Car stumbling under accelaration (data log included)
05-20-2018, 12:57 PM
#1
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Car stumbling under accelaration(data log included). Thought it was fixed, it was not
Hi guys,
Last year just before I stored my car for a winter it developed a bad stumble under light acceleration all of the sudden while driving, the car almost wanted to die and there was popping coming from exhaust. There was no codes or engine light.
I took the car out this year and its not as bad as mentioned above, there is no exhaust popping or engine wanting to die but the stumble its there. Its bad under light accelation, at WOT it is ok until it reaches 5000 rmp then it stumbles again.
The car is 93 z28 with 95K miles, I am pretty sure the opti is original, I bought it in 2000 with 60K and I never touched it.
The has had a problem with long cranking while its warm ever since I bought it. I replaced few parts over the years, injector, ICM and coolant temp sensor, nothing worked. I was finally able find out that while engine is crankng it had no spark or injector pulse, my buddy a mechanic who was doing the testing is sure its the opti. It would start eventually after 5-6 seconds of cranking, so I just left it and lived with it since everything else was OK.
Now I got this new problem. I don't know if the opti is finally failing or its something else. Another problem I had when I bought the car was a it had a bad stumble only at WOT starting in third gear around 4000 rpm, first and second gears were fine. I changed spark plugs and wires and it was fixed.
I did the scan today to collect some data using Scan9495 and now I am wondering if its the spark plugs again. Last time they were changed was over 10 years ago, but they have like 15k miles on it, I don't know exactly what king of spark plugs shop used and the stumble is worse now then when I first bought the car.
I didn't check the fuel pressure yet, my fuel pressure gauge just stopped working for some reason, I will have to get new one and let you guys know what the pressure is.
First data log I collected was start up and idle
Second is slow accelatarion in 4th,5th and 6th gear with a stumble
Third is WOT 1st to 3rd with stumble starting near 5000 rpm.
Any input would be much appreciated. Thanks guys
Update down below.
Last year just before I stored my car for a winter it developed a bad stumble under light acceleration all of the sudden while driving, the car almost wanted to die and there was popping coming from exhaust. There was no codes or engine light.
I took the car out this year and its not as bad as mentioned above, there is no exhaust popping or engine wanting to die but the stumble its there. Its bad under light accelation, at WOT it is ok until it reaches 5000 rmp then it stumbles again.
The car is 93 z28 with 95K miles, I am pretty sure the opti is original, I bought it in 2000 with 60K and I never touched it.
The has had a problem with long cranking while its warm ever since I bought it. I replaced few parts over the years, injector, ICM and coolant temp sensor, nothing worked. I was finally able find out that while engine is crankng it had no spark or injector pulse, my buddy a mechanic who was doing the testing is sure its the opti. It would start eventually after 5-6 seconds of cranking, so I just left it and lived with it since everything else was OK.
Now I got this new problem. I don't know if the opti is finally failing or its something else. Another problem I had when I bought the car was a it had a bad stumble only at WOT starting in third gear around 4000 rpm, first and second gears were fine. I changed spark plugs and wires and it was fixed.
I did the scan today to collect some data using Scan9495 and now I am wondering if its the spark plugs again. Last time they were changed was over 10 years ago, but they have like 15k miles on it, I don't know exactly what king of spark plugs shop used and the stumble is worse now then when I first bought the car.
I didn't check the fuel pressure yet, my fuel pressure gauge just stopped working for some reason, I will have to get new one and let you guys know what the pressure is.
First data log I collected was start up and idle
Second is slow accelatarion in 4th,5th and 6th gear with a stumble
Third is WOT 1st to 3rd with stumble starting near 5000 rpm.
Any input would be much appreciated. Thanks guys
Update down below.
Last edited by alex-z28; 07-15-2018 at 03:48 AM.
05-26-2018, 11:53 AM
#4
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Re: Car stumbling under accelaration (data log included)
Does the engine have any modifications? Stock tune?
