Further developments added 2/7/15
update 2/20/15
Trick tools
Completion
The message which follows the quote below was added to a forum thread where a guy describes his effort to solve a driveability problem which was caused by a rotted out coolant temperature sensor(CTS). There are some aspects of my vehicles problem which related to problems he faced,, such as the location of the CTS.
http://forum.planetisuzoo.com/viewtopic.php?f=1&t=56345&p=716677#p716677
[quote="bradzuzu"]Ya alot of people have had problems with leaks and stuff. If you've never done one before it's a good call[/quote]
I am a lot late to this discussion but there may be people who might benefit from the diagnostic i just went through to chase down a problem that in its final stage became a hard-failure, engine dying after a normal cold startup and running fine for less than two minutes. A code 14 would be set and that indicated a failure in the coolant temp sensor(CTS) circuit.. Before the problem degraded to a hard-failure, the engine was giving fast idle symptoms and strange surging when engine was warm.. I thought this was going to be a simple fix until i found out where the coolant sensor was buried,,, behind the engine of all places.. I was about to cut a hole in the floor when further diagnostics were considered in order to accomplish a temporary fix.. The coolant temp sensor is a very influential sensor, as far as the ECM is concerned, affecting fuel flow, timing and air flow(?).. The big problem was how to test the CTS' functionality without a scan tool or access to the sensor.. Fortunately there is a green connector on the left side of the engine compartment behind the air filter.. It is connector H-5, a 16 pin connector, identified in the shop manual as an "engine harness connector".. Pin 14 and 15 of that connector are involved in the CTS circuit. At this connector you can check the resistance of the CT sensor.. The check is done with the connector unplugged so first disconnect the battery, seperate the connector and measure resistance across pin 14 and 15 on the engine side of the harness. According to the shop manual: max cold of -41*F should give 100,000 Ohms. Max hot 266*F should be about 70 Ohms ..If your vehicle won't start at all you are faced with the challenge of testing the hot resistance,, but this is not an impossible challenge since you can force the ECM to ignore all sensors by putting it in "Field Service Mode",,, accomplished by jumpering pin one and three of the ALDL,, the same connector used for getting Codes from the ECM.
I was getting a code 14 but i wanted to verify that the sensor was bad without tearing appart the engine. The resistance checks were way high on my CTS,,,, 1,200,000 cold and 500 hot.. The engine would start when it was cold and then after two minutes it would die like a ton of bricks hit it. I could start it again by using flooded-engine procedure (dying immediately) and/or starting it in "field service mode", (running in limp-in mode).
In the effort to verify that the sensor was the fault, without the usage of a scan tool and without the capability of accessing the sensor's connector, i was totally stumped and frustrated,,, then an idea came to me,,,, how about jumpering, with a resistor across the sensor's side of H-5 to immitate the sensor's low resistance when hot.. Using a 100 Ohm resistor, i backprobed the engine side of H-5 at pin 14 and 15,,, and to my total amazement the vehicle starts and runs without setting any codes... It now drives good and may continue to do just fine until i can do the repairs.
This is not
a perfect solution and is more of a diagnostic step than a fix, but as fieldmods go, it ranks
right up there with the story behind being divinely-coaxed to go to an auction where
this Trooper was found...
There are some vague spots in this diagnostic so i will fill them in if
anyone has questions...
ALDL,
References and contributors.
Further developments 2/7/15
Continued efforts are under-way to determine a way to change the CTS without top-engine disassembly. At this time it looks possible, if you have a bullet camera taped to a usb flex-light and a monitor or equivelent so you can see for navigation of tools behind the engine.
Removal and reconnection of the CTS plug is the toughest part but a fabricated strip
of flat metal to form a hook-tool worked ok but you've got the be careful with how the tool is used as the plug is removed, a rocking action lifts the tab, then a gentle/gradual pull is added. The plug will lean forward as you do this so if you can put pressure on its front surface it may disconnect easier.. Reconnecting is not too hard and is made more precise with my CTS Pliers. The other end of the metal strip can be formed to help direct the plug into place and press it on past the lock tab. A real long pair of pliers with a shaped gripping surface would be ideal for pulling the plug and reconnection, especially if it has a locking device so control of the plug is maintained while other steps are accomplished.
I haven't removed the sensor yet but access can be accomplished with a swivel, a short extension 3"+ and a 19mm deep socket on one side of the swivel and another extension between the swivel and the ratchet.
Removing the sensor should not be as difficult as threading in the new one. To simplify installation, 3/4" piece of heatshrink tubing will be used in the same manner as is done for installing spark plugs. The hose will offer
an ability to control the sensor and reach the hole, its loose fit will aid in avioiding cross-threading. Once i have an M16x1.5 threaded test hole, i will do a few mock-installes to get a feel for the threads via the hose's slippage/grip on the sensor.
If you have more time than money this may be a reasonable solution and the reward of doing it yourself cannot be measured in dollars since confidence is always of great value. We must never let our freedom to fix our vehicles get undermined by the people who want us to be dependent on them at a price....
Update 2/20/15
An uncertainty remained over my diagnosis, due to wiring between the CTS and the
multi-pin connector (H-5) in the engine compartment, so it seemed that further
steps were justified to test the sensor's operational resistance at the sensor. This was not going to be easy without an extension wire from the terminals.
