Q for Craig Smith >>>

[Streetracer00]

Craig, I've been having some voltage issues and was wondering if I could use a firmware update. Would it be possible to check these numbers for me and see if there is an update available for my ECU? Let me know.. thanks!

P/N: 30-115010
S/N: 01029 1029
Firmware Rev: B2BEDI_A
Date: 11/30/99 - 2/7/00

 

[Craig Smith]

What do you mean by "voltage issues"? To answer your question, your ECU is not current. However, if you are having trouble with voltage fluctuation, your first step should be to resolve that issue. Newer firmware revisions seem to deal better with variations in battery voltage, but those variations still pose a problem that should be dealt with. An alternator capable of maintaining steady voltage even with a decent load on it would be at the top of my list of recommendations.

 

[Streetracer00]

Well..

Sorry, you're right, they are battery voltage fluctuations. I've had the battery checked out and the alternator as well. The voltage starts off at 14.1 on a cold start, and slowly drops to around 13.5-13.6 while driving around. The Dashboard shows a "Battery correction" of .8%, which I thought was odd. The car is currently down now, and that's why I thought an ECU upgrade would be a feasable idea without too much downtime.

 

[bobc455]

Personally I find the battery correction to be a pain. It would be nice if I could always be at 14.2 volts, but in the real world when you're idling at 600 RPM with the lights on, fuel pump(s) on, fan running, etc., it's not uncommon for me to be at about 12.7 volts. This causes whatever problem in the ECU to make my idle rough, forcing me to run either too rich or too lean (depending on whether the fan and lights are on).

I have received the aforementioned firmware update and although it helped (at least the car stays running now), I still wish you could disable that gal-durned voltage correction! Either I have to tune for a rich idle or have the engine surge like crazy whenever the fan kicks on (which seems to always happen on those hot days in traffic, 455's just don't seem to be cool running motors).

Streetracer00, just tune the best you can and we'll have to be happy with that.

-Bob Cunningham
bobc@gnttype.org

 

[4C FED]

I've have a Powermaster 200 Amp Alt. installed.
With or without 4 Spal fans running, I don't have any more than a .2 volt change.

 

[Streetracer00]

Hmm..

On my car ('98 Cobra) the stock alternator is a 130 amp unit which I think is sufficient. Are you guys actually upgrading to bigger alternators or is there something that I'm missing here? I would love to see 14 volts 24/7 and not just on startup.

 

[Craig Smith]

I had a 140 amp East Coast Auto Electric alternator that would keep my voltage constant with anything but a wrench across the battery terminals. I would guess that a 130 amp unit should do very close to the same.

The bigger the injector you have, the more pronounced this type of problem would be. With older firmware revisions, the battery correction you observe in the dashboard is applied to the injector pulsewidth. Newer revisions only apply this percentage to the injector opening time, which is all that should be affected. However, with large injectors, that injector opening time becomes a much larger part of the gross pulsewidth. Here's a little rundown.

The ECU will either calculate an injector pulsewidth or look one up from the base fuel table, depending on if you are in speed/density or Alpha-N mode. The value entered into the Injector Opening Time field is then added to that pulsewidth. At idle, this number is generally small. With mondo injectors, this number is VERY small. The smaller the pulsewidth from the fuel table, the bigger percentage of the gross pulsewidth the injector opening time will be. So, in some cases, even with the newest ECU firmware, battery voltage fluctuations can have quite an impact on idle quality.

As in Bob's situation, sometimes it is quite tough to keep the voltage up. I had good luck with my alternator but my car idled at 1500 RPM. What has me curious is how a setup like that would respond to a lack of battery voltage compensation as Bob has suggested. I would guess that there would be some difference in how it ran merely from the change in voltage, but it would be interesting to see which way had MORE of an effect on the car. Maybe it's time to go play...

 

[Streetracer00]

I see

I am using 83lb/hr injectors and I've noticed the injector pulse width fluctuates and makes the car run fat/lean and surge... the battery correction is usually at a steady .8% when the car is running. On startup it is at 0% with the battery voltage at 14.1. Would looking at my program help at all? The surge is so annoying. Thanks for the replies!

 

[Craig Smith]

Looking at your program wouldn't really allow me to tell you much, but it sounds like you need to richen the car at warm idle. If it is fat on startup, take some coolant temp enrichment out of it.

The entire VE table should be calibrated when fully warm, and the other tables based on CTS readings should be tweaked after that happens. Tune the car for the conditions it will see while driving around and you will have the best luck.

