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Hi. I have been battling my 1988 Automatic Corvette for a while now. For the last few months, I have noticed a loss of power most of the time. Feels like im driving uphill even on a flat road. Acceleration takes forever even at WOT. I have replaced and worked on much of the fuel and ignition systems. My attention has turned to sensors that may be affecting my ratios so i bought a bluetooth aldl scanner from 1320 electronics and downloaded their app. After i got it all set up, i was able to get some readings including a couple of codes. I would appreciate if anyone could tell me what these specially mean and what i can do about the bad ones. Also i was wondering if i am able to change my idle speed using aldldroid or do i need something like tuner pro.
Last edited by Elijah Rodriguez; Feb 11, 2021 at 09:54 PM.
I have an AutoXran OBD 1 scanner and don't recognize the meaning of most of your codes.
What kind of fuel pressure and manifold vacuum is it reading at idle??
What is TPS voltage value before startup; looks like voltage is way too low during idle? Should be ~0.54Vdc before startup and ~0.7Vdc at normal idle.
Is power low even before full warmup?
Is the air cleaner clean?
Are spark plugs & wires in good order?
Off hand looks like the ECM isn't seeing throttle position properly. With engine off check it with a DVM.
Idle is high and uncontrolled at 1200 rpm with zero IAC counts. TPS voltage is low as already mentioned. BLM of 139 is a bit lean, but not a problem at this point.
Something is causing excessive airflow at idle as evidenced by the high rpm and zero IAC position, either a huge vacuum leak or too much throttle opening. Check that the throttle is fully closing and readjust tps voltage.
Note: I don't really trust your scan tool's definition file since some values have strange scaling such as the mass airflow signal (need to divide by 256), although the raw (8 bit unlimited airflow signal) looks about right at 12 gm/sec @ 1200 rpm.
Clear the codes to start fresh and see which ones come back again, then go out and try to reproduce the original complaint (at WOT) while recording and save the log.
Last edited by tequilaboy; Feb 12, 2021 at 02:31 PM.
Agree from the readout that the TPS is whacky. Its too low voltage. IAC counts are actually zero?
What does TPS voltage read with the engine off?
Does the green dot beside the Code 33 indicate that this code is set, with an SES light coming on? Ignore the Code 32, but 33 needs to be investigated.
Idle is high and uncontrolled at 1200 rpm with zero IAC counts. TPS voltage is low as already mentioned. BLM of 139 is a bit lean, but not a problem at this point.
Something is causing excessive airflow at idle as evidenced by the high rpm and zero IAC position, either a huge vacuum leak or too much throttle opening. Check that the throttle is fully closing and readjust tps voltage.
Note: I don't really trust your scan tool's definition file since some values have strange scaling such as the mass airflow signal (need to divide by 256), although the raw (8 bit unlimited airflow signal) looks about right at 12 gm/sec @ 1200 rpm.
Clear the codes to start fresh and see which ones come back again, then go out and try to reproduce the original complaint (at WOT) while recording and save the log.
A while back, I adjusted this little screw on the throttle body that holds the throttle valve open slightly. You can screw it in to let more air in at idle or any time your foot isn't on the gas. I now see how that can mess with the computer and close the iac to compensate. I adjusted the pin to where the throttle body is way less open at rest. Then i recorded it using the app. These are the results:
TPS voltage still too low at 0.25 volts. Cell 0 BLM is very lean (155 and climbing). Note: 160 is the maximum allowed BLM. Why so lean? Are you running small injectors, low fuel pressure or high ethanol content fuel?
I added a column to show the Mass Air Flow/256 to correct the scaling. I also deleted the 2nd row (units) to play better with Datazap. I would like to see a log during actual driving conditions to see more fuel trim behavior.
Also would be good to see the full scale (WOT) tps reading to determine if it is a bad sensor, or just maladjusted. If full scale tps is reading way to low ( < ~3 volts or 70% tps)), you may not enter PE mode under heavy throttle/WOT.
