high BLMs and red hot converter
08-13-2018, 08:53 PM
#1
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Posts: 5
high BLMs and red hot converter
I need some help/suggestions.
94 z28 automatic, 80k miles. Was told when we bought it that it had a cam. Cannot verify. Stock other than that, including exhaust.
Car was running rough, had a miss. Did the following:
New plugs
New wires
New opti spark
Still had issues.
The car had new charcoal canister, fuel pump and fuel filter last fall.
I bought a Snap On MT2500 scanner and the o2 sensor readings were going crazy on the right side. Upon further investigation, the last exhaust manifold bolt was broken off in the head.
I wound up tearing it down, removing head, drilling out bolt and putting it back together. I suspect I had an intake leak on the rear pass side as well based on the condition of the gasket material.
Now that it is back together, it runs better, but there is still lack of power and hesitation.
Both the right and left BLM readings are 160
TPS 0.54
MAP 98
IAC POS 160
Left BPW 8.3
Right BPW 8.4
So far, I know just enough about this thing to be dangerous.
I know BLM should be 128.
I think MAF is working from what I can tell from the scanner.
Fuel pressure is at spec
I cannot find a vacumn leak anywhere
after a very short test drive of 1-2 miles tonight with scanner hooked up, cat converter was red hot.
Can a cat only glow from burning raw fuel?
Could the cat have been ruined by exhaust leak at head before and its glowing due to the fact its already shot?
Suggestions on high BLMs?
Does anyone have acceptable range values for readings from MT2500?
Any suggestions are appreciated
Thanks
94 z28 automatic, 80k miles. Was told when we bought it that it had a cam. Cannot verify. Stock other than that, including exhaust.
Car was running rough, had a miss. Did the following:
New plugs
New wires
New opti spark
Still had issues.
The car had new charcoal canister, fuel pump and fuel filter last fall.
I bought a Snap On MT2500 scanner and the o2 sensor readings were going crazy on the right side. Upon further investigation, the last exhaust manifold bolt was broken off in the head.
I wound up tearing it down, removing head, drilling out bolt and putting it back together. I suspect I had an intake leak on the rear pass side as well based on the condition of the gasket material.
Now that it is back together, it runs better, but there is still lack of power and hesitation.
Both the right and left BLM readings are 160
TPS 0.54
MAP 98
IAC POS 160
Left BPW 8.3
Right BPW 8.4
So far, I know just enough about this thing to be dangerous.
I know BLM should be 128.
I think MAF is working from what I can tell from the scanner.
Fuel pressure is at spec
I cannot find a vacumn leak anywhere
after a very short test drive of 1-2 miles tonight with scanner hooked up, cat converter was red hot.
Can a cat only glow from burning raw fuel?
Could the cat have been ruined by exhaust leak at head before and its glowing due to the fact its already shot?
Suggestions on high BLMs?
Does anyone have acceptable range values for readings from MT2500?
Any suggestions are appreciated
Thanks
08-14-2018, 10:29 AM
#2
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,646
Re: high BLMs and red hot converter
Who tuned it for the cam? Any chance the injectors have been changed?
The spot data above obviously indicates there is a problem, but isn’t adequate to do any serious diagnostics. Was the data taken at idle? Was the PCM in long term fuel trim (LTFT = BLM) cell 16? If so, what are the LTFT's in the other 17 cells? What are the short term fuel trims (STFT)? The 160 LTFT means the PCM is adding 25% extra fuel, above what the standard calculation should be providing. If that is in response to a “false” lean condition, the plugs should be fouled and wet. Are they?
A large cam with a lot of overlap can allow air and raw fuel to enter the exhaust at low RPM, the O2 sensors “see” the air, report lean, and the PCM jacks up the LTFT’s, and pours in even more fuel. The fuel/air burns on the cat, the cat overheats and melts, restricting exhaust flow, reducing power.
The fact the MAF sensor is giving you readings doesn't mean the readings are correct. A pulse width of 8+ milli-seconds at idle (what is the idle RPM?) is 2X to 3X what it would normally be.
IAC counts at idle should be 20 to 40. 160 means the PCM is telling the IAC valve to open to it's max position. But there is no feedback as to the actual position.
MAP should only be 98 kPa with the engine not running, or at wide open throttle. At idle with a stock cam MAP should be about 35 kPa. With a larger cam, MAP at idle could be 50 kPa ot even higher with a radical cam.
