the blur

A while ago, we were discussing stock TPI motors, with new injectors suddenly having a problem with high BLM's.

Did anyone ever figure this out ??
A stock TPI motor, needing new injectors because the factory injectors short out. Using FIC #22 or Accel #21, car runs great. Like new, but when scanning, the BLM's are very high.

My BLM's are 150+ in all cells, but with the new injectors, the car runs AMAZING. I know there are no vacumme leaks, nothing is wrong. But when I datalog, I see the BLM's are just almost maxed out.

Was there ever a solution ?

the blur

This is a closed thread discussing the issue.
http://forums.corvetteforum.com/c4-t...jectors-6.html

gerardvg

Year of the vette would be a great help

I know the 85 had 24lb injectors standard, and later ones slightly smaller. Fuel pressure can cause some of your issues, my 85 standard would only just make 30 psi and most would say 38 is what they get. I put a aftermarket fuel pressure regulator in to crank it to 40/45 psi cause she loves that .
Any more makes the idle way too rich, so check what fuel pressure you have and that the fuel filter is not blocking.

The ecm will try to adjust the air fuel ratio and use the oxygen sensor to measure it, it will roughly know what it is doing via the MAF airflow TPS sensor voltage and monitor the air fuel ratio via the oxygen sensor. So maybe check your oxygen sensor is not fouled up and the spark plugs/leads are good.

You may need to give her a tune and it will come good, but if your fuel pressure is down you may need to raise it slightly.

If you are not getting any codes and she performs as she should then don't worry too much about it till you get a factory service manual that has all the info you need to test things.

l98tpi

Dive it for a couple hundred miles and see if the change. If not, you may need to have the ECM retuned.

Churchkey

Copied the following a long time ago, don't recall who posted the info nor have I tried the procedure.

RESET BLM'S


Open the hood on your Corvette after the engine has sat overnight or fully cooled off.
Then turn the headlights on.
Unhook the Negative or positive battery cable for 5 minutes.
Reconnect the battery cable.
Shut the headlights off.
Then without touching the gas,
start you car.
Let it idle till the engine is fully warmed up & the main cooling fan kicks on & cycles off.
Then shut the engine off.
Restart your Corvette.
Go for a 10 minute ride in town & on the highway.
You have just reset all BLM tables.

the blur

And the BLM's go right back up, as there is a difference with the new age fuel injectors.

Cliff Harris

The BLMs and error codes are stored in the RAM in the ECM. You can reset both of them by disconnecting the ECM power connector. You only need to disconnect it for a couple of seconds (I measured it on my oscilloscope). The BLMs will be reset to the default value of 120 (at least they are on my car). This is the guy:

the blur

And the BLM's go right back up, as there is a difference with the new age fuel injectors.

WW7

Not to start a controversy , but when Mick Stevens did my tune after my 383 install he mentioned that the Bosch 3 injectors required more manipulation to get them to work right in the new engine. He said alot of people install the newer injectors in there stock cars and don't realize that they aren't the same as the stock Multec injectors, that they need to be retuned to work properly.He said alot of guys buy them, put them in, and never check to see where there BLMs are...This is from a guy that has tuned for a long time...WW

the blur

It's not just the Bosch 3, it's any new injector. In my case ACCEL. There is something different with the spray pattern, or resistance curve, or something.. that drive the BLM's through the roof.

WW7

Yes, thats what I was refering to when I said Mick told me people install the newer injectors in there stock cars and don't realize the injectors aren't the same. I don't know much about injectors so I can't remember exactly what he said was different, but he said (newer injectors) didn't work exactly the same as the older injectors and this had to be worked around in the tune and required more work... I didn't have a problem because I was starting with a new motor and a new tune...WW

Bandit1977

Ok,
As a newby to the C4 and the L98, can you explain simply what BLM means.
Seeing as I'm considering swapping to the newer Bosch III's from FIC I'd like to know what the problem/issues might be with going this way.
Thanks,
Ken

WW7

Block Learn Multiplier (BLM) is the long term fuel adjustment that the ECM "learns" to keep the air/fuel ratio within acceptable parameters. A BLM of 128 is considered the ideal, while anything higher shows Lean condition and anything lower shows Rich condition..As long as the blm is fairly close to 128 the computer can compensate by adding or subtracting fuel using a short term correction called an Integrator, this works at a faster rate ( many times per second ) to correct the A/F ratio and help keep the BLM at the correct number. . Hope this helps...WW

Bandit1977

Yes that helps, sounds logical, thanks for explaining it.
So how do you see the BLM readout?...a scan tool or do you need a laptop (with the right software installed) plugged into the ALDL?
Thanks WW7.

Ken D

WW7

You can use either the laptop or a scanner,but only if the scanner has the ability to show it... I have an AutoXray 6000 scanner that shows a complete readout of the integrater and the Blm readings..I also have a laptop with Datamaster installed that I use for datalogging and for helping figure out any problems Im having with my 89. Out of the 2 , the laptop with Datamaster gives the most complete information, plus it can be used to gather information to tune your car with... You need a laptop, Datamaster program, and the connection cable (ALDU1) from Moate's to get the system up and running...Datamaster gives you 20 free uses to see if you like the program before you have to purchase it...WW


http://www.moates.net/

http://www.moates.net/aldu1-and-cabl1-p-127.html

http://www.ttspowersystems.com/DataM...downloads.html

mtwoolford

thank you

Cliff Harris

The so-called magic number 128 is just that -- a number. It doesn't mean anything special by itself. As long as you're not up against the limits (108 and 160) then you're OK. The main thing is that is remains relatively stable +/- 5 or so. If it's wandering all over the place then you have a problem.

The 128 number is for pure gasoline. If you have ethanol in your fuel then the BLMs will be higher. Fouled oxygen sensors and vacuum leaks will also affect your BLMs. Eliminating the smog pump or EGR and removing MAF screens (if you have a MAF) can also change BLMs. This is not a simple system where 128 fits all possible scenarios. Your BLMs may vary...

the blur

>>relatively stable +/- 5 or so<<

per cell, or across all cells ?

samsonb

Are there any decent tuners that can easily fix a high BLM with the Bosch III injectors in an L98?

Cliff Harris

The main thing about changing injectors is that the ECM has an injector flow rate value stored in it. It ASSUMES that this is the correct flow rate and bases it's calculated injector pulse width on that value. If you do anything to affect the injector flow rate (like change injectors or fuel pressure) the value should be tweaked accordingly.

The ECM uses the INT (integrator) value to tweak the BLMs. If the INT is consistently higher or lower than the BLM cell the ECM is currently operating in, it will adjust the BLM toward the INT value. It does this in steps, incrementing or decrementing the BLM one value at a time. It keeps track of the INT value and does a running average over several historical values to arrive at the value used to adjust the BLM. This is why it takes a while for the ECM to "learn" after a reset. It's tweaking the BLM values.

Anyhow, the BLM table looks like this (in my car -- the boundary values vary by year):

Because the MAF air flow rate increases with RPM, the ECM spends almost all of its time in the BLM cells on the diagonal: 0, 5, 10 and 15.