accel dfi problem

[emtcee1973]

i have a gen 7 dfi setup in my 67 its a 383 motor. the problem i am having is after the motor is warmed up the a/f ratio meter jumps from being normal to real lean and back again and so on.the correction starts at 5% and jumps to the max of 25%..it does this at idle and sometimes while driving.what should i be looking for?? i have checked for vacum leaks and found none and i have new fuel pump installed as well..fuel pressure is good..my intake port temp reads as high as 165 degrees at idle(is that too high?)any suggestions would be appreciated..
mike

[Jim Nilsen]

Are you watching right above the correction bar and seeing it go ACTIVE when it goes to -25 and back and forth? The ecu will not correct anything in open loop when it is cold and as soon as the correction bar goes active it is closed loop.

Once you are in closed loop/active you can correct the VE table to bring it to the center. You can use your AUTO CAL button to have the computer place the value that is closer and then manually adjust it until it stays in the center or as close as it will until you work with the A/F ratio to give it what it likes. Also watch the timing and see if it is correcting itself to stay running, the computer will retart or advance timing to adjust for the idle. You can also work with IAC to smooth it out some and make it so it all stabilizes.

There is a lot to look at when you are learning and it takes a lot more than just the 3 tables to get it right, especially down at idle.

Are you running a wideband or a Hego? The wideband will tell you the actual A/F ratio even in open loop before the computer goes Active. This really helped me a lot to know how things were at start up. It does however make you have to think more about what the engine wants in the A/F tables at warm up and it all changes as soon as it goes to closed loop if they aren't all working with what the engine wants.

Hope this helps and remember that I am just learning too and am just telling you what I am doing to tune and there may be easier ways. I can say that the tune I had before I blew my engine was doing real well for me being a beginner and everyone who heard it and rode in it was impressed as to how it ran. The new engine is a different animal and is making me go back through it all again. You also have to work with the TAU table and you acceleration modifier for your drivability.

Good luck

[emtcee1973]

thanks for the reply..the ecu is in closed loop when this is happening,its a wideband setup by the way.It's odd because lets say the motor is warmed up and has been running for say 15 minutes it will be fine but if i take it out and run it for a while thats when it seems to occur..not sure what else to do..

[Jim Nilsen]

thanks for the reply..the ecu is in closed loop when this is happening,its a wideband setup by the way.It's odd because lets say the motor is warmed up and has been running for say 15 minutes it will be fine but if i take it out and run it for a while thats when it seems to occur..not sure what else to do..

are you in the gas pedal when it happens or in steady cruise? If your acceleration tables are not right you will see the bar go all over the place when you are in the gas from what I have found. The little bar tells you everything in the now moment. That's the beauty of the system is that you see real time and it will tell you exactly which cells it is happening in.

The best thing I did was to get a friend to drive while I adjusted the tables. Going from one to another and back again to find what it wants and then when you are all done you go to 3d and blend.

It took me a bit to figure out the TAU table and it is very sensitive and hard to tell sometimes when you are giving it too much or not enough but when you get in the ballpark it will smooth everything out and take a full pedal without coughing or stumbling and the bar will stay in the middle.

Practice is the key, you will not become a tuner in a few hours, it takes days to really wrap your mind around it all and once you think you have it there is more you can do. I always keep the timing table for last to keep me on the safe side and you can't really get good feedback from the engine on the timing if your other tables are not right from what I have found.

Keep at it and remember to always keep saving the program no matter how little the changes you make are. I have thought I was going the right direction and then one change and it all seems to go bad and without being able to look at what you were doing later you will be lost as a beginner, I know this the hard way and save all that I can now. The other smart thing to do is get a usb memory stick and keep putting your programs in it, that way you can work offline easier and won't lose them in case the computer you have gets damaged in the car somehow, You might think it won't happen but it can.

[emtcee1973]

this happens at idle and it started acting like this recently..sometime it happens when i'm on the gas and once in a blue moon it happens at cruise..thats why im kinda stumped..but i do appreciate your feedback..

[Jim Nilsen]

Since you have a wideband is the actual A/F ratio below or above the A/F ratio in the fuel table? I know it seems like an obvious answer since it is trying to lean the fuel up it should be rich in the actual a/f from the wideband. Maybe I have it backwards and need to learn more too.

