Where to get fault codes scoped?



I know it seems obvious .Did you check the gap? That can seriously cause misfires idle problems stutter and hesitation. Also what did the old plugs look like? Were they fouled, did they have any grayish brownish powder deposits on them? You can tell a lot about a car by looking at its plugs.


new wires. do it.


Son had an 06 Cadillac come in the shop yesterday.

When he opened the hood, here’s what he found.

Engine cover says 3.6L, emission sticker says 4.6 LITERS.



I wonder what the vehicle history is, and maybe if that engine cover was recycled or accidentally re-installed on the wrong car at the shop.


Bing, I ran it late at night and saw not even a hint of sparking (arching) but I still believe the wires must be an issue.
I went from a couple of minor backfires to it running like crap the second the plugs were changed out. One thing we did notice, the specs called for 50 mm gapping but he found the ones in the car were set at 55, so he replaced them at 55


I ran the car at night and did not see a single spark in the front 4 (the back 4 cannot be seen just looking at the engine), but I have to believe the wires were either bad, or he jacked them up when pulling them “hamfisted” as you alluded to. This guy spent 2 hours replacing just the plugs and I could see he had great trouble doing the work


Thanks, I will see the person who does the cables sees this


He said he thought just the plugs would be adequate…New mechanic forthcoming. PS I used to do my own work but blew 10 discs in a bad motorcycle wreck…no more auto repairs for me


Right away Cavell. Because things are worse and he felt “badly” taking my money, he offered to swap the wires gratis as I have a lower rad hose ready to explode, so he’ll charge me a small fee for that work…or should I pay a better shadetree to do the wires? The shop wanted $164 just for the labor on the wires Cavell, too steep for me at this time…


Can I just get the $55 wires instead of the $90 ones?


The firing order, does this change the location of the plug wires on the chart he posted? Thanks Bing


Through all of this we still haven’t gotten to the original question of where to get the misfire diagnosed. GM cars of that era will not log a specific misfire fault code. They simply log a P0300–Random Cylinder Misfire. But in the data section of the scan tool the user can select cylinder misfire data and see in real time–and in history–which cylinder is misfiring and how often. I would think any competent mechanic would have the ability to do this. Maybe a plug wire or 2 got crossed, not snapped on completely, and is now causing a misfire. Why not visit your local garage for a little bit of scan tool diagnosis and know for certain where the problem lies?


If the OP can’t afford the labor to replace the wires, how can they afford a $100.00 diagnostic fee at a garage?



The condition of the car and the condition of the checkbook aren’t really related, are they? I will always believe it’s better to do a diagnosis of the work needed before proceeding with a repair. The car runs worse now than before the mechanic in question changed the plugs. Maybe he broke a wire. Maybe he crossed a couple of them. Maybe he knocked a vacuum line loose at the rear of the engine while reaching around back there. Maybe there’s a sensor unplugged somewhere. I think the issue needs to be properly and completely diagnosed before starting to replace parts–especially if money is tight.


Yes they are.

Example: I’ve had people come into the shop with their vehicles with blown head gaskets.

I quote them a price to repair the head gasket.

If they can’t afford the repair, or if the cost of the repair is more than the value of the vehicle, I then offer to add sodium silicate to the cooling system to seal the head gasket leak.

So they end up with a repair that costs less than $200.00, instead of $1000’s.

The vehicle is fixed, and it gives them time to find a replacement vehicle.



Exactly my point. The car is overheating. You know the car has a blown head gasket. So you know what to do next. Would you add sodium silicate (or any other sealer) if the car had a stuck thermostat, a broken water pump pulley, or a failed cooling fan? With the car in question above we still don’t know for sure that plug wires will fix it. We need to know what’s broken in order to try to fix it.


Tester has it right Asemaster, of course the checkbook doesn’t change the issues I’m facing, but it matters a great deal or this site would be pointless. We’d all just take our cars to the dealership they were from and pay double or more for the repairs. We would absolutely get it done perfectly since they have model-specific testing equipment, they know the subtle nuances of a car like this Northstar engine (prone to overheating, AC issues etc. but this is the real world where we don’t all clear 6 figures. I am even more challenged because I got run down by a Postal truck on my motorcycle and blew 10 discs, I now pull half my former income getting social security and I’m too “broken” to perform most repairs myself. So I lean on you guys to walk me through my options, and BTW I am so grateful for each and every one of you. Tommy


Asemster, I realize you are trying to give me real-world cold, hard facts, and I appreciate that, but unfortunately I have to do my best not to make erroneous repairs as I’m permanently disabled (so my funds are tight). I made a big mistake not having my shadetree mechanic change the wires as well, but he thought the wires might be ok since the car was running very well prior to the backfires on my drive home that day. We opted to change the plugs and see if that was the issue (backfire, plugs, no tuneup in years = reasonable guess. HOWEVER I would never have gone cheap and bailed on the wires if he’d told me what a nightmare changing the plugs was on this model. It’s like changing the oil and putting the dirty filter back on…I’m not stupid…but he didnt tell me how labor intensive going back for the wires would be… neighborhood shop wanted $169 just for the labor!!! I’ve never heard of such a thing…almost $2 bills to install plug wires? Wow. I’m grateful for your help today, my guy is coming to replace the wires this morning.


BTW, so we’re all on the same page, we don’t have enough evidence to assume my head gasket is blown, I have no bubbles/rad fluid on my oil dipstick and my car was running like a beast until the backfire (which is normally fuel or fire as I recall.) I know I sound like a total noob, but I spent hundreds of hours working on cars in my youth, it’s just that it was in the 80’s 90’s and newer cars are much different, I do understand most of what you guys are explaining to me…


Cavell, I’m going to follow your instructions as you’ve clearly got a good working knowledge of what I’m facing. I am having my guy replace the wires today and replace the bulging lower rad hose before it blows (and 13 qts of new fluid of course)
After we replace the wires, if this doesn’t solve my misfires/backfires, I will take it to be scoped tomorrow. I can afford some stuff this week…