A/F Changing When Engine Is Warm

[Chuck Leeper]

"HINT to FAST.... add injector opening tables to the system so we can program for varying charging system loads. The factory puts them there for a reason."

As I recall, the FAST has a batt volt compensation table in it.

 

[bobc455]

As I recall, the FAST has a batt volt compensation table in it.

Not user-accessible

-Bob C.

 

[HighPSI]

HINT to FAST.... add injector opening tables to the system so we can program for varying charging system loads.

I'm pretty sure you won't get this for the Classic box. I have been pushing to get it on the XFI. Hopefully, this feature will be available in the near future

 

[ZBass28]

Next time the car is surging at idle, try connecting it to a battery charger.
This will increase & stabilize the voltage. see if the idle smooths out.

Tried this and am really not sure what the results (if any) really indicate. Started the car, it ran fine for the first 10 minutes as usual. Took note of the voltage display on the FAST dashboard and it was showing 13.9v when it first started. After about 10 minutes of running it started displaying 13.5v, and as low as 13.4v.
I grabbed my battery charger and hooked it up, no change to the reading. The indicator on the charger itself was showing a reading like it was charging a half-dead battery, or at least a battery that needed a charge. The voltage on the FAST dashboard never went back up and the process of the car gradually leaning itself out proceeded.

Within another 5 minutes I had gone from running at 13.75-14.00 A/F to 14.25-14.50 A/F. Took the car out and of course it was worse, but by the time I got back home to shut it down it was now showing right around 14.0 A/F, which means it richened itself back up a bit.

At this point I think I am done with this engine build. 7 years of nothing but minor problem after problem that never go away. I'm fairly disappointed with the FAST unit as well and think I will convert back to the stock PCM style of control for my car, if I even keep it.

If anyone has any last minute advice I'm all ears. At this point I do not want to spend money just to test a theory though. If it was as simple as a WBO2 swap I'd be all for it. I don't want to spend that $ if that's not the cause.

 

[Chuck Leeper]

Haven't been following too close, but have you put it in open loop, to see if the performance improves?
Since you want to spend no more $$, maybe borrow a stand alone O2 sensor, [IE: LM-1] and see if the A/F still changes. That will pretty much eliminate the FAST/O2 setup, as the culprit...

You don't have a vac situation w/ the gas tank, do you??
I had 1 that had the vent blocked off.. Would run for a few minutes, then go lean... The Fp was pulling fuel, creating a vac on the tank, and dropping FP..

 

[ZBass28]

The car is running in open loop up to 2000 rpms.

As far as I know there shouldn't be an issue with the gas tank. Car has had this setup for 7 or 8 years, but this is the first time something like this has taken place.

I'm not sure I follow the scenario of getting the stand alone O2, or moreso, I don't know what an LM-1 is. I haven't followed the boards or tuning forums much until recently.

 

[Lonnie]

You have proven the voltage is not consistent.

I'm not sure what kind of charger you are using...... you need a serious charger that is capable of starting the car. Put it on high & it will bring the voltage up to the upper 14v range. Then see what your o2 reading is. A small trickle charger is not enough.

Also check your voltage with the haeadlights, cooling fans etc running. See if this changes your Af ratio.

What type of injectors do you have?
What FAST software version are you running?

I had this exact problem. You can run a better injector (low impedence), or a better alternator that more accurately controls voltage. I had 50# injectors which are were very sensitive to this. Switched to 85's & it was fine. Remember the FAST voltage compensation table was programmed to match a certain injector. Your injectors may be totally different.

 

[ZBass28]

You have proven the voltage is not consistent.

I'm not sure what kind of charger you are using...... you need a serious charger that is capable of starting the car. Put it on high & it will bring the voltage up to the upper 14v range. Then see what your o2 reading is. A small trickle charger is not enough.

Also check your voltage with the haeadlights, cooling fans etc running. See if this changes your Af ratio.

What type of injectors do you have?
What FAST software version are you running?

I had this exact problem. You can run a better injector (low impedence), or a better alternator that more accurately controls voltage. I had 50# injectors which are were very sensitive to this. Switched to 85's & it was fine. Remember the FAST voltage compensation table was programmed to match a certain injector. Your injectors may be totally different.

The charger is just a Century 10 Amp charger.

Injectors are 65# low impedence Siemens Deka. By version of FAST do you mean the version in the ECU? Whatever was in there back in 2000 is what is there. If just CCom software, I was having this problem running both the DOS laptop version and also the newest CCom version run from my desktop.

This would be nice if this is the problem, although I am still confused as to what is tipping you that there is a voltage inconsistency. Just the fact that it changes from 13.9 to 13.4? With headlights and fans running I have seen it read as low as 13.2v on the FAST dashboard. How accurate is that number though?
And lastly, what alternator would you suggest running then that can supply the voltage needed?

Would be great if this is the solution.

Thanks

 

[ZBass28]

Went out and bought a Sears Die Hard 40amp rapid charger with the engine start option. I let the car run for the first 10 minutes, and as usual it ran great.

