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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Quick engine / alt circuit question

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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 11, 2010 9:52 pm

So is the DME relay bad?

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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 10:17 pm

I think the dme relay is fine since it's properly powering the pink LS1 wires during start/run. I also think the porsche computer provides ground to the dme relay for the fuel relay (G5 / DME relay is a special double relay of some sort). LS1 pcm wants to provide 12v+ to a relay for the fuel pump so a direct hookup would fry things, so something else has to be worked out.

Looks like this is an area where people solve the problem in different ways.

Here's one take:

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Here's another (by 944lt1, although he doesn't mention which wire, it's probably a more elegant solution than grounding pin5):

944-lt1's solution
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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 11, 2010 11:36 pm

OK...
Pin 5 on 14 pin "Fuel Pump Relay"

And

Pin 9 on RED Plug C2 "Fuel Pump Relay Control"


These do not get tied together?

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Re: Quick engine / alt circuit question

Post  endrnet on Mon Apr 12, 2010 12:41 am

If I understand my little adventure this weekend, no do NOT directly connect those two wires.

Looks like there are three options:
1) Roll your own relay for pcm red pin 9, plus one of these:
1a) relay gives GND to firewall plug pin 5
1b) relay gives fused 12v+ directly to fuel pump

This has the advantage that the fuel pump is on when the PCM thinks it's on. Elegant, but you're hacking more electronics together.

2) Simply GND firewall plug pin 5, permanently.

This has the advantage that it's cheap, easy, and uses existing porsche wiring. Pump is on when key is in RUN. Not as elegant, but bulletproof.

3) Run the pcm red pin 9 directly to a wire under the dash that wants 12v+ instead of gnd to turn on the pump. Dunno what this would be.

This would have the advantage of accomplishing #1's elegance without additional relays/fuses if you're confident digging under the dash and you want to retain the stock pump behavior.




Leaving your car in RUN without the engine started, turns on all kinds of stuff all over the car, so why not the fuel pump too. I'm going to leave mine this (#2) way and see if I find a reason to change it later.

pirat
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Re: Quick engine / alt circuit question

Post  gt1scca on Mon Apr 12, 2010 2:54 am

You could splice into the oil pressure sender wiring, allowing the pump to only operate when oil pressure is present. Not only would this reduce the risk of a leak-induced fire, but would protect the engine internals if oil pressure went South...

Yet another option.

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Re: Quick engine / alt circuit question

Post  Bridar on Wed Apr 14, 2010 9:24 am

I strongly suggest controlling the Fuel Pump through the PCM. This is for safety reasons. The PCM is designed to: 1) stop the fuel pump if the engine does not start (e.g....broken fuel line or injector that could ignite or explode), and 2) stop the fuel pump if the engine has been running but suddenly stops (e.g....if the car is in a wreck you do not want to have fuel pumping out through a broken fuel line!). You will not have this feature if you only use key switch control, though the idea of linking the oil pressure switch to a relay may work as well. But why go through all that when the wiring already exists, you just have to reterminate a few wires?

BTW--The LS1 will still run without VATS, but only for 20 seconds to maybe 1 minute. I learned this from a bad VATS Bypass module. The engine ran fine once it was diagnosed and replaced.

I chose to use the origninal DME/Fuel Pump Relay since this would provide the cleanest looking approach. If you dont want to use that relay you could always hook two relays together, the first controlled by the ignition switch, the second controlled by the PCM. You may be able to get by with one relay, but I wasn't sure if the PCM output was already key controlled or not. The PCM signal is also controlled by the software, so I felt safer to have redundancey built in through the keyswitch. If you do not trust your old DME Relay, just carry a jumper in the glovebox and cross terminal 87b with terminal 30 for a temporary fix. Just remove it after you are home since the pump will run all the time even with the key switch off. Here is how I wired mine:

update on 5/7/10: I updated this image to provide further clarification that the design is for a 968 and that the correct wiring for all models can be found by cross referencing from the Electrical Pin Out Diagrams that I have placed in my photo gallery. I also corrected the 85b wire to BK/GR (was YE/BK) [the wires sometmes change to a different color as they enter the central fuse box].

Image updated on 5/7/10:
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Last edited by Bridar on Fri May 07, 2010 6:32 am; edited 1 time in total (Reason for editing : picture corrected.)
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Re: Quick engine / alt circuit question

Post  endrnet on Fri Apr 16, 2010 5:16 pm

I have to admit that the image of the car wrapped around a tree with the pump emptying the tank onto the ground is a pretty compelling safety argument to relay the fuel pump through the pcm.