Can you datalog it so you can observe what everything is doing? It would be interesting to see what your timing is also doing at the same time. You could also set the datalog to show the IAC and what it is doing too. As I get my mind wrapped around all of this I find I can't keep up with it all and the datalog from the wideband can be a lot of help to see it without the distraction of driving.

The big question is? Did you have a proffesional tuner get you going or are you doing it all yourself? I am impressed with anyone who is trying to tackle the tuning on their own and actually able to pull it off. I had help from Rob at FFI and to have a base program that was a bit better than the plug n play from Accel was a big help.

[MrForce]

Jim, thanks for the props. To the OP, Jim is on the right track by trying to see what is causing the sudden correction. Do you have two fuel values that are right next to each other in the table but very different in values. Example a 45 that jumps to a 73? Same with Spark. You might try disabling the WBO2. That does not stop it from reading, but it won't make corrections. You can then watch and see how big a change you get without the correction kicking in. Another thing to check for is an exhaust leak ahead of the sensor, that can seriously affect O2 readings.

Keep us posted.

Rob

[emtcee1973]

thanks for the replys guys..my wideband and the dfi a/f ratio's are the same, so iknow they are insync...the numbers in the ve table at idle are very close to each other so i don't think thats the problem..i still have to check for an exhaust leak at the collector..its really like i'm losing fuel pressure but im not...the needle on my guage is rock solid...and i did check for vacum leaks and found none...i did the propane trick and had a vacum guage hooked up..i really haven't had time the last couple of days to play around with it but i should have time in the next few days..i will keep you guys posted if you are still interested..thanks
mike

[emtcee1973]

ok, i took the car out for a short run today.so i started it up and let it idle for a good half hour...got it to temp then took it out for a run...i got on it pretty good,spun the motor to about 4800rpm..first time i did that no stumble a couple of minutes later the stumble is there...so i bring it home and let it idle for a minute or two then all of a sudden the fuel pressure drops to like 25lbs..the motor starts to stumble and finally dies..now i let it cool down and start it up again i rap the throttle fuel pressure stays like a rock,after it warms up i rap the throttle again and the fuel pressure goes down when i do that..it comes right back up though..i tried three different fuel pumps and the same thing occurs..im thinking fuel pressure regulator??? what else would cause this only when the motor is warm?? also i have good voltage at the pump, about 13.5v..even when i rap the throttle the voltage stays at 13.5...the fuel pressure is supposed to go up when i stab the throttle,right?? where else should i look ??

[Jim Nilsen]

ok, i took the car out for a short run today.so i started it up and let it idle for a good half hour...got it to temp then took it out for a run...i got on it pretty good,spun the motor to about 4800rpm..first time i did that no stumble a couple of minutes later the stumble is there...so i bring it home and let it idle for a minute or two then all of a sudden the fuel pressure drops to like 25lbs..the motor starts to stumble and finally dies..now i let it cool down and start it up again i rap the throttle fuel pressure stays like a rock,after it warms up i rap the throttle again and the fuel pressure goes down when i do that..it comes right back up though..i tried three different fuel pumps and the same thing occurs..im thinking fuel pressure regulator??? what else would cause this only when the motor is warm?? also i have good voltage at the pump, about 13.5v..even when i rap the throttle the voltage stays at 13.5...the fuel pressure is supposed to go up when i stab the throttle,right?? where else should i look ??

My fuel pressure stays the same no matter what rpm or throttle position unless the pickup lost fuel. You may very well have a regulator problem, what kind of regulator do you have and how is your system configured? Is your bypass at the beginning of the rails or the end of the rails? Do you have a vacuum line connected to your regulator and where is the vacuum line connected to the engine if you have one? Is it an adjustable regulator?

It really does sound like a bad regulator. Erratic pressure levels definately can be directly related to a bad regulator most of the time. It would be highly unlikely that you could be continually getting a bad fuel pump.

It may sound like a bunch of work and I have been there with fuel problems so I understand the frustration.

Reconfiguring the the lines may be your best alternative in the long run. Going with a bypass regulator in the back and going with one line to the engine will solve a bunch of other problems that could arise later also. I will never regret redoing my system the way I did even though it cost me more money. The good thing is that you ususally don't need to buy any more line to do it. I really like the Aeromotive regulator and it has never once fluctuated more than a pound one way or the other unless the pickup starved.

It definately sounds like you found the problem, now you have to work on the solution and that can be found in several threads.

