Weird $OD Spark Advanced FIXED, sorta

[dave w]

I don't know what is mechanically wrong with the engine, EVERYTHING is new including the engine. Data log showed weird spark advance numbers, see screen shot below. Turns out the weird numbers in TunerPro RT is because the spark advance is a negative number ( used a timing light with a dial to confirm negative advance).

Anyway, I disabled all spark retard programming in the $OD PROM Chip. Now the data log shows normal spark advance. Truck runs much better with spark retard disabled!

I'm open for suggestions as why or what causes the spark advance to go negative. I define negative spark advance as degrees AFTER TOP DEAD CENTER. In this case, the negative spark advance was 5 degrees ATDC. Typically spark advance is degrees BEFORE TOP DEAD CENTER.

Tried different computer, same result negative spark.

Tried different Memcal, same result negative spark.

Knock sensor measured 4K ohms. Knock sensor wire, computer to connector measured 0.6 ohms.

Tried different (KNOWN GOOD) GM ignition module, same result negative spark.

Tried different coil (stock GM), same result negative spark.

Disable ERG in PROM, same result negative spark.

Tried different MAP sensor, same result negative spark.

Tried different CTS, same result negative spark.

Weird, weird, weird problem!

dave w

[woody80z28]

Wow, that is really weird. I've never seen that before.

What is it in, truck? Just curious because it doesn't look like a lot of spark. I just datalogged mine today for the first time in forever because I'm getting a Code 43, but only spark retard at WOT...pulling 5-8* and it feels super slow...

[dave w]

It's bone stock 350 TBI re-manufactured engine. BCC is BJYL.

dave w

[ony]

could the wires be reversed in the dist on the magnitc pickup, i ran into that 1 time

[1project2many]

1) I think you've figured this part out, but the "wierd" numbers are only Tunerpro's ADX interpretation of the 16 bit value which represents spark advance. Without telling TP that you have a signed integer the values are being interpreted as unsigned values with a maximum positive limit of 65,535 before the conversion formula.

2) In Tunerpro I'm seeing BJYL with a maximum spark retard value of -9.8 degrees. (Yes, this is a double negative. This should be minimum spark advance). If datalogging revealed spark values no greater than 5 degrees ATDC then the spark advance was within the factory limits.

So the questions are:
1) Does the displayed spark advance match the actual spark advance? A: It appears that it does.
2) Is the pcm indicating spark retard?
3) Is the knock sensor detecting knock?
4) If the knock sensor is replaced with a resistor, will the spark values return to normal?

I have experience also with the wrong pickup coil (similar to wires being reversed) and have seen spark advance do the opposite of what is expected. But as I remember the displayed advance did not match actual. Was the distributor changed when the engine was replaced?

[dave w]

The engine seemed to be running fine for several months after the engine was replaced, then the engine experienced a loss of power symptom

The distributor was replaced, but the engine still had a loss of power symptom.

The attached 3-22-18_01.xdl is the first $OD data log I recorded when the pickup arrived for me to look at. This data log doesn't show any real significant knock retard.

The vehicle owner is OK, with the "custom" chip, he needs his pickup on the road.

I will try a resistor instead of the knock sensor, at a later date, the pickup is not currently available for me to work on.

I'm hoping to get a few other ideas to try, before asking to work on the pickup again.

The attached 4-22-18_01.xdl is the most recent data log, before the vehicle owner accepted delivery with the "custom" chip.

dave w

[1project2many]

Here are two theories to investigate:

Viewing 3-22-18_01.XDL I see a restart at approximately 4:40.
At 4:40:716 I see knock counts increasing and knock retard of approximately 1.8 deg.
At 4:43:112 all traces of spark knock appear to be gone, and spark timing is significantly retarded.

GM released calibrations for 92 - 95 vehicles intended to reduce cold startup spark knock. You can read a copy of one of the service bulletins here (http://www.gm-trucks.com/forums/topic/42459-94-57-cold-start-knock-and-tsb-s/). Installing the cold knock fix calibration was one step in a matrix which included potentially changing oil filter type and replacing main bearing inserts. BJYL is one of the calibrations which was replaced. As I remember, shutting the engine down when warm would allow oil to drain out of the journals. The spark advance delivered during restart was enough to hammer at the bearings for a short time until oil pressure supported the crank. Over time this would cause excess clearance to develop in the mains. I wonder if it is possible that this truck's engine may be experiencing the same problem, and the knock that's showing at startup is the result.

But this doesn't answer the question about why spark is retarded when no knock is occurring. I would have to look at the code, but I wonder if the pcm will store a value akin to "block learn" for spark if it detects knock during startup. I have never heard of this happening but the theory could explain what's happening. I did scan for additional restarts in the 3-22-18_01.xdl file but I didn't see any. Possibly you will have additional log files to compare?

