Batt volts vs Flashscan log..

[Chuck L.]

I am seeing a significant difference in voltage reported on the logs, vs the vom readings I am getting.
Alt is stock, 05 H2 unit.
KOEO:
Batt reading on log = 11.8.
On the output side of the pcm feed fuse = 11.8
@ the alt out stud = 11.8

Engine running, no accessories on: [fuel pump is all]
Log = 13.2-13.5
Alt = 14.45
Batt = 14.15
Dash ga = "about" 14

Once fans come on, the logs have shown as low as 11.9. No other accessories running. Log averages low to mid 12.
Fan[s] draw 11A each.

I have done volt drop tests on all connections. [+ & - sides] None found, that are over normal. Batt in trunk = about .3v drop.
All + & - cables are 1/0 size. Neg is directly to engine and frame and body, @ the front of the body.
Entire wiring system is new.
I've not been able to determine if this variation in scan volts vs batt is normal or not... NE1 have suggestions/comments?:confused:

[Mr. P.]

Interesting. The observations you have posted are exactly what I have seen in my own truck, except I have never thought to actually run a tap with a VOM and see what the system voltage reading would be while driving in traffic, I just assumed that the PCM's reported voltage value would be correct! Apparently it's not. Hmmmm.....

Mr. P.

PS - what fans are you using that only draw 11-amps each?? Mine draw 25-30 amps each at full blow!

[Chuck L.]

Interesting. The observations you have posted are exactly what I have seen in my own truck, except I have never thought to actually run a tap with a VOM and see what the system voltage reading would be while driving in traffic, I just assumed that the PCM's reported voltage value would be correct! Apparently it's not. Hmmmm.....

Mr. P.

PS - what fans are you using that only draw 11-amps each?? Mine draw 25-30 amps each at full blow!

Thanks for the response!
The fans are SPAL 11". They are sold under the BeCool name at Summit. We did amp draw tests B4 I put them in. We also covered them, to force a load on the motors.. Draw went up about 1/2 A.
I have a 180*, [supposedly], stat in my LQ4 engine/a PRC alum rad, and am seeing temps in 95* ambient, running near/at/over 200*. This is leading me to wonder just how well these fans are really working!
This engine makes under 400 FW, and should stay at or really near stat..

I haven't data logged my 08 5.3 Silverado, but I see the volt meter ranging from over 14, to near 12... Do you know if there's a control mechanism in the PCM to regulate alt output?? As near as I can tell, it's internal in the alt.

What fans do you use? [We wondered about the 11A, too.]:confused:

It seems that correct volt reporting is also seen on the older Buick TR ecms. When scanned thru a Scanmaster, there are owners asking the same ?? about the actual vs reported.
We were thinking the ecm/pcm is reporting a regulated voltage being used in the pcm.. Y/N??
This pic of the ft end of the car shows the radiator.. NO reason it should be lacking!

Maybe, we'll get some more replies and get closer to an answer...:hihi:11588

[Mr. P.]

...I haven't data logged my 08 5.3 Silverado, but I see the volt meter ranging from over 14, to near 12... Do you know if there's a control mechanism in the PCM to regulate alt output?? As near as I can tell, it's internal in the alt...

Well it all depends, and I'm not sure. I need to go to my alternator folks (Alterstart) and get a brain-dump on these contemporary units. Also, the charging system changed in the trucks in late-2003, so I dunno if the field is self-regulated (like older alternators) or PCM-regulated and how this may have changed in 2003+.



...We were thinking the ecm/pcm is reporting a regulated voltage being used in the pcm.. Y/N??

THAT would make perfect sense - the PCM has voltage divider circuits in it to deliver precisely 5.0-volts to the various engine control sensors, I bet it also has a similar regulated circuit that caps internal PCM buss voltage at 13.0-volts (give or take), that would make a lot of sense because all motherboards use regulated voltage; I would now bet $1 that this is the value being reported by the GM.VOLTS or SAE.VOLTS PID.



...What fans do you use? [We wondered about the 11A, too.]:confused:

Funny that you should ask - I make & sell an electric fan kit for GMT-800 trucks (99-07), I've done over 50 of them word-of-mouth during the last 3-years, I retail them for $549 complete/shipped/insured/tested/warrantied. I use SPAL 16" fans, my own proprietary control harness, and my own proprietary low-profile shroud. All wiring is correctly sized (10-gauge) and crimped *and* soldered, with appropriate fusing and relays. We parked a few trucks side-by-side, and my kit pulls half-again more air than the GM 2005+ fans, and those pull half-again more air than the LS1 fans and FAL fans (FAL truck kit is a sad joke). The big SPALs pull 25+ amps at full blow, and when you have a rowdy cam with lumpy idle and the alternator voltage falls for a split second the amperage draw can reach 80-amps (the Torrent E-Fan kit has been made for that).

