Voltage Differences

s300 and SManager software questions & answers
Javcolin
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Voltage Differences

Post by Javcolin »

Hi,

I'm having an issue regarding Voltage.

while car is Idling, Smanager is reporting 13.9v when the fan comes in it drops to 13.7v but my AFR changes from perfect 14,7 AFR to lean condition when fan comes in. So that is an indication that the Injector dead times are off. but I'm using DW 1300cc and that injector is included in the pre establish dead times. so I know they are good.

So what I did was to hook up my multimeter to the battery and checked the actual voltage at the batery so when the fan is on it measures close to what Smanager sees, but when the fan comes on I can see on the multimeter that the battery voltage drops to 13.0 - 12.9v so that is why my AFR lean out.

Any Idea why Smanager is not picking up the correct Battery voltage? What ECU Pins is Smanager retreving the battery voltage from?

Thanks in advance
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Hondata
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Re: Voltage Differences

Post by Hondata »

SManager is reporting the ECU voltage, not the battery voltage.

If your AFR changes with a voltage change then it is the injector dead times. What dead times did you use?
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Javcolin
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Re: Voltage Differences

Post by Javcolin »

Hi,

I used DW 1300cc that are provided on the injector quick select seccion.

I understand the fact that there might be a dead time offset, But I have used those same injectors on my EM1 and work very well.

Besides smanager is not detecting a voltage change where the actual batery is dropping voltage, had been said that I did tweeked the 12v dead time cell. with no success as the tracer is most of the time on the 14v cell, even when the fan comes on and battery drops to 13.0v - 12.9v but smanager reports 13.9v - 13.7v so the tracer does not touch the 12v cell for the ecu to compensate for the voltage drop at the battery, whcih is indeed affecting the AFR

Could this be realated to wiring issue?

My car is a Turbo CRX with a B - Series engine, battery had to be relocated to the trunk as there is no room for it at the engine bay,
Battery is an AMG for a moanloner power cable runs from battery to a distribution block at the passenger foot well from there short lead to the fusebox that was relocated to the passenger footwell too. from distribution block to starter

Ground from battery negative post grounded to the frame rail where the spare tire was held in place,

positive lead is a 4awg gauge, same for the ground.

any help will be much appreciated,

Thanks
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Spunkster
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Re: Voltage Differences

Post by Spunkster »

This could be a wiring issue if the voltage the ECU is seeing is not changing.
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Hondata
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Re: Voltage Differences

Post by Hondata »

I think there is a different in voltage between what the ECU sees and what the injectors have, so they are not being compensated for the voltage drop.

Use a multimeter to measure the voltage between the alternator stud and battery positive terminal, both with fan off and fan on. Also you could measure from the battery positive to the ECU pin and the injector power connector as well.
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Javcolin
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Re: Voltage Differences

Post by Javcolin »

Hi,

Do you want me to measure from the battery positive terminal to A25 at the ECU? that would be the positive side correct? then to check for voltage at the injector, one lead to the yellow/black stripe at the injector and the other lead to chassis ground?

I haven't tried this as I have been very busy, but what I did before you posted this was to check the Alternator output. positeve lead on the multimeter to Alternator Stud and negative lead alternator body ground, it measured 14.2 - 14.1V. kept the positive lead on Alt. stud and move the ground lead around the engine/Intake/head and thermostat basically same voltage reading, 14.2 - 14.1v.

So next test was with the positive lead still on the Alt's Post and the negative lead to chassis ground and voltaged dropped. to 13.9 -13.7v (this is what the battery sees) so checked one side of the engine ground (at the engine side) and voltage as same as the Alternator, moved the lead to the chassis and emediateley the voltaged dropped, so kept moveing the negative lead to several bolts / places around the chassis/ engine bay and voltage was the same 13.9 - 13.7v

once the Fan came on the voltage dropped further more to 13.2 - 13.0v while the Alternator was at 14.1 - 14.0 volts.

So i'm confused why as soon as I make contact with the chassis (positive lead to alt. stud) the voltage drops that much. apparently i have my grounds good. there is continuity through out.

Any Advice on what to do next? will try what you suggested this weekend,

Thanks in advance
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Hondata
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Re: Voltage Differences

Post by Hondata »

If I had $1 for every battery relocation that had problems then I'd just retire.