The best thing to do is run a data log of the PCM under varying operating conditions. Scan9495 software (free download) was written specifically for the 93-95 LT1. The author is a member here, and always responds to software issues. I routinely review these data logs for people, and have published a 20+ page guide to interpreting LT1 scanner data.
https://www.camaroz28.com/forums/com...95-lt1-874306/
Or maybe your scanner can record a data log over an extended period of time. As long as you can post it in .csv or .xls format, I can review it for you.
The spot data above obviously indicates there is a problem, but isn’t adequate to do any serious diagnostics. Was the data taken at idle? Was the PCM in long term fuel trim (LTFT = BLM) cell 16? If so, what are the LTFT's in the other 17 cells? What are the short term fuel trims (STFT)? The 160 LTFT means the PCM is adding 25% extra fuel, above what the standard calculation should be providing. If that is in response to a “false” lean condition, the plugs should be fouled and wet. Are they?
A large cam with a lot of overlap can allow air and raw fuel to enter the exhaust at low RPM, the O2 sensors “see” the air, report lean, and the PCM jacks up the LTFT’s, and pours in even more fuel. The fuel/air burns on the cat, the cat overheats and melts, restricting exhaust flow, reducing power.
The fact the MAF sensor is giving you readings doesn't mean the readings are correct. A pulse width of 8+ milli-seconds at idle (what is the idle RPM?) is 2X to 3X what it would normally be.
IAC counts at idle should be 20 to 40. 160 means the PCM is telling the IAC valve to open to it's max position. But there is no feedback as to the actual position.
MAP should only be 98 kPa with the engine not running, or at wide open throttle. At idle with a stock cam MAP should be about 35 kPa. With a larger cam, MAP at idle could be 50 kPa ot even higher with a radical cam.
The best thing to do is run a data log of the PCM under varying operating conditions. Scan9495 software (free download) was written specifically for the 93-95 LT1. The author is a member here, and always responds to software issues. I routinely review these data logs for people, and have published a 20+ page guide to interpreting LT1 scanner data.
https://www.camaroz28.com/forums/com...95-lt1-874306/
Or maybe your scanner can record a data log over an extended period of time. As long as you can post it in .csv or .xls format, I can review it for you.
08-14-2018, 10:43 AM
#4
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Location: Hell was full so they sent me to NJ
Posts: 70,646
Re: high BLMs and red hot converter
PS: In closed loop O2 sensor reading are supposed to swing rapidly back and forth between lean (as low as 0.10- volts) and rich (as high as 0.90+ volts). If that's what you mean by “going crazy on the right side”, what was the left side O2 sensor doing? They both should be jumping up and down rapidly in closed loop.
08-16-2018, 10:01 AM
#5
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Join Date: Apr 2003
Location: Pgh, PA
Posts: 2,628
Re: high BLMs and red hot converter
Been a while since I posted on here. I went through all this with a cammed car as well. Mine is a 224/230 .600/.600 108 LSA. After numerous scans and talking with Injuneer, PCMforLess, etc. I finally just purchased TunerCATs, ProScan, FreeScan, etc.
Did new plugs, wires, tested injectors, opti, 2X checking for vacuum, coolant, or exhaust leaks. New AC Delco O2's. Played around trying to open the throttle blades a bit, clear, and rescan. Tried setting idle position higher (from 800-1000 RPM), and a plethora of other things.
Finally, I got a Wide Band, installed it at the Y, and tuned it myself. An Open Loop tune. Added a little timing (took all the surge out), and added or removed fuel until I could make WOT runs from basically idle to redline while my AFR stayed right at 13.0. Then I made a tune scalling the fuel up something like 2% and down 2% and made runs til I found where she pulled the best, no knock, and drove nice. It is frustrating that I had to go to an open loop tune for a bolt on & cam car but several seemed to think perhaps it was just too much overlap with such a tight LSA. I can't begin to try to guess how many hours I put into trying to get it to run right in closed loop. I literally tried every suggestion I was given.
What are the specs on your camshaft?
Did new plugs, wires, tested injectors, opti, 2X checking for vacuum, coolant, or exhaust leaks. New AC Delco O2's. Played around trying to open the throttle blades a bit, clear, and rescan. Tried setting idle position higher (from 800-1000 RPM), and a plethora of other things.
