'89 Chevy L05 diagnostics

[fjm719]

I recently became the second owner of a box-type vehicle built on a 1989 Chevy G30 cutaway-van 1-ton chassis with it's original 350 TBI small block (RPO L05) driven by a 1228747 ECM labeled with the AKWC code.

In this thread, I seek to use TunerPro RT to diagnose a couple lingering concerns and to determine what re-tuning might be appropriate.

I invite feedback from others on the forum.

Except where noted below, I understand all EFI-related components and drivetrain parts to be stock/original:

• Transmission TH-400 3-speed automatic (RPOs MX1 and M40)
• Rear Axle: 4.10 Dana (RPO GT5)
• Speedometer: mechanically driven (RPO D1T) with mechanical needle and mechanical odometer/trip
• Cruise Control: yes (and it still works!)
• Air Conditioning: yes (RPO C60)
• Emissions System: Federal Standard, above 10,000 lbs (per RPOs NA5 and NB3), but the radiator sticker suggests that it actually conforms to Light Truck rules

Other items of note:

• I have an 12-pin ALDL-to-USB OBDI cable from OBD Diagnostics that I have successfully used with TunerPro RT
• So far, I have can communicate using the $4F xdf and the $4F LD V1.1 adx files provided at: http://www.gearhead-efi.com/Fuel-Inj...Information-4F
• Mileage: 114,000 miles
• Typical gross weight: 9,000 lbs (+/-400 lbs) fully loaded, as recently confirmed by multiple visits to scales
• Tire size: LT225/75R16 (I recently converted tires and wheels due to unavailability of radial tires at the original 16.5X8LT size), which have a larger-than-stock circumfrence
• Frontal area: just shy of the 83 sq.ft. noted in the fine print of emissions sticker on the radiator shroud
• The AIR pump failed (stopped turning freely) and was taken out of the serpentine belt path by the previous owner at 92,570 miles.
• I found bits of very worn/rounded metal (typically 4-8mm long) in the outer part of the air cleaner and in the upper side of the AIR check valves. These were presumably bits from the failed AIR pump that have rattled around long enough to have their corners rounded off.

Some of this data was already presented in my introduction thread: http://www.gearhead-efi.com/Fuel-Inj...482-First-post

In coming posts I plan to document

• my recent service, maintenance, and diagnostic work
• driving logs from TunerPro RT
• symptoms related to limited top-end power
• symptoms related to reduced fuel economy

Thanks, in advance, for any help that you're able to offer.
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[fjm719]

As mentioned in my last post, I’m currently working to diagnose two general symptoms. I dig into fuel economy first.

The prior owner observed fuel economy in the range of 10-15 mpg, up until roughly the time the AIR pump seized around 92,570 miles, followed by “lower” fuel economy. It’s not clear if the events were related or coincidence.

Shortly after getting the vehicle this spring, I installed new wheels and tires, because radial tires were no longer available in 16.5x8.0. With the new, larger tire diameter, I’ve found that the actual miles-traveled exceeds what’s reported on the odometer by a factor of 1.036.

I recently completed a ~5K mile trip with fuel economy reported in the following charts. After correcting for my new tire size, mileage ranged from 7.3-11.4 MPG. I averaged 9.4 MPG. This agrees with the prior owner’s recent observations: mileage appears to be meaningful lower than when the vehicle was newer.

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Starting before my trip, I consulted the 1989 GMC Light Duty Truck Fuel and Emissions Including Driveability manual, which framed my approach:

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Thermostat:

Using an infrared thermometer pointed at the thermostat housing, and watching through an open radiator cap, I observed a marked increase in flow when the thermostat housing reaches roughly 185F. The engine has two temperature sensors. The single-terminal device on the left-side of the block appears to drive the dash’s rudimentary temperature gauge. This gauge seems active, seems to rise normally after engine startup, and then tends to hole in the vicinity of the middle of the temperature gauge’s un-labeled center tick mark. Thermostat judged OK.

Fuel Pressure:

I temporarily installed a fuel pressure gauge immediately upstream of the throttle body and found a steady 11psi whenever the fuel pump should be running, regardless of how hard/fast I revved the engine. Fuel pressure judged OK.

Air Conditioning:

I used A/C roughly half the time since ownership. I have not been able to distinguish any dependence of mileage based on A/C use.

