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rehab basics (for somewhat mechanically inclined chicks)

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Hey fellas, can use some tips and advise please!!!


I picked up a 1990 Comanche Pioneer 4.0 a few months ago while moving and changing jobs. It was bought at an auction so I know absolutely nothing about the history of this vehicle. For all I know it sat in a yard or field or barn for the last several years. It runs decent and some of the basics had been already replaced ie. alternator, plugs, battery, hoses. I am a female with a background in airplanes. I have a decent amount of mechanical skills and have LOVED learning about this truck! I own a fair amount of tools and torque wrenches and such (inherited from 3 brothers that don't live near me).


I had the brakes, exhaust and transmission replaced because they were safety issues and beyond my scope of time or experience to repair. Now I am working on the not so pressing items. There seem to be so many things that appear worn or questionable, but I can't replace them until I can identify what they are. Many of these things are relays and wiring harnesses, etc. I have been looking for sources and manuals to help me with this.


These are some of my issues/questions and will gladly accept any other ideas and suggestions! Hint, electrical is NOT my strong system at this time. I am teaching myself and I am learning more about it with airplanes. I know many things can be diagnosed with a meter, I just haven't gained that skillset yet.


1) the truck runs OKAY, but not awesome. The lifters(?) are knocking away. How difficult is it to repair this issue?


2) it seems to take a few seconds too many to crank. In the past month there has been 3 occasions where it wouldn't start. After waiting, it eventually would start. I replaced the starter and the positive battery cable (which was worn). It cranks stronger, but still seems to take too long. I am looking next at the vacuum lines because they are cracked and old. After that I don't know which direction to go. There are so many relays and such that could be contributing to the problem and I don't want to randomly replace things hoping to hit the malfunctioning item. I want to make educated decisions.


3) How do I decide what to replace first? I have been trying to focus on one system, such as the fuel system. I have been replacing items in a line as I can identify them. For example I replaced the fuel pump, strainer, lock ring, fuel filter. But beyond that, I am not sure what relay goes to what and there are wires that are not connected to anything. I realize there are test ports and connections that are meant for items I don't have on this vehicle, so not everything is going to go to anything.


4) Would it be helpful for me to get a computer diagnostic test?


5) I think it would be helpful to clean the engine so I can better see what is worn and leaking. This lead me to wonder if there is a basic lubricant that is okay to spray on different mechanical parts of the truck (like WD-40, but better)?


6) Overall, there seems to be no end to the items that can be replaced or repaired. I just don't know where to start or how to be smart about the choices. I have been using RockAuto, NAPA, Advance Auto (and similar) stores and websites to shop for parts. Would love to hear what some of you gents have had good luck with.


I have to run off to work so I will not be able to monitor this forum until I get home. But I will greatly appreciate any words of wisdom that can be shared.


Appreciate your time guys and gals!


1wingnut yeahthat.gif

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Your numbered issues.


You will hear alot of things referring to RENIX for the 90 and below engine/drive train etc.

A combo of RENault and bendIX.

1. 4.0 engines (especially after sitting?) will make lifter noise. I got mine from a barn after had been sitting for 3 years. It made noise. I changed the oil, ran some Marvel Oil through it, changed oil again. Ticking really reduced. since I've been driving it it makes almost zero ticking except at cold start.


2. Another problem that seems inherent with the 4.0. Turn the key to on, wait 5 seconds, turn to start.


3. Here's a labeled diagram of the main relays for a RENIX 4.0. There are more relays in and around the dash area.



4. The good: RENIX era diagnostics can be done with a digital multi meter as there is no on board diagnostics

The bad: there is no on board diagnostics.


5. Yes, I use Simple Green to clean engine. I have also taken apart almost every eletrical connector and cleaned and greased them and put them back together.


6. Lots of people use those stores and sites you mentioned...some parts just can't be found except at a junkyard. Anjything from a RENIX Cherokee willlwork for the MJ. Good luck.


More info to come from this group...