Finally, I got a Wide Band, installed it at the Y, and tuned it myself. An Open Loop tune. Added a little timing (took all the surge out), and added or removed fuel until I could make WOT runs from basically idle to redline while my AFR stayed right at 13.0. Then I made a tune scalling the fuel up something like 2% and down 2% and made runs til I found where she pulled the best, no knock, and drove nice. It is frustrating that I had to go to an open loop tune for a bolt on & cam car but several seemed to think perhaps it was just too much overlap with such a tight LSA. I can't begin to try to guess how many hours I put into trying to get it to run right in closed loop. I literally tried every suggestion I was given.
What are the specs on your camshaft?
09-03-2018, 06:49 PM
#6
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Thread Starter
Join Date: Aug 2018
Posts: 5
Re: high BLMs and red hot converter
I was finally able to get the car to connect to the Scan9495 software and save a couple of data files. The larger one is approximately 10 minutes of idling in the garage (reved it a few times)
The smaller one is a quick trip down the street. Cant go far or the converter glows.
Any help is appreciated
Thanks
Brian
The smaller one is a quick trip down the street. Cant go far or the converter glows.
Any help is appreciated
Thanks
Brian
09-04-2018, 11:57 AM
#8
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Location: Hell was full so they sent me to NJ
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Re: high BLMs and red hot converter
Only took a cursory look at the "idle" file to make sure it was OK.
Left O2 is screwed up. Hardly ever moves far enough from the PCM bias voltage of 0.450 volts. The PCM is looking for readings at least 0.100 volts either side of 0.450 volts as a sign the sensor is heated up and working properly.
Doesn't get hot enough to work accurately, and that means it doesn't go into closed loop at idle. But when you rev the engine it seems to heat up the left O2 sensor to the point where it works briefly. When it's not in closed loop, the PCM can't correct rich or lean conditions. The right O2 is indicating a very lean condition.
For the brief period it goes into closed loop after you revved it, the LTFT's go to 157 L/160 R, and the STFT's go to 137 L/180 R. That means the left bank is getting 31% more fuel than the PCM would normally supply, and the right bank is getting almost 76% more fuel than it would normally supply. If that's a false lean condition, it's pouring a lot of raw fuel into the exhaust. If that's a "true" lean condition, it's hard to see at first glance why it's only seriously lean on the right side.
That's just from a quick visual scan to make sure the file looks valid. I'll do a more in depth review.
Left O2 is screwed up. Hardly ever moves far enough from the PCM bias voltage of 0.450 volts. The PCM is looking for readings at least 0.100 volts either side of 0.450 volts as a sign the sensor is heated up and working properly.
Doesn't get hot enough to work accurately, and that means it doesn't go into closed loop at idle. But when you rev the engine it seems to heat up the left O2 sensor to the point where it works briefly. When it's not in closed loop, the PCM can't correct rich or lean conditions. The right O2 is indicating a very lean condition.
For the brief period it goes into closed loop after you revved it, the LTFT's go to 157 L/160 R, and the STFT's go to 137 L/180 R. That means the left bank is getting 31% more fuel than the PCM would normally supply, and the right bank is getting almost 76% more fuel than it would normally supply. If that's a false lean condition, it's pouring a lot of raw fuel into the exhaust. If that's a "true" lean condition, it's hard to see at first glance why it's only seriously lean on the right side.
That's just from a quick visual scan to make sure the file looks valid. I'll do a more in depth review.
Last edited by Injuneer; 09-05-2018 at 11:47 PM.
09-05-2018, 11:08 AM
#9
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,646
Re: high BLMs and red hot converter
Based on "idle" log:
From the data log, it's running extremely rough at idle. The IAC is open to 74 counts, struggling to keep the RPM on target (650 RPM). As long as it's in closed loop (only after you rev it and get some sort of response out of the left O2 sensor) the idle seems to smooth out. That's because the right bank O2 readings are back in control, unfortunately due to the right STFT's being jacked up to 180+.
Left O2 is not working correctly, possibly because the heater is not working.... just gets below 0.350 volts when you rev the engine, probably warming it up just enough. Have you ever replaced the O2 sensors? But after the throttle closes and it idles for a while, the sensor seems to cool down, it goes right back to open loop, and the engine starts running rough again. It has to be misfiring like crazy, or the cam is so big, and the tune is so poor it's pouring raw fuel in the exhaust.