Goodluck and if you need anymore help just give a shout.

[emtcee1973]

thanks jim...the regulator is an adjustable one that i got when i put the stealthram intake on the motor so i'm not sure what brand it is..i have a vacum line hooked right into it,the line itself is only like 5" long which is connected directly to the back of the upper plenum.i was also thinking that my venting is not adequate? i just have a vented gas cap,is that enough?also the regulator is situated at the end of the fuel rail run..

[emtcee1973]

so i just hooked up a tee fitting on the output side of the fuel pump under the car so i could hook a guage to it..and the needle on the guage is all over the place..is that normal? i mean does the fuel pump pulse or something?this was at idle obviously,the guage on i have hooked up on the manifold is steady though..

[Jim Nilsen]

so i just hooked up a tee fitting on the output side of the fuel pump under the car so i could hook a guage to it..and the needle on the guage is all over the place..is that normal? i mean does the fuel pump pulse or something?this was at idle obviously,the guage on i have hooked up on the manifold is steady though..

The fuel pump should keep a steady pressure if the regulator is working right.

What kind of lines are you using? hardlines or hose?

As long as you aren't driving anywhere you could remove the cap and see if it needs more venting, the pressure gauge should show some kind of change from what you are seeing now if it is part of the problem but a stock vented cap should be good.

Changing you system with a bypass regulator in the rear after the pump and one line going forward really does make the system work better from my experience.

keep us posted.

[emtcee1973]

thanks jim...is there a drawing or schematic of a system with withe a bypass regulator setup? do i eliminate the regulator at the fuel rail? how does it work? when you say one line do you mean eliminate the return?
mike

[Jim Nilsen]

thanks jim...is there a drawing or schematic of a system with withe a bypass regulator setup? do i eliminate the regulator at the fuel rail? how does it work? when you say one line do you mean eliminate the return?
mike

if you go back in this thread there is all the info you need.

Yes you do eliminate the regultor at the fuel rail and the return line from the engine bay. You will have the regulator in the back and it will return to the tank from there. This eliminates the fuel from getting heated up in the loop to the engine bay. Corvettes do it this way.

I will look for a pic of my fuel system at the rear of the car and post it for you.

Maybe if you search for Aeromotive regultor the threads will come up for you quicker

[emtcee1973]

thanks jim i really appreciate the help!! just one more question for you,if the pump is pumping all that fuel to the rails on a single line does the unused fuel just sit there waiting to be used?i mean isn't the regulator just taking the fuel right from the tank and putting it right back there???

[Jim Nilsen]

thanks jim i really appreciate the help!! just one more question for you,if the pump is pumping all that fuel to the rails on a single line does the unused fuel just sit there waiting to be used?i mean isn't the regulator just taking the fuel right from the tank and putting it right back there???

The regulator is holding back the fuel in the rail at whatever pressure you have it set at to relieve the excess back to the tank. Mine just deadheads to the fuel rails which are looped on both ends to equalize the rails. You put the pressure gauge at the rear/farthest away from the inlet to the rails to get the true reading.

Here is a pic for you of my setup, The fuel comes in from the tank to the red filter and exits the regulator and goes to the fuel rail with one line, the excess goes out the bottom/return of the regulator and goes back up into the tank and is adjusted to 45 psi in my case. Short and sweet. i have had good success so far with all hardline in the back, I almost put teflon braided from the tank/trunk floor but so far it is doing good. I keep inspecting it to see if it leaks and for cracks but so far so good. The baseplate is mounted on winsheild wiper mounts to take the vibration and isolate the noise.

[emtcee1973]

thanks jim!! i can't thank you enough for your help..your setup is really clean, it looks fantastic!! i will keep you posted when i get the car running...
mike

[thedugan]

Im having the same issue. Thanks for the info in this post

[emtcee1973]

Just wanted to give an update..i rerouted the fuel lines and went with a single line going to the rails.that seemed to help but there was still a drop in pressure(not as bad though)..so i decided to drop the tank and take a look at the pickup..i found the strainer to be dirty..i ran air through it and it had quite a bit of restriction..so i think between the clogged strainer and the vapor lock issue i have found the problem.thanks again jim for your help...since now i have only one line running up to the rails do i need to increase fuel pressure? i have it set right now at 45psi...i know the ls1's run a higher pressure so i figured i ask..
mike