Would also be nice to see the AFR target to confirm PE entry, but your definition file (*.adx) is lacking (assuming your scan tool app ALDLdroid uses TunerPro style *.adx files).
Last edited by tequilaboy; Feb 13, 2021 at 01:49 PM.
TPS voltage still too low at 0.25 volts. Cell 0 BLM is very lean (155 and climbing). Note: 160 is the maximum allowed BLM. Why so lean? Are you running small injectors, low fuel pressure or high ethanol content fuel?
I added a column to show the Mass Air Flow/256 to correct the scaling. I also deleted the 2nd row (units) to play better with Datazap. I would like to see a log during actual driving conditions to see more fuel trim behavior.
Also would be good to see the full scale (WOT) tps reading to determine if it is a bad sensor, or just maladjusted. If full scale tps is reading way to low ( < ~3 volts or 70% tps)), you may not enter PE mode under heavy throttle/WOT.
Would also be nice to see the AFR target to confirm PE entry, but your definition file (*.adx) is lacking (assuming your scan tool app ALDLdroid uses TunerPro style *.adx files).
i am running some sort of aftermarket injectors, but i was told they are stock lb/hr which would mean 22lb/hr if i am correct. I have an adjustable fuel pressure regulator, but i have no idea if it is where it needs to be. I just know that my fuel pressure reads around 40 while operating at idle. I also run 93 octane gas.
i was able to get some readings while taking a small lap around my neighborhood since roads are icy. At one point i floored it for a few seconds because it was only a small strip of road. I hope that was long enough. I apologize, i am not familiar with the terms PE mode or AFR target. The app i am using is ALDL Scan and im not sure where to locate those values.
Agree from the readout that the TPS is whacky. Its too low voltage. IAC counts are actually zero?
What does TPS voltage read with the engine off?
Does the green dot beside the Code 33 indicate that this code is set, with an SES light coming on? Ignore the Code 32, but 33 needs to be investigated.
The tps voltage with the key in the on position went back and forth between 5 and 6
WOT looks better. TPS voltage still on the low side, but is high enough to enter PE based upon fueling and rich O2 readings. You should be able to adjust the sensor to increase the voltage.
It is knocking and pulling quite a bit of timing (7-8 degrees). This may be what you feel in the car.
MAF flow looks ok, but is a bit high and appears to be limited a bit by the Max Air Flow vs RPM table (example below).
WOT looks better. TPS voltage still on the low side, but is high enough to enter PE based upon fueling and rich O2 readings. You should be able to adjust the sensor to increase the voltage.
It is knocking and pulling quite a bit of timing (7-8 degrees). This may be what you feel in the car.
MAF flow looks ok, but is a bit high and appears to be limited a bit by the Max Air Flow vs RPM table (example below).
OP: How did you hook up the 1320? There's a procedure. If not correct, may be running with diagnostic mode on.
All: Idle screw (and speed) setup, there is a procedure in the FSM. From factory, the screw head is blocked, factory didn't want that changed.
NOTE: If you do unblock your idle screw, need to add a method to lock the screw in position once set. If left to itself, the screw will move. I used a small metric lock nut on mine, once I figured out it was set wrong in the first place!
I trust tequillaboy's analysis more than mine. When I see low airflow at high throttle angle, I suspect exhaust restrictions. Knock-retard from lean conditions (High BLM) is also an indication of charge-dilution by exhaust back pressure. The 88 has pre-cats. I had an 88 that had one pre-cat disintegrate and plug the main cat. It ran ok until large throttle openings, and still ran "ok" it just didn't "go" very well.
I like "datazap" presentations. I'll have to look into this tool now that Data Master (yes, I'm old) is no longer supported.
Mine is straight piped, but has stock headers with the air pump hoses disconnected, but not capped off. Exhaust doesn't leak out of the holes, but there is a vaccum suction.
