ECU Draining Battery?

[thejollyrancher]

Hey everyone,

I finally got my 1g Talon up and running for about a day or two when I hit another problem

The car worked fine and the battery saw good voltage for about 2 days after I fixed a MAF issue. But when I went to go start it today it wouldn't start. Instead I put the key to accessory and heard a very slow click and upon every click all the power would die, the car would slowly power back up, and click and die again. So I checked the battery voltage and the car was seeing 12.3. When i turned the key to Accessory the battery voltage immediately drops to below 3 volts. The voltage stays really low even after I take out the key, but immediately goes back up to 12.3 after I hear a click from the dash about 10 seconds after i turn the car off. I think this click is the ECU shutting down.

Is the ECU draining that much power? I've attached a few pics of the ECU.

 

[needbooost]

What makes you suspect that it your ecu? With no lights on and the key out of the ignition you car shouldn't draw any current. Try jumping the car and check the voltage from the alternator to ground 13.9-14.6 is ideal on the stock alternator.

 

[jbeaton9292]

You changed your maf im almost willing to bet that its your altinator fuse. My car was doing this same thing that fuse is close to your maf and odds are your cover is missing like most 1g cars. That fuse will cause what your explaining check it, it should be held in by 2 10mm bolts its kinda off by itsself mine easnt even bolted down!

 

[thejollyrancher]

I checked the alternator really recently and it showed good values. Its a brand new alternator as well. I dont have a means to jump the car right now to test it again but ill try to get on it. That being said Im fairly certain its okay.

The car does not draw any current after the ECU turns off.

So I just checked the alternator fuse and that seems fine as well. Ive had the cover on the fusebox as well so I haven't really been messing with it at all.

I just tested the car without the ECU plugged in at all and the same thing happens. When the key is on Accessory the car sees no more than 3 volts.

 

[We're on Boost]

Wow.
Well, a few thoughts:
The click you hear inside the car is probably the MFI relay which is kind of in the center stack below the dashboard. Although, the MFI relay should click off about 2 seconds after you turn the key to off (as I remember). 10 seconds sounds like too long.
Battery voltage of 3 volts is awful low. I can only think that there is a loose or corroded battery cable terminal somewhere, or else your battery has gone bad, or is just very discharged. Do you have a hydrometer to check the battery acid density in each cell? That is usually the best way to check the status of a battery.
Are you measuring your battery voltage with a meter right on the battery? Or are you getting the voltage numbers from your logger?
How do you know the car does not draw any current when turned off?

More later ---

It would be interesting to know how much current (amps) is actually going through the battery when you see 3 volts. The trouble is, if it is a lot of current, it will blow the fuse in your multimeter, which if it measures amps at all, will probably only handle up to about 10 amps. So if you were to try that, I would check first what kind of fuse is in your meter and make sure it is cheap and easy to replace!

When I needed to do something like this I bought a panel meter with matching buss bar. These things are cheap and you can buy them in lots of different max amp sizes. The one in the pic here is 30 amps max. You can get them up to 200, I think even 300 amps. If you want to know more about panel meters I can give you more info about them later.

But really, I would first get a hydrometer to check the battery, and I would check all the terminals for good connection. A lot of the people who work at car parts places these days won't even know what a hydrometer is. So do some homework on them first, before you go to buy. They are cheap and simple, kind of fragile though, made of glass.

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[thejollyrancher]

Thanks for all the information, I really appreciate it. I'm am determining the voltage by means of a volt meter directly hooked up to the battery. I don't think the car is drawing current when off because I can leave the car off overnight and see no change in voltage at all. The car just looses voltage when the key is in the on position (not accessory, sorry for the mistype earlier)

I just charged the car to a good voltage above 13 v and when i turn it to on it seems that the voltage drops to 4 and climbs up to 5. Every time it hits 5, the relay clicks, and the voltage drops to 4. This process started begins rapidly and gets slower and slower.

I'm going out to get the things you suggested and I'll report back with the readings! Thank's again.

 

[We're on Boost]

Ok good. A battery hydrometer usually looks like the pic below.

