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 the IAT 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 stripe 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 with duct tape over them. 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 with duct tape over them. 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. On an ’89 or ’90 you will find 4 wires going to 1 wire. 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. If it’s an ’89 or ’90, you have 4 wires going to 1 wire.
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.
37 thoughts on “Sensor Ground Upgrade”
I was going to do this tip yesterday and got to the factory crimps and saw what u were referencing. However,. My omes on my multimeter stayed around 1 might have went to 1.2. factory crimps were solid. I gave em some good Yanks. Saw no variation in multimeter so I wrapped everything back up good and moved on. If my resistance didn’t move and the crimps are solid is there any reason to solder those wires together anyway?
Thoughts on moving the CTS from the block to the t-stat housing?
I have both areas instaled and when checking between the two with my mt 2500 the t stat reads hotter quicker and is always 10 to 15 degrees hotter than engine block.
The Renix ecu was designed for reading the engine side mounted sensor, do you think its wise to use the t stat location?
BTW my LT fuel trim stays around 117 to 108 in both locations.
I have a 1990 jeep cherokee and i have 5 brown going into one???
Kevin, there were some variations throughout the years. I’m not surprised.
You should not be looking for DC voltage, but ohms.
And can only get 0.04 Dc out of it
From Tip 5:
Set your meter to measure Ohms. Be sure the ignition is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.Backprobe 2
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
Thanks found out im an idot and didnt know how to use my new multimeter. Have 4.86 volts but cant set my tps to 8.2 output can only get it to 6.5 without it reving out. I have a manual trans but useing an auto tps cuz i aint paying $486 for a manual one any thoughts why i cant the the 8.2 output i need?? Thanks for your time this page it pretty amazing!!!!
Glad you got the meter sorted out.
How many OHMS resistance did you have when using Tip 5?
Also, output voltage from the TPS should be about .82 or so.
Use an automatic TPS BTW.
Trying to adjust tps on 88 Cherokee.
Getting 1 ohm resistance. 4.13 input, -.71 output….. what am i missing
1 ohm resistance when and where?
Have you done Tip 5 yet?
That’s a negative .71 output and does not change with adjustment
Josh, so the output voltage doesn’t change when moving the TPS?
If that’s the case, the TPS is bad.
If you continue removing wire loom on the harness from this point and head towards the relays on the passenger side fender you’ll find at least 6 more of these duct tape covered splices (I lost count), some of them are on Batt. +12V, Ignition On and Start wires as well as ground wires. I also found one in the wiring next to the distributor. Some are soldered, but none were properly weather sealed with heat shrink tube and RTV silicone. I think the OEM wiring harness is riddled with these type of un-reliable splices. Where the harness moves under the radiator I have not found any splices so far (doing an open cooling system conversion on my ’88 Comanche and started digging into the wiring while the cooling system components were out of the way). These tip have been a huge help, thanks for putting all this information online – saved me a bunch of time and frustration!
Yeah. Hecho en Mexico harnesses.
At least the most critical ones, and the ones that cause the most problems driveability wise are easy to find….
That stuff over the connectors looks like miniature duct tape, doesn’t it?
I looked at that duct tape and thought “what moron did this?”
Yep. Some folks see that for the first time and think someone has been into the harness before!!
I have a 90. I found 4 wires crimped to 2 wires just below and to the left of the MAP. Is this the only connection I am replacing? The exact one in the picture above. It kind of sounds like there is another set of 3 wires that join the 4.
Pic doesn’t show. Color codes on the wires?
I meant the picture above in your write up. 4 brown/white to 2 brown/white.
So I followed the brown with white from MAP sensor and followed brown and white from engine and found all six wires spliced together. Looks ok to me but should I put an iron to it and add some solder? Is that what you mean we should do. Or should I cut this splice out rejoin the six wires and do my own solder job? I’m a little confused. how do I get a photo to you?
Also, for clarification, does your photo show the completed upgrade?
That’s an AFTER photo. Do your own solder job.
Cruiser my harnes looked exactly like your photo you posted here after unwrapping what was clearly the original tape (both black and the duck tape). The factory splice was all 6 wires in a nice combination crimped and soldered connection. I suppose this may have been done many moons ago at a dealer but it was was not anytime recent. Mine is a 1989.
Hey Cruiser54. I did #27 and eliminated the C101 connector. If I recall correctly, the DC resistance went from .8 ohms with the C101 connector to .1 – .2 ohms range with soldered wired, all bundled up nicely. Seems like a nice change and there may be some performance difference with my power now – it’s a very subtle thing and don’t know if I am just fooling myself. Anyway, now I see that #6 means I have to unwrap some of the work done on the new harness bundle. Any recommendations? Are the advantages of this one upgrade worth the trouble? Thanks again for your help. Rhythmrocker (red rooster on NAXJA).
If your resistance is that low, and it doesn’t change when wiggling the harness, leave it be.
Thanks for that – I will pass on #6.
I have a question regarding the data ports on my renix . I have an 89 Jeep Cherokee Laredo . When I plug in my scan tool, specifically made for renix engines, I get no data what so ever . Any suggestions where to start hunting ? Any and all help is appreciated !! Thank you !
Which scan tool do you have? does it respond at all? Light up etc?
So when I checked for ohm like you mentioned I’m getting a solid 4.5 reading. I just chased the wires back into the harness and made my new solder connection. I’m still getting a consistent 4.5 reading. Any help would be appreciated
4.5 is quite high. You’re working on Tip 5?
I’m kind of at a loss here… I’ve got a 1988 XJ limited. It had a low rpm at idle and when coming to a stop. I’m talking like 250 rpm’s. I’ve done tips 1,3,4,5,6,8,11,14,18,27,31. Still can’t seem to figure it out. I’ve replaced the IAC and nothing changed. Any tips? Thanks
check your intake manifold bolts and make sure they’re not a little loose.
I can’t find the IAT or anything coming off the throttle body as described.
IAT is Intake Air Temp sensor. It’s behind the throttle body screwed into the intake manifold. 2 wire connector.
Is 30 ohms even possible? I am getting 30.