Warm Start stumble/multiple attempts... where to start looking?

[petethepug]

I found out the hard way that the crank position sensor / CPS can go bad and not throw a code. It had hard starts, slow starts, no starts & stumbling out starts until it finally gave a P0335 and the tach died.

Just as soon as the engine is restarted, symptoms are gone. Two weeks later, same. Ironically the cps on our 02 Audi allroad did the same until it refused to start.

 

[Charlie207]

Yes, after shutoff the heatsoak causes it to go up. Think it's normal.

My fuel pressure rises to about 84psi after every shutoff. Watched it via my Torque App 5 times yesterday, and did a screen record on a couple of them, but Imgur only allows 60 second video clip uploads. Either way, the pressure slowly rises to ~84psi over the course of about 2 minutes.

As for holding the gas-pedal to the floor prior to turning the key, yes, that prevents the engine from starting. After I let off the accelerator and turned the key again, it fired right up.

 

[Charlie207]

check valve in the fuel pump, high under hood Temps and no return line. it is what it is.

It was 12 degrees yesterday. I can't imagine there were high underhood-temps.

Where is the fuel pressure sensor located?

 

[Charlie207]

NM...this video explains it. Looks miserable.

 

[Doubeleive]

It was 12 degrees yesterday. I can't imagine there were high underhood-temps.

Where is the fuel pressure sensor located?

I would guess that outside temps really do not have much to do with it, provided it had been driven and was up to normal operating temperature first. heat rises you def do want too touch a hot engine even it is -40 below. the fuel rail is right there at the top where the most heat is and as soon as you re-start it within a couple seconds the fuel pressure is going to return to normal. you can watch the gauge literally drop like a rock back to 44psi
if the fuel remains high after a re-start then you may have a issue.

 

[Charlie207]

I would guess that outside temps really do not have much to do with it, provided it had been driven and was up to normal operating temperature first. heat rises you def do want too touch a hot engine even it is -40 below. the fuel rail is right there at the top where the most heat is and as soon as you re-start it within a couple seconds the fuel pressure is going to return to normal. you can watch the gauge literally drop like a rock back to 44psi
if the fuel remains high after a re-start then you may have a issue.

Nope, fuel pressure drops instantly to 44ish, like you describe.

Might be worth firing the parts cannon at a new CPS, to see if that helps. Or, maybe a new TPS too.

On a side note, would a new TPS help with sluggish* throttle response.

 

[mikez71]

I found out the hard way that the crank position sensor / CPS can go bad and not throw a code. It had hard starts, slow starts, no starts & stumbling out starts until it finally gave a P0335 and the tach died.

Just as soon as the engine is restarted, symptoms are gone. Two weeks later, same. Ironically the cps on our 02 Audi allroad did the same until it refused to start.

Same thing happened with my '94 BMW 318ti, bad crank pos sensor.
Started off as a couple hard cranks before intermittent starting, and finally failing on me while driving.
Old CPS wiring insulation was disintegrating into gummy twizzler like material when I took it off..

BUT since Strutaeng's flood clear start method works.. Guess he maybe right!

Something similar I read on hptuners forum.. GenV's use fuel trims to determine transmission pressures..
And as the injectors age and leak, fuel trims go down, causing trans pressure to drop and start causing problems.
Dunno how true..

 

[hagar]

Did your tuner reply back? I have been a tuner for 20 years, and it is mega common to need to tweak the hot start with a cam. You generally have a guessed base adjustment on cranking VE to compensate for the change in cranking efficiency from a cam. You start with a rough learned value based on the application, then it sometimes needs slight adjustment to dial in. It's never an issue when cold because all the extra air density has no problem lighting too much cranking fuel.. it becomes a problem when the engine temp is up.
It could be adjusted too much, or too little, just takes a quick couple changes to nail down.

 

[Doubeleive]

Nope, fuel pressure drops instantly to 44ish, like you describe.

Might be worth firing the parts cannon at a new CPS, to see if that helps. Or, maybe a new TPS too.

On a side note, would a new TPS help with sluggish* throttle response.

