93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
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Joined: Dec 1969
Posts: 234
From: Honolulu, Hawaii
93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
My 93 Camaro Z28 A4, has been a garage queen since having kids. It sees maybe 50 miles a year if even that. So, previously i thought it was bad gas so i ran the old tank down and put in fresh gas and a bottle of sea foam via the Brake Booster + gas tank and replaced the fuel filter. The car would idle fine but anytime i got to about 2000rpm or so it would buck and shake like the engine was going to fall out. I managed to capture this data log jumping on the freeway today. The entire log starts from my driveway and 2 stops before entering the freeway and slowly crawling onto the on ramp under 2000rpm. The car would shake bad if i gave it more gas. I noticed the LTrims were maxed out at 160 which indicates a lean condition and it gave the max 25% fuel enrichment. However, im unsure what the cause is. Is it ICM, Opti, O2's, fuel injector clogged? Below is a sample of the start of the freeway run. I'll paste the entire CSV on dropbox.
==93 Camaro Z28 A4 - 2000rpm stumble and shaking==
==MSD 6AL - Crane Ign Coil + Swapped with Accel Ign Coil it was better but still studders...next up ICM?==
==Car has not been driven in rain just sat there so it went from working to not working. Fuel Pressuse is good at 43psi and vaccum test holds 30mg==
CSV of DataMaster Log
https://www.dropbox.com/s/wc7mfllmba...oShop.csv?dl=0
DataMaster UNI file (Playback in DA)
https://www.dropbox.com/s/vodb2ecvw5...oShop.uni?dl=0
==93 Camaro Z28 A4 - 2000rpm stumble and shaking==
==MSD 6AL - Crane Ign Coil + Swapped with Accel Ign Coil it was better but still studders...next up ICM?==
==Car has not been driven in rain just sat there so it went from working to not working. Fuel Pressuse is good at 43psi and vaccum test holds 30mg==
CSV of DataMaster Log
https://www.dropbox.com/s/wc7mfllmba...oShop.csv?dl=0
DataMaster UNI file (Playback in DA)
https://www.dropbox.com/s/vodb2ecvw5...oShop.uni?dl=0
Last edited by Wilson; May 31, 2023 at 12:43 AM.
Administrator
Joined: Nov 1998
Posts: 71,098
From: Hell was full so they sent me to NJ
Re: 93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
Does the fuel pressure hold under heavy throttle? Would think after years sitting with corrosive (10% ethanol in HI ?) fuel the injectors would need professional cleaning. Is “vacuum test holds 30mg” a test of the AFPR, and are units 30”Hg?
Have you examined the spark plugs and checked the plug wires for arcing? Is Opti original OEM?
Are you running stock 1-wire O2 sensors, or a heated 4-wire conversion? Extensions on the O2 harness?
Do you have head flows (link opened but no content), and cam specs? Estimated flywheel HP?
I'll try to open the data log file tomorrow…… long time since I've seen a DataMaster file. Any codes?
Have you examined the spark plugs and checked the plug wires for arcing? Is Opti original OEM?
Are you running stock 1-wire O2 sensors, or a heated 4-wire conversion? Extensions on the O2 harness?
Do you have head flows (link opened but no content), and cam specs? Estimated flywheel HP?
I'll try to open the data log file tomorrow…… long time since I've seen a DataMaster file. Any codes?
Thread Starter
Registered User
Joined: Dec 1969
Posts: 234
From: Honolulu, Hawaii
Re: 93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
Glad to see your still around and helping everyone. I'll post my comments in line. Thank you again for all these years of troubleshooting! 
Does the fuel pressure hold under heavy throttle? Would think after years sitting with corrosive (10% ethanol in HI ?) fuel the injectors would need professional cleaning. Is “vacuum test holds 30mg” a test of the AFPR, and are units 30”Hg?
**Fuel Pressure gauge shows it holding under throttle and doesnt drop
**Thought about pulling the injectors and sending the Ford SVO 24# off for cleaning but some friends said if it was injectors it would be happening all the time not just at 2000+rpm
**Vac test i pulled the evap solenoid hose off the passenger side intake (small hose) and hooked it up to a vac gauge. Held 30mg which seems to be within normals (non-vac leak)
Have you examined the spark plugs and checked the plug wires for arcing? Is Opti original OEM?
**Spark Plugs/Wires haven been in the car over 15yrs havent touched them. Then again i dont think i even drove 500 miles in the last 10yrs.
