I have a 92 mitsubishi expo 1.8L LVR with 200,000
miles last week it just stalled when going around the corner. No spark,
removed the ejector line and all 4 ejectors fired and sprayed fuel. I'm
looking at replacing the dist. but whould like to know how to test it
before I buy one. I was told to check for a 5 volt signal on the input to
the dist. which come from the ECU. I was told it fires the bipolar
transistor in the dist assy. I don't want to find out that the problem was
the ECU or even maybe the timing jumping a tooth. does this make sense?
Did you check the ECU diagnostic output pin for an error code. All you
need is a jumper wire and an analogue meter.
This vintage ECU is prone to failure, (but is also easy and cheap to fix).
When was your timing belt last changed / checked.
And because you asked, Pin 6 on the dist plug should have an active
ground to fire the coil. Normally there is a pulse train at this point,
supplied by the ECU, if and when other sensors tell the ECU when the
crank position is correct to fire a SP.
When pin 6 is grounded, pin two will swing from 12 volts to ground (if
the transistor is working) and the coil should fire. Note that the
ignition switch needs to be in the "run" position for this to happen.
The manual suggest the following procedure to test the transistor.
1. attach a 1.5 volt battery (negative side) to terminal 5 of the
connector block. Connect the positive to terminal 6 of the connector
block, intermittently, while measuring the resistance between pins 6 of
the 6 pin connector block, and pin 2 of the two pin connector block
(negative meter lead to pin 2).
2. Battery connected, very low resistance
3 Battery disconnected, very high resistance.
Pin 6 should be Green-Yellow
Pin 5 should be Black
Pin 2, on 2 pin connector block, should be White-Black
O BTW, the primary of the coil is across pins 1 and 2 of the two pin
connector, the secondary is across pin one and the rotor.
But first thing I'd do is check the ECU trouble code. If the signal is
constantly high, the ECU is toast. If the signal is constantly low, the
ECU has no power, If the signal is a 50% pulse train, the ECU is working
fine. Any other pulses are actual error codes.
All this is based on a 1992 Mitsubishi 1.8 liter eclipse, but it should
be the same.
If you don't have an analogue meter (that's a meter with a dial), buy
one, a cheap one (under $10.00 CDN) will do just fine for these tests.
All you need is one that can measure a voltage of 20 volts or less and a
resistance up to 20,000 ohms.
First, I want to thank you, so so much for taking the time to explain and
answer my question. I’m buying a Mitsubishi factory service manual
but, I won’t have it for a week or so. This will give me a good
point to start at.
I’m a little confused on the ECU diagnostic pin. I don’t know
where to find it. I do have a
Simpson 260 meter & O-scope. Is this a point on the ECU where you can
verify the pulse train and determine that the module is working properly?
I have read where replacing both the dist & ECU did not resolve the
problem. I think this was due to the timing belt jumping a tooth.
I’m not sure if this applies to my situation. My belt was replaced
back at about 115,000 mile, so it may be due. Maybe, the best thing is to
do all three. Normally, I won’t waste time on a car with this much
mileage, but it was such a good running car. I miss not having it. Thanks
again for your help
On an eclipse, the diagnostic plug is located on the right side of the
fuse panel, which is against the left wall of the passenger compartment,
under the dash.
It's a 12 pin connector, with nothing attached to it. Usually covered
by a plastic dust cover.
Pin one outputs a pulse (attach the positive of the meter here),
depending on the error code or status of the ECU (vehicle ignition needs
to be in the "run or ON" position).
Pin 12 is a ground point (attach the negative of the meter here).
However, you may not need the ground on pin 12 to enable the ECU output.
Attaching the negative lead from you meter to a good ground should be OK.
Attach the meter with alligator clips, then turn the car to the "run"
position. Watch the needle deflections, that's the code output.
Longer pauses, indicate the space between digits of the error code.
Example; two long pulses, one longer pulse, then three short pulses,
(signals then repeats) is code 23 on an eclipse, which is "number 1
cylinder, top dead center sensor" , output error (on a 1991 Eclipse),
yours may be different. Your service manual will have all the codes.
With your meter and O-scope, you should be able to test every electronic
item in your car, including all the engine management sensors.
If the ECU is toast, let us know, don't replace it. There is a web page
that has all the details on how to repair it, for about $5.00 CDN in parts.
If you have 85,000 miles on the timing belt I would suggest you replace
it now, as well as the balance shaft belt, tension pulleys, and water
pump ( I guess it depends on how long you want to keep the car, hows the
compression on the engine).
Remember, these details apply to an Eclipse, of your vintage, your car
may be slightly different.
Yes,I did see that connector. And now,it all makes sense. Is the fix for
the ECU the replacement of the 3 electrolytic caps? That would be way to
easy.... From what I'm reading, it appears that this Mitsubishi ECU was
one of the most likly to fail.
I was getting unexplained bucking every now and then. I just thought it
was a bad fuel ejector.
Would that be the processor doing a reset because of the caps? I took a
quick look at mine and they all look good, maybe I should replace them.
