still shutting down at 5800 rpm. More specifically, when you first start it up and run it WOT (the first time) it will rev to 6300+. Then the next time (2 minutes later) it shuts down at 5500-5800. There is not coughing or missing up to the point where it shuts down..it just stops. I have data logged with no conclusive reasons why this is doing this. I have replaced the MAP sensor (I'm DFI) nothing... I have checked all of the wiring to the ECM..nothing. The injectors are not going static. They are also new and did this when it had 30lb injectors too. FUEL or SPARK right? I guess now I'll try the ignition module and coil. Any other ideas because I am out of them!

 

When was the last time you changed the spark plugs, wires, cap, rotor?
I have seen plugs cause this on cars and boats. The engine will run up to a certain rpm and then just die.
If you have not changed them in a while I would try that before spending money on coils and expensive stuff.

 

Thanks Tony. Wires are new, plugs are new. Cap and rotor a couple of years old. I will check them tonight. I have an extra ign coil laying around and an extra coil so I might throw them in since I have them. This is sooooo frustrating

 

Jerkyboy,

Ok. I may be able to help you on this one as I have had many of similar symptoms as you with my DFI 377 SC setup.

When you say stop...what is it doing exactly? Is it cutting out and the rpm drops? What about fuel pressure? is it constant?

I am sure all your VE tables and spark tables are set right?
What about your rev limiter? both stages for fuel and spark?

If everything else if fine I would look under the Tau vs Map table.

let me know if the above metioned tables are set first before we get into the tau v map table.

 

By the time you make the 2nd pass the ECM is very likely in closed loop mode; are you sure it is seeing WOT so that it sets the BLM cell # to 15 with the quiescent value of 128 and the INT to 128 so that there is no fuel trim due to O2 sensor readings??

 

Z- I've gone over and over the VE tables and steady state ignition and everything is set to 7200 with appropriate values thru those cells. Fuel cut of is set at 7200 and ignition at 7500 rpm. Tau vs Map I know nothing about. With a fuel gauge attached to the widshield, WOT starts at just over 40lb and goes down to just over 30lb. Seems that if I was running out of fuel, it would cough or sputter, but this feels and sounds like spark is going away. Once it hits the "spot", the engine feels like it's spinning in neutral for a few seconds with the throttle not controlling anything (if that makes sense)

65z01 - my DFI shows closed loop correction until I mash the gas, at that point, the scale goes to zero with I believe indicates open loop. Sometimes, I can slowly rev it up to 6300rpm "rolling on it" but a "snap" WOT will cause this condition every time.

 

Are you running a WB?

The reason that I ask about your tau vs map table is because I had a lean spot that I could not tune from the VE table.

I had TJwong sent me an DFI 377 TT tune from Accel and I copied the tau v. map table and it fixed everything.

If you leave it in open loop does it still do it?

What correction limit are you setting it at? You shouldn't use more than 5% correction at that rpm if you have a decent tune.

 

At what rpms does the fuel pressure drop? That is a classic symptom of a fuel system that can't keep up with the demand. It could be as simple as a clogged fuel filter. It could be a kinked fuel line, clogged sock, and of course a weak fuel pump. If for some reason, this isn't THE problem, it is still A problem. Going lean at WOT, at higher rpms can ruin all kind of expensive parts. Check it out.

RACE ON!!!

 

I was on a dyno a few weeks ago and was monitoring both banks with a WB. Never got leaner than 13.5 or so at WOT. Should I see that much FP drop at WOT? I am running a walbro 255L/H fuel pump. I guess it wouldn't be a bad idea to pull it out and look at the sock. Same with the filter. I will check for a kinked line as well.

Z- I can turn on the switch that leaves it in open loop but doesn't WOT automatically push it to open loop? The correction is set at 15% because I had an exhaust leak on the o2 side so I gave it wide parameters to correct until I got it fixed.

The more I am thinking about it, the more I am concerned about the fuel delivery. Since the compression is so high I was running some 108 fuel booster for a few tanks until I was talking with some folks that said it won't do anything. Could I have gummed the filters up with that cr*p?

 

I run a walboro 225 and at WOT all the way up to 7200rpm I see maybe 1 or 2 psi drop. Sounds like something isn't right. How old is the Walboro unit?

