Location of LSx /Gen III PCM 

                                               

                                                  CHEVYTHUNDER.COM 

 

This document is being provided to help facilitate your decision in providing the most accurate information in the purchase of your LSx-Gen III engine harness.  Foremost, is to provide  me with the the measurements pertaining the the length of the harness to install the PCM (power train control Module) in a location on your vehicle that is convenient to you. 

There are three major  factors in relation to this, the size of the vehicle and available space needed to install the pcm, and the ease of installation. Smaller vehicle such as compact trucks and cars, the length of the harness as measured from the engine center line to the pcm connector ends, wont require a long length, such as the standard of 50 inches (127 cm), this may be shorten considerable and again, this will also depend on the final location of the pcm. Vehicles such as the 1970-1981 Camaro's, Nova's and Malibu's are on the borderline in the harness length and for the most part the standard harness works fine. large vehicles such as trucks may or may not need to have a longer harness and again, this all depends on pcm location. 

The following pictorial will help assist you in your decision and will result in a neater installation.

                    

First, start from the centerline of the rear of the engine and measure from that point and be sure to allow for any bends or turns around any obstacles you may have to encounter.  

The best type of measuring tape should be flexible, such as the type used by sewing hobbyists

Hold the end of the tape in place with a piece of  tape at the engine centerline (reference point "A"), and when routing the tape, hold it is several places to keep it from slipping and skewing your measurement. Add 6 inches (approx. 15 cm). 

 Mounting of pcm on the R/H or L/H inner fender well. 

This will work only if there is enough hood clearance between the top of the pcm and the hood. Must allow at least 1/2" (13 mm). The harness wiring must not be routed along any high power or ignition wiring such as spark plug wires. Do not run within 2 inches (50mm) if this cannot be avoided. Avoid parallel runs along other wiring. The pcm must be mounted with the connector ends facing down. 

The standard length harness (50 inch-127cm) is suitable to mounted the pcm on either fender well. If you need a shorter or longer length, this must be specified when purchasing the harness. You must specify which side you plan to mount the pcm when ordering the harness.

 Mounting of the pcm under dash

WARNING: Check the location of the opening to insure it will not damage any wiring, accessories or other critical automotive functions BEFORE drilling and cutting!

NOTICE: Running the wiring through the firewall will require, the minimum of a 2 inch  (50 mm)  opening to pass the pcm connectors through to the passenger compartment. the opening must be clean and filed to make it free of sharp edges and burrs.

After you have insure the location of the opening is in a un-obstructive area, you can run your flex tape to get the length of harness you desire. 

The wiring must be protected with a specially designed grommet for wiring harnesses. This can be obtained from most major automotive suppliers.  Do not just wrap the harness with tape to create a "bulge" when it passes through the firewall.

Mounting the pcm under the dash requires that you investigate to make sure there is enough room to the installation with a factory retainer or with custom mounts.  The approximate  dimensions of the pcm is as follows with the terminal connectors installed: 8.5" x 9 " x 3" tall ( 212x225x75 mm). This is without the mounting bracket which will add anywhere from 1/2" to 3/4" (13-19mm) to the sides and up to 1 inch  (25mm) to the height.

The standard length harness will cover most installations, but if you are installing in a smaller vehicle, you may desire a shorter length to accommodate your set up and make for a neater, cleaner appearance.  This must be specified when purchasing the harness.

The pcm can be mounted in any position as it is not normally subject to entry of water. 

When mounting the pcm on the drivers side, it must not interfere with the automotive functions such as the movement of the brake or accelerator pedals or the movement of the steering wheel.

 Mounting of the pcm under seat

WARNING: Check the location of the opening to insure it will not damage any wiring, accessories or other critical automotive functions BEFORE drilling and cutting!

NOTICE: Running the wiring through the firewall will require, the minimum of a 2 inch  (50 mm)  opening to pass the pcm connectors through to the passenger compartment. the opening must be clean and filed to make it free of sharp edges and burrs.

After you have insure the location of the opening is in a un-obstructive area, you can run your flex tape to get the length of harness you desire. 

The wiring must be protected with a specially designed grommet for wiring harnesses. This can be obtained from most major automotive suppliers.  Do not just wrap the harness with tape to create a "bulge" when it passes through the fire

Mounting the pcm under the seat should be an option only after it is determined that under dash or under hood installation is not desired or if it is just totally impractical.  Under seat location is only practical if there is a minimum of 3 inches and only if it does not interfere the the adjustment of the seat, either manually or electrically operate.

Routing of the harness must be either on the edge of the transmission tunnel (reference "C" above) or between the door and seat (reference "D" above). The harness must be installed under the carpet and must not be ran in the area of the foot well.

NOTICE: Maximum length for under seat pcm mounted harnesses is 70  inches (182 cm). Take this is consideration when measuring and location of harness passing through firewall.

Mounting of the fuse block

The mounting of the fuse block must be done in an area that is free from any chance of it being damaged. 

DISCLAIMER: It is the responsibility of the reader to follow proper installation procedures and practices. Although care has been insure that basic procedures are included, specific component design, mechanical and electrical procedures, and the qualifications of the reader are beyond the control of the author, therefore the reader assumes all responsibility, and the author is relieved of any damages, whether indirect, consequential, including but not limited to personal or property or any other damages arising out of use or misuse of any information, or for any omission of information.

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