GEN1 LWB 3.0L Troubleshooting random shutdown - SOLVED

chadzeilenga

Active member
Hi All,
As most of you know, I recently replaced the 3.0L 6G72 in my 89 Montero due to a series of discoveries after my HG issue. The replacement engine is now up and running and I have one issue that I'm still fighting, so I'm diving into the Powertrain Diagnostic Procedure to get to the bottom of it.

First, a description of the problem:
The Montero starts up and idles great, no CEL and has no driveability issues when cold. Once warmed up there is an intermittent issue that appears as a random miss/no fuel while under load or sometimes an abrupt shutdown while stopped in-gear at a busy intersection (like tonight). Underhood I wiggled all of my connections and no change and after ~15min of periodic cranking, it fired and I drove it home. I have done the following since troubleshooting this issue: New fuel filter, swapped FPR, Coil & Power Transistor from old engine.

Second, some diagnostic questions:
- Since my problem happens while I'm driving or at least warmed up, should I start with the driveability section, or just work through the no-start tests for good measure?
- What is the best way to connect to the ECU while doing the diagnostic tests with an Ohmeter?
 
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Salonika

Monterror Pilot
#1: First thing I’d check or replace would be coolant temp sensor if you have no history on it.
#2: what history do you have on crank or cam sensors?
 

chadzeilenga

Active member
Hey Sal,
Thanks for the quick response.

#1 - When I was troubleshooting the low coolant temp (stuck thermostat) I swapped all the sensors near the thermostat from the old engine to the new.
- AC Temp Sensor - NEW OEM
- Coolant Temp Sensor - NEW OEM
- Engine Temp Gage Unit - OLD Engine
- Thermoswitch - OLD Engine

I should probably take a 2nd look at the harness condition at each of these connections though.

#2 - By crank sensor, you mean the distributor assy? I'm not seeing the cam sensors referenced in the MPI section of FSM.
 

Salonika

Monterror Pilot
Sorry, my bad, I’m not familiar with your particular engine. I’m just throwing out what I know. Apparently yours is significantly different, are the Gen-1’s OBD-1 or 2 equipped? When it dies on you, will it no start right back up?
 

chadzeilenga

Active member
Hello,
I’m reading through the diagnostic manual drive ability tests and am not sure how to conduct without the DRBII. Any advice?

I don’t have any CEL illuminated.


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chadzeilenga

Active member
I checked all of my underhood connections tonight and all were good.

Also pulled the plugs to check for any indication on the plugs and they all looked clean. If I had an injector/fuel issue would I see something on the plugs?

77e0818573f5439831d0d9cfbfd7b215.jpg



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chadzeilenga

Active member
Hello Sal,
I had some very slight idle bounce when I first had the new engine running, so I pulled the IACV and cleaned it off and now the idle is smooth.
 

chadzeilenga

Active member
A quick look under the cap explains the issue. Rotor should point to center if firewall when installed since #1 jogs in the cap...my finger is where #1 is

81c447bcc9def53a3a96e03787df7183.jpg



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Oso

Forest Defecator
sounds like your coil and/or power transistor are over heating. i know you swapped them from the old engine but it would be worth checking them per the fsm. keep a voltmeter in the rig to check them when it shuts down. another possibility is the harness connection at the power transistor. Ive seen intermittent missing and complete shutdowns from transistor issues. good luck.
 

chadzeilenga

Active member
Hey Oso,
I spliced in a replacement connector at the power transistor as my wiring was not in good shape. Much better connection now.

On a warm engine I checked the coil and was over on both the primary & secondary. I checked (2) spares that were cool and I have good value of 0.8 Ohm on primary and 12.02 kOhm on secondary. Installed and issue seems to be gone. Will need to see if the complete shutdown is separate from the misfire under load.
 
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Oso

Forest Defecator
They tend to heat up while running which naturally raises resistance. That’s why it’s important to check when it shuts down. The engine is warm and so is the coil. I had one test ok cold and then bad when hot. That was a learning experience early on for me.

Hopefully both issues are solved. Please post up and let us know.
 

chadzeilenga

Active member
Hi all,
A long overdue update. Been very busy with family, Christmas and work, so the Montero has mostly sat. I think I have found the sources of my issues

1. Replaced all of the harness to the front of the engine temp sensors/coil etc. my existing harness had some cracks and harness from donor was in great shape.

d2f4dc0dba0bd9c429727e206a5ce3bb.jpg


6ae425109354276271242e12319ff506.jpg


2. Had a bad plug wire on new DENSO 7mm set I installed. Found the old set had less resistance than the new, so installed those.

3. Fuel pressure was ~42psi with vac line connected to regulator. FSM State’s 38psi, will replace this so it is to factory specs.

4. Found a very small cut in the vac line going to FPR, need to replace with silicone once I figure out size. I think 6mm

5. Installed a good OEM fan clutch which locks when engine is warm.

With all of that done my stumble at higher RPM is gone. I’m not yet sure if the random shutdown is gone, but I’ll have to drive some more to ensure.


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