No start condition with VE tuning.

**Update** Running 7/25/25 (spoiler, bad MAP sensor brand new out of the box)

I'm adding a turbo and want to tune in the VE mode and eliminate the MAF. Truck ran fine with the MAF plugged in. Now it won't start at all after removing MAF. Tries to fire occasionally, but really just cranks over.

I've added a IAT sensor and deleted the stock MAF.
Added my 2 bar sensor and updated the file to support the right tables.
Extrapolated the data from 105-210 to fill in the new VE table.
MAP sensor has the right calibration.
Write all to the truck for the new changes.
I've made all the necessary changes in the tune to put it into VE mode (ie change the Dx MAF fail, make sure all the settings disable the MAF,

I just don't know what to change in which direction to start. I've swung it both up and down 5-25% in the VE table with no change. Any advise on where to begin to get it to fire up would be great.


Its a 2003 4.8L from a Tahoe swapped into a 1954 International truck.
Mods: Ported 243s, Sloppy stage II cam, headers to turbo, WB

Current file attached. Attachment 162503

Record a log of trying to start it. Might not be getting enough idle air, what throttle body are you using?

dont forget to match your high octane and low octane in you spark tables

also to get it started in your base running air flow make everything 140 and up 14 and it should start

140 degrees and up

you VE table only shows a 1 bar sensor it should go from 0-201 kpa

First question should be, since this is a swap vehicle, has it EVER run? Did it run prior to you doing the 2 bar conversion?

Quote:

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Originally Posted by nanygoat

you VE table only shows a 1 bar sensor it should go from 0-201 kpa

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The Main VE table goes to 210. The start up VE only has up to 105. It didn't change with the file conversion and I couldn't find any info on if this matters or not. It wasn't discussed in any of the five videos on VE starting.

For the base running airflow, we are talking the ECT vs Idle airflow in P/N and gear?

And I did the low to high octane spark tables first with all the other changes.

Yes, this truck has been running for about two years with the 1bar sensor and MAF. I'm adding a turbo to the build and was advised to do VE instead of MAF for better tuning and throttle response. If I put the MAF back on it, it will run. Currently it is running the older style stock DBW throttle body. I've got a newer stock LS3 style with a different intake to put on it, but wanted to get it running first so I'm only doing one thing at a time.

It does act like it isn't getting enough air to me as well. I just don't know how to tune the DBW to add more air with all the extra tables and such. I'm confidant with cable throttlebodies, but this DBW is new to me.

Couple logs of trying to start it


Attachment 162551Attachment 162552Attachment 162553

It's coming down to 9 volts trying to start. This is likely at least part of the problem.

I just saw that. I'll look into it. Could have been I was cranking it for too long. I'll put a booster on it and see if that changes.

Okay, I've been watching a lot of youtube tuners and making some changes. I brought the VE tables way down, reduced by about 25-30%. I increased the startup airflow and running idle airflow by about triple. Truck will now fire and run okayish. But now it runs for about 45-70seconds and then just shuts off. After it shuts off it won't restart. If I reflash the file, it will start and run again for about the same time and then just shuts off again and won't restart. Any ideas? I've attached the last couple logs where it was firing and running for a short time.

Attachment 162888Attachment 162890

Just noticed that the MAP isn't reading anything but 105kPa. Maybe that's part of the problem.......

Deff. a problem.

Let us see the current .hpt file.

The quickest and easiest for you may be to plug the MAF back in and make it run on that, make note of the air flow and nbo2's readings, tune the VE table to get close to the MAFS readings and at least it should stay running for you in SD after that. Looks to me as if your potentially way to rich at idle and the MAPS being stuck at reporting 105 kpa would do it.

I'm not convinced that is a huge problem yet.

It should at least fire. Have you checked fuel pressure?

Post the tune file that goes with the most recent logs where you say it will fire and run for a little bit.

Quote:

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Originally Posted by drjaredshelton

Okay, I've been watching a lot of youtube tuners and making some changes. I brought the VE tables way down, reduced by about 25-30%. I increased the startup airflow and running idle airflow by about triple. Truck will now fire and run okayish. But now it runs for about 45-70seconds and then just shuts off. After it shuts off it won't restart. If I reflash the file, it will start and run again for about the same time and then just shuts off again and won't restart. Any ideas? I've attached the last couple logs where it was firing and running for a short time.

Attachment 162888Attachment 162890

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Looks like these were the logs of it running, only looked at one of them, but you MAP should not stay pegged at 105, especially while idling at 800 with zero throttle input. You need to troubleshoot your MAP sensor. Add map voltage to your channel list, and check at the sensor, i believe the signal voltage floats to full scale when its unplugged/wiring issue.

Quote:

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Originally Posted by Alvin

I'm not convinced that is a huge problem yet.

It should at least fire. Have you checked fuel pressure?

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I only looked at the log that wouldn't fire. The one where it idles.. yes the MAP sensor needs to be looked at asap.

I missed that at first too, usually don't see much or any change in the MAP at cranking RPM, One of the logs in the first set you posted is showing activity on the MAP sensor

I had a PSI harness with the map wired wrong (everyone makes mistakes)

But the odd thing is the MAP sensor would stick on certain values. Like on time 105.. next time 82, next time 33, etc.. It was very confusing.

That is definitely an interesting one , were you able to narrow down the exact issue that was causing it?

yeah two pins were swapped at the map sensor.

Okay, that all helps a lot. Thanks guys. I ordered a new MAP sensor and just have to wait for it to come in. The tune is on my laptop. I'll try and upload it later.

Quote:

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Originally Posted by Alvin

yeah two pins were swapped at the map sensor.

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I wonder if that is happening on this one, because at key on it reads 105, and then when it gets running and I give it a little gas it goes down to 55-70; which to me would be the opposite with throttle wouldn't it? Although with a 2bar sensor, shouldn't it be reading 210 if it was flopped? I am using an aftermarket harness from speedway. Maybe it has always been wrong, but it ran on the MAF instead......

Key on not running should read atmospheric pressure, add the MAP voltage channel and see what voltage the PCM is seeing, I would check the wiring first, you will have a 5v, a ground, and a signal to the PCM that will vary between roughly 0.5 and 4.5v based on pressure, with the sensor unplugged you need to figure out which wire is which, 5v is usually gray, and ground should be black, you will need to confirm the 5v and ground with a meter.

If this is 2 bar COS you have to choose 2 bar MAP sensor from the channels menu. When you do it will read 0.0 Kpa KOEO. When you start it, it should read correctly. Just one of the GEN 3 quirks.

Quote:

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Originally Posted by edcmat-l1

If this is 2 bar COS you have to choose 2 bar MAP sensor from the channels menu. When you do it will read 0.0 Kpa KOEO. When you start it, it should read correctly. Just one of the GEN 3 quirks.

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Ah ha. Thats good info. I'll look at that for sure

Success! Bad MAP sensor right out of the box. Got a new one put on today and immediately fired up and running correctly. Barometric pressure is more on par at 84-85 (I live at about 5700ft) and it responds correctly when it starts. I had to take a ton out of the VE table to get the fuel right at idle. But it runs and idles the best it has ever. I added a ton to the idle airflow, but now that it is starting correctly, I may be able to bring that back down to more normal numbers. Maybe its fine the way it is?

New question. My TPS says 0.00 volts on a DBW throttle body. Accelerator pedal position is reading and throttle responds to input from my foot. Is this a DBW thing or am I looking at the wrong parameter logging?

Lastest log of start up and idle with a couple slight revs.

Attachment 163039

Latest tune file where it starts and idles
Attachment 163040