Microsquirt initial start up woes! Fires then immediately dies.

BestGuess

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Aug 21, 2021
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Swapped a stock 5.0 HO motor and a T5z into an 80 model. I'm on the home stretch of getting it ready to drive around the neighborhood for the first time, but having some issues with start up. I'm not exactly new to Megasquirt, I have MS3 goldbox on my other car (turbo LS car). So I do have some knowledge with Tunerstudio however, I wouldn't call myself a pro. I wired the micro up in the Mustang, sensors seem to be reading, calibrated the TPS, checked to make sure I have oil pressure, fuel pump is priming, did an injector test and the seem to be firing, I seem to have spark at all holes, all the normal stuff. The issue is getting it to stay running. Finally got it to fire better after setting the spark output to "Going Low" after some searching.

I am using a set of decapped LS truck fuel injectors. I had those cleaned and flowed and they're good to go. They're around a 850cc injector once decapped I do believe. I did recalculate the required fuel and I have messed around with the VE table to see if making and changes to it would do anything, so if anyone takes a look at that it's probably all jacked up. Another issue is setting the dead time and voltage correction for those LS injectors. Currently have the dead time at 1.000 and the voltage correction at .200. Some LS engine guys run that deadtime with decapped LS injectors and Micro, but typically the LS engine has around 58psi base fuel pressure. I think the 5.0 with a stock FPR has around 30psi with the vacuum line connected, so I'm not sure how that effects the latency.

Another thing that I'm running on this engine is an LS1 style 3 bar MAP sensor from EFI Source. I use one on my other turbo car and had an extra.

I've attached the base tune I'm using and a quick datalog of me trying to crank it. Not a lot of info in there as I don't have an exhaust on the car yet and no place to stick the wideband. I would think the engine would still fire and run even though there's no wideband there.

Maybe something in that base tune is set wrong and I keep missing it? Maybe another set of more experienced eyes will see something I'm missing.
 

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a91what

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Mod Dude
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you want to "include AFR" in the general settings

the ign settings look correct for a TFI ign.

looking at the pw in the log file, it appears that the injectors stop firing as you transition from "crank" to "run"
I see nothing that would cause this behavior, but shut the nitrous settings off until you get a start.
 

BestGuess

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you want to "include AFR" in the general settings

the ign settings look correct for a TFI ign.

looking at the pw in the log file, it appears that the injectors stop firing as you transition from "crank" to "run"
I see nothing that would cause this behavior, but shut the nitrous settings off until you get a start.
Thank you sir. I left the nitrous settings on and have forgotten about them. Was wiring up the nitrous kit and making sure things were going to work and left them on. Will shut the nitrous controls off and include AFR in general settings and report back after I see what happens.
 

BestGuess

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No difference. Tries to fire up, runs rough for a second and dies. Not able to keep it running with the pedal. Trying to think what would cause the injectors to basically shut down.
 

a91what

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When this type of thing happens I update the firmware. Please reflash to 3.4.x (newest) on msextra.com you can do this in the (tools?) Menu
 

BestGuess

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When this type of thing happens I update the firmware. Please reflash to 3.4.x (newest) on msextra.com you can do this in the (tools?) Menu
When this type of thing happens I update the firmware. Please reflash to 3.4.x (newest) on msextra.com you can do this in the (tools?) Menu
Was able to get in touch with a buddy of mine and he said to find which of the fuel correction tabs in the data log was pulling to 0% correction. I found that barometric correction was set to 0% across the board. I’m setting it to 100% across the board and we’re gonna see what that does. Instructions within microsquirt also tell me to set it to 100%.
 

a91what

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This makes me wonder where you got your base tune from... the "old way" of doing baro correction and the "new way" require different settings in the baro sensor setup. I am thinking you used an older base tune on new firmware. either way glad you got it sorted out
And I just gave it a quick test and it fired off and I was able to keep it running by the pedal. Progress!!
 

BestGuess

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This makes me wonder where you got your base tune from... the "old way" of doing baro correction and the "new way" require different settings in the baro sensor setup. I am thinking you used an older base tune on new firmware. either way glad you got it sorted out
I got to be honest, I really don’t know where I got it from. Did a search on google and found one.
 

DOHCtor

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May 23, 2004
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Try this as at starting point. You probably already know this, but you really should get the wideband installed, enabled and properly set up in Tuner Studio, then write to the controller, while ensuring all of your other sensors are active and their settings written to the controller. The wideband will not be happy with open exhaust, or without the proper length extension off the header. I pulled quite a bit of fuel at idle, in the VE table, so you will want to play with that once you get a wideband installed. Try to reach around 14.0 at idle 13.8 to 14.7 could work well. Good luck.
 

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DOHCtor

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Updated - Try this as at starting point. You probably already know this, but you really should get the wideband installed, enabled and properly set up in Tuner Studio, then write to the controller, while ensuring all of your other sensors are active and their settings written to the controller. The wideband will not be happy with open exhaust, or without the proper length extension off the header. I pulled quite a bit of fuel at idle, in the VE table, so you will want to play with the VE values in the idle area, once you get a wideband installed. Try to reach around 14.0 at idle, by adjusting the VE table. 13.8 to 14.7 could work well for idle. Good luck.
 

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BestGuess

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next on the to-do list is exhaust. This car is an original 4 cylinder car and I want to keep it single exhaust. Got to get some more piping to make the Y pipe from the two headers and plan on running a single 3” exhaust out the back in the stock location. I have the wideband, just no exhaust to put it in yet. All other sensors seem to be working. I don’t have the IACV wired up as I’m using that output for something else. But I was able to crank the car today briefly and it idled on it’s own with the TB adjusted to be open a little. Once I get a few things more squared away I’m going to work on the tune for sure.
 

BestGuess

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I'm new to nitrous tuning and don't currently have a SSR to use to pulse the nitrous in. But I am using the FIDLE output to control the on and off of the solenoid and using the SpareADC as the input for the nitrous. Currently the kit I have is supposed to be jetted for a 125 shot and I will be using it as a dry shot. The kit I have is an old Nitrous Works plate kit where the plate bolts right behind the TB. I'll be running E85 and the injectors I have are around 850cc I think.
 

DOHCtor

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May 23, 2004
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next on the to-do list is exhaust. This car is an original 4 cylinder car and I want to keep it single exhaust. Got to get some more piping to make the Y pipe from the two headers and plan on running a single 3” exhaust out the back in the stock location. I have the wideband, just no exhaust to put it in yet. All other sensors seem to be working. I don’t have the IACV wired up as I’m using that output for something else. But I was able to crank the car today briefly and it idled on it’s own with the TB adjusted to be open a little. Once I get a few things more squared away I’m going to work on the tune for sure.
Gotcha on the IACV, exhaust and wideband plans. I had the same Nitrous Works plate before. It worked great up to 175 shot, which is max on that plate IIRC.
 

BestGuess

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Gotcha on the IACV, exhaust and wideband plans. I had the same Nitrous Works plate before. It worked great up to 175 shot, which is max on that plate IIRC.
Do you happen to have any pics of your engine with that plate kit? I temporarily have the solenoids hanging off the included hard lines in that kit and I'm wondering how or where I might brace the solenoids.
 

DOHCtor

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I wish I did have pics of that engine. I used flexible nitrous lines, and firewall mounted the solenoids to keep heat and vibration down on the system components. Also makes room to employ proper filters, along with making maintenance and jet changes easier. You could still mount the solenoids to the intake with a bracket, but the flexible lines will make life much easier.