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Slippery Slope Expert
 
Steam Driver's Avatar
 
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Aem 30-300

I am wanting to install the AEM 30-300 wife-band O2 sensor and meter in my SC which is going to be EFI. However the O2 sensor harness is about six feet too short.

The installation instructions for the unit say to avoid cutting or lengthening this harness. Is this a hard and fast rule? If so, why? Accuracy, reliability? I am pretty sure I have seen this unit used by people in this forum, so how did you get around this?

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Old 06-04-2018, 12:10 PM
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Steam, I can't answer your question directly but recall that when I installed my AEM gauge a coulle of years ago, they had an extension harness available for reasonable money. I believe I bought the gauge, extension, mounting "cup" and bracket from Summit (i don't believe Pelican sells that stuff because it's pretty generic). Best of luck, John/CT.
Old 06-04-2018, 12:24 PM
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You can extend the wires, it will be fine. Just make sure to use appropriate wire gauge size, especially on the heater circuit (pins 3 & 4 on LSU 4.9 connector). Extend the gauge harness side, not the sensor wiring itself. The instructions do mention on page 12 that you can extend the wiring, just make sure to use appropriate wire gauge for length (20 AWG minimum recommended).
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1976 911S Signature Edition - 3.2SSt (JE 98mm 9.5:1 pistons, 964 Cams, ARP Rod Bolts, Big Port SC Heads, 3.2 Carrera Manifold, ID725's, B&B Headers, TS HyperGate45 Gen V, TS RacePort, BW S360, AEM Infinity 506, E85)
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Last edited by '76 911S 3.0; 06-04-2018 at 01:26 PM..
Old 06-04-2018, 01:22 PM
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I just extended my 4.2's with some home made splices,
for the 4.9 I just had these chaps, Ballenger make me up a 36" extension (matching plugs on both ends) for a fair price
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Old 06-04-2018, 01:53 PM
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I inquired of AEM on this and they said the harness apcan be shortened/extended as needed. Use 20 gauge wire, good crimps.
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Old 06-04-2018, 03:45 PM
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whata ya think Jayson,

crimp or solder ?
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Old 06-04-2018, 04:04 PM
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Always crimp. Soldering makes the wire rigid and will become brittle over time. A good crimp will last the lifetime of the harness. I know there will be other people with other schools of thought on this one that will more than likely chime in; however, I have built motorsport (milspec) harnessing for the last 6 years and have never once soldered wires together (unless a factory connector called for it like the 14 pin connector in the engine compartment). I have also never had a failure of a crimp after it passed the pull test.
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1976 911S Signature Edition - 3.2SSt (JE 98mm 9.5:1 pistons, 964 Cams, ARP Rod Bolts, Big Port SC Heads, 3.2 Carrera Manifold, ID725's, B&B Headers, TS HyperGate45 Gen V, TS RacePort, BW S360, AEM Infinity 506, E85)
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Old 06-04-2018, 04:12 PM
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I prefer non-insulated splices like these (with adhesive lined heat shrink on them to thwart water ingress):



And for the garage enthusiast, a crimping tool like this will suffice:


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-Jayson
1976 911S Signature Edition - 3.2SSt (JE 98mm 9.5:1 pistons, 964 Cams, ARP Rod Bolts, Big Port SC Heads, 3.2 Carrera Manifold, ID725's, B&B Headers, TS HyperGate45 Gen V, TS RacePort, BW S360, AEM Infinity 506, E85)
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Old 06-04-2018, 04:17 PM
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Quote:
Originally Posted by Steam Driver View Post
I inquired of AEM on this and they said the harness apcan be shortened/extended as needed. Use 20 gauge wire, good crimps.
Good to know.. i have the long harness, and have about 4 feet of it coiled up under my dash.
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Old 06-04-2018, 04:34 PM
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Your experience is good to hear Jayson, i was not in the mood to apply old naval mil-specs to the task.

What about the wire type used to increase the harness or wire lengths.
Any recommendation on number of strands, bare copper vs tinned,
insulation type, etc. Maybe a easy to find Mil, Sae, or UL, CSA, whatever
you can suggest. Cant' find a Radio Shack next door any more, and Home Deposit is slim pickings.
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Old 06-04-2018, 06:38 PM
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Quote:
Originally Posted by '76 911S 3.0 View Post
Always crimp. Soldering makes the wire rigid and will become brittle over time. A good crimp will last the lifetime of the harness. I know there will be other people with other schools of thought on this one that will more than likely chime in; however, I have built motorsport (milspec) harnessing for the last 6 years and have never once soldered wires together (unless a factory connector called for it like the 14 pin connector in the engine compartment). I have also never had a failure of a crimp after it passed the pull test.
ALWAYS CRIMP but there is a different reason.