 

[Streetracer00]

I know..

That FAQ link you gave me a while back explained that to me as well. It surges on decel and sometimes it idles okay, sometimes not. I have noticed in the VE tables when the Speed-Pro changes the pulse width on the injectors, it starts to surge. It will change it from say 1.2 to .9 or something and then the car will suddenly go lean, then try to fatten up.. surging in the process. I think the .8% battery correction doesn't help either.

 

[S2V6RACER]

Craig, I would like you to look at one of my datalogs from this weekend.

Where do I e-mail it to?

 

[carbuff]

Add me to the list...

Hi guys,

Add me to the list of people who has trouble with battery fluctuations! My problems stem from my one-wire alternator I believe...

Craig, that East Coast Auto Electric that you used, was it a 1-wire by chance? Mine works great as soon as I put a load on the motor. But when I start it in the garage and let it sit, the alternator will not start charging until I put a load on the motor, even if I rev it up past 2000 rpms. And the motor idles horribly until I get the battery voltage up (but it does run).

I think this was also contributing to my lean idle problems I was having. I gather that you guys are saying the correction is causing you to run rich with low voltage? Mine is just the opposite. Until I get the voltage up, I get a very lean idle... Even with 0.8 battery correction...

Funny, I was just going to post about this when I saw this post. Guess I'm not the only one...

Bryan

 

[Streetracer00]

Hmm

That just reminded me of something else. In my datalogs, I show that my voltage actually goes DOWN during WOT, sometimes as low as 13.2 - that's not normal is it?

 

[idaho gn]

the batt voltage could go down from when you first start the car.

for innnstance with the car sitting not running just sitting say the voltage is 13 volts. you jump in and start the car you use some energy out of the batt. so if you put a meter on it it might drop to 12 (this is an example). ok so the battery is one volt low from where it started so the alt says oh no it needs to be 13v the alt will jump to 14.5v output right off the bat(charging) and slowly decrease as it makes its way back to 13 volts but this happens every time there is a current draw on the battery no matter how large or small and everytime that the alt sees a change in batt voltage the one thing to rembember is that with the car running it will be putting out slightly higher voltage than the batt is at static (car not running) cause you are using energy to keep the car running unless the car idles so low that the alt cant put out any voltage then you will see a discharge untill you speed up the engine or if the alt is overcharging you will burn out the batt


sorry for rambling

shawn

ps nate you voltage is probablly going down because you are turing the alt faster and it is charging the batt faster (getting it closer to static)

 

[Glen]

Alternator output should be 14.5 - 14.7 Volts, unloaded. Period. As AMPS increase (load) voltage drops, for same given RPM. Voltage is current which is FLOW. AMPS is the power pushing the FLOW. So, as your voltage decreases, amps should be increasing. The bugger in this, is resistance. Poor connections, bad grounds.

On a modern FI car, sanes any power acc. running, you should idle AND maintain 14.5 -7 volts, at any given RPM. Turn on A/C and voltage will drop and amps will increase. Same with headlites, wipers, etc. Running a Fast ECU does not change this.

The voltage correction made by the Fast ECU is also made by a OEM PCM , wither it be a GM, Ford, Chry. The purpose is to make small adjustments in injector pulse width based on preprogramed parameters. That being an injector is rated at a flow, measured at 14.5 volts or 12.5 V. Any deviation from this and the flow deviates. So a correction is added to bring the injector to the correct flow.

So, what do you do? Perform a battery load test. Check the battery cells for a bad or weak cell. Check battery connections, chassis grounds, connecters. Anything that will add resistance. Check your power lead from ALTERNATOR to BATTERY. Is it of suffienct size to handle the load. Big fuel pump=big amps. Is your pump getting the full 14.7 V's. As heat increases under the hood, volts will decrease. Heat is resistance.

It is better to run a wire with many strands than a wire with few. Electricity flow AROUND the wire, not thru it. More strands, more capacity for same given gauge wire. The wire from the battery to Alt. should be at least an 8 gauge.

If your vehicle is idling poorly when warm (hot), I would check another source, such as, air temp adjustments. I don't know about yours, mine was an early model that made automatic air temp adj. I made all kinds of adjustments too no avail. Put the AIC up on the cowl by the winshield and my problem got better. Craig Smith did an update to my ECU so I could adjust the Air Charge Temp. Now it works great and took care of the idle problem. I've seen AIC temps up over 130' and higher.

