DIY LTCC or similar system for LT1s

[kur4o]

I started the tuning season and finally managed to find some bug.

I exhausted all other option of failure but the controller.

On some driving and a hard 2nd WOT pull, and let off, some random misfires started. Engine changed sound and rough running like you just broke off something.
The misfires were most pronounced at low speed low tps. ANd it almost died at idle, some heavy surging. I tried to isolate a cylinder but in the logs it was almost anywhere, Left right bank equal gain of oxygen in the exhaust.

I drive a mile with that condiftion before pulled off. Looks like after heavy deceleration it was more pronounced.

After 10min with engine off. It started fine and drove fine after that with no signs of anything bad happen.[I hope the bearings survive the punishment]

You can see the WOT pull at 1440 on log1 and after that till engine off it was having the missfires. The second log is after engine have been off for some time.

[spfautsch]

After 10min with engine off. It started fine and drove fine after that with no signs of anything bad happen.

Couple questions:

1) Did you attempt to restart it immediately, or were the 10 minutes needed before it would re-start?

2) Can / have you tried to reproduce?

I wouldn't blame you for not attempting, but I've never encountered this so I doubt I'll be able to reproduce as I've done plenty of WOT pulls to 6500 and let off. If you do, and can reproduce throw it in neutral immediately, get off the road, shut off and try to restart (immediately).

My guess here is that it ("it" being the controller logic) jumped out of sequence 90 degrees due to slop in the timing set or some other factor I'm not considering. Working from this assumption, I should be able to make the firmware so it continually verifies sequence so the worst that could happen is a couple cylinders miss before sequence is re-established. It's something I've intended to do for some time but have had other opportunities that required attention.

I'm not necessarily pointing the finger at them, but the number of DTCs you have coming and going through both logs is quite alarming. I'm not going to go in detail on this, but it's probably not a good idea testing an experimental ignition system in a vehicle with so many DTCs.

Off topic for kur4o's issue, but as you're all probably guessing I still haven't made much progress on the installation manual. I do intend to summon the motivation to make the project more complete and accessible, but the lack of interest by others who possess kits makes me start to question if there's enough interest to warrant it. Are you waiting on me to get off my duff and complete the manual or ??? Honest feedback would be truly appreciated.

[kur4o]

I didn`t try to start it immediately due to checking all possible cause for it. Coils, cables opti logging.
I didn`t try to reproduce, wanted to be sure for the cause first.
If I try to reproduce , better to have some logs with it.

The dtcs are false, you can ignore them. There is no DTCs set. I stream other data instead of the dtc bytes.

I too have made hard wot pulls so far without issues. The main difference here is that I let off immediately upon upshifting and there was very rapid deceleration with hard braking[It will give very fast reverse movement of the chain].

It didn`t feel like 90* off. It was more like on/off of all coils. Also definitely rougher running. The misfires were mainly on higher load conditions. Like weak spark or something.

You can see at the very end of the first log, map and rpm jumping up and down.

The logs have some higher rate of errors and some data drops. I suspect bad connection from the dyi serial cable.


So far I haven`t had any issues at all, it will be nice to have an installation manual, some pictures with connectors and wiring diagram will do it all. I have some temporary coil mountings and I am doing some fine tuning and testing recently.

Digging in the crap idle condition I have, transient fueling, cyl trims, EOIT, CL stability and so on. I do have some valuable data with logs, but no definite answer how and what.

Time to start part3 of idiots guide.

[spfautsch]

I didn`t try to start it immediately ...

If I try to reproduce , better to have some logs with it.

I can build a serial console command that will create the condition on demand. I won't ask you to test and possibly grenade your engine. Better let me do that with a $20,000 build with forged internals. Or not.

The dtcs are false, you can ignore them. There is no DTCs set. I stream other data instead of the dtc bytes.

Thanks for clarifying.

It didn`t feel like 90* off. It was more like on/off of all coils. Also definitely rougher running. The misfires were mainly on higher load conditions. Like weak spark or something.

Step back from your assumptions and imagine for a moment what a 90 degree v8 would act like if we instantaneously added 90 degrees of delivered spark advance on top of the PCM's commanded advance. Or say had a traditional distributor installed one or two teeth advanced. The spark is going to be lighting the mixture off just after the piston has started compressing it. At this point in time the mixture will be very inconsistent, with the fuel vapors concentrated near the piston and mostly air towards the top of the cylinder. Combustion (when it happens at all) is going to be extremely weak due to almost no mixing of the charge and very little compression.

Also, this scenario is really the only possibility I can imagine that hasn't already been encountered and resolved.

