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Troubleshooting "new" Renix 87' Comanche


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Hey y'all,

 

First time Jeep owner, just bought a 87' Comanche with 2wd and the 4.0l paired to a 5-speed! 

This is my first time seriously working on any car so it has been a bit overwhelming as I only have basic automotive knowledge. 

 

When I bought the Jeep, the owner said it had an overheating problem, and had replaced the overflow tank, the water pump, and thermostat, to no avail. Unfortunately the coolant and fuel gauges don't work. After towing it home, I drove it around the block and it died 100 yards from my house. I'm wondering if it is the alternator. To make matters worse, after lightly pressure washing the engine bay (covered the distributor and exposed wires), the truck will no longer start. 

 

Here is a basic list of my most important problems:

 

1. Truck won't start. There is spark, and engine cranks. I don't know what to do, after following the first four steps on http://cruiser54.com/ (ground refreshing, C101 cleaning, Connector & relay/receptacle refreshing, and Coil/ICM contacts), it still won't start. The C101 was completely covered in tar which was quite a sight to see... Also, the vacuum lines are all attached, but pretty brittle. However the ones attached to the purge tank are practically falling off from erosion. IMG_7288.JPG.6f44c59204ce448d78ef6b6af9d52ce6.JPG 

 

2. Coolant gauge won't read, what should I check for? The forum posts i've read have confused me on the matter. This is important as I will be able to tell whether my truck is overheating or not and if I can diagnose the problem.

 

3. Turned off while driving and battery died. Alternator? How do I test?

 

Thanks for your patience, any help would be awesome. I'm super excited to get my truck running and get it on the road. It had been sitting for 17 years before the previous owner did some basic maintenance to get it running, but not much more. I'm a little worried about getting the CA emissions system to pass smog though... One step at a time. 

 

IMG_7284.JPG.3140ec1dd4c04043da18c428660662e6.JPG

 

63097596260__E19BF696-B6C0-4994-BF20-8B0B35844538.jpg.a427bebf504c2ec5a63d3cee01a89949.jpg

 

 

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15 minutes ago, wilto said:

1. Truck won't start. There is spark, and engine cranks.

is there fuel pressure? you can see if there's fuel at the rail from the schrader valve

16 minutes ago, wilto said:

Coolant gauge won't read, what should I check for?

on the back of the head near the fire wall there is a single connector, verify its plugged in, if so the sender is probably bad, but it could be a bad gauge

18 minutes ago, wilto said:

Turned off while driving and battery died. Alternator? How do I test?

do you own a dvom yet? if so what is the battery voltage, resting it should be 12.4/5 running it should be closer to 13.6

I would also check the fuse links near the battery @Ωhm can assist with test procedures

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welcome to the club. :wavey: i was once where you are now. your jeep will be your best teacher in mechanical experience.   like you said one step at a time. work those tips and ask along the way and help will come. all nuts and bolts:holdwrench:

 

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19 minutes ago, jdog said:

is there fuel pressure? you can see if there's fuel at the rail from the schrader valve

I cranked it and nothing came out :/ 

I added some more fuel for good measure but no luck. This is odd as it was working before. 

19 minutes ago, jdog said:

on the back of the head near the fire wall there is a single connector, verify its plugged in, if so the sender is probably bad, but it could be a bad gauge

IMG_7293.JPG.0e5a442170a5edb2c8eee0dc3ada1fbb.JPG

Is this what you're talking about? It just is snapped on there. 

19 minutes ago, jdog said:

do you own a dvom yet? if so what is the battery voltage, resting it should be 12.4/5 running it should be closer to 13.6

I would also check the fuse links near the battery @Ωhm can assist with test procedures

I'm letting it charge, now I'm getting a multimeter soon so I can test it. 

Thanks for the help everyone btw!!!

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13 minutes ago, MiNi Beast said:

welcome to the club. :wavey: i was once where you are now. your jeep will be your best teacher in mechanical experience.   like you said one step at a time. work those tips and ask along the way and help will come. all nuts and bolts:holdwrench:

 

Thanks! :) I feel welcome already, y'all reply quick! 

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10 minutes ago, wilto said:
24 minutes ago, jdog said:

also hows the ground at the left taillight, that is the gound for the fuel pump

Driver's side? I see a bunch of connections (one of which with mild corrosion), but no ground. 

 

G107

1542431404_G10788.jpg.0baebc5feef3d5cad788cdc8ea0c0570.jpg

 

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Welcome aboard, from one 87 to another.

 

Two things you need to do to help identify and fix issues are:

 

1. Cruiser's Renix Tips at www.cruiser54.com

 

2. Nickintimedesign Renix Engine Monitor (REM).  You will find it at www.nickintimedesign.com :L:

 

There are some manuals on servicing these Jeep in the DIY section.  I would recommend the 87 and/or the 88 wiring diagram manuals and the Renix Fuel Injections Manual.