The MAP readings are too high. It's either a huge cam, or a huge vacuum leak, or the valves are adjusted way too tight. The glowing cat is a combination of raw fuel and excess air, burning on the cat. The purpose of the cat is to promote oxidation.... = "burning". Intended to oxidize small amounts of unburned hydrocarbons and carbon monoxide. It glow with large amounts of air and fuel, because it is working, and the burning fuel is releasing a huge amount of heat.... it's doing exactly what it's supposed to do...... but there's just way too much air and fuel in the exhaust.
I really wonder if it was tuned for the cam at all. Spark advance at idle looks stock. Target idle RPM is stock.
Based on "drive":
Left O2 seems to be hot enough to work, so it does stay in closed loop most of the time. Left O2 still seems to have slow response. After the drive, seems to be idling a lot better.... IAC is lower, MAP is better, less variation in RPM. But while driving the LTFT's and STFT's are sky high. I don't think I've ever seen a cell before with a 200+ STFT. It is struggling to get enough fuel into the system. And it's in all cells - low RPM, high RPM, low load, high load. Whatever has it running short on fuel is affecting both sides, although it seems there is always a bit more extra fuel being added on the right side.
Fix the left O2 first. If the heater in the sensor was totally bad, or there was a wiring problem, there should be a code, and there isn't. The problem you are having is more like what we see on a 93 with a one-wire (unheated) O2 sensor, in a header that has moved the sensor too far from the engine.
Then start checking possible sources of the serious lean condition - check the valve adjustment. You indicate fuel pressure is OK. Might check the injector part # and verify it is at least a 24 #/HR injector.
From the data log, it's running extremely rough at idle. The IAC is open to 74 counts, struggling to keep the RPM on target (650 RPM). As long as it's in closed loop (only after you rev it and get some sort of response out of the left O2 sensor) the idle seems to smooth out. That's because the right bank O2 readings are back in control, unfortunately due to the right STFT's being jacked up to 180+.
Left O2 is not working correctly, possibly because the heater is not working.... just gets below 0.350 volts when you rev the engine, probably warming it up just enough. Have you ever replaced the O2 sensors? But after the throttle closes and it idles for a while, the sensor seems to cool down, it goes right back to open loop, and the engine starts running rough again. It has to be misfiring like crazy, or the cam is so big, and the tune is so poor it's pouring raw fuel in the exhaust.
The MAP readings are too high. It's either a huge cam, or a huge vacuum leak, or the valves are adjusted way too tight. The glowing cat is a combination of raw fuel and excess air, burning on the cat. The purpose of the cat is to promote oxidation.... = "burning". Intended to oxidize small amounts of unburned hydrocarbons and carbon monoxide. It glow with large amounts of air and fuel, because it is working, and the burning fuel is releasing a huge amount of heat.... it's doing exactly what it's supposed to do...... but there's just way too much air and fuel in the exhaust.
I really wonder if it was tuned for the cam at all. Spark advance at idle looks stock. Target idle RPM is stock.
Based on "drive":
Left O2 seems to be hot enough to work, so it does stay in closed loop most of the time. Left O2 still seems to have slow response. After the drive, seems to be idling a lot better.... IAC is lower, MAP is better, less variation in RPM. But while driving the LTFT's and STFT's are sky high. I don't think I've ever seen a cell before with a 200+ STFT. It is struggling to get enough fuel into the system. And it's in all cells - low RPM, high RPM, low load, high load. Whatever has it running short on fuel is affecting both sides, although it seems there is always a bit more extra fuel being added on the right side.
Fix the left O2 first. If the heater in the sensor was totally bad, or there was a wiring problem, there should be a code, and there isn't. The problem you are having is more like what we see on a 93 with a one-wire (unheated) O2 sensor, in a header that has moved the sensor too far from the engine.
Then start checking possible sources of the serious lean condition - check the valve adjustment. You indicate fuel pressure is OK. Might check the injector part # and verify it is at least a 24 #/HR injector.
09-14-2018, 07:36 PM
#10
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Posts: 5
Re: high BLMs and red hot converter
Fred,
Thanks for the help.
You are right, the car idles terrible.
Have owned the car for 4 years. Ran great for 3 years with just general maintenance.
Problems started last fall.
I did plugs, fuel pump and filter and new charcoal canister last fall. Ran pretty good after that.
This spring ran bad again.
Did plug wires and optispark.
Discovered it had a broken bolt on exhaust manifold on right side and I convinced myself that was the problem,pulled intake and head and drilled out bolt and fixed that.
