BLM Question
Thread Starter
Heel & Toe
Joined: Jun 2005
Posts: 18
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BLM Question
I have a 94 stock LT1. I have a ping at load 1500 - 2500 rpm. At idle my BLM is 122 both banks. When I give it a little throttle it will climb to 140 both banks and then I get spark retard 6* - 10* New o2 sensors can see them fluctuate. If I go WOT BLM goes to 160. I do notice the cells change with speed and load. It seems to be running lean (BLM 160) hence the ping. My sensors at idle C/L are:
IAC = 30 counts
MAP = 34KPa increases with throttle
MAF = 8Gm/Sec increases with throttle
TPS = .63 - 4.08(wot)
IAT seens to be incrementing
Vacuum at idle = 18hg and steady
Fuel pressure at idle is 42psi climbs to 45psi under load and 48psi (wot)
I did clean the maf with maf cleaner and changed the plugs wires and fuel filter then the pining started. The question is what is causing my blms to go to 160? Thanks for any help on this.
IAC = 30 counts
MAP = 34KPa increases with throttle
MAF = 8Gm/Sec increases with throttle
TPS = .63 - 4.08(wot)
IAT seens to be incrementing
Vacuum at idle = 18hg and steady
Fuel pressure at idle is 42psi climbs to 45psi under load and 48psi (wot)
I did clean the maf with maf cleaner and changed the plugs wires and fuel filter then the pining started. The question is what is causing my blms to go to 160? Thanks for any help on this.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Have you ohm'd the injectors cold and hot?
Running lean comes from 1 of 2 possible places..
the fuel system componants
or
the direction of the ECM or programming.
if you have not changed the program (tune) then it has to be from tired injectors.
As they age they get weak...lazy, slow to react. That means they spray less and late. Lean. The inj baskets get dirty and gummed up.
IF the ohms is within allowable 16 no less than 12, then a dose of a quality inj cleaner may offer some relief. If its sticky inj then add 1/2 bottle of marvel mystery oil to <1/2 tank of gas and run it ALL thru before refilling.
An over abundence of alcohol in your fuel may also be a reason...winter blend? Thats regional.
Did you use some gimmick platimum plus 44 plugs with a split tail, or the reccomended delco plugs?
Wires will cause ping as well. I've had brand new acell wires cause a severe knock. Ping is unlikely by definition. (pre-ignition)...unless the plugs you installed were a different heat range.
Running lean comes from 1 of 2 possible places..
the fuel system componants
or
the direction of the ECM or programming.
if you have not changed the program (tune) then it has to be from tired injectors.
As they age they get weak...lazy, slow to react. That means they spray less and late. Lean. The inj baskets get dirty and gummed up.
IF the ohms is within allowable 16 no less than 12, then a dose of a quality inj cleaner may offer some relief. If its sticky inj then add 1/2 bottle of marvel mystery oil to <1/2 tank of gas and run it ALL thru before refilling.
An over abundence of alcohol in your fuel may also be a reason...winter blend? Thats regional.
Did you use some gimmick platimum plus 44 plugs with a split tail, or the reccomended delco plugs?
Wires will cause ping as well. I've had brand new acell wires cause a severe knock. Ping is unlikely by definition. (pre-ignition)...unless the plugs you installed were a different heat range.
Last edited by leesvet; Oct 24, 2012 at 07:14 PM.
Thread Starter
Heel & Toe
Joined: Jun 2005
Posts: 18
Likes: 0
Thanks for the reply. I actually had the injectors cleaned/checked and the intake manifold gasket replaced by Abel Chevrolet in Rio Vista. They couldn't find the problem either. If I run through all the gears it run's great no issues car has lots of power. Highway mileage was about 26.5 and the temp was about 194.
Instructor
Joined: Dec 2011
Posts: 136
Likes: 3
From: pittsburgh pa.
food for thought: most gasoline has 10% ethanol, if your car sits with the same fuel for some time, any moisture will cause algae. try treating your fuel. also the ethanol is a stronger chemical than gasoline and the older cars weren't engineered for it.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
BLM is only a function of the ECM to be used as "reference" .....Block Learn Memory.
Its not the source of knocking or misfiring, but more like documentation of the problem. BLM allows the scanner to see what the engine has been doing as 8 separate cylinders..it helps to ID the problem cyl. IF all are doing something odd that sends you back to the control systems for all. Fuel or spark.
IMHO, if blms are unstable that to me says AFR is unstable. Back to fuel system or air leaks. Knowing a stealership worked on the car, I'd get it looked at by a qualified mechanic ! ! !
Its not the source of knocking or misfiring, but more like documentation of the problem. BLM allows the scanner to see what the engine has been doing as 8 separate cylinders..it helps to ID the problem cyl. IF all are doing something odd that sends you back to the control systems for all. Fuel or spark.
IMHO, if blms are unstable that to me says AFR is unstable. Back to fuel system or air leaks. Knowing a stealership worked on the car, I'd get it looked at by a qualified mechanic ! ! !
Thread Starter
Heel & Toe
Joined: Jun 2005
Posts: 18
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What is the best way to check the Air Fuel Ratio (AFR)? Could an opti be giving me the problems I am having? I have been running the car with techron fuel injection cleaner before I took it to Abel. Abel was supposedly the best corvette shop in northern California at least that is what all the write up said. I was shocked to find out they couldn't fix my car. I do have over 100,000 miles on the car I have replaced the water pump but left the opti alone. I am assuming that if the car was running right at partial throttle the trim cells would change and the BLMs would remain at 128 in a perfect world.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Start over again, did it ping before you worked on it or did you work on it because it pings? What gear does it ping in?
