Calling all electrical gurus
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Calling all electrical gurus 2001 Tahoe 5.3 DBW/60e - Running factory ECU and harness
Sloppy Stage 2 Cam
BTR Trunnion upgrade
PAC 1218 Springs + Hardware
All swapped into a 1981 Ford Granada
Needing help fixing a dead miss on CYL 5 & 7.
Put this car back together a few months ago after having a factory trunnion come apart (on the passenger Bank). With it all together, car fired off and ran great. After ensuring that my repair was good, I decided to clean up the engine bay (both by washing it, and rerouting the harness). Immediately after washing the engine bay, I fired the car off and let it run (still zero issues- this was mainly to help everything dry off and make sure the water didn't find its way anywhere it didn't belong).
With all that being said, I then re-loomed/rerouted the primary harness from the ECU to tuck it more neatly behind the intake (including re-routing the subharness for the Bank 1 injectors and coils so they split from the main harness a little earlier than factory. The was the majority of the changes, the only other being that I "deleted" the MAF and wired in a 2 wire IAT on the intake (the car is tuned SD). *The ONLY wire cut aside from the MAF pigtail was one ground for the Bank 1 Coil harness, extending it roughly 6in so it could follow the rest of the bank 1 Coil/Injector harness (The Bank 1 coil ground leads to a large ground splice in the main harness).*
After completing the work, I fired the car off and had a dead miss on CYL 5 & 7. I immediately assumed my Coil ground was bad, and respliced it (Using 14ga wire). This didn't change anything. I double checked my work to verify no other wires had been damaged during the work- and to the best of my knowledge there weren't.
To make a long story shorter, I then checked Resistance to ground on every pin of the circuit to verify no short to ground (with the exception of the GND obviously), all checked out there. Verified my 12V feeds at both the coils and injectors, all was good there (even under load, Feed voltage = Alt voltage). I then backtracked to some more simple options, and swapped CYL 5 & 7 injector + tried using a known good test coil on each CYL, no luck. We then used a coil tester & test light to verify signal function from the ECU to both the coil and injector, all tested good there (We do have a Snap On Zeus with a 4 channel scope is the test light is not a reliable enough option for testing these..).
At this point I was thinking either A: I somehow killed the a couple of Mosfets/Coil drivers in the ECU (This is pretty familiar to me coming from the Ford and BMW world, definitely haven't heard about it with a Gen3 ECU). Or B: I'm the unluckiest man in the world, and it wiped 2 cam lobes simultaneously. With that being said, I pulled the Valve cover to verify the Cam wasn't wiped, and did a compression test. Both Cyls test with 5psi of the reference cylinders.
Short summary:
Wiring checked good to the best of my knowledge (any input appreciated)
New plug wires (replaced while doing the trunnion upgrade)
New plugs (NGK TR55, the were already new, replaced CYL 5 & 7 again in wishful thinking)
Verified good coils
Verified functional Injectors
Compression tested good
Valve train is doing its job
NOW FOR THE WEIRD PART: If I unplug EVERY OTHER SPARK PLUG WIRE, Cyls 5 and 7 will hit. Obviously the car won't run on 2 cylinders, but they will fire as the engine is turned over.
Normally I feel like the go-to guy for electrical answers lol, but I'm out of ideas. Any help appreciated.
Sloppy Stage 2 Cam
BTR Trunnion upgrade
PAC 1218 Springs + Hardware
All swapped into a 1981 Ford Granada
Needing help fixing a dead miss on CYL 5 & 7.
Put this car back together a few months ago after having a factory trunnion come apart (on the passenger Bank). With it all together, car fired off and ran great. After ensuring that my repair was good, I decided to clean up the engine bay (both by washing it, and rerouting the harness). Immediately after washing the engine bay, I fired the car off and let it run (still zero issues- this was mainly to help everything dry off and make sure the water didn't find its way anywhere it didn't belong).
With all that being said, I then re-loomed/rerouted the primary harness from the ECU to tuck it more neatly behind the intake (including re-routing the subharness for the Bank 1 injectors and coils so they split from the main harness a little earlier than factory. The was the majority of the changes, the only other being that I "deleted" the MAF and wired in a 2 wire IAT on the intake (the car is tuned SD). *The ONLY wire cut aside from the MAF pigtail was one ground for the Bank 1 Coil harness, extending it roughly 6in so it could follow the rest of the bank 1 Coil/Injector harness (The Bank 1 coil ground leads to a large ground splice in the main harness).*
After completing the work, I fired the car off and had a dead miss on CYL 5 & 7. I immediately assumed my Coil ground was bad, and respliced it (Using 14ga wire). This didn't change anything. I double checked my work to verify no other wires had been damaged during the work- and to the best of my knowledge there weren't.
