Hi, guys I'm new here. I have a all stock 2000 C5 FRC with 50k miles. The car runs good but it has a little high rpm spark rattle. I have used MCCC and seafoam to eliminate the possibility of carbon knock. The car is 100% stock and I run 93 octane. I changed the factory plugs from 41-952 to 41-110 and had no change, still a little WOT spark rattle. I them put in TR6 plugs to see if it would rattle less. With the TR6's it doesn't spark rattle through 2nd hear but will start to in 3rd about 5k rpm.

I have no knock sensor codes or other issues. I'm thinking the factory tune has too much timing at WOT. Am I crazy or is this possible? I would appreciate input! Thanks!

-Don

 

I had the same issue with my bird. Low mile, mint, stock car. When I started really driving it this year it would knock at high RPM under full throttle, like a rattle. I asked a bunch of questions on here and got some good answers, but ultimately I didn't really need to do anything about it. I was over thinking. I fill up at the same gas station with all my cars normally. Well I was out with wifey one saturday and of course it knocked if I got on it form 2nd gear on. I drove 20 miles to a Sunoco who usually has 94 available. Turns out they didnt, but I filled it up with 93, went and romped on it and the knock was a solid 75% gone. Hearing good things about it I ordered a can of this stuff....


.... and threw some in the tank. Knock gone. Burnt that tank up, filled up again and threw some more in. No knock. Now I have half a can of the stuff just sitting on a shelf in my garage because I dont need it. I just had **** gas from the get go. Once I burned it all away and started filling up elsewhere I have had zero issue.

BTW - i was thinking the same thing about factory tuning etc. I would take gas out of the equation first. Oh, and DONT go buy the shitty octane booster at your autoparts store, Walmart etc. If you want to try some, try what is in the link.

 

I'll have to try the Torco on my car. I get the same spark rattle, but I think the cause is the previous owner using a Hypertech "tuner" and setting it to "performance tuning" which does nothing but advance the timing. My car had 37k when I bought it so I'm inclined to say it's not carbon buildup. I do see 3-4 degrees of knock retard on the scan tool when I hear the rattle.

We can also only get 91 oct here.

 

Thanks, I've tried every station and it's the same on all the fuels. I've used Mobil, shell, BP, speedway and marathon. It runs exactly the same on all of them. Do I really need a booster? If so to me I think the ECU needs tuned better to run on premium pump. I'm really thinking it has too much timing. If colder plugs and higher octane reduces spark rattle wouldn't that be a sign of too much timing for the pump fuel and stock plug heat range?

 

Are you sure it has the stock tune in it?

 

Not 100% but the car is stock down to the paper air filter and exhaust. How can I tell if someone has programmed it?

 

My guess is it probably wasn't touched since it's bone stock, but you could hook up a scan tool while driving and check what the spark advance is, then check that against stock values. The real answer would be review data in HPTuners or something like that, but that's a ~$300 purchase if you don't have it already. Maybe a local tuner could hook it up and check it.

 

91 octane may be your issue, though I would think it should be OK for the stock tune. Your situation may be different from mine, but it was fairly apparent that crap gas was the culprit. Again, I no longer use booster. Just did for a bit.

There are also other factors that were pointed out to me when I had this issue. One being that todays gas may be a lot different from gas 10 years ago. Added ethanol, etc. Just throwing that out there. The car may have run just dandy on 91 octane when it was new.

 

I use only 93 octane. The only scan tool I have is a scanguage II which won't tell much. What type of guage do I need? There aren't any tuners around me locally sadly. The closest to me would be Louisville, Ky. The rattle is more annoying than anything. I'm hesitant to enjoy the car fully until I hear no knock at all.

 

Same here... I want to get that gremlin flushed out before I do anything fun with it.

Any scan tool that can show you spark advance and knock retard values will work. I use the Hypertech for that; it reads pretty much everything and can display something like 20 values at once...so at least it's good for that even if it may have screwed up my tune.

My issue may also be related to a tune that was intended for higher octane, since the car is not originally from CA.

If all else fails, you can send your PCM out to Slowhawk or PCMofNC or someone like that for a mail-order tune (~$150-200 I think?), for which you can specify what octane you use, etc., or take it somewhere and have it dyno tuned (~$500) If that doesn't eliminate it I don't know what will.

 

How about: What's is the fuel psi??

 

I'm not sure. It's all stock. Has a new fuel filter also. I've also ran quite a bit of seafoam through the tank so I know the lines are clear, but as far as actual fuel pressure I'm not sure. Will my scanguage II read fuel pressure?

 

Also seafomed tank as well as intake. Intake foaming barely produced any smoke from the exhaust. so carbon build up got ruled out. Made no difference in knocking. Worth a shot I guess, but i pretty much threw money out of the window.

 

If the tune is stock, and you're sure the gas is good, I would check the cats. If they are starting to block up, you will get pinging under load.

 

I will have to check into the cats. I do get ping under load at 1500-2k rpm and a slight spark rattle at 4500+ rpm I'm almost positive it's all stock. It runs like a scalded dog, but it has that slight annoying spark rattle.

 

dirty injectors? running lean?...... or failing IAT sensor? IAT sensor location?
a couple of ideas for you

 

Check fuel pressure and find out where your timing is at. I had some nasty knock from my new engine because of carbon build up due to the break in procedure. Did you shut the car off before the can ran out. I let the car sit over night for the best results. Smoke doesn't mean anything. I logged the car while I drove it and had great results.

Might need it more than once. These cars get nasty build up if there simply not romped on every now and then.