Usually they give you a method whereby you can correct the reading for temperature, but that correction is small, and I think what we're looking for here is pretty gross!

You do have to check all 6 cells. Hopefully your battery is not totally sealed. Gotta be caps you can take off the top, to get at the acid inside.

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Another thing is - when you measure the 3 volts on the battery with your meter, where exactly are you putting the probes?
If you are putting the probes right onto the actual posts that come out of the battery, then you are truly measuring the battery voltage under that condition. If you are getting 3 volts right on the posts, then I think you have a bad or seriously discharged battery, because there is no way that the ignition "run" circuit can draw enough current to drag the voltage of a good battery all the way down to 3 volts.
But if you are putting the probes onto the the cable end, you know, like the female clamp that goes around the post, and getting your 3 volts there, then you probably just have a bad connection between the cable clamp and the battery post.

So for example, if you measure 3 volts on the clamps and at the same time measure close to 12 volts on the actual battery posts, then you have a bad connection there and you need to get one of those little round wire brush thingies to clean up the clamps and posts, and clean out all the crud in where the clamps come close together to make sure that isn't hanging up the clamp from tightening onto the post.

If your 1990 is like mine, the fuse for the ignition "run" circuit is in a little 3-fuse box that is hanging right onto the + battery clamp. It is only a 30 amp fuse. Later models had a 40 amp fuse for that same function. The 30 amp fuse seems to be enough on the 1990. I am just saying that, if there was a short somewhere that was allowing a lot more than 30 amps to flow from that circuit, that fuse would be blown and you would get nothing. By the way this 30 amp fuse also handles the current that goes to the solenoid on the starter, which can take close to 30 amps all by itself (with the key turned to "start") and this might be why later models have a 40 amp fuse in that position.

 

[thejollyrancher]

I just tested the voltage from the posts and connectors. The posts see a constant 12.2 and the ring connectors drop to 3 volts. I don't think it's a connection issue because without the key in both the connectors and the battery see 12.3. But I cleaned the terminals anyways.

I measured the current with the car at 3v and got no reading at all.

At this point I tried the car again and I just got a whining sound from behind the center stack until I removed the key.

Upon testing the battery with a hydrometer, I got values of 1200 on every Cell. My hydrometer tells me That's bad.

 

[We're on Boost]

Hmm, well 1200 is not very good but it is not very bad either, it is just a little into the "bad" range. On mine the "fair" range starts at 1225 and the "good" range starts at 1260. Plain water I think would be 1000 (specific gravity of 1.0). Gold and tungsten both have identical specific gravities of 19.3 just thought I'd throw that in for extra credit

So, if that is the best your battery can do, it is bad. But chances are if you put a slow charge on it, like 6 amps or less, (less is better in this case) and let it charge for 12 to 24 hours, it might very well come up to spec and be just fine. The worst thing is to take it to a parts store that would give you a "quick charge" where they smoke it with, I don't know, 80 amps or something, for 10 minutes or so. Bad.

Here's the biggie though. If you have 3 volts on the cable and 12 volts on the post (with the key on), there is definitely a problem between the cable and the post.
With the key off, you have 12 volts both places, that is because when there is no current flowing, there is no voltage drop. Here's the formula:

V=IR

where V is voltage
I is current in amps
R is resistance in ohms

When I is 0, V is also 0, even if the resistance is thousands of ohms. So the voltage drop is 0, meaning you get the same voltage reading in both places.
Then you turn the key on, so now there is some current, blammo, you get voltage drop.
Let's say you get 1 amp of current with the key on, and let's say the resistance in that connection is 9 ohms, that gives you a 9 volt drop across that connection.

So what I don't know is, why do you get a reading of 0 amps when the car is at 3 volts?
Oh wait, probably 3 volts isn't enough to trigger the MFI relay.
Anyway, there must be some current, because there is voltage drop there in your connection. Maybe there is a very small current and a very high resistance, unlike in my example above. For example, there could be 0.03 amps of current, and 300 ohms of resistance, that would give you 9 volts across that connection. 30 milliamps. Maybe your meter won't really see that. By the way 0.03 amps is about what current you would see through a typical relay coil at 3 volts. So that .03 number is only a slightly wild-assed guess.

