Where to get fault codes scoped?



I should have been more clear on the lower rad hose bulging, my car wasn’t overheating, it did however run hot when the temps here were 110 degrees, the tranny was overheating until we replaced the tranny filter, gasket and fluid, this made all heating issues go away (I was also leaking tranny fluid like a mother). The overheating and leaky tranny made the car run hot, everything cooled down once we fixed the tranny issue and changed the oil. Question? Any idea why only the lower rad hose blew up like a tennis ball but the upper hose showed no signs of wear? Thanks. We are changing the wires today and the lower rad hose, I will tell you if this solves my misfires.


I can afford this stuff this week, Tester, can you tell me what the firing order is on this car? Several people posted the order and even pics, but not all had the same order? Does this also tell me the order of the plug wires? I want to make 100% sure he puts them back properly, the front 4 look “obvious” but the back 4 you can barely see…


Since you are following along, I should tell you i had to replace the intake manifold a few months ago, and we had to put in a good-condition “pre-owned”, God help me if that went bad twice in 3 months, even used that was bank to install.


We are replacing the wires today Tester, if this doesn’t solve the issue, I will pay to have it scoped tomorrow. One question, if the car still runs horribly when we replace the wires, it means my mechanic made a mistake because I only had a minor backfire driving home that day, after he changed the plugs, it was twice as bad. Let’s assume he’s not a tool and the wires were put on in the correct order, what would the next likely issue be to check? Is there something on the coils he could have broken when he removed them to get at the rear plugs? There are 4 identical devices (coils?) at the back of the car side-by-side that he had to remove. I thought I read in the comments this model only has 3 coils, so what are the 4 identical devices he had to remove? Yes, of course if the plug wires fail to fix the misfires, I will pay to have it scoped tomorrow, I’d just like to have some idea what the possibilities are when I take it in, so the place that runs the scan doesn’t try to sell me unnecessary repairs. Thanks Brother


there are 2 motors for the aurora. the 3.5 v6 and the 4.0 northstar v8. 3 coils on the v6 and 4 coils the v8. you dont have to remove coil assy to reach rear plugs. or i should say, you dont want to have to do it. the ICM base plate has 4 screws that attach it to the valve cover. the lower 2 screws are kinda hard to reach.


Exactly why I would want to do some basic testing before proceeding. It’s rare in my experience to have plug wires be good before changing plugs and bad immediately after. If the mechanic broke one or more when changing the plugs (which is quite possible at this age) he certainly would have felt it and known.

Hopefully a new set of wires properly installed will correct your problem. Good luck.


Found this for a '98 Aurora:
Picture 5

As @insightful posted in post 6, this is exactly the firing order, cylinder identification, and coil identification from my $200 GM factory manual for the 4.0.

Just as an aside though, I put over 150,000 miles on my Aurora and it is not a cheap car. Never hardly went into the shop without a minimum of a $300 repair bill. There also are a number of things that can cause this car to be sent to the freeway in the sky. If funds are limited, it might be wise to find a car that might be a little more cost effective.


Your timing is amazing, he is on his way to install the wires now, I will forward this info. Hey Cavell, if after the wires are done and it still misfires badly or backfires mildly like it did when we began, I will do as you suggested and have it scanned professionally. He has a handheld that gave us the PS0300 (random multiple misfires) but the $90 scan will hopefully be more specific. That being said, what would you check next? I was thinking we test the coils (I got the specs at Auto Zone, easy tests) and then look at fuel pressure. From what you guys have told me, the fuel pressure regulator,(sending unit?) the fuel filter, one of the injectors could cause a backfire at speed…any other obvious things I’ve overlooked?
Thanks so very kindly for all your precious time.


I got the specs and instructions how to test the coils…I will have him do it if the wires don’t solve this today, thank you


I know you’re right about the maintenance, but I have a few “rules” that I live by as cars go; Buy a used car in great condition and stick with it. ditching your used car for another is buying headaches you don’t know anything about. If you are car savvy, you already know what work is coming down the road (mine leaks oil so I know an oil pan gasket will be needed one day). I know almost every single part that has issues and I know what I’ve already replaced. Every car you buy means the starter you just replaced on your beater may be coming soon on your shiny new “used” car. 2) I have to own a powerful car, that always costs (gas, oil, tranny etc) I’m 54 and I’ve been driving for 39 years, never even a fender bender, I’m a great driver but also because I’ve got the horses to get away from trouble (drunks, stupid kids, women with cell phones)… Thanks, one more message…


The car is fixed! The plug wires fixed everything, the rough riding, the backfires, the OBDii code P0300, the shaky cam and he changed the lower rad hose and it’s running cold as ice! I know I’ve got an oil pan gasket coming eventually and solving the “disappearing coolant”, but it runs like a Ferrari today, so thank you for all your time and advice. I did the math and you guys ultimately saved me $400! Peace


The plug wires fixed EVERYTHING! Thanks so very kindly for all your help Cavell, it runs like a bandit, no misfires, no shaking block, no backfires and you saved me over $400 had I paid for a scan, had this done at a shop and paid full price for parts…
I’m so thankful for all your help this week! Peace


To everyone who helped me this week, thank you, the plug wires solved all my problems, the backfires, the misfires, the OBDii code P0300, it now runs even better than before the problems, to summarize, never change your plugs without the wires too, and pay attention to the pros, they (you all) saved me $400 and fixed my car to boot! I’m thankful to all of you. Peace


Glad you’re glad. Thanks for letting us know.