How to make my 89's check engine light work with LS swap

[subtlez28]

How do I make my 89's check engine light work with LS swap?

Sorry if this is the wrong section for this question, but I figure it is swap related.

I just picked up a clean 89 Scottsdale that has a 00' LS engine swapped in. It is using a stock 4.8 and ECU, and what I am told is a Painless harness.

I have 2 leads from the harness that are for a check engine light. The info I need is on the truck side.

The light is currently on all the time as the stock ECU is gone. I just want a heads up on where to tap into the dash harness to make it work with my new ECU.

Thanks in advance!

 

[subtlez28]

BUMP Are all you LS swappers using aftermarket gauges?

Someone on here has to know how to tap into the CEL's wiring.

Can you point me to a wiring diagram or break down of the gauge pack and harness?

Thanks!

 

[Johnbalderas90k1500]

A check engine light is just a bulb that gets illuminated when a problem occurs within the emission control systems. If you have a check engine light on then a scanner or code reader is needed to identify the specific code. Its possible that all the sensors and actuators belonging to the "LS" computer system may be missing.

 

[Johnbalderas90k1500]

I'm not sure where you are located but in California you need to have a smog referee clear your "engine swap" to be legal to smog in CA.

 

[SAATR]

A check engine light is just a bulb that gets illuminated when a problem occurs within the emission control systems. If you have a check engine light on then a scanner or code reader is needed to identify the specific code. Its possible that all the sensors and actuators belonging to the "LS" computer system may be missing.

I'm not sure where you are located but in California you need to have a smog referee clear your "engine swap" to be legal to smog in CA.

And this pertains to wiring the CEL into the 89's harness.... how?

Sorry if this is the wrong section for this question, but I figure it is swap related.

I just picked up a clean 89 Scottsdale that has a 00' LS engine swapped in. It is using a stock 4.8 and ECU, and what I am told is a Painless harness.

I have 2 leads from the harness that are for a check engine light. The info I need is on the truck side.

The light is currently on all the time as the stock ECU is gone. I just want a heads up on where to tap into the dash harness to make it work with my new ECU.

Thanks in advance!

PM Lextech. He may have the diagram with the info that you need.


Sent from my XT912 using Tapatalk

 

[great white]

So, there's some missing info here, it's being described incorrectly or I'm missing the boat a bit.



The CEL on the 89 is driven by the 7477 ecm. You say this is gone, so it must be hooked up to the new PCM if it is "on". The CEL will not illuminate on an 89 if it's not connected to something.

If it is connected to the LS PCM, you need to find out what codes are in there and resolve the conflicts. Or you can have the PCM re-flashed to disable DTC's that your truck does not support (IE: fuel level, vapor recovery, etc).

If the dash light (CEL) is not already hooked up to the LS PCM, the 7477 ECM (original to the truck) must still be in there. If the 7477 is still in there it's likely setting DTC's because it is missing the original sensors. cure for that is to remove it. An 89 chassis will run fine without the PCM as long as the drac signal is still coming from the cluster to things like the cruise control (unless that has been changed also).

Does this truck actually have the dash cluster from the 89 or is there a different cluster in it?

I'm not an "LS swap guy", but I know the chassis side of the wiring.

It sounds like your wiring harness is a "standalone" one if it's from painless. I would recommend you contact them for advice on the cel hook up.

I'd say your "stock" LS PCM is probably looking for inputs that your chassis does not support. The way to fix that is to have someone turn off the error reporting for those DTC's in the calibration files.

 

[subtlez28]

I'm not sure where you are located but in California you need to have a smog referee clear your "engine swap" to be legal to smog in CA.

Luckily I have no emissions testing here in my area (Southern WI). And when it comes, fingers crossed they exempt 20+ year old vehicles.

And this pertains to wiring the CEL into the 89's harness.... how?



PM Lextech. He may have the diagram with the info that you need.


Sent from my XT912 using Tapatalk

Thanks! I I'll do that.

So, there's some missing info here, it's being described incorrectly or I'm missing the boat a bit.



The CEL on the 89 is driven by the 7477 ecm. You say this is gone, so it must be hooked up to the new PCM if it is "on". The CEL will not illuminate on an 89 if it's not connected to something.

If it is connected to the LS PCM, you need to find out what codes are in there and resolve the conflicts. Or you can have the PCM re-flashed to disable DTC's that your truck does not support (IE: fuel level, vapor recovery, etc).

If the dash light (CEL) is not already hooked up to the LS PCM, the 7477 ECM (original to the truck) must still be in there. If the 7477 is still in there it's likely setting DTC's because it is missing the original sensors. cure for that is to remove it. An 89 chassis will run fine without the PCM as long as the drac signal is still coming from the cluster to things like the cruise control (unless that has been changed also).

Does this truck actually have the dash cluster from the 89 or is there a different cluster in it?

I'm not an "LS swap guy", but I know the chassis side of the wiring.

It sounds like your wiring harness is a "standalone" one if it's from painless. I would recommend you contact them for advice on the cel hook up.

I'd say your "stock" LS PCM is probably looking for inputs that your chassis does not support. The way to fix that is to have someone turn off the error reporting for those DTC's in the calibration files.

Sorry, some info is missing, and I made an error. I had it in my head the factory ECU was under-hood (forgetting the trucks vintage). It is likely buried in the dash. I agree it is likely there or the light would not be on. I was over-thinking it.

I'll confirm when I get the truck back (having some minor paint flaws fixed).

The Painless harness is stand alone. It has a lead for a CEL. So, I'm thinking I just need the wiring diagram to tap into the factory CEL.

Thanks for the input guys!

 

[subtlez28]

Thanks to Lextech's PM, I got this issue worked out.

For anyone wondering:

There is a Brown/White wire in the 89 PCM connector A pin 5. Cut that wire at that connector and run it to C2-46 of the Gen3 PCM. Unless something else is messed up in the harness---that should do the trick.

In the case of the Painless Harness, it also had a brown and white wire labeled for the CEL. It also had a red (pinkish) power wire for the CEL but was not needed for the dash light since it is already power (The ECU just grounds it via the bro/whi wire).

 

[Aleks2505]

There is a Brown/White wire in the 89 PCM connector A pin 5. Cut that wire at that connector and run it to C2-46 of the Gen3 PCM. Unless something else is messed up in the harness---that should do the trick.

In the case of the Painless Harness, it also had a brown and white wire labeled for the CEL. It also had a red (pinkish) power wire for the CEL but was not needed for the dash light since it is already power (The ECU just grounds it via the bro/whi wire).

I am doing my LS Swap right now and this is extremely helpful. Wonder what you did for your gas pedal? Did you go DBWire or DBCable??

 

[BRGarage]

I am doing my LS Swap right now and this is extremely helpful. Wonder what you did for your gas pedal? Did you go DBWire or DBCable??

I just completed my swap into an '89 C3500 dually. The stock throttle cable from my 2000 parts truck fits perfect with slight modification on the firewall side.