Tire Pressure:

My new tires have a higher load-range that what had ever been used on the vehicle previously. I have regularly maintained pressure at 70psi, which is far higher than the weight-relaxed 45psi for 8-ply-rating printed on the assembler’s under-hood sticker. Tire pressure judged OK.

Excessive loads:

Based on scale data and other accessories I’ve removed (full width mud flap, aftermarket receiver hitch, tool boxes, etc.), I find current gross weights to be equal or lower than the gross weights when the vehicle was newer.

Acceleration:

I generally attempt to drive with the minimum feasible throttle position, drive no faster than ~58 mph, go easy from standing starts, minimize use of brakes, etc. Based on first hand knowledge of the prior owner, I judge my driving habits to be far more conservative than how the vehicle was driven when newer.

Air cleaner element:

Replaced with NAPA SFI 22088 prior to recent trip. Then inspected periodically and found to be remaining quite clean. I also applied a bit of heat to the thermally-active shutter in the air cleaner housing intake and found that it responded well. Air cleaner judged OK.

Vacuum hoses:

All vacuum hoses were found to be routed as shown on the Vehicle Emissions Control Information label. All hoses were found to be free of defects. However, a mechanic’s stethoscope did allow me to pinpoint an acceleration-dependent whistling at the front left corner of the throttle body. Disassembly showed that part of the gasket (between throttle body and intake manifold) had been sucked into the throttle body barrel, resulting in a serious vacuum leak. I replaced the gasket (prior to my recent trip data) and found immediate resolution of the whistling.

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Ignition wires:

No defects found. Spark plug wires, distributor cap, and distributor rotor were all replaced prior to my recent trip.

Timing:

Checked with timing connector unplugged. Found to be 0 deg, as specified on the Vehicle Emissions Control Information label.

Spark plugs:#2 and #8 were found to be loose, with #2 actually rattling axially with the engine running. No major problems observed, other than #2 may have looked lean. Spark plugs replaced with Delco CR43TS prior to my recent trip. Unless there is some kind of damage to one of the tapered seats in the heads, the spark plugs were/are judged to be OK. As found after 10K miles and 10yrs of use by prior owner...replaced by me:

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New plugs after 5K miles (while checking compression):

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Compression:

Checked upon completion of my trip. It’s very time consuming to access and remove all the plugs, so testing was performed while warm, but not necessarily while completely hot. No oil was added to any of the cylinders. All cylinders found to pump to 155-164psi in five or six pumps. All plugs had held torque since before the trip. No meaningful differences observed between neighboring cylinders. Compression judged to be acceptable.

TCC:

No torque converter clutch present on the TH-400 transmission.

Brakes:

All four corners have free-spinning hubs. All brakes (front disc, rear drum) have been found to be cool during service stops. Parking break works positively and reliably. Though the brakes are a bit squeaky when hot, brake drag is not judged to be a concern.

Re-fill fuel:

My prior mileage chart included a trendline representing a rolling average, to eliminate the inaccuracies that could stem from inconsistent pump click-off limits. Also, I reported the average of 9.4 MPG, which comes from 23 fill-ups. Fill-up procedure judged not to cause a meaningful effect.

Exhaust restrictions:

I placed a 0-5 psi fluid-stabilized pressure-gauge at the position of each AIR check valve. This is atop the stainless tubing that originates from each exhaust manifold. I only observed negligible pressure, regardless of engine rpm. I don't recall being able to get it over 1 p.s.i. Rather, if seemed like the AIR feeders were typically under vacuum. Backpressure of exhaust (including muffler and two different catalytic converters) judged to be ok.

This leaves three outstanding areas:

Speedometer calibration:

Since changing tires, the actual speed was calculated to exceed the speed reported by the speedometer by a factor of 1.060. This is noticeably different than the factor found for the odometer. It’s unclear to me whether the vehicle speed sensor (VSS) used by the ECM measures directly from the cable and odometer geartrain, or whether it measures off the needle assembly which may be subject to miscalibration of the cup and spring. In either case, is it conceivable that a mismatch between the VSS-indicated speed and the actual speed could cause the ECM to operate in regimes that are inconsistent with the factory calibration expectations?20240531_014329 - Copy.jpg

System Check:

This is what motivated me to seek out TunerPro Rt and this forum. I plan to expand on this effort in a subsequent post. Do you have any advice on how to avoid damaging the ECM during these early, diagnostic stages?

