'89 Chevy L05 diagnostics

[1project2many]

Welcome to the forum! I absolutely love the level of detail which you are bringing to this project. I hope you are able to find a way to improve efficiency for your engine.

I am impressed that you were able to locate a set of CR43TS plugs!!! They are discontinued. Folks don't understand the "commercial" grade of the plugs included larger electrodes which lead to longer life. Well done!

In regards to the O2 sensor I would watch sensor activity for responsiveness, and I would look at the sensor output to see if it's frequently reaching maximum and minimum values while operating at cruise. Early ECM's are notoriously poor at flagging a lazy O2 sensor.

The Zirconia element of an O2 sensor will generate a voltage when there is a difference in oxygen content between the exhaust gas and ambient air. If for any reason the O2 sensor "ambient air" sample is corrupt, the sensor readings will be incorrect. My understanding is the ambient air sample is taken from the area inside the metal shield on the outside of the sensor, or in some designs, from air trapped inside the signal wire. It is conceivable that the signal could read incorrectly despite the sensor being fully functional. I have seen cases where leaking oil caused high HC content air (read smoky) to form under the engine which in turn forced the O2 sensor lean. Although it's rare, I do believe it's possible for the sensor reading to become "shifted."

I expect you will find the low baud rate of your ecm will not always offer a representative sample of what the O2 sensor is "seeing." At the dealership we would break out a voltmeter when we had to monitor signals for the old ECM's. That was the only way to see what was happening! When I started ECM tuning in the '90s the DVOM was a critical component to getting accurate signal readings. Bob of Dynamic EFI designed a tool that reads sensor data at a frequency much closer to what the ecm actually sees. That is a substantial part of what makes the Dynamic EFI option attractive. But it doesn't mean you can't make improvements with the stock ECM.

I do want to mention that the original owner claiming reduced fuel economy after AIR pump failure does not necessarily correlate the two issues. Based on information you have, is it possible the previous owner may have been lax in recording fuel economy prior to the AIR pump failure? I ask because, as a mechanic, it sometimes seems like people will not look for change until there's an event that requires them to look for symptoms. Is it possible that fuel economy had been slowly decreasing over time? Regular and expected wear over time will cause reduced ring sealing, camshaft timing delay, reduced valve sealing, increased valve guide and seal wear, carbon buildup on valves (and associated compensations), and intake manifold deposits. Is it possible that your L05 is experiencing issues related to any of these conditions? If so it would be tough for the ECM to flag an issue. These problems can each cause a small change in efficiency. Added up they can cause a noticeable change.

Finally. if your diagnostics are not able to flag an issue, would you consider making changes anyway? There are cams that are much better at providing improved economy and performance than the '89 TBI cam. Engine knowledge has improved dramatically in the 35 years since the L05 cam was developed.

[MO LS Noobie]

Well said 1project2many, all excellent points

[fjm719]

Regarding the pinging condition, just observe the knock retard parameter.

MO LS Noobie,

Is "Knock Counts" (circled below) the "knock retard parameter"?
Knock_Counter.jpg

Alternatively, are you referring to one of the tables I see on the left side of TunerPro RT?
knock_tables.GIF

Or should I be looking elsewhere?

[MO LS Noobie]

Yes, the knock count parameter (fig. 1). The tables referred in fig. 2 are what the computer uses to set the knock counter. The harmonics are different for every engine. That's why you need to be careful when changing things, they impact a lot of other tables.

[fjm719]

Dave,

Am I right that these four tables are from a generic controller? Or were these intended to be what one might expect from a 160-baud controller or a stock 1228747/AKWC?

I now understand that they all use show engine speed (in RPM) as a vertical axis, as appears in the left column. I understand that they all use manifold absolute pressure (in kPA) as a horizontal axis as shown in the second row.

I understand that the first two images tabulate a volumetric efficiency parameter that may or may not have units of measure. I understand from your later response that these are "programmed" as part of a tune. I conclude, then, that they are not learned or updated in any way by the 1228747 ECM. I understand that these values are, in some way, combined with the BLM values in determining the duration (and perhaps intensity) of the injector sprays.