I am not saying it is your issue, but I personally wouldn't bother with replacing just a tps I would just buy a new throttle body, if it was from a money standpoint I would just buy a used one and roll the dice.
*sluggish might not be the throttle body, that's when I would take a closer look at the maf and see if it is causing shift issue's
if it was jerking and shifting funky that definitely points me to the maf IF the transmission is known to be good
if it "coughs" so to say when giving it pedal for no other reason that has been the throttle body in my experience OR if it idles weirdly low to almost shutting off.
in any case I would try and look at the scanner data and see if anything rears it's head before firing the parts cannon.
check for any vacuum leaks, check that the intake is on securely, especially around the maf and throttle body any un-metered air is going to cause problems
I have seen the maf cause a multitude of problems, my experience has been that at or around or after 160k the maf can be a problem. 160k on a maf is eol in my book

 

[mikez71]

Did your tuner reply back? I have been a tuner for 20 years, and it is mega common to need to tweak the hot start with a cam. You generally have a guessed base adjustment on cranking VE to compensate for the change in cranking efficiency from a cam. You start with a rough learned value based on the application, then it sometimes needs slight adjustment to dial in. It's never an issue when cold because all the extra air density has no problem lighting too much cranking fuel.. it becomes a problem when the engine temp is up.
It could be adjusted too much, or too little, just takes a quick couple changes to nail down.

Hagar! Long time no talk (since I had that KR issue)

Is this the adjustment, or somewhere else?

 

[hagar]

Hagar! Long time no talk (since I had that KR issue)

Is this the adjustment, or somewhere else?

View attachment 445574

That is the primary culprit right there! Change all the 100s to 85s as a start, and it should fire up much much better when hot.

 

[hagar]

See if 85 helps. If it gets better but still struggles, go to 82. If it gets better at 82 and still struggles, go to 80. Go until it stops getting better and starts getting worse, then back up to the best point. If it isn't starting perfect at that point when hot, let me know and we can go into the throttle opening tables. The modern stuff is all about balancing the throttle opening with crank fuel, and then how it comes down from the points you find that get it started. The ve cranking should fix it with the small cam, but not all small cams act the same. Sometimes things just stack up weird with cams and air intakes and exhausts and stuff. Normally straight forward, but can once in a while need a little more attention. I am sure this is the case with your tuner. Just one of those ones that normally works well, but things in your combo are creating an abnormality.

 

[Charlie207]

See if 85 helps. If it gets better but still struggles, go to 82. If it gets better at 82 and still struggles, go to 80. Go until it stops getting better and starts getting worse, then back up to the best point. If it isn't starting perfect at that point when hot, let me know and we can go into the throttle opening tables. The modern stuff is all about balancing the throttle opening with crank fuel, and then how it comes down from the points you find that get it started. The ve cranking should fix it with the small cam, but not all small cams act the same. Sometimes things just stack up weird with cams and air intakes and exhausts and stuff. Normally straight forward, but can once in a while need a little more attention. I am sure this is the case with your tuner. Just one of those ones that normally works well, but things in your combo are creating an abnormality.

Is there a more generic suggestion I can give my tuner - BlackBear Performance - to look into for the warm-start stumbles, that won't bug them? I still haven't heard back, but assume they are off for the holidays, which is fine.

I'm not really a fan of having the data locked down so I can't even see what I'm logging. And, even worse, there are literally zeros dyno-tuners within any reasonable distance.

 

[hagar]

Is there a more generic suggestion I can give my tuner - BlackBear Performance - to look into for the warm-start stumbles, that won't bug them? I still haven't heard back, but assume they are off for the holidays, which is fine.

I'm not really a fan of having the data locked down so I can't even see what I'm logging. And, even worse, there are literally zeros dyno-tuners within any reasonable distance.

He will know how to fix it. No need to tell him what to do, it's super common knowledge for someone that tunes as much as him. I was giving some DIY advice if it was changeable on your end, if he has it locked down, all you can do is wait.

