LS Swappers - need some ideas on a P035x coil circuit error

[Jackson's Dad 64 C10]

This post reminds me that I have never done a build thread in the 7 years we have been working on this turd! My son and I are finishing up a long term project 1964 C10 short bed, fleetside big back window truck. It came off the frame, No Limit suspension, air ride, lots of changes... We transplanted an LY6 6.0 out of a 2010 Silverado 2500. I've integrated the BCM (don't quite know if that is completely sorted yet), using an E38 ECM, factory harness reworked by me, 6L90E trans with the Lokar electronic sport shifter, and Dakota RTX instrumentation with the BIM.

First start up was Monday night, after chasing our tails trying to pressure lube the engine. FINALLY got oil to all 16 rockers. The truck started on the first try and idled pretty smoothly, but I'm getting P0351, P0352 and P0353 errors. The DTCs are Ignition Coil Primary/Secondary malfunction (for A, B and C - Cyls. 1,2,3). I'm stumped on diagnosing this one. I've followed most of the troubleshooting chart, minus checking the frequency of the ignition control circuit. I dove straight into switching coil packs around - no dice, and I've checked voltage on the circuit (battery voltage). I ohmed out the control wires from the ECM to the junction connector at the coil rail, and all the way to the individual coil pack connectors. The control wires were all .1-.3 ohms resistance. The common low reference wires were fine too. I'm starting to wonder if the plug wires aren't the issue. We used the same Scott plug wires we used on my son's Gen 3 swapped '91 Z28, so we know they work on the LS platform. Am I missing something obvious here, or am I getting down to a bad coil driver in the ECM? I'm mainly looking for a gut check on anything that I might have missed. Thanks in advance!

-Chris

[A1971Blazer]

Can't help you much on that engine but on my early (2002 LS1) I had some issues with misfiring. To determine if it was indeed getting fire to the plugs, I just used an inductive timing light on each plug wire to see if they were getting fire.
It turned out that my issue was simply a faulty connector to the coil pack harness.

[Jackson's Dad 64 C10]

Good call on the timing light. I hadn’t thought to toss that on my modern engine! I checked continuity on all my connectors last night and they were good. I just ran into an acquaintance at the drag strip tonight, and he does a lot of LS swaps at his restoration shop. He told me to make sure the harness has a ground that goes directly to the block. He’s had the exact same experience before when he did a swap that didn’t directly ground. I took all the harness grounds to a bus bar, which is grounded directly to the battery negative terminal. I’m going to tie that bus bar to the block tomorrow to see if it makes a difference.

[AussieinNC]

99 times out of 100, it is a bad ground....

You cannot have too many grounds on these....

[LS short box]

On my LS swaps I always run the battery ground cable directly from the battery to the engine block. Then from the engine block to the frame. Also depending how your harness is configured on the after market ones I have used they have two lighter gauge ground wires. I bolt them to the back of the making sure head surface is really clean.
Another good source for tech info is LS1tech.com

[Jackson's Dad 64 C10]

When I swapped a 5.3 into my son’s Z28, I did essentially the same configuration I’ve done here. All my Gen 3 harness info came directly from LS1Swap.com. Unfortunately I’m working with a Gen IV engine on the truck and it’s a whole different animal. The ground config is a little something like this: battery to block, block to both frame rails (each side), battery to common ground on frame rail, with a 4AWG wire going from that ground point to the bus bar, which is under the dash. All the harness grounds were brought to the top of the harness (lineman spliced, soldered and adhesive shrink on all of them, and they all measured out at 0ohms resistance when I verified continuity before installing). I also have straps from frame to core support, cab and bed. This thing should not have any issues grounding. I was very meticulous when reworking the harness because it’s easier to avoid issues altogether than it is to track them down later.

I just unplugged all the plug wires from the coil packs and the plugs, and plugged them back in. The boots are tight, and I kept working them till I heard them click into place. I’m kind of stumped right now. And a little irritated because the hydroboost unit seems to be leaking. I can’t win with this truck right now! But it looks cool…

[Jackson's Dad 64 C10]

We’ve made some progress on the truck and finally did the first test drive on Monday. 7 years of work on this thing and we are just ironing out the final new build issues. It starts to shudder around 45 mph, and I’m trying to decide if it’s the converter itself, or if it’s just making the possible misfire I mentioned above more obvious. It idles well, accelerates smoothly and sounds good. HP Tuners shows 0 current misfires on all 8 cylinders when scanning. I’m sort of stumped on this one. Im starting to think that I need to find a buddy with an oscilloscope and need to learn how to use it. My working theory is that a scope should show me if I have any issues on the individual control circuits. Any input from the wise folks on here?

[jjzepplin]

Silly question but did you get the whole donor and drive it or was it just the engine purchase?