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  #21  
Old December 28th, 2006, 08:20 PM
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Quote:
Originally Posted by Andrew Vick
The tune resistor on a 95 is in the wiring harness in the engine bay, drivers side, very close to the clutch master cylinder. Looks somewhat like a spade fuse about a 1/2 inch long by 1/4 inch wide. IIRC, it has a black/white wire going to it.
I dug around a bit and I think I found it based off your description of the size and black/white wire, but the strange thing is on mine it was exposed, lying near the mass air sensor. (See photos)

It would not surprise me if the previous owner had this swapped for some reason. My truck is a NAS 1995, but it spent most of its life in Italy. When I replaced both oxygen sensors, I noticed one of them had been replaced and a non-LR o2 sensor was in there. I'm wondering if, at some point, someone peeled back the wiring harness to check on (or change) that tune resistor.

So...
Question 1: is what I have in my hand in the photos the tune resistor? (If so, I'm assuming it's the small black square in the middle)

Question 2: It is normal for it to be floating around in the bay like that?

Question 3: Anyone know exactly which one I need now running without cats? According to: http://www.v8engines.com/faq-inj.htm#tuneresistor it seems I need a "white tune resistor" - where can I get my hands on one!

Thanks for everyone's help,

Hutch
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  #22  
Old December 28th, 2006, 09:23 PM
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That's it. Mine isn't exactly floating around, but I did remove it from the harness last winter trying to figure out why it wouldn't start. Now, all we need is the resistor.................
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  #23  
Old December 29th, 2006, 11:24 AM
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Quote:
Originally Posted by Andrew Vick
That's it. Mine isn't exactly floating around, but I did remove it from the harness last winter trying to figure out why it wouldn't start. Now, all we need is the resistor.................
Mine isn't floating around neither, some good electrical tape will take care of that! :-)
I also took picture of what I would use to replace the standard resistor (please note that the resistor in the picture does _not_ have the right Ohm value.... this is just an example I had in a box, it's a 1 Watt, it was said earlier than 1/4 Watt would work fine too but 1W is easier to handle because 4 times larger). I would put some shrink wrap around it so that it would look cleaner (but this is just gravy! :-) ).
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
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it is not hoarding it is selective collecting
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  #24  
Old December 29th, 2006, 03:27 PM
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Quote:
Originally Posted by evilfij
From RPI:

And for the more Technically minded.

Tune resistor info (for those that want to know)

A Green tune resistor (green referring to the color of the wires) will always give a non-cat tune, and White is always a cat tune. By the way, the default (Limp Home) tune is a cat map, so this usually makes a non-cat car run very rich.

The wire colors are Black/White and Black/Grey (where the first color is the primary color, and the second is the trace). The Green tune resistor value is 470 Ohms, and White tune is 3900 Ohms. Ordinary 1/2 Watt resistors are just fine, although the original is a Metal Oxide 2% item (which I always use anyway). In this location I sometimes use a 1 Watt resistor, because the larger physical size makes them easier to handle.
So, I stand corrected, the 1/4 Watt might not be strong enough, it is mentioned 1/2 Watt. The "White tune resistor" is just a 3900 Ohms resistor.
I looked at the Radioshack web site to see what they offer in term of resistor. It does not looks like 3900 Ohms is part of the "standard" package.
Looks like http://www.radioshack.com/product/in...entPage=family would work (you'll have spares! ;-) ).
Put a 4.7K and a 22K resistor in parallel and you get a 3872 Ohm resistor (5% tolerance) which will work perfectly for you (close enough from 3900 Ohms).
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
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it is not hoarding it is selective collecting
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  #25  
Old December 29th, 2006, 03:31 PM
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MonLand thanks for the pics and help on the resistors.....

OK - Let me try to get this straight. From reading up on this page:

http://www.v8engines.com/carbs-2.htm#Tune-resistor


It seems that the color refers to the color of the wire not the resistor (makes sense I guess). That being said, then it seems I did NOT find the correct wire for my 1995 D90 running without cats:



"The wire colors are Black/White and Black/Grey (where the first color is the primary color, and the second is the trace). The Green tune resistor value is 470 Ohms, and White tune is 3900 Ohms."






Does it sound like I need to find a green wire according to this sentence?:





"A Green tune resistor (green referring to the color of the wires) will always give a non-cat tune, and White is always a cat tune."






Yet further down the page it says:






"For the ECU to be able to make adjustments to its fuel trim (be adaptive) you still need to run Lambda sensors even if you do not have a CAT in your exhaust system, this means you require the White tune resistor. Without this Lambda feedback to the ECU the self diagnostic capability of the ECU is seriously compromised."






HUH??!!! The first quote says a non-cat truck needs a green tune resistor and a cat truck needs a white tune resistor, and the quote just above says the opposite?!!??


Does anyone have any ideas/input here? Am I missing something obvious?


