2003 Suzuki Aerio about 248K
my youngest kids car it is a to and from work car they never go very far 10 mile trip is about it.
about a month ago it started running rough getting a cylinder 4 misfire

pulled the plugs they looked fairly old , so buy 4 new plugs no change so order 4 coils
the #4 coil was definitely flaky sometimes it would fire sometimes not

replaced all 4 coils kept 1-3 as backups and labeled them and put them away.

things were good for a while , now is where I admit I bought the amazon coils 4 coils for 5 dollars more than one was going to cost me about anywhere else.

so they tell me late Saturday night it is running very rough again started on their way home from work , ok I will look at it in the morning.
npf in the morning I unplug all 4 coils one at a time and it loads down with each one unplugged plug it back in and back to normal.
I drive them to work in their car and just as I am getting to their work it starts , ok cool at least it is happening chug home the 2 miles and start unplugging #4 no change , do the others and definitely #4 is the issue no spark.

replace #4 it with the old #1 coil and no change #4 seemed hot but I didn't think too much about it and put #4 back in as it wasn't appearing to be the coil that was the issue

let things cool down hood up for 45 minutes go in the house and research wiring 3 wires in this plug + is fore , - is aft and middle is signal
test I have power and ground , run it for a while to get it to happen again driving around with the meter waiting for it to fail , it took a while but it did fail

so I figure I have a wire that is opening up when it gets hot , and I am hoping ground or power as it is easy to borrow ground or power as that is common across al 4 coils.

after it does it again and it took a while I have power I have ground I don't have a scope to test for signal.
I take a razor and cut back the tape holding the bundle and spread out the wires looking for any sort of abrasion or broken wire I don't see anything but #4 starts firing again figure ok swap #3 and #4 see if it follows cable or coil.
while doing this realize how much hotter #4 is than #3

let it run for an hour and it keeps running fine

it may have been how the wire was getting pulled , it is unwrapped now , it may have been that coil overheating

I can't find my inferred thermometer so I ordered a new one so I can get a better read on the temp of the coils

the wiring was also bent at some sharp turns like the red line I drew in.


what do you think , bad coil overheats and causes the issue , the wiring is the issue , or something else.

Can I get the cllift note version of the post please

has anyone tried any of the sub 200 dollar oscilloscopes I am seeing them on amazon for as little as 40 dollars

my old early 80s scope died a few years ago so I don't have a way to measure signal.

intermittent electrical ignition issue on 21 year old car.
but you would have to read the entire thing to understand what has been done to offer possible solution.

unless that possible solution is you have a cheap good running car you want to drive to WI and sell me.

Kia’s seem to be easy to get your hand on,,,,,
How many you want?


I always look for ground issues first…//

On GM applications, I would sometimes find terminals that were opened slightly larger than normal. These would act up hot, as they relaxed more. I made up a whole set of terminal test wires, I could feel how snug the terminal was in relation to other terminals. It also was common to find the wire degraded inside the insulation (nothing apparent on the outside) just behind the crimp for the terminal end. You could pull on the wire and watch it stretch a little right behind the terminal/connector.

especially as this isn't happening now that the strain is off the wire at least not yet I am thinking it was the strain on the wire as it heated up pulled out one of the connections in the plug but the meter still got connection as I held the probe in the cable.

if this keeps working I am leaving it as is wires separated and no strain. rather than wrapping up how they were.

There are connector kits available for some applications, which include the pre-wired connector, pigtails and crimp connectors with heat shrink tubing. Might be a solution if the issue pops up again.

that is exactly what I am thinking if it follows the cable pigtail , but I will solder it in and shrink tube it, crimp connectors always just become my next issue.

I have been soldering for so long and I have a butane powered iron that I can solder in a couple minutes more than crimp.

GM actually required butt connectors for warranty work. With the right crimp tool and the heat shrink ends, I've never seen issues from them.

Cheap butt connectors aren't worth the materials they are made from.

Just out of curiosity.....are the wires copper, graphite or something else ?

the wires to the coil I believe are just copper look to be about 18ga the coil sits right over the plug and have a spring looking coil inside of the tube that goes down and pops over the top of the spark plug.

Thanks ! 18 sounds kinda light to me to carry that type of voltage/amperage........but I'm certainly no expert. On the other hand, wouldn't the smaller wire be more adversely affected by heat..........? Wouldn't that create more resistance ?

they are small wires

each cylinder has it's own coil I suppose they could be 16 with very thin insulation

each coil has it's own power , ground and signal so all the real high voltage is strait down from the coil to the spark plug , it doesn't take a lot of current to make high voltage

Got it !! Thanks !

It just did it again , and it followed the cable not the coil.

I still have power and ground , still no good way to measure signal


I am already ordered the last 7 inches of the cable with plug from Napa the are a whole 10 dollars an it will be there tomorrow.

Pain in the butt, but ohming the wire from the connector to the PCM is about rhe only way to test it.

replacing the connector seems to have fixed the issue , also seems we had a double issue

I replaced the connector , I test fit it on the coil then took it off and soldered the connections well the heat appears to have done something to the connector because it would go on and work even half on but not clip again.
well, I zip tied it to stay on not my proudest moment turning a wrench but it needed to work long enough that I could be sure that was the issue. and I could replace the connector again.

it was running on all 4 but as soon as I started moving not well.
car was on E with the light on it had been a month and a half of freeze thaw since the last fill up so I am sure there was water in the tank and very little gas.
I went and put 8 gallons of gas in and a can of seafoam and it is running normal now.

the zip tie is holding

it makes me wonder if GM knew heat did a number on those connectors and that is why the require crimp connections.

seems odd to put a heat sensitive connector on the top of a engine.

so now that it is running normal again , flat tire yesterday evening , edge of side wall on the inside of the tire.
so it has to be replaced , have the road hazard so good news but not that great of news as the tire that was purchased this fall and has maybe 500 miles on it has been discontinued.

new tire should be here tomorrow


White , Yes 18ga when I went to strip the wire

Glad to hear you got it sorted out.

Thanks for the update Pete!!