OP: How did you hook up the 1320? There's a procedure. If not correct, may be running with diagnostic mode on.
All: Idle screw (and speed) setup, there is a procedure in the FSM. From factory, the screw head is blocked, factory didn't want that changed.
NOTE: If you do unblock your idle screw, need to add a method to lock the screw in position once set. If left to itself, the screw will move. I used a small metric lock nut on mine, once I figured out it was set wrong in the first place!
The creator of 1320 walked me through the steps to get the tool set up and which switches to flip on the tool for my specific car. After i readjusted my throttle body screw (which was causing too much air to enter the engine at idle) the iac was able to keep the computer's desired idle. My only questions now are: what can i do to get these readings to where they need to be and how can i change my computer's minimum idle speed to somewhere around 900rpm using the scan tool.
Next steps should be fairly obvious, but you can't increase the desired idle rpm without re-programming or tuning the ecm/memcal/eprom/bin file. This can't be done with a scan tool. You need a programmer and appropriate hardware and software if you wish to do it yourself, or find a capable tuner.
Adjust the tps in an attempt to reach 0.54 volts at idle. This is the standard setting. This won't solve your problems but will ensure that the ecm can differentiate between idle, part-throttle and WOT and help prevent false code setting.
Clear codes by disconnecting ecm power. See which codes come back over time after correcting tps voltage.
Check the timing (should be 6 degrees advanced with EST disconnected) and correct if necessary.
If knocking persists, try a more knock resistant (higher octane) fuel if available. May be false knock, consider ecm tuning to address if all else fails.
Collect more scan data under all conditions and look for fuel and knock trends.
Increase fueling to correct for the lean blm readings. This can be done by increasing fuel pressure (crude), or ecm tuning (preferred).
Get a more complete/correct *.adx file for use with your scan tool.
wash, rinse and repeat.
Last edited by tequilaboy; Feb 20, 2021 at 08:57 AM.
Seems to me, the coolant temp sensor for ecm is bad. Also, need to set TPS as mentioned to .54, then set and relearn IAC (probably remove and clean with throttle body cleaner since you are going to do a relearn. There is a specific IAC relearn procedure in the service manual. If you don't have a manual, now is the time to get one. After those procedures are done, clear codes and see which ones comes back. I am not addressing the O2 readings at this time but will need to be checked. There are a couple more things I see but don't want to speculate until the earlier is done.
Last edited by corvette95; Feb 20, 2021 at 09:55 AM.
Next steps should be fairly obvious, but you can't increase the desired idle rpm without re-programming or tuning the ecm/memcal/eprom/bin file. This can't be done with a scan tool. You need a programmer and appropriate hardware and software if you wish to do it yourself, or find a capable tuner.
Adjust the tps in an attempt to reach 0.54 volts at idle. This is the standard setting. This won't solve your problems but will ensure that the ecm can differentiate between idle, part-throttle and WOT and help prevent false code setting.
Clear codes by disconnecting ecm power. See which codes come back over time after correcting tps voltage.
Check the timing (should be 6 degrees advanced with EST disconnected) and correct if necessary.
If knocking persists, try a more knock resistant (higher octane) fuel if available. May be false knock, consider ecm tuning to address if all else fails.
Collect more scan data under all conditions and look for fuel and knock trends.
Increase fueling to correct for the lean blm readings. This can be done by increasing fuel pressure (crude), or ecm tuning (preferred).
Get a more complete/correct *.adx file for use with your scan tool.
wash, rinse and repeat.
I apologize for asking many obvious questions. Im 17 and im aspiring to learn, so i appreciate yours and everyone else help in this thread. Today i was able to adjust my tps to read .54 volts when the key is in the "on" position and i adjusted my fuel pressure regulator to 43 psi at idle instead of the 39 or 40 psi that it was previously. I disconnected the battery to reset the codes, then reconnected it, started the car up and checked for codes and none came back. took it around the block and it ran great. This is what i logged:
The creator of 1320 walked me through the steps to get the tool set up and which switches to flip on the tool for my specific car. After i readjusted my throttle body screw (which was causing too much air to enter the engine at idle) the iac was able to keep the computer's desired idle. My only questions now are: what can i do to get these readings to where they need to be
and how can i change my computer's minimum idle speed to somewhere around 900rpm using the scan tool.