The O2 sensor actually pulls in atmospheric air through the multi-strand core of the wire! If you solder it you will plug the wire up.
I first thought the explanation was bull until someone gave me a link to a document on Bosch's website where they explained exactly why you must crimp.
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Old 06-05-2018, 06:57 AM
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Weird, just installed the same model and the harness was plenty long. I installed the sensor way back in the muffler inlet and ran the harness to the the square corner of the engine bay / torsion tube, over to and through the tunnel and all the way up to the dash. Harness tucked up nice and out of the way and still plenty of length.
Old 06-05-2018, 01:33 PM
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Not weird depending on the final location of the guage (under IP off center, center console, A-pillar or ?).

If you purchase an advertised "extension" harness, make sure it's an extension (male and female connectors) and not just a slightly longer replacement sensor-to-gauge harness.

S

Last edited by 911pcars; 06-05-2018 at 05:26 PM..
Old 06-05-2018, 05:23 PM
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Quote:
Originally Posted by Quicksilver View Post
ALWAYS CRIMP but there is a different reason.
The O2 sensor actually pulls in atmospheric air through the multi-strand core of the wire!
Hmmm. That's interesting.
I have a Bosch 4.9 LSU in my hand. Its a 5 wire. I'm trying to figure out how air is pulled in through any of the PTFE coated stranded wires.

I was reading Bosch's Tech spec Y 258 K01 020-000e and they refer to the following in terms of air reference:
The PTFE formed hose is part of the reference air volume of the sensor and
must be kept sealed and undamaged. For installation, the minimum bending
radius of the hose must be 20mm (for long PTFE hose) resp. 12mm (for short
hose). Keep the PTFE formed hose away from sharp edges and avoid contact/
friction with frame/engine assembly.
The first fixing point for the cable to the car body should be 200mm to
400mm after the end of the PTFE formed hose, depending on movement of the
exhaust system.
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Old 06-06-2018, 10:16 AM
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Routing harness





I’m installing the 30-300 in my ‘86 and wanted to share some pictures of how I ran it into the cabin through the acces for the main harness. I found that a 1/2” piece of PEX worked perfect. As you can see in the picture, I cut a piece into a taper and sanded it smooth to prevent damage to the existing harness. I lubed it with Goo Gone, which is kinda oily. It slid in fairly easy. I made sure the taper was turned away for the harness to prevent it damage. You may have to restore the shape of the PEX to get the plug to fit, but it was very easy. This leaves me with plenty of harness length.
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Last edited by 86911cab; 01-08-2020 at 08:17 AM.. Reason: Spelling
Old 01-08-2020, 08:10 AM
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Quote:
Originally Posted by Quicksilver View Post
ALWAYS CRIMP but there is a different reason.

The O2 sensor actually pulls in atmospheric air through the multi-strand core of the wire! If you solder it you will plug the wire up.
I first thought the explanation was bull until someone gave me a link to a document on Bosch's website where they explained exactly why you must crimp.
This is NOT TRUE. The oxygen does not go up the multi strand core.

I prefer solder. Crimping can result is oxidation between dissimilar alloys.

Soldering stiffens wire??? So what!! This is left over from Aerospace usage where there is lots of vibration.

I have seen this on standard O2 sensors where the voltage is less than 1 volt. In the 9-5 Saabs there is a ground junction near the ECU for the O2 sensors that fails even though crimped and potted and heat shrink tubing protected from the factory. The brass crimp and copper can eventually corrode.
This is a real head scratcher with O2 error codes that changing sensors does not cure. The solution is to take the junction out and solder it and use shrink tubing insulation.

I have done many of these. Soldering has lasted forever. I would not dare crimp that connection after crimping from the factory has already failed.
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Last edited by dicklague; 01-08-2020 at 09:59 AM..
Old 01-08-2020, 09:50 AM
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While I am on my soap box, the AFR instrument I love is the Daytona-Sensors WEGO IV. This is a real MIL-spec unit that has great features and will function for years.

I have had one in my 1973 911 for over 10 years and love it. AND it has available a
12 ft extension part with real sealed connectors. You know like Aerospace quality.

Pelican used to carry them. You can find them at Wego IV AFR INSTRUMENT by Daytona-Sensors - IG3TECH

This is hardware you can rely on.

Best part is data storage of up to 2 hours of running you can download through usb to free software.

Just my 2 cents worth. It sure helped me tune my MFI!! And it is rock solid RELIABLE.

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RGruppe #79 '73 Carrera RS spec 2.7 MFI
00 Saab 95 Aero wagon stick
01 Saab 95 Aero wagon auto
03 Boxster
90 Chevy PU Prerunner....1990
Old 01-08-2020, 10:08 AM
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