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first welcome to the club


i hope to have answer some of them the best that i know how and i assure that others will chime in. also may want to pull the carpet and do a look see :brows: in case the rust monster decided to take up shop



1) there could be a build up on lifters which i would consider a system flush of the motor which is designed to clean up remove some of the buildup another option would be to add some mystic oil. before taking things apart. :dunno: miles on the engine not saying that it’s an issue since you mention that it may have been sitting for a while. pictures of this machine would be nice.


2) it is normal for a few seconds prior to the engine to kick off. and these are also could be signs of a failing CPS.


3) with these machines of joy that is based on order of precedence if you are contemplating a full restoration or get it on the road and enjoy it as you work thru list as to listen to it


4) most of the questions could be asked of the tech section. If you are considering a computer diagnostic test the dealer may be a good choice if ya know someone there btw you may have a remix and the cps sensors are not being produce any more.


5) Simple green is you friend and its friendly to the environment there may be others


6) that’s is true just when you think you got them cleared up another one gets ya. That’s the joy with working with a twenty year old which I do believe that they don’t mind at all :yes:

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First... WELCOME TO THE FORUMS! :jump:

Second....don't forget to add your truck here ( viewforum.php?f=34 )

third...first thing you should do is clean up all the grounds, explained in this post ( viewtopic.php?f=2&t=33143 )

fourth...if its a Renix engine buy a CPS while you still can...even if you don't use it right now, you will have one for later.


Also you said you had background in airplanes...happen to be a Piper Comanche? :clapping:

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If you don't know what CPS is, it is the crankshaft position sensor, and is a common failure point considering failure to start sometimes. It mounts on the transmission bellhousing near the top on the driver side. If the trans was replaced, and the shop did not remove this, they may have damaged it... get a new one either from a dealer or wherever else. It has been told that the dealer has discontinued these, but some are still available.


I'm a Jeep dealer tech, and for your truck, I do not beleive that going to the dealer for a computer scan will help you at all. Most dealers anymore no longer have the correct cables to plug into your truck, and on top of that, the Renix system doesnt keep memory, so codes do not get stored if a problem arises. As was said, working with us and with a multimeter, you can figure out whatever you need on this system.


It also sounds like you are doing a lot of possibly unnecessary work. There arent that many relays to go through involving engine running, but it is possible that with age some of them are corroded and not working properly. I ran into this on my boss's MJ... the AC relay was corroded inside and would no longer make good contact making his AC not work... easy fix, but took a while to figure out. Many things on the MJ are like that, just be patient, and ask for help.


Another thing that could cause running issues is the oxygen sensor. Its also an easy fix and was reccomended by the factory to be replaced every so often for good running. On many of the trucks the factory mounted a timer under the dash to make a light come on at a predetermined time or milage to make you replace the o2 sensor. Its relatively cheap and can make a huge difference in the way your truck runs. Age and milage will also be a factor in the fuel injectors. If you get to the point of replacing those, ask around first, as there are some upgrades that can be done here for the same price or less as new injectors. Running some fuel system cleaner through can't hurt anything either.


Good luck and feel free to keep asking any and all questions that may come up.

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Wow, just got home and I am overwhelmed with the many responses. ALL of them are helpful and I am appreciative!! Thank you all :bowdown:


I don't know what it is about this little truck, but I am bitten by the Comanche bug. It is like a puzzle to figure out the problems and see what makes it go. I have the money to buy another car if needed, but right now I am enjoying the simplicity of this ride. And as each of you know, there isn't a day that someone doesn't come up to me and tell me how cool they think these trucks are.


Thank you for the links and the advice, I will get to work on the items suggested and happen to have a big ole bottle of Simple Green in my garage. It is so good to know there is a community of folks out there that are willing to share what they know and are patient with a newbie.


I will remember to include pictures and more details with future postings. (and yes, there will be many future postings)


Cheers all!


P.S. to XxStirCrazedxX, actually I have flown a Piper Comanche in the past.... I never even made the connection! Good catch

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