[VeilsideTT]

Ever since I put in my 67GTQ on stock fuel, my car wants to go lean. At first I had my AFC hooked up wrong and thought that was the problem. Now I have my AFC2 hooked up 100% correct, I have the FPDB and today I ran 5 gallons of C14 mixed with a couple gallons of 94. I also maxed out the AFC at all RPM points above 4000rpm. The car still goes leam. I saw 14:1 and 15:1 on 2 different runs today. Also, I only hit 17.7psi on one run and 18.0 on the other. What could be my problem? I assume my WB is working properly since at idle it cycles between 14.4:1 and 15.3:1.

The first day I had my WB hooked up the car could stay around 12:1 at 16-17psi and that was on 94 octane. What could have caused this change? Do I just need to get a fuel system? I would assume that the stock fuel system could sustain 18psi on racegas.

 

[neonafk]

seth, im saying maybe not, your car makes ALOT of power, its pretty new and fresh, i hear that people can't hold 500 rwhp on stock fuel without going lean, now some others maybe can? idk? whatver man, i think its the fuel sysytem, time for an upgraded pump.

Brett

 

[jaynite]

get 2 pumps and anarchy's new meth kit...he made another kit that works with the stock ecu. jay

 

[stoker6]

Did you reset the ECU after changing over to higher octane?

At 17-18psi you're quickly approaching the limits of the stock fuel but I wouldn't think you should go as high as 15:1 or even 14:1.

 

[VeilsideTT]

Brett, keep in mind I was running C14. I wouldn't be surrised if I ran lean at 18psi on pump but this stuff is 112 (114 maybe?) octane.

Jay, Ive looked into that but I am hesitant to use it for low boost with small injectors. From what I've gathered, his system works by either dumping the meth at a certain RPM or injecting progressivly using ijector duty cycle. It seems that either way I will run really lean at a measly 18psi. I would turn the boost up but my tranny wouldn't like that very much. Maybe I'll ask him if he has a VERY small nozzle for me. I still have a hard time belieing that the stock fuel system can't handle 18psi on racegas.

Stoker, no reset ECU but I assume it has reset on its own since the battery was dead for a day or 2 after I put the gas in. Wouldn't reseting the ECU cause the car to pull less timing anyway? Are yu saying that you would expect the car to lean at 18 psi on even when running racegas?

 

[stoker6]

Yes, you'll run a bit leaner w/ race gas.

The ECU reset will erase all previously learned fuel and timing corrections and will give the ECU an opportuinity to learn new maps w/ the higher octane fuel. But, it sounds like it has been reset.

 

[VeilsideTT]

A bit leaner with racegas? How can that be? I would expect to run richer with racegas.

 

[Stu Hagen]

Print and post your AF graph so we can look at it. Also, I suggest making NO fuel changes right at 4K This has been known to really run the car into a lean mode.
Also, Race Gas does make things run leaner. There are some good articles on how diff fuels and what they do to the AF
You should be able to maintain no leaner than 11:5/1 up to 500whp on stock fuel Its been done all the time. I also suggest looking at get a new fuel filter, and check that your injecters are up to par.

Stu

 

[Mike_Austin]

A bit leaner with racegas? How can that be? I would expect to run richer with racegas.

...and why would you expect it to run richer? Sounds like you're confusing detonation resistance with air fuel ratios.

Steve Hayes recently pointed out that race gas tends to have a lower specific density than pump gas. That means slightly less fuel mass gets injected compared to pump gas causing slightly leaner AFRs. Think of it as the same volume of fuel but slightly less mass since race gas is less dense. The effect is probably fairly small and not your main issue but it exists.

It definitely sounds like your fuel system is the issue. Some are are better flowing than others but anything over 500 (6 spd) rwhp is pushing it IMHO. You're probably around that point.

Personally I wouldn't even consider running a turbo that big on stock fuel without a wideband O2 in the car and tthe wastegate connected directly to the turbo exhaust housing and . With a boost controller, you're more likely to get boost spikes. Then again, I did a fuel system when I went single with an SP57 (SP63 now).

