Cold Weather Detonation
 

Tonight was the first "cold" night here in Northern Florida (upper 40's, you northerners don't laugh!), and my car is now detonating pretty hard. Car was recently dyno tuned with new 42 pound injectors and 90 mm MAS. Car ran great in the sweltering heat, but tonight's pinging really surprised me. If I got into it anywhere above 4000 rpms, right when the boost fun starts, I'd have to get right off it because of detonation. Any suggestions or similar experiences out there? I really can't have a car that runs great in the heat and sucks in the cool weather.

Usually I would recommend an adjustable fuel pressure regulator, but since you're using the hated "returnless" fuel system, you may want to invest in a "switchable" chip.

Just program one of the options to bring a little more fuel into the equation...

You also might want to investigate if its time for a 255 fuel pump.

Thanks Hammer for the input. You actually bring up a point I've been meaning to ask. I don't know the rating on the Vortech fuel pump which came with my kit. I am being told I should put a 2003 Cobra fuel pump on the car, which will do a better job not just with pressure but volume. This was strongly suggested at the dyno tuning session when I went with the 9 mm MAS and 42 lbs injectors.

Hey sleeperGT,

I have a 87 GT S/trim w/ 42LB injectors, TFS heads, corba intake 80mm pro m, AFM PowerPipe, custom cam, custom diablo chip msd and Holley 255 forced induction fuel pump and I have to tell you, I had to learn the hard way your fuel pump is key with boost!!! So, I would for sure upgrade your fuel pump soon.

Good luck, Be safe...

I'll echo the sentiments of a bigger fuel pump. My choice would be a GSS340. It's a high pressure 255 lph in-tank pump.


When you had your car dynoed, what did the a/f ratio look like?? If it's detonating during 40* weather, I'd be scared to drive it during the day!

Also, you might want to invest in a BTM.

A GSS340 is for a return-style fuel system...a lot different than the new Mod motors run. I would be looking to the '03 Cobra solution as well.

Keep in mind this may be a timing issue as well. If the dyno tune was set up "on the edge" in the warm weather, it WILL ping in cold air due to the cooler, denser, more oxygenated air mass. You should be looking into a way to pull out some timing in the cold as well.

Gentleman - Thanks for the input! I took your advice and had the Cobra fuel pump installed. And since I was going to have to get another tune I added a 70mm AccuFab Throttlebody and C&L upper intake plenum. I was promised the all weather tune and the car now runs great, however it was a warm day, in the 70's. The car did go from 323 rwhp to 339 rwhp. Another note was that the air temerature was 180 degrees coming in and I peaked at 15 psi of boost, yikes!! This is with the stock pulley from Vortech. I was told I really need to look into an aftercooler to get the temperature down.

Cool bro,

Good luck with your ride.
I hope you keep it tuned when ever you change parts. Tuning is most important with a S/C car or any for that matter.
When will you upgrade your heads? I gained around 50 rwhp with trickflow t/w heads and then I added a custom cam and diablo chip and I still have a plain old cobra intake and I have 490 rwhp street tuned on the rich side with pump gas.
I am aiming for 580' ish to the ground soon on pump gas. I hope all works out for you.

(Take it side ways!!!)

490 hp!! That is amazing! I really think my next upgrade is going to be an aftercooler. I really want to do this for engine safety reasons, but my tuner told me he could easily take me well over 400 rwhp with my current setup which is just bolt on's and the intercooler. I've gotta financially recover from this last round of upgrades and tune and the holidays before I hit that next upgrade. But it is coming soon. Thanks for the input!

Let me start by saying, "KICK ***!!". I love hearing about blown Mustangs.

Ok, on to the blower thing. If you check my users ride listing for the 89 GT you'll see that I had, yes had, a 306, E cam, out of the box RPM heads 2.02/ 1.60 variety, a little ceramic coating here and there, S-trim, After cooler, Lucas 42s, and a who's who of engine managment electronics. Running a concervative 14# of boost, I dyno'd 556@6000rpm. Every bit of that was done with the fuel and timing. And to top it all of, it was as driveable as a new GT. I miss that car.

anyway, the moral to the story is to get the Air/Fuel problem situated and the rest is a breeze. If I had more time I'd break ita all down for you, parts wise, but I'm tired and hungry. If you want you can email me and I'll be glad to shoot you a list of what I used and all the parameter settings I had. But for now, I'm outie.
Later.

Big - I definetly want to hear the parts upgrades you did. I'll send you a PM. I won't be doing the computer setup, so I'm not as concerned about that as my tuner will take care of that, he really knows his stuff. Thanks!