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Re: Ignition Coil [Re: Trailmonkey] #1106035 03/10/21 06:02 PM
Joined: Sep 2006
Posts: 2,710
OldColt Offline
Roll Me Over
*****
An ignition coil requires the output of a condenser for a high voltage inrush to energize the coils to create the needed output. Simple switching of 12v is meaningless. Mitsubishi coils are about the most reliable one will find which is why they are used by the largest number of manufactures in the world.

This is why I probed you with a simple trick question. You Tube will not teach you how to test or fix anything. Those of us who do know how things work as well as do diagnostics do not make videos.


Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.
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Re: Ignition Coil [Re: Trailmonkey] #1106038 03/10/21 07:19 PM
Joined: Oct 2020
Posts: 12
L
Lev_from_CA Offline
Need a Spot
Hi OldColt, thanks for sharing your experience (your 3.8 Mivec build is awesome, I've been watching it on ExPo).

(From a newbie) How would you test an ignition coil? I'm aware of testing resistance of the primary and secondary circuit, using a HEI spark tester (eg. OTC 6589), and using an adjustable spark tester (e.g. Lisle 50850, since spark in atmospheric pressure and air mixture performs differently than under cylinder pressure and ICE air/fuel mixture). Also, do you have a reference you could recommend for learning automotive electrical diagnosis? I've been learning about voltage drop testing (test lights (incandescent and LED), LoadPro, carbon-pile load tester for big loads, etc.), pressure transducers with scopes (for finding mechanical engine timing, under-performing valve springs, worn cam lobes, etc.), and similar fun stuff piece-meal, but would love to have a big reference book for that stuff.

For reference, here are the resistance specs I found for an aftermarket ignition coil on RockAuto (for 91 Montero 3.0L): Primary 0.4 - 1.2 Ohms, Secondary 8.5k - 18.5k Ohms (from https://www.rockauto.com/en/moreinfo.php?pk=942701&cc=1207684&jsn=810)

Re: Ignition Coil [Re: Trailmonkey] #1106039 03/10/21 09:18 PM
Joined: Sep 2006
Posts: 2,710
OldColt Offline
Roll Me Over
*****
Lev, you have it spot on.
With Mitsus it is very rare to find a coil failure. The igniter is generally what fails. Proper tech for testing them I can not help with since in my 48 years of driving and working on Mitsues the only ignition failure I have had was a bad MSD 6 unit on one of my 2.6L race Colts. That can not be blamed on any Mitsu bits.
Only failure of a mitsu part I have experienced was the 5V power inside the ECU of my DOHC converted Diamante wagon, we were a long way from home in nowheresville Maine. Nothing but tall trees. Luckily once it cooled down it ran.
I am soon going to update my Pajero build over there as well as start a parallel thread here.


Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.
Re: Ignition Coil [Re: Trailmonkey] #1106040 03/10/21 09:23 PM
Joined: Aug 2020
Posts: 191
T
Trailmonkey Offline OP
Wheeler
Im getting power to the coil, apparently not being triggered, not sure if the distributor isnt working, or the other parts mounted on the same bracket as the coil.
I can mechanic like a b*tch, hate electronics.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Ignition Coil [Re: Trailmonkey] #1106041 03/10/21 09:51 PM
Joined: Aug 2020
Posts: 191
T
Trailmonkey Offline OP
Wheeler
Yeah I tried on my old coil and got nothing. But I did see evidence of it arcing from the case to the steel laminates.
Put the new coil in place and still no spark.
Either the 2 condensers and or the black thing mounted on top of the bracket with 3 wires ( J121 Power Unit ), or its the distributor.
My guess anyways.

It has had this short studder from time to time like it cuts out for a split second, just this time it stopped totally
New engine, cap/rotor, plug wires and plugs, same old distributor.
Would it be your opinion that is the pick up sensor on the distributor ?
ECU codes all is normal.

Last edited by Trailmonkey; 03/10/21 10:14 PM.

91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Ignition Coil [Re: Trailmonkey] #1106042 03/11/21 01:38 AM
Joined: Aug 2020
Posts: 191
T
Trailmonkey Offline OP
Wheeler
Keep trying to open the FSM pdf and says cant open file.
I have Adobe Acrobat reader on my phone. Sure would be helpful if I could.
Or find someone thats worked on these enough to know them and chat with me on a few issues. This winging it stuff sucks, and I know im not very good with it, never really brought it up on here, but im disabled and had been struggling over the years with lasting effects of a server concussion. So my trouble shooting skills are not all that good anymore. As also my getting a point across in a conversation, so bare with me. Im trying.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Ignition Coil [Re: Trailmonkey] #1106045 03/11/21 04:38 AM
Joined: Feb 2005
Posts: 7,456
rxinhed Offline
Trail Leader
*****
Your phone may not have enough memory resource to display such a large file.

Re: Ignition Coil [Re: Trailmonkey] #1106046 03/11/21 04:59 AM
Joined: Aug 2020
Posts: 191
T
Trailmonkey Offline OP
Wheeler
Public library is still closed here. No computer.

Got to be one of only a few things, condenser, resistor, power transistor, distributor pick up unit.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Ignition Coil [Re: Trailmonkey] #1106056 03/11/21 03:15 PM
Joined: Feb 2005
Posts: 1,511
ryany Offline
Body Damage is Cool
The 3.0 12V is known to have issues with the distributor internals - I haven't played with one personally but have heard a number of people who've had failed parts.


