Electrical Guru's

[4X4HIGH]

Ok guys, I need someone with good electrical knowledge. As some of you might know I just finished my Autometer gauge install along with some LED's for things like turn indicators, Hi Beam indicator, SES light and Brake warning light. All of the LED's work as/when they should BUT I have an issue that I REALLY need to fix QUICKLY. I went for an emissions test this past saturday and failed the Nox portion of the test (everything else passed with flying colors). I remembered that when Brian at TBIchips burned a chip for me he disabled the EGR function (I told him I needed any emissions stuff to remain) so this is why my Nox numbers are way too high. Now fast forward to a couple days ago when I contacted Dave w for a lending hand to help me figure out how to correctly use my chip burning hardware/software that I purchased a couple years ago to turn the EGR function back on (I/we were successful in doing so). I basically wired a light between the 2 wires going to the EGR solenoid so that I know when the ECM is commanding the EGR to be on, here is where my problem lies. When the EGR is commanded by the ECM to turn on the SES light will light very but very dim making me think there is some sort of back feed to the SES light. Does anyone know how I can fix that? I removed my temporary light to the EGR thinking that may be causing the issue but it still does it. I have to go back for a retest on the emsissions this saturday and if that light comes on it is an automatic fail and I don't need that to happen.

 

[Indy4x4Fab]

and this is y carbs and diesels are better, then tbi. sorry but never ran in to this problem. ask throttleissues, he may have ran in to this before. and hes in socal, closer then me. hes my go to guy for problems like this. hope he can help.

 

[wasted wages]

you may have to place a small resistor across the LED to bleed away the backfeed....also if you place a diode in the wire leading to the LED,, it will only allow voltage to pass one way....It could be that the solenoid or ECM is pulling some stray ground voltages thru the LED thus causing it to light up very dim..

a diode acts just like an electrical check valve in the fashion that it will only allow voltage to flow one direction...

may be worth a try.... you can get diodes and resistors at any radio shack...

 

[folkenheath]

Scott, you can block feedback into another circuit by using a small diode, you can get them for less than a buck at radio shack. Get the 100V units, there are the same size that come in MSD kits to stop engine run-on from alternator feedback in older vehicles. A diode is like a one way check valve for electricity.

The problem is, to figure out where to put it in your circuit to still allow the EGR to function and allow the engine light to turn on when it really needs to. Also, you have to make sure to install it the right direction, so that the electricity will only flow the way you want it to. I hope it at least get's you started on the fix.

Also, keep in mind, if you are using an LED, it IS a diode (a light emitting one), so it will only let the current flow one direction, or it shouldn't work.

Edit: it looks like wasted types a lot faster than me!

 

[dhcomp]

Scott, you can block feedback into another circuit by using a small diode, you can get them for less than a buck at radio shack. Get the 100V units, there are the same size that come in MSD kits to stop engine run-on from alternator feedback in older vehicles. A diode is like a one way check valve for electricity.

The problem is, to figure out where to put it in your circuit to still allow the EGR to function and allow the engine light to turn on when it really needs to. Also, you have to make sure to install it the right direction, so that the electricity will only flow the way you want it to. I hope it at least get's you started on the fix.

Also, keep in mind, if you are using an LED, it IS a diode (a light emitting one), so it will only let the current flow one direction, or it shouldn't work.

Edit: it looks like wasted types a lot faster than me!

Thinking out loud here, but what if he swaps the 2 wires on his CEL LED? Essentially, reversing the diode?

 

[4X4HIGH]

I figured a diode would be the answer BUT wouldn't the diode still allow whatever backfeed to go to the SES light? If the diode was put in the wrong way then the SES light wouldn't work at all.

 

[folkenheath]

Thinking out loud here, but what if he swaps the 2 wires on his CEL LED? Essentially, reversing the diode?

If he did that it would at best not work (it's a light emitting diode, it only works one way), or more likely, it may toast the LED.

Scott, wasted may have a good idea with the resister in parallel with the diode. It may just bleed off excess current being drawn through by the ECU. Jekquist may be able to help you out better.

