Misfire troubleshooting, could it be a bad IAT or IAT connector housing

Maybe an Intake Air Temp sensor and/or IAT connector problem.

This may seem "left field"... however, I have been chasing a P03xx ghost-in-the-machine problem for over a year now and I stumbled into a piece of trivia that may be the ultimate root cause. Hear me out.

If you search for stuff I've posted and pay attention to timeline, you will find that I have done everything you are doing to solve a misfire problem, and much more. Including complete custom wiring harness for coils and injectors.

After all of the stuff I previously posted was done, the Liberty seemed to be running fine for a couple of months.

Then about a month ago, out of nowhere, I got a rogue P0300 (indeterminate misfire) *plus* random P0301 and P0302 codes. So I cleared the codes and waited. 30-50 miles later the codes pop up again. WTF.

I have a local mechanic who really knows electronics, but this is a weird one. He mentioned that it might have something to do with the IAT sensor. No explanation, no rationale, just a suggestion that popped into his head out of the blue like some sort of Oracle of Delphi thing.

It turns out that the connector for my IAT doesn't quite lock onto the IAT itself, so it can wiggle loose and still be in place. I cram the thing down as far as I can, but it still doesn't lock (aftermarket pigtail POS). It seems to do the trick but after a couple of weeks of bouncing over parking lot speed bumps the P03xx and random cyl misfires pops again, so I check that connector... which slides right off with a slight tug. Cram it down again... a couple of weeks later the codes pops again. Again it slides off with no resistance.

I had a spare segment of wiring harness I got from a salvage yard that included an original Mopar IAT connector. I cut that off into a pigtail and spliced it in place of the POS aftermarket pigtail and it locks on. Going on 2 weeks with no codes so far, still locked on tight.

Like I said, weird... and has not yet stood the test of time, but I have a good feeling about this. Remember that bad plugs that are b]not correctly gapped will always be your #1 culprit, but my plugs are new and I pulled them again to measure before doing this IAT connector test. Not the plugs, definitely.

If you decide to try this possible fix, and cannot track down and splice an original connector pigtail from ebay or a trip to a salvage yard, it can be accurately fabricated. The most important thing is that the housing must lock firmly in place.

There is no exact Mopar part number for the pigtail connector housing because it is part of the complete wiring harness, but the plug that actually locks has the following markings: AMP F4 PBT GF15. This was originally an AMP housing, and AMP is a division of TE Connectivity. When I track the lineage through TE I found this:

HOUSING ONLY (https://www.te.com/en/product-2822363-1.html
Purchase: https://www.digikey.com/en/products...3-1/5762219?s=N4IgTCBcDa4BxjAZgGxILQEYQF0C+QA

FEMALE RECEPTICLE (https://www.te.com/en/product-171662-5.html?compatible=2822363-1)
Purchase: https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/171662-5/1891347

WATERPROOF WIRE CAVITY SEAL (https://www.te.com/en/product-2822357-1.html)
Purchase: https://www.digikey.com/en/products...-1/5357192?s=N4IgTCBcDa4BxjAZgKwHYC0BGEBdAvkA

...and you will of course need some TXL wire (check confirm the correct gauge), buy some at AutoZone.

***You need all 3 to complete fabrication***, plus some 18awg TXL (or silicon insulated) wire from AutoZone, shrink tubing, and a decent crimping tool. Don't buy parts directly from TE (commercial quantities only), use the DigiKey purchase links (above) or look up the parts elsewhere (Mouser.com).

I will continue to monitor the results of installing a proper locking connector for the IAT, and if this turns out to be yet another goose chase I will update this posting and eat crow.

It's quite interesting your post. I had one month of unread messages.
Did it solve your problem?

Yes and no. I put over 1000 miles on the Jeep and then a misfire happened again. Pulled the IAT connector, and the #1 coil and injector wires. Everything looked fine so I reset the PCM and drove for over 100 miles and it popped again.

So I went back into the engine compartment and looked over all of the connectors and wiring, in general. I believe that this rogue misfire may be due to the tangled nest of insulated wiring resulting from my 1st attempt at harness fabrication (coils and injectors) because I was lazy about trimming lengths for efficiency. I have been meaning to rebuild those harnesses with correctly-sized wire lengths because the 1st set have a bunch that are 12-18" too long and flop all over the place.

As I got ready to order fresh wire and connectors, I did a little deeper reading and found out that there are several artifacts in play that could trigger a misfire MIL, including:

1. Wires that are all tangled together can produce a phenomenon called "crosstalk" (akd "crossfire"). When a charge goes through a wire, the length of wire radiates a field of energy that can actually "jump" to another wire like some kind of ghost and simultaneously energizes that idle wire. There are 2 ways to avoid this:

1a. Keep all wires parallel to, and separated from, each other. Here's a good cable-tie-origami YT: . I have not had another misfire since I rearranged the existing wiring so that everything is parallel, or widely separated by airspace.

1b. If 2 wires must cross, they shoud cross as close to 90-degrees as possible. If you cannot manage 90-degrees, maintaining an airspace of at least 1 inch between the wires (cable-tie-origami separator) should work ok.

1c. This wire management effort is applicable to *all* sensor and fuel/ignition wires equally, because the PCM is constantly sampling inbound sensor signals and issuing outbound signals to the various mechanical components, engine *and* transmission. Signal interference of any kind, caused by crosstalk anywhere, can produce PCM misinterpretation and subsequent erroneous performance adjustments.

2. Exposing wires to engine heat is a problem.

2a. For my 1st harness rebuild I used TXL (thin-walled crosslinked) wire because of its heat resistance and because it is the most physically flexible of the 3 types of crosslink wires (TXL, SXL and GXL). The choice was arbitrary, but after the occasional resurface of rogue misfires I started to really dig down and review nuances of wire specs, and from what I have deduced,... and correct factory-spec is actually SXL (standard crosslink, which was referred to as "automotive primary wire" in one or two instances out of dozens of crosslink descriptions). It turns out that TXL has thin insulation covering, which implies the wires will run hotter (bad, but no as bad as Home Depot wire) and therefore be more jittery relative to signal/power transmission. Stable signal and power is key. Here is a good overview of the 3 types of crosslinked wires types: https://nassaunationalcable.com/blo..._0wZ3KsBVb0TluuAIoM3Ozo69CTsN4_cQVLSfZXAFtPc4 . I regularly see the notation "automotive primary wire" associated with SXL wire, so that is what I am rebuilding the harnesses with.

2b. Adding a wrap of 1/4" (or larger if bundling multiple wires) heat resistant sleeving helps to further reduce heat penetration and add crosstalk separation. See: https://www.amazon.com/MGI-SpeedWare-Split-Sleeve-Expandable-Overlap/dp/B07HXSL2SH?th=1 .

In summary, the recommended wiring best practice is to
A. Make sure all of your connectors are unbroken and lock onto coils and injectors firmly. Ditto for all sensors.
B. Implement good wire management, avoiding crosstalk risks, and keep all wires as short/direct as possible.
C. Wrap all wires with heat-resistant mesh and use high-temp electrical tape like Tesa 51036 (also replace any garbage hardware store electrical with Tesa).

I will post an edited version of this as a separate reference.

While a solid locking IAT connector is vital, I think my root problem is the messy harness. More later.