 20k miles for replacement. The gaps are usually .065" to .070" at that point. Well this one time I decided to leave them in for 30k+ miles, and eventually I noticed a slight hesitation, a seemingly random miss at idle and when I eased into the gas. Just a little skip every few seconds, nothing alarming, but changing those plugs out immediately healed the problem. I never got a misfire code, nor did I notice any decrease in MPG. Only problem was the symptom described. I have to think the ignition system was performing close to the edge of failure at that point, but again economy didn't take a hit.