 

[dhcomp]

If he did that it would at best not work (it's a light emitting diode, it only works one way), or more likely, it may toast the LED.

Got it.

 

[4X4HIGH]

If he did that it would at best not work (it's a light emitting diode, it only works one way), or more likely, it may toast the LED.

Scott, wasted may have a good idea with the resister in parallel with the diode. It may just bleed off excess current being drawn through by the ECU. Jekquist may be able to help you out better.

Ok, so any idea on what kind/spec diode to get? Also would maybe installing a larger resistor than what i'm already using possibly cure the issue? I know using a larger resistor will make the LED dimmer but that's ok as it is real bright as it is so being dimmer wouldn't hurt me the least.

 

[dhcomp]

Scott,

Will your emissions guy accept your LED Check Engine Light setup as compliant?

 

[Fordum]

Scott, I'm really fuzzy right now, had to look up what SES meant, But I'm missing something from your post.
Is the SES light also an LED? If so, I'm guessing you changed it.

If so, odds are thats your problem. An LED is often more sensitive than an incandescent bulb.
In other words, the filament on your old bulb would get warm when the EGR came on, but would not glow.

If so, the quick and dirty way to pass the test is to temporarily put the original bulb back in.
If not, then a bigger (more resistance) resistor inline with the LED should do the trick.
But, its going to be trial and error to see what size. I'd double it to start with.
The resistances add, as I'm sure you know, when placed in series, so just keep adding them until you get what you want.

Another thing to consider.
An LED is a diode. Its rare, but I have had circuits fail to work when I replaced a bulb with one because there were time when the current had to flow the other way.

Also, on a related note, LEDs are usually very sensitive to reverse voltage. A normal silicone diode is rated at about 50 volts as the lowest reverse voltage you can buy. Most of them are several hundred volts.
All the ones I buy are rated at 1000 volts reverse. Called Peak Inverse Voltage or PIV.

Most LEDs are in the range of 3 to 20 PIV. So, don't use one as a diode for most things.

 

[folkenheath]

Ok, so any idea on what kind/spec diode to get? Also would maybe installing a larger resistor than what i'm already using possibly cure the issue? I know using a larger resistor will make the LED dimmer but that's ok as it is real bright as it is so being dimmer wouldn't hurt me the least.

You can get a 100V diode from radio shack, like $1 a pair.

Also, on the resistor, I think he was referring to putting one in parallel, to give the current an alternate path around the LED instead of through it. This would also reduce the brightness of the LED when it is on. I don't know about what value to try for the resistor.

And yes, using a value slightly larger than you have might help too even in series. What value are you running now? I was running about 1000 ohms on my LED for my fan light, but I don't have an SES light LED.

 

[4X4HIGH]

Scott, I'm really fuzzy right now, had to look up what SES meant, But I'm missing something from your post.
Is the SES light also an LED? If so, I'm guessing you changed it.

If so, odds are thats your problem. An LED is often more sensitive than an incandescent bulb.
In other words, the filament on your old bulb would get warm when the EGR came on, but would not glow.

If so, the quick and dirty way to pass the test is to temporarily put the original bulb back in.
If not, then a bigger (more resistance) resistor inline with the LED should do the trick.
But, its going to be trial and error to see what size. I'd double it to start with.
The resistances add, as I'm sure you know, when placed in series, so just keep adding them until you get what you want.

Another thing to consider.
An LED is a diode. Its rare, but I have had circuits fail to work when I replaced a bulb with one because there were time when the current had to flow the other way.

Also, on a related note, LEDs are usually very sensitive to reverse voltage. A normal silicone diode is rated at about 50 volts as the lowest reverse voltage you can buy. Most of them are several hundred volts.
All the ones I buy are rated at 1000 volts reverse. Called Peak Inverse Voltage or PIV.

Most LEDs are in the range of 3 to 20 PIV. So, don't use one as a diode for most things.

Yes, I changed ALL of the indicator bulbs over to LED's.

Negative on using a standard bulb since the factory SES light is in the stock speedo which is now gone. If a larger resistor will do the trick then that's what i'll do. The resistor that i'm currently running is a 470 Ohm 1/2 watt.

