My turbo street truck has recently started to crank for a looooooooong time before starting. A preliminary net search reveals things like fuel filter, check valve in the fuel pump.......

What's the best place to start here to figer' this thang out? So far no problem, but I drive this thing often and far, would rather get it figured out first.

 

Fuel pressure bleed down, does it start quicker if you cycle the fuel pump a few times?

 

bump the cranking fuel?

 

I will experiment with multiple key cycles next time I'm driving it and see if that makes a difference..

Doug, what exactly in the cranking fuel? Cranking VE table or something else??

I have also wondered if richening up the primary VE table in the idle area cells would help. It idles pretty lean, sometimes pegs the WB lean while idling long enough.....

 

so once you determine its not a mechanical issue

look under Engine> Fuel >Cranking Fuel> FA (fuel adder) Multiplier stage 1 vs time and bump fuel like 5% all around as an experiment. it takes a while since you want a cold start for every test.

and the going lean at idle could be a couple things.

First I would verify your base running airflow (Engine>Idle>Airflow>base running airflow) actually mathes your idle air needs. alternate tuning this, and your IAC effective area to get your IAC step count to around 50 or so. You'll probably have to do a couple TPS re-learns (i'm sure you know how that works)

once you have a stable hot idle then you can really dial cold starts.

another benefit to having the IAC effective area dialed is that throttle transitions become way smooth since the IAC can soften the airflow with the Throttle Follower

 

recently for no reason, and without you having made any changes whatsoever ?

And what is your definition of loooooooooong ?

Like 2 turns, 5, 10, 20 ? a time period ? other ?

Presumably no fault codes are present ?

 

Yes Stevie, it seems to have come out of nowhere, best I can tell anyways......

Oh boy, hittin me with the data, numbers and whatnot lol. I get it though, it's the only way to really quantify something. Because otherwise it's totally subjective....

I'd roughly estimate that when it does this that it will crank for 5 seconds with nothing... Then I'll back off the starter and try again... Same deal.....

I should also mention.... When it's doing this, I will crank as mentioned in the line above and when I release the starter it will go totally (or nearly) quiet and THEN, the engine will fire off!!

I have only been able to drive it once since posting this but today I fired it up cold and I cycled the key a few times before attempting to start and it fired INSTANTLY... Kinda points to a fuel pump check valve or maybe a fuel pressure regulator??? (Stock LQ4 Reg)

Nah, no fault codes, other than the failed MAF of course since I'm 3 bar SD.

 

If it was a ck valve, you should be able to turn the pump on, wait for it to pump up,
then try a start. Depending on what operating system, some you can adjust the fuel prime.
Since it was ok, I would look for something, maybe do a comp. tune, plugs, fuel filter, etc.
You could even have dirty injs., not allowing a good prime. Those things are hard to track down.

 

For over 10 years I ran pumps with no check valves and a system that bled down. Never in that time has starting ever taken 5 seconds.

Maybe 2 seconds at worst, but rarely even that. So there is no way that is in any way a problem.

By all means check fuel pressure when cranking and starting.

Check for fuel being injected ( not too much, not too little )

Check for spark

And of course check there is air available.

 

Were you removing the check valves from the pumps or using pumps that didn't have them?

 

I never use check valves with 044's

But I moved to an in-tank setup with 450's in the last year or so.

 

That can be a timing error such as crank sensor or the reluctor wheel has moved. Only a guess as this can be a lot of fuel problems also.

 

Is this a swap into an older vehicle?

Andrew

 

It's a 90 GMT400 with an 03 ish LQ4... Been driving for a year or two since I built it... Drive it all over the Oklahoma City Metro.. I have noticed that 1st crank cold it fires off instantly. If I drive it somewhere even in town and park it..... THEN I have to crank on it for a while for it to start again.