To make a long story shorter, I then checked Resistance to ground on every pin of the circuit to verify no short to ground (with the exception of the GND obviously), all checked out there. Verified my 12V feeds at both the coils and injectors, all was good there (even under load, Feed voltage = Alt voltage). I then backtracked to some more simple options, and swapped CYL 5 & 7 injector + tried using a known good test coil on each CYL, no luck. We then used a coil tester & test light to verify signal function from the ECU to both the coil and injector, all tested good there (We do have a Snap On Zeus with a 4 channel scope is the test light is not a reliable enough option for testing these..).
At this point I was thinking either A: I somehow killed the a couple of Mosfets/Coil drivers in the ECU (This is pretty familiar to me coming from the Ford and BMW world, definitely haven't heard about it with a Gen3 ECU). Or B: I'm the unluckiest man in the world, and it wiped 2 cam lobes simultaneously. With that being said, I pulled the Valve cover to verify the Cam wasn't wiped, and did a compression test. Both Cyls test with 5psi of the reference cylinders.
Short summary:
Wiring checked good to the best of my knowledge (any input appreciated)
New plug wires (replaced while doing the trunnion upgrade)
New plugs (NGK TR55, the were already new, replaced CYL 5 & 7 again in wishful thinking)
Verified good coils
Verified functional Injectors
Compression tested good
Valve train is doing its job
NOW FOR THE WEIRD PART: If I unplug EVERY OTHER SPARK PLUG WIRE, Cyls 5 and 7 will hit. Obviously the car won't run on 2 cylinders, but they will fire as the engine is turned over.
Normally I feel like the go-to guy for electrical answers lol, but I'm out of ideas. Any help appreciated.
2001 Tahoe 5.3 DBW/60e - Running factory ECU and harness
Sloppy Stage 2 Cam
BTR Trunnion upgrade
PAC 1218 Springs + Hardware
All swapped into a 1981 Ford Granada
Needing help fixing a dead miss on CYL 5 & 7.
Put this car back together a few months ago after having a factory trunnion come apart (on the passenger Bank). With it all together, car fired off and ran great. After ensuring that my repair was good, I decided to clean up the engine bay (both by washing it, and rerouting the harness). Immediately after washing the engine bay, I fired the car off and let it run (still zero issues- this was mainly to help everything dry off and make sure the water didn't find its way anywhere it didn't belong).
With all that being said, I then re-loomed/rerouted the primary harness from the ECU to tuck it more neatly behind the intake (including re-routing the subharness for the Bank 1 injectors and coils so they split from the main harness a little earlier than factory. The was the majority of the changes, the only other being that I "deleted" the MAF and wired in a 2 wire IAT on the intake (the car is tuned SD). *The ONLY wire cut aside from the MAF pigtail was one ground for the Bank 1 Coil harness, extending it roughly 6in so it could follow the rest of the bank 1 Coil/Injector harness (The Bank 1 coil ground leads to a large ground splice in the main harness).*
After completing the work, I fired the car off and had a dead miss on CYL 5 & 7. I immediately assumed my Coil ground was bad, and respliced it (Using 14ga wire). This didn't change anything. I double checked my work to verify no other wires had been damaged during the work- and to the best of my knowledge there weren't.
To make a long story shorter, I then checked Resistance to ground on every pin of the circuit to verify no short to ground (with the exception of the GND obviously), all checked out there. Verified my 12V feeds at both the coils and injectors, all was good there (even under load, Feed voltage = Alt voltage). I then backtracked to some more simple options, and swapped CYL 5 & 7 injector + tried using a known good test coil on each CYL, no luck. We then used a coil tester & test light to verify signal function from the ECU to both the coil and injector, all tested good there (We do have a Snap On Zeus with a 4 channel scope is the test light is not a reliable enough option for testing these..).
At this point I was thinking either A: I somehow killed the a couple of Mosfets/Coil drivers in the ECU (This is pretty familiar to me coming from the Ford and BMW world, definitely haven't heard about it with a Gen3 ECU). Or B: I'm the unluckiest man in the world, and it wiped 2 cam lobes simultaneously. With that being said, I pulled the Valve cover to verify the Cam wasn't wiped, and did a compression test. Both Cyls test with 5psi of the reference cylinders.