Mike

 

[MKIV4Door]

A bit leaner with racegas? How can that be? I would expect to run richer with racegas.

There is a significant difference in burn characteristics between the two.

 

[Mike_Austin]

One more thought on this. Some race fuels are oxygenated. They will definitely burn leaner than non-oxygenated fuels since there will be more oxygen in the combustion chamber if all other things are equal.

The stock ECU should adjust for this in closed loop assuming it's given sufficient time. I have less confidence that it will adjust fully under open loop (under boost to put it simply).

Oxygenated race gas is evidently used in some series where cars run with intake restrictions due to the rules and can actually provide more power under those conditions. I wouldn't suggest running it in a forced induction car like ours though.

Mike

 

[VeilsideTT]

Stumove, I will get those up as soon as I can. Hopefully tonight.
BTW, I put 4k back to 0% on the AFC and it had no effect.

I see what you guys are saying about the amount injected but isn't AF measured after the burn is complete. I would assume that the difference in specific density would be outweighed by the amount of unburned fuel put into the exhaust after cumbustion . Since high octane burns slower I would assume that more of it would be leftover after the burn, thus causing a richer AF.
I would really like to hear more info about this if you guys have it. It seems very interesting and I would like to fully understand how and why it works that way.

Also, I am considering that my new WB could be off. Yesterday, I grew the courage to stay on the gas for a little and watch my other gauges. This was on 116 octane gas BTW. The WB read lean as usual but my EGTs never went above 600 right behind the exhaust housing and the knock sensor on my AFC showed NO knock, not even a little. A friend also said he saw a puff of black smoke blow out of the back of the car.

Also, what do your WBs read after you let off of the gas? Mine goes off the chart above the highest point my WB can read which is 22:1. Is this normal or could this be another indication that the WB may be off.

 

[balticMKIV]

not sure about the octane thing, but when I completely let off the throttle, my fjo goes to 20:1 also.

carlo

 

[VeilsideTT]

Hmm... mine shoots up off the charts, past 22:1.

 

[stoker6]

Trust the WBO2, especially if you purchased it new. Don't be tempted to gauge safety by EGTs, it is just a secondary indication.

I've compared the FJO to a WBO2 on the dyno and it was within .2AFR. The FJO is about the best tuning tool you can get. If it only monitored timing and/or knock we'd be set!

If I was you, I would stop getting on the gas at all, as you're damaging your car. If it was me, I'd park the car until I had my fuel issues worked out.

 

[silvino]

People's cars usually feel the best right before they blow so it's good he's trying to fix things up.

This is a prime example of why I like to point out that when people post crazy dyno charts with "untuned" and brag about how they'll make more power when tuned, etc. See how dangerously lean you are right now? You're going to lose a bit of power when you get back into the 11.x range but you'll also be able to enjoy your car much longer .

What exactly do you have done to your stock fuel system? Anything modified/changed from stock at all?

Good luck on getting things settled.

seth, im saying maybe not, your car makes ALOT of power, its pretty new and fresh, i hear that people can't hold 500 rwhp on stock fuel without going lean, now some others maybe can? idk? whatver man, i think its the fuel sysytem, time for an upgraded pump.

Brett

 

[VeilsideTT]

Fuel is completely stock accept for FPDB. Another reason why i think the WB may be off is that the car felt great a weak ago when it was running 12:1. Now, I'm shooting black smoke and running leaner, but the car doesn't feel as fast... weird.

I think what I'm gonna do is send my WB (not FJO) back to the company. If it is defective... great. If not I think the car has to sit for the winter. A new tranny and at least alchohol injection are in order.

 

[VeilsideTT]

Ok guys, I just pulled a plug and it came out looking like a white/yellowish-green color. From looking at www.MKIV.com it says that that color and "sooty" look indicate a rich mixture...

Could that first picture in the MKIV.com tech articles in anyway resemble a car's plugs that is running lean instead? I wish I could find my camera to take a pic.

 

[neonafk]

any luck with with this? any luck with the o2 sensor wideband thing?

Brett

 

[jaynite]

i was under the impression that black smoke means your running rich...