When I removed the intake I also convinced myself that it likely had a vacumn leak since both front and rear were not sealed well and had oil between gasket material on intake and block surfaces.
Put the car back together with no change in the way it ran.
Checked and rechecked for vacumn leaks and found nothing.
Installed a new elbow between MAF and throttle body because it was showing age.
Checked ohms on injectors - range between 13.4 and 13.6.
This was all prior to the log files from Scan9495 that I posted before.
Since the last scan and your comments, I have done the following:
I put a new 02 sensor on the left side. Runs better, but still not good.
I adjusted the valves, zero lash + 1/4 turn down. ran a little better, but still not good.
I did a smoke test with a home made smoke machine. I had a very small vacumn leak at the connections to the purge solenoid. Fixed those and did not find any others.
I ran the Scan 9495 software tonight and have attached that log file. It is in garage idling approx 10 minutes. Reved it at 3 mins, 6 mins and near the end.
Re checked fuel pressure (41 psi) car has a brand new Delphi pump and new fuel filter.
I do not see a part number on the injectors. We have had the car for 4 years and it ran good with same injectors before.
Thanks
Brian
Thanks for the help.
You are right, the car idles terrible.
Have owned the car for 4 years. Ran great for 3 years with just general maintenance.
Problems started last fall.
I did plugs, fuel pump and filter and new charcoal canister last fall. Ran pretty good after that.
This spring ran bad again.
Did plug wires and optispark.
Discovered it had a broken bolt on exhaust manifold on right side and I convinced myself that was the problem,pulled intake and head and drilled out bolt and fixed that.
When I removed the intake I also convinced myself that it likely had a vacumn leak since both front and rear were not sealed well and had oil between gasket material on intake and block surfaces.
Put the car back together with no change in the way it ran.
Checked and rechecked for vacumn leaks and found nothing.
Installed a new elbow between MAF and throttle body because it was showing age.
Checked ohms on injectors - range between 13.4 and 13.6.
This was all prior to the log files from Scan9495 that I posted before.
Since the last scan and your comments, I have done the following:
I put a new 02 sensor on the left side. Runs better, but still not good.
I adjusted the valves, zero lash + 1/4 turn down. ran a little better, but still not good.
I did a smoke test with a home made smoke machine. I had a very small vacumn leak at the connections to the purge solenoid. Fixed those and did not find any others.
I ran the Scan 9495 software tonight and have attached that log file. It is in garage idling approx 10 minutes. Reved it at 3 mins, 6 mins and near the end.
Re checked fuel pressure (41 psi) car has a brand new Delphi pump and new fuel filter.
I do not see a part number on the injectors. We have had the car for 4 years and it ran good with same injectors before.
Thanks
Brian
09-15-2018, 04:39 PM
#12
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Location: Hell was full so they sent me to NJ
Posts: 70,646
Re: high BLMs and red hot converter
Replacing the left O2 sensor solved the issue of not going into closed loop. Now both left and right sides Cell 16 show 160 LTFT's and low 150's STFT's. A bit better, but still not OK.
The MAF readings are about 1.5X to 2.0X what I would expect them to be, so the injector pulse widths are very high as well. And the pulse widths reflect the fact that is it adding 50% extra fuel to keep it from going lean. MAP still seems too high, unless the cam has very high overlap. Where does all the air and fuel go?
How are you measuring zero lash.... spinning the push rod, or moving it up and down?
Have you seen Shoebox's recommendations:
4th Gen LT1 F-body Tech Articles
The MAF readings are about 1.5X to 2.0X what I would expect them to be, so the injector pulse widths are very high as well. And the pulse widths reflect the fact that is it adding 50% extra fuel to keep it from going lean. MAP still seems too high, unless the cam has very high overlap. Where does all the air and fuel go?
How are you measuring zero lash.... spinning the push rod, or moving it up and down?
Have you seen Shoebox's recommendations:
4th Gen LT1 F-body Tech Articles
09-17-2018, 05:41 AM
#13
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Join Date: Aug 2018
Posts: 5
Re: high BLMs and red hot converter
I have read Shoebox's writeup.
I am adjusting the valves with the car running and clips installed over the rockers to minimize throwing oil everywhere.
Back them off one at a time until they clatter, tighten till clatter stops + 1/4 turn down.
I am adjusting the valves with the car running and clips installed over the rockers to minimize throwing oil everywhere.
Back them off one at a time until they clatter, tighten till clatter stops + 1/4 turn down.
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