So,I now think I can test both the Dist & Ecu. Your information has been
very helpful. My bet is now on the ECU and not the Dist. I'll let you
That is the usual fix. I would do the ECU capacitors on spec. But first
check the diagnostic output codes.
Pay close attention to the larger capacitor right in the middle of the
Usually there is some material, like contact cement, used to hold it a
bit better to the PCB.
On two of the ECU's I've worked on, under that material, there has been
a break on the thick trace on the PCB. Almost looked like it was on
purpose, as the gap was about 1/2 mm wide.
Using your scope, you can also check the TDC sensor, pin 4 (Blue wire)
of the 6 pin block
and the crank angle sensor, pin 3 (brown-yellow wire) of the same
Should see a 5 volt pulse train as the engine cranks.
On my Eclipse, they are both located in the dist.
OBTW, the capacitors are an industry wide problem. I've even replaced
them on a year 2000, IBM Aptiva system board, as well as switch mode
I need your help once again. On the 12 pin connector, there are only seven
I take it that pin 1 is yellow/red (pulse train) pin 12 grn/blk (Ground).
Second: question, you mention that there is a 1/2mm gap, is that for the
cap spacing ? Or a problem that needs to be addressed.
Third: I noticed on the pc(ECU)board that there are 4 transistor drivers,
are they for the fuel ejectors, and the one transistor driver in the
middle for the Dist driver to excite the coil. That's just an observation
on my part.
My last question. I remember reading in a post, that if the timing belt
jumps the ECU will know and halt the pulse to fire the coil. This may be a
form of protection for the valve and piston clearance.I'm not sure if this
is true for this vintage Mits.
Thanks once again, I can't thank you enough for all your help
P.S. I'm still waiting for my factory service manual.
My eclipse manual (Laser manual) shows pin 1 as yellow, pin 10 as
white,pin 11 as yellow-white, pin 12 as black
The row of pins that includes the "key" (two missing pin positions) is
the low count pins ( 1 to 6) Pin one is on the side that has three pins.
Pin one is closest to the edge.
The 1/2mm gap was in the actual copper, circuit trace. Almost like
somebody cut part way threw the trace, maybe making it a safety blow out
Don't know for sure about the transistor drivers. Injectors are wired
to pins 51, 52, 60, and 61 of the ECU pins. Pin 62 controls the purge
control solenoid. Pin 54 is the drive for the power transistor in the dist.
When I installed the timing belt on my sons Laser (Eclipse, sort of) I
was one tooth out. The car ran fine (but gutless), till you got to a
hill then it hardly moved.
Can't answer for sure about your last question, but my guess is it's not
smart enough to know if the belt jumps a few teeth, but it would not
see and pulses for the TIC and crank angle sensor in the dist if the
belt is totally broken.
I see there is a difference on the color code. So'I look over the Net and
I see over and over again that the caps seem to be the problem. Since I
can't wait any longer for this service manual, I decided to check the
caps, and guess
what,the 100 uf is shorted. So tomorrow, at work
I will bring it to our electronics lab and desolder all three caps.
I hope I did cause any problems on my dist. I started to remove some of
the parts to check the coil. I need to get a new gasket for the cover.
I hope this will solve the problem, because right now both of my cars are
I see that you have help quit a few people with
this problem. How did that women make out with her car? Looks like she got
4 ECU at a junk yard and all four were bad, but at 50 cents each I guess
she got a good deal.
Not everybody gives feedback of a successful repair.
You never did tell me what you found on the diagnostic output lead.
To test all aspects of the dist., you did not have to take it out of the
It's keyed, so you can only install it in one direction.
I'll be off the air for a while, it's summer.
Good luck with your cap repair, I guess you know you can use larger
value caps, if you want.
All the factory manuals came in today. I replaced the caps and then
retired but no luck.
The caps were not shorted at all. I was reading the wrong points. They
really looked good, but I replace them always. I found the data out which
is pins 112 & 113 on the ECU. The funny part is I'm get 5 long pulses and
5 short pulses I check and rechecked the only thing I can see is maybe its
a 44 trouble code which is a bad ignition coil or power transistor. However
the manuals says that for the 2.0L not 1.8L
I check the Dist now that I have the schematics of the wiring diagrams.
The power transistor a NPN the pins are: pin 5 emitter pin 6 base and pin
12 (on the Tach) the collector. The manual says you should get 3 volts to
fire the base to emitter 'm getting 1.75 volts. Here is the part that
looks wrong. The base to collector has resistance in one direction, less
than 300 ohms very high in the other direction.I seem to remember that
this should be high in both directions. The emitter base ratio is less
than 10. (30 ohms foward biased) (150 ohms reverse biased)I still hate to
replace it cause I read where another person had a problem where he said
the transistor failed the test (low volts) but found the caps to be the
problem. Maybe I should read all the voltages on the ECU ??????
What your thoughts
I did find a fault code 55 for the 1.8 L
model. It is known as IAC Idle air control valve
sensor. I sure this has no effect on my ignition problem. It may however
prove that the ECU is working maybe??????