I understand that the second two images tabulate spark advance, presumably in degrees of the crank (though perhaps it could be degrees of the distributor???). I understand that these are "programmed" as part of a tune. I speculate that these values are combined with a variety of other inputs and parameters to actually control when the coil fires.

That leaves me with the text strings in the top rows of the tables. I'm guessing that "upper" and "lower" somehow refer to how the tables were split up by RMP for export. I'm guessing that "Averages" somehow implies that the ECM uses these values for non-transient response. I take "Spark Advance" to describe the values that are tabulated throughout the last two images. I interpret "WBO2" in the first two images to mean "Wide Band Oxygen", but I'm not clear how it describes or affects what's in the first two images.

Attachment 20113

Attachment 20114

Attachment 20115

Attachment 20116

[fjm719]

Attachment 20121

Dave,

Thank you, again, for all of the detailed information. Regarding the image you attached, is that intended to be a generic VE table, or were you intending to show what might be learned in something like the Dynamic EFI device?

I understand the left column to include a relatively high range of engine speeds (in RPM). I understand the second row to be the manifold absolute pressures (kPA). The values in the field of the table would be the volumetric efficiency numbers. However, its still not clear to me what the units of measure are for the VE values--or their physical meaning. Also, it's not clear to me whether the ECM is using these VE values directly, or whether they're being mathematically combined with other parameters to determined the injector pulse duration/intensity for a given RPM/MAP circumstance.

[dave w]

The tables I posted were specific to a Dynamic EFI "Tune". The 1228747 tables are similar, with the exception of the Air Fuel Ratio table.

The Fuel Tables (VE) and Spark Tables are the most significant tunable values with two exceptions: Injector Flow Rate / BPW and Base Timing / Initial Timing.

[fjm719]

In a prior post, I outlined the troubleshooting guide for low fuel economy from the 1989 GMC Light Duty Truck Fuel and Emissions Including Driveability manual.
http://www.gearhead-efi.com/Fuel-Inj...l=1#post102565

That guide includes a generic topic called “System Check”, which is covered in Section 3 of the same manual:

System_Check.JPG

My vehicle has ALDL 12-terminal connector under the dash with five pins populated:

20240531_214249 - Copy.jpg

The Service Engine Soon light illuminates when the key is turned on and is off when the vehicle runs. Therefore, the bulb is judged to be OK and the ECM is able to control the light. However, As a newcomer to OBD1 systems, my next step was to short pins A and B with the key in "run" and the engine "off" to look for codes.
ALDL_pin_out.JPG

Other than code 12 (diagnostic mode working), no other codes were displayed. I did not attempt any "A-jumped-to-B" diagnostics with the engine running, but could if anyone suggests this could have value.

I then worked to connect TunerPro RT. I purchased an ALDL-to-USB cable with a 12-pin (GM OBD1) connector from OBD Diagnostics, 310-793-2410, http://obd2allinone.com. The necessary drivers for the cable were available in the “Diagnostic Software” section of the OBD Diagnostics website, via a link at the top labeled as “VCP Drivers” that took me to https://ftdichip.com/drivers/vcp-drivers/. The relevant zip was a link right near the top of the page, under the heading of “Virtual COM Port Drivers”. The zip file available lower on the page did not appear to include an executable setup file. I appear to be using version 2.12.36.4 for my cable driver with a Windows 10 laptop.

In my case, the cable lives as COM6. After reading a few posts from this forum, I settled on the following settings:

Settings_General.GIF

Settings_DataAcq.GIF

TunerPro RT is able to connect to the ECM when I click the icon with two blue arrows Icon_connect.GIF . The LD .adx file appears to display more information for me than the HD .adx file.