Preliminary observations:
Have you ever checked the fuel pressure? At high RPM is does seem like there is a bit of leaning out, based on the PE mode O2 sensor readings at 5,000+ RPM compared to 4,000 and 3,000 RPM. Recognize that the O2 sensors are not particularly accurate at the rich conditions encountered in PE mode (~WOT). But usable for trends.
Check TPS volts. Closed 0.59 Volts is OK, but at WOT you only reach 3.37 volts (94-96%) which is low. Should reach about 4 volts more than closed throttle. Check for a floor mat under the pedal, or something blocking the blade rotation.
Pressure loss on intake at WOT is over 4 kPa compared to barometer. Make sure air filter is clean.
Again, preliminary, there is a lot to look at in the three separate files.
Preliminary observations:
Have you ever checked the fuel pressure? At high RPM is does seem like there is a bit of leaning out, based on the PE mode O2 sensor readings at 5,000+ RPM compared to 4,000 and 3,000 RPM. Recognize that the O2 sensors are not particularly accurate at the rich conditions encountered in PE mode (~WOT). But usable for trends.
Check TPS volts. Closed 0.59 Volts is OK, but at WOT you only reach 3.37 volts (94-96%) which is low. Should reach about 4 volts more than closed throttle. Check for a floor mat under the pedal, or something blocking the blade rotation.
Pressure loss on intake at WOT is over 4 kPa compared to barometer. Make sure air filter is clean.
Again, preliminary, there is a lot to look at in the three separate files.
05-27-2018, 09:16 AM
#5
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Re: Car stumbling under accelaration (data log included)
Does the engine have any modifications? Stock tune?
Preliminary observations:Have you ever checked the fuel pressure? At high RPM is does seem like there is a bit of leaning out, based on the PE mode O2 sensor readings at 5,000+ RPM compared to 4,000 and 3,000 RPM. Recognize that the O2 sensors are not particularly accurate at the rich conditions encountered in PE mode (~WOT). But usable for trends.
Check TPS volts. Closed 0.59 Volts is OK, but at WOT you only reach 3.37 volts (94-96%) which is low. Should reach about 4 volts more than closed throttle. Check for a floor mat under the pedal, or something blocking the blade rotation.
Pressure loss on intake at WOT is over 4 kPa compared to barometer. Make sure air filter is clean.
Again, preliminary, there is a lot to look at in the three separate files.
Preliminary observations:Have you ever checked the fuel pressure? At high RPM is does seem like there is a bit of leaning out, based on the PE mode O2 sensor readings at 5,000+ RPM compared to 4,000 and 3,000 RPM. Recognize that the O2 sensors are not particularly accurate at the rich conditions encountered in PE mode (~WOT). But usable for trends.
Check TPS volts. Closed 0.59 Volts is OK, but at WOT you only reach 3.37 volts (94-96%) which is low. Should reach about 4 volts more than closed throttle. Check for a floor mat under the pedal, or something blocking the blade rotation.
Pressure loss on intake at WOT is over 4 kPa compared to barometer. Make sure air filter is clean.
Again, preliminary, there is a lot to look at in the three separate files.
So I went on to check the air filter. I have a aftermarket CAI so I can't see or get to the air filter from top of the car I have to remove the plastic cover underneath the car to get to it (well its easier then taking the cover and entire CAI from the top to get to the air filter). When I took the plastic cover under the car I found this inside.
I have no idea how this got inside but it did. The K&N filter was pretty dirty as well. After I cleaned it and put everything together the car is running good again. I did few slow acceleration and couple WOT pulls and its fine.
If it was not for your help and looking at the data log I would have never thought something could be clogging my air filter (I mean what are the odds something got sucked inside, clogging the air filter) and have such a big negative impact on the car, I would probably be changing opti and I would end up with same problem.
I did also check the fuel pressure and TPS sensor.
Fuel pressure while the fuel pump is primed it was around 39-39.5 psi, lower then what Haynes manual says it should be, between 41-47 psi. At idle it was at 36 psi, it got to 40 when applying throttle, and 45 psi with vacuum line off.