**Opti - is my second unit brand new GM from back in early 2000 when the crazy was with the merizer electric water pumps (Group Purchase).
Are you running stock 1-wire O2 sensors, or a heated 4-wire conversion? Extensions on the O2 harness?
**Stock 1wire O2 sensor. I do recall extending one side on the Y pipe when the SLP shorty headers went it. Was working all this time for 20yrs but always thought about converting them to heated 4 wires one day...
Do you have head flows (link opened but no content), and cam specs? Estimated flywheel HP?
**Heads were cleaned up by a buddy 20yrs ago with polished bowls and 3 angle valve jobs. Havent touched it since. I believe there are CC 1.6 roller rockers and springs installed.
I'll try to open the data log file tomorrow…… long time since I've seen a DataMaster file. Any codes?
**Had a fun time finding a laptop that still had a Serial Port and running Windows XP. I haven't trusted the Data Master on the DTC as its blinking random codes i think due to it thinking there is a data Disconnect (Red data Error on dashboard). I couldnt find the Autoxray stand alone unit and no Autozone carries the OBDI scanners. I feel like i got the rare unicorn LT1 with SD and OBD1. I'll have to try on a different laptop (Win10) with a usb serial and Scan9495 (As it says it supports 93). Any modern scanners that work on 93?
**Fuel Pressure gauge shows it holding under throttle and doesnt drop
**Thought about pulling the injectors and sending the Ford SVO 24# off for cleaning but some friends said if it was injectors it would be happening all the time not just at 2000+rpm
**Vac test i pulled the evap solenoid hose off the passenger side intake (small hose) and hooked it up to a vac gauge. Held 30mg which seems to be within normals (non-vac leak)
Have you examined the spark plugs and checked the plug wires for arcing? Is Opti original OEM?
**Spark Plugs/Wires haven been in the car over 15yrs havent touched them. Then again i dont think i even drove 500 miles in the last 10yrs.
**Opti - is my second unit brand new GM from back in early 2000 when the crazy was with the merizer electric water pumps (Group Purchase).
Are you running stock 1-wire O2 sensors, or a heated 4-wire conversion? Extensions on the O2 harness?
**Stock 1wire O2 sensor. I do recall extending one side on the Y pipe when the SLP shorty headers went it. Was working all this time for 20yrs but always thought about converting them to heated 4 wires one day...
Do you have head flows (link opened but no content), and cam specs? Estimated flywheel HP?
**Heads were cleaned up by a buddy 20yrs ago with polished bowls and 3 angle valve jobs. Havent touched it since. I believe there are CC 1.6 roller rockers and springs installed.
I'll try to open the data log file tomorrow…… long time since I've seen a DataMaster file. Any codes?
**Had a fun time finding a laptop that still had a Serial Port and running Windows XP. I haven't trusted the Data Master on the DTC as its blinking random codes i think due to it thinking there is a data Disconnect (Red data Error on dashboard). I couldnt find the Autoxray stand alone unit and no Autozone carries the OBDI scanners. I feel like i got the rare unicorn LT1 with SD and OBD1. I'll have to try on a different laptop (Win10) with a usb serial and Scan9495 (As it says it supports 93). Any modern scanners that work on 93?
Administrator
Joined: Nov 1998
Posts: 71,098
From: Hell was full so they sent me to NJ
Re: 93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
Working on the log. Some spurious interference on the data wire producing impossible numbers scattered throughout the log. Might account for the flashing red light. Makes it hard to review the data... example 5,900 RPM, 255Ms injector pulse width, 292-deg coolant, 255 IAC counts, etc. I like to look for max, min and average numbers, but the data errors make that impossible.
There's some much better (free) software available for producing this info. Scan9495 (works on 93 also) was written specifically for the OBD-1 LT1 by a member named GaryDoug. Has a more useful data. Runs on later versions of windows, pulls codes, clears codes, SRS and ABS on some models, two-way communication, just need a cable from ALDL. Cables:
https://www.camaroz28.com/forums/com...95-lt1-874306/
I have a guide to running the log, and a paper on understanding the data:
https://www.camaroz28.com/forums/com...-guide-886891/
I did stop reviewing the data logs a while back, see note in my scanning guide thread. Make an exception for a 23 year member! I'm retired now, but my time is seriously limited, trying to straighten out insurance claims for a tree damaging my leased daily driver, and someone steals it out of the body shop. Comcast/Xfinity internet is constantly cutting out and they can't seem to fix it. I'm scheduled for hip replacement surgery in a week, and have a large number of pre-surgical doctor visits and tests.... etc.