You have some odd readings as well.
if 34 kpa vac gage should read 19.5
if wot is 100 kpa ,not knowing what is normal for your area, then fuel pressure should change by 9.6 lbs more than idle of 34kpa. You are only changing by 6 psi
get the kpa with key on engine off that is what it should be at wot.
get fuel pressure by cycling the key with engine off or jumping the fuel pump relay, that is what it should be at wot. I have no idea what normal is on a 94 but the change in fuel pressure has to match the change in manifold pressure.
More info is needed but my money is on the fuel system.
You have some odd readings as well.
if 34 kpa vac gage should read 19.5
if wot is 100 kpa ,not knowing what is normal for your area, then fuel pressure should change by 9.6 lbs more than idle of 34kpa. You are only changing by 6 psi
get the kpa with key on engine off that is what it should be at wot.
get fuel pressure by cycling the key with engine off or jumping the fuel pump relay, that is what it should be at wot. I have no idea what normal is on a 94 but the change in fuel pressure has to match the change in manifold pressure.
More info is needed but my money is on the fuel system.
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Thread Starter
Heel & Toe
Joined: Jun 2005
Posts: 18
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The car was running with a miss before but not pinging. At that time I changed the plugs, wires, fuel filter, cleaned the maf. Car ran smooth but know I have this ping. Never had it before. I did disconnect the battery before working on the car just to be on the safe side. I wouldn't think that could mess up my tune could it? No codes have been stored. I will check the MAP kpa tomorrow and find out what it is doing with the engine off. If 34kpa = 19.5 in hg then my vacuum gauge was reading correctly. I am 200 ft above sea level. BTW when I took the car to an elevation of 4500 ft, all the symtoms went away no ping. This ping is under heavy load too 1500 - 2500 rpm any gear.
Thread Starter
Heel & Toe
Joined: Jun 2005
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It is a real audible ping. My datalog form datamaster is showing the 140 - 160 blm and timing is being pulled just off idle. My blm's increase just off idle too. You can see the knock counts go up as it starts to ping. It seems like there might be something with the MAF it starts off at 8 gm/sec then climbs to 175 gm/sec at 5000 rpm and WOT. Any other way to check the MAF?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
160 means the ECM is adding as much fuel as possible to compensate for a lean condition. The ECM limits the BLMs to the range 108 to 160, so you're maxing out on the lean end.
Is your O2 sensor OK?
Do you have a ruptured fuel pressure regulator diaphragm?
[EDIT] I was wrong on the BLM 160 = rich (as pointed out later in this thread). I was thinking the injector pulse width was proportional to the BLM. Sorry for the bad information. [/EDIT]
Last edited by Cliff Harris; Feb 2, 2013 at 02:34 AM. Reason: Corrected bad information.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
I am 200 ft above sea level. BTW when I took the car to an elevation of 4500 ft, all the symtoms went away no ping.
Last edited by 65Z01; Oct 26, 2012 at 06:02 AM.
Thread Starter
Heel & Toe
Joined: Jun 2005
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I was in closed loop. Up to that point the ECM is trying to add fuel to an already lean condition. That is why it is stuck at 160 (WOT). Even just off idle the ECM is trying to add fuel and pulling timing. I had replaced the 02 sensors that is the first thing I thought of since they already have over 100,000 miles on them. Unfortunately I was unable to datalog in the higher elevation. I just noticed that the pining had stopped under heavy load.
Pro
Joined: Aug 2010
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From: Hamilton Ontario
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
I was in closed loop. Up to that point the ECM is trying to add fuel to an already lean condition. That is why it is stuck at 160 (WOT). Even just off idle the ECM is trying to add fuel and pulling timing. I had replaced the 02 sensors that is the first thing I thought of since they already have over 100,000 miles on them. Unfortunately I was unable to datalog in the higher elevation. I just noticed that the pining had stopped under heavy load.
If the blm is 160 and the car is pinging it is lean.
If the fuel pressure is correct at those times it is not the pump lines or filter.
If it was ignition it whould not change the BLM unless a misfire then the O2 would read lean and O2 would try to fix it but it should not ping if it has trouble firing the plugs and would look and smell rich with all the extra fuel.
If it did not ping before you cleaned the MAF it is probably not the injectors.
The only thing changed is the work on the MAF I would have to think it is the MAF as the only thing that could make it lean that has been touched since it did not ping. If it under reports the airflow then the tables will not provide enough fuel and the O2 will attempt to fix it but if maxed out at a BLM of 160 it can not fix it.
Safety Car
Joined: Sep 2001
Posts: 4,134
Likes: 531
From: Glenbeulah Wi
It is a real audible ping. My datalog form datamaster is showing the 140 - 160 blm and timing is being pulled just off idle. My blm's increase just off idle too. You can see the knock counts go up as it starts to ping. It seems like there might be something with the MAF it starts off at 8 gm/sec then climbs to 175 gm/sec at 5000 rpm and WOT. Any other way to check the MAF?
Thread Starter
Heel & Toe
Joined: Jun 2005
Posts: 18
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Ok this is were I'm at. I ran the car today untill it was in closed loop. I then disconnected the MAF and took it out. Car ran ok with no audible ping while under heavy load. I decided to log this event. Datamaster said that I was still in closed loop I though that it would go into some limp mode and open loop. The blms still seamed to be on the high side (lean) Timing was still being pulled not sure why. I reconnected the MAF and did another log. Not much had changed between the two logs. I did check the entire intake for cracks and leaks non were found. I did read an article with an LT1 with similar symptoms, he replaced his OPTI and solved his problems. Could the OPTI have noise on one of the resolution signals causing the high BLMs and pulling my timing.