Optical Sensor Filter Harness

[rnash4]

Would like to get this forums opinions on the optical filter sensor harness (aka noise suppression harness) found on the 1994-95 6.5s. Did a search but didn't find much. My '95 still has this harness installed but I was operating under the assumption that if if aint broke, don't fix it. It doesn't seem to be causing any problems, but the general consensus on some other forums is to take if off and ****-can it upon sight. AFAIK the 94-95 years were the only ones to have this installed. Some say the OBD-1 system needs it, but for different reasons......I have heard some say it was put on there to keep the OS from interfering with AM radio reception. Others say it was for keeping stray signals out of the OS for proper operation. I did find some info on the Oregon Fuel Injection site that said a bad OS harness could cause a stalling problem, or NOT having the harness installed could cause stalling. Seems to be a lot of BS out there regarding this filter harness and it's function.

Sooo.....should I take if off and trash it, or leave it alone? Any info would be appreciated.....

[Robyn]

Hi

The harness you refer to can cause issues.
The OBD2 systems did not use it....
Yes there is a lot of BS out there.

Stalling is usually caused by the PMD failing or otherwise having issues...

If the PMD is on the IP Get a fresh one (Flight systems is my fave brand and mount it on a good cooler AND USE heat conductor paste between the PMD nd the cooler,

Mount the cooler down in the bumper just inboard from one of the "Nostrils" to keep it out of the rain....

Use an extension cable.....
IF YOU DO NOT KNOW WHICH RESISTOR IS IN THE CURRENT PMD USE A #5

Adding a fresh filter harness is not a bad idea either.....

Hope this helps.

[rnash4]

"Adding a fresh filter harness is not a bad idea either....." Thanks for the reply, Robyn....so I take it that you think this filter harness should be on there and has a valid purpose? Just for fun I searched for a new one, part#12553327.....no luck.
If the filter harness was only for AM radio reception I would remove it now......but I don't believe that is what it is for. On the other hand, if your filter harness does go bad, and you can't get a new one, might be forced to remove it anyway.
The only issue I have is a very light and occasional "fish bite" and thought maybe this filter harness might be the cause of it. Got a new Flight Systems PMD kit mounted in the bumper with #9 resistor.

[Robyn]

The electrical signal from the optical sensor must be clean going to the ECM
A dirty signal (Noise) will/can cause the computer to complain.....
This may be a bidirectional signal....I am not sure on that...

As far as AM radio goes ????? There is a lot of other things under the hood that can mess with the radio signal ......

There are many areas in the flow of data to the ECM that must have clean data....

[arveetek]

I have not had a filter harness on my 1995 Tahoe for many years now. No ill side effects that I have been able to notice.

Casey

[rnash4]

I have not had a filter harness on my 1995 Tahoe for many years now. No ill side effects that I have been able to notice.

Casey

Do you remember when you removed the filter harness, was the engine harness long enough to plug directly into the OS without any problems? I think the filter harness is about 6-8 inches long......

[arveetek]

Do you remember when you removed the filter harness, was the engine harness long enough to plug directly into the OS without any problems? I think the filter harness is about 6-8 inches long......

Yes, there was plenty of engine harness to plug directly into the pump.

I did a complete engine rebuild about 2.5 years ago, and I ended up replacing the engine harness at that time due to age. All of the plugs were getting brittle and falling apart. I purchased a new harness here:

https://quadstartuning.com/collectio...wiring-harness

Casey

[rnash4]

Yes, there was plenty of engine harness to plug directly into the pump.

I did a complete engine rebuild about 2.5 years ago, and I ended up replacing the engine harness at that time due to age. All of the plugs were getting brittle and falling apart. I purchased a new harness here:

https://quadstartuning.com/collectio...wiring-harness

Casey

Thanks for that info Casey. Have looked at those new wiring harnesses on that site......figured I would replace mine at some point also. My truck only has 130K but is nearing 30 years old.....those plastic connectors are showing their age.

[arveetek]

Yes, there was plenty of engine harness to plug directly into the pump.

I did a complete engine rebuild about 2.5 years ago, and I ended up replacing the engine harness at that time due to age. All of the plugs were getting brittle and falling apart. I purchased a new harness here:

https://quadstartuning.com/collectio...wiring-harness

Casey

My rig is also nearly 30 years old, but I have 412K miles on the odometer, so she definitely deserved a new harness when I rebuilt the engine!

Casey

[rnash4]

My rig is also nearly 30 years old, but I have 412K miles on the odometer, so she definitely deserved a new harness when I rebuilt the engine!

Casey

I remember your rebuild thread......followed along on a lot of it......all your hard work seems to have paid off for sure.

[arveetek]

I remember your rebuild thread......followed along on a lot of it......all your hard work seems to have paid off for sure.

Thanks! I was wondering at the time if I was crazy for all the work I put into her, but I'm glad to feel like I can drive her another 300 to 400K miles at this point! I also just finished swapping in a 14 bolt semi-float rear axle, and just returned from a 2,000 mile trip with our camper and I'm pleased to report that we had no mechanical problems!

Casey

[rnash4]

Thanks! I was wondering at the time if I was crazy for all the work I put into her, but I'm glad to feel like I can drive her another 300 to 400K miles at this point! I also just finished swapping in a 14 bolt semi-float rear axle, and just returned from a 2,000 mile trip with our camper and I'm pleased to report that we had no mechanical problems!

Casey

When you replaced your eng harness, did you run it on top of the manifold and get it out of the valley? That's what I planned on doing......I raised my FFM using threaded rod and pipe and got those fuel lines out of the valley also. Makes it easier to change the filter, check for leaks, and replace the fuel lines.

[arveetek]

When you replaced your eng harness, did you run it on top of the manifold and get it out of the valley? That's what I planned on doing......I raised my FFM using threaded rod and pipe and got those fuel lines out of the valley also. Makes it easier to change the filter, check for leaks, and replace the fuel lines.

Yes, it's on top of the manifold now. I ditched the FFM years ago and went with a Racor filter on the firewall.

Here's a pic showing the harness on top of the lower manifold, passenger side:






Another angle, also showing my fuel filter setup on the firewall:







Pic with my final air cleaner mod completed, where I was able to retain the factory 97+ air cleaner with the HX35 turbo:







Casey

[rnash4]

Thanks for the pics....I can see how you ran your eng harness......looks good. I like the Racor setup, but I also like the OE setup with integrated WIF sensor and heater......never had any problem with the FFM so decided to keep using it. Have read where you can add a heater and water sensor to the Racor but didn't want to mess with figuring all that out (lazy) lol.