HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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Fuel pump wired into LS computer or left on Porsche ignition circuit

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Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  Jasonscottw on Thu Sep 01, 2016 11:58 pm

So . . . Apologies if this is a 101 question, and yes, I've tried the advance search without finding an answer.
I'm running the corvette style return set up on my 5.3 conversion. I'm super close to having the car running but having a conceptual mind F!ck about the fuel pump, and probably over thinking it, BUT:
does the fuel pump need to interface/be controlled by the GM PCM, or can I leave it as is/the way it came wired into the 944 ignition? I get that there are perhaps better/higher volume pumps, but can it remain independent from the LS PCM? Many thanks . . .
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Jasonscottw

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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  sharkey on Fri Sep 02, 2016 12:05 am

i believe you can leave it wired to as factory but most rewire it to run off its own relay triggered by the gm pcm. ive read that the dme relay can be troublesome and its more reliable to wire it seperate.

sharkey

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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  Jasonscottw on Fri Sep 02, 2016 12:13 am

Thanks- guess I'm still confused, in that scenario, as to how the GM PCM would know when to call for fuel, Would it simply turn ON the fuel pump circuit whenever the GM PCM was energized ON by the stock Porsche ignition/key turn? Is there a step I'm missing?
This is where I get really really confused- any advice super appreciated-
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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  sharkey on Fri Sep 02, 2016 1:00 am

the gm computer has a switched output to turn the fuel pump on. when the key is turned on and the pcm is energized it will turn the fuel pump on for 2 seconds to prime the fuel system, then shuts it off. when the pcm detects a crankshaft signal it turns the fuel pump on.

sharkey

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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  Jasonscottw on Fri Sep 02, 2016 11:53 pm

Thanks. Any idea what pins I jack into on the PCM?

Also, right next to PCM, running into the main harness, there is a 6 pin connector labeled:
-PCM ignition
-inj2 ignition
-inj1 ignition
-coil ignition
-02 ignition
-maf ignition

Is this meant to connect to a GM key/ignition?

What do I do with it if I'm using 944 key/ignition?

Long story, but a guy that I hired to do the final wiring kept the car (and my $) for 18 months, and all that he accomplished was throwing a stand alone harness into the car. I went and grabbed the car back, but now I'm trying to make sense of his work, and the work I did a couple years ago.

The final electric has me stumped- thanks
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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  sharkey on Sat Sep 03, 2016 12:09 am

without knowing whos harness it is its tough. my educated guess says those would be switched 12v+ to those items. normally when i build a swap harness i use a fuse block and hook those to fuses and use a 40 amp relay to turn on the fuse block.

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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  Jasonscottw on Sat Sep 03, 2016 12:23 am

Thanks Sharkey- that's my guess as well. But is there a reason why all those 6 things would be separated out? Just two injectors? I guess what I'm asking is: on an LS, DO those circuits need to be triggered before other ignition events?
Like get energized in the "accessory" mode when you turn the key?
Or could it be some sort of testing set up? That probly a wacky idea, but the PCM already has its own plug for 12volt power (but maybe that's unswitched? It has two wires both labeled 12+, which is confusing me as well)

Ugh. Just wAnt to drive fast already . .
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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  sharkey on Sat Sep 03, 2016 1:21 am

the pcm has its own 12 volt constant and switched sources. the things listed will all be power going directly to those things.

inj1- that would be injector bank 1, the bank with 1,3,5,7. inj2 would be bank 2, or 2,4,6,8. both those are power supplied directly to the injectors, the pcm controls the ground side of them. each inj1 and inj2 should be fused with a 10 amp fuse.

pcm- would be switched power for the computer. the pcm has several 12v inputs

coil- this would be power directly to the ignition coils, the pcm controls a signal wire to the coils. usually its split up into bank 1 and 2, but can be run all together. 15 amp fuse.

02- this would be the 12 volt switched wire directly to the o2 sensors for the heater circuits.

maf- 12 volt switched to the maf sensor. generally id combined this with the 02 sensor heater power.

all those things can be turned on in the run position. like i said, run a small fuseblock and run these circuits to it with their own fuses. this provides better protection to the circuits and helps with diagnosing a potential problem in the future.

sharkey

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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  Jasonscottw on Sat Sep 03, 2016 4:02 am

Thanks. i get it now.
Last 2 questions:

1)Best place to pull switched power to go to fuse block? Tap into the switched power going to the starter? Or is there a more elegant way? Probly heavy gauge wire in any case? FYI Im using the stock Porsche fuse box to power everything except for the motor-

2)Is it likely that the other 2 prong connector, both labeled 12v, that feeds directly into the PCM is constant 12v? Any idea why two wires? One is red, the other red with a white stripe. I realize your flying blind w/o seeing it in person, but any thoughts?

Many many thanks Sharkey-
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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  spence on Sat Sep 03, 2016 4:20 am

A nice way to get 12 switched power is to attach the old coil wires together located by the passenger side headlight. This will then power the green wire in the 14 pin connector.

You need to find a pinout for your ecu and go though all the wires and label them. Its not hard, all the wires numbered on the ecu and the connectors are colour coded.
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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  Jasonscottw on Sun Sep 04, 2016 9:23 pm

Thanks

Did you run new wire back to fuel pump, or did you splice in somewhere else? I've been trying to find the green/black wire under the fusebox, but there seem to a few in the vicinity of the fuel pump fuse and relay-
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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

Post  spence on Mon Sep 05, 2016 5:51 am

The fuel pump wire is not in the fuse box. Its in the 14pin connector. Its pin 4 and its green/black and goes right to the fuel pump.

Search... All your questions have been covered a million times
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Re: Fuel pump wired into LS computer or left on Porsche ignition circuit

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