SERIOUS problem: tuning gurus needed.

[lazaris]

Stu,

Did you find anything out? That spike in EGT appears to be detonation.

 

[KL Mallender]

Laz, I believe you may have it backwards, detonation shows up as a drop in egt from normal trace log. Typically a spike in temp during a logging run indicates that a misfire or incomplete combustion cycle has taken place in cylinder resulting in burning in the pipe, my suggestion would be to back off timing to known safe value and retest looking for level temperatures thru rev range, your torque peak will be at lowest egt reading if constant timing value is used, keep in mind that if your fuel mapping is wacked, you are chasing your tail trying to keep up on timing.

Kevin.

 

[lazaris]

Kevin,

If the spike in EGT temp is caused by this missfire then combustion chamber temps should go down. He melted a plug possibly more which indicates higher chamber temps.Which is usually detonation where combustion chamber temps skyrocket. This occurance is due to the fuel not have having enough resistance to detonation for the timing used in the engine. I agree there maybe a spark issue as well as noted buy the lower temps on that same cylinder during the 2 step operation.

 

[S2V6RACER]

Stu, it appears as the #1 is loaded harder (3rd gear) is when the temps are starting to go out of whack. I would suspect the flat area of EGT #1 at around the +-7 second the point where it was going into detonation then went way lean.

I don't know what to tell you other than take Otto's advise and maybe even dual feed the rail, throw 5% on #1 and take it SLOW!!!!!

 

[KL Mallender]

I agree Lazz, it detonated first which is low egt, when plug left no fire-high egt.

Kevin.

 

[norbs]

I;d take it to a dyno and watch the egt's on #1 and slowly creep up on boost and tune on C-16 not Alky. Watch all the egt's carefullyand adjust accordingly. I'd run about 25 degrees timing, low timing is going to add more heat in my opinion.

 

[forcedfedv6]

check fuel injector wiring harness for grounding to that cylinder, get a bigger fuel line for that stock rail and also modify the rail to take the bigger fuel line that will lower your injector pulse with by a lot, make sure your alternator is charging at WOT and it doesnt have a drop to like mid 12's volts, thats not enough juice to feed the fuel pumps and obviously #1 cylinder is the first one to suffer from fuel starvation, my other suggestion would be a high performance fuel rail and bigger feed fuel line, my buddy nordy ran mid 9's@30psi with a stock fuel rail and going to a 1,200 aeromotive Fuel pump, bigger feed line and modified fuel rain inlet to accomodate the new line.. Good luck and keep us posted on what the fix is.

 

[S2V6RACER]

The plug not firing correct (burned up) could have caused a delay in the ignition of #1 and that caused it to burn in the exhaust stroke. If it completely missed it would go cold, rather quick. I am more concerned about the flat line there before it skyrocketed.

The information gathered on the 2 step is inconclusive. When it is cutting cylinders some go cold ( I have seen 1 or 2 colder), the longer on the 2 step the more pronounced. At least that's what I have had in my application with the MSD 7AL doing my 2 step work.

 

[Blazer406]

I want him to flow the fuel system at pressure :biggrin: to see where his double pumper stacks up..... and where ours falls.....

We flowed at 70-75 psi...

 

[lazaris]

I agree Lazz, it detonated first which is low egt, when plug left no fire-high egt.

Kevin.

I agree there. I think its more of an improper fuel distallation curve ie: detonation resistance of the fuel used for the timing and combustion pressure. More so than a lack of fuel. Remember hes using pump gas and alcohol, not race fuel.

 

[KL Mallender]

Spot on Lazz, we do everything we can to improve airflow throughout the engine but the collective imperfections of air inlet velocities,runner & port flows in and out of the chamber pretty much rule out that any two cylinders will actually "Want" the exact same fuel pulse and ignition timing, the best engine control system will have varible cyl to cyl adjustments along with the patience required to test-adjust-test-adjust-test and hopefully not spill the milk during the process. Batch fired systems at best hit a target average that will leave some cylinders effectively rich and others lean. The trick is to set up a controled air "leak" to the Hot cylinder in question allowing said cylinder to injest less air to that cylinder causing it to richen thus lowering temp internally. Now you'll ask "How", simplest is a needle air bleed at base of intake runner but before injector, and yes a very fine/small bleed is used. Been there, done that. Best way is the newer stand alone systems that have both fuel and timing adjustments.

Kevin.

 

[Blazer406]

.....Best way is the newer stand alone systems that have both fuel and timing adjustments.

Kevin.

IMHO... the one on the XFI... while cool... isn't ideal. I think you should be able to add fuel based on a certain manifold pressure..... cause we suspect (with a pretty high confidence level) .... (in our particular case).... #3 and #4 are too lean... so I went in and added 2% fuel to #3 and #4...... while I might have helped the WOT lean condition on those cylinders.... the car idles differently.... more rough than before the corrections.

I suspect that the airflow distribution problems vary from idle to WOT under boost quite a bit..... just a hunch..... and that what might work for WOT.... might be too fat or still too lean at part throttle.... and there might be something completely different going on at idle.....

Just a hunch....

 

[SloGN]

sounds to me like that you need to feed the fuel rail from both sides.

The drivers side of the rail @# 1 injector is the last one to recieve fuel. when the demand is high enough there is simply not enough pressure to feed that injector. I bet that 1-3- will both show lean by reading the plugs.


One thing to note here guys that if it did have Knock you would see a rise in egt temps during the knock. so if the EGT's show hot with out knock it's just simply running out of fuel there. Also AFR's will show a tad leaner during a knock retard session too.

I'm currently replacing headgaskets due a issuse close to this.

 

[GN SBS]

Bump for the weekend.

Idea of testing on the dyno and adding a ton of additional variables to the dash / log file is interesting. Would allow a set of eyes on the data as the pull was being made as a safety.

 

[lazaris]

Stu,

Did you ever find the problem on this or test it again?