IAT Relocate

[flint54]

I keep reading about folks moving the IAT from manifold to airbox, and have

to wonder how much difference it could actually make. I understand the

principle, but the difference between manifold temp and air temp for me

doesn't seem like much, maybe 50 degrees only (in summer). Wish there

were actual data. Any opinions or comments? Anyone here done this?

[Jeep Driver]

Yeah I have read about that also and the result is it will run rich. I chose to lean it out for economy and HP. Runs 5-8 degrees hotter......but better........more crisp.

[flint54]

Thanks for your reply. Not sure I understand it completely. How

did you lean out yours? MAP? Seems that economy and HP are somewhat

opposite each other. I was also thinking, perhaps wrongly, that the O2

sensor will tell PCM about an over-rich condition, which in turn would

back off the injector pulse, resulting in little real difference. I was also

thinking, perhaps also wrongly, that real changes require altering PCM

program (mapping) which isn't easy (or possible) with ours? Much to

learn here.

[cruiser54]

I've done 3 of them. You are correct about the O2 sensor trimming the fuel via the ECU. But the ECU also uses IAT input for ignition timing. Colder air temp=more advance.

[Jeep Driver]

I've done 3 of them. You are correct about the O2 sensor trimming the fuel via the ECU. But the ECU also uses IAT input for ignition timing. Colder air temp=more advance.

 

 

Yeah but I'm wondering just how sophisticated the '88 systems are?

 

The original owner rebuilt the engine in mine 10 years ago and apparently retained all the original sensors. Even if he had replaced all of them at the time of rebuild (I'm certain he did not) they still had age on them in spite of only having 5K miles on the engine. So I started out with none of the sensors working except the intake pressure sensor. The only sensor that effected running temp directly and was the IAT. Cooling system is new with constant electric fan and temps consistently 5-8 higher across the driving range than prior to sensor changes. After new cooling system the temp gauge remained buried at 190 regardless of rpm/driving condition. It is my conclusion the the one sensor with the most effect on fuel trim was the IAT.

[HOrnbrod]

I tried this (temporarily) on my 91 HO after reading all I could find on the pros and cons of IAT relocation. I relocated the existing IAT sensor and relocated it using a longer harness up to the front of the engine near the intake and plugged the manifold bung early last summer. I ran it like that all summer and didn't notice any improvement (or degradation) in performance, idling, or anything else. But I did see a slight 1-1.5 MPG decrease and I could see on the A/F meter that it did run a bit richer driving around town. This tells me that the IAT input doesn't have all that much influence on the HO ECU once it's in closed loop. This agreed with what I had read - most who have done this have experienced decreased mileage. But I also have a Unichip installed that changes the ECU A/F mapping , so this could have had some effect, although the Unichip itself does not alter the ECU IAT signal. I have no idea what would happen with the Renix system but suspect it would be the similar. In my case it was not worth doing.

 

It's an easy mod to do though, and recommend the OP retain the original IAT sensor in the manifold location and install another one in the intake and wire in a toggle switch to monitor and compare conditions from each IAT sensor.

[Jeep Driver]

I tried this (temporarily) on my 91 HO after reading all I could find on the pros and cons of IAT relocation. I relocated the existing IAT sensor and relocated it using a longer harness up to the front of the engine near the intake and plugged the manifold bung early last summer. I ran it like that all summer and didn't notice any improvement (or degradation) in performance, idling, or anything else. But I did see a slight 1-1.5 MPG decrease and I could see on the A/F meter that it did run a bit richer driving around town. This tells me that the IAT input doesn't have all that much influence on the HO ECU once it's in closed loop. This agreed with what I had read - most who have done this have experienced decreased mileage. But I also have a Unichip installed that changes the ECU A/F mapping , so this could have had some effect, although the Unichip itself does not alter the ECU IAT signal. I have no idea what would happen with the Renix system but suspect it would be the similar. In my case it was not worth doing.

 

It's an easy mod to do though, and recommend the OP retain the original IAT sensor in the manifold location and install another one in the intake and wire in a toggle switch to monitor and compare conditions from each IAT sensor.

 

In my case I went from non working sensors to a complete and operating system and it was a vast improvement.

 

I think since I had open loops for coolant temp and air temp my ECU was sending out a fuel signal that was cold/choke and it ran that way all the time.......rich.

[cruiser54]

I've done 3 of them. You are correct about the O2 sensor trimming the fuel via the ECU. But the ECU also uses IAT input for ignition timing. Colder air temp=more advance.

 

 

Yeah but I'm wondering just how sophisticated the '88 systems are?

 

The original owner rebuilt the engine in mine 10 years ago and apparently retained all the original sensors. Even if he had replaced all of them at the time of rebuild (I'm certain he did not) they still had age on them in spite of only having 5K miles on the engine. So I started out with none of the sensors working except the intake pressure sensor. The only sensor that effected running temp directly and was the IAT. Cooling system is new with constant electric fan and temps consistently 5-8 higher across the driving range than prior to sensor changes. After new cooling system the temp gauge remained buried at 190 regardless of rpm/driving condition. It is my conclusion the the one sensor with the most effect on fuel trim was the IAT.

 

 

I did this on an 87, 88 and 90.