 

[JeffB]

i can cruise around all day with the fans on and the fuel pump on high (i have a weldon dial-a-flow) and my voltage is 12.9-13.1 (as indicated in the FAST logs, not sure what it is at the battery)... but when i'm WOT the voltage drops to as low as 11.5... the fans, water pump, fuel pump, etc. are all the same so is this drop a result of a drain from the ignition system and injectors?

i got a thingy from precision turbo that plugs into the alternator and allows you to set a voltage and supposedly the alternator will put that out under all conditions... haven't installed it yet... anyone have experience with this? right now my alternator just has the 1 wire plug...

 

[Glen]

1st off, Jeff, U want to check your alt. output. I check at idle and no load, then small load, followed by 2000 RPM and heavy load. A load is anytime something turns on, ie. fan, lights, a/c etc.

At idle, no load, u should have 14.5-.75 volts. This takes into account 1. fuel pump 2. ignition system 3. ECU.

Idle, slight load such as fan(s) or lights U should have approx. 13.75-14. volts. A/C on, 13- 13.5 volts.

2000 RPM, heavy load, A/c on, lights on brite, wipers, anything U can turn on that will put a load on the alt. I want to see 13.75-14.25 volts. If not, look hard at the alt.

Now, as VOLTs go down, AMPs go up, thats a reflection of load. Thats what U want. U will have to check with FAST for there amp draw for the ECU, but I would guess it is very small, very, very small, compared to the other parts.

Pumps, fans, lights etc., these can all draw 20 amps or more, EACH. Start adding these up and you can have at a minimum, 60 amp draw at any time. This is why a very high output alt., even from the factory, are required for FI. Most factory alt. are in the 130 amp range.

What increases these draws above the stated factory rating? Wires that are to small for the load, poor connection due to either corrosion or loose fit. Bad grounds. Bad units. HEAT, and you can't beat heat, only manage it.

Wire from the alt to battery connection should be at least 8 gauge. From battery to relay to unit... 10 gauge. One relay per unit. 2 fans=2 relays. Use a high strand count wire, electricity travels around the wire strands, not thru them.

As for the ECU correcting for the voltage loss..... it always will. As the engine heats up, the resistance in the injectors and other sensors goes up, reducing voltage. To verify, measure the ohms across an injector when it is cold, then drive the vehicle ten minutes and remeasure the same injector. Then fig'r it for all 6 or 8 and you will see why the ECU will always have a voltage correction. It's the ECU's way to adjust to keep the injector on time correct.

All parts..... ignition boxes, ignition, fuel pumps- factory and aftermarket, everything has a rated amp draw. Start checking them, adding them up, etc. and U will see it better.

 

[Craig Smith]

Computers also adjust for battery voltage because injectors open and close at different rates as voltage varies. This is probably the biggest factor in the equation. Tune a car with a 16 volt battery, put in a 12 volt battery without retuning it, and see if you can even get the car to idle properly... probably not.

 

[Chuck Leeper]

VOLT DROP??

If the battery is trunk mounted, then the issue of wire size for the charging circuit becomes an even larger problem.

Given NHRA'S stand on cut off switches, I think the charge wire has to go to the battery cut off also. I use #6 wire to do this.

COMMENTS?? wire at #6... too large? too small??
I don't like the aftermkt relay deals that are sold.. just another item and connections to go FUBAR....

 

[Scott231]

Re: VOLT DROP??

Originally posted by Chuck Leeper
Given NHRA'S stand on cut off switches, I think the charge wire has to go to the battery cut off also. I use #6 wire to do this.

COMMENTS?? wire at #6... too large? too small??

I don't like the aftermkt relay deals that are sold.. just another item and connections to go FUBAR....

Chuck,

It is my understanding that the alternator charge wire will either stay "hot" (if connected to the non-load side of the cut-off switch) when the cut-off switch is activated or if the alt charge wire is connected to the other terminal of the cut-off switch, it will back-feed the electrical circuits and the car will continue to run (until the key is turned off). Obviously, the second option here is a no-no.

As such, when using option #1 you retain a "hot" alternator charge wire...which the NHRA also deams "illegal". The aftermarket relay gizmos are designed to kill the connection between the alternator and the battery when the kill switch is thrown.

Me...I just live with the always-live alternator wire becasue, like Chuck, I don't need anything else to go wrong with my car.