Getting two wire on those terminals could be done with the right approach and a
grabbing tool which was made to reach the connector would also hold a fixture to plug wires into the terminals of the CTS. Once i did this the diagnosis
was accomplished, the CTS was bad,, at cold temps the resistance exceeded the ohm meters high-range of 2,000,000 ohms. When the engine was warm the resistance dropped to 600,000 ohms. So the next step is clear, attempt to remove the CTS without removal of the air inlet and ingnition coils from the engine.
Now for the sake of stimulating your fieldmod/creative selves here is an explanation of the tools made for attaching the test wires to the CTS.
Those wires were made of 20g dual conductor speaker wire pealed in half to be fed through a guide tube which i could hold with the grab-tool. To the end of the wire i attached a crimpable "Molex-.062 socket" terminal. The Molex terminal is prefered over the ez-crimp type because it has lock-tabs which are useful as hooks to hold the connector at the end of guide tube so the socket can be pushed onto the pin while the guide tube is being held by the grab-tool.. The guide tool was made from a bar-straw and a partially drilled out fiberglass tent-pole. It was quite a set-up and with the camera and monitor in place -for observion of tool movements- the task was accomplished,, direct measurement
of the senor through a test-conductor gave the final detail in this diagnosis, CTS resistance was way above specifications.
Completion Update; 4/28/15
While i waited for some long days and warm morning to roll in i drove on the
100 Ohm resistor field-mod and had few problems.. Only ones to note are a few cold mornings when that first effort at startup was a bit tricky,, a turn of the key to get it started and couldn't touch the accelerator once its running..
I had to wait for opreating temps to increase and then all was like normal..
This morning while i investigated loosening the sensor and accessibility to the coolant drain i had to take the fan off to get at the coolant drain -another
of the many blunders-of-engineering- since getting enough of a grip to loosen it
at it location, at the back right of the lower radiator chamber, is obscured by the trans-cooler lines.. Removal of the fan set in motion the effort to complete the job. Draining about 1.5 gal of coolant was done while loosening the
sensor. While it was still keeping the coolant back i fashioned a removal tool out of an 11/16 deep socket with the heatshrink slid over its OD and secured with tape. That would facilitate grabbing a-hold of the sensor at the nut surfaces and turning it out of the threads and lifting it out. I videoed the process and will post it soon on my youtube channel "dahlenaz07".
I had hoped to use the same heat-shrink/socket setup to insert the sensor and thread it in but the swivel was not cooperating and a shorter socket didn't help, nor did a different placement of the swivel. I resorted to just a length of heatshrink and some fidgeting with it until i felt the sensor grab the threads and make a rotation or two.. From the camera view it seemed to be
started so i pulled the heatshrink off and took a risky move and grabbed the 19mm deep socket. Fortunately it was threaded in correctly and i was able to
turn it almost to the original position with the tab facing squarely aft..
The next step is refill the coolant and check for leaks. Here again, the
camera is the only way to do this for sure with the backup being a piece of dirty panneling placed where some drips landed while the sensor was removed and the coolant overflowed...
Next step is getting the plug in possition and started.. This was accomplished with the hook-tool and grabber-tool.. Again verifying correct positioning and a final push with the opposite end of the hook tool, which is flat.. After a bit of carefull fidgiting to overcome the lock-tab resistance and the seals as the plug slides into the sensor socket and onto the pins..
This would have been so much easier if the engineers would have put it at the front of the engine!!!! With the connector now snapped on and a check of resistance at pin 14 and 15 of the green H-5 connector behind the air cleaner housing it was time for an ops-check... the fan was still removed so placing nust under each of those intended to hold the fan on provided spacers to tighten the pully and start the engine.. It started immediately and the computer kicked-up the idle in response to a functioning coolant temperature resistance of 2000 ohms.
How about that!!!
Now the only reassembly remaining is installing the fan,,, and shroud -if i had one...
I will post more info and links to images and videos once i have that ready.
Contact me if you have questions.
Abstract-fabrication and anywhere auto repair signing off. dzp
And some people say there's no God,,,,, how wrong they are,, they'll apply
faith in the doctors, the FDA, the government and all the rest of mankind's
substitutes,, and never once think that we just might be on the wrong
wavelength and out of
touch with creative inspiration.......Thank you Jesus,, and all others who provided diagnostic details.
Cold starts may be a challenge and driving right off the start is not advised, so let the engine warm a bit before touching the accelerator.. A variable resistor or a switch in the parallel circuit might improve this fieldmod and the cold start issue. d...z
...
Assembly Line Data Link,
white three pin connector, left side of center console, used to retrieve ECM codes.
Jumper pin 1 and 3 then turn key to run possition and count check engine light flashes. Also provides limp-in mode when engine is started with jumper in place.
Eddie at Napa
Hancocks Garage, Eloy, Az.
Isuzu Trooper shop manual
Online information,
I have many extra Molex connectors
I can make the devices used in the above description
Contact Abstract-fabrication, Trick tools
,, a way to change the coolant temp sensor
on a 3.2 liter Isuzu engine
without tearing appart the top of the engine
