[TheCrazy1]

Hi, hopefully someone can help figure out what's going on here! I have a stock 98 Cobra, just Flowmasters and K&N. I took it in for a chip and custom dyno tuning a few weeks ago only to find that it's pinging too much to be tuned. I was disappointed to find it's only putting down 248RWHP. It's pinged for a long time and the only thing that seems to help is to put a couple gallons of 100 octane unleaded in the tank. I've replaced the fuel pump (it actually died awhile back), the coil packs, plug wires, spark plugs, MAF sensor and all the fuel injectors. The guy doing the tune told me there's no trouble codes, O2 sensors are working fine and suggested that I replace the whole exhaust system. Occasionally, I get a sulphuric smell when I drive it hard as if the cats are overworked. Periodically, I get a rough idle as if the engine is straining to run, but after driving it, this clears right up. I've even replaced vacuum hoses and checked for leaks and everything looks good. So my question is.... do you guys think the exhaust system could be causing this ping, and is there anything else you can think of to check? Any input on this is welcome! Thanks.

[KeAnBe46]

How advanced is your timing? I dont think an exhause system would do that though...When I was running my 89 5.0, I advanced the timing by 4 degrees and the engine would ping when I ran regular fuel...when I put high octane fuel in my car the pinging went away...Ill talk to my mechanic back home and Ill let you know what he says, but I really dont think that the exhause would cause your car to ping cause normally that would be an internal issue.

[TheCrazy1]

Yeah, I'm skeptical about the exhaust system causing the problem since it doesn't seem to be restricted at all. The technician said that the timing was right at the specified advancement. He retarded the timing a little bit on the chip's program to help save the engine. Also, I forgot to mention that it only pings under heavy load, but not necessarily WOT. I can be cruising along in 2nd gear at about 2500rpms, then suddenly put the pedal down an inch or so and hear the preignition for a second or so until it self adjusts. That'd be really cool if you could ask your mechanic about it! Thanks for posting.

[blackfang]

What fuel octane are you running now?

[KeAnBe46]

ok, what fuel were running before you put 100 oct in the car and your cat is most definitley going out so if you get the sulphuric smell then your cat is melting or as you posted over heating to the point of melting...back to the pinging, if you are running anything under 92 oct then youll ping cause the motor is predetinating and if you run anything over the 92 youll be fine cause the cobras are setup to run only on high octane and nothing lower...so if you ran anything lower than 92 there is your problem. other than that, if it still pings then i cant tell you what the problem is. if you have any other questions just let me know.

[TheCrazy1]

Aah, you guys may have a point, the highest pump gas available here in California is 91 octane which I've always used. Chevron, 76, or Mobil. I also try to use the stations that have a seperate nozzle for each grade of gas to avoid any residual lower grade gas or 'pump errors'. This car came from Texas where I believe the premium grade is higher octane than here. That could possibly have something to do with it. Since I put in the 100 octane, it's been running good and I haven't noticed the smell, but I haven't ruled out the possiblity that the cats are going out. I don't have the money for new exhaust right now, but I'm hoping it passes the next smog check... if it doesn't, then I'll do what it takes to fix it. Thank you all for the replies, if you have any more ideas that hit you, bring 'em on!

[broken_joke]

what was your air/fuel ratio when they were tuning? when they were stepping into it on the dyno did they notice anything else besides the pinging? that's all i can think of

[TheCrazy1]

I don't know the exact numbers of the air/fuel mixture, but he did tell me that he richened up the mix and it improved it somewhat, but not enough to get rid of it completely. The chip has been programmed a bit richer with a couple degrees of timing pulled out and it's tolerable for now, and I'm careful as to how I drive. I'm really stumped on this one too! It's got an occasional rough idle which makes me wonder if it's something else entirely. For now, i simply don't have the money to spend on it, and it definately runs better with the chip than without.. (tried it both ways back to back). Anyway, I'm gonna chill on it for now and just try to get over this wisdom tooth surgery!! Thanx to all for taking the time to reply!

[KeAnBe46]

No problem

[Nor 5.0 Cal]

Im in cali and i run 91 and have had no ping, I ordered a case of some octain booster so i will start running that when i get it. What are some other soluting to the 91 octain in cali?

[TheCrazy1]

Another alternative to running octane boost is running a high octane unleaded racing fuel. There's a station not too far that sells the VP 100 octane from the pump. I think it's going for 4.99 a gallon currently. A couple gallons of this mixed with the 91 octane brings up the average a bit. However, for daily driving, this could get expensive! When I was in Louisiana last summer, I noticed that they had 93 as their premium... and it's cheaper than here! They always find a way to rip us off here with an inferior product.... grrrr

[GToddyT5]

That's really surprising to me that they don't have 93...as a lot of cars call for it, especially newer ones.