TPS ground modification?

[Comanchero87]

So I have a 14ohm reading on the multimeter with key on TPS connected. Been trying to find the write up on the Ground Harness Modification but came up empty. Every search just comes back with showing that if the ohms are higher than 1 then ground harness modification is required. Nothing about actually preforming it. Is it just splicing in a alternate ground on the "B" terminal wire? Thanks guys

[cruiser54]

First off, do it with the key off. Wiggle the harness along the valve cover and near the MAP sensor while observing the meter reading.

 

You can also check the ground wire at the MAP, IAT, and CTS. All on the same circuit.

 

I did the write-up on this that addresses the poor crimp connections in the harness and also directs the sensor ground circuit around the C101 at the same time.

 

Find your Intake Air Temp sensor. It's the sensor just to the rear of the throttle body, has 2 wires, and screws into the intake manifold.

Where it's connector plugs into the harness you will see that one of the wires on the harness side is brown with a white stripe. Follow the brown with white strip wire back into the harness. You'll have to open up the split-loom plastic sheathing to follow it. It will come to a splice with 2 other brown with white wires. They're from the TPS and the CTS. The 3 wires will be spliced to a single wire headed toward the C101 connector if you have an 87 or 88. If you have an 89 or 90, you do not have the C101 bulkhead connector.

 

Now go to the MAP sensor. Follow the brown with white wire into the harness from there. You will find a splice with 2 more brown with white wires. At the splice you will find the 3 wires connected to a single brown with white wire going toward the C101, or just along the firewall towards the engine if you have an 89 or 90. Along with the MAP sensor that you traced, they are the ECU sensor ground port and the diagnostic connector on the passenger inner fender.

 

You now have 2 sets of 3 brown with white wires, one near the firewall and one near the engine.

 

Cut the splices out of each set of wires eliminating not only the crappy factory splices, but also the single wire between them. Bring both sets of 3 wires together. Solder the 2 sets of wires together and insulate them properly with tape or shrink tubing.

 

Zip-tie up your new sensor loom to allow for engine movement. I prefer to cover it with some new split-loom or wrap it neatly with electrical tape when done.

 

 

 

Revised 12-02-2011

[mvusse]

Okay, so you now have a bundle of 6 wires that are not grounded.

[cruiser54]

I know it sounds confusing to read but that's not it at all.

 

The circuit continues to the ECU and then to the dipstick tube stud. The problem with the crimps is that they are loose many times. The problem with the C101 is that the resistance within it can be high.

[Akula69]

I know it sounds confusing to read but that's not it at all.

 

The circuit continues to the ECU and then to the dipstick tube stud. The problem with the crimps is that they are loose many times. The problem with the C101 is that the resistance within it can be high.

 

What Mvusse is trying to say is when you cut out the splices and the wire going between them, you eliminate thier attachment to a ground up by the firewall. The harness does go on to the block ground, but you would need to ensure that the Neg cable from the battery is makeing good contact as well (too many of those cables are undersized and corroded). What I believe you left out of your writeup was where you re-attached them to the gounding system.

 

Did you replace the wire you cut out? (not the splices - because you soldered those back together).

[Comanchero87]

Ok so I will wait and see if this info changes before I attempt to Modify my ground harness. Yesterday went through and refreshed the firewall ground, the dip tube ground, drivers side tail light ground, c1o1 connector and added a ground from the battery strait to the fender. My c101 on the right side has 3 pins on the second row up. After cleaning I noticed the body side of the harness dident seem to have contacts for the 3 pins located on the second row. Anyone feel like pulling their c101 to see if I have a problem there. Also looking through other posts I noticed I have no transducer after the egr valve. Is this because its an 87? Should I have one? As for the Key off. I get 1ohm with key in off position. So I'm not really sure if this info is correct.

[cruiser54]

I've done this mod 3 times but it's hard to explain. The CTS, TPS, and IAT grounds come together in a crimp of 3 wires in the harness along the valve cover. Those 3 wires are crimped to a single wire that travels over to the firewall area (through the C101 if you have one). That single wire then crimps into another 3 wires going to the MAP, ECU, and diagnostic connector. There is plenty of wire left to cut out the single wire (bypassing the C101 if you have one), cut the crimps out of each bundle of 3, and solder the 2 bundles of 3 directly together.

[cruiser54]

I've got a PDF file of a hand-drawn diagram I made a while back. Anybody able to post it here if I send it to them?

[Comanchero87]

Update key off. 5ohms at "B" on TPS, 6ohms at MAT.

[cruiser54]

Need 1 ohm or less. Did you wiggle the harness while probing?

 

I just noticed where you live. Fly me over there and I'll do the ground circuit mod for you.

[cruiser54]

FWIW, if you see higher than 1 ohm of resistance in this circuit, and you have an 87 or 88, you should refresh your C101 connector and then retest.

 

Hornbrod has the hokey diagram and says he will post it.

 

And if anyone wants to improve on my diagram, feel free to do so. But, you should do the mod before doing the diagram.....

