AnotherOldJeepGuy

I used the REM to look at RPM with and without AC. There was about a 80 RPM increase or so with the AC on. So not a big change but in my case, some.

Data Collection #1 complete. I used 12oz. of fluid in 379 miles. I described my data collection and seep-only leak (no visible dripping or residue) to my favorite ai companion (duck.ai), and asked if the amount of coolant loss I measured could reasonable be expected for a seeping leak at the thermostat housing over the miles seen. The duck's math suggested it was. I don't really know if that's accurate or not, but, I still plan to try and eliminate the known leak, retest, and go from there....

I see why you are asking. I read your post and went out and looked, and to take the requested picture. No evidence of any ground at that described location I can find on my 4.0L 1990

Yeah I got the stepper motor (well 2 at the moment since I just put in a new one), but not the stepper motor exerciser . Just for fun I put in the number on the box from OHM's pic into an ebay search, the tester has turned into a fuel injuctor pump!!

Interesting stuff! No idea what that is either, but whatever it is, I don't have one! . It does answer the question of if the IAC is used in time other than IDLE, or at least I think it does and the answer seems to be yes as best I can tell. Doesn't say anything really of how it is used differently in different modes, but does say that it is used. It also mentions it does look at if the AC is on or not in IDLE Mode, although it doesn't really say anything about if the target IDLE RPM is intentionally being set differently with respect to the AC on/off or what that might be. So I decided I would ask my go-to ai (duck.ai) and the duck tells me a properly running 1990 4.0L Renix would see a 50-200 RPM increase if AC was turned on depending on various environmental conditions. That is probably a good enough answer to squelch my curiosity .

I went ahead and replaced the IAC just because the remaining thing here is idle is good with AC off but with AC on it's still a little less smooth. So the IAC is something fairly low cost and an easy minor hail mary, so I did it. The one I took out is from 1990 so I have got my money's worth out of it either way. It does seem a bit smoother, but that could be just me, or it could be real. Initial REM numbers are a bit lower, 118-122 where they were 129-130 on July 5. I don't know if that is "better" or not. Should the ECU maintain, or attempt to maintain the same idle RPM with AC on and AC off? The REM documentation says to expect RPM between 600-900 at idle, but also says it "should be around 750", but doesn't really say anything about if this is or is not with AC on. Does the IAC have any function other than at idle? I assume no, but I'll ask any since I don't really know and I'm sure the experts here do know!

As I understand it the ECU makes tweaks based on real time sensor input as well as historical inputs. I've been told here it can take as much as 40 startups for it to optimize. So if the IAC was a recent replacement to fix the problem, it could have actually fixed it but you might not be able to tell right away. This over time adjustment was what schooling the ECU was meaning. But since there is nothing you have just changed, that theory falls short. If you are really bored, you can read my recent conical that ended with this education being at the end and the step that finally got the issue from still failing to not failing, but bring some snacks, it's a long read

I recently had issues that I apparently fixed, but I had to give it about 25 miles running bad for the computer to realized it was fixed. If this started with the new IAC, or you just replaced the IAC attempting to fix it, there's a change you just need to school the ECU. The difference for me was night/day before and after the 25 miles of training. Also a common suggestion here is to make sure all your exhaust/intake bolts are tight, because they do tent to work loose. I know for a fact I improved things by finding a few a little loose and snugging them up.

Turns out I have quite a lot of specs that light up, and I expect a lot of them are not really something that can be cleaned away. But what I was able to determine was that the only glow that matched the expected glow was a small area at the thermostat housing. I was able to match this to the expected color by swabbing the inside of the dye bottle with a q-tip and comparing any glow I could find to the glow on the q-tip. This area at the housing is not an active leak, I can't see it leak. That housing was pretty ruff when I replaced the gasket a few months back when I put in a new water pump, and it did have to do it more than once to get (I though) installed with no leaks. This leak appears to be so small that I don't have a lot of confidence it is my only coolant loss, so the additional chemical analysis suggested will most likely still be done, but I'll try to eliminate this known leak first and see what happens. (note it's all wet because of some cleaning)

OK got my additive and flashlight, added the dye in today. I made one mistake I'll note here for the benefit of anyone referencing, I neglected to snoop around with the flashlight before putting in the dye. Why does that matter? It matters because the black-light flashlight doesn't only work on the dye! I can walk around my house and garage nowhere near my Jeep, and see things that will light up. So, while I do see some specs here and there in my engine compartment, I really don't know they were not already there. So for future reference, if you are doing this look around before you put the dye in and make note of any thing that already lights up! If you see anything, if you can, clean it off so that it doesn't shine, then later if you see a shine you will be sure it came from the dye! For me, this just means I need to clean up any specs I see, and drive around again. I learn something new every day on this "keep my Jeep running" journey!

I am not disputing any difficulty noted, being more difficult that it looks is very common, but it looks like a pretty straight shot from the cap to the tank...

Don't see why not. I know I have siphoned some before just never tried to drain the tank. Might be difficult to get 100% out cause making the hose be at the absolute lowest spot might be difficult, but seems like you could get most of it.

Look well done!

Well apparently this can only be used on "orange" coolants: But it appears this one can be used with the "green" coolant I have. I'll start with this diagnostic and see if I can find a visible leak.

Right. I am collecting my comparisons first thing in the morning after engine has set overnight.

I am planning to get some kind of dye to attempt to confirm there is or is not any visible leak.

I thought I knew what a compression test was, a tool (that I don't have) that is inserted in to each spark plug hole to measure pressure? But first I ever heard of there being a wet and a dry version. So perhaps I know even less than I thought I did. Never heard of a "leak down" test.

Is this something like what you are referring to? https://www.amazon.com/K-Seal-ST3501-Permanent-Gasket-Repair/dp/B00QYZIVA6/ref=pd_bxgy_thbs_d_sccl_2/143-8891960-5551068?pd_rd_w=hUGRC&content-id=amzn1.sym.9bef5913-5870-4504-8883-3ba89d7f8e39&pf_rd_p=9bef5913-5870-4504-8883-3ba89d7f8e39&pf_rd_r=NSR08A2EZ2XP0FB1457E&pd_rd_wg=g9m2v&pd_rd_r=1b1904b5-2886-4ccf-add6-ad927b46cdd2&pd_rd_i=B00QYZIVA6&psc=1 I generally think if it's too good to be true it probably isn't, but on the other hand, mostly good reviews, so hmm..

Interesting.

Well, the replacement motor got here earlier today. If I can get to this wiring without removing the wiper assembly and it works I might return it. But if I have to take it all apart, I'll probably just put in the new motor and be good for another 36 years. We'll see

Data point 1. I'll keep collecting for a bit, but this data point is not real encouraging..

Hear are a couple things I have done as a result of suggestions here over time. 1. Check that all your intake/exhaust bolts are tight. I was able to spray water on the engine while running where these manifolds connect to the engine and heard a noticeable RPM drop. After tightening these bolts a repeat of the water test no longer affected REMs. These loose bolts are apparently not uncommon and can cause vacuum leaks as well as incorrect oxygen readings. 2. I found a failing exhaust gasket (the "donut) at where the exhaust manifold connects to the next pipe by putting the output port of my shop vac into the tailpipe and spraying soapy water at various locations along the exhaust manifold looking for leaks. This gasket is very close to the exhaust oxygen sensor and can also effect oxygen readings.

Good luck! Post how it turns out with pics! I'm curious if your elbow part is as tight as what I just got at the brass fitting, can just barely get it on there (meaning it is so tight I am a bit concerned how long is will last without splitting). Haven't tried it at the MAF end yet.

I'll take a look. What about these kits, any good?