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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Quick engine / alt circuit question

Post  endrnet on Sat Apr 10, 2010 7:43 pm

I'm trying to test fire my motor, make sure it's going to fire and run before I commit to lacing up all the various systems that are a pain to remove.

I do not have the front accessory drive belt on because I do not have the water/ps pump tubing ready and full of fluids.

It cranks. It won't start. Fuel rail remains empty... guessing no fuel pressure.

I'm wondering if the blue wire from the porsche ignition that splices into the alternator signal wire is looking for current from the alt to trip the dme/fuel relay.

If that "wondering" is right, I further wonder if I can fool it into starting without the alt by bridging the signal wire to batt+.

Can anyone confirm this? Or perhaps just tell me not to worry about running the water/steering pumps without fluid if it's only for a minute? (obviously I won't run it long without coolant anyway).

Thanks for any help!
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Re: Quick engine / alt circuit question

Post  Admin on Sat Apr 10, 2010 8:11 pm

Can't confirm that, But why not just run a hot wire to the pump. One wire from the battery to the pump plug would take all of about 3 minutes. Assuming you are not using the factory dme relay for anything other than the fuel pump.

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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sat Apr 10, 2010 9:09 pm

On another forum, I read that fuse #34 must be pulled. Wiring is a little different than indicated in the manual.

Here is the thread: Look at the 5th post....
[You must be registered and logged in to see this link.]

Dont know if this helps at all...

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Re: Quick engine / alt circuit question

Post  gt1scca on Sat Apr 10, 2010 9:14 pm

That is a wiring detail for a Renegade harness, installed in a 1986 Turbo...
The fuse info is specific to that harness.

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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sat Apr 10, 2010 9:30 pm

Good to know. I did not pick that up in the thread.

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Re: Quick engine / alt circuit question

Post  endrnet on Sat Apr 10, 2010 9:57 pm

NOTE: This is for a 1987 NA

I found it.

Pull relay G5.

Bridge 30 & 87b (marked on underside of relay very clearly).

That runs the fuel pump, regardless of key position.

Nice low-voltage way to turn it on.

Still won't start though. I guess I gotta check for spark, etc, sigh. That HP tuner kit is looking better all the time.
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Re: Quick engine / alt circuit question

Post  gt1scca on Sat Apr 10, 2010 10:05 pm

Aron,

"Hot-wiring" the pump temporarily from the battery will be fine. You may damage the alternator if you wire it without the stator turning.
Bridge 30 & 87b (marked on underside of relay very clearly)
That will by-pass the DME relay - same effect as a hot-wire.

How long has that fuel pump been sitting?
944 pumps tend to die when they sit in gelled gas too long.

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Re: Quick engine / alt circuit question

Post  endrnet on Sat Apr 10, 2010 10:11 pm

My guess is about a year. After I did the relay hotwire, there was *clearly* fuel pressure in the rail.

Good to know about the alt.


Obviously I have some other problem.

There is one lonely sensor on the top/back of the block, vertical, round, 3 pins, my camaro harness has nothing for it. Hm. Sometimes Google doesn't have all the answers... No idea what it is, hope it's not important.

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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sat Apr 10, 2010 11:02 pm

the oil pressure sender? Round cylinder top of block at the rear, about three inches tall?

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Re: Quick engine / alt circuit question

Post  gt1scca on Sat Apr 10, 2010 11:11 pm

Idea

LS PCM requires oil pressure reading to start, IIRC.
Forgot about that...

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Re: Quick engine / alt circuit question

Post  endrnet on Sat Apr 10, 2010 11:34 pm

It's maybe 1" tall, but my motor is a 2006 L33, so perhaps they made it smaller.

I thought oil pressure was only read to feed the dash idiot lights... although it would make some logical sense for it to want OP to start. Wonder where my connector is on this f-body harness.

Thus far the only mod to my harness is feedin the pinks with ignition power and splicing with alt sensor.
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Re: Quick engine / alt circuit question

Post  gt1scca on Sat Apr 10, 2010 11:57 pm

Also check vacuum lines, especially at the MAP sensor.
Sounds crazy, but the LS must have sensor info to run...

"When the ignition switch is turned to the "ON" position (before engaging starter), the PCM energizes the fuel pump relay for two seconds allowing the fuel pump to build up pressure. The PCM first checks speed density, then switches to the Mass Air Flow (MAF) sensor. Engine Coolant Temperature (ECT) , Throttle Position (TP) , and Manifold Absolute Pressure (MAP) sensors are also used to determine the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36°C (-33°F) to 14.7:1 at 94°C (201°F) running temperature. The PCM controls the amount of fuel delivered in the starting mode by changing how long the injectors are energized. This is done by pulsing the injectors for very short times...

When the engine is first started, and engine speed is above 400 RPM, the system begins "Open Loop" operation. The PCM ignores the signal from the HO2S and calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP, and TP sensors."