I hooked a multimeter up and when the FAST dashboard was saying 13.8v, that was the exact reading I was getting at the battery. FAST dash dropped down to 13.5v and the readings at the battery started to vary between 13.4-13.7v.
FAST dash started to show 13.2v and this was confirmed at the battery. At this point the A/F started to change slightly, hitting around 14.0-14.2 instead of the 13.8 range it should have been in. I decided to turn on the headlights, brights, radio and HVAC fans to full, thus dropping the voltage on FAST and at the battery to anywhere from 12.9v to 13.2v, with a steady 13.15v showing most of the time. A/F did lean out just a tad during this and would seem to get better if I turned all the stuff off.

At this point I decided it was time to throw on the charger and see what happens. Set the charger to 40amp fast and turned on, could hear a slight change in the way the engine ran, nothing much but just a slight variation in the idle. Looked at the FAST dashboard and it was still reading 13.3-13.4v, however reading at the battery with multimeter was 14.12v. It never got higher than that though AND with the charger on the car actually ran leaner (like in the high 14 range to 15.12). Turn the charger off and the car would get a little richer.....that doesn't seem to make much sense to me and would seem to go against the whole idea of this experiment.

Thoughts?

 

[Lonnie]

I was speaking of the ECU, not the c-com software.

I believe there were a few LT1 upgrades since 2000 on the ECU. This may improve your idle quality.

Why are you running open loop at idle?

The charger may take enough alternator load off the motor to free up the idle. This raises vacuum & changes the fueling.

Set the idle mixture & run in closed loop. (no reason not to unless you have a huge cam) Watch the AF ratio stability & o2 correction, turn on charger & see if the correction changes & the idle improves.

 

[ZBass28]

Ok, looks like I will send the ECU in for an update then since it's old school.

I used to run in closed loop all the time (including idle) and the car would idle like crap. It would never idle smoothly. I was told by someone (years back we're talking) to let the car idle in open loop, set the VE to hit the target A/F approximately and see how it idled. After that it would idle smoothly. I ran open loop up to 2000 rpms just so that the car would run smoother around town as well.

I can switch back for testing purposes, and for good if it makes a difference.

Cam is not huge, but it's decent sized. 236/236 duration and .560/.560 lift, on a 114 lsa.

Is the 40 amp DieHard battery charger enough to use for diagnosing this, or is something even bigger required? With it hooked up, the most I saw was 14.15v testing with a multimeter.

Can I send you my current FAST file just in case there is something that I have overlooked?

 

[bobc455]

Although idling in closed-loop may help to diagnose the problem, I like to idle in open loop.

Idling in closed-loop would contribute to surging as the mixture kept changing slightly.

(Actually I run everything in open loop now- I removed my O2 sensor after I was happy with the tune, so it wouldn't wear it out and I have to buy a new sensor. I only put the sensor in when I'm going to tune for some reason.)

IIRC FAST revised the algorithm for voltage-correction at one point, I think I sent my box in for a software upgrade and it seemed to help.

-Bob C.

 

[ZBass28]

Ran the car idling in closed loop....

Basically my VE numbers were dead on, even in closed loop the corrections were 0.0% to -3.1% and the car ran as it always did. Again voltages dropped from 14.15v at start up and 2 minutes of run time down to 13.4v after about 10 minutes of run time. At that point the corrections were still well under -5% but touched a few times into the 4.x range. Then as I was checking the voltage with multimeter and getting ready to hook up the batt. charger, the car started to surge pretty wildly up and down from 1200 rpms down to 750rpms back and forth. A/F would jump over 15.0 and then down to the high 11's, and you could see corrections of +11% all the way to -11%...not really sure what brought that on all of a sudden and that quickly.

It started to clear up a little on its own, but I hooked the battery charger up and the voltage reading at the multimeter went back to 14.1v. It took a while for the car to smooth out a little but it did. However, the idle was now about 50-100 rpms higher and the A/F and corrections were starting to swing the other way. A/F was now getting into the mid 14's and corrections swung to the positive side showing anywhere from +4% to +6.x% just to maintain the 13.8 A/F I am looking for.

It's not looking like the addition of battery charger is helping any, as the car still does what it always does. The car doesn't run any better in closed loop, I'm just able to see what corrections its making.....which were basically the same ones I would have to make when it was in open loop and I saw it was leaning out.

I'm at a loss...I can't for the life of me imagine what could go on in that one instant to make the engine swing back and forth like that from high 11's A/F to low 15's.

I'm starting to think there must be some mechanical problem somewhere, a break in an intake gasket or something that's causing these "mood swings" my engine experiences. It never did this before in the last 7 years.

 

[Lonnie]

You can try setting all the cells immediately around your normal idle cell to the same # this minimizes fuel changes when the idle fluctuates. This may stabilize your idle. I'll take a look at your file if you want.

 

[ZBass28]

Lonnie,

I have tried that recently. In fact, I did it with the timing too so that everything in a certain area remained a constant. I still would have the same problems.

I'll copy the current tables tomorrow and send them over to you. Thanks for taking the time. I honestly don't think there is anything there out of the ordinary, but I'm looking for anything to grasp at. This sudden poor running thing has kind of just appeared out of the blue, which is why I am beginning to think there has to be some mechanical explanation to this.

 

[ZBass28]

Where would you like me to send the file to Lonnie?

 

[Lonnie]

sales@lonniesperformance.com

I'll try to give you some feedback.