IMO with what you have shared, the only reason you are cooling as well as you are is because you have a really good radiator; I would also advise you change out to a 160* thermostat (remember, they begin to open at 160*, not fully open at 160*!) and my own truck as well as all my customers maintain a 192-195 running temp at freeway cruise in the 105* summertime heat. 11" fans are just not enough coverage area to keep the truck cool IMO. OR are you running three of them?!

Some pics of the Torrent E-Fans on a project 2-years back (last year's pt.net calendar cover truck, I am proud to say):

http://www.allensrodeophotos.com/Steve/HPMFans/_DSC0132-wr.jpg

http://www.allensrodeophotos.com/Steve/HPMFans/_DSC0154-wr.jpg

Mr. P. :)

[Chuck L.]

I will go to the 160 stat, as I need to cut all the under hood heat I can... Fighting hi IATS, and timing losses..Building a cold air box today! [100*/45% H again.]
[How do you work around having those turbo inlets breathing rad temp air??]

Do you have/sell a GOOD quality 160* stat? Looks like I may be changing fans this winter. [Perhaps a single 16" with your controls would work??]
If you would, please, let me know what you find out with your inquiry at Alterstart.

Again, Thanks for the input!:grin:

Back under my rock....:anitoof:

[slows10]

Are the 11" fans mounted on a shroud that covers almost the whole radiator? Or are they just 2 fans mounted right on the radiator. The pics that Mr. P show look like he has a complete shroud with the fans set back from the radiator a bit. It is all the difference in the world.

[Chuck L.]

Are the 11" fans mounted on a shroud that covers almost the whole radiator? Or are they just 2 fans mounted right on the radiator. The pics that Mr. P show look like he has a complete shroud with the fans set back from the radiator a bit. It is all the difference in the world.

the fans are shroud mounted. The shroud covers the entire core, and is sealed to the edges.
Here's a pic of the core support and fans.11590

[Mr. P.]

slows10 - yes I incorporate a full shroud.

ChuckL - wow you don't have much room to work with, your radiator is only 24" wide?! Your approach is what I would have done, according to the spec sheet together those 11" fans pull 2800-CFM, a single 16" SPAL pulls 2400-CFM so you're ahead with the dual 11" fans. I have done a set of 13" SPALs in an S-10 with 28" radiator, and that was just enough to keep a 6.0L at acceptable ECTs (200-ish).

And I hear you on the CAI box, I need to make one for my truck too, my IATs are stupid high.

Mr. P. :)

[Chuck L.]

slows10 - yes I incorporate a full shroud.

ChuckL - wow you don't have much room to work with, your radiator is only 24" wide?! Your approach is what I would have done, according to the spec sheet together those 11" fans pull 2800-CFM, a single 16" SPAL pulls 2400-CFM so you're ahead with the dual 11" fans. I have done a set of 13" SPALs in an S-10 with 28" radiator, and that was just enough to keep a 6.0L at acceptable ECTs (200-ish).

And I hear you on the CAI box, I need to make one for my truck too, my IATs are stupid high.

Mr. P. :)
I am still getting the low volts reading.. Mr P, have you received any feedback from your source as to what may be going on??

On the CAI:
I built a box that's not totally sealed and not insulated. [18 ga sheet stock.] It is plumbed directly into the core support opening. The filter in now a 7" Spectre, [Like the ones on the truck turbos.]
Here are the results:
Ambient 96*/35% humidity.
Box has 1 probe, the second probe is in open under hood air.

The tests are done by driving at normal speeds from 40 to 100MPH.. [Country living has it's perks!]:hihi:

I took 8 readings, and found the difference in the 2 locations were, under hood as high as 127*, and the box temps never exceeded 102*. The majority of readings for the box were ambient,[96*], and rose to 100-102* at extended "stop lite" times. The temp dropped to ambient within 1/2 mile.

Next test is to insulate the box, and see if there's any advantage.. I doubt it, as ambient is what it is. I would suggest that the spread will drop as weather cools...

Now, it's time to hook up the a/c!:grin:

BTW, on the ect.. I added a qt of water, [system evidently had some air in it from the stat change], and used some pipe insulation to plug off the top edge of the rad @ the core support bar. ECT's did not go over 185*.