So far I haven`t had any issues at all, it will be nice to have an installation manual, some pictures with connectors and wiring diagram will do it all. I have some temporary coil mountings and I am doing some fine tuning and testing recently.

Thanks for the feedback, but you've already jumped off the cliff with me. I was mainly asking for opinions of others who have purchased kits. I'm seeing more and more folks on the corvette forums doing LS swaps on these cars and I would hate to spend a lot of time and effort only to sell another five or six kits that never get used for their intended purpose.

[kur4o]

I would disagree with the out of phase 90 degree theory.

I looked at some graph first case is spark to be delivered in an advance which will result in 20* before middle of piston travel upwards on compression cycle.The engine will run like total crap and likely will stall, the piston will move up while ignition will push it down. Total stall situation.

If the spark is retarder after tdc 90* it will be total power loss. I know how that sounds so it was definitely not the case.


Looking at the logs check 1587 to 1596. The engine is idling in failure mode[perfect idle with awesome map readings]. After that you can see some light throttle pushes. I was checking stuff here to isolate cause.
On each throttle push massive misfires with some knock from the engine. Like total spark failure, or very weak spark blown away by the pressure.

I can only speculate something freak out the dwell calculation. or the spark advance signal taken from the pcm got phased out in a death loop with dwell starting too late.

I also dont rule out some hardware breakdown, cables, wiring, coils got too hot. Not very likely[due to the recovery rate] but still a possibility.

[spfautsch]

Looking at the logs check 1587 to 1596. The engine is idling in failure mode[perfect idle with awesome map readings].

Ok, this rules out jumping out of sequence. Your initial description of how it was running afterwards seemed to indicate it was consistently bad. Sorry, I was busy entertaining a house full of people yesterday and didn't have a chance to look at the logs very carefully.

Take a look at your ignition voltage in that log. There's a very abrupt sag in voltage that starts @ 1442.6.

I'd be interested in seeing what the controller thought coolant temperature was here. But we'd need to be logging the controller to know that.

Which dwell table are you using again? Where are your coils mounted in relation to exhaust headers, etc?

I can only speculate something freak out the dwell calculation. or the spark advance signal taken from the pcm got phased out in a death loop with dwell starting too late.

All these calculations are done on the fly so your issue should have cleared up as soon as whatever variable responsible returned to normal.

I also dont rule out some hardware breakdown, cables, wiring, coils got too hot. Not very likely[due to the recovery rate] but still a possibility.

The coils too hot idea is another reason I'd want to know if a stop / re-start resolved the issue.

At this point I'm leaning towards a combination of a dead / weak charging system possibly coupled with an intermittent open ECT connection making the controller think coolant temp was pegged cold.

[NomakeWan]

Off topic for kur4o's issue, but as you're all probably guessing I still haven't made much progress on the installation manual. I do intend to summon the motivation to make the project more complete and accessible, but the lack of interest by others who possess kits makes me start to question if there's enough interest to warrant it. Are you waiting on me to get off my duff and complete the manual or ??? Honest feedback would be truly appreciated.

Thanks for the feedback, but you've already jumped off the cliff with me. I was mainly asking for opinions of others who have purchased kits. I'm seeing more and more folks on the corvette forums doing LS swaps on these cars and I would hate to spend a lot of time and effort only to sell another five or six kits that never get used for their intended purpose.

Hey there! Sorry for long time no response. I actually saw this post yesterday (I have email notifications) but I was also in the middle of a huge drive from one end of the state to the other. Now that I'm back home I can answer.

For me, I have all the parts I need (save for the opti passthrough I need to make because I don't want to splice wiring, and the actual spark plug wires because I haven't finalized a coil mounting solution). I was waiting on the code to mature a little, but when that happened, it was already a little "too late." Not because I don't want to do this--I very much do. In fact, now that Torqhead has pulled out of the C4 market indefinitely, the DIY-LTCC is really the only way to go. But because I ran into several critical issues with my '95 that required a lengthy teardown. The car is currently up on the lift in my garage in a disassembled state. I'm hoping to have it assembled by summer...I'll already be missing the registration deadline on it. Tons of things are changing on that car, and it was going to be my testbed, so since it's down so are my plans to test the LTCC.

My dad's '94 still runs (in fact it's the car we just took on that massive road trip), but it has issues that make it not a good candidate for testing right now. Chief among them is the noisy serial bus and, more importantly, the opti signal is currently doing something that defies logic. See thread here: http://www.gearhead-efi.com/Fuel-Inj...ion-at-low-RPM

And since the DIY-LTCC still relies on the opti signal to run, yeah.

So at least for now, the project is shelved on my end until I have a testbed that can host it. That won't be until I get my '95 reassembled.