 

 

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fuel, air and spark is needed. check that works. spark needs to be there with fuel to fire off. does it pop at all or just roll over? you double check throttlebody connections and cps.  verify spark at coil and also at plug. distributor maybe wet as other things from power washing. :doh: but it was so dirty. :crazy: hey look at it again are you sure?.  :shhh:

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9 minutes ago, MiNi Beast said:

fuel, air and spark is needed. check that works. spark needs to be there with fuel to fire off. does it pop at all or just roll over? you double check throttlebody connections and cps.  verify spark at coil and also at plug. distributor maybe wet as other things from power washing. :doh: but it was so dirty. :crazy: hey look at it again arw you surw.  :shhh:

Will do. It does turn and there is spark coming from the spark plug wires. I will read the Fenix FI manual to learn more about the fuel system and see what I can figure out. Hahaha yeah I was too afraid to get closer with the sprayer and stopped cleaning when I wasn't able to start to the thing! 

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14 minutes ago, wilto said:

So I should probably buy a new sender? 

you can but, unplug it and see if the gauge moves with the key on, if not run a jumper wire to ground to it and see if the gauge moves. if it moves to 230 then its the sender, if not its the cluster or wiring

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3 hours ago, wilto said:

Hey y'all,

 

First time Jeep owner, just bought a 87' Comanche with 2wd and the 4.0l paired to a 5-speed! 

This is my first time seriously working on any car so it has been a bit overwhelming as I only have basic automotive knowledge. 

 

When I bought the Jeep, the owner said it had an overheating problem, and had replaced the overflow tank, the water pump, and thermostat, to no avail. Unfortunately the coolant and fuel gauges don't work. After towing it home, I drove it around the block and it died 100 yards from my house. I'm wondering if it is the alternator. To make matters worse, after lightly pressure washing the engine bay (covered the distributor and exposed wires), the truck will no longer start. 

 

 

Problem number 1: That thing on the passenger side firewall is NOT an overflow tank. It's an expansion/surge tank, and it's part of the pressurized cooling system. If you spend much time on this site, you're going to see references to the "closed" and "open" cooling system. 'Open" systems have an overflow tank. The Cherokee and Comanche went to an open cooling system in (IIRC) 1991. Your '87 has a closed system -- that bottle on the firewall is supposed to be filled to the halfway level when cold -- no more, no less.

 

You will also encounter references to "burping" the cooling system. The problem is that the expansion tank is higher than the engine. Any air in the system has to be purged to ensure that the system is filled to the proper level. This usually involves starting the engine with the cap (which is a pressure cap) loose. You allow the engine to idle until it heats up enough for coolant to start bubbling out of the expansion tank. Then you immediately shut it down and let it cool off. At some point, after a few minutes you'll see (and maybe hear) that coolant is being sucked out of the bottle into the engine. At that point, you add coolant to ensure that the lines to and from the tank never suck air.

 

Once it cools down and stops sucking coolant -- fill it to the halfway mark and do it again. It usually takes about three cycles to get the air out. If you don't get the system burped, it WILL overheat.

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3 hours ago, wilto said:

2. Coolant gauge won't read, what should I check for? The forum posts i've read have confused me on the matter. This is important as I will be able to tell whether my truck is overheating or not and if I can diagnose the problem.

 

 

The coolant temp sensor for the gauge is on the left (driiver's side) rear of the head, at the very rear corner of the engine. It has a single pigtail going to it. That's power, from the gauge -- the circuit grounds through the sensor. Step one: With the ignition ON, pull the wire off the sensor and see if you have 12 volts at the wire.

 

Next -- the sensor is a variable resistor. With the ignition ON, when the wire is disconnected from the sensor and not touching anything, the gauge should rear cold. Then ground the wire directly to the engine block or any good ground. The gauge should read all the way to the hot side. If it fails that test, the gauge is bad. If the gauge is good, you probably need a new temperature sensor.

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Yeah so I just checked the coolant temp sensor plug at the back of the head. It reads at about 10 volts, and when I ground it with the multimeter, the reading goes haywire. Performed both with ignition on. No readings on the coolant gauge, seems to be stuck at 125. So cluster/wire bad? or perhaps a fuse? 

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16 minutes ago, wilto said:

Yeah so I just checked the coolant temp sensor plug at the back of the head. It reads at about 10 volts, and when I ground it with the multimeter, the reading goes haywire. Performed both with ignition on. No readings on the coolant gauge, seems to be stuck at 125. So cluster/wire bad? or perhaps a fuse? 

 

There's only one fuse for the gauges so, if the other gauges work, the fuse is good. So the gauge isn't communicating with the sensor. That could mean a broken wire between the cluster and sensor, or it could mean a bad gauge. You will have to decide which. If you get power at the pigtail, it's probably a bad gauge.

 

But ... why did you ground it with the multimeter? The test is to ground the pigtail directly to the chassis or engine block. Run the test again. Ignition in the RUN position. With the wire disconnected and not touching anything, the gauge should read cold. With the wire grounded, the gauge should swing all the way to the hot end of the scale.

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Update:

Started the Manche'! Turns out the CPS connection was bad. For some reason after unplugging it and plugging it back in (after several previous tries), the truck started right up. However I am only getting .35AC so I ordered a new one despite it working. Finally figured out how to use a multimeter lol. Thanks for all your help. 

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