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Re: Quick engine / alt circuit question

Post  endrnet on Fri Apr 16, 2010 5:42 pm

Is there a reason that you do not re-use the relay to power the pcm? It powered the porsche computer, why not the gm computer? Not enough amps? Seemed to run mine ok for the few seconds I had it running.
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Re: Quick engine / alt circuit question

Post  Bridar on Fri Apr 16, 2010 6:08 pm

The only reason I didn't use the DME relay to power the GM PCM was because I didn't know precisely how many amps it would draw, and for me long term reliability is paramount. I supose you could measure the current draw and see.
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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 18, 2010 12:09 pm

OK....

Bridar's modification diagram does not match the manual.
PIN# - MANUAL - BRIDAR
Pin 3 - to PCM Pink (12v SW) - not used
Pin 5 - not used - connect to ground
Pin 7 - not used - Connect to C101H

Questions:
1) I believe bridar is a 968. Does the electrical translate directly to a 944 turbo?
2) Should I ground Pin 5 as indicated?
3) Should I run and connect Pin 7 to C101H at connector?
4) Bridar's switched power: is this not the same as the manual PIN 3??
5) If switched power is different than Pin 3, Bridar has switched power from ignition going to C101D. This is PIN 9 on the RED PCM connector. is the idea to run the wire directly from the PCM in the interior or is the intention to actually run it to the C101D connector under the hood?

I am getting a little twisted up on the electrical. I have never done it before and not sure how to trouble shoot it. Having this definitively nailed down would be great. Just when I think i have it something new pops up.

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Re: Quick engine / alt circuit question

Post  Arthropraxis on Sun Apr 18, 2010 3:11 pm

The 968 must be different, I can't find the 14 pin connector in the passenger side footwell. I can find 2 but they are both 12 pin if I remember correctly.
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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 18, 2010 3:22 pm


As far as I know, this relates to the 14 Pin under the hood.

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Re: Quick engine / alt circuit question

Post  Arthropraxis on Sun Apr 18, 2010 4:55 pm

If you read his writeup in the gallery he references the firewall 14 pin and another under the glovebox in the passenger side footwell. The firewall connector on the 944 has the AC request signal, on the 968 it is in the passenger side footwell. So, the wiring for the 944 and the 968 have some differences. You should be able to follow how he diagrams wiring it but the wires will come from different connectors 944 vs 968.
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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 18, 2010 5:23 pm

Gotcha. I am only referring to the DME relay that was shown in the above post.

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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 18, 2010 7:59 pm

After the lecture on safety (which convinced me, he's totally right) I *am* going to ground pin5, but through a relay controlled by the PCM.

Since I had to break down and buy aftermarket relays, I'm going to re-run the power for the PCM directly from the battery through my own fuse for orange, and through the same fuse via a relay controlled by the 944 DME relay for pink. I'm planning to use a 10A or 15A fuse for the PCM and 14 AWG wire.

That'll preserve the original intent of the 944 wiring as much as possible, while improving on the safety issues around the fuel pump.

While I'm at it, I'm planning to install a hidden kill switch for the fuel pump signal wire from the PCM. Sortof my own home-brew manual-VATS.

Now I just need to find that tach wire...
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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 18, 2010 10:11 pm

Doesnt bridard's DME Relay wiring diagram shown resolve this?

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Re: Quick engine / alt circuit question

Post  Bridar on Fri May 07, 2010 6:46 am

In an effort to try to alleviate some of the confusion I inadvertently created by posting my fuel pump relay hook ups for my 968, I have created a cross reference for the Porsche wire harness connections between the DME/Engine harness and the body harness. This is a large excel file that I converted to 6 jpg images and placed in my gallery. This should allow us to communicate to each other when referencing wire colors across year models. Note that the 968 uses only the T1 and T21 connectors. Very early year model cars may not even have connectors for some particular wires that you may need to splice into, such as cooling fans, AC request, etc. But in general the cross reference that I have created should be enough for you to get the car running with hook ups for the tach, fuel pump, oil pressure, water temp, etc.

It would also be helpful if each of us would put the year model of their car, their swap engine, and swap engine type in their profile. Porsche changed their wiring a little almost every model year so one can get messed up if they try to copy another's wiring method directly. When in doubt--consult the wiring schematic!

Hope this helps to clarify some things.
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