I'm looking for some help on getting my car to have a better cold start. This is only a issue with the first cold start of the day. As I spin the engine over, it takes about 2 seconds before the engine very slowly comes to life. It flares up very slow. Now if I shut the car off immediately and restart the car, it fires up perfectly. The BRAF and IAC counts are dead on.


I am running e85 and the fuel pump is a Walbro 535 - No Check valve.

Has anyone else experienced this and is there anything in the tune that I could modify to correct this issue?

thanks

 

Yeah, sounds like you need more fuel if you are running E85 when it's cold. E85 is very hard to light off when cold and you need to richen it up substantially in most cases.

 

okay I can add more fuel. I did already add 35% to the FA stage 1, but what confuses me is, if after the weak cold start, i shut the car off and immediately start it again....coolant temp is still basically the same....it will fire right up.

 

Can you post a log/tune?

 

Your fuel pressure is draining back overnight because the pump has no check valve. The engine has to refill the lines before it starts, causing the slow crank. The second start is instant because pressure is already there.

The real fix is adding a check valve to the fuel line. You can try tweaking the "cranking fuel" in the tune as a temporary band-aid, but it won't solve the root problem.

 

It drains back when you shut the key off regardless if it's over night or not.

It builds pressure as soon as you turn the key on unless the pump is weak.

OP, cycle the key twice or turn they key on, wait a couple seconds, before a cold start and see if it makes a difference. I'm guessing it doesn't.

My car is on E85 w/ ID 1000's and it starts just fine regardless of the temp. I haven't touched the cranking fuel tables.

Without a log and tune, we are just guessing.

 

Here is the tune that I am running now. Thanks for you help!

 

Can you post the log that goes with the tune? I can't tell anything from those screenshots.

 

Here is a cold start from this morning and a few days ago.
The 9-15-25 Delphi 17 has 55% added to the FA Mult stage 1 and 2. The 9-11-25 Delphi 16 tune has 40% added to the FA Mult stage 1 and 2

 

interested in this... my '11 5.3 in my '86 C10 acts the same way. to add a kicker, I have the dual tanks working & 2 AC DELCO 238 in tank pumps and when running pass. pump the truck fires right up with very little/no "stumbling", but the driver side pump it stumbles and has a hard time with initial startup and if sitting for a time......

 

Keep in mind the FA Multipliers are only for cranking so that's half the battle. I would also modify the OL EQ ratios and richen those up substantially in the colder areas and try to throw more airflow at it as well in the colder regions.

One other thing, are you flashing in your changes right before taking these logs? In order to fail over to SD mode it takes a couple of ticks for the computer to switch from MAF mode to SD mode every time it's flashed or power is removed. One thing you can do to help smooth out this "transition" to SD mode is to put something like 15 g/s in your first cell in the MAF table or something that makes more sense for your combo. That way it's not trying to idle with only 2.95 g/s of airflow for that very short amount of time waiting to fail over to SD.

 

Heres an update for anyone following: I did what NicD said to do and changed the 1st cell in the MAF table to 15 g/s, added 10% in the OLFA EQ ratio table up to 86 degrees, and 5% in the 104 degree column, I removed 15% from the FA Mult stage 1 and 2 table, So now I am sitting at 40% over the stock FA stage 1 & 2 tables, I also doubled the Prime pulse mass, First Pulse mass and Second Pulse mass. Not really know how this was going to affect the startup.
Results: 1st cold start of the day, .76 seconds of key on to fire, once it started to fire up it took 1.29seconds to flare to 1480 and start to taper down. No dips in the RPM after start. I believe bumping my Friction initial AF up fixed the RPM dipping problem.

So this is best cold start up I've had with this setup. Still room for some improvement but I'm happy these changes put me in the right direction.
I did shut the car off, waited 20 seconds and started it back up and it fired immediately, rpms flared straight up to 1460rpm and tappered down nicely without any huge dips in the RPM.

 

Very happy with this cold start.

 

The dip in RPM after a flash is from the MAF not having failed over yet to SD, that is fixed with the larger value in the MAF table's first cell. Once it's been running and stopped as long as power hasn't been removed it will still have the MAF code stored and it will go to SD immediately next time on start up. I've never had to bump Friction initial on any Gen3 PCM before, not saying that didn't help but that's usually not the root cause of an initial RPM dip.

That sounds good to me. Once it really starts to get cold outside you may find that you need to add even more fuel in the colder areas. On cars running One R I have to add nearly 200% or more to cold start areas, but that is ~93% Ethanol and extremely hard to light off when it's cold.

 

Im not understanding this. What MAF code Are you talking about? The 15 g/s I put that 1st cell in the MAF table?
If I disconnect the battery I will loose this?
Sorry can you please explain this to me.

Thanks for your help!

 

You have a 2 bar Speed Density tune on your car. Every time you flash the PCM or disconnect power from the PCM it has to "set" the MAF code again to fail over into Speed Density and that takes a very short amount of time. But in that time it's trying to use a non-existent MAF so simply putting a value in that first cell of the MAF table that represents a more valid running number will prevent it from wanting to die on startup until it throws the MAF code and fails over.

 

Got it. Thanks for the explanation.

 

Just to add to NicD's explanation, some of the factory computers take longer than others to fail the MAF. I have no idea why, nor do I have a list of which OS numbers are better/worse about this, but it is VERY noticeable in some p59 PCMs. I just put a reasonable idle airflow number in the first MAF table cells on all of them now just in case.