 

Chris, the pump is about 3 years old. 1 or 2 psi drop. yikes, maybe fuel is my problem. Is there a test I can perform on the pump itself? A replacement is only $100 or so. Are all of you high hp guys using a stock GM filter?

 

You should see ZERO fuel pressure drop at WOT. Just because you were lucky enough that the mixture didn't go lean on the dyno, *I* think you're playing with fire until you can get it to hold steady. I have checked mine with the gauge taped to the windshield during a 1/4 mile pass. I don't spend a lot of time looking at the gauge until I'm in the highest gear that I can wind out, creating the greatest fuel demand. I set my pressure higher than I normally use and I over wound the engine, again to maximize the demand. In my case, the needle never even wiggled.

RACE ON!!!

 

I didn't realize that. Here is a FP reading from my old 383. The FP is definitely dropping over rising rpms but the AF stayed steady.



Again, is there a way to test these pumps? Is a 255 LPH not enough pump? if not what is the next step? Thanks again for all of the help.

 

See my previous posts. Inspect the WHOLE fuel system before you comdemn the pump. I once had a fuel leak in the rubber hose INSIDE of the tank from the fuel pump to the metal outlet tube. Every trouble shooting test pointed at a bad pump. Luckily for me, I refused to believe it. I was 500 miles from home at an NHRA Division 7 Bracket finals, at the time.

RACE ON!!!

 

Check everything before you condemn the fuel pump...and yes I am using the stock GM type fuel filter

 

Dave,

You have a problem with your fuel pump most likely or the voltage supply to it.

Perhaps its the alternator...it may be heating up after the first run, which I think you reported as being good, then heating up and not putting out good voltage that your pump needs to work right.

I would run some wires out to the alternator (don't trust the stock in dash readout) and see what your alternator is putting out while at WOT. It should be no less than 13.5V and be closer to 14volts. The reason I say check the alternator is the walbro pump is "hot wired" to the alternator itself to obtain higher voltage which will maximize the pumps fuel flow. Its highly dependant on voltage supply.

I believe this is the reason why you started seeing your fuel coming up short on the 30# injectors also. There is no reason that you should not be able to use them. I am now running 10.3s on the brakes with my 30s and monitoring with a WB02 through the entire run with A/F ratios in the mid 12 for max torque and high 12s/low13s in the upper RPMs. The first run with the open headers the 02 saw the extra oxygen and it ran mid 10s through the entire run, till I limited the amount it could correct...so the injectors themselves can dump a LOT of fuel when things are right.

Don't overlook the obvoius stuff either.. The Fuel Filter.

good luck and let me know if you need anything.

PS: When you monitor the fuel pressure it should "jump" up when you nail the throttle, due to the fact that you are now removing the vacuum. Same as when you pull the vacuum line off when setting the pressure. It should also hold dead steady and not waiver through the entire RPM range.

 

I am not sure if the DFI goes to open loop under WOT. maybe TJwong can shed some light on this.

I think it is something with the fuel whether it be something mechanical or electrical. I'm not running a stock fuel system with my car so I can't tell you if the stock fuel system can hold up to 500hp.

I have to agree with everyone that your fuel pressure should not drop at all when under WOT.
You should really get a fuel guage with your setup.
I just don't understand why it would not do it when it is cold????

 

One of the key selling points of aftermarket engine management systems is their ability to do closed-loop WOT unlike the stock ECMs which will switch back to open loop under a WOT condition. I would suspect that you're still in closed loop mode when going into WOT.

Ron

 

Ron,

I know you are running the fast. do you guys have a table under the fuel tab that is called: Tau Vs. Map?

 

Jesse brought up a good point. I will need to monitor the alternator output at WOT. I have the racetronix plug in play FP assembly which is wired direct to the alternator. However, this problem is rpm dependent. I would think that if there is a voltage problem, it would happen immediately at WOT not at just a specific rpm. The wildcard here seems to be heat..
So here's my plan next week while I'm off:
replace fuel filter
check alt voltage WOT
check for kinked fuel lines
pull fuel pump, check sock etc..
new plugs
new ignition module
coil?
if above fails, jump off Bay bridge

Z-I was looking a the Tau vs. Map a little. It seems that this table is for taking into consideration a little unmeter fuel? There were some trig formulas on the help section on DFI which instantly causes me to freeze just like I did in college