Aerodynamic drag:

When GM calibrated the ECM for this cutaway van, it was only a chassis and cab. GM had no way of knowing what kind of boxy additions would later be added by the aftermarket conversion company. Although the vehicle’s poor aerodynamic shape has remained consistent and would not be a cause of a step-change in fuel economy, is it possible that a better tune might have always been available, given the particular drag characteristics that would have been unknown to GM? Unlike steeply sloped roads which would seem to have a first-order effect on power demands as a function of speed, aerodynamic drag would seem to have a second order effect on power demand as a function of speed. What schools of thought exist on the relationship between aerodynamic drag and engine tuning?

[dave w]

I’m thinking the overwhelming tuning challenge is the 1228747 ECM.

The Dynamic EFI ECM is great option to achieve your tuning goals.
https://www.dynamicefi.com/

[fjm719]

I’m thinking the overwhelming tuning challenge is the 1228747 ECM.

Thanks, Dave.

Could you be more specific regarding the challenges associated with the 1228747 ECM?

Also, I'm still working through diagnostic investigations--it's hard to say what tuning needs, if any, lie ahead.

[MO LS Noobie]

Fuel Pressure:
I temporarily installed a fuel pressure gauge immediately upstream of the throttle body and found a steady 11psi whenever the fuel pump should be running, regardless of how hard/fast I revved the engine. Fuel pressure judged OK.
THIS SHOULD BE CHECKED UNDER LOAD, IE GOING DOWN ROAD, WOT, NEAR REDLINE, probably not the issue.

Timing:
Checked with timing connector unplugged. Found to be 0 deg, as specified on the Vehicle Emissions Control Information label.


TRY UP TO 5 DBTDC, BE AWARE OF PINGING.

Exhaust restrictions:
I placed a 0-5 psi fluid-stabilized pressure-gauge at the position of each AIR check valve. This is atop the stainless tubing that originates from each exhaust manifold. I never observed negligible pressure, regardless of engine rpm. I don't recall being able to get it over 1 p.s.i. Rather, if seemed like the AIR feeders were typically under vacuum. Backpressure of exhaust (including muffler and two different catalytic converters) judged to be ok.
THIS SHOULD BE CHECKED AT BRIEF WOT WHILE PARKED. MAX 2 PSI.

This leaves three outstanding areas:

Speedometer calibration: PROBABLY NOT AN ISSUE.
Since changing tires, the actual speed was calculated to exceed the speed reported by the speedometer by a factor of 1.060. This is noticeably different than the factor found for the odometer. It’s unclear to me whether the vehicle speed sensor (VSS) used by the ECM measures directly from the cable and odometer geartrain, or whether it measures off the needle assembly which may be subject to miscalibration of the cup and spring. In either case, is it conceivable that a mismatch between the VSS-indicated speed and the actual speed could cause the ECM to operate in regimes that are inconsistent with the factory calibration expectations?

System Check:
This is what motivated me to seek out TunerPro Rt and this forum. I plan to expand on this effort in a subsequent post. Do you have any advice on how to avoid damaging the ECM during these early, diagnostic stages?

Aerodynamic drag: HUGE FACTOR, NOTWITHSTANDING THE FACT THAT THIS HAS NOT CHANGED.
When GM calibrated the ECM for this cutaway van, it was only a chassis and cab. GM had no way of knowing what kind of boxy additions would later be added by the aftermarket conversion company. Although the vehicle’s poor aerodynamic shape has remained consistent and would not be a cause of a step-change in fuel economy, is it possible that a better tune might have always been available, given the particular drag characteristics that would have been unknown to GM? Unlike steeply sloped roads which would seem to have a first-order effect on power demands as a function of speed, aerodynamic drag would seem to have a second order effect on power demand as a function of speed. What schools of thought exist on the relationship between aerodynamic drag and engine tuning?[/COLOR]

Engine, body, PCM grounds (T-STAT HOUSING) are suspect. Oxygen sensors have limited life (50K miles)

[dave w]

Thanks, Dave.

Could you be more specific regarding the challenges associated with the 1228747 ECM?

Also, I'm still working through diagnostic investigations--it's hard to say what tuning needs, if any, lie ahead.

The tuning challenge with all 160 baud OBD1 computers is how SLOW 160 baud really is.

Tuning with air fuel ratios is better than tuning with Block Learn Multipliers (BLM's) for optimizing fuel economy. OBD1 computers like the 1228747 are not Plug-n-Play with air fuel ratio meters. The Dynamic EFI computer has a configurable channel for air fuel ratio data to stream real time into the data log.

