Need help/ideas as to the cause of this No start on first try issue

[BAD LS1]

Couldnt find anything close to this problem in a search, so here we go!

I dont have any one vehicle to post a tune of but im looking to get some idea to help theorize what is taking place or better still the order of events needed for the engine to make a quick start up.

Here is what happens:

The complaint is the engine will not start on the first attempt, you hold the key and it just cranks and cranks and cranks. let off the key back to "ON" for a split second, crank it again, bam instant authoritative light off! Not EVERY time though does it need this proceedure however.

Commonality between the vehicles that do this: All are Gen IV conversions, PCM types are '99 plus, and the platforms truck, F-Body, and Vettes. All have had aftermarket stroker cranks and aftermarket cams and cam timing sets. Some are in the vehicle the PCM came from, some are swap vehicles. No Cranks sensor or cam sensor codes are pressent, the LS2 conversion kits did have the cam sensor wiring verified (they didnt start at all or for shit when wired wrong) and are using the the stock gen III crank sensors. These conversions are using the LS2 sensor and the half moon reluctor on the big cam gear. Case learns have been performed on the vehicles that would allow it to work, no change.

To me it allmost seems like there is no crank signal. Problem is that i cant tell for sure because the scanner disconnects from the PCM everytime you go to crank to start the engine. However the tach doesnt appear to "wiggle" at a couple hundred RPM like it does when a normal starting vehicle is cranking. The things start and run perfect after that second key hit though. Fuel pressure has been proven adequate (60 psi) at the rails too on all of these during crank FYI.

So my question is, how does the PCM sync the crank and cam signals to allow it find #1 or however it works to allow an imediate start? Seems that these aftermarket cranks with the supplied reluctor is suspect to me. Could it be off time ever so slightly? Or is there simply some settings in the PCM that should be manipulated to get rid of this event.

There are 4 vehicles i know with the same exact issues... different ages, different CI, different platforms... all one common fault though.

Ideas, thoughts, sugges

[planethax]

Try a charger on the battery when cranking.
That may eliminate the scanner disconnecting during the crank.

[98Camarod]

what are the fuel systems?

[HoP]

I'd put a fuel pressure gauge on it and verify that you have a fuel pump burst. Make sure your pressure comes at to its preset pressure. Sometimes an aftermarket fuel system can be to large for a 3 second burst and it will not be at its adequate fuel pressure.

Sounds like its low on pressure and then when you try it for the second time the pump then makes up the difference and it lights.

[BAD LS1]

They all do the initial prime when the key is turned on as commanded by the PCM of like 2 seconds.

All but one 2001 truck with a 416 has a aftermarket fuel system, just bigger injectors. And that stock fuel system type (return style) truck had just recently gotten a new GM fuelpump/sending unit, it also has a new gm regulator installed on the rail too and no change. The rest are different variations of return style aftermarket systems.

I do know for fact that 1 of them bleeds down after the prime as i just looked at it yesterday using the electronic fuel psi gauge in the cab, but its a rock solid 60 once its running, obviously weird shit can when its cranking. In theory this could leave dead space in the lines that has to be filled and the volume of fuel has to come forward to make pressure and it all takes time.

[MStefak]

Post up one of the tunes, it sounds like the FA multi stage vs time tables or the pulse mass tables.

I had this issue before when attemping quicker starts. Ive also had issues with the delays as well.

[98Camarod]

They all do the initial prime when the key is turned on as commanded by the PCM of like 2 seconds.

All but one 2001 truck with a 416 has a aftermarket fuel system, just bigger injectors. And that stock fuel system type (return style) truck had just recently gotten a new GM fuelpump/sending unit, it also has a new gm regulator installed on the rail too and no change. The rest are different variations of return style aftermarket systems.

I do know for fact that 1 of them bleeds down after the prime as i just looked at it yesterday using the electronic fuel psi gauge in the cab, but its a rock solid 60 once its running, obviously weird shit can when its cranking. In theory this could leave dead space in the lines that has to be filled and the volume of fuel has to come forward to make pressure and it all takes time.

That's what I was getting at. If you have an aftermarket return style system, the fuel pressure bleeds off rapidly. my system doesn't keep pressure on the initial prime, but the pressure is rock solid once it's running like you said.

