little LS swap help, Gen 3

marty79

marty79

Well-Known Member
Joined
Dec 2, 2015
Location
Newton, NC
I've finally hit a bump in my 5th LS swap and it has me confussled lol.
Either Coil harnesses are on backwards, or pass side and driver side harness is on wrong, or IDK, something is weird that 1/7 and 2/8 are not firing....it's symmetrical for both sides of engine so I feel like it's probably simple, I'm just missing it...
Just fired up this 89 YJ with Gen 3 4.8 with 289heads (came like that), unknown standalone harness (customer brought with engine), AX15 so no electronics there..ECU from Ebay came pretuned
Started right up but Coils 1 & 7 and Coils 2 & 8 not firing at all so it runs like crap obviously. Pink wires are hot, grounds are good...that's as far as I've gotten.
No codes yet but didn't run it long. So basically running on 4 cylinders only
Any help from the LS swap folks please!
 
This is my first one where customer brought motor, trans, harness and stuff so that's why I don't know who made the harness, no labels on it, and since my last several have been Gen V I've lost touch with the earlier generation LS electronics and such.
There's plenty of slack in the harness to swap pass/driver side but haven't yet until someone says to fearing to mess up anything further
 
2468 and 1357 are the combined groups, the four in each group share a ground and a hot. Either you got the cylinder numbers a little off or the harness pinout is wrong/missing pins. Or the Ecu is bad. 1357 is driver side cylinders, 2468 is pass
 
braxton357 said:
2468 and 1357 are the combined groups, the four in each group share a ground and a hot. Either you got the cylinder numbers a little off or the harness pinout is wrong/missing pins. Or the Ecu is bad. 1357 is driver side cylinders, 2468 is pass
Click to expand...
ok right, so since it's both sides front and back coils, you reckon my harness is on backwards?
I did swap the harness to 1/7 and 2/8 and no change, still didn't fire so I know those 2 aren't backwards. is it possible the ones that are firing 4/6 and 3/5 could be wrong causing the other 4 to not fire? thanks bud
 
So like I said, each coil has 4 wires, each bank of 4 shares a chassis ground, 12v keyed pos and reference ground pin from ecu. Then each coil gets it's own ref signal from ecu--the wire thats a different color on each one--you're going to have to trace that wire back from all 8 coils to the c2 red ecu connector and make sure they are actually pinned and in the right place and if so ohm them out to make sure wire isn't cut somewhere.
 
braxton357 said:
-you're going to have to trace that wire back from all 8 coils to the c2 red ecu connector and make sure they are actually pinned and in the right place and if so ohm them out to make sure wire isn't cut somewhere.
Click to expand...
ok gotcha, I had to do that on one of the Gen Vs so I'm familiar with that. So this whole "possible bad reluctor ring" I'm reading about....ignore that I assume till I verify the wiring is good...
 
braxton357 said:
So like I said, each coil has 4 wires, each bank of 4 shares a chassis ground, 12v keyed pos and reference ground pin from ecu. Then each coil gets it's own ref signal from ecu--the wire thats a different color on each one--you're going to have to trace that wire back from all 8 coils to the c2 red ecu connector and make sure they are actually pinned and in the right place and if so ohm them out to make sure wire isn't cut somewhere.
Click to expand...

How much do you charge for all your build fixes?
 
Update... all wiring to each respective coil and injectors checks out, kinda wish it hadn't lol. All grounds check out. Power is good also..I feel like there's a simple common denominator since its 1st and last coil on each side.
 
Maybe the ECU is from a 4 cylinder truck? Who flashed the ECU? Are you Sure you have the right ECU/harness blue/green or red/blue?
 
braxton357 said:
Is it throwing a code?
Click to expand...
PO463 fuel level sensor circuit high (positive this ain't it)
PO654 engine rpm output circuit current/ history. I've never seen or heard of this code..looking into it now
 
Everything else aside...wtf is a 289 head?

There's 862, 243, 799, 706, 317.


Sounds like the coil harnesses aren't pinned correctly.
 
Croatan_Kid said:
Everything else aside...wtf is a 289 head?

There's 862, 243, 799, 706, 317.


Sounds like the coil harnesses aren't pinned correctly.
Click to expand...
Sorry 862 heads lol
Thats what I'm trying to figure out..they have 12v, good ground and the color correspondence to each coil from ECU is right..that 4th wire unsure how to test them
 
When I do continuity on injectors they all beep rather than just injector 1 so is this the issue? Don't injectors share the circuits?
 
So i guess to backtrack, how do you know those cylinders arent firing, because no heat was coming out the exhaust or because you pulled the coils with plugs on them and tested
 
Last edited:
braxton357 said:
because you pulled the coils with plugs on them and tested
Click to expand...
This..pull injector harness or coil plug on 1/7/2/8 no change, pull 4-6-3-5 engine runs way worse
 
So it could be an injector issue or a coil issue? I mean have you put a spark tester or grounded plug on one of those coil packs to make sure there's no spark
 
braxton357 said:
So it could be an injector issue or a coil issue? I mean have you put a spark tester or grounded plug on one of those coil packs to make sure there's no spark
Click to expand...
I mean no but in my 15yrs of wrenching unplugging coils or injectors and no change usually means no fire. But ill do it just to check that off the list.
 
marty79 said:
When I do continuity on injectors they all beep rather than just injector 1 so is this the issue? Don't injectors share the circuits?
Click to expand...
They share some circuits.
Not all of them.
But yeah, you could use a noid light.
Or keep guessing.
 
I feel bad for the folks who are paying for this expert service.
 
Back
Top