If I'm right about my photos not being the right tune resistor, then I guess I have to find the right one buried somewhere in the loom. Additionally, does this mean I REMOVE the resistor in the white wire and put a 470 Ohm one in this mysterious green wire?


Hutch
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  #26  
Old December 29th, 2006, 03:36 PM
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Quote:
Originally Posted by hutch
size=3]OK - Let me try to get this straight. From reading up on this page:[/size]

http://www.v8engines.com/carbs-2.htm#Tune-resistor
Read this one instead, seems to be cleaner: http://www.v8engines.com/faq-inj.htm#tuneresistor
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I have an ex MoD and an ex wife. The two no longer conflict with each other.
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it is not hoarding it is selective collecting
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  #27  
Old December 29th, 2006, 04:08 PM
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The tune resistor is not the small black unit located near the mass air flow meter. That is an ignition resistor (white wire with white/black wire). That only relates to power and the coil, nothing else.

The tune resistor is located about 2 feet up the main EFI wiring harness from the ECU plug. You have to open up the harness to see it (its a small thing covered in heat shrink inside the harness).

My suggestion would be change to an aftermarket ECU chip as these will ignore the tune resistor all together, but don't change the small device near the mass air flow sensor thinking you'll get any performane changes. You may burn up your coil faster, but that would be about it.
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  #28  
Old December 29th, 2006, 04:28 PM
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so is that two feet before the harness splits into two pices or before? Also if it is after the split which road, the one less traveled by?
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  #29  
Old December 29th, 2006, 04:36 PM
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Quote:
Originally Posted by ECR
don't change the small device near the mass air flow sensor thinking you'll get any performane changes. You may burn up your coil faster, but that would be about it.
Actually I think power flows the other way in that resistor (don't have the diamgram in front of me) I think that is power from the coil signal to the ECU, not to the coil... who knows... its Friday!
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  #30  
Old December 29th, 2006, 10:03 PM
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Quote:
Originally Posted by ECR
The tune resistor is located about 2 feet up the main EFI wiring harness from the ECU plug. You have to open up the harness to see it (its a small thing covered in heat shrink inside the harness)
Ok - Good deal. Dumb question - can you clarify when you say"ECU Plug" I'm assuming you mean (duh!) where the main harness plugs into the ECU itself under the passender seat. So in other words I should be able to unplug the harness from the ECU, peel back the wiring protection, and find this guy about 2 feet from the ECU?

Sorry to sound like I just repeated what you said, I just want to be sure....

Thanks Mike,

Hutch
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  #31  
Old January 9th, 2007, 12:47 PM
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Did the tune resistor fix the issue or is it still smelling bad???
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  #32  
Old January 9th, 2007, 10:04 PM
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I haven't put the tune resistor in yet.

I talked to Byron (he posted earlier on this thread) on the phone and he has successfully done it and said it improved things big time. He also adjusted his throttle position sensor and MAF as well.

I removed the tuffy box and opened the wire harness as much as I could and I did not see a the tune resistor that Byron was describing. I may neeed to dig more towards the passenger seat. He's on his way back to colorado and I'm going to try to see if he can send some pics when he gets settled.

In the mean time, I found a great thread here. Check out Mark Adam's post regarding tune resistors. Very good info:
http://www.pistonheads.com/gassing/topic.asp?p=2&f=9&t=200769&h=3


Another thread here:
http://www.pistonheads.com/gassing/topic.asp?h=3&t=223687&r=2737362&hm=18441#2737362

...shows the actual resistor itself.

To be honest I'm contemplating putting the cats back on and throwing in the towel. Not sure if I'm ready for a battle. I've created more drama around my truck in the last year and according to my wife it affects my mood. Heh Heh. Nonsense!

Does anyone know if putting on a "performance cat" like a CatCo universal cat will affect the ECU's ability to regulate fuel? I'm assuming it won't interfere but I really want to end this stink.

Hutch

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  #33  
Old January 10th, 2007, 02:15 AM
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Hay Hutch,
I have been in Park City so I will give you a call when I get back. It should be Friday but there is a storm comming but I will call as soon as I can.
Byron
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  #34  
Old January 10th, 2007, 08:58 AM
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Random Technology cats.
Little to no resistance, long life, no down side (OK they aren't cheap), no ECU issues.
Same units we use on the ECR ROX SS exhaust. I've had them on my own V8 90 for 3 years now and they still look brand new.
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  #35  
Old January 10th, 2007, 02:07 PM
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Been using Dynatech PowerCats for two years now, but don't know how they would effect a GEMS ECU. They are 'racing' cats, super-high-flow all-stainless interior. I passed California smog with them about 3 months ago.
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  #36  
Old January 10th, 2007, 04:21 PM
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Thanks for the recommendations. From the sound of it, it looks like performance cats won't affect the ECU's ability to function properly. Mine is a 95 so no GEMS as far as I understand. I'm just trying to avoid more adjustments after putting after-market cats in.