[GMPX]

There's not really much EFILive can do about the voltage PID being inaccurate. I have found that the voltage PID does track up and down when varied on a bench power supply but it never reads exactly what a DVM does.
I am pretty sure do they don't have a scaling table for the battery voltage, they certainly do for ECT, IAT etc because they are not linear in response, but battery voltage, not so sure.

Cheers,
Ross

[Chuck L.]

There's not really much EFILive can do about the voltage PID being inaccurate. I have found that the voltage PID does track up and down when varied on a bench power supply but it never reads exactly what a DVM does.
I am pretty sure do they don't have a scaling table for the battery voltage, they certainly do for ECT, IAT etc because they are not linear in response, but battery voltage, not so sure.

Cheers,
Ross

Ross,
I just completed some readings that Joe and I were discussing..
W/ KOEO:
I read the C1 #20 pin that is supplied voltage from the 20A fuse..12.61V
Same reading at the fuse.
I then checked the keyed supply pin C1 # 19..Same reading.
I then read the same pin using C1 pin 1, as the ground... Same readings.
I found no volt drop on the neg side of the system.
I then rechecked the batt.. 12.67 [It's in the trunk]

I am going to jump into the connector and test the above locations with the engine running

Engine running:
Batt 14.24
Constant power..
PCM C1 pin 20 to body grnd 14.22
PCM using C1 pin 1 for grnd 14.24

Key switched power, engine running:
C1 pin #19 to body grnd 13.60
#19 to C1 pin 1 13.62

Looks that the keyed power is about a .6V drop from constant, regardless of the ground location.

PCM PID is still reporting 12.3-12.5 v.
Might you know which voltage source the PCM gets the PID info?

I'm not really happy w/ that .6v drop at the key. Will look into it.



THANKS FOR THE HELP!

[GMPX]

PCM PID is still reporting 12.3-12.5 v.
Might you know which voltage source the PCM gets the PID info?
No I am sorry I don't know exactly what voltage source the PID is sampled from, however, I would say it's the battery supply (permanent power) rather than one of the IGN feeds. I think you'll just have to accept it for what it is though, in the end we can't change the ECM internal design, it is what it is.

[Chuck L.]

No I am sorry I don't know exactly what voltage source the PID is sampled from, however, I would say it's the battery supply (permanent power) rather than one of the IGN feeds. I think you'll just have to accept it for what it is though, in the end we can't change the ECM internal design, it is what it is.

I have no problem with that...I just thot that when a log value shows it's off from the known value, I should try to find out why. This car is assembled from a bare hulk, with LOTS of "opportunities" for me to mess something up...:grin:

I'm going to try to log the PID "control module volts, VPWR sae.vpwr", and see what it gives me....[If it's available.]

Thanks for your help!

[Chuck L.]

I guess this could go in the FWIW file:

While tracking down a goofy fuel ga reading,[ga would read <1/4 tank with KOEO, and nearly 1/2 engine running.] I decided to take a serious look at all the grounds in the entire car. The car has been on the road for <2 yrs.
The original set up had all grounds on clean metal, star washers on/between every connection, batt cables and body/engine ground straps were 1/0 cables. [Batt neg was thru cable, not the frame.] All body ground points are welded on to the body. [Dash/a/c/radio/etc.]
The clue to the grnd issues showed up when I found 22ohms, tank to batt ground.[Thru welded stud on body.] I redirected that ground to a terminal strip @ the batt. Now .2 ohms. The gauge worked better, but I was getting a .69V drop on the neg side at the tank. [In tank fuel pump.] I doubled up on the tank ground and that went to <.3V. Gauge was "closer" to real. [I knew how much I had, as I weighed the fuel when I drained the tank].
The voltmeter, nor the fuel gauge still didn't look right..A conversation with the tech @ Autometer, indicated I should look for 2 ohms or less on the -12 volt power to the gauges. I had 16.6 ohms. :nixweiss:
I then disassembled all the cables at the ft of the frame, ground all contacts, added no corrode paste, and reassembled. After the cleaning I had <2/10.
The volt meter is now accurate @ 14V with a fully charged batt, while driving. The gas ga is even closer, too.


Hope this may help others that have similar problems...MURPHY IS ALIVE AND WELL!

[joecar]

Hi Chuck, thanks for posting.

Murphy is very much alive and understands resistance and voltage drops (among other things) :)