It could also be that you are doing it wrong, I mean the way you are putting the meter into the circuit. The meter has to be in series with the wire you are measuring the current in. You have to take either the negative or positive cable clamp off the battery post and put one probe to the post and the other probe to the clamp or ring terminal or whatever you have there. All the current is going through the meter then, which is why it is potentially dangerous to the meter. The ignition circuit itself only has about 2 amps running through it with the key to run. But there might be currents to other things, I don't know if the total current through the battery would be safe for your meter.

Whatever you do, when the meter is set to measure amps, don't touch one probe to positive and the other probe to ground. You'll have instant smoke!

Actually at this point, I don't think you really have to measure the current. If the voltage drops from 12 to 3 just between the post and the ring terminal on the cable, your problem has to be in-between those 2 points.

 

[thejollyrancher]

Thanks a lot. That's a lot of useful information to take in, especially the bit about the gold and tungsten . You're right, I was measuring the current incorrectly, now I know for the future. So the problem is in the connection from the terminal to the ring connector. I guess the next step is to try out new ring connectors and make sure everything is making proper contact. I'll get right on that tomorrow and update the thread again.

 

[We're on Boost]

Ok, good deal.

Yeah the gold and tungsten thing comes up in theories about fake gold bars, how they could be just gold plated tungsten. You would not be able to tell they are fake by weighing them. I guess you would have to test them some other way!

I hope the problem is as it looks right now. If it still doesn't work out, we might have to draw sketches. I might have a wrong picture in my head of how you are placing the probes from your meter, when you get the 3 volts. If you have a scanner, you could draw a sketch and post a scan of it to show me how you are using the meter. Or I could scan a sketch that would show you how I would do it. Or something like that.
In the mean time, don't take any tungsten gold bars!

 

[thejollyrancher]

I replaced the ring connectors and gave the terminals a good shine and the car works so far! I think what was throwing me for a loop was the fact that the connectors saw 12v and then it dropped. That made me think the connection was fine. But I get it now and I have some useful knowledge under my belt! Thanks for your help wereonboost

 

[We're on Boost]

Wow - Outstanding!

I've been round and round on this type of issue a lot with my car, so am glad to pass along the info.

One of my more fun findings was that the aftermarket lead cable-to-post clamps I bought were painted, basically everywhere! So the parts of them that needed to make electrical contact with my ring terminals had to be filed with a flat file to get down to a clean lead surface.

I killed a couple of batteries along the way too, mostly due to long periods where the car would sit there unused, being worked on or whatever. So one of my favorite findings is the CTek Multi US 3300 battery maintainer. Wow what a great device. It is a combined slow charger (3.3 amps max) and long-term battery maintainer that you can leave hooked up to your battery as long as you want. When the battery is fully charged, this thing goes into "maintain" mode, where it puts out small pulses of low-amperage to the battery to keep it fully charged without cooking it. I have 3 of these things now, but the first one went on my 1990 about 3 years ago and it's been great.

www.amazon.com/dp/B000FQBWCY/ref=pe_175190_21431760_C1_cs_sce_3p_dp_1

This gizmo even has one mode on it that is marked with a snowflake. That is for use when you have to keep your car outside in some really cold place, oh you know, like maybe Alberta Canada or someplace.

 

[thejollyrancher]

That sounds like a purchase I'll be making soon! Thanks for the link.

 

[We're on Boost]

By the way did you get your problem resolved that you posted about at the end of October last year, the bogging down thread? From the log you posted on Oct 29 it was clear that when you get on the gas (TPS 90+ percent) that your "front O2 sensor" voltage would drop to 0, which means it is very lean then, which it shouldn't be. However at idle the O2 sensor voltage was cycling like it is supposed to, indicating normal at that condition. Is it fixed now?

 

[erkitner]

V=Volts
I=Intensity (you forgot to mention that) which is measured in Amperage
R= Resistance (measured in Ohms)

Love these formulas!

DSM4Life!

 

[thejollyrancher]

PM'ed!

 

[We're on Boost]

Love these formulas!

DSM4Life!

Yeah, a little bit of science here and there can sure help.