Aurora Backfire at 1500 RPM light load

1996 150K miles. new plugs, wires, fuel filter, air filter, 1 way vacum valve on brake booster, new EGR valve.

No computer codes in memory or check engine light. Runs fine except when crusing at light throttle under load (like slight hill) will develop a slight miss and backfire. Speeding up or slowing down stops it immediately.

Any ideas on where to start?

Yes. Please read my post in the "Valuable Northstar" thread. You have classic symptoms relating to plugs and/or wires. I would also like to recommend to everyone the use of Chevron Techron Concentrate. Not the Fuel Injector Cleaner, the 20oz(or two 12oz) CONCENTRATE. This is a great additive. Buying a used car and not knowing what fuel the owner has been burning, and for periodic top end cleaning. You will notice it running smoother after a couple of treatments. You could follow Chevron's program of cleaning steps using their; Clean UP,Stay Clean,Inj.Cleaner then Techron if you think your still running rough. But you'll notice the biggest difference after the Techron to an otherwise decent running engine.

Yes. Please read my post in the "Valuable Northstar" thread. You have classic symptoms relating to plugs and/or wires. I would also like to recommend to everyone the use of Chevron Techron Concentrate. Not the Fuel Injector Cleaner, the 20oz(or two 12oz) CONCENTRATE. This is a great additive. Buying a used car and not knowing what fuel the owner has been burning, and for periodic top end cleaning. You will notice it running smoother after a couple of treatments. You could follow Chevron's program of cleaning steps using their; Clean UP,Stay Clean,Inj.Cleaner then Techron if you think your still running rough. But you'll notice the biggest difference after the Techron to an otherwise decent running engine.

Yes, I read about the OEM wires and plugs and .060" gap and I did have 2 original spark wires go bad within 3 months of each other at about 90,000 mi. I just don't remember the symptoms (backfiring) being like I'm experiencing now. It always happens between 1400 and 1800 RPM and the preceeding miss is very subtle (but I guess that could point to one wire)....I DO remember the dealer telling me to look for carbon tracking and evidence of arcing at the very end of each spark boot and changing just that wire. This actually worked the first time. Then when another wire went, I said the heck with it and changed 'em all to some after market yellow ones.

Wish the Alzheimer's would go away! Do you really think I should fork the $170.00

I live in the Philadelphia, PA area and I just but new plugs and wires. The AC Delco plugs were $50 any set of other decent plugs is going to be about the same price. The AC Delco wires were $90. The other brands ran from around $70 to $100. So why not spend the extra $20 bucks for the lifetime warranty. Just think, next time the wires will be free.

Hello my friend;

Checkout the idle control motor, possible problem,or the fuel pressure regular,if you smell gas, that is the problem.

I had a similar problem, it turned out to be the regular.

Take Care:

(Driving along in my Oldsmobile)

Backfiring through exhaust(bang), or intake(cough)? When I had the wrong plugs in mine it would cough up through the intake while cranking it.

I don't know if I'd call what I had a 'backfire', but I always got it under load just under 2000 rpm, say 1800-1900. Like you I could give it some throttle and it would go away or I could ease off. Once it was a bad plug making the wire short to the block. About a month later I actually had a chunk of carbon get stuck in the plug gap. I wouldn't have believed that it the mechanic hadn't saved it for me before he cleaned it out and put it back in- most likely because I was steamed at having my car back in one month later for the same symptom :). It acted the exact same way. I'd get it up to 30ish just after it shifted it would start bucking and heaving.

I haven't had trouble in the last 18,000 miles with new delco platinum plugs and delco wires- well, that and some really good carbon cleaning stuff called BG 44K instead of the Chevron, but same idea...

I haven't had trouble in the last 18,000 miles with new delco platinum plugs and delco wires- well, that and some really good carbon cleaning stuff called BG 44K instead of the Chevron, but same idea...[/QUOTE] All that carbon build-up is from shit gas!

Hello my friend;

Checkout the idle control motor, possible problem,or the fuel pressure regular,if you smell gas, that is the problem.

I had a similar problem, it turned out to be the regular.

Take Care:

(Driving along in my Oldsmobile)



Tried the regulator to no avail. Assuming the ICM is in the intake? I'll take a look there and will check the condition of the plugs. Not sure what I put in 50K miles ago. I sprayed water in the wires in the dark and saw no arc....

BG44 is supposed to be the best. I'm gonna order some online. I have the hanging bottle that you can use to slowly leak it into a vacum port, but I doubt that will be the fix.

Backfiring through exhaust(bang), or intake(cough)? When I had the wrong plugs in mine it would cough up through the intake while cranking it.

Sounds like a muffled low cough through the intake always under very light load lugging up a slight hill at 1800 RPM.

I'll let everyone know what I find when I pull the plugs. Maybe I put something stupid in at 100K miles!

BG44 can be bought online here...
http://www.carfood.net/megpowcarcle.html

Another thing I noticed....looong crank times in the AM after sitting all night. I'm gonna put in a fuel filter

Putting in AC Delco Platunum plugs and wires. AT 100K I had put in KEM wires and Autolite Platinums. A mechanic here told me the KEM's are junk.....we'll see if it fixes the problem. Fuel filter was not plugged and pressure is 41lbs at the schrader valve...not sure what the spec is.

Maybe someone else can do better with the northstar engine specifically, but I used to have trouble with a Pontiac I used to have similar to yours with the long crank times. Turned out to be a combination of the mass air flow sensor and the temp sensor in the air intake. The two of them would screw the fuel/air mix all to hell when the car was nice and cold in the morning. A good scanner ought to be able to spit out the voltages and such fromo your various sensors there to compare with standard ranges. On the other hand all that car ever did was die at intersections instead of coughing while driving.

So, tmcnall, what were your results?

I just changed my plugs and wires on my 96 with 100,000 miles. It has never ran better. No more back fire or miss. Also, no more ticking noise from the engine that I thought was preignition. I also eliminated the flexible conduit and installed wire guides to keep the front plug wires seperated as they run past the coil bank to the back of the engine. Thanks for the all the good info on this thread!

I Had These Symptoms A Few Times. I Resolved My Problems By Swapping Out Coil Packs From A Junk Yard. The Third Time I Just Went Out And Bought 4 New Packs. Under Load At Low Rpms The Engine Would Buck And Backfire.

-sorry Didn't Realize That This Was An Old Thread