$4F-1228747-LD-V1.1.adx:
LD_ADX.jpg

$4f-1228747-HD-V1.1.adx:
HD_ADX.jpg


Also, the data in the left window seems to be fully populated However, I'm uncertain whether it comes from my use of the forum's $4F XDF files or whether it has somehow been captured from interfacing with my vehicle's ECM. I don't think that I've seen anyone with a .bin corresponding to the AKWC code.
left menu.GIF

I am unsure of what makes a good driving route for data collection—steady sections? A variety of speeds? A variety of driving styles? Do any separate threads exist on this topic?

In any case, I'm using a 6.2 mile trip from home to work that includes:

• Slow movements through parking lots to reach the street
• City driving (five lights) that includes the transition from open loop to closed loop
• voluntary WOT acceleration to enter a highway,
• Highway driving with cruise control at 55mph
• City driving (three lights) into my work’s parking lot

To show day-to-day variation (or lack thereof) I’m attaching two recent logs. They include differences in what stop lights were encountered, but are otherwise quite similar.

In my upcoming posts, I intend to work through each of the “System Check” topics and sensors.

[fjm719]

I am impressed that you were able to locate a set of CR43TS plugs!!! They are discontinued.

My local O'Reilly's had them in stock, though the Delco boxes suggest they were manufactured offshore. So it's hard to say what aspects of the "commercial" spec persist, but I thought it was worth a try.

Based on information you have, is it possible the previous owner may have been lax in recording fuel economy prior to the AIR pump failure?.....Is it possible that fuel economy had been slowly decreasing over time?

Yes, this is definitely possible. The prior owner's early fuel economy was well documented. My fuel economy is well documented. However, the timing of the deterioration is anecdotal. I should have better emphasized that caveat in my original writeup.

Regular and expected wear over time will cause reduced ring sealing, camshaft timing delay, reduced valve sealing, increased valve guide and seal wear, carbon buildup on valves (and associated compensations), and intake manifold deposits. Is it possible that your L05 is experiencing issues related to any of these conditions?

I was hoping to rule out some of this with the compression test, but you're right. Some of these are definitely possible.

Finally. if your diagnostics are not able to flag an issue, would you consider making changes anyway?

I am open to changes, but my overwhelming preference is to make sure I've addressed the easier/lighter jobs first. Getting the engine out of one of these vans is no small task and doing so would likely require seeking out better facilities than the gravel driveway and work parking lots I'm currently using for the diagnoses. At 10'8", the vehicle also requires a ~12' door height to be worked-on indoors---which currently requires me to ask favors of friends and family. So, anything is possible, but I'd say it would likely be next summer before I would bite off a full engine teardown.

[fjm719]

Dave,
I'm not sure if it's relevant, but using your snips from the adx definitions, I noticed that the same bit/offset (0x40, 0x00 offset) that throws the flag in the LD adx, happens to correspond to "Battery Voltage High" in the HD adx. I don't have the experience to know (or the historical involvement from when these adx files were developed) to tell which criteria is used to decide on the correct ADX file. Was there a different reason you included the 3rd and 4th snip in your prior message?

[dave w]

Dave, Was there a different reason you included the 3rd and 4th snip in your prior message?

TunerPro RT can be edited, I showed the Monitor’s edit screens.

[fjm719]

In further pursuit of improved fuel economy, I start my journey through the “System Check” list with the first of two items that immediately caught my (admittedly inexperienced) eye after logging a couple trips: engine speed.

My understanding is that engine speed is derived by the ECM using the signal(s) from the distributor on pins B5 and B3 of the ECM. I’m not clear if the frequency of events on those terminals gets divided by 4, divided by 8, or multiplied by some other round factor. However, it seems that the ECM should be able to calculate a very accurate RPM, when at steady state.

My vehicle does not have a factory tach, but the prior owner did install a Sun super tach II aftermarket tachometer.

