Cranks perfect after sitting two days, renix 4.0

[dkmcgowan]

Then I think my idle speed issues are solved now as well. It is idling well, cold, warm, drive, and park.

 

So that's two main issues gone, cranking and idle speed.

 

Now there is still a slight miss and roughness.

 

I got in two oem mopar o2 sensors today, plan to try one tonight.

 

I also did a seafoam this weekend in the intake. While it didn't really help, it did show an exhaust leak at downpipe, I put on a new donut seal and that seems to be fixed.

 

I got another set of plugs I plan to install in case the old ones got worn out when I drove around for 3 weeks in open loop with a bad o2 sensor.

 

More to come but knocking out things slowly I guess.

[dkmcgowan]

So I did some additional work tonight.

 

First...  The OEM Mopar O2 sensor switched faster and the engine ran better than with the NTK, I believe the O2 sensor is now working perfect.  I could watch in on the MT2500 and it seemed perfect.  I was able to find a dealership that had two of them in stock, I bought both, I might look for another one to have just in case.  There are not many left out there anywhere.

 

Next, I did more tweaking with the butterfly stop.

 

.003 is the official number I believe.  You want to open the butterfly and set the gap between the butterfly and the throttle body to .003. It should move up and down and slide out with a little resistance, but pretty easily.  The .004 you insert will also slide out, but it should have a good amount of resistance.  If you place in .005, it should feel like you have to pull on it hard to get it out, it should definitely feel pinned against the throttle body completely.  At this point you are at .003 and that is where I believe it is supposed to be.  I verified on 2 other Comanches, so that's 3 of them now.

 

Second, I believe by default, at least in 1989 Comanches, verified on 3 now, the air bleed should be tightened all the way in by default, so all the way tight or clockwise.

 

My ECU wants to keep my idle at 600 RPM.  I wish it was a little higher, but that is where it wants to keep it and it works.  It doesn't matter if I'm in park, drive, A/C on, A/C off, breaking hard, or whatever, it will settle at 600 RPM.  It will go up when you go into park, but then adjust itself, it will go down when you turn on the A/C, but adjust itself, the IAC is in control and wants 600 RPM.

 

So here is what I learned.  If you want to get the benefit from the IAC, you want it to be in control.  If you want a higher idle, you can use the butterfly stop to "manually" set your idle.  You need to re-adjust your TPS after adjustment, but you can set the idle like an old carb engine by using the butterfly stop.  When you adjust to open the butterfly, you will reach a point where the IAC loses control and closes itself all the way and cannot lower the idle anymore, then you have taken over.  If you do this, you will have a constant large RPM difference between park and drive, because the IAC cannot compensate.  You will have an idle drop with A/C on because it cannot compensate, essentially if you open it up enough, the IAC will shut itself closed trying to max compensate by removing air, it will not be enough, and then it's no longer in control of the idle your butterfly stop screw is.

 

That is not the correct setup.

 

I was able to adjust the butterfly stop to completely closed while the engine was running and watch the IAC shrink and let more and more air in.  I was then able to start opening the butterfly and watch the IAC push out and cut off more and more air to compensate.  You start to lose the ability with a warm engine, for the IAC to compensate effectively, at about .005 gap from butterfly to throttle body.  It also starts to lose the ability to keep the RPM high enough if you close it all the way.  The .003 setting let's it adjust up and down as needed with enough room for compensation and keep my idle at 600 RPM no matter whats happening with the motor.

 

Will see how it does on the way to work tomorrow, but I think I understand now how it all works.

[dkmcgowan]

So this morning it fired right up, it started idling high, and slowly lowered it's idle as it warmed up.  This seems like much more normal behavior.  Before with the butterfly open too much, it would start idling low, and as it warms up, your idle goes up, so the opposite, meaning the IAC is not in control.

 

It runs good when cold and the idle is right above the second line, maybe 720-750, right where I want it.

 

Then as soon as it reaches a certain temp, it decides to try and keep the idle at 600 rpm.