The voltage at the TPS sensor was 0.67 volts at idle on the blue wire and 4.089 volts at full open throttle, that was same reading I got when I put the gas pedal down or flipped the throttle by hand at TB. The Haynes book says that if its not between 4.5 and 5 volts replace the TPS sensor, do you agree as well Fred I should go ahead and replace it. I am looking a book now and I see that I didn't check to see if I was getting 5 volts on the gray wire.
So the only problem that I still have is long cranking time when engine is warm because its got no spark or injector pulse during that time, do you think that is the problem with the opti?
Last edited by alex-z28; 05-27-2018 at 09:37 AM.
05-27-2018, 04:36 PM
#6
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Re: Car stumbling under accelaration (data log included)
Test the fuel pump pressure with the engine under load. Tape the gauge to the windshield, take it out on the road, and see what the pressure is at 5,000 RPM, wide open throttle. Should not drop below 40 PSI. Dirty fuel filter might not show up at idle, but may show up under heavy engine load.
When the pump primed and shut off after a couple seconds, how fast did the pressure drop? Rapid loss of pressure can result in extended cranking to get the engine started. After the initial prime, the ECM will not allow the fuel system to turn on until it sees the low resolution pulse signal from the optical cam position sensor in the Opti. I'll go back to your cold start log and look to see if there is a delay in the fuel permit signal when it first cranks.
TPS sensor - key on, engine off, pull the harness connector off the sensor and check for 5.0 volts between the black wire and the gray wire. If you have 5.0 volts, physically examine the throttle blade to insure they are perfectly horizontal with the pedal on the floor. If they aren’t, check the throttle cable. If they are, pull the sensor off the throttle shaft and look for damage to the rectangular hole in the sensor that slips over the throttle shaft.
Free download of the 1993 factory service manual, courtesy of GaryDoug. Better than Haynes.
https://www.mediafire.com/?40mfgeoe4ctti
When the pump primed and shut off after a couple seconds, how fast did the pressure drop? Rapid loss of pressure can result in extended cranking to get the engine started. After the initial prime, the ECM will not allow the fuel system to turn on until it sees the low resolution pulse signal from the optical cam position sensor in the Opti. I'll go back to your cold start log and look to see if there is a delay in the fuel permit signal when it first cranks.
TPS sensor - key on, engine off, pull the harness connector off the sensor and check for 5.0 volts between the black wire and the gray wire. If you have 5.0 volts, physically examine the throttle blade to insure they are perfectly horizontal with the pedal on the floor. If they aren’t, check the throttle cable. If they are, pull the sensor off the throttle shaft and look for damage to the rectangular hole in the sensor that slips over the throttle shaft.
Free download of the 1993 factory service manual, courtesy of GaryDoug. Better than Haynes.
https://www.mediafire.com/?40mfgeoe4ctti
06-03-2018, 12:56 AM
#7
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Join Date: Jun 2002
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Posts: 217
Re: Car stumbling under accelaration (data log included)
Test the fuel pump pressure with the engine under load. Tape the gauge to the windshield, take it out on the road, and see what the pressure is at 5,000 RPM, wide open throttle. Should not drop below 40 PSI. Dirty fuel filter might not show up at idle, but may show up under heavy engine load.
When the pump primed and shut off after a couple seconds, how fast did the pressure drop? Rapid loss of pressure can result in extended cranking to get the engine started. After the initial prime, the ECM will not allow the fuel system to turn on until it sees the low resolution pulse signal from the optical cam position sensor in the Opti. I'll go back to your cold start log and look to see if there is a delay in the fuel permit signal when it first cranks.
TPS sensor - key on, engine off, pull the harness connector off the sensor and check for 5.0 volts between the black wire and the gray wire. If you have 5.0 volts, physically examine the throttle blade to insure they are perfectly horizontal with the pedal on the floor. If they aren’t, check the throttle cable. If they are, pull the sensor off the throttle shaft and look for damage to the rectangular hole in the sensor that slips over the throttle shaft.
Free download of the 1993 factory service manual, courtesy of GaryDoug. Better than Haynes.
https://www.mediafire.com/?40mfgeoe4ctti
When the pump primed and shut off after a couple seconds, how fast did the pressure drop? Rapid loss of pressure can result in extended cranking to get the engine started. After the initial prime, the ECM will not allow the fuel system to turn on until it sees the low resolution pulse signal from the optical cam position sensor in the Opti. I'll go back to your cold start log and look to see if there is a delay in the fuel permit signal when it first cranks.