[HOrnbrod]

Image Not Found

[cruiser54]

Cut the crap out between the dotted lines and solder it together. The mod will be very evident once you get the split-loom covering off the harnesses. Any questions, post them up.

Thanks Don.

[Comanchero87]

So after jiggling the harness and c101 got it down to here.

So I split the harness. First connection I found was this. Fuel injector grounds I suppose.

Kept working up from the MAT sensor ground and found this Duck taped connection

So I cut the crimp out and soldered the connections

And wall ah. I guess I don't need to modify it the rest of the way. Dident read the last posts before I went digging

PO loved rat nesting the engine

bay I guess

Next electrical project

Thanks fellas

[cruiser54]

Comanchero87, you've got guts!! If you had split open the loom near the MAP you would have found another set of three wires. That set needs to be soldered to the set you already soldered and bypass the C101. But, I'm glad to see that low resistance reading. Have you probed it and wiggled the harness near the MAP since thesoldering job?

 

I updated the instructions to include not only looking for the splices by color code but to expect duct tape over them also.

 

And thanks for the photos.

[Comanchero87]

Ya I was getting some 1.2ohm readings so I squeeze the harness after the MAP and right back down to .9ohms. So Looks Like I should complete the mod to keep it from jumping up and down. Have to get some better electrical solder. I'm Using my plumbing solder and Flux and is not working so great. I guess thats what happens when you put a plumber on a electrical job. Reset the TPS to .83volts took for a test drive. No more high idle. :clapping: The MAT is showing 12ohms on a hot engine same with the Engine temp sensor. O2 has 12.7 volts, and jumps between 1 and 5 volts on a idling engine. The MAT and ETS seem out of spec. :mad: Ive got a new IAC on the way along with new Vac tree and thermostat. I should have bought the MAT and ETS also. Next parts binge I guess.

[cruiser54]

Get the other crimp removed, remove the single wire between the two and solder the 2 bunches of three wires together. Make sure that the grounds at the dipstick tube stud are removed, cleaned and that the stud is bare metal. That's where the ECU eventually grounds.

[Comanchero87]

By the way the Multi Meter is from Napa 32bucks. Its the Best investment a budding comancheiac can make. If you own a renix Jeep buy one you are going to need it.

[cruiser54]

So, have you eliminated the other crimp near the MAP sensor and soldered that group of 3 wires to the original 3 you soldered? Pics would be nice.

[Comanchero87]

So I started digging after the MAP for the other connection. It is after the C101 and before where the split loom sheathing T's a bundle heading downward.

So cut the single wire heading toward the C101. And Hooked up the 3 green with white wires coming from the MAT,CTS,TPS and hooked them up with the 3coming from the MAP,?,?

And ??????? Steady even jiggling the harness.

Thanks again guys, hope this makes a nice addition to the search option on this site.

[Comanchero87]

So, have you eliminated the other crimp near the MAP sensor and soldered that group of 3 wires to the original 3 you soldered? Pics would be nice.

:waving: Thanks for all the help Cruiser. Would have been lost without your guys help

[cruiser54]

You got it!!! Thanks for the replies and photos. I'm hoping this will help others who would like to do this. I think you've proven that diving in and following the instructions will make perfect sense once you open the harness..

[Comanchero87]

before

After....a little better. They are new used connectors. The electrical tape makes them look ugly.

Before the ground mod

after. Still need the correct size split loom. Napa had 2feet of 3/4 for 5bucks....ya no thanks. I bought 1in at 99cents a foot. Just to see but its way to big.

The actual splice location after the mod. Notice the wire going from the bottom section of the Incoming C101 harness and the upper outgoing c101 harness. This is where it ends up after you cut about 6inch section off of the 3 wires on the lower section and a couple off the upper. Its hard to tell from the pic but its about 4-6inches up the harness from the MAP.

[cruiser54]

So how's it running now?

 

I modified/updated my TPS write-up to include wiggling the harnesses parallel to the valve cover and over near the MAP sensor while checking the resistance in the sensor ground circuit.

 

I've also become aware that there isn't always a group of 3 wires at each crimp but sometimes 2 or 4. Makes no difference how many, just bundle them all together into a bypass harness like you did and it works fine.

[Comanchero87]

My Comanche has power! Its like a brand new truck. Ive been driving it around for three years thinking the 4.0 was a drag @$$ motor. Boy was I wrong this thing is a beast. Before if I got above 5grand it would be ticking and sounding like crap. Now its all power up until almost redline (i think still waiting on full gauges). Amazing what a couple hours of research on CC.com and a couple ours of work can do. Side note manifold bolts were loose also, causing a small exhaust leak at high temps. The MJ sounds and feels like it has a brand new motor! don't forget to put look for the duct tape. No need split the whole harness either. I would advice people to cut just the loom after the T going down through the firewall and before C101 on the top Harness. Once you find that connection cut the sheathing on the bottom C101 directly below the top C101 ground connection. On mine at least, they were directly across from eachother. Theres about 4 more duct tape crimp connections lingering in the main engine harness. One is the fuel injector grounds, mine was soldered and duct taped over, so I just re taped it. There is others that I dident mess with.