Hard to start when engine is cold

86_Capri · Mar 14, 2026

Mustang5L5 said:
Save your tune and make a new one. Try this table. This is specific to my car so it may not be perfect, but curious if these changes here make your cold start issues better.

Set your Cranking Pulse to these numbers

Set your priming pulse to these

Log your cold starts, and a few hot starts as well. Pay attention to your AFR. You have a delay of 30 seconds and active under 150 degrees so the widband won't adjust fuel under that time/temp and just reads a value. If you are still seeing numbers under 12.5 or so you are way rich. Ideally you want to cold start in the 12.5-13.0 range, and as your engine warms up you will want that to climb up closer to your AFR table setting as the ASE tapers off.

Based on logs i saw, assuming no fault int he wideband you were just pegged at 7.5.

Ok I’ll give it a shot. I really appreciate your help with this.

Mustang5L5 · Mar 14, 2026

Just make sure you save the current tune you have elsewhere.

Mustang5L5 · Mar 14, 2026

Also, recalibrate your TPS min and max. I was seeing ranges of -35 to 131 for TPS values as you were working the throttle. SHould be 0-100.

86_Capri · Mar 14, 2026

Yes I saw that too. I think something might be hanging up on the gas pedal in the car.

Mustang5L5 said:
Also, recalibrate your TPS min and max. I was seeing ranges of -35 to 131 for TPS values as you were working the throttle. SHould be 0-100.

86_Capri · Mar 14, 2026

I made the suggested changes to the priming and cranking pulse % and the car fired right up (you are good!). Now the down side is the car willonly run for a few seconds or so and then stall out unless you keep it going with the throttle. I also saw a min afr of 7.5 again on the datalog, I'm not sure that is correct though because I thought I saw between 12 and 13 on the gauge so I'll have to look into that. Any ideas on what my next move should be?

Mustang5L5 · Mar 15, 2026

It’s probably still fuel related if I had to guess. Probably needs more or less, but the AFR being stuck at 7.5 is odd. Which wide band/controller are you using?

I’ll take a look at this log later on tonight

86_Capri · Mar 15, 2026

Mustang5L5 said:
It’s probably still fuel related if I had to guess. Probably needs more or less, but the AFR being stuck at 7.5 is odd. Which wide band/controller are you using?

I’ll take a look at this log later on tonight

I believe it’s the innovate MTX-L gauge and the sensor that came with the kit. I was wondering if adjusting IAC percentage would help. I’m just trying to think of different things here, you’re obviously way more knowledgeable with this than I am.

Mustang5L5 · Mar 15, 2026

I wouldn't touch anything else for now. I still think this is fuel-related and you can probably tweak it further to get the startup a little bit better. Problem is with the AFR stuck at 7.5 it's hard to know what adjustments need to be made. You are prob still a bit on the rich side, so pulling some fuel out of the ASE might be what is needed here to get it to idle on it's own after start.

I'm curious why you are seeing 12-13 on the gauge, but the MS is only seeing 7.5? I'm not familiar with this wideband so not sure of how it operates. When you cycle the key to on and crank you are immediately seeing correct readings on the gauge?

I do notice right at 34 seconds, it jumps to 11.4. I wonder if there is a warm-up procedure needed and it doesn't take a reading until that is complete. If so, you'll need to make sure this is done before you cold start and take a log.

Once this is sorted out. You'll want to do a log from cold start crank and out to engine being warmed up. That way you can see how long the ASE lasts for and if it stops too early or doesn't add enough fuel later. But first need to figure out the AFR issue

86_Capri · Mar 15, 2026

Ok I won’t mess with it. As for the wideband. When I turn the key to the on position it displays “htr”. I’d have to look at the manual again but as far as I can remember there is a certain amount of time needed for the sensor to heat up before it can take a reading. I’ll have to double check on that one though

Mustang5L5 · Mar 15, 2026

For the sake of tuning, you might need to wait until the sensor is heated up before you crank and get your initial cold start datalog. Really what you would look at is the AFR immediately when it fires, and in the initial 10-30 seconds after start. That will tell you if you need to pull fuel from your cranking pulse, or add/remove fuel from your after start enrichment. If you are in the 11-12 range after start, I could see it being hard to maintain idle. In that case I’d remove a little fuel and try again and see if you can get it to be around 13.0-13.5 after start where it might run a bit smoother.

Oh and you’ll have to do this for a wider range of temps. Cold starting at 50 degrees will use a different cell than cold starting at 85 degrees, so what you do here might need to be adjusted when temps are warmer later this summer. Usually less fuel for warmer temps.

If you have an hour to kill, watch this video. Not all will apply but about halfway through it talks about what I’m mean with regards to ASE and the taper lenght and how Steve is trying to maintain a certain AFR. Might make more sense here after watching a bit of it.

But this is what logging that AFR is key for tuning. You can also watch it real time and make adjustments based on what you see real time.

View: https://youtu.be/GjyyWQhGGJE?si=SkMDynpvFiCBZIPY

86_Capri · Mar 21, 2026

Mustang5L5 said:
For the sake of tuning, you might need to wait until the sensor is heated up before you crank and get your initial cold start datalog. Really what you would look at is the AFR immediately when it fires, and in the initial 10-30 seconds after start. That will tell you if you need to pull fuel from your cranking pulse, or add/remove fuel from your after start enrichment. If you are in the 11-12 range after start, I could see it being hard to maintain idle. In that case I’d remove a little fuel and try again and see if you can get it to be around 13.0-13.5 after start where it might run a bit smoother.