Short summary:
Wiring checked good to the best of my knowledge (any input appreciated)
New plug wires (replaced while doing the trunnion upgrade)
New plugs (NGK TR55, the were already new, replaced CYL 5 & 7 again in wishful thinking)
Verified good coils
Verified functional Injectors
Compression tested good
Valve train is doing its job
NOW FOR THE WEIRD PART: If I unplug EVERY OTHER SPARK PLUG WIRE, Cyls 5 and 7 will hit. Obviously the car won't run on 2 cylinders, but they will fire as the engine is turned over.
Normally I feel like the go-to guy for electrical answers lol, but I'm out of ideas. Any help appreciated.
Sloppy Stage 2 Cam
BTR Trunnion upgrade
PAC 1218 Springs + Hardware
All swapped into a 1981 Ford Granada
Needing help fixing a dead miss on CYL 5 & 7.
Put this car back together a few months ago after having a factory trunnion come apart (on the passenger Bank). With it all together, car fired off and ran great. After ensuring that my repair was good, I decided to clean up the engine bay (both by washing it, and rerouting the harness). Immediately after washing the engine bay, I fired the car off and let it run (still zero issues- this was mainly to help everything dry off and make sure the water didn't find its way anywhere it didn't belong).
With all that being said, I then re-loomed/rerouted the primary harness from the ECU to tuck it more neatly behind the intake (including re-routing the subharness for the Bank 1 injectors and coils so they split from the main harness a little earlier than factory. The was the majority of the changes, the only other being that I "deleted" the MAF and wired in a 2 wire IAT on the intake (the car is tuned SD). *The ONLY wire cut aside from the MAF pigtail was one ground for the Bank 1 Coil harness, extending it roughly 6in so it could follow the rest of the bank 1 Coil/Injector harness (The Bank 1 coil ground leads to a large ground splice in the main harness).*
After completing the work, I fired the car off and had a dead miss on CYL 5 & 7. I immediately assumed my Coil ground was bad, and respliced it (Using 14ga wire). This didn't change anything. I double checked my work to verify no other wires had been damaged during the work- and to the best of my knowledge there weren't.
To make a long story shorter, I then checked Resistance to ground on every pin of the circuit to verify no short to ground (with the exception of the GND obviously), all checked out there. Verified my 12V feeds at both the coils and injectors, all was good there (even under load, Feed voltage = Alt voltage). I then backtracked to some more simple options, and swapped CYL 5 & 7 injector + tried using a known good test coil on each CYL, no luck. We then used a coil tester & test light to verify signal function from the ECU to both the coil and injector, all tested good there (We do have a Snap On Zeus with a 4 channel scope is the test light is not a reliable enough option for testing these..).
At this point I was thinking either A: I somehow killed the a couple of Mosfets/Coil drivers in the ECU (This is pretty familiar to me coming from the Ford and BMW world, definitely haven't heard about it with a Gen3 ECU). Or B: I'm the unluckiest man in the world, and it wiped 2 cam lobes simultaneously. With that being said, I pulled the Valve cover to verify the Cam wasn't wiped, and did a compression test. Both Cyls test with 5psi of the reference cylinders.
Short summary:
Wiring checked good to the best of my knowledge (any input appreciated)
New plug wires (replaced while doing the trunnion upgrade)
New plugs (NGK TR55, the were already new, replaced CYL 5 & 7 again in wishful thinking)
Verified good coils
Verified functional Injectors
Compression tested good
Valve train is doing its job
NOW FOR THE WEIRD PART: If I unplug EVERY OTHER SPARK PLUG WIRE, Cyls 5 and 7 will hit. Obviously the car won't run on 2 cylinders, but they will fire as the engine is turned over.
Normally I feel like the go-to guy for electrical answers lol, but I'm out of ideas. Any help appreciated.
TECH Regular
Joined: Dec 2011
Posts: 420
Likes: 115
You have verified that cyls 5 and 7 are completely wet with gas? (You have fuel, but not spark)
Verified that no connector pins are loose in their connectors, or bent? Wiggling the harness or connectors has no impact on the situation? Verified that the coil triggers aren't shorted to each other?
Verified that no connector pins are loose in their connectors, or bent? Wiggling the harness or connectors has no impact on the situation? Verified that the coil triggers aren't shorted to each other?
Thread Starter
Registered User
Joined: Oct 2022
Posts: 4
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Funny you say that, the wires are rerouted and tucked behind the Alternator as well. We've seen similar noise issues regarding this on Dodge transmissions. I'll make sure to check that. Shame I haven't scoped it yet, that would've been a dead giveaway.
