Help... went from 3 Bar Custom OS to 2 Bar... Now won't start

[chrisxiv]

Just like the thread says. I was running a 3 bar custom Speed density OS. I got a 2 bar map sensor, wired it in place of the 3 bar. Confirmed the pinout was correct. The truck fired up, but ran extremely poor. I did some work with to the VE table. But the truck got the point of not even staying running at all. So I after much frustration and going nowhere with it, I decided to revert back to 3 bar with the MAP sensor I was using before, (thinking it could be a bad 2 bar sensor.)... The Truck has yet to start and stay running for more than 1 second. It sputters and dies like the fueling is way off. I noticed my Boost controller reading the Max psi at key on engine off, when it used to read either 0 or 1 psi.

I figured this could be a short or an open circuit between the MAP, PCM and the boost controller somewhere, but after checking the wiring countless times, I'm confident my wiring is not the issue. The scanner reads 105 KPA with KOEO. Pretty sure it used to read about 101kpa in 3 bar. When the truck tries to fire the cells that populate seem to be the lowest KPA cells on the chart. This is surely MAP related causing the fueling to be in another dimension. I have updated the scanner to show the correct MAP sensor each time. I even reverted back to an older 3 bar tune, but to no avail. I noticed after the engine dies, I can hear the fuel pump re-priming itself. Is it possible that something could have gone arai when converting the OS? I have done custom OS w/ HPT on about a dozen vehicles over the years and never had any issues. This one has me stumped.

Maybe I am missing something here? Any Ideas on what I should try?

[chrisxiv]

This is a 0411 P01 PCM with the red and blue connectors. Vehicle bin file started with a 1999 camaro M6

[5FDP]

Is the linear and offset settings correct for the MAP you are using?

Is VATS off?

It helps if you post the tune file.

[chrisxiv]

here's the 3 Bar tune. No VATS. The offsets i've been working with.


I'm not ruling out a fault with the wiring, but Like I said, I've checked it multiple times.

[blindsquirrel]

If you don't know the actual specs for a MAP sensor, it's pretty much useless. Buy something with known, published specs.

[5FDP]

What 2 or 3 bar sensor are you using?

Also you VE table doesn't have enough fuel in it to keep it running. You have values all the down around 1 to 5, which is basically zero fuel.

There are other problems too. Like that timing table is pretty ugly. It's got like no timing in it for cruising around, you don't need it at sub 25 degrees all the time. LS engines love 35-45 degrees under light load, far better for fuel mileage too.

Your base running airflow table seems really low as well, may want to look into that too. You have less airflow in it than a stock 5.7 camaro does, as well as a stock 5.3 with a cable throttle body.

[chrisxiv]

I just noticed something with the tune file.... In editor, when I click the button for OS, nothing comes up. Its blank. So If I want flash to a custom OS or revert back to the factory GM operating system, how would I do that?

[chrisxiv]

Im running the LS9 sensor. I think pn is 12592525 ?

i know the VE is is extremely low on this tune. The truck ran very good on this tune, unless under high vacuum conditions. Only problem was that the IPW would bounce around uncontrollably and start to buck when at steady 0 or 1% throttle, under light to no load conditions. This was the reason for wanting to try it out on the 2 bar OS.

but I'm with you and you're definitely right about the VE table. It has no fuel in those cells. I noticed this awhile back, but the fueling has always been very rich down low and under decel. If I fix the timing, will it allow me to bump up the fuel in those cells?

[5FDP]

The OS tab is blank because the upgraded OS is applied. Just look at the calibration details page, it says what OS it is running in there.

The LS9 MAP sensor is 312.5 and -11.25 for the settings, that is why it won't want to start because your data is way off.

If you had to pull that much fuel away in the VE to make it run it makes me wonder if the injector data is correct or if your fuel pressure is super high.

With big injectors you also need to cut the minimum fuel milligrams in the tune way down, otherwise your idle will always be very rich. Yours is at 0.037 and you should chop it all the way down to like 0.014 or so.

[blindsquirrel]

You do not HAVE to use a 3 bar OS with a ''3 bar" sensor, or a "2 bar" sensor if you're using the 2 bar OS. However, the MAP linear/offset have to be correct for whatever the sensor is, in any/either OS. A 3 bar OS will work just fine with a 2 bar sensor providing the settings for the sensor are correct (or even the stock 1 bar OS with the 2 or 3 bar sensor). And, there's no difference in function between the 2 bar and 3 bar custom OS other than the scaling of the VE table axis.