BTW, this "issue" didn't arise until I burned a new chip with the EGR fuinction on. If I install the chip that Brian at TBIchips burned for me (with the EGR turned off) I don't have this problem.

 

[zombie1969]

Not sure if this was mentioned but did you check all your grounds.Power back feeding it usually caused by a bad or missing ground.

 

[Fordum]

OK, got a nap while waiting for a drive to clone, so I'm thinking a little clearer.

I suspect that you are looking at the wrong thing. The light drivers in a computer are fairly positive. They are either off or on.
Don't see a lot of maybes......
So, if the light does not light with the egr function disabled, then its probably not being turned on by its control.
And, I doubt that its an internal problem. Most likely its a simple shorted wire.
Check the harness, and especially check the plug to the computer.

I'm going by a Ford computer, been so long since I pulled a GM, I don't remember what it looked like.
But its got to be a plug in unit. So unplug it and check the pins in the computer and the socket for water, dirt, really old dirty grease, or any kind of conductive crossover.

If you have a pinout, try unplugging the computer, and checking the ohms between the egr wires and the ses wires.

Could be a backfeed, but I doubt it.
Of course, if the increased resistance works, don't worry about it.

 

[Fordum]

OK, that does it, I gotta stop sleep-posting. I'm not sure what the heck I wrote above. Fell asleep in the middle and lost my train of thought.

Here is a schematic from an 87. Yours is probably different, but probably not too much.

Notice the EGR is PWM. Pulse width modulation. The coil is supplied with 12 volts, and the computer pulses the ground with pulses of different lengths depending on how much it wants it to open.
The power for this comes in on line 439, which is in the same plug as 487 which is the ses light control. And they are right next to each other.

The 487 line goes to the external light controller, which is what turns the light on and off.

If there is not short, its possible that the pulsing load on the 439 line is creating noise on the 487 line and the light controller is picking it up.
And flashing the LED according to the noise.
A filament bulb would not be on long enough for the filament to warm up, but the LED reacts a lot faster.

If that were so, you could put a capacitor across the LED wires to slow down its response.
You would want to use a non-electrolytic one, or make darn sure of its polarity.

Starting to fade again.


Going to bed.

 

[Blue85]

EDIT: wow, this happened to me again. I don't see responses, I post and then a bunch more show up. Am I just missing page 2 before I post?

So now that I am caught up, I would guess that you changed to LEDs after you disabled EGR. It might work well enough to put a resistor in parallel with the LED to give a similar load to the lamp. Actually, your LED is probably a series resistor + LED, so you would put the parallel resistor across the whole thing. So what value resistor? The best thing would be to measure the current through a standard lamp and then divide 12V by that number. If it's to be just a single 1/4 unit, it can't be any smaller than about 600 Ohms (only 20mA), so to go smaller means series or parallel combinations or a higher power resistor. Or just wire a lamp and LED in there together but hide the lamp. This is all working from the assumption that the lamp and lamp driver worked with the EGR originally.

There is some module not shown in the schematic above "check engine lamp driver". If that guy is still there in 89, it could probably be modified to work with an LED.

It might also work to put a filter cap between that line 487 and the black 150 - if it's just noise triggering the driver. Do you have an oscilloscope?

 

[jekquistk5]

The 487 line goes to the external light controller, which is what turns the light on and off.

If there is not short, its possible that the pulsing load on the 439 line is creating noise on the 487 line and the light controller is picking it up.

I am betting its this, combined with the led being extremely sensitive. And a cap will slow it down. Honestly I would try a bigger resistor first. There are many things that could be causing your problem, eliminate the simple ones first.

 

[Fordum]

I have to go back for a retest on the emsissions this saturday

How did it go?

 

[4X4HIGH]

How did it go?

I actually went back on friday for the retest. This was with a reburned chip with the EGR turned on and while the numbers for NOx did come down they were still too high and it failed again. Dave is working with me on getting a chip burned that will hopefully get me through. I have another alternate idea up my sleeve (legal idea) if all else fails which I "think" will work.