ECU failure causes(Solved), now temp guage(Solved). Yay.

[Mi|<E]

Allrighty so ive a BP in a 94 DOHC using a Protege BP10 ecu and mazda harness -

Ive had the car running several times for about 4-5 minutes and when it
gets to temperature the car just shuts off. When I try to restart it there
is no Check Engine Light (CEL) and I have only half of the red lights on the
right side of the guage cluster (Bottom 2 lit, top 2 not on).

This problem seems to remedy itself randomly when I go wire hunting
and unplug/replug some of the harness. It is not the ECU - ive tried
plugging in the BP09 Fordo one and it does the same thing after a
failure , no CEL light when ignition is set to first position as above.

From what ive read I may have a bad distributor from our pals at
Mitsubishi.. but any other input / suggestions would be appreciated,
im running out of things to check

[SuperK]

there's a temp sensor that'll shut the engine off to prevent it from overheating. Follow the harness till you find it, replace it, it's faulty.

Oldman had this problem on his K8. Could be yours.

[Mi|<E]

Oh good simple things to test and fix

[Mi|<E]

It turns out it was not the coolant temp sensor as it checks
out fine on the ohmmeter.

Heres a kicker for you, the car starts, runs and the speedometer
even works with no modification from me (thats a big deal as its
a 94 DOHC mx-3 with electronic speedo with a 93 BP in it).

The one problem now - temperature guage doesnt want to work
for me and the fan as far as I can tell isnt coming on.

Ive read I need to use the mx-3 coolant temp sensor with the protege
harness in order for it to work correctly. The only problem
with that is the 94 coolant temp sensor has a different plug

Now would a 93 mx-3 coolant temperature sensor do the trick here?
And does anyone know how the fan works exactly? Like does it
take its reading from the ohms of the CTS (coolant temp sensor) or
does it take a signal from the ECU which is reading the CTS ohms?


Oh and one more thing, how does one rig the coolant fan to be always on?

I can drive the car around with it on all the time for now, that would ease
my concerns of overheating.

[shameem]

For the coolant sensor - go with one that came out of the same car type as your ECU - if you have a protege ECU - get a protege coolant sensor - it is like <20 bucks at autozone - and it will fit the harness nicely.

I think 92-94 proteges use 3 coolant sensors - one for the ECU, one for the fan and one for the temperature gauge in the dash. The wiring is extremely similar to the SOHC models.
(In DOHC models the fan is controlled by the ECU).

Did you just plug in the dash harness or did you actually follow wiring diagrams? The SOHC and DOHC dash harnesses may be "slightly" different (different wire colors - different functions etc) - so if you just plug a SOHC harness into a DOHC dash without looking up wiring diagrams - you *may* have problems...

The speedo sensor is in the transmission - it has got nothing to do with the engine. I think its on a separate harness that goes directly to the dash.

[Mi|<E]

Oh no no it wasnt just a random plug and go. I took the wiring diagrams
from both Protege and Mx-3 and made the necessary splicing. The
pretty picture is in my worklog (link below in red).

The ECU and wiring harness are from a 91 Protege LX 1.8 DOHC. Ive
also got all 3 temp sensors from that engine. The ECU temp sensor
(2 wire green top) read out good on an ohm meter. It turns out the
fan connector was rather rusty and a quick scrub got it going whilst
I jumpered the Fan Relay located under the coolant reservoir on the
drivers side. Its just the temperature guage on the dash cluster that
doesnt want to work for me. Im wondering if a temp sensor from a
93 Mx-3 would work with the Protege ECU ?

Your right about the speedo, its just when I get the G-series tranny
in there after its rebuilt that I will have problems with the electronic
speedo. I hear it can be 'shimmed' and still work though? I'll find out
when I get to there.

But as for now its got all 3 Protege temp sensors, Protege harness
and a Protege BP10 ECU.

As the car warms up the idle comes down - so if im not mistaken the
2 wire green color temp sender to ECU is working fine.

But the temp guage on the dash isnt working. This is the single wire
grey plug ? Maybe I'll mull over the wiring again, the 94 DOHC might
need a 2 wire or something different. Im trying to keep track of
everything so it can be documented and ready for 94mx to 1st gen BP
swappers.

I wonder how the single wire sensors are tested? Do they just shunt at
a certain temperature?

I dont have my protege service manuals with me as they are on my
laptop Have to check tomorrow.

[SuperK]

in the 94/95 DOHC, the temp sensor for the gauge cluster is on the right side of the engine, right behind the thermostat. It's a single little black wire.

I don't know where it is on the BP, but it could be in a similar spot? Is there a single wire running right behind the coolant thermostat housing?

[shameem]

Yes it is just a single Black/Orange wire - somewhere near the thermostat - very easy to mistake for a ground wire. The one wire sensor is the same as 2 wire - except it gets its ground connection directly from the block. The 2 wire has the separate ground to avoid loop effects since it goes to a digital system.

[Mi|<E]

So I had two wired in the harness plug reversed. And the temp sensor connector was on
ground instead of on the sensor. Not sure how that happened so I'll blame it on the help
I got . Or the EGR that isnt in the engine now. Its always the EGR.

I'll make the correct changes to my wiring how to. Thanks for the help to the above posters,
much appreciated.

Temp gauge works great now and the fan even comes on.

Next step is to get it timed right... 11 BTDC here I come.

[Ryan]

I'm having temp guage problems with my BP swap as well.

I don't know exactly which is which of the three, but the one that goes into the end of the thermostat housing is from my MX-3, and the rest are probably original BP sensors. I am using the SOHC harness and 91 BP09 ECM.

The car seems to run fine. When the temp needle stops moving the fan comes on almost right away. The only problem is, it stops moving at around 11:00. After the "safe" but before the red. It doesn't seem that hot. Should I try out a protege/escort sensor? Maybe I'll just go see which one does what...

[Mi|<E]

I used a BP sensor and my 'hot' is at about 10 o'clock

[Ryan]

I'm going to put in my SOHC sensor tomorrow, I'll let you know how it goes. its the green one.

[Mi|<E]

Oh the temp gauge sensor is the tiny one on the driver front of the head
with a small slide plug and one wire.

[Ryan]

I'm confused. The green plug didn't change anything.

Are you talking about the combined one wire clips that fit onto the front of the SOHC head?

[Mi|<E]

This one (in the center) :
This is a BP but the SOHC B6 sensor is in approx the same location
Page B1-078 on the 1992 workshop manual if you want to look there