Deadtime an issue?

[eclipsh]

So here's the deal, I'm running 780cc FIC injectors, a 3rd gen MAS and a stage 3 EPROM. Ever since installing the setup my fuel trims have refused to set. I recently added an SAFC to the mix to try and tune close enough for my trims to work. No luck.

So... looking at my airflow reading change of 66% and my injector change of 58% (can be upped with fuel pressure) could I remove the EPROM and tune the car without major issues?

I am trying to isolate the problem with my system and I am almost certain it is the chip. If I can tune the car with the stock chip and get my trims to set I can be certain the EPROM I bought is the issue.

So... is the dead time on my injectors going to kill any chance of tuning this beast? Are there any other big pits I'm going to fall into that I don't know about? I'm willing to try this but I want some input before I do.

Thanks for your time!


EDIT: If this does work I have a Cyclone intake I'm going to try and run by adjusting it's kick-in with a potentiometer. Any gurus out there who know electronics enough to point out a good 0-5v potentiometer that could handle car voltage (I'd be running it off a tach-signal)?

 

[FORMONTOYA]

Yes, dead time can mess with a tune.


I run DSMLink on my car with the HRC 625cc injectors. The manual calls for a dead time of 180 and I couldn't get my fuel trims in line correctly. Tom stepped in and offered a suggestion of 435 or thereabouts (he didn't say why, just said "try it" and see what happens) and now my trims are where I would expect them to be. I never "called him on it", but was just happy to finally get things in line.

Every car is different, what works on car A might not be the same for car B.

my 0.02.

 

[eclipsh]

So are you basically saying it won't work?

 

[CanadianTSi]

Your not going to have enough compensation with just the S-AFC to make it work...

 

[FORMONTOYA]

I agree, the 780s are definitely pushing the envelope of being "doable" with a SAFC. Some say they can do it, while most say it wont. I've never tuned with a SAFC so I can't say from experience.

The dead time setting did not cause my car to not run, it just gave me fits trying to get the LTFT lo and mid in line. I could get one or the other at or about 0, but the other would be off by more than the recommended +/- 5% as called for in the manual.

But the car ran decent, just not the way I wanted it to (me being an anal SOB).

 

[eclipsh]

I agree, the 780s are definitely pushing the envelope of being "doable" with a SAFC.

Normally I'd agree, but I'm looking at the 8% difference between the 3gMAS and 780s as compared to stock setup. Tuning for 8% with an SAFC and a FPR seems doable but I'm not well versed in this area. It sounds like the dead time will be more of an issue than anything.

So I guess the question on that is, does anyone know the dead time for the stock injectors and FIC 780s?

 

[FORMONTOYA]

780s are PTE injectors with a global/dead time of -38/315.
750s are FIC injectors with a global/dead time of -40/330.
Just confirm which you actually have.

All this according to the DSMLink manual as the base starting point. Your final results may vary after the "dial-in" procedure is finished.

 

[eclipsh]

They have a bell-shaped sprayer tip and I bought 'em from FIC. They look very different from standard DENSO injectors.

 

[FORMONTOYA]

I've not seen a set of FICs that did not fall in the "50 increment" category (550, 650, 750, 850, 950, 1000, 1150, 1600). But that doesn't really mean much. That's the only reason I mentioned it.

However, as you can see, the global/dead time settings are fairly close for both as a base starting point. So you should be good with either setting to start "dialing-in" the injectors.

I don't recall the tip design of either, so I can't say in regards to what they look like

 

[eclipsh]

Sorry, need to clarify something, I have no way to program dead time in that I know of. I am just running a stock ECU with an EPROM chip.

So I guess what I need to know is if the dead time on the FIC 780s is substantially different form the dead time on the stock 450s. If it is I may not be able to do this.

I guess I am probably just going to have to try this experiment out. I was hoping to find any issues I might have been missing that I could try to compensate for with my FPR and SAFC or some other simple tool/trick.

 

[92awddsm]

So I guess the question on that is, does anyone know the dead time for the stock injectors and FIC 780s?

This might help you.

http://dsmtuners.com/forums/showthread.php?t=201909&highlight=injector+deadtime

 

[steve]

So I guess what I need to know is if the dead time on the FIC 780s is substantially different form the dead time on the stock 450s. If it is I may not be able to do this.

Yes, the Delphi/Rochester injectors that PTE and FIC use need 312 to 336 uS of extra deadtime over the factory Denso 450 injectors. If you go back to who ever made your EPROM chip they should be able to change the injector global, deadtime, and MAF comp to match your new setup.

Steve

 

[eclipsh]

Thank you, that does help some.

So help me understand this please since I am new to all this end of tuning.

By pulling my EPROM which is supposed to have the correct dead time on it and putting the stock chip back in I would be decreasing the dead time that is currently being run.

So... does that mean that the injectors would be open longer than they should be and I would be running rich? Or does it mean the injectors can't handle the extra time being open and it will wreak havoc?

If it is simply an issue of running richer that would be in my favor since I need to compensate for the 8% lean I'd be running pulling the chip.

Or does it mean that the computer won't know what the hell is going on and I will never be able to get the car running right?

 

[eclipsh]

Yes, the Delphi/Rochester injectors that PTE and FIC use need 312 to 336 uS of extra deadtime over the factory Denso 450 injectors. If you go back to who ever made your EPROM chip they should be able to change the injector global, deadtime, and MAF comp to match your new setup.

Steve

Actually my problem is that the chip was burned to use with these injectors but it has never worked properly so I am trying to figure out if I can run the car without it or at least prove that the chip is the problem and figure out a solution. As of now the burner and I cannot come to an agreement on a solution, i.e. I'm screwed.

 

[steve]

The ECU figures out from the current airflow/rev, intake temp, and barometric pressure the air mass being drawn in each cylinder. From the fuel map it gets the AFR so that it knows how much fuel is required. Knowing how big the injectors are (injector global) it can figure out how long to open the injector to get the right mass of fuel. This is the basic injector pulse width.

The problem is that the injector is electromechanical so it takes time from when the electical signal starts to the time the fuel starts flowing and some amount of time after shutting off the signal for the injector to close. The sum of the difference is the "dead" time that the injector isn't spraying fuel when it should. The number needs to be added to the basic injector pulse width to get the correct injector pulse width to get that amount of fuel.

If the deadtime is too short the engine receives too little fuel and burns leaner.
If the deadtime is too long the engine receives too much fuel and burns richer.
Since deadtime is a fixed correction it is a larger percentage of the total at short IPW's like at idle compared to WOT.

Steve

 

[eclipsh]

OK, so given that:

Stock dead time = 765ms

FIC 750 = 765 + 315 = 1080

765/1080 = 70.83%

So if I were to pull the EPROM chip and install the stock chip I would theoretically be running 29% lean plus the 8% lean from the MAS/Injector difference = 37% lean?

Yeah... not going to work. Even pushing my fuel pressure up insanely high and adding fuel all over the board with my SAFC it would be tough to make that work.

So Steve... any ideas why my fuel trims would refuse to set after installing an EPROM chip?

Thanks for all the help guys, if adding rep points would do anything I'd be dumping 'em on.

 

[steve]

So Steve... any ideas why my fuel trims would refuse to set after installing an EPROM chip?.

A couple of things have to happen. You have to go into closed loop and the coolant temp has to go over 186F before the fuel trims will update.

On 91+ ECU software, it will try to go closed loop once the coolant temp goes over 86F. If the O2 feedback trim doesn't start swinging and the O2 cycling it's not in closed loop. Most common cause is too much or too litle fuel or a bad ECT sensor. The 90 software waits until 106F before it attempts to go closed loop.

Steve