[dave w]

Here are two theories to investigate:

Viewing 3-22-18_01.XDL I see a restart at approximately 4:40.
At 4:40:716 I see knock counts increasing and knock retard of approximately 1.8 deg.
At 4:43:112 all traces of spark knock appear to be gone, and spark timing is significantly retarded.

GM released calibrations for 92 - 95 vehicles intended to reduce cold startup spark knock. You can read a copy of one of the service bulletins here (http://www.gm-trucks.com/forums/topic/42459-94-57-cold-start-knock-and-tsb-s/). Installing the cold knock fix calibration was one step in a matrix which included potentially changing oil filter type and replacing main bearing inserts. BJYL is one of the calibrations which was replaced. As I remember, shutting the engine down when warm would allow oil to drain out of the journals. The spark advance delivered during restart was enough to hammer at the bearings for a short time until oil pressure supported the crank. Over time this would cause excess clearance to develop in the mains. I wonder if it is possible that this truck's engine may be experiencing the same problem, and the knock that's showing at startup is the result.

But this doesn't answer the question about why spark is retarded when no knock is occurring. I would have to look at the code, but I wonder if the pcm will store a value akin to "block learn" for spark if it detects knock during startup. I have never heard of this happening but the theory could explain what's happening. I did scan for additional restarts in the 3-22-18_01.xdl file but I didn't see any. Possibly you will have additional log files to compare?

I really appreciate the theories.

The vehicle stalled an died with modest throttle acceleration, that's why the restarts.

The only log files I have other than the 3-22-18_01 have programming changes that mask the problem, like minimum temperature for knock retard.

Wish I could have some logs when things were working OK.

The second computer that was tried, had been on the shelf for several months so I don't think a learn would stick that long without power.

dave w

[1project2many]

The second computer that was tried, had been on the shelf for several months so I don't think a learn would stick that long without power.

I agree. I am thinking of a learned value determined at each startup based on whether or not knock is detected. This could be tested in another vehicle by establishing a baseline at startup with no knock then simulating knock during a subsequent restart.

[skandolis]

i had a simalar issue recently, ended up being the new balancer had the timing mark in the wrong spot due to a timing cover change. new balancer was at 12:00 old one was over on the side like an old school timing tab... i was starting out with seriously negative timing instead of 0 degrees......

[dave w]

i had a simalar issue recently, ended up being the new balancer had the timing mark in the wrong spot due to a timing cover change. new balancer was at 12:00 old one was over on the side like an old school timing tab... i was starting out with seriously negative timing instead of 0 degrees......

Thanks for the post. I didn't even think about the harmonic balancer timing indicator could be inaccurate. If, or when the truck is available to me again, I will put a degree wheel on the harmonic balancer and verify TDC.

dave w

[delcowizzid]

My guess is there's a spark bias scaler set at 0 instead of 20

[dave w]

My guess is there's a spark bias scaler set at 0 instead of 20

That's an interesting thought. I tested with a stock Memcal. I even downloaded the same BCC from this site, found Zero differences.

dave w

[ony]

sometimes i have to put a,b and so on in the file i started with my files get corrupted some times for no reason?

[delcowizzid]

Can you add a link to the files or add the xdf adx and the stock bin here that you are using

[dave w]

Can you add a link to the files or add the xdf adx and the stock bin here that you are using

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?303-16197427-PCM-Information-0D

dave w

[dave w]

sometimes i have to put a,b and so on in the file i started with my files get corrupted some times for no reason?

I used my Ostrich 2.0 to verify buffer with chip to confirm the Memcal file vs. the file I downloaded from gearhead-efi.

[delcowizzid]

Your guys xdfs are weird I wondered why the factory cal only had 15 degrees at 100kpa its setup to minus the bias off the main spark tables for some silly reason edited xdf and pow real spark figures 28 degrees up top at full throttle lol.have you ever confirmed actual advance matches commanded advance before this issue

[1project2many]

The bias is subtracted from the main spark tables. The values shown in main tables don't match actual spark advance unless the bias is taken out.

[dave w]

It's HAPPEN AGAIN!! :mad1:

I have another vehicle with a WEIRD Spark Advance!

13499

13500

Two completely different vehicles, one in Oregon the latest in California. One external engine difference is BOTH are using Holley TBI Throttle Bodies.

Lighting CAN strike twice in the Same Place!:confused:

dave w

[brian617]

Dave, I've seen weird glitches like that with unrealistic numbers even with a Snap On scanner. I just chalked it up to intermittent communication issues with older obd1 vehicles. The question is are the symptoms related to the glitches in displayed spark advance? Cause and effect sort of speak.