TPS sensor - key on, engine off, pull the harness connector off the sensor and check for 5.0 volts between the black wire and the gray wire. If you have 5.0 volts, physically examine the throttle blade to insure they are perfectly horizontal with the pedal on the floor. If they aren’t, check the throttle cable. If they are, pull the sensor off the throttle shaft and look for damage to the rectangular hole in the sensor that slips over the throttle shaft.
Free download of the 1993 factory service manual, courtesy of GaryDoug. Better than Haynes.
https://www.mediafire.com/?40mfgeoe4ctti
I changed fuel filter, now the fuel pressure is higher when fuel pump primes. Took the car out with fuel pressure gauge hooked up. The pressure never dropped under 40 psi and under WOT it was constant at 48 PSI.
I checked for fuel pressure drop after fuel pump primes and it was dropping 1 psi/min.
I checked volts between gray and black TPS wires and I was getting 5.07 volts, I didn't have small enough tools to get in and take TPS out and inspect it. I looked at the TB blades to see it they were horizontal with gas pedal floored and they were.
And lastly I made a log of long cranking while engine is warm to see if there is a delay of low resolution pulse signal from the optical cam position sensor in the Opti, The log in the my first post was when engine was cold, so it started faster. This last log the engine was warm and cranked longer but sometimes it takes even longer to start.
06-03-2018, 10:19 PM
#8
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Re: Car stumbling under accelaration (data log included)
while this may not be your problem on prolonged cranking it is simple to check.
After you shut off motor pull the vacuum elbow off the FPR. If there is any sign of fuel in it your FPR is bad. This can cause prolonged cranking.
After you shut off motor pull the vacuum elbow off the FPR. If there is any sign of fuel in it your FPR is bad. This can cause prolonged cranking.
07-15-2018, 03:41 AM
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Re: Car stumbling under accelaration (data log included)
So I thought I had this issue fixed when I found out that plastic bag got to my air cleaner. The car ran fine after that until today. It did same thing as before, acceleration and stumble gets worse the higher gear I go in. In 5th and 6th gear its the worse by far. In 6th gear it won't accelerate even at WOT. Went golfing today and it was acting up again, on the way back home and drive again later on was OK.
Not sure where to go from here, do I keep driving until the car completely dies on me or change the opti, my buddy thinks that the problem since I also have that long cranking issue. I am planning on driving with my fuel pressure gauge hooked up and see the fuel pressure when the car is acting up to eliminate the fuel pump.
Not sure where to go from here, do I keep driving until the car completely dies on me or change the opti, my buddy thinks that the problem since I also have that long cranking issue. I am planning on driving with my fuel pressure gauge hooked up and see the fuel pressure when the car is acting up to eliminate the fuel pump.
Last edited by alex-z28; 07-15-2018 at 03:46 AM.
09-06-2018, 03:33 PM
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Re: Car stumbling under accelaration (data log included)
UPDATE Sept 6
So I had a bad stumble happened to me again after 15 min of driving 3 weeks ago while I was trying to accelerate. I had fuel pressure gauge hooked up and the pressure was steady while that was happening. I let the car cool down little bit and was able to make it home OK with out further issues. So I ended up replacing opti spark two weeks ago. I replaced it with brand new Ac Delco unit it had a new Mitsubishi sensor in it. Well it looks like it didn't do much good as I still have problem with the car.
The car still has long cranking issue and its lacking like 50 HP, like it did before, in my 2nd and 3rd data log in my first post. The car is idling fine (actually the engine is running smoother now with new opti then before). While just cruising the car is fine but the power is not all there when I try to accelerate. In higher gears its more noticeable and when I floor it the exhaust doesn't sound the same as well. In 6th gear it feels like trying to go up hill at 1000 rpm, and feels like there is a faint stumble as well. I should mention that 3 times when the stumble was the worst was after the car sat for 2 weeks or more and then the stumble would happen 15 mins into driving, other times it would run fine or it would run like its now, under powered.