Upon review of my initial log files, I immediately noticed that the RPM reported on my aftermarket tach (Sun super tach II) exceeded the RPM in the cruise portion of my log files. I guessed that if the aftermarket tach was correct (and the ECM misunderstood engine speed), then I could be operating in non-optimum portions of the fuel and spark tables. I tested this by using an optical tachometer aimed at a piece of reflective tape on the harmonic balancer, while another person held the throttle at various positions. My results, below, show that the aftermarket tach was reading high and that the ECM reading was spot on. Therefore, the RMP discrepancy was judged not to be a meaningful cause of lower fuel economy.

Since I have no indication that the aftermarket can be field re-calibrated (and because I don’t know of a good explanation for the discrepancy), I intend to simply place a tape label on the aftermarket tach’s face indicating it’s tendency to over-report RPM by ~7%.

[1project2many]

The ECM measures time between reference pulses from the distributor then, using a constant that represents the number of crankshaft degrees between reference pulses, calculates how many 360 degree events could occur in one minute.

The aftermarket tachometer can be recalibrated if you have the knowledge and tools. Sometimes aftermarket electronics are built with lower quality parts that deteriorate over time, such as capacitors. Many folks it easier to replace the tach than to repair it. But before condemning the tach I would check to ensure the it is set for 8 cylinders.

But you have done well by confirming the engine is operating at the rpm shown by the ecm. This allows you to have faith the logs are showing correct RPM information.

[fjm719]

Thanks, 1project2many!

The aftermarket tachometer can be recalibrated if you have the knowledge and tools.

The next time I have it off, I'll see what it takes to get the tach case open. Internet research suggests that similar Sun models have at least one trim potentiometer on board.

But before condemning the tach I would check to ensure the it is set for 8 cylinders.

I did already check that the tach was set for 8 cylinders. If it was set at "6", I suspect that the tach would over-report by 33%, rather than the +~7% I'm currently seeing.

[fjm719]

Continuing my search to regain the vehicle’s original fuel economy, I pursued the second of two “System Check” items that immediately caught my attention in my TunerPro RT logs: coolant temperature.

My engine has two coolant temperature sensors. One sensor (1-terminal) located between the #1 and #3 exhaust ports on the left head sends a signal to the dash gauge. The second sensor (2-terminal) in the intake manifold near the thermostat housing supplies a signal to the ECM on pin C10.

Upon review of my TunerPro log files, I immediately noticed that the temperature reported by the ECM (roughly 205degF) greatly exceeded the temperature reported by the in-dash gauge (roughly 185 degF).

I guessed that the intake-mounted CTS was faulty, generating a temp-resistance relationship that differed from the ECM’s calibration curve. My thinking was that if the ECM misunderstood the engine’s temperature, then it may lead the vehicle to operate in a non-optimum region of the spark and fuel tables.

I purchased a replacement 2-terminal sensor (Standard Motor Products TX3). Prior to installation I suspended the new sensor in a pan of water on a stovetop. I measured resistance between the pins with a digital multimeter. I calculated temperature by averaging the readings from three different digital thermometer probes suspended in the waterbath.

Next, while replacing the sensor on the engine, I connected a potentiometer to the wiring harness and simulated various resistances to the ECM. This confirmed for me that the new sensor would/does provide the resistances expected by the ECM over the range of concern (up to at least boiling).

While I had the engine bay open, I repeated the potentiometer activity with the wiring to the dash gauge. It appears that the calibration curve of the in-dash gauge is significantly different than the calibration of the ECM or the intake-mounted CTS. I did not spend time removing or checking the head-mounted CTS.

A few days after putting things back together, I checked the calibration curve of the original sensor. It closely matched ECM expectations, GM expectations, and the replacement sensor. It likely didn’t need replacing.

Since the gauge-to-ECM discrepancy is not fully explained by my calibration checks, I am left to believe that the head-mounted sensor has a different calibration curve. Alternatively, the head sensor location is simply far cooler than the intake-mounted sensor.

In any case, I conclude that the ECM is getting accurate temperature from the intake and the CTS calibration is not a meaningful contributor to reduced fuel economy. So 0-for-2 on the values that jumped out at me in the logs.