I have read many threads and many post of forum members praising the performance of their Bosch III injectors. But, it seems a few that have actually datalogged their cars the BLM's are way out of whack. Also, many have lost considerable fuel mileage with the injectors. Has anyone corrected the BLM's and fuel mileage? If so, I would like to hear/see your results. I need new injectors and the Bosch III is an injector that I'm considering. But, I just want to make sure that the crazy BLM situation has been resolved. I can retune my car, that's no problem if that needs to be done.

Thanks, and hopefully this thread isn't going to start an agument. Just a positive discussion on how to remedy the BLM and fuel mileage situation.
-Mike

 

I don't think it is only the Type IIIs that drop the mileage...I bought a set of Type IIs in 2007(before Jon was on the CF scene) that dropped my mileage on my '89 about .5 mpg....I really didn't care I just do city driving anyway......I get ~13mpg now but I have some deep gears, some flow mods and a heavy pedal foot and I drive the thing like I stole it as much as possible. The mileage thing is kinda like splitting hairs if you ask me.......My only complaint it that the type IIs are kinda loud though are the Type IIIs that loud too?

 

this has come up a lot so let me offer my opinion on the subject. There are guys getting worse and some getting better mileage, I keep in touch with most of my customers and have found in most of the worse cases that the old set of injectors which were replaced had 1 to 4 injectors not operating correctly. If there was an injector reading less than 10 ohms, those injectors were not working properly.. so with 6 good injectors the mileage would be better but, that engine was lean. I would like to here from customers on this thread on the actual mileage they are getting. The performance of the car is 90% of the time much better, including starting, accelleration and overall smoothness. The high BLM could be from a varity of things. Alot of guys replace the injectors and still have issues with the TPI as a whole. In other words for the system to work properly all parts of the system must be in spec. There is no magic injector. These flow at the same volume as the stockers but have a quicker on/ off. Leaving the onboard mileage computer a little confused. I would always insist on a manual check of fuel consumption to determine what it really is. These cars in general seem to get remarkable fuel economy, much higher than the manufacturer suggests on the window sticker. With most of these c4's not being daily drivers fuel consumption is secondary to performance and reliabilaty. The only real replacement for the c4 is another set of multecs, which are not E10 compliant and will fail eventually. Back to the BLM issue. Brian Cunningham on the c4gru posted this. It explains that the high blm reading does not mean the car is lean, it just means that the computer is adjusting for the fuel demand.

BLMs

BLM stands for "block learn multiplier." the PCM uses the grid of cells referenced by engine load and speed to correct for discrepancies due to air and fuel quality. The PCM will be expecting the engine to run a certain way depending on the MAF sensor calibration or the VE tables.

But because the car is not running in an ideal world, there will be correction needed for differences in air temperature, density, humidity, as well as fuel octane, quality. On top of those two big variables, there are also the changes that happen due to normal wear and tear on the engine and its sensors.

The BLM is how the PCM adjusts to correct the fueling. By default, in closed loop, it attempts to get an air:fuel ratio (AFR) of 14.7:1. When at this ideal, the BLM will read 128, or no correction.

If the PCM senses the combustion is too lean (not enough fuel), it will add fuel and the number will increase (> 128). If it senses the combustion is too rich (too much fuel), it will remove fuel and the number will decrease (< 128). By default it is set to modify down to 108 and up to 160, but those settings can be changed as well.

There are two sets of BLMs: long-term and short-term. As a consistent trend in O2 sensor feedback forms while driving, the PCM will set a "permanent" modifier to accomodate the initial PCM tune being wrong; this is called the long-term modifier. Until those are changed, the PCM uses a short-term modifier which adjusts fueling on the fly depending on O2 sensor feedback. It is best to tune from the long-term BLMs, as the short-term can vary based on inconsistent variables. Both sets of BLMs are reset to 128 when power to the PCM is lost or a new tune is flashed.

Using these BLMs, one can sense whether there is a problem with something mechanical; things like exhaust leaks (the BLMs will rise, as the O2 sensors sense unmetered air thinking the combustion is running lean), or fouled spark plugs or O2 sensors (the BLMs will decrease, as the O2 sensors see less air and think the combustion is too rich). The BLM can also show a need for a change in the PCM tune; if the VE tables are set too high (low BLMs) or too low (high BLMs), or if the MAF sensor is miscalibrated. Even timing can affect combustion efficiency and thus BLMs.