95 Montero SR
3.8 MIVEC, Advance headers, 2 1/2" exhaust, Magnaflow muffler, OME shocks & rear springs, 2" body lift, 3" tank lift, 4.90s, TRE front locker, factory rear locker, Roger Brown Rock Sliderz, 315/75r16 (35") tires, Sport big brakes
Re: Ignition Coil [Re: Trailmonkey] #1106062 03/11/21 06:36 PM
Joined: Oct 2020
Posts: 12
L
Lev_from_CA Offline
Need a Spot
TLDR: examine the distributor (pickup, igniter/crank angle sensor, optical disc and sensor), power transistor, and ECM. For diagnostic procedures you'll need the FSM and some google-fu...

Originally Posted by Trailmonkey
the black thing mounted on top of the bracket with 3 wires ( J121 Power Unit ).

That's the power transistor/ignition control module/power unit/coil igniter/igniter switch. The igniter inside the distributor is a different thing (confusing I know). Here's some diagnostic instructions from 2005 for ignition coil and power transistor, in case you haven't tried it this way yet: http://4x4wire.com/forums/ubbthreads.php/topics/608592/re-not-turning-over.html#Post608592 (later in that thread, 1/12k Ohm readings are said to be fine)

The 91's distributor includes a crank angle sensor/top dead center/camshaft position sensor, also called the igniter (this is the optical sensing unit, here's an article on 3sg explaining how it works: https://stealth316.3sg.org/2-cas-91-92.htm); these are somewhat similar to the GM Optispark and Nissan optical disk sensor distributors of early 90s. If these start failing, it may cause weak spark/misfire/no-start (on complete failure) conditions. It seems possible to test it with just a test light at the sensor connector. The distributor pickup failing may also cause similar conditions. Looks like the part number for your distributor is MD148008 with the sensor part number MD618278 (seems discontinued and not available separately; found this via PartSouq and Ilcats, but Mitsu ASA or epc-data should have same info and nice parts diagrams). Here's some info on theory of operation (from a 89 Sigma/Galant w/ 6g72, should be similar to yours): https://workshop-manuals.com/mitsubishi/sigma/v6-2972cc_3.0l_sohc/powertrain_management/... Some folks with Optisparks have had success taking them apart and cleaning the optical sensor; a common failure cause was water intrusion (e.g. from washing engine bay with hose). For the Nissan distributors, testing the optical sensor seems possible with a multimeter: https://www.underhoodservice.com/tech-tip-nissan-optical-distributor-test-2/ (and they posit that a failing PCV valve may coat the optical disc and cap terminals with oil, so a good cleaning may help).

Originally Posted by Trailmonkey
I did see evidence of it arcing from the case to the steel laminates.

Does that suggest a grounding issue in the distributor? Is that one of the distributor igniter's functions?

Originally Posted by Trailmonkey
It has had this short studder from time to time like it cuts out for a split second, just this time it stopped totally

The crank angle sensor or pickup tube would be plausible here, the power transistor also. Intermittent power transistor degradation could be due to overheating, once cooled down it may work fine. Final no-start could be due to power transistor failure. Additional data on when the stutters occurred (after long drives in hot climates? in heavy rain?) may help inference here. Also, the ECM should set codes for crank angle sensor and TDC sensor in certain situations, did you check it (maybe the dash bulb is burnt out and a code is present but hidden)?

The condensers/capacitors can be shorted also, but I'm not sure how that'd cause the observed behavior.

Just a spitball here, but it could be the ECM itself (from a thread circa 2005: http://4x4wire.com/forums/ubbthreads.php/topics/646126.html ; btw electronics/computer repair shops exist that can repair ECMs cheaper than buying new):

Originally Posted by conner
The coil develops its high voltage by energizing the primary winding. The period of time this is energized is called coil saturation or dwell. This builds a magnetic field that when the circuit is opened the field collapses to the secondary winding which in this case provides high voltage to the distributor cap. Excessive resistance in the primary circuit can reduce the secondary voltage produced by the coil considerably. So a bad transistor(coil trigger) in the ECM could in fact allow a weak spark at the coil wire, but will not be able to bridge the rotor gap.

The usual recommendation is to smell the ECM (in glove box area for the 91) and look for a fish smell when cranking. A more involved approach is opening up the cover and looking for leaking capacitors, damaged traces, water damage, etc.

Conclusion: it seems reasonable to suspect the distributor igniter (as OldColt said, these seem to fail occasionally), the ECM (30 years old from the era of quaternary ammonium salt containing capacitors leaking 10+ years later, corroding traces and causing havoc), or the power transistor (could have become removed from the bracket acting as its heat sink and cooked itself to death). All three seem plausible to explain sporadic weak spark/misfires until a sudden no-start condition. More information on diagnostic process and exclusion of hypotheses would be necessary. (Or you could put spare parts in and go from there)

PS: this is assuming all other parts of no-start diagnosis (air, fuel, compression, timing) are good (no clogged fuel filter, no dying fuel pump, fuel in tank, no towel in intake, no melted pistons or chipped valves, no skipped timing teeth, no sheared woodruff keys, no discharged battery/non-charging alternator, etc.)

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