 

It runs and it's not bad, but I just wish the idle was higher.  I'm trying to decide what I like better.  The computer being in control, which seems like the right way, or overriding with the butterfly stop to get the idle I want, which I'm pretty sure is wrong.

 

I'm going to leave it this way for now.  I wish I could modify the ECU to tell it to add 50 or so rpm.

 

Here is where it's at below.

 

[dkmcgowan]

So I have been adjusting things more.  My car just doesn't like .003, even if the other two Comanches did.  I found that adjusting the butterfly stop to .004 things run better.  I'm probably right over .004.  I also have the air bleed screw out maybe 1/2 a turn.  I've got my idle at exactly on the 3rd mark, the one right below the 1.  This is where it runs best.

 

I set butterfly to .004 and then would turn the air bleed out 1/4 a turn and drive around a bit, I got up to 1 full turn, then started backing it back down until it felt the best and I was close to the line, which was somewhere near 1/2 a turn out on the bleed screw.

 

So the idle seems fine for now...

 

I still have a miss and slight surge feeling at idle.  It's not that much and I'm just being picky, it's idling really well now.  The MT2500 shows it much closer to 128 on LT and ST fuel trim and the idle needle barely moves now at idle.

 

But I wanted to keep replacing part, so I went ahead and replaced the fuel pump with a new Bosch unit.  I also replaced the fuel filter and all the fuel hoses.  I was a few psi below spec on the fuel rail with a gauge, so that's fixed.  It "might" miss a little less now, not sure, hard to tell, but I think it's better.  The new Bosch unit is actually much quieter than the OEM one, which is not what people say is normal, so I think my pump was going out.  The hose inside the tank was really cracked up as well.

 

So it needed replacing, but I think it was still working...

 

I figure it's time to close this thread and maybe if I still have issues I will summarize what all I have done and make a new post about the surge or pulsing I'm feeling.

 

thanks for all the help everyone

[88mjblue]

Thanks so much for taking the time to write everything out, detailing all the work you did, and for making those videos. I will be trying to replicate your butterfly stop screw and air bleed screw adjustment procedures to hopefully solve my low idle. I have the same exact numbers/symptoms as you did, and have done (almost) everything you have done to try and solve it along the way. 

 

My experiences with the O2: I too have been having trouble with the NTK sensor, and will start checking dealerships/ebay for an OEM sensor. I have the MT2500 scanner as well, and observed O2 sensor Voltage was switching slowly, sometimes not at all.

[cruiser54]

Thanks so much for taking the time to write everything out, detailing all the work you did, and for making those videos. I will be trying to replicate your butterfly stop screw and air bleed screw adjustment procedures to hopefully solve my low idle. I have the same exact numbers/symptoms as you did, and have done (almost) everything you have done to try and solve it along the way. 

 

My experiences with the O2: I too have been having trouble with the NTK sensor, and will start checking dealerships/ebay for an OEM sensor. I have the MT2500 scanner as well, and observed O2 sensor Voltage was switching slowly, sometimes not at all.

12 volts or more to the O2 sensor heater? 

[88mjblue]

Idle solved!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

After over a year of tinkering (and giving up) I have finally solved my low idle! (I never thought this day would come :banana: )

 

By using the feeler gauge method as described by dkmcgowen here, I was able to dial in my idle. I found that for my 88 MJ, I got a smooth idle exactly at the 750 rpm tach gauge mark by going with 0.003" (+/- 0.0005) using the same method in the video above.

 

 

So Mcgowan, like the other 2 comanches you sampled, mine too likes it a bit tighter than what you found on yours. And mine also has the air bleed valve completely closed.

 

 

Cruiser54, I think you should update your Renix tip on the butterfly adjustment procedure to include using a feeler gauge to get the adjustment exact (or close).

I followed your tip exactly when I first made the adjustment (and subsequent adjustments/cleanings) with the throttle body removed, and stopped at just the first movement of the butterfly valve as described – it turns out this was too closed (and no, it was not digging into the throttle body at this point). By opening it up just a hair (to 0.0035") this made a huge difference and solve my low idle. TPS at 17% (confirmed through MT2500), This tiny adjustment was the trick, this was not Uncle Bob stepping in: the IAC still functions.