Just like before I am not getting any codes, the only code I got it code 61, something to do with my a/c. The fuel pressure is at 41 while idling, 44-45 while driving and 50 under wot. I am looking at changing tps sensor since Fred noticed its low in the data log in my first post, voltage I am getting while the car is parked is 4 volts and it was 3.37 while driving under wot according to the data log.
Today I went and looked at my plugs and wires make sure they are OK. Wires look Ok, no burned marks on them and they were changed to msd 8.5 mm over 10 years ago. I just pulled spark plug #1 and # 3 first (since they were the easiest to get to) and noticed that plug #1 was soaked in gas all the way down the threads as well, electrode was dry but everything else was wet and smelled of gas (got a pic of it), while # 3 was dry. I know Fred you mentioned above according to the data log it looked like the car was running little bit rich. I replaced injectors over 10 years ago in hopes they were leaking causing long cranking issue and it didn't help. I checked the hose to the FPR looking for fuel smell or gas and I didn't notice anything. Fuel filter was changed month ago and air filter was cleaned as well same time.
Not sure whats going on right now, i don't think issue is with opti because its doing same thing as my old one, but i will check make sure its sending signal, my buddy is a mechanic and i can get access to oscilloscope (i know i could just use voltmeter as well).
any help would be appreciated, thanks guys
So I had a bad stumble happened to me again after 15 min of driving 3 weeks ago while I was trying to accelerate. I had fuel pressure gauge hooked up and the pressure was steady while that was happening. I let the car cool down little bit and was able to make it home OK with out further issues. So I ended up replacing opti spark two weeks ago. I replaced it with brand new Ac Delco unit it had a new Mitsubishi sensor in it. Well it looks like it didn't do much good as I still have problem with the car.
The car still has long cranking issue and its lacking like 50 HP, like it did before, in my 2nd and 3rd data log in my first post. The car is idling fine (actually the engine is running smoother now with new opti then before). While just cruising the car is fine but the power is not all there when I try to accelerate. In higher gears its more noticeable and when I floor it the exhaust doesn't sound the same as well. In 6th gear it feels like trying to go up hill at 1000 rpm, and feels like there is a faint stumble as well. I should mention that 3 times when the stumble was the worst was after the car sat for 2 weeks or more and then the stumble would happen 15 mins into driving, other times it would run fine or it would run like its now, under powered.
Just like before I am not getting any codes, the only code I got it code 61, something to do with my a/c. The fuel pressure is at 41 while idling, 44-45 while driving and 50 under wot. I am looking at changing tps sensor since Fred noticed its low in the data log in my first post, voltage I am getting while the car is parked is 4 volts and it was 3.37 while driving under wot according to the data log.
Today I went and looked at my plugs and wires make sure they are OK. Wires look Ok, no burned marks on them and they were changed to msd 8.5 mm over 10 years ago. I just pulled spark plug #1 and # 3 first (since they were the easiest to get to) and noticed that plug #1 was soaked in gas all the way down the threads as well, electrode was dry but everything else was wet and smelled of gas (got a pic of it), while # 3 was dry. I know Fred you mentioned above according to the data log it looked like the car was running little bit rich. I replaced injectors over 10 years ago in hopes they were leaking causing long cranking issue and it didn't help. I checked the hose to the FPR looking for fuel smell or gas and I didn't notice anything. Fuel filter was changed month ago and air filter was cleaned as well same time.
Not sure whats going on right now, i don't think issue is with opti because its doing same thing as my old one, but i will check make sure its sending signal, my buddy is a mechanic and i can get access to oscilloscope (i know i could just use voltmeter as well).
any help would be appreciated, thanks guys
Last edited by alex-z28; 09-06-2018 at 03:42 PM.
09-07-2018, 09:08 AM
#11
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Re: Car stumbling under accelaration (data log included)
I'll take a look today if I can. Apparently I missed the log in post #7. I'll look at that too.