At WOT, when the PCM enters PE mode, the BLMs are still used but for the most part no more feedback is recorded (unless the mixture runs very lean, then more fuel can be added). Therefore, it is important to be sure the car is running properly before entering PE mode, so that the desired WOT AFR is used and not a modified setting from the lower RPMs (seen more in detail below).

When the PCM enters PE mode can also be modified, both by RPM and throttle position; by default, it is at less than full throttle, how much so depending on RPM. For example, in the stock tune, as little as 28% throttle is necessary for PE mode, when over 4400 RPM.
so as you can see a high blm does not mean the injector is at fault, a before the injector swap scan would be the only way to compare what it was. But, very few do. I have seen BLM counts stuck at the 160 mark with a stock set of multecs many times. We have over 1000 sets of Bosch 3's out there Lets hear from you.

 

I have read almost all posts about injectors and am still confused. I thought the injectors were controlled by the ECM based on the O2 sensor. So if that is true, how can changing the injectors affect gas mileage? I can see a heavier foot because it runs so much better.

 

you are 100% correct.. lets face facts when your car is not running well, like hesitating, spits etc as they do when the multec start to fail most guys would drive on the easy side because mentally they do not want to hurt something.. When the car runs great you are always in the pedal.. human nature

 

My take is that some III's are LS type meant to operate at 60lbs FP., and some are designed for the ford rail at 39#. Meaning that (for example) an LS type 24# inj. is meant to be 24# @60lbs, not at 45lbs fp.. When using this version in a car using 44.5'ish fp., the blm will drop, as it would be like replacing a 24 with approx. a 22#. If using the the ones designed for the ford fuel rail, operation is designed for 39lbs.. Using this version @44.5 the would then cause the car to run a bit richer. Which ever version, I believe either can be made to operate correctly through changing inj. constant and other additional tuning (not fuel pressure changes).

 

it makes no difference on what it is used on.. Lets take the LS1 injector it is rated at 28lb at 4 bar (psi) Bosch sold the Identical injector for use in the Fords, it has a different part number because the o rings are different but its the same injector.. in the ford its rated at 23.25 at 39 psi. The same injector again is used in a european BMW 5 series.. rated at 24 because they use 3bar.. There is a direct relationship to input presure to flow volume. The injector coil works the same regardless of the input pressure so therefor there is no design difference. Its simply that the more fuel pressure in the more flow out.. In turbo apps we raise the fuel pressure 1 to 1 in relationship to the boost. This is done to equalize the increased pressure pushing up on the injector from the manifold side keeping the injector flowing the same as if it were naturally aspirated

 

Once the weather warms up a bit I'll probably order a set. I'm a pretty good tuner, and will be able to report back the changes. I have tuning software, datalogging software, and an adjustable fuel pressure regulator. So, I can try different tuning methods and even different fuel pressure to see if I can get these issues resolved. Only thing is I need a larger injector, so hopefully my changes will still be able to help others.

My understanding of the long and short term blm's are the closer you can get them the better the tune you will have. Letting the PCM adjust from 160 to 128 is not what I'm looking for in my car, and at least for a couple of cars that's what I've read.

Jon, your point on these cars being older and other worn out components coming into play could be a major factor in the results we are seeing. Also, seems like very few cars have had a before and after data scan. Most may be running and probably are perfectly fine.

 

right, the inj. doesn't know what car it was designed for. The change in fuel pressure will have a direct result in blm (as I stated above). The ratings of lb. is with using "x" fuel pressure., the type II's were rated at 44.5. So to achieve the same result with a III, a 28 would then need to be used to approximately create the same result as a 24, if using 44.5 fp.

 

I recently installed a new set of Bosch 3's, that I purchased from Jon, in my completely stock 87 coupe. I really can't address any of the technical issues you guys have brought up (because I really don't understand most of them) or the fuel mileage (because I really haven't checked it yet). However I can tell you they have made a tremendous difference in the way my car starts, idles and runs. It is amazing the difference they make. I went from cranking, cranking and cranking then feathering the throttle when it finally did start to now where I turn the key and instantly I'm at a smooth consistent idle. And as far as running... it has absolutely no idle surge and no hesitation when I accelerate.

Since I've started restoring this car I've sunk a lot of $ in it.. I must say that so far these injectors from Jon have given me the most bang for the buck!!

 

Jon, I have seen many of the video's you made showing superior atomization and flow control of the Bosch vs. Multec. What is the fuel pressure used in these videos, and do you use identical pressure for all comparative video's ??

