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1fast72nova
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 Posted: Mon Oct 19, 2009 6:47 pm Post subject: GM TBI how important is.... |
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How important are the MAT, Coolant temp, TPS and MAP sensors?
I know the O2 can be deleted with little effect.. how about those?
how about running a variable resistor in place of/instead of the MAT and coolant sensors, would that give any manual tuning latitude?
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dieselgeek
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| Posted: Mon Oct 19, 2009 7:45 pm Post subject: Re: GM TBI how important is.... |
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| 1fast72nova wrote: | How important are the MAT, Coolant temp, TPS and MAP sensors?
I know the O2 can be deleted with little effect.. how about those?
how about running a variable resistor in place of/instead of the MAT and coolant sensors, would that give any manual tuning latitude? |
Having the sensors is a good idea - having them unplugged is a BAD idea. Speed Density, AND MAF systems, use the "ideal gas law" to calculate fuel mixture. It's more than just a few jet sizes too.
If you can't run the actual sensors (I see absolutely zero reason for this, however), you would want to use resistors to "simulate" the warmed-up temp of the engine. At that point, you have a really complicated carburetor.
Here's a snippet from the "MegaManual" which is the most widely used EFI guide anywhere on the planet:
However, when EFI came along (in the mid 1980s) temperature sensors were used to determine the instantaneous fuelling and spark advance in some cases, and reducing noise became essential. The manufacturer's solution was 'two-wires' sensors that use a dedicated ground return to the ECU (instead of the much more noisy high current ground). MegaSquirt® controllers adopt a similar scheme.
On a GM TBI computer, as I stated before, the temp sensors can cause as much as a 150-200% change in fuel. If the sensors are not connected, the computer thinks that the engine block temp, and the air temp, are literally at -40* F. The computer enriches the fuel mixture as much as 200% (this is GM data).
The engine *might* run on a warm day, but it won't run good. You also lose your barometric corrections.
Now for the MAP sensor - forget it. It's absolutely necessary. It's the only way the computer knows how much "load" is on the engine. *some* speed-density systems out there, have a backup "Alpha-N" mode which relies on the Throttle Position Sensor next - not compensating for load in any way, you now have a "mechanical" style fuel injection system that might get you home.
I highly suggest reading the Mega-Manual (www.megamanual.com) to understand how a computer determines how much fuel the engine needs. You don't have to read the whole thing, but it's a good read.
-scott |
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1fast72nova
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| Posted: Mon Oct 19, 2009 8:08 pm Post subject: |
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so the MAP sensor is the only requirement?
I suspected as much but wasn't sure. .. and a really complicated carb is all FI is anyways ;p
but i have a crazy idea in mind anyways 
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dieselgeek
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| Posted: Mon Oct 19, 2009 8:15 pm Post subject: |
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| 1fast72nova wrote: | so the MAP sensor is the only requirement?
I suspected as much but wasn't sure. .. and a really complicated carb is all FI is anyways ;p
but i have a crazy idea in mind anyways |
MAP and RPM.
but shit, why even run the MAP? I already know how your idea is gonna run, you might just consider hooking the injectors up to switched ignition and ground. I'm sure it'll "run" about the same. |
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1fast72nova
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dieselgeek
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| Posted: Mon Oct 19, 2009 8:51 pm Post subject: |
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| 1fast72nova wrote: | | wrong, guess again... |
Err, whose guessing here? |
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1fast72nova
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| Posted: Mon Oct 19, 2009 9:30 pm Post subject: |
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you are b/c you think I'm doing something with injectors...
which I may in the future but that's not what this crazy idea is...
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1fast72nova
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| Posted: Mon Oct 19, 2009 9:45 pm Post subject: |
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anyways, while i have an EFI brain to pick...
the map sensor. under idle/high vacuum conditions it's going to reduce fuel and under load/low vacuum it's going to increase fuel...
by approx how much? how is that fuel map mapped?
do you have an example i could look at?
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spidergearsman
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| Posted: Tue Oct 20, 2009 9:02 am Post subject: |
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installed a zzz 350 in a customer's 88 formula
the L79 cam had crap for vacuum , installed a 25 ohm resistor in the signal wire
worked good until he couldn't take the piston slap
had a spare truck 350 short block , he was happy after that
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1fast72nova
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| Posted: Tue Oct 20, 2009 10:37 am Post subject: |
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ok, next to last question... everything is sounding good so far.
can I trigger the brain to fire the injectors using the tach output off an HEI?
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dieselgeek
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| Posted: Tue Oct 20, 2009 10:38 am Post subject: |
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| spidergearsman wrote: | the L79 cam had crap for vacuum , installed a 25 ohm resistor in the signal wire
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which signal wire? one of the temp sensors? |
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1fast72nova
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| Posted: Tue Oct 20, 2009 6:11 pm Post subject: |
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| 1fast72nova wrote: |
can I trigger the brain to fire the injectors using the tach output off an HEI? |
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spidergearsman
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| Posted: Tue Oct 20, 2009 6:17 pm Post subject: |
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the ignition module triggers it from the pulses of the pickup coil
sine wave
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