Oh and you’ll have to do this for a wider range of temps. Cold starting at 50 degrees will use a different cell than cold starting at 85 degrees, so what you do here might need to be adjusted when temps are warmer later this summer. Usually less fuel for warmer temps.

If you have an hour to kill, watch this video. Not all will apply but about halfway through it talks about what I’m mean with regards to ASE and the taper lenght and how Steve is trying to maintain a certain AFR. Might make more sense here after watching a bit of it.

But this is what logging that AFR is key for tuning. You can also watch it real time and make adjustments based on what you see real time.

View: https://youtu.be/GjyyWQhGGJE?si=SkMDynpvFiCBZIPY

I’ll have to take a look at the video when I get a chance.

86_Capri · Mar 21, 2026

So it turns out there was more to my issue than just the tune. My coil was on its way out and finally just quit altogether. I did wind up taking the car to get dyno tuned yesterday and it did pretty good. It’s not perfect on start up yet. Probably still a little rich and the idle surges until warm but eventually smooths out. The car will occasionally stall out when put into gear if you don’t give it some throttle to keep it going. It looked like the iac was possibly sticking and recovering quick enough. We put a different one on while at the dyno and it definitely helped, so I have a new one on order. I can post up the current tune and a data log to see what you think.

First picture is estimated engine power and the second is power to the wheels. Overall pretty happy with it.

CAMTWO1070 · Sunday at 2:39 PM

86_Capri said:
Hoping I can pick your brains here. I just recently started having an issue where my car wont start when the engine is cold. I have fuel and spark. I'm able to get it to light of by hooking a remote starter up and advancing the timing and working the throttle. Once the engine starts I return the timing back to 20* btc and it runs and idles good. A little info on the setup, 5.0L controlled by a microsquirt (tune is not finished) GT40P heads, aftermarket cobra intake, Comp Cams 35-302-8 cam, 65mm bbk throttle body, and 2.5" flowmaster exhaust.

Steve(a91what) had worked with me to get the car running and idling pretty good with out stalling. This was back in 2019. I would drive the car occasionally, but life got busy and the car took a backseat. Since then I've the car on occasion over the last year or so and it ran pretty good considering the tune is no where near finished. It always started within a few seconds of cranking and didn't need any input from the throttle. Now last week I went to take the car out and I had a heck of a time getting it started, but finally did after flooring the pedal while cranking to shut the injectors off. After I came back from my drive, just a few miles, I shut the car off and then was able to restart it while it was still hot without an issue. So at this point I'm thinking the problem is bad gas. I drain the tank down past 1/4 and fill it with fresh 93 octane a few days later hoping this would fix the problem. Unfortunately it didn't. So does anyone have any idea why this would start happening all of a sudden?

It seems that you need to fully research your parameters of your modifications as they are needed to know to get the tune dialed in.

First thing you need to do is scale your fuel injector timing and spark timing to match the Camshaft...

Your Comp Cams 35-302-8 camshaft plays a huge role in how your engine breathes, especially when you are cranking it over cold.

When you change the camshaft, you change how air moves through the engine at low speeds.

How the Camshaft Affects Your Cold Start

Less Vacuum: Your aftermarket camshaft has more duration and overlap than a stock cam. This means the engine does not pull a strong vacuum while it is cranking.
Low Air Speed: Because the air moves slowly during a cold crank, the fuel does not mix well with the air. Instead of staying as a fine mist, the fuel turns into big drops and sticks to the cold metal walls of your intake manifold.
The Result: The engine needs the right amount of fuel to catch, but your old settings might now be throwing in way too much fuel for the low amount of air entering the engine.

Fuel Timing Events (Injection Timing)

What it is: Fuel timing tells the MicroSquirt when to open the injectors in relation to the position of the pistons.
The Problem: If your fuel timing is off, the injectors might be spraying fuel onto an intake valve that is closed. When the engine is freezing cold, that fuel just puddles up.
The Fix: When you work the throttle to get it started, you are letting in a big gulp of air to dry up those puddles. As your tune is unfinished, your injection timing table likely needs to be adjusted so the fuel sprays right when the air is moving fastest.

Spark Events (Ignition Timing)

What it is: Spark timing tells the spark plugs exactly when to fire.
Why Advancing It Helps: You mentioned that advancing the timing with your remote starter helps it fire up. When an engine is cold and flooded with fuel, the mixture burns very slowly. By advancing the spark, you give the fire more time to burn that heavy, wet fuel mixture.
The Problem: Once the engine warms up, a fast spark is too much, which is why you have to turn it back to 20 degrees for a good idle. Your MicroSquirt has a specific table for Cranking Advance. Right now, that table is not giving the cold engine enough advance to ignite the bad mixture.

Good Luck getting it fully dialed in. then save that tune as youll most likely have a tune for each of the seasons or atleast 3 unless you know how to use the automatic weather correction tables..

Hard to start when engine is cold

86_Capri

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