0411 swap done, did crank relearn...now it doesn't run

[gearheadE30]

Like the title says, I got my 0411 swap done on my 2000 Tahoe Limited and works great. I have EFILive and am not new to tuning, so it wasn't too big a deal. However, when I was going through the checks after getting it running, I discovered that CMPRET was about 38 degrees. I should have had a code off that far with the original ECM, but I didn't that I'm aware of.

I wasn't able to get the distributor clocked enough to bring that number down any further, so I checked and found some pictures online and it appears that the distributor was a tooth off. Set to cyl 1 TDC, pulled and reclocked the distributor, and now everything looks like it should. Reinstall, dial it in so CMPRET is between 0 and 3 degrees, and I figure I'm golden.

Except I'm not. Pending P0300 for tons of misfires, and TCC lockup shows disabled due to misfires. It also doesn't idle at all (instantly stalls after starting), which tells me that timing is off...but if CMPRET is 0, how can timing be off. It will run if I keep my foot on the gas.

What did I do wrong? Is there something else I missed in that procedure? I've never heard of setting the cam position retard causing new problems, and searching turned up nothing at all.

 

[98 Nitro]

When I set my cam retard I knocked the line from the passenger side valve cover to the airbox off and set that code but it ran. Also starting then dying could be the VATs passlock.

I thought Tahoe limited already had an upgraded tune from factory?

 

[gearheadE30]

VATS is disabled, and in any case VATS failure would cause a start and die regardless of throttle position.

I did eventually get it to idle after many start and die attempts. It's like it had to re-learn the idle valve position. I pulled the battery cables to reset any learning in the ECM, and it went back to not idling until probably 20 start and die events.

All the vacuum lines look good, but that was definitely a good thought.

Common misconception about the Limited - the cal is slightly different (no speed limiter being the main difference) but there isn't much performance difference. I went to the 0411 to prepare for a manual transmission swap and to support engine modifications.

 

[gearheadE30]

So far my best running guess is that the distributor is worn out (cap and rotor are fine but it has some vertical play in the shaft) and that's what is causing my issue. Cap and rotor aren't perfect, but not bad enough to be causing a problem. Otherwise, still no solution at this point. And I'd really rather fix the problem than just turn off misfire diagnostics.

I also did another look through for vacuum leaks but did not find anything.

 

[gearheadE30]

I installed a new distributor and I was actually able to dial in the CMPRET...and I got it to about 4 degrees and the engine started sputtering and then cut out. Strange.

Lots of diagnostics later, it appears that somewhere between the coil and the plugs, my spark is disappearing. I have spark (according to an inductive tester) at the coil feed to the cap, but I don't have spark at any of the plug leads leaving the distributor. Cap and rotor are making proper contact.

I did swap the old cap on, which should still work even though it is worn. The timing light is showing spark now, but the engine refuses to fire. I think all of my cranking trying to diagnose the engine flooded it pretty darn badly, so I'm going to let it think about what it's done wrong overnight and give it another look in the morning.

I've never seen a new distributor cap just not work like this, but so far that's what all the signs are pointing to...

 

[gearheadE30]

Well, I tried to start this morning and the timing pickup is still showing nice consistent spark at the plugs now, but the truck never even tried to fire. Fuel pressure looks good, and it seems that I can smell fuel as well which is the best guess I have that the injectors are actually firing.

If I hadn't had it running (perfectly) I would have guessed that I stabbed the distributor in there 180 degrees out, but it did run just fine for 5+ minutes.

Going to pull the battery and see if resetting things makes it any better, and pull a plug to see if they are wet or dry.

 

[HotWheelsBurban]

Cap/rotor could be cracked. The only bad side to the Blue Streak parts is the plastic is brittle when handled roughly. Probably happens with other brands too.

 

[gearheadE30]

Turns out the cap was defective out of the box, much as you suggested. Pulled it off and found burn marks/arcing evidence below the cap electrode. Swapped the old one on and it at least runs now.

Misfire counts are dramatically reduced with the new distributor. The old gear had some wear, as did the bushings (vertical thrust bushing, mainly). CMPRET is at 1 degree. However, there are still enough misfires occurring to kick the torque converter out. I do still have a pending P0300 fault for misfires, and got a blinking SES light on my test drive that eventually went away. I didn't even know there was a blinking SES light function on these trucks, so I'm not sure what caused that.

My guess is that my 262000 mile engine has a worn cam gear and a slightly loose timing chain contributing to the misfires, and that the 0411 ECM is fast enough that it can sense them unlike the old black box ECM

Data traces show cylinders 2 and 3 being the prime misfire contributors, at least on a short trip through town.

Not quite sure what do to with it at this point. Obviously I can't be driving around with no TCC lockup, and I never had an issue with it before. I'd love to have a good idea of how the misfire logic works and what limit it has to cross to cut the TCC out, but I have not been able to find that information yet. It seems like a bit of a cheat to 'detune' misfire detection so the converter will lock up as opposed to fixing the problem.

It still also baffles me as to why this problem never showed up before with the old ECM.

 

[HotWheelsBurban]

IIRC a blinking check engine light means "there's something serious going on that you need to look at asap".
I grew up in a family owned independent auto parts store in the 70s and 80s. You'd be surprised how much stuff gets handled roughly! I've spent most of my adult life working in various retail stores, and things haven't changed a lot since then. If you've ever seen how stockers and unloaders handle pallets of expensive stuff like TVs and furniture, you'd never want to buy anything from a big box store! I'm not surprised at hot wheels and other toys being damaged in shipping.
Glad to hear you've sorta figured it out!

 

[gearheadE30]

Sorta haha.

It appears that the blinking CEL can be triggered by severe misfires, which is in line with the only code stored which is a pending P0300. One interesting point is that it happened when I had shifted the transmission into 3rd and was running along at 55ish mph trying to see if misfire behavior was different at different engine speeds. Apparently it is. However, I don't feel any misfires so even if they are significant events, there isn't a lot of energy behind them.

I think I took an EFILive log of misfire activity before I swapped the distributor, but from memory my typical misfire counts are about 70% lower than before at cruise and are maybe 20% better than they were at idle/low load. Just watching the laptop while driving, the front cylinders (2 and 3 in particular) have the most misfire activity.

It is still baffling to me as to why I didn't have a problem before swapping in the 0411 ECM.

I don't really want to throw $85 worth of plug wires at it (I am not a fan of swapnostics without direction) but that is the last easily-accessible related component that I haven't replaced. EDIT: I have personally put about 60k miles on this truck and I have no idea how old the wires were when I got it. So it might be time to replace them anyway.