Still unsure of the vacuum test, and it's objective. Is the 93 setup the same as the 94 and later:
http://shbox.com/1/evap_sol.jpg
The EVAP solenoid does not connect to the 94+ manifold, only to the lower nipple on the throttle body. Were you trying to pull a vacuum on the solenoid to prove it was closed and not leaking air into the manifold?
There's some much better (free) software available for producing this info. Scan9495 (works on 93 also) was written specifically for the OBD-1 LT1 by a member named GaryDoug. Has a more useful data. Runs on later versions of windows, pulls codes, clears codes, SRS and ABS on some models, two-way communication, just need a cable from ALDL. Cables:
https://www.camaroz28.com/forums/com...95-lt1-874306/
I have a guide to running the log, and a paper on understanding the data:
https://www.camaroz28.com/forums/com...-guide-886891/
I did stop reviewing the data logs a while back, see note in my scanning guide thread. Make an exception for a 23 year member! I'm retired now, but my time is seriously limited, trying to straighten out insurance claims for a tree damaging my leased daily driver, and someone steals it out of the body shop. Comcast/Xfinity internet is constantly cutting out and they can't seem to fix it. I'm scheduled for hip replacement surgery in a week, and have a large number of pre-surgical doctor visits and tests.... etc.
Still unsure of the vacuum test, and it's objective. Is the 93 setup the same as the 94 and later:
http://shbox.com/1/evap_sol.jpg
The EVAP solenoid does not connect to the 94+ manifold, only to the lower nipple on the throttle body. Were you trying to pull a vacuum on the solenoid to prove it was closed and not leaking air into the manifold?
Administrator
Joined: Nov 1998
Posts: 71,098
From: Hell was full so they sent me to NJ
Re: 93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
Seems to be starving for fuel. Worst long term and short term fuel trims I have ever seen.
You're holding constant throttle position, RPM's are bouncing all over the place, and:
As you noted, long term fuel trims (LTFT) are maxed out at the programmed limit of 160. That means the LTFT's are adding 25% extra fuel.
160 / 126 = 1.25
Then look at the short term fuel trims (STFT) - they are maxing out at 254 or 255. That's the largest possible number for an 8-bit field. NEVER saw them go that high.
255 / 128 = 1.99
The LTFT and STFT are multipliers.
1.25 x 1.99 = 2.49
The fuel trims together are adding another 150% above the fuel it should take to run the engine. And it's still running poorly.
It's either starving for fuel, or (less likely) faulty (lean) O2 sensor readings are driving the fuel trims higher, and pouring in extra fuel the engine doesn't need.
The spark plug appearance should tell you which it is.
You're holding constant throttle position, RPM's are bouncing all over the place, and:
As you noted, long term fuel trims (LTFT) are maxed out at the programmed limit of 160. That means the LTFT's are adding 25% extra fuel.
160 / 126 = 1.25
Then look at the short term fuel trims (STFT) - they are maxing out at 254 or 255. That's the largest possible number for an 8-bit field. NEVER saw them go that high.
255 / 128 = 1.99
The LTFT and STFT are multipliers.
1.25 x 1.99 = 2.49
The fuel trims together are adding another 150% above the fuel it should take to run the engine. And it's still running poorly.
It's either starving for fuel, or (less likely) faulty (lean) O2 sensor readings are driving the fuel trims higher, and pouring in extra fuel the engine doesn't need.
The spark plug appearance should tell you which it is.
Thread Starter
Registered User
Joined: Dec 1969
Posts: 234
From: Honolulu, Hawaii
Re: 93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
Working on the log. Some spurious interference on the data wire producing impossible numbers scattered throughout the log. Might account for the flashing red light. Makes it hard to review the data... example 5,900 RPM, 255Ms injector pulse width, 292-deg coolant, 255 IAC counts, etc. I like to look for max, min and average numbers, but the data errors make that impossible.
There's some much better (free) software available for producing this info. Scan9495 (works on 93 also) was written specifically for the OBD-1 LT1 by a member named GaryDoug. Has a more useful data. Runs on later versions of windows, pulls codes, clears codes, SRS and ABS on some models, two-way communication, just need a cable from ALDL. Cables:
https://www.camaroz28.com/forums/com...95-lt1-874306/
I have a guide to running the log, and a paper on understanding the data:
https://www.camaroz28.com/forums/com...-guide-886891/
I did stop reviewing the data logs a while back, see note in my scanning guide thread. Make an exception for a 23 year member! I'm retired now, but my time is seriously limited, trying to straighten out insurance claims for a tree damaging my leased daily driver, and someone steals it out of the body shop. Comcast/Xfinity internet is constantly cutting out and they can't seem to fix it. I'm scheduled for hip replacement surgery in a week, and have a large number of pre-surgical doctor visits and tests.... etc.
