Phantom Spark Retard

[truethinker]

I posted this over on the GM Performance forum but figured since i'm using EFIlive I'd ask it here too.


Vehicle Info:
1996 Chevy K1500, 5.7L, 220k miles

Original engine(block and rotating assembly), Aftermarket heads, ramjet intake, headers, 4L80E swap, 411 swap with EFIlive, etc. . . .

If memory serves, this occurred once or twice before the 411 swap two years ago and has been getting worse since.

Also, fearing a faulty 411, I replaced it the other day. No change.

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SYMPTOMS

-the engine revs very slowly and in choppy fashion when in P/N. The higher the rpms, the smoother and snappier the engine.

-when driving, anything more than the lightest of throttle/engine load will cause an extreme loss of power and a very choppy engine running condition.
--when I say loss of power, I mean that you could floor the throttle and not move more than a couple feet in a minute.

-The only effective way to drive is to start in 1st and apply throttle by "feel", staying below the engine load threshold where the engine begins to stumble and die. Just as in P/N, the higher the rpms, the better the engine runs. So I have to run to around 4000 then shift to 2nd and run to high rpm and shift to 3rd and so on.
--When staying under that "threshold" the truck feels normal and responsive. But that "threshold" is less than 8% throttle on the level and even less on a grade/ under load.

-Once up to speed on level highway, the truck can maintain speed as long as I don't apply more than slight throttle. Also, the slightest up hill grade and increased load on the engine, requires a manual downshift(sometimes to 2nd) just to climb the grade.

-AFR is within proper range at all times and there is no MIL illuminated(tested the MIL with EFIlive. It works just fine)

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I know what is causing all these symptoms.
-While slowly applying the throttle, the timing is fine until I hit that "threshold" and then the spark is retarded to the maximum EFIlive is able to read. (I don't have specific numbers as my power steering line failed the other day as I was getting ready to log some data for the forum.)

This makes sense with all the symptoms. . .

But I have no idea what is causing this phantom spark retard.

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Some info on when this happens.

Sometimes it happens upon cold start. The problem is present the moment the vehicle is started. Once I get it up my driveway and am able to drive on the level, I always make it to about the same spot on my way to town. It's about a mile from my house. It then corrects itself and runs great. I could have the throttle floored and be causing the engine to bog and spit and sputter but when it decides to correct itself, it will break the tires loose and take off. . .

The other time that this happens is after driving for a while. The truck will be running fine and then all of a sudden it just dies down and I start to decelerate due to the retarded timing.

-When this was happening before(while I was at school), I could predict it. I would leave Blairsville, PA and drive about 30 minutes with periods of heavy uphill grades and level terrain. Immediately before the Wal-mart in Ebensburg, PA this problem would occur. I would pull into Wal-mart and go inside for 30ish minutes then when I came back out the truck ran fine.

--I can only think of two points of interest here. This location when the problem would occur was directly after the steepest uphill grade, so directly after having the greatest load on the engine.

---The problem never happened on the way back to school, which was mostly a downhill trip/level trip aside for two areas which are pretty steep.


Now when this happens, there is no pulling over for thirty minutes. I could let it sit overnight and still the problem persists. And now I only get about five miles on the highway toward state college, PA(uphill) and it happens.

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I'm certain that this is not heat related, as in, I'm sure that it's not a matter of a component heating up and faulting. This is because, if I reload my tune with EFIlive and in the process, reset the ECM, the problem goes away.

Also certain that it's not a loose or shorting wire as it's too predictable.

Definitely engine load related as increasing the load on the engine cause the spark retard "threshold" to be reached at a much lower throttle position.

I don't know if the computer is commanding this retarded timing or if another component is causing it and EFIlive is reading it and showing it to me. Either way, the timing is retarded to the maximum.





I appreciate your time in reading this and any input would be greatly appreciated:
Jesse

[Aloicious]

when you say 'spark retard' are you referring to KR, or just everything (i.e. burst knock, torque management, KR, etc, etc)? do you have a tune and hopefully a log that you could post up for us to look at?

if its only KR, have you tried replacing the knock sensor? they can get faulty with age.

[truethinker]

I wont have a log until i get that powersteering line fixed.

It's not knock. I'm simply referring to the fact that overall spark timing is being retarded. Don't know what's doing it.

[hquick]

Post your tune Jesse.

[truethinker]

Will do.

[truethinker]

Here's the tune I'm using right now.

I've tried it with a normal O.S. and using the MAF. I've tried shutting of traction control and abuse mode, etc. This problem existed with both the 4L60E and now the 4L80E.

Could some sensor or something, be failing and sending faulty information without setting a code?


Also, just a note on the ignition system.

MSD Blaster coil
MSD 6A Ignition Box
MSD wires
Once upon a time, I had an Accel coil wire. It was a "cut to length" kit. It burnt off at the coil and was arching between the boot and the coil mount. I just chalked that up to me not properly attaching the coil wire end. But who knows.

[Boost]

Subscribed. I hope you are able to clear this up, faulty knock sensors sound like a reasonable possibility. I had a similar (load) symptom on an '89 Grand Prix, except I could not confirm that it was KR with EFILive. After experimenting with the MAP sensor, wiring and PCM all night, I gave up and blamed it on the fuel pressure regulator... Good luck and keep us posted

[drdarthinvader]

is your vehicle running rich you have high ve numbers with low ifr numbers and high o2 switch points and throttle cracker table altered,and having the aust ipw voltage table> your engine might not like these mods?

[truethinker]

When I get back home ill have to check and make sure I sent the right tune. The tune I'm running is mostly stock. Haven't touched the switch points. Haven't tuned ve. Just set the ifr and used tuned the trans some. Maybe the unmodified tune file I started with wasn't so unmodified after all.

[truethinker]

Yes. Fuel trims are high compensating for a rich condition. I figured that was just a matter of needing to tune VE.