Hard to start when engine is cold

[86_Capri]

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?

 

[AeroCoupe]

Bad ECT sensor or some other sensor?

 

[86_Capri]

That was one of my thoughts, but I figured since the coolant temp and air temp looked good in tuner studio that they weren’t the issue. They’re easy enough to swap just to rule it out

 

[OX1]

Leaky injector flooding cyl. but that would be only one out of 8, figure other 7 would fire still.
Check fuel pressure? Maybe bleeding down when car sits for a while.

 

[86_Capri]

The fuel pressure does bleed down, but as soon as you turn the key on the pump primes the system and there’s about 38 psi. It just seems weird that it’ll start by manually advancing the timing and then run fine once the timing is put back. Should the Microsquirt be advancing timing during cranking to get the engine to fire? It just seems odd that something like this would happen out of the blue. ‍

Would it help if I posted the tune file?

 

[Mustang5L5]

Would it help if I posted the tune file?

Post the tune file, but it would also be helpful to post a log of a cold start. That way we can see parameters like injector pulse width and how much (or little) fuel is being added during a cold start.

 

[86_Capri]

Post the tune file, but it would also be helpful to post a log of a cold start. That way we can see parameters like injector pulse width and how much (or little) fuel is being added during a cold start.

Ok sounds good. I’ll try and get that asap

 

[AeroCoupe]

If anything wouldn’t you want the timing to retard during cranking?

 

[86_Capri]

I attached 3 different datalogs. First is cold cranking the engine with no manual throttle or timing manipulation. Next is cold cranking with manual throttle manipulation. you be able to see it almost wanted to fire and would slowly turn over even after I let off the remote starter. Finally is a log of starting the engine. It took quite a bit of timing advance and working the throttle to get it to fire, but i did get it to start. Hopefully this is helpful. I wish I knew more about how to read these logs, but unfortunately I don't lol. So I'm relying on you guys to help me out here. Appreciate any info. Thanks!

 

[Mustang5L5]

Can you post your tune file?

Your spark advanced is fixed. Do you have fixed advance, or used table set under ignition settings??

 

[86_Capri]

Whoops, I forgot to set it to use table after I rechecked the timing to make sure it was matched up with tuner studio

 

[Mustang5L5]

Send latest tune, and possible a old version back when the car ran well? You can actually compare tunes in TS to see what the differences are.

 

[86_Capri]

I’ll post it later tonight. I only have one version of the tune though. That’s the weird part, nothing has changed with the tune or the car. This just happened out of nowhere.

 

[Mustang5L5]

OK. I;ll dig in later tonight. I saw the fixed timing and focused on that. But now I know the reason so I can look elsewhere.

 

[Mustang5L5]

S0mething is definitely up with your AFR. During the starts where it wouldn't fire, you were first stuck at 7.5 and then pegged to 22. When you finally got it to run it was still stuck at 7.5 until the After Start Enrichment turns off, and then it starts to read normally.

Post up your tune so we can take a look at your settings. You might have a delay on the wideband becoming active. but for anyone else taking a look...check out the AFR.

 

[86_Capri]

Here's the tune

 

[86_Capri]

I was just looking at the cold start cranking log and I saw that the max spark advance was only 11 degrees. Do we think that could be part of the issue?

 

[Mustang5L5]

That's typical during crank. As soon as engine state changes from start to run, it should jump up into the 20's. Since your timing was fixed the logs don't show the jump. Your cranking RPM is set a little high. You can try experimenting with dropping it down to 350 or just about your crank RPM which seems to be around 200.

You have a LOT of fuel in your cranking pulse. I think ambient temp is about 40 degrees? If so you are dumping around 335% of that particular VE table values. That's a lot. By comparison i'm dumping 185% at the same temp. When you were driving it around, was it a lot warmer out when you didn't have issues?

Your priming pulse values also seem to be high.

My guess is you are pig rich on start which is why it won't start up. I was noticing your AFR was stuck at 7.5 which is very rich, and I wonder if it's because you are just dumping so much fuel in during your cold start.

I bet it hot starts fine as you are putting in much less fuel? I wonder what your AFR ratio is after hot start? Might still be too rich if it's below 12.

 

[Mustang5L5]

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

Your ASE numbers were close to mine. But try less fuel on startup and see if that makes an improvement.


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 on cold start and need to pull fuel from your cranking pulse or ASE. 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. When you get above 150 degrees, the wideband will start adjusting and you can see what percent fuel it's adding on your dash or in the logs.

Based on logs i saw, assuming no fault int he wideband you were just pegged at 7.5 during your starts which means just a ton of fuel. Surprised you don't see it spitting out the tailpipes and smell it?

 

[86_Capri]

That's typical during crank. As soon as engine state changes from start to run, it should jump up into the 20's. Since your timing was fixed the logs don't show the jump. Your cranking RPM is set a little high. You can try experimenting with dropping it down to 350 or just about your crank RPM which seems to be around 200.

You have a LOT of fuel in your cranking pulse. I think ambient temp is about 40 degrees? If so you are dumping 330% of that particular VE table values. That's a lot. By comparison i'm dumping 185% at the same temp. When you were driving it around, was it a lot warmer out when you didn't have issues?

Your priming pulse values also seem to be high.

My guess is you are pig rich on start which is why it won't start up. I was noticing your AFR was stuck at 7.5 which is very rich, and I wonder if it's because you are just dumping so much fuel in during your cold start.

I bet it hot starts fine as you are putting in much less fuel? I wonder what your AFR ratio is after hot start? Might still be too rich if it's below 12.

Yes, it was June when I was working remotely with Steve. Yes it does seem to start fine when it’s hot. So you would suggest taking some fuel out during cranking?