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Re: Quick engine / alt circuit question

Post  gt1scca on Sun Apr 11, 2010 12:12 am

Back to the first post for a second...

Has the PCM been flashed? VATS?
If VATS is still enabled in the PCM, you'll never start it.

I just assumed, but if VATS hasn't been disabled, there's the root of all evil.
No power to injectors, fuel pump...

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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 12:16 am

Got my pcm from sparepcm. I definitely requested vats delete and it's on the paperwork...


EDIT:

Wouldn't fuel pump be powered by porsche relays? Am I missing some major wiring? Note the only mods I made to harness, the rest of it is unused atm.
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Re: Quick engine / alt circuit question

Post  gt1scca on Sun Apr 11, 2010 12:25 am

endrnet wrote:I'm wondering if the blue wire from the Porsche ignition that splices into the alternator signal wire is looking for current from the alt to trip the dme/fuel relay.
This is still a possibility if VATS is disabled. Only safe way to know is belting-up the accessories. Also, if the alternator doesn't spin, it won't produce an output.

EDIT:

Another Q (or 2): Is the fuel enable wire (blue, I think) from the LS harness wired to the DME relay? How is this section wired exactly?

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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 9:41 am

Nope, there's a bare blue wire hangin off the pcm though.
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Re: Quick engine / alt circuit question

Post  gt1scca on Sun Apr 11, 2010 10:22 am

Go here...
[You must be registered and logged in to see this link.], to find pinouts for the 5.3L, then you can track down that blue wire. Pinouts on the 5.3 are similar to other diagrams, but the PCM plugs may be configured a little differently.

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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 10:32 am

Even though it's a 5.3l L33, it's setup to run like a fbody... the computer did not come with the motor.

I spent the last 10 minutes tracking down the pins on my disconnected wires and looking up their corresponding function on ls1tech

BLUE

blue 42 (fan1 relay)
orange 20 (pcm batt)
orange 57 (pcm batt)
green 58 (serial data)

RED

white 10 (tach)
yellow 33 (fan2 relay)
brown 46 (idiot light "engine malfunction")
red 9 (fuel pump relay)


I wonder if I just need to give the orange wire 12v+ directly from battery...
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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 11, 2010 10:51 am

The only other thing that is at teh back of the back of the block behind the intake manifold is the crank position sensor. Mine is kind of short and flat but it is a three pin connector. if thats not hooked up.....

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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 3:21 pm

Well my voltmeter tells a new story now.

While I can force the pump to run by bridging 30/87b in the dme relay, leaving that relay out deprives the pink start/run power wires of 12v, which the pcm needs.

Seems to me that the right solution is to wire the fuel relay control from the pcm to the proper wire in the porsche fuse block, but I don't recall that connection being mentioned previously. I probably just overlooked it.

I'm looking at the porsche manuals, but I'm not a wiring diagram guru. Thoughts?

It's probably just a single wire under the dash...
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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 4:54 pm

Hmm, pin 5 on the 14 pin plug from the firewall/drivers plug, when grounded runs the fuel pump when key is in "run/start" position.

Poor man's solution:
Ground pin 5.

Correct solution:
Porsche wants ground to run the fuel relay and LS1 PCM wants to provide 12v+ to run the fuel relay, so buy a relay and run red pin 9 from PCM through it, and pin 5 from porsche 14 plug through it for ground.

Only difference is the pump will run more than it otherwise would if you leave the key in RUN without the engine started.
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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 6:13 pm

Grounding the porsche pin 5 on the drivers firewall connector did it. Engine started *right* up. Seems a little rough but it definitely wants to go. It sounded like I let a monster out of a cage.


Twisted Evil
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Re: Quick engine / alt circuit question

Post  Bluemach1 on Sun Apr 11, 2010 6:40 pm

excellent! Did you figure out what that sensor was that was not connected?

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Re: Quick engine / alt circuit question

Post  endrnet on Sun Apr 11, 2010 7:02 pm

Yes the unused vertical sensor behind intake is the GM oil pressure sensor. Next to it on the block is the cam position sensor and the crank position sensor is just above the starter.

I'm using aftermarket gauges, and the PCM doesn't seem to care about oil pressure, oddly enough, so I'm going to leave it alone.

My aftermarket electronic gauges are setup below the stereo where the "pocket" was.

Sunpro Oil Pressure sensor is in one of the unused NPT fittings of my oil filter relocation bracket and it registers 20-25psi during cranking. Coolant temp sensor is going to be in an in-hose fitting. For the voltage gauge, I just tapped the stereo lead since it's right there.
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Re: Quick engine / alt circuit question

Post  gt1scca on Sun Apr 11, 2010 7:57 pm

endrnet wrote:Grounding the Porsche pin 5 on the drivers firewall connector did it.
You basically did what the DME relay is designed to do.
Congrats, I think.

More than one way to peel dat unyun...

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