 

In the end, I probably made some unnecessary repairs/part replacements, but it was worth it in my opinion.

Just as an FYI, here's everything I did prior to solving my idle: (some may have helped along the way, I will never know......)

- full kelley's WiP cable mains upgrade (plus additional fender ground and ground strap replacement)

- C101 eliminated + sensor grounds soldered

- Throttle body removal, cleaning, new gasket

- IAC (replaced, but was unnecessary)

- MAP (replaced, but was unnecessary)

- CTS and pigtail replaced

- Vacuum harness front/rear new

- CCV tubes and grommets new

- tested all sensor wires for continuity back to ECU

- O2 sensor wires tested for heater voltage, ground, ecu

- tested harness resistance

- new exhaust manifold and intake/exhaust gasket, torqued to spec

- 746 injectors

- 1989 ECU

- passed fuel pressure test (31, 39)

- CPS tested (6 AC Volts)

- new fuel filter

- removed and cleaned MAT

- distributor indexed

- EGR valve new (confirmed working with MT2500)

 

And probably some more stuff that may/may not have helped.

 

Thanks again everybody who helped me along the way, especially dkmcgowen for that last step.

[dkmcgowan]

I'm pretty positive the number is .003, glad it worked!

 

I've set my back to .003 and IAC works and controls the vehicle like it should. I have the idle up a little higher right now because I still have another issue somewhere.

 

My next plan, hopefully last, is extreme. I noticed what could be some oil in my fresh radiator fluid, so I'm going to do a head gasket, while it's off a valve job, and of course do the intake and exhaust manifold gasket while it's out.

 

Then I think I'm going to be good.

 

But that's 3 Comanches now, so I feel good about .003 being the number.

[cruiser54]

So, for clarification, you used a flat .003" feeler gauge on either side of the throttle plate? 

[dkmcgowan]

So, for clarification, you used a flat .003" feeler gauge on either side of the throttle plate? 

 

Yep, used flat feeler gauge...  You have to "feel" it because .002, .003, and .004 are all so close to together...  I placed it in the center of the throttle plate, I would open, close it on the feeler gauge, then pull upwards.  I got it to where I felt like the .002 came out really easy with no resistance, the .003 had very little resistance and the .004 felt like it had a lot of resistance, then I felt like I was at .003

 

Then make sure to set your TPS again.

 

I like to leave the air bleed screw all the way closed, then if you need to "fine tune" it, use the air bleed and open it up a little more, then you don't have to adjust the TPS again, but from what I can tell on 3 Comanches now and almost mine (have other issues), you shouldn't have to tweak it at all really

[cruiser54]

I'll try this sometime.

[dkmcgowan]

So I never could get my idle perfect...  I got frustrated and pulled the head and took it to the machine shop.  Cylinders 5 and 6 both had valves that were not seating all the way.  I got it checked out, cleaned, re-surfaced, and had  valve job done.  I just got it installed again...  I have to put the rest back together, but I'm feeling like I find the real issue.

[dkmcgowan]

So I put the new head on the engine, put it all back together, and guess what....   The idle is still hunting and surging...

 

At this point I have rebuilt the top end of the motor, replaced every gasket, and every sensor...

 

So I tried a new distributor in case it was the cam sensor, no help...

 

I then had a friend that had a random 90 Cherokee Renix ECU, not sure if it was from an auto or a manual.  I plugged it in, and the idle is fine, fixed the problem...

 

It was the ECU after all that.  I have tons of new parts on my brand new 4.0 motor now though, so should all last a long time.

 

So the ECU that everyone says is bullet proof and NEVER goes bad, can have problems sometimes at least.

[cruiser54]

Not NEVER, but rarely. 

[dkmcgowan]

It's an auto ecu and I just converted to manual, looks like my idle is around 675 maybe, should I track down a good manual ecu for any main reason? I see them on ebay for 60-80, you also mentioned having one, should have taken you up on that test you offered weeks ago.

[cruiser54]

Auto is fine.