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?

[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.]

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...

[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.]

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):





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!

Back under my rock....

[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.

[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!]

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!

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