C4-owner

Hello

My first post here!

I have recently changed my injectors on my 1990 L98 to Accell 24lbs due to rough idle and low rpm hesitation. The engine now runs fine
Did a scan before and after replacement of injectors with Datamaster. My engine ran very rich on idle before replacement. It looks better now but still seems to run a bit rich both on idle and with higher rpm's. Short term counts are mostly arond 120-122.

The only "tune" i did was to change injector size from 22 to 24 in my bin file. Does this really change anything or is it just info in the file?
If it really changes injector flow maybe i should try with 26 in my bin file?

This was my furst burn of any chip so i really dont know much about it. Hope you understand what i try to explain, my english is far from perfect since i am from and living in Norway(Scandinavia).

Raymond

VenkmanP

Does that mean your LTs are at 108?


If it is <edit>rich</edit> in all cells by ~8% and all else is functioning correctly then that makes sense.

However, since your car was running rich with both old and new injectors, it would be a good idea to repair the problem you have first.

C4-owner

My LTerm-C Counts are almost allways at 108. My LTerm Adj are changing but 95% of the time below 128.

Before i changed my injectors it ran very rich at idle and was ok in higher rpm's, my o2 sensor vere at 0.8 to 0.9 volts all the time with no xcounts at idle. Now it seems to be a little rich but i have xcounts all the time and it runs fine. I might try changing to 26 in my bin file and do another scan. Ideally i guess it should be near 128 Short term counts allmost all the time?

I dont think i have other problems with my ecm system. It's got a new 02 sensor, egr valve, iac, plugs, rotor, cap and so on.

Raymond

tequilaboy

Normally it is desireable to have the long term counts (or blms) near 128 for all cells. This means little or no correction is required when in closed loop. The short term counts will oscillate around 128, but this is intentional to force x-counts.

If the short term counts deviate too far, the long term counts will move in the direction of the short term counts, which should in-turn bring the short term counts back closer to 128.

Long term counts of 108 is very rich. The ecm is doing all it can to lean out the overly rich mixture. 108 is the lower blm limit value.

Increasing the injector constant will result in global enleanment. The calculated pulse will be reduced across the board with an increased injector constant.

This should bring your long term counts back up towards 128.

VenkmanP

If your LTs are 108 you have serious problems and you need to fix them before you do serious damage to the engine and the cats.

Sam Lam

C4-owner: I have to ask the questions "why would you want to place 24 lb hr injectors in a car designed to run with 22 lb hr injectors? Doing this has just added another problem to your list of issues while the original problem may be still waiting for your action. I agree with Vic!

C4-owner

Is it right that my ecm can control my engine as long as i have xcount readings from my o2 sensor and my short term counts are around 120-122? I guess it is on the "edge" of control but it should be possible to tune it into normal operation?

I dont know what my serious problem could be as i have replaced allmost all important items regarding ecm control, as i mentioned before. I have also replaced my map sensor and tried another ecm. All other sensors looks normal acc Datamaster. My tps is 0.75v at closed throttle, considered normal iaw my manual.

I have used the same memcal in both ecm's id:ANHW, dont know if this is correct for my car(90 auto with 3.07 rear diff, but i guess it is bypassed by my new prom when i am operating in normal closed loop.

I bought 24 lbs injectors as they are listed as replacement parts at Corvette Central, Mid America and so on. The difference is only 2lbs, shouldnt it be tuneable?

The only thing i can guess can be faulty on my car are partly clogged cat and maybe my pre-cats(if they can clog?).

I think i might try to do a scan with Tunerpro also just to see if they come up with the same readings.

Anyway, thanks for all replays, all info that can bring light over this are welcome!

Raymond

tequilaboy

I think a 2 lbs./hr flow difference is enough to move the blms from near 128 to 108.

In my car, if I reduce my injector constant in the ecm by 1 lb. I see the blms drop by about 10 counts into the 116-118 range.

I don't think you have any serious problems, only a combination of too much fuel pressure and/or slightly too large injectors. Both of which you can compensate for by normal tuning methods.

I didn't see any mention of fuel pressure in this thread. It would be interesting to see what pressure your running at.

You can either reduce the fuel pressure or raise the injector constant to bring the long term counts back up where they belong near 128.

Sam Lam

as you are injecting about 10% MORE fuel than the control system is designed to accomodate. A friend of mine put 24 pounders in his 88 convertable and was not able to regulate the fuel pressure to achieve the correct BLM values. He changed the injector settings in the ECM and this solved his problem.

VenkmanP

Installing 24 lb injectors in a car which had 128 BLMs with 22lb, with no change to the engine program, would change the BLMs to ~117. While not optimal, this would not cause any significant problems.


My understanding of his posts is that the BLMS were 108 and the car was running very rich before he changed injectors.

My understanding from his posts is also that he has already adjusted the program for the 24lb injectors.

If they were 128 with the 22 lb they not be 108 after he changed to 24lb and changed the constant.

Regardless of cause, 108 BLMs is a serious problem. He is washing the engine with gas.

I doubt you have _any_ problems with your "ECM system". Most likely you have some basic mechanical faults. Playing with ECM tuning when there are basic mechanical problems is a bad idea.

VenkmanP

No. STs are completely irrelevant here. All that tells you is that the LT of 108 is not low enough. Which an LT of 108 pretty much tells you by itself.

the blur

i thought the ecm can adjust from 0 - 255 ?
i'm seeing 150 blm at times, but short term is always 128.
car runs great.

what range of long term (blm) can the ecm handle?

tequilaboy

The normal range of BLM adjustment is from 108 (min) to 160 (max). These limits can be extended if required.

On a related note, I've recently seen a case where 24 lb. rated injectors at were flowing more like 27 lb. injectors. The fuel pressure had to be set down to about 36 psi to get the blms in order, even with the injector constant already corrected to 24 lb./hr.

To compensate, the injector constant was increased to 27 lb./hr in the bin, and the fuel pressure was set to 45 psi to make for a more efficient spray pattern and to provide some room for future adjustment. This combination produced good results for the car in question.

the blur

so even if I see 150 BLM's at time, I should not worry about running lean and burning down the motor ?
It seems the computer can compensate quite a bit.

I watch the rich / lean flag on the scanner, and it mostly shows lean. but it does jump to rich more than enough. and the o2 cross counts are up there too.

But it's just everyone is fixated on this 128 number... so when I saw 150, I started to worry.

I have also heard that with the oxagenated fuel, the BLM's go up to adjust..