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[PlayingWithTBI]

^^^This, plus you can automatically tune you VE tables using "Learn VE" and the WBO2.

[Sledhead2]

I am going to propose a few things, this might provide some thought.

How much has gas changed since 1989? meaning when the gas mileage was x, gas was of a certain blend, Is there a chance the gas in your area now has more ethanol in it?
Gas cars and E85 cars don't get the same gas mileage.

Another item I can think of, is the timing, could the timing chain be showing some wear and thus timing is a little off at higher RPMS, sure your timing mark is at zero and the computer is sending spark at correct time in theory, but a worn chain might not be opening and closing valves just right, this will carry right on thru to the distributer cap. New cars have cam sensors and crank sensors so the computer knows exactly where they are at. Your chain is not shot just getting worn.

The plugs look good, I think your compression is good and over all I think you have a healthy engine, but maybe somethings are starting to show their age, much like us. I was a lot stronger and faster in my 20's, I can still run but not as fast or hard.

[fjm719]

Is there a chance the gas in your area now has more ethanol in it?

I can't speak for the former owner, but all fill-ups I've performed have been with 87 octane gasoline. The stations have been across 10 different states, so it's hard to make specific geographic conclusions. However, I'm reasonably sure I've seen statements like "may contain up to 10% ethanol" at every pump I've used during the period graphed in my prior post. I note that the 1989 User's Manual says that up to 10% ethanol is acceptable. I'm unsure of the ethanol blend history earlier in the vehicle's life, but in 1989 GM was at least contemplating the blend we seem to see today. I note the User's Manual also cautions against octane ratings less than 87. Part of my recent travels were through Wyoming where "regular" seems to universally be 85 octane. I used the 87 octane "mid-grade" while in Wyoming.

Another item I can think of, is the timing, could the timing chain be showing some wear

Any thoughts on how to quantitatively or qualitatively check for timing chain slop/wear? It's a G-body van, so nothing up front is easy to reach. Maybe checking for rotational lash using the distributor (easily accessible through removal of the doghouse in the cab) as a proxy for the cam? I'm open to ideas.

[fjm719]

Dave,

Am I right that "wide band" O2 sensors and "air fuel ratio meters" are the same devices? If so, would a conversion to something like a Dynamic EFI be satisfied with retrofitting a wide-band O2 sensor in the same position currently used by the vehicle's conventional O2 (100-900mV) sensor. The stock O2 sensor is near the exit of the left exhaust manifold, well before the crossover that joins with the exhaust from the right side of the engine.

Also, I've looked through the four images you shared. Without a little more explanation I'm not sure I have the knowledge or experience to understand your tables. I'm guessing the three text strings in the top left of the table are axis labels, table titles, or descriptions of what's being tabulated in the field...but I'm not sure. Also, are there assumptions regarding the units of measure being used for the axes or the cell values.

[fjm719]

MO LS Noobie,
Thank you very much for your response.

Fuel Pressure:
My test did include WOT, but it was while sitting with the transmission in Park. I see your point that I should have checked a higher-flow condition. It was a bit a hassle to fit in the pressure measurement fitting (ignition components needed to be gotten out of the way and hard lines needed to be unclamped from the block) in behind the throttle body. There is a place further back, near the tank, where I could tee into a soft line, but my gauge lead is only ~3 feet long and wouldn't really reach to a accessible spot while underway. So this re-check may wait a few weeks until I have another convenient opportunity to break into the line at the throttle body.

Timing:
Is your recommendation of 5 DBTDC intended for the condition when the timing connector is unplugged? My understanding is that the timing is varied widely, based on tuning/conditions, once the connector is plugged back together. Also, am I right that the pinging would show up as a non-zero value from the knock sensor? If so, is there a non-zero threshold or frequency at which the pinging becomes a concern?

Exhaust Restrictions:
This was checked at idle and at 2000 rpm per the 1989 GMC Emissions manual. After seeing nothing over 1psi, I did briefly rev to high-throttle positions and might have grazed 1.25 psi, but I can't truly say I hit WOT. I went back and see that I misreported the gauge range (it actually had a 0-10psi range). However, I stand by the assessment that 1psi was about the highest I observed when revving up to near redline RPMs. I certainly couldn't get it anywhere close to 2 psi.

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Speedometer Calibration:
Can anyone state, specifically, how the VSS data is actually used by the 1228747 ECM. Is it simply to place operations within appropriate rows of tables? Or is there some other kind of math being driven by the VSS signal?

