Ohm meter. Pull breaker. Continuity? Yes/no. No continuity, no power flows.
Is your idle rpm correct to spec?
Cavell, I need your expertise if you don’t mind? I got the oil and filter changed, the tranny filter and gasket changed and the car ran like a beast, the low pressure disappeared (yes, I think the oil filter was that badly fouled). On my way home yesterday, I backfired at 30 mph and it was sluggish on throttle response. Today I had a shadetree mechanic I use for small jobs change my spark plugs (but not the wires) and now it runs terribly, like it’s not running on all 8, the backfire is more frequent and even the pulley at the serpentine belt is a bit “wobbly”, ran an OBII with a tester and it came back with code P0300 “Random multiple cylinder misfire detected”. Granted, I should have changed the wires out, but what could have made brand new plugs cause the car to actually run worse?! I can’t afford to just keep guessing, buying new coils when it could be the plug wires arching, a vacuum leak, the timing could be off (he lost his timing gun)…I would genuinely like to hear your opinion if you would please. Thanks so much
Hey George, would you mind looking at my latest update reply to Cavell? I had my oil n filter changed, my tranny filter/gasket changed and everything was perfect until today, on my way home I “backfired” at 30 mph so I had my “shadetree” mechanic change my plugs and it runs terribly now, clearly not “running on all 8” Thanks much
Wyattspoppa
BTW, I don’t know the spec but before today, it idled nicely (not too high or low, )
Please see my latest post M-Man, I really need your help my new friends
I have to ask, don’t you find it odd the spark plug replacement guy gave the car back to you with it running worse than when you have it to him? Didn’t he start it up and at least test idle the engine after replacing the plugs? Suggest you return the car to him and ask him to figure it out what went wrong. Possibly the spark plug wires got interchanged, so two or more are going to the wrong plug. Backfiring is often caused by ignition timing problems. That’s where to start. After that valves mis-timed or not closing properly, overly rich mixture, and some cars have an anti-backfire valve than can be faulty. Checking the compression might provide a clue.
If I had this problem, besides verifying the plugs are connected up correctly, I’d ohm out the connections from the distributor cap to the end of spark plug wires to make sure there are no opens. And I’d look at the engine idling in total darkness to see if any sparks are jumping around in the engine compartment.
You won’t believe this, but all it took was an oil/filter change and a tranny/filter/gasket change and it ran perfectly! The oil filter was just that fouled! Yesterday I backfired at 30 mph, paid a shadetree guy I use to change the plugs and now it runs like crap, like it’s not running on all 8. I assume I blew it not changing the wires, got a fault code P0300. Guess we’ll either get a full scope done (P0300 is vague, “random multiple cylinder misfire”) or just do the plug wires and go from there? Peace
the plastic intake has a spring loaded flapper valve designed to vent when you backfire. the earliest northstar motors had an aluminum intake but they went to plastic in 95? and added the flapper door. if it does not seal you will almost always hear a whistle. it will result in a minor vacuum leak but you should not have a misfire code 0300 from it. i have never seen a fully failed/broke flapper. usually just a minor vacuum leak will result. the egr valves do stick open. but you would see a p1406 code? or similar. i bought new delco plug wires ($110) for a misfire and it worked for 3-4 months .than mis returned. i put on a newish set from the boneyard for $8 and mis went away the wires seem to be hit or miss. any aftermarket wires for $50 work fine
the 4t80e trans has a reuseable gasket and it does not have a filter. only has a mesh screen inside. there is an internal drain plug that lets you drain the side pan of 2 extra qts so you can change most of the fluid with a pan drop. its still messy though. the 4t80e weighs 256lbs. the 4t60 weighs 200lbs. i have removed both. ugh.
Hey Cavell,
My hero, where can I go to get a full scan? (pep boys, a local auto electric shop, etc) Someplace that will give me a reading without selling me on a bunch of BS repairs, just a reading, I can afford it this week Thanks
Also, how much should I expect to pay to have the wires installed? The shadetree guy who did my plugs charged me $80 and I could see the job was a nightmare for him, took 2 hours…and now my car runs worse, like it’s running on only 5 or 6 cylinders, not 8, even the cam is shaking. Perhaps I should have the wires done at a shop unless you think just the wires is easier than the plugs and I can have shadetree guy put them on.
I hear ya, he clearly has a nightmare time installing the plugs, it took like 2 hours and I could see the back ones gave him much trouble. I think I’ll pay the $90 and have it scoped for real, not the handheld with the generic code P0300 "random multiple misfires. I can see small burn marks on the front wire plugs where they lay on the block, I know I should have changed the wires, my mistake…
You aren’t asking me but when you pull the wires off the plugs, there is always the chance the things will pull apart some and not give a good connection. Especially if they are old. The other thing is if the wires were crossed.
If you have a wobbly pulley, depending on which one, it is possible your crank pulley is coming apart which will throw everything off. Not unheard of at all.
Idle the engine when it is totally dark. You might be able to spot some sparks jumping around and figure out where the high voltage insulation on the wires is wearing out.
Thanks GSJ, I will do it tonight. I can’t believe what some shops want for this stuff. One shop wants $165 to change my wires…just my plug wires (wires another $100
Also, the diagnostic $110 and not applied to the repairs!
Please consider me asking you as you clearly know modern automotive electronics…I thought distributor caps were still a thing! Apparently I have 3 coils. My shadetree mechanic showed me small burn marks on my front plug wires where they rest on the block. He also said he saw arcing
Oh, and no way this guy crossed wires, that’s a rookie mistake, this guy bleeds oil, it was me who asked if we could just do the plugs and skip the wires until we knew they were bad, when did plug wires cost $90?
remove plastic beauty cover. remove wires. coil pack is on top of rear valve cover. should take 10 min to do front plugs. the car may have a strut tower brace which you remove to reach rear plugs. yes they are sort of hard to reach but you just have to bend over a little bit more. of course you know you dont set timing. computer does it.
Hey George, as you’re one of the most respected posters on the site and you’ve helped me before, I hope you dont mind my inquiries. I’ve finally put some money and time into the Aurora, here’s what’s been done recently;
I replaced 2 bad coils which fixed many issues, I just had to replace the serpentine belt for the 4th time in as many years, but this time I also replaced the tensioner which was tearing the belts (sharp edge) and the coil and motor mount they attached to. I had the tranny filter cleaned/replaced, replaced the stripped radiator cap, 2 bulging rad hoses, one disconnected air hose (I forget what those are called) it now runs like a beast. No more misfire fault codes, no more slamming into gear by the tranny but we have a new code 171 “too lean bank 1”, not getting enough gas (which is comical, I get about 12 mpg) This happened yesterday after my mechanic did the serpentine belt. Any ideas?