Locking tunes is a choice some make, I have personally never locked a tune in my life. You either know what you are doing or you don't. I have done tunes for people while knowing they fully intend to try and reverse engineer it, it has never once created a competition for me. The numbers are useless if you don't fully understand what they all mean, you can't just input numbers from one tune into another, unless you want just a generic tune like a handheld store bought, for a near stock vehicle. I think some people do it also so it doesn't make them look bad if someone messes with things and breaks something, but as far as I am concerned, you paid me, it's yours to do what you want with. I of course tell people to not mess with it, but it's their vehicle to do what they want. I bet 50 percent of the stuff i tune these days has its own hp tuners because people thought they wanted to learn how to tune, but couldn't figure it out. Lots of them have the training books and everything. If you know how to tune, and read those books, it's comical the info they give you. It's like giving a mechanic a single screw driver, and telling him to rebuild an engine.

 

[mikez71]

I have seen a couple 'tuning school' videos that don't seem to tell you anything.
It's like they're reading the descriptions off of the HPtuners program.. (can't do, teach!)

I've heard good things about cringers videos (from others that seem to know what they're doing... )
Still need to watch them, but I think it's over my head..

SilverSurfer77

This channel is filled with really neat stuff.

www.youtube.com

"adjust cranking VE" (Volumetric Efficiency) ... @hagar said.
Thanks for that hagar!

 

[Charlie207]

I have seen a couple 'tuning school' videos that don't seem to tell you anything.
It's like they're reading the descriptions off of the HPtuners program.. (can't do, teach!)

I've heard good things about cringers videos (from others that seem to know what they're doing... )
Still need to watch them, but I think it's over my head..

SilverSurfer77

This channel is filled with really neat stuff.

www.youtube.com

"adjust cranking VE" (Volumetric Efficiency) ... @hagar said.
Thanks for that hagar!

I'm happy with the rest of the tune, it's just the warm start issue.

 

[hagar]

I have seen a couple 'tuning school' videos that don't seem to tell you anything.
It's like they're reading the descriptions off of the HPtuners program.. (can't do, teach!)

I've heard good things about cringers videos (from others that seem to know what they're doing... )
Still need to watch them, but I think it's over my head..

SilverSurfer77

This channel is filled with really neat stuff.

www.youtube.com

"adjust cranking VE" (Volumetric Efficiency) ... @hagar said.
Thanks for that hagar!

As far as I am concerned, if you don't know enough to build a custom camshaft in your head while being told the combo of the engine, you don't have enough knowledge to be a competent tuner. You need to have that perspective of how and why things work, to know how to tune. It's not coincidence that all the good tuners are old guys. I am getting old at 42, but I was lucky enough to start when I was 20 and things were just coming on line. You seem above average on understanding stuff, but the next step is to fully understand the reason things are being done. You should see how crazy it gets with coyote cam timing and shit. Don't stop learning at the basics level needed. The more you learn, the better you become at the basic.

 

[mikez71]

You are getting old at 42.. but I'm even older! (+8)
I appreciate your vote of confidence, but I'm simply never gonna gonna get there!

Yet, I will try to pickup any low hanging fruit that comes my way..
..so I appreciate all your explanations.. (and everyone else's)

Internet is a boon forsure.. made it possible for this forum!

MERRY CHRISTMAS TYF!

 

[mikez71]

Read of some other changes to help startup. Dialing in VVE being the base of it..
But there is a startup airflow (idle) map as well...
I wonder if multiplying those values by .85 would be the same as adjusting cranking VE to 85? However this map references temperature, unlike cranking VE map.
Or does this affect transition after starting to idle speed only?
(Does engine run time include cranking time?)

I know BBP will fix it, just posting for our(my!) own curiosity..

..

 

[hagar]

Read of another method to help startup...
There is a startup airflow (idle) map as well...
I wonder if multiplying those values by .85 would be the same as adjusting cranking VE to 85? However this map references temperature, unlike cranking VE map.

I know BBP will fix it, just posting for our(my) own curiosity..

View attachment 446241..

I use that table as well. Some big cams have a hard time finding idle, so I will often use that table in conjunction with initial idle rpm adder vs time at start up to give the engine a crack of the throttle at start up, then bring the idle down over a short time gradually. As a bonus it sounds cool. Lots of exotics start like that.. quick rev after start, hold for a few seconds, then they come down to idle.