Hutch
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  #37  
Old January 10th, 2007, 07:20 PM
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If a 95, I'm a bit stumped as to why cats effect the EFI performance at all. O2 sensors are in front of the cats, and since the sensors only read for air/fuel ratio adjustment, what's the diff if there is a cat or not? Only difference would be less back-pressure....

DW
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  #38  
Old January 10th, 2007, 07:49 PM
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I know - it's strange. That's why I was confused when I hollowed out the cats and instantly I could smell the exhaust. I can't drive a mile without stinking of it - you know it's bad when people can smell it on you!

In addition to the links above, here is also good info:
http://www.rpiv8.com/faq-inj.htm#tuneresistor
http://www.rpiv8.com/carbs-2.htm#Tune-resistor



(Actually I think Ron referenced content in these links in a post earlier in this thread)

Here is Mark Adam's Post from the Piston Head forums (might as well have this info searchable here as well)
##############################
Everything you ever wanted to know about the Tune Resistor....

All 14CUX ECUs contain five sets of engine tune information. The tune to be used is selected by the choice if Tune Resistor. All 14CUX vehicles are fitted with a Tune Resistor, except certain North American Specification (NAS) vehicles. In some cases NAS vehicles may have provision for a Tune Resistor to be fitted (i.e. socket fitted to the loom in the normal place), whilst others have this resistor taped inside the wiring loom to prevent anyone interfering with it.

Always ensure that the correct Tune Resistor is fitted to the vehicle. If an interchangeable Tune Resistor is fitted, then it is located as follows. Follow the wiring loom back from the ECU plug. About twelve inches (30cm) away, a small group of connectors and relays emerge from the loom. Amongst them is a small blue plastic two-pin plug that connects to the Tune Resistor.

The Tune Resistor itself is located in a clear plastic heat-shrink tube, connected to a blue plastic plug by two wires. Tune resistors are identified by the colour of these connecting wires. There is considerable variation according to application so please check for the correct version for your vehicle. If the vehicle is modified then the supplier of the modified ECU software should have specified the correct tune resistor to use.

Colour Ohms Cat Common Application
Red 180 No Australian 3.9
Green 470 No Europe & UK 3.9 (or 3.5 Disco)
Yellow 910 No Gulf States 3.9, or Europe & UK 4.2
Blue 1800 Yes Gulf States 3.9, or Europe & UK 4.2
White 3900 Yes Europe & UK 3.9 (or 3.5 Disco)

If there is any doubt about the presence or value of a Tune Resistor then the simplest method of checking it is as follows. Disconnect the ECU plug, and measure resistance between pins 5 and 27. The table above gives a list of the possible values:

Note that certain NAS vehicles do not use Tune Resistors, even though there may be a facility to fit one. In these cases the ECU will always operate as if a White Tune Resistor were present, and Oxygen Sensors are mandatory. If a Tune Resistor is later fitted, then it will be ignored. This is a function of the software version used inside the ECU, so of course it may be modified by a software upgrade.

For those of you who wonder if there is some advantage to be gained by experimenting with the resistor value - the answer is no! It must assume one of five particular values if it does not then the system will detect a fault condition.

It is of particular importance to ensure that the choice of a cat or non-cat tune is correct.

If a non-cat tune is selected where cats are fitted, then the cats may be destroyed. This happens because a non-cat tune will exercise no control over the cruise fuel setting. If the mixture is excessively lean or too rich, this can cause very high hydrocarbon levels (unburnt fuel) in the exhaust. This in turn can be burnt in the cats, leading to severe overheating. Certain fault conditions that cause over-fuelling will be undetected, which can also lead to severe catalyst overheating (and even a fire). Any input from Oxygen/Lambda sensors will be ignored.

Where a cat tune is selected, but no oxygen sensors are fitted, the car will run terribly rich. Eventually this will cause a fault flag to be set within the ECU, thus forcing it to drop into limp-home mode.

Note that the default (or limp home) tune is a cat tune, and will therefore always cause rich running on a car not equipped with Oxygen/Lambda sensors. If no Tune Resistor is fitted then the default tune will be selected (other than NAS vehicles described above).

Should the Tune Resistor be changed or disturbed for any reason, the ECU should be reset afterwards by disconnecting it for ten seconds. Failure to do this may cause the ECU to select the default tune.
##############################
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  #39  
Old January 11th, 2007, 08:28 AM
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I wonder what NAS trucks have no tune resistor? I am sure it would be an easy fix to fit a different country chip. I also wonder why gulf states and australia have different tune resistors than UK????
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  #40  
Old January 13th, 2007, 07:16 AM
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Look at the blue 2 pin plug that is about 10 or 12 inches away from the ECU. If there is nothing in it then you have no resistor.

I'm fairly sure this applies to the '89 Range Rover (an odd ball) for one example.
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