 

all the flows were done at 43.5 psi.. we always use this unless we are doing a video using ls1 or a engine that uses a 4 bar system. For turbo demos we sometimes use up to 80psi.. The Bosch 3 is the Best replacement for the multec that we have found.

 

I don't know about other peoples issues, I can only speak from experience.

I have a set of Design III's from Jon in my LT4. The car has never run so good or idled so smooth.

THe partial throttle response was AMAZING, and still is, its a MASSIVE change over the multec.

After having them for a while I had an issue, and thought it was injector related. I was wrong, it was my gas. And I found out even more of the horrors of ethanol.

Stopping at a local station (ALL stations in Florida have 10% ethanol or less) was when my issue popped up. I later found out that the "10%" mix, is done when the tanks are filled, and not controlled at all.

My tank was almost 70% ethanol. Causing a lean condition and scaring the crap out of me. Jon was really nice and helpful even when I was trying to blame these great injectors on my problem.

After I got a fresh tank, the car is the same as its always been. I noticed a small mileage drop on the dash, but no change on calculating it myself.

Jon has an amazing product, that everyone with a TPI or LTx should be looking into.

 

Jon, I have to disagree. I went to Bosch that I bought from you and my mileage is way down, I drive the exact way I drive all my cars. My mileage went to 13 city and 24 hwy, from 19 city 29 hwy when the originals were good.
Also, when I start my car, the car smells rich and does not start leaning out till the car gets up to temp. O2's are brand new, so I don't think the Bosch's work well w/early LT1's.

 

Randy, you need to contact Jon.

Here is an update on the 93 injectors from Jon in another thread.

i'm glad they worked so well. What we basically did was copy the flow from the oem to a Bosch 3 on the flow bench. The 93 Injector number according to the data that is out there says its a 20lb injector rated at 50psi.. I can tell you this, thats total BS.. The stock injector flows a tad over 24. The Bosch 3 24 is rated at 39 psi so that was too big. We took a Bosch 3 rated at 23+- and modified the discharge plate so it flowed identical side by side with the OEM at various pulse rates. So I guess we have the only correct replacement for the 93. All the other years we can use a off the shelf core that flows the same as OE. We will be putting up a listing for the 93 on its own as the injector from the 92 is too small and the 94-96 is a little too big.

 

randy i am glad you came in.. i was going to email you tomorrow. go to this thread and read from the end up. http://forums.corvetteforum.com/c4-t...jectors-3.html
It seems the 93 has a problem with the injector that we were selling for the 93 only.. all other years have no problems. I need to send you another set that will take care of the problem. Again, this seems to only affect the 93 and possibly some late 92's that use the 93 injector and ecm. Please pm me with your address so we can send them.. no charge for any of this. You have to remember that the books call for a 22 lb injector in the 93 the injector # crosses to a 20lb rated at 50psi. That is not correct and the ecu is very sensitive to the constant that is programmed in the tables, we have duplicated the flow of the stock injector to ours. These should take care of the mileage issue. When you put these in you must reset the ecu.

 

I just got to put my 2 cents worth in about the III. I got mine from Jon also, and wouldn't get them from any other place. Jon is a class act, and is always eager to help out with any problems. I haven't noticed a change in my fuel mileage, and don't really care to much about that, but the car seems to still run a tad rich. I imagine I can lower the fuel pressure a bit, maybe that will take care of that problem. The thing is, the car is stock, (as far as I know), but since I put the new Bocsh III in, the car scares the crap out of me. Its an automatic, and if I mash on it, it lights the tires up instantly and goes sideways, and its almost uncontrolable. When it hits second gear, it lights them up again for a few feet. Is this normal??? as I am not sure if a stock vette will do that. I know it didn't do that before I pulled the Multecs out. I certainly have respect for it now, and make sure I'm point forward in a streight line before I hit the gas. Once the spring brakes, I will check the mileage again, but my dash was saying 20 around town..

 

My results are very similar to yours. Based on the SOTP meter there is a definite improvement in performance.

In my case, 1 of the multecs was completely shot. The amazing thing is the car still managed excellent MPG's (21 city / 30 hwy.).

The rough, lopey idle is gone! The extended cranking, hot engine starts are gone! I only have around 12 miles on the car since the injector replacement, so I don't have any MPG data as of yet. Unfortunately, thats gonna have to wait till Spring.

 

Jon,

I recently performed some data logging on my 90' with the Bosch III's installed. Again I only have apprx. 12 miles on the car since the install.

Would you be interested in this data?

 

please send it to info@fuelinjectorconnection.com
thanks