Aerodynamics:
Is there something that would/could be set up differently in the programming/bin/calibration if one knew the aerodynamic specifics of the vehicle? Of does the tuning simply aim to cover the full range of loads that might ever be placed on the engine.

Grounds:
I've checked a few, but not all, to date. I've added this to my to-do list. These are the three I'm aware of, currently. Should I expect others?

-Near battery:
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-Left Rear of Engine:
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-Just in front of Thermostat Housing (apologies for blurred/obstructed picture):
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O2 sensor:
The vehicle's very detailed service records do not indicate any O2 sensor replacements in the vehicle's 114,000-mile life. I have a new one, ready to install, but I had been hoping to gather a couple TunerPro RT log files and share with you all before swapping out the existing unit. My research to date says that most O2 sensors seem to fail high or fail low--which I don't think I'm seeing. However, I've been unable to determine whether they ever "drift" with age. Specifically, is there any realistic chance that O2 sensor "drift" could cause the 500mV position/threshold to correspond to a different O2 concentration than it did when new?

[MO LS Noobie]

You set your base timing with the connector disconnected. Then when you connect it the computer will adjust it for various loads and RPMs. My suggestion is to increase the base timing slightly and you quite often get a substantial increase in horsepower and therefore mileage.
You're exhaust back pressure it seems to be okay.
The oxygen sensors will drift, causing excessively rich or lean conditions.
Regarding the pinging condition, just observe the knock retard parameter. Very slight amounts especially on initial acceleration are acceptable.

[MO LS Noobie]

I am unaware of specific aerodynamic tuning, but has seen good results by rounding edges, modifying airflow underneath the vehicle, and helping the airflow fold back together behind the vehicle

[MO LS Noobie]

I mostly have experience with the OBD2 vehicles, there are several other here that have more knowledge on tuning the OBD1 units

[dave w]

Dave,

Am I right that "wide band" O2 sensors and "air fuel ratio meters" are the same devices? If so, would a conversion to something like a Dynamic EFI be satisfied with retrofitting a wide-band O2 sensor in the same position currently used by the vehicle's conventional O2 (100-900mV) sensor. The stock O2 sensor is near the exit of the left exhaust manifold, well before the crossover that joins with the exhaust from the right side of the engine.

Also, I've looked through the four images you shared. Without a little more explanation I'm not sure I have the knowledge or experience to understand your tables. I'm guessing the three text strings in the top left of the table are axis labels, table titles, or descriptions of what's being tabulated in the field...but I'm not sure. Also, are there assumptions regarding the units of measure being used for the axes or the cell values.

AFR Meters are typically a system of parts, the Display and Sensor. Often AFR Meters will use sensors with 0 volt to 5 volt range. Factory O2 sensors are typically 0 volt to 1 volt range. The "nickname" Wide Band came about because the AFR Meter typically uses a sensor with 0 volt to 5 volt range.

AFR Meters are "Stand Alone" measurement tools. Typically, a new Oxygen Sensor bung is welded into the exhaust pipe so an AFR Meter Sensor can be installed. Tuning with an AFR Meter requires two sensors in the exhaust, the factory O2 sensor and the AFR Meter Sensor.

A couple of the tables I posted are matched to the Volumetric Efficiency (VE) Table programmed into the chip. GM uses Kilopascals (Kpa) as the unit of measure for engine vacuum. Typically, a numerically low Kpa happens when an engine is under a light engine load and a numerically high Kpa when an engine is under heavy load. For example, going down a 6 mile long 6% grade at 70 MPH the engine load will be in the 30 ~ 50 KPa range. For example, going up a 6 mile long 6% grade at 70 MPH the engine load will be in 70 ~ 90 Kpa range. Typically, an engine under light load and low RPMs requires less fuel than an engine under heavy load at high RPM's. A look at the VE Table pictured below shows the "amount of fuel" programmed into the chip depending on RPMs vs. Kpas. Seems logical the VE table shows low numbers at light load / low RPM and high numbers at heavy load / high RPM.

The challenge with tuning is figuring out what value needs to be programmed into the VE Table for an optimal Air Fuel Ration (AFR) of 14.2:1 with 10% Ethanol gasoline. Typically, good tuning will yield Air Fuel Ratios averaging between 13.7:1 ~ 14.7:1 with 10% Ethanol gasoline.

VE Table.PNG