[chrisxiv]

The OS tab is blank because the upgraded OS is applied. Just look at the calibration details page, it says what OS it is running in there.

The LS9 MAP sensor is 312.5 and -11.25 for the settings, that is why it won't want to start because your data is way off.

If you had to pull that much fuel away in the VE to make it run it makes me wonder if the injector data is correct or if your fuel pressure is super high.

With big injectors you also need to cut the minimum fuel milligrams in the tune way down, otherwise your idle will always be very rich. Yours is at 0.037 and you should chop it all the way down to like 0.014 or so.

Thanks, I'll give that a try and see how it goes. I'm just having a hard time grasping the fact that the truck ran well on this tune, but now it's not even close to wanting run.


I also read somewhere that the early OS's were unable to run negative values for the MAP offset. So I input the reciprocal as the low. I probably should have bumped the high up the same difference, but I wasn't exactly sure if thats was correct either. The injector data was copied over from the Siemens Deka 80's that I received from the supplier that I got them from. I've tried lower values in the minimum fuel milligrams all the way down to zero. But didn't see any improvement, So I just went with what the data suggested.

As far as the MAP offset goes, I've been toying around with different figures to try to get rid of the surging(i wouldntt really call it surging. More like rapid pulsing or bucking) at light or no load conditions. It always does it at the same MAP, so rather than mess with the short pulse adders anymore with the injectors, I started to play with the MAP offset to see if it got me anywhere. I'm not going to lie and say that the offset I'm using is right, but this is the value that I experienced the least amount of the surging with the bouncing/bucking I was getting. In the logs, the IPW would jump back and forth at 1.2g/s to 2.4g/s under that low of a load. But this is another issue for a day when this thing actually runs again.

[chrisxiv]

You do not HAVE to use a 3 bar OS with a ''3 bar" sensor, or a "2 bar" sensor if you're using the 2 bar OS. However, the MAP linear/offset have to be correct for whatever the sensor is, in any/either OS. A 3 bar OS will work just fine with a 2 bar sensor providing the settings for the sensor are correct (or even the stock 1 bar OS with the 2 or 3 bar sensor). And, there's no difference in function between the 2 bar and 3 bar custom OS other than the scaling of the VE table axis.

Yes. I realize this. I didn't switch the OS w/o also switching the sensor as well.

[Bill@HPTuners]

Did anyone notice that his VE table 800-1200Rpm 40-55kpa is set to like 2-4 whereas a stock calibration is set to 50-60? Personally I would start there.

[Bill@HPTuners]

also you need to understand what a VE table is, it is NOT a fueling table, it is an AIRFLOW table, you are telling the ecm how much AIRFLOW is coming into the engine at any given point. Typically is not an acceptable practice to make massive adjustments to the VE table to correct fueling issues. We've always found that the stock VE table will be very close and a value of around 130 is about the highest you should ever see in an LS1 VE table anything over 130 or under 30 is pretty questionable.

[chrisxiv]

also you need to understand what a VE table is, it is NOT a fueling table, it is an AIRFLOW table, you are telling the ecm how much AIRFLOW is coming into the engine at any given point. Typically is not an acceptable practice to make massive adjustments to the VE table to correct fueling issues. We've always found that the stock VE table will be very close and a value of around 130 is about the highest you should ever see in an LS1 VE table anything over 130 or under 30 is pretty questionable.

I noticed this almost right away after I applied the 3 Bar enhancement. I am running a autometer digital boost controller that I have piggybacked off the stock MAP sensor to get the boost readings.. I thought that this may have been the reason for the low numbers on the VE table. I am completely versed and have a good understand of what VE is with regards to EFI tuning. I have tuned around 100 LS-based vehicles over the past 15 years. I wouldn't consider myself a professional tuner, as I gain more knowledge every time I open the laptop. FWIW, most of the vehicles I've done have been NA up until recently. I figured this was just a result of the 3 bar enhancement. The truck runs very good with this tune flashed, as surprising as it sounds.

I was able to correct the issue I was having in the OP. I ended up referring to an incorrectly posted pinout online for the 2 bar sensor and reversed the wires.


As far as the VE table goes, what would cause it to be this far off? The only thing I can come to is incorrect injector data, unless the boost controller is throwing the MAP readings way off. I temporarily disconnected it with no change.. I'm running an a1000 pump with the pressure turned down a bit as well. So it's not seeing too much FP.

I posted another updated tune to look at. Please feel free to critique as much as you feel necessary. I'm always open for input.

[Bill@HPTuners]

bad injector data would be one of the most common reasons.