Help w/ECU and check engine light non-op

[s'ko]

I am having some problems w/my Check engine light on my EJ18 motor.

 

This is from an EJ18 OBDI motor swapped into my BRAT. I am trying to get it to pass inspection so I can register it. The referee will be looking to see that the check engine light is wired in and working.

 

Here's the scoop.

 

I am using a turn signal light bulb as the CEL. The CEL ecu wire hooked up to the bulb light as a ground and there is a wire coming from the fuse box to power the light, 15 amps. It worked and all of the error codes were fixed. I went and made a hole in my dash to mount the CEL and while I was finishing it up, the light stopped working. Fuse that it's connected to is not burnt out.

 

Ohms meter shows continuty but when I turn the key on, there are no volts coming from the wire. I took the tachometer wire to the light and started the engine and the light lit up. I connected the black test plug and the light does not come on. (before when it was connected, the CEL lit up) I took the ECU cover off and looked at the circuit board and there does not seem to be any burns or signs of a short or it being fried.

 

So anyone know what's happening? Should I just get a new ECU and not try and fix this?

 

Thanks

 

BW

[Cougar]

I have had to replace an IC in the ECU on a unit I worked on in the past that had the same kind of trouble. The ground to the lamp is controlled by the ECU. Was the replacement bulb the same kind of bulb as the original one?

[s'ko]

I have had to replace an IC in the ECU on a unit I worked on in the past that had the same kind of trouble. The ground to the lamp is controlled by the ECU. Was the replacement bulb the same kind of bulb as the original one?

 

The light is not the original one.

 

it's a standard light bulb, similar to one from a turn signal.

 

I have another ECU lined up and I plan to use an LED to light up the new on.

 

BW

[OB99W]

[...]it's a standard light bulb' date=' similar to one from a turn signal.[/quote']I'm sure that Cougar is asking about the bulb because the ECU circuit is designed to "sink" a limited amount of current, and some bulbs could easily exceed that amount.

 

 

I have another ECU lined up and I plan to use an LED to light up the new on.

(I can't tell from what you said just how you intend to use the LED, so perhaps the following information is something you already know.)

 

If an LED is used without current limiting, the ECU lamp-driving circuit can be damaged similarly to with a wrong bulb. If the LED doesn't include a built-in current-limiting resistor (i.e., designed to run at about 12 volts), you'll have to wire one in series with the LED. The resistance value determines the current -- typically to limit the LED current to somewhat over 20 milliamps, a 470 ohm resistor could be used; for 10 milliamps (the LED will be dimmer, and may not be easy to see in strong daylight), use a 1,000 ohm (1 kohm) resistor.

[s'ko]

I'm sure that Cougar is asking about the bulb because the ECU circuit is designed to "sink" a limited amount of current, and some bulbs could easily exceed that amount.

 

 

(I can't tell from what you said just how you intend to use the LED, so perhaps the following information is something you already know.)

 

If an LED is used without current limiting, the ECU lamp-driving circuit can be damaged similarly to with a wrong bulb. If the LED doesn't include a built-in current-limiting resistor (i.e., designed to run at about 12 volts), you'll have to wire one in series with the LED. The resistance value determines the current -- typically to limit the LED current to somewhat over 20 milliamps, a 470 ohm resistor could be used; for 10 milliamps (the LED will be dimmer, and may not be easy to see in strong daylight), use a 1,000 ohm (1 kohm) resistor.

 

So from what I am reading I probably maxed out the current in the circuit and fried it. Next question, does anyone know the amount of current it is suppose to run at? I guess I could hook up a multimeter and determine that output w/o the engine on and then set the current at that. my guess it should be around 10 volts. That is what the other wires are reading w/the engine off. Does that sound about right?

 

BW

[Cougar]

I'm not sure what you are saying here. I think the original bulb is a 12 volt bulb and I would guess the current for it would be around 80 milliamps (.08 amp) but I'm not sure. I guess you have a good reason why you just don't get a normal replacement bulb for this.

 

You may have damaged the circuit by using something else in place of the original bulb but maybe not. I have replaced the IC that runs that circuit and it had the normal bulb in place.

[OB99W]

[...]I guess I could hook up a multimeter and determine that output w/o the engine on and then set the current at that. my guess it should be around 10 volts. That is what the other wires are reading w/the engine off. Does that sound about right?

The voltage source is the car's battery (and charging system' date=' with the engine running). The ECU provides a switched connection from that voltage to the CEL. I'm concerned that you may not be understanding the relationship between "voltage" and "current". The amount of current that flows is related to the battery voltage [b']and[/b] the characteristics of the "lamp" (bulb with filament, or LED); that relationship is determined by Ohm's Law, which anyone interested might want to search for on Google.

 

By the way, although Ohm's Law explains the voltage/current/resistance relationship, measuring the resistance of a bulb or LED with an ohmmeter won't provide very useful data, for several reasons that I won't get into here. (For those of you needing at least one more word on the topic, it's "nonlinear". )

 

Not exceeding the current draw of the original lamp is key, although that may or may not be directly related to the problem you're having.

[s'ko]

I'm not sure what you are saying here. I think the original bulb is a 12 volt bulb and I would guess the current for it would be around 80 milliamps (.08 amp) but I'm not sure. I guess you have a good reason why you just don't get a normal replacement bulb for this.

 

You may have damaged the circuit by using something else in place of the original bulb but maybe not. I have replaced the IC that runs that circuit and it had the normal bulb in place.

 

The reason I didn't use the normal replacement bulb is b/c this is part of my EJ 18 BRAT swap. BRAT had a carbed feedback system w/o a CEL.

 

OB99W: you are right. I don't think I understand the info about current. I will have to do some research and probably call my brother who is an electrical engineer to pick his brain. My main concern is not messing up the newer ECU that I am getting.

 

I had to wire something in there so that when I get it smogged, the light will turn on and the referee will see that I hooked it up correctly. Otherwise I will fail and then have an illegal swap. If I didn't have to get it smogged I would just leave it as is b/c the car is running fine w/o the light.

 

BW

[86BRATMAN]

s'ko I thought all the feedback carb cars had an ecs light in the tach. All the ones I've come across have.

[s'ko]

s'ko I thought all the feedback carb cars had an ecs light in the tach. All the ones I've come across have.

 

I took apart the combination meter/gauge cluster and looked at all of the lights and there is no ECS space.

 

I went to the dealer and there are two lights that go into the cluster. one is a 1.3 watt and one is a 3 watt. I am going to go with a 1.3 watt bulb to make sure I don't damage the new ECU.

 

Thanks for all of the input.

 

BW

[Cougar]

You're welcome for the help. I think the 1 watt light will be ok. You could use your LED idea if you want and that would work also.