 

id check fuel pressure like others mentioned

if you don't have one you can rent a fuel pressure gauge from autozone and see what it's doing in each instance

key on (does pressure build and hold or bleed off)
then while cranking, running (whats fuel pressure vs manifold vacuum)

like you said, could be a regulator, pump check valve or maybe a leaky injector

you can pull the rail with the injectors still attached, prime the pump and see if any are leaking

 

I had this exact issue on 2 vehicles. Started fine when cold but when warm it would damn near sound like I killed the battery. Both came out of no where and it was the same fix for both. I increased heat shield at the starter I added an addition hot cable to the starter and i added big *** ground to the motors and both cars are fixed and running still to this day. All the extra heat under the hood just finally took its toal on electronics so I fixed it
Maybe not your issue but a easy enough one to fix

 

Yep, I need to check the fuel pressure. All good suggestions. I'm thinking the injectors ought to be OK, I decapped them and flow tested the **** out of them on my shadetree flow bench before I put them in... Doesn't mean they're still good of course, but I'd think they would be.

Good info. Thanks for the suggestion. I don't think it's the heat, because last summer I drove it around and saw the hottest coolant temps I have with this setup with the shitty fan that used to be in it. Anyways, ECT was like 215-220*F IIRC was the hottest I ever saw it, I'm sure the underhood temps were pretty high also.. Never did it then though???

You're spot on about grounds. I learned the hard way from previous vehicular debauchery that you can never have too many grounds. I put pretty thick ground cables going between: block, body, frame.. A few of them are even redundant with extra grounds duplicating those three main areas.




Now let me ask you guys this... I stabbed a cam in this thing a ways back and subeone on this very forum was kind enough to help me get the idle airflow stuff dialed in after I installed the bigger cam.. I have always done all of my own tuning, thanks largely in part to all of the talent floating around on this board, among others.. RonSSNova, truckdoug, ddnspider, ChopperDoc, subeone, Lsxford, BCNUL8R... I'm probably forgetting some because it's kinda late and I'm a few beers in at this point, so apologies to anyone if I have forgotten! Anyways, subeone got me fixed up where it was much better than before.. However, the RPM sometimes will dive down, and rarely... the engine will kill out.... I'm not bitchin! Super grateful subeone et al! But, I wonder is there more improvement to be had there that could be causing this?

 

Quick check to identify if fuel - spray brake cleaner (1-2 sec) into intake manifold and give her a crank. If it responds well, you need to chase fuel supply pressure or parameters.

 

I have all the same exact issues that the OP does.

1) Car will start within 1 revolution (instantly) when *Cold*
2) In a taco bell drive though for example, when idling for a long time and waiting for people to give their orders, things get hot... After I finally give my order, I turn my car off so the people behind me can hear their order (my car is loud). But It takes a SCARY amount of cranking before it finally fires up. To the point where I feel "****, im stuck here in a drive through" and it'll finally start *whew*. I'm talking maybe... 1st hot crank continuous for about 20 revolutions. letting off. Then cranking again for 20 revolutions... letting off. Over and over, before it finally starts.
3) After a cold start, and once things warm up, when I come to a stop sign and go to neutral, my RPM's will drop to 500 and the engine will almost shut down.

So all 1, 2, and 3.... are exactly the same problems OP is having. DarthVader replied to my thread on this here: https://ls1tech.com/forums/pcm-diagn...dle-issue.html

Keep in mind, I haven't yet had a chance to try much of his suggestions (post 6 specifically) as I've been out of town. But he understands the issues pretty well, and has a good idea of what to change. Just wish I had time. (Thanks again Darth). Maybe those parameters will help you.

EDIT:

Lsx 427 swap - Speed Density - Open Loop - All sensors in working condition as far as I know - No fueling problems...again, as far as I can tell/know. However, My problem #2 tells me that all my cranking isn't actually helping it start, it's simply just needing to cool down enough to be able to start again. Perhaps the cranking however IS helping, by cooling down the rails (billet rails + aluminum intake manifold heat soak?) - and finally allowing it to start...

 

Thanks for the input guys, gonna chew on this for a bit and think about it.