If your getting error code 55, then your ECU is running.
Don't rule out the IAC sensor, until after you have tested it.
Pin numbers almost match, I have base on pin 6 emitter on pin 5 and
collector on pin 2, tach feed.
Are you sure you ment pin 12, or might it be a typo.
Think of the power transistor as two diodes, with a common point (the base).
Base/emitter and Base/collector.
IN both cases, you should get a high resistance in one direction
(base/emitter for example) and a low resistance in the other direction
(emitter/base). Remember that there may be other components in the
circuit, which could give you a false reading (a tach for example).
It's best to use the test in the service manual, as it actually tries to
operate the transistor. You need a 1.5 VDC battery to simulate the
pulse train from the ECU. The procedure is in the "Ignition system -
Remember that if you fire the transistor (Ignition in run position) you
should get a spark on one of the plugs.
With the ignition switch in "run" position, you should see 12 volts at
the tach connector (pin 12 for you, pin 2 for me).
When the transistor fires, you should see a ground at this point.
The transistor switches a ground onto the coil to charge it, then
removes the ground to fire it. You can simulate this by applying a
ground, very temporairly, to (pin 2 for me, pin 12 for you), while
holding a grounded screw driver next to the center pin of the
distributor (pull the cap off). Ignition switch in "run" position. If
the coil is good you should get a good spark.
As well, you can measure the resistance of both sides of the coil, the
values are in the service manual.
Actually on this dist, you should be able to test everything.
I did the battery biasing test from the manual. They said to hook the
battery +1.5 volts to pin 6 base and -1.5 volts to pin 5 the emitter which
is grounded when connected to the dist. Then take the ohm meter and connect
the neg probe to pin 12 the tach(collector) and the pos probe to pin 5 the
emitter. This was done with both connectors removed from the dist.
It failed because it had continuity with or
without the battery connected. From the diagrams of the manual I can not
see any other path to addd to the low resistance reading. Again looking at
the diagrams with the CONNECTORS OFF I only see the the power transistor in
series with the primary dist. coil.
I tried the temperary grounding of the tach wire pin 12 (collector)with
connectors on. This of course is bypassing the transistor totally. I did
not get any spark from the secondary of the coil. This may be due to the
low resistance from the collector to emitter. I think it's time to replace
the dist. I don't know of any other testing I can do.
OK, one last test.
Disconnect pin 5 from the multi position connector. This is the pin
connected to the emitter of the power transistor. It provides the
ground for the coil, when the transistor triggers.
Disconnect pin 6 from the multi position connector. This is the pin
connected to the base of the transistor.
Now momentarily ground the tach lead (pin2 for me, pin 12 for you).
Monitor the secondary output, if all is well you should get a spark.
This bypasses the transistor, and takes it out of the circuit. Remember
that the ignition should be in the "run" position, and just to make
sure, measure the primary coil side for 12 VDC at pin 1 (on my diagram
the lead is called "Ignition switch 1G1"). If the tach side isn't
grounded, you should also see very close to 12VDC.
Here's another way to do the same thing. Disconnect both connectors
from the dist. Apply 12VDC to the primary side of the coil (pin 1, the
one that is common to both the primary and secondary coils). Ground pin
2 (pin 12), the tach lead, momentarily. The secondary should spark
(center point of dist, cap removed).
Here's a rambling thought. If the transistor is indeed gone, you could
attach an external one, by connecting the collector to pin 2 (12), the
base to pin 6, and then grounding the emitter. Of course you'd want to
disconnect pins 5 and 6 from the dist.
Please be aware that semiconductor representations on these service
manuals, are just that, representations of real circuits, and do not
represent actual electronic wiring. That power transistor could be a
Darlington, for example.
Today was a great day.. First thanks again so much for helping. I hope I
can return the favor someday..
After doing that test I decided if was time to replace the Dist. So I took
my Simpson, and went to the junk yard and purchased a dist. When I when to
test it before buying it, I end up getting the exact same readings on the
replacement. So now I not sure what to do. The guy said he took it from a
running 93 Expo. Well, for $65.00 I took the chance. I didn't feel very
good about because I didn't think it would work. The screw on the dist cap
was broken. I had to retap to get it secure.
So I came home, took a few hours break, and then I replaced it, and guess
what, I worked.....So here is my conclusion. It wasn't the so called
transistor and it was not the coil. What I think the problem was in the
camshaft or crankshaft sensor. Thats the only part of the dist I didn't
check. The manual is misleading you have resistance from the emitter to
collector pin5 to pin12. This test makes you think the transistor is bad,
but infact it good. They speak of continuity and no continuity. They
should say what the resistance values are.
So to any reading this, I hope it helps you solve your problem. The garage
wanted $350.00 plus labor for a rebuild. I was vey close to doing it but
decided to check this board. And thanks to Ray who took his time to help I
was able to get the fix with out spending hundreds of dollars. I'm
enclosing my e-mail incase I'm not reading this
board. firstname.lastname@example.org please feel free to ask any questions I have the
complete factory manual from Mitsubishi.
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