Engine warmed to closed loop and operating temp. What is your IAC count? Everything but the motor off should be about 20 to 30 counts. I believe on a 90 you don't have adjustment for the TPS. If you have higher than 30 counts, turn the screw out to close it off, rev and see what happens. If it is under 20, turn the screw in to let more air in, rev and recheck.
You don't, You need to reprogram it. Why do you want to do that?
I am concerned about the spark advance increase between the first 2 yellow markers.
Edit: After a closer look into both the ABTS bin and your logs, the spark advance signal does appear to be relative to the reference pulse, so the actual advance (relative to tdc) will be advanced an additional 5.98 degrees above what is shown in your logs. Can be confusing if you can't see both signals at the same time.
The rapid spark advance increase is the code 43 forced knock test in-progress (which can lead to engine damage if the knock sensor really is malfunctioning, so be careful).
Note: This is normal behavior, but the code 43 forced knock test spark ramp-up (up to 24.96 degrees over time) can be alarming to see. Once it knocks, the extra advance ramps out quickly with no harm done, but it is still scary to see the magnitude of the advance while it is occurring. This is a risky and poorly designed feature intended to test the knock sensor.
Keep an eye on the spark advance and knock retard behavior.
Can you attach a copy of your *.adx file? I will check the signals for accuracy and scaling.
For reference, your bin file should be ABTS based on the prom id/scan id. I will take a look into my copy of ABTS to verify the spark advance behavior. Do you know if it has ever been tuned or if it is a virgin (factory) bin file?
Last edited by tequilaboy; Feb 24, 2021 at 12:50 PM.
I am concerned about the spark advance increase between the first 2 yellow markers.
Edit: After a closer look into both the ABTS bin and your logs, the spark advance signal does appear to be relative to the reference pulse, so the actual advance (relative to tdc) will be advanced an additional 5.98 degrees above what is shown in your logs. Can be confusing if you can't see both signals at the same time.
The rapid spark advance increase is the code 43 forced knock test in-progress (which can lead to engine damage if the knock sensor really is malfunctioning, so be careful).
Note: This is normal behavior, but the code 43 forced knock test spark ramp-up (up to 24.96 degrees over time) can be alarming to see. Once it knocks, the extra advance ramps out quickly with no harm done, but it is still scary to see the magnitude of the advance while it is occurring. This is a risky and poorly designed feature intended to test the knock sensor.
Keep an eye on the spark advance and knock retard behavior.
Can you attach a copy of your *.adx file? I will check the signals for accuracy and scaling.
For reference, your bin file should be ABTS based on the prom id/scan id. I will take a look into my copy of ABTS to verify the spark advance behavior. Do you know if it has ever been tuned or if it is a virgin (factory) bin file?
I believe my adx file is called A059-8192baud.adx i couldn't give you an answer before because I was using "aldl scan" (doesn't use adx) instead of "ALDLdroid". I was able to figure out the source of my engine codes. My maf sensor relay was bad. Once i replaced it, the codes went away. I suspect my maf sensor is also bad. I saw a forum on here that said that if the purple wire going to the maf sensor is getting 12 volts while the engine is running, the sensor is bad. On top of that, the new scan app shows my maf sensor readings were in the red. I am still having trouble with hard starting and i still get a loss of power (seems less restrictive than before i replaced the relay). My oil pressure readings are all over the place but i think it is just the sensor because once i turn the electronics on in the morning(engine off) it will read anywhere from 40-60 psi which is obviously false.
Please Help With ALDL Scan Codes