Are you actually trying to do heavy acceleration in 5th and 6th gears, at low (1,000) RPM? Those gears are not intended for that purpose, and placing so much strain on the engine results in high cylinder pressures. That will show up any existing weakness in the ignition system, resulting in misfires.
Are you actually trying to do heavy acceleration in 5th and 6th gears, at low (1,000) RPM? Those gears are not intended for that purpose, and placing so much strain on the engine results in high cylinder pressures. That will show up any existing weakness in the ignition system, resulting in misfires.
09-07-2018, 01:09 PM
#12
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Re: Car stumbling under accelaration (data log included)
I'll take a look today if I can. Apparently I missed the log in post #7. I'll look at that too.
Are you actually trying to do heavy acceleration in 5th and 6th gears, at low (1,000) RPM? Those gears are not intended for that purpose, and placing so much strain on the engine results in high cylinder pressures. That will show up any existing weakness in the ignition system, resulting in misfires.
Are you actually trying to do heavy acceleration in 5th and 6th gears, at low (1,000) RPM? Those gears are not intended for that purpose, and placing so much strain on the engine results in high cylinder pressures. That will show up any existing weakness in the ignition system, resulting in misfires.
No I am not doing heavy acceleration from 1000 rpm, it kinda feels like that when I do it though, when I try to do light acceleration in those gears (1500 rpm and higher) and it was not like that before. The car is missing power in all gears but its more noticeable in higher gears.
Last edited by alex-z28; 09-07-2018 at 01:15 PM.
09-07-2018, 02:18 PM
#13
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Re: Car stumbling under accelaration (data log included)
The log in post #7 indicates the system voltage drops as low as 8.0 volts at the first turn of the key, seemingly even before the starter starts cranking the engine. Then while cranking (about a 2.5 to 3.0 second period - doesn't seem that long) the voltage ranges from 9.2 to 10.4 volts. That could be extending the cranking time. Could affect the ECM and the injectors. Weak battery? Even with my MoTeC engine control system, I solved an extended cranking time by replacing a stock starter that was drawing excessive amps and pulling down the battery voltage.
Also shows the A/C clutch is engaged while the starter is cranking the engine. There is no "A/C Request", and the clutch disengages when the engine starts. A/C pressure builds from 81 PSI to 92 PSI. That would seem to add load to the engine. But it's not something I ever noticed, one way or the other, while reviewing data logs. Maybe it's normal to engage the clutch at low RPM during start to lube the compressor????
Both the low resolution and high resolution pulses show up as expected when cranking.
I'll spend more time on it when I get a chance.
Was there a "new" log attached to your post from yesterday, or is my mind playing tricks on me?
Also shows the A/C clutch is engaged while the starter is cranking the engine. There is no "A/C Request", and the clutch disengages when the engine starts. A/C pressure builds from 81 PSI to 92 PSI. That would seem to add load to the engine. But it's not something I ever noticed, one way or the other, while reviewing data logs. Maybe it's normal to engage the clutch at low RPM during start to lube the compressor????
Both the low resolution and high resolution pulses show up as expected when cranking.
I'll spend more time on it when I get a chance.
Was there a "new" log attached to your post from yesterday, or is my mind playing tricks on me?
09-08-2018, 02:42 PM
#14
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Re: Car stumbling under accelaration (data log included)
No, I didn't post any new logs since post #7. The battery is brand new got it beginning of the year, I went thru few batteries over the years, different brands as well nothing helped with long cranking issue. Maybe I have issue with my starter as well then. My buddy the mechanic says we can test to see how much amps starter is drawing, he thinks should not be more then 200 amps.
Last edited by alex-z28; 09-08-2018 at 05:38 PM.
09-09-2018, 07:51 PM
#15
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Re: Car stumbling under accelaration (data log included)
so i just replaced the tps sensor because i was not getting 4.5 volts or higher at wot and I am still not getting that voltage with the new one. I get 5 volts at the tps, 0.71 at closed throttle and 4.14 volts at wot. Throttle blades are horizontal. I will use the scanner to see what computer sees again at wot because the log shows it read even lower 3.37 volfs at wot, so why i am not getting the 4.5 volts?