What total distance and gauge is the positive run from the alternator to the battery and then back to the front of the car? If you have 4awg and about 15 feet of run to the battery and your fuel pump is using 10A and the fans use 15A each then you will lose 0.4V between the alternator and battery. More drop depending on how good the connections are and the exact length.

But then the way the alternator is connected to the rest of the system matters (using the stock fuse box there are isolated). And the ground sides matter too.

The crux of the problem is that the injectors are getting a different voltage than the ECU.

Use a multimeter with the engine running. Put one end on the battery positive and use the other to measure the voltage at the ECU pins, injectors and alternators. Do this with both the fans on and off. You probably will have to extend the length of the multimeter probes with some extra wire.

Then do the same thing on the negative side from the battery terminal. Measure to the alternator body ground, engine grounds, ECU grounds, thermostat with both the fan on and off. Note all the voltage differences.

In a perfect car the voltage drop will be 0V between any positive wire and any other. And the grounds will be all 0V above the battery negative.

Hopefully once you do this you will find something that is causing a drop on either the positive side or negative side that causes 90% of the problem and you can just live with the battery being somewhere where it shouldn't.
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Javcolin
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Re: Voltage Differences

Post by Javcolin »

Hi,

It has been a while and finally had a chance to the test you suggested and here are the results

The voltage with Fan off / Fan On was:

Battery Voltage 13.32v / 12.9 - 13.0v
Smanager reported 13.9 -14v / 13.8v

Battery Negative pole to Chasis 2.5mv / 2.5mv

Battery Negative pole to Alternator chasis 1.25v / 1.077v

Battery Negative pole to Thermostat Ground 0.940 - 1.25v in that range / 1.044v

Battery Negative pole to other ground points from 7mv to 17.4 mv the highest / 7.4 to 15.9mv the highest

Battery Negative pole to ECU A23 1.12v / 0.800v - 1.5v


Voltage Fan Off / On

Battery Psitive pole to Alt (+) 233mv / 235mv

Battery Positive pole to ECU A25 (+) 52mv / .400 v This Reading increases to 1v then jumps to 0 and cycles up to 1v on and on

Battery Positive pole to A1 Injector #1 (+) .400v This reading drops to 0 then increases to 0.400v

Battery Positive pole to A3 Injector #2 (+) .400v This reading drops to 0 then increases to 0.400v


I see and issu with the ground but i don't know what to do from here to have it fix, any pointers on what to do next? to my limited knowledge I have a problem with alternator and thermostat Ground but no Idea how to fix those.

Thanks
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Hondata
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Re: Voltage Differences

Post by Hondata »

Concentrate on the battery negative to thermostat ground. It should be really close to 0V. Definitely not over 1V.

Where is the battery grounded? How is the engine grounded?
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Javcolin
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Re: Voltage Differences

Post by Javcolin »

Battery is Grounded at the Spare tire bracket.

Engine is grounded at the transmisson to chasis, Valve cover to chasis and an extra ground from the block to chassis.

I will clean and check again all the ground and report back.

Thanks for the help
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Hondata
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Re: Voltage Differences

Post by Hondata »

What about the transmission ground? A lot of people get the valve cover ground wrong too - it should be from the stud not the actual valve cover.
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Javcolin
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Re: Voltage Differences

Post by Javcolin »

Transmission goes from Chassis to Tranny case,

What stud are you refering to? I have it on the valve cover itself from one of the little threaded rings to chasis.
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Hondata
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Re: Voltage Differences

Post by Hondata »

The 8 studs that hold the valve cover on. The threaded blind holes in the valve cover should not be used as they are insulated from the cylinder head.
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Javcolin
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Re: Voltage Differences

Post by Javcolin »

It's bee a long while but got an update.

What I did was cleaning all my Grounds so as body to bare metal. relocated valve cover ground to stud as you suggested.

I did all the vltage drop test and now is much better, voltage at the alternator is 14.0v - 14.1v reported voltage by Smanager is 13.7v - 13.8v voltage at the battery is the same as what Smanager reads.

Voltage when fan comes on is 13.5v - 13.6v both at the battery and what Smanager sees. so it did improved and most importantly my AFR is more stable.

is that half a volt too much drop? would i benefit if I install a high output alternator?

Thanks
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Hondata
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Re: Voltage Differences

Post by Hondata »

Good, it seems that you have improved things greatly.

0.5V drop from the battery to the ECU reading is normal. The main thing is the the voltage differences on the negative side.
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