[oakley6575]

This is what I have been fighting every single day of the last year since I built my LS motor. I have ls3 injectors so I know the injector data is correct. I have a stock ls3 intake manifold with the returnless rail. My fpr is before the rail with a vacuum reference.

When the truck is warm, if I shut it off and run into the store or wherever, when I come back it takes 2-3 cranks before it will fire. Never fires on the first try. I have tried every singe starting table in the tune without any luck. I get solid fuel pressure during the first crank so I know it isn't an fuel delivery fail.

The only other thing that I haven't been able to check is for leaky injectors. Have you checked your injectors to see if they bleed fuel pressure into the cylinders?

[BAD LS1]

Here is a tune from one of the swap cars with the problems. a 2000 Camaro PCM. 416CI LS3 based, decent sized cam and ported LS3 heads. Return style fuel system, 60 PSI, SD 60 #'s.

The car was tuned on the dyno starting with SD first then brought the MAF back on line and it holds a 12.5 AFR and made 490 thru an unlocked, 3000 stall 4l60E and 9" rear. Its has good street manners and runs nice, just is plagued by this second crank to start issue.

[C5XJEDIX]

my exp is the longtubes on the cranksensor/ wires are harsh!i just got done with this exact same problem here .three tow's later ,and all of the grounds checked/fixed/improved vats disabled!then it died on me again/followed by cranking with no spark or inj pulse!my tech exp that screems crank sensor!then it finally thew a code for a crank sensor!
i checked crank endplay-damaged sensor /and the connector.i replaced the sensor and the connector pigtail! so far so good!put about 200 miles on it!.my sensor did have about 130k on it!prob the only stock thing in my ride!lol
2001 vette auto with a callies 408 lQ9

[BAD LS1]

Interestingly enough, the 2001 Silverado with the 416 and stock type fuel system just stopped by! So i data logged the cranking issue. Now for it to fail, it has to sit for about 2-3 min, and crank it for about 4-5 sec and RPM reads about 168, injector pulse width comes up but doesnt even fart, the out of the blue it will light. You shut it off, and try again it immediately pops on the first hit.

I thought i had the tune for this truck in this computer, but i dont have it avail to look at right now as he already left.


Take a Peek!

[BAD LS1]

FWIW, while this was taking place, the tach was dead ass laying on zero... any other time when it starts normally the tach does indeed wiggle around off the needle.

I read or heard somewhere that the tach inside the vehicle on GM vehicles use the cam sensor to give it its marching orders? i always thought it was off of crank signal... can anyone add to that?

[oakley6575]

Its funny that the vehicles we have problems with are all rectangle port heads.

But I am suffering from the same crap everyday. It is frustrating and it seems like there is no end in site.

[wyochimneysweep]

Did u replace the stock steel heads with aluminum heads?

[oakley6575]

Did u replace the stock steel heads with aluminum heads?

? What steel heads?

[BAD LS1]

? What steel heads?

Only ones i can think of were like the 99-00 LQ4's?

Anyway yes, Every single one of my problem childs are reqtangle port jobbers too! Aside from this issue they can be a real PITA to get part throttle driveabilty anywhere as close to how nice the cathedral port head mills seem to act.

[oakley6575]

Only ones i can think of were like the 99-00 LQ4's?

Yea that's what I was thinking.

Anyway yes, Every single one of my problem childs are reqtangle port jobbers too! Aside from this issue they can be a real PITA to get part throttle driveabilty anywhere as close to how nice the cathedral port head mills seem to act

I'm right there with you. I don't see the part throttle driveablility issues so much maybe because my converter is so loose. But when I'm cruising on the freeway, 70mph with the converter locked, it isn't as smooth as I would like. I just don't know which way to move spark. I wouldn't be against some tfs or afr cathedrals. Maybe 235cc or something. Of course that would come when I get a huge payday.

[oakley6575]

I only have hard starting issues when the ect is high (anyting above 160). Cold starts are perfect. It is a MYSTERY and can't seem to find anyone with good advise

[Sam88gta1]

Subtract 5% from the cranking fuel table until the problem goes away.

[oakley6575]

Subtract 5% from the cranking fuel table until the problem goes away.

Yea I wish it was that easy