Still unsure of the vacuum test, and it's objective. Is the 93 setup the same as the 94 and later:
http://shbox.com/1/evap_sol.jpg
The EVAP solenoid does not connect to the 94+ manifold, only to the lower nipple on the throttle body. Were you trying to pull a vacuum on the solenoid to prove it was closed and not leaking air into the manifold?
There's some much better (free) software available for producing this info. Scan9495 (works on 93 also) was written specifically for the OBD-1 LT1 by a member named GaryDoug. Has a more useful data. Runs on later versions of windows, pulls codes, clears codes, SRS and ABS on some models, two-way communication, just need a cable from ALDL. Cables:
https://www.camaroz28.com/forums/com...95-lt1-874306/
I have a guide to running the log, and a paper on understanding the data:
https://www.camaroz28.com/forums/com...-guide-886891/
I did stop reviewing the data logs a while back, see note in my scanning guide thread. Make an exception for a 23 year member! I'm retired now, but my time is seriously limited, trying to straighten out insurance claims for a tree damaging my leased daily driver, and someone steals it out of the body shop. Comcast/Xfinity internet is constantly cutting out and they can't seem to fix it. I'm scheduled for hip replacement surgery in a week, and have a large number of pre-surgical doctor visits and tests.... etc.
Still unsure of the vacuum test, and it's objective. Is the 93 setup the same as the 94 and later:
http://shbox.com/1/evap_sol.jpg
The EVAP solenoid does not connect to the 94+ manifold, only to the lower nipple on the throttle body. Were you trying to pull a vacuum on the solenoid to prove it was closed and not leaking air into the manifold?
I went back and looked at my older photos from the vacuum test and i actually pulled the lower nipped on the throttle body so that goes to the EVAP solendoid so that test is off. The value was not 30Hg like i recalled it was actually 19Hg.
I'll try and pull vac off the intake feeding the fule pressure regulator, that might be more accurate in testing for intake leak.
But thanks again for taking the time look over. Its been a hell of a journey these last 20+yrs. Went from having college life to family life and the Camaro has been a life long journey so far. Hope to get it running good again so the kids can enjoy it.
Thread Starter
Registered User
Joined: Dec 1969
Posts: 234
From: Honolulu, Hawaii
Re: 93 Camaro SD - Cant get past 2000rpm without violent bucking and shaking
Seems to be starving for fuel. Worst long term and short term fuel trims I have ever seen.
You're holding constant throttle position, RPM's are bouncing all over the place, and:
As you noted, long term fuel trims (LTFT) are maxed out at the programmed limit of 160. That means the LTFT's are adding 25% extra fuel.
160 / 126 = 1.25
Then look at the short term fuel trims (STFT) - they are maxing out at 254 or 255. That's the largest possible number for an 8-bit field. NEVER saw them go that high.
255 / 128 = 1.99
The LTFT and STFT are multipliers.
1.25 x 1.99 = 2.49
The fuel trims together are adding another 150% above the fuel it should take to run the engine. And it's still running poorly.
It's either starving for fuel, or (less likely) faulty (lean) O2 sensor readings are driving the fuel trims higher, and pouring in extra fuel the engine doesn't need.
The spark plug appearance should tell you which it is.
You're holding constant throttle position, RPM's are bouncing all over the place, and:
As you noted, long term fuel trims (LTFT) are maxed out at the programmed limit of 160. That means the LTFT's are adding 25% extra fuel.
160 / 126 = 1.25
Then look at the short term fuel trims (STFT) - they are maxing out at 254 or 255. That's the largest possible number for an 8-bit field. NEVER saw them go that high.
255 / 128 = 1.99
The LTFT and STFT are multipliers.
1.25 x 1.99 = 2.49
The fuel trims together are adding another 150% above the fuel it should take to run the engine. And it's still running poorly.
It's either starving for fuel, or (less likely) faulty (lean) O2 sensor readings are driving the fuel trims higher, and pouring in extra fuel the engine doesn't need.
The spark plug appearance should tell you which it is.
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