How to test 7MGE ign control module? Hit & miss starting problem 89Toyota Cressida

> wrote:
>On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>
>I have a factory service manual, so far haven't found a mention of a TDC (t=
>op dead center) sensor. I don't think it's on the cam or crank since I don'=
>t recall ever seeing anything like a sensor on either - I'm guessing it's m=
>ost likely on the distributor.=20

Toyota will call it something else. There is at least one sensor going
into the computer that tells the computer what the crankshaft position is.
If you have wires coming out of the base of the distributor, that would do
it.

TDC sensor tells the computer when to fire the plugs. The computer tells
the ignition control module when to fire the plugs. The ignition control
module puts current into the coil to fire the plugs.

All of these things fail (even the coil, and that hardly ever fails).

>
>> have you tested the icm yet?
>
>
>What's happened since I first posted this - while getting familiarized with=
> the wiring to the ICM, I was nosing around, grabbed and jiggled the harnes=
>s connector to the coil. Now the car fires up instantly every time and runs=
> smooth as silk as before this issue developed. I can't say for a fact that=
>'s what did it but that's the only manipulation I did and it's been running=
> without issue since. Maybe corrosion on the connector reached a critical p=
>oint and was impeding spark?=20

Absolutely. Now take the whole thing apart, clean it with DeOxit or
Cramolin, put a little dielectric grease on there, and put it all
back together.

While you are at it, you might as well do the same to all the other
ignition system connectors because if one is going bad, others will be
going bad in the future.

>It's unclear from the previous input what I'm supposed to do to test the pu=
>lse from the ICM. Am I supposed to be able to use the inductive timing ligh=
>t to get a pulse from one of the ICM wires?

Nope, but you should be able to see it on an analogue voltmeter. An
oscilloscope makes the job easier but a meter is fine. Skip the DMM.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On 09/21/2013 02:52 PM, Scott Dorsey wrote:
> > wrote:
>> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>>
>> I have a factory service manual, so far haven't found a mention of a TDC (t=
>> op dead center) sensor. I don't think it's on the cam or crank since I don'=
>> t recall ever seeing anything like a sensor on either - I'm guessing it's m=
>> ost likely on the distributor.=20
>
> Toyota will call it something else. There is at least one sensor going
> into the computer that tells the computer what the crankshaft position is.
> If you have wires coming out of the base of the distributor, that would do
> it.
>
> TDC sensor tells the computer when to fire the plugs. The computer tells
> the ignition control module when to fire the plugs. The ignition control
> module puts current into the coil to fire the plugs.
>
> All of these things fail (even the coil, and that hardly ever fails).
>
>>
>>> have you tested the icm yet?
>>
>>
>> What's happened since I first posted this - while getting familiarized with=
>> the wiring to the ICM, I was nosing around, grabbed and jiggled the harnes=
>> s connector to the coil. Now the car fires up instantly every time and runs=
>> smooth as silk as before this issue developed. I can't say for a fact that=
>> 's what did it but that's the only manipulation I did and it's been running=
>> without issue since. Maybe corrosion on the connector reached a critical p=
>> oint and was impeding spark?=20
>
> Absolutely. Now take the whole thing apart, clean it with DeOxit or
> Cramolin, put a little dielectric grease on there, and put it all
> back together.
>
> While you are at it, you might as well do the same to all the other
> ignition system connectors because if one is going bad, others will be
> going bad in the future.

+1 on this, was going to be my suggestion as well. Might as well do
every accessable connector under the hood, ignition/FI related or no.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

On 09/21/2013 10:15 AM, jim beam wrote:
> On 09/20/2013 09:23 PM, wrote:
>> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>>
>>>> Where is this located?
>>>
>>> crank, cam or distributor.
>>
>>
>> I have a factory service manual, so far haven't found a mention of a
>> TDC (top dead center) sensor. I don't think it's on the cam or crank
>> since I don't recall ever seeing anything like a sensor on either -
>> I'm guessing it's most likely on the distributor.
>
> on an old distributor, each of the lobes was timed for each ignition
> point, and that's what you're looking for here. depending on the type
> of distributor it'll have a reluctor or other sensor with at least one
> "pulse" generator for each of the four firing positions. [on your
> 4-banger.]

Cressida is an inline six, if I'm not mistaken (related to if not the
same as a contemporary non-turbo Supra) Definitely worth fixing as that
is a classic of quasi-modern engines and "they don't make 'em like that
anymore" (and that's a bad thing.)

that said, I haven't a clue where the appropriate sensor is on that vehicle.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

Nate Nagel wrote:
> On 09/21/2013 10:15 AM, jim beam wrote:
>> On 09/20/2013 09:23 PM, wrote:
>>> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>>>
>>>>> Where is this located?
>>>>
>>>> crank, cam or distributor.
>>>
>>>
>>> I have a factory service manual, so far haven't found a mention of a
>>> TDC (top dead center) sensor. I don't think it's on the cam or crank
>>> since I don't recall ever seeing anything like a sensor on either -
>>> I'm guessing it's most likely on the distributor.
>>
>> on an old distributor, each of the lobes was timed for each ignition
>> point, and that's what you're looking for here. depending on the type
>> of distributor it'll have a reluctor or other sensor with at least one
>> "pulse" generator for each of the four firing positions. [on your
>> 4-banger.]
>
> Cressida is an inline six, if I'm not mistaken (related to if not the
> same as a contemporary non-turbo Supra) Definitely worth fixing as that
> is a classic of quasi-modern engines and "they don't make 'em like that
> anymore" (and that's a bad thing.)
>
> that said, I haven't a clue where the appropriate sensor is on that
> vehicle.
>
> nate
>

TDC sensor is Honda terminology. The L-6 engine Toyota Cressida in 1989
had three pickup coils inside the distributor called NE, G1, and G2. If
the ECU likes what it sees, from those three, it sends the IGT signal to
the igniter over-and-over again, which grounds the coil over-and-over
again producing spark in the secondary system over-and-over again.

GW