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How to test 7MGE ign control module? Hit & miss starting problem 89Toyota Cressida
My '89 Cressida with 7MGE has developed a problem where it takes numerous tries to start.
Crank a few - pause - crank a few - pause - crank a few - pause - crank a few - starts Once it finally starts it runs like a clock. No problem. It got worse over the period of probably a month or so - now it does it pretty consistently when cold but will also do it after getting up to operating temp and sitting for 5 - 20 mins. If I turn it off and restart immediately it will fire up again. Sometimes it will start right up cold too. The immediate cause is clearly no spark as per inductive timing light. Then suddenly there's spark and it runs. I've determined there's fuel - disconnected the fitting to the fuel rail when symptoms show up, wrapped it in paper towels and cranked - fuel is flowing. So, what does this suggest? ICM going funky? What other culprits? What's a good way to test the ICM? Thanks for all input. |
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
On 09/16/2013 08:46 PM, Geoff Welsh wrote:
> wrote: >> My '89 Cressida with 7MGE has developed a problem where it takes >> numerous tries to start. >> .... >> >> The immediate cause is clearly no spark as per inductive timing >> light. .... >> What's a good way to test the ICM? >> > > The ECU sends the IGT signal on the Y-G wire to the Igniter. If that's > pulsing, then the the wire at the negative side of the coil should be > pulsing. You may be able to see the pulsing as a flashing bulb with a > test light, but I would use a lab scope to check for a square wave. > > GW i hesitate to recommend a scope because, although they are by far the best tool to use, it's unlikely they have access to one if they're asking the question - and inexpert use can be expensive if they get a back-emf spike into it. i know modern scopes are supposed to be protected, but electronics flea markets are full of scopes with a channel out for that kind of reason. -- fact check required |
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How to test 7MGE ign control module? Hit & miss starting problem 89Toyota Cressida
> wrote:
>My '89 Cressida with 7MGE has developed a problem where it takes numerous t= >ries to start. > >Crank a few - pause - crank a few - pause - crank a few - pause - crank a f= >ew - starts > >Once it finally starts it runs like a clock. No problem. It got worse over = >the period of probably a month or so - now it does it pretty consistently w= >hen cold but will also do it after getting up to operating temp and sitting= > for 5 - 20 mins. If I turn it off and restart immediately it will fire up = >again. Sometimes it will start right up cold too. > >The immediate cause is clearly no spark as per inductive timing light. Then= > suddenly there's spark and it runs. I've determined there's fuel - disconn= >ected the fitting to the fuel rail when symptoms show up, wrapped it in pap= >er towels and cranked - fuel is flowing. > >So, what does this suggest? ICM going funky? What other culprits? > >What's a good way to test the ICM? I'd look at the TDC sensor. I think on those cars there is also a second flywheel pickup. If the ICM doesn't see the engine turning, it won't do anything. If the sensor has a shorted turn it might be working okay at high RPM but not at starting RPM. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
On 09/17/2013 06:00 AM, Scott Dorsey wrote:
> > wrote: >> My '89 Cressida with 7MGE has developed a problem where it takes numerous t= >> ries to start. >> >> Crank a few - pause - crank a few - pause - crank a few - pause - crank a f= >> ew - starts >> >> Once it finally starts it runs like a clock. No problem. It got worse over = >> the period of probably a month or so - now it does it pretty consistently w= >> hen cold but will also do it after getting up to operating temp and sitting= >> for 5 - 20 mins. If I turn it off and restart immediately it will fire up = >> again. Sometimes it will start right up cold too. >> >> The immediate cause is clearly no spark as per inductive timing light. Then= >> suddenly there's spark and it runs. I've determined there's fuel - disconn= >> ected the fitting to the fuel rail when symptoms show up, wrapped it in pap= >> er towels and cranked - fuel is flowing. >> >> So, what does this suggest? ICM going funky? What other culprits? >> >> What's a good way to test the ICM? > > I'd look at the TDC sensor. I think on those cars there is also a second > flywheel pickup. If the ICM doesn't see the engine turning, it won't do > anything. If the sensor has a shorted turn it might be working okay at > high RPM but not at starting RPM. > --scott > that's step two - eliminate the simple stuff first. -- fact check required |
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
On Tuesday, September 17, 2013 9:00:18 AM UTC-4, Scott Dorsey wrote:
> > I'd look at the TDC sensor. I think on those cars there is also a second > > flywheel pickup. If the ICM doesn't see the engine turning, it won't do > > anything. If the sensor has a shorted turn it might be working okay at > > high RPM but not at starting RPM. Where is this located? |
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
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. > 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 harness 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 point and was impeding spark? It's unclear from the previous input what I'm supposed to do to test the pulse from the ICM. Am I supposed to be able to use the inductive timing light to get a pulse from one of the ICM wires? |
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How to test 7MGE ign control module? Hit & miss starting problem89 Toyota Cressida
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