[S.O.B.B.]

I also get weird spark numbers.I also thought it was just glitchy.it has not given any symptoms of any kind I'm identifying in logs.13502
13503

[dave w]

The engine is running poorly, with or without TunerPro RT connected. I'm going to jump off the cliff and make the bold assumption, the spark is going negative without TunerPro RT connected.

It's really weird, absolutely nothing in common between the two vehicles, expect both recently had installed Holley Throttle Bodies. Both vehicles ran great for a period of time after the Holley Throttle Bodies were installed, then not!

Nothing in common means: different definition files, and different computer part numbers. The first vehicle had the problem using a bone stock chip. The second vehicle has a custom chip from me, using a G1 adapter.

dave w

[Fast355]

The engine is running poorly, with or without TunerPro RT connected. I'm going to jump off the cliff and make the bold assumption, the spark is going negative without TunerPro RT connected.

It's really weird, absolutely nothing in common between the two vehicles, expect both recently had installed Holley Throttle Bodies. Both vehicles ran great for a period of time after the Holley Throttle Bodies were installed, then not!

Nothing in common means: different definition files, and different computer part numbers. The first vehicle had the problem using a bone stock chip. The second vehicle has a custom chip from me, using a G1 adapter.

dave w

My first question given my experience with Holley TBI units would be is the MAP sensor signal connected to the correct port on the throttle body. I have had better luck not using the one on the rear of the TBI unit. If you look at the way the throttle body is cast and the way the IAC ports are configured the port on the rear sits right in an area where the IAC gives it a false reading as it opens wider. The Holley units have a full manifold vacuum port on the front of them that gives more consistently reliable results. Cold startup and warmup will be exceptionally bad with the low vacuum reading delivered with the IAC opening. There was a good picture on here of the IAC port and how the rear vacuum port intersects it.

https://i.imgur.com/UBmC02Y.jpg

[dave w]

Moved MAP vacuum source to the front port, still has WEIRD problem.

Fast355, thank you for the Holley information.:thumbsup:

Attached is the latest $OD data log.

dave w

[1project2many]

I would want to verify the accuracy of the data. Is the ecm actually calculating weird spark values? Or is it random data?

I might try to start by confirming the rpm signal is steady, then I might want to try using a scope on the REF and EST lines to see if timing is actually changing as much as indicated.

[dave w]

I agree a scope would be a diagnostic tool for a problem like this.

I think the problem is real, the engine performance is severely degraded during the times the weird advance is happening.

According to Google, I'm 550 miles away from the pickup. I'm thinking the chances of finding a scope cable that long would be challenging! Ok, a touch of humor, but it's still going to be challenging to find a shop that can scope the pickup.

I'm thinking maybe disable all knock retard in the chip once again, which might "fix" the problem again? I understand that fixing the problem in the chip is not a "permanent fix"! If fixing the problem in the chip works, what is the actual fix?

dave w

[1project2many]

According to Google, I'm 550 miles away from the pickup. I'm thinking the chances of finding a scope cable that long would be challenging! Ok, a touch of humor, but it's still going to be challenging to find a shop that can scope the pickup.
We can order the cable inexpensively from Alibaba. But the shipping time from China is really poor this time of year.

I'm wondering if the REF (input) signal is being affected which in turn is affecting both fuel and spark, or if the problem is only occurring in the EST (output) side.

There are limits in the chip for minimum and maximum spark advance values. Those are generally applied after most of the spark advance calculations are made including knock sensor corrections. There are some occasions where a timing change is effected outside the limit checks, such as a timing change applied in $58 due to power steering activity. I believe it is a good idea to double check the min and max values and ensure they match the desired operating range. I also wonder if setting min and max timing to create a much smaller window wouldn't be a good diagnostic step. If the displayed timing varies dramatically even with a narrow window (say 10-20 degrees) you could look at code to see if there's an adjustment to timing outside the limits. You might also increase the temperature or rpm required to enable EST so the engine runs on module timing. If it will not run smoothly on module timing then you'll probably have little chance of making it run correctly with EST operating. There may also be a separate limit to how much knock correction is allowed. You could reduce the maximum allowable correction.

[dave w]

Altitude Spark Bias = ZERO!

I don't know why the weird spark advance is related to Altitude Spark Bias????????

With Altitude Spark Bias set at the factory setting of 9.8 = weird spark advance!!!

With All other Spark / Knock parameters set COMPLETELY STOCK except Altitude Spark Basis = Zero, then no weird spark advance.:confused:

dave w