Cranking Issue

[Jgarretts86]

98 pcm, ls2 based 403. Runs great and I have the SD tune pretty dang spot on. The problem I?m having is I have to cycle the key (fuel pump) at least twice for the car to crank. If you try to crank it on the first key cycle, it just spins over with a pop through the exhaust every now and then. If you cycle the key twice, it usually fires right up. This issue is happening hot and cold starts. Issue just started when I changed fuel rails and went from a fast 102 intake to a single plane super Vic with 4500 accufab throttle body. What?s up? I?m guessing not enough prime pulse mass for the big single plane intake. Any help thanks.

[5FDP]

Is fuel pressure at what is needs to be on the first prime??

[kingtal0n]

Yep sounds like either the fuel pressure is bleeding down over time while off,

or

cam sensor isnt plugged in or is bad

[Jgarretts86]

I suspect low fuel pressure in the rails after the key on prime. Like I said after second pump cycle it fires right up. It does this if it?s been sitting a while or just a few minutes. I will put a pressure gauge on the rail and report back.

[Jgarretts86]

I don?t think the injectors are spraying enough fuel into the intake runners on the initial injector pulse. This issue started when I swapped to the super Vic and accufab throttle body.

[Jgarretts86]

Ok, took me a week but I finally got around to checking the fuel pressure....
Key on it primes to 62 lbs.
When the pump stops priming, it holds 55 lbs. and does not drop.
Running pressure is 64 lbs.

I have tried adding up to 40% more fuel to the "Prime Pulse Mass" with no luck. You cycle the pump two or three times the car will fire right up. Am I still not adding enough initial fuel?

[Jgarretts86]

I am also getting code P0343 "Camshaft Position Sensor High Circuit". I hate to think it's the crank sensor. The one in it is an oem GM sensor less than two years old. The car runs fine once it's cranked......

[smokeshow]

Am I still not adding enough initial fuel?

Without posting any files, we can't tell.

[Jgarretts86]

Current tune attached. Again, the car runs fine once it cranks. This issue started when I swapped to the single plane intake and throttle body. Nothing else changed. I've checked my wiring, all looks good. I'm getting that P0343 code for the cam sensor though.

[5FDP]

Code P0103 needs to be on first error and not no error reported.

That VE table put in a nice way is awful, like very awful. Same with the timing, this isn't a small block 350, the timing curves on the LS engines should be way different.

[2xLS1]

Fix the cam sensor code. Doesn't need cam sensor to run but needs it to start first hit.

[Jgarretts86]

Code P0103 needs to be on first error and not no error reported.

That VE table put in a nice way is awful, like very awful. Same with the timing, this isn't a small block 350, the timing curves on the LS engines should be way different.

No offense taken. But I will say the car runs 6.70 flat at 103 in the 1/8 mile on motor with that tune. Very responsive, no surging, and great street manners even though its mostly a weekend track car that mostly sees WOT which is why I just old skooled the timing at 26 degrees where it seems happy. I have a wideband O2 on the car and it stays within 5% of 12.5 afr cruising and at the track. I'm not saying it's perfect, but its running very well on that tune. I know the timing is a band aid and far from ideal, but I don't see how the VE is so bad and it runs so good. I'm here to learn and get advise, so I appreciate the input.

[5FDP]

Just seems hard to believe that it's a steady air fuel ratio when it's like that.



Cruising at 12.5 afr is awfully rich too, not that good for plugs or the engine when there isn't enough air in the cylinders at those speeds. If you are commanding stoich at cruising speeds it should stay around stoich. If you create an AFR or lambda error against the commanded AFR/Lambda it will clean up that VE table and make it worlds better.

Are you running stock LS2 injectors or something else?

[Jgarretts86]

Cruise down the road with same tune attached. Where is my VE bad? I thought I had it pretty good haha.

[Jgarretts86]

I am putting the car into PE right off of idle. If I let the AFR get anywhere above 13.2 under load I start getting a bad lean pop and misfire. Plugs look great. The VE spike at 100 map from 1200 to 2800 is me throwing a lot at it for off idle to wot throttle response. Check out the run log I posted up. And it has stock LS3 injectors.

[5FDP]

Have you even tried running more than 26 degrees of timing in it all the time to stop some of these other issues?

I've never touched a vehicle with that throttle body setup but running 35-45 degrees of timing at cruising speeds seems very do-able. Just seems like it's masking a problem by locking in things the way you are.

[Jgarretts86]

Have you even tried running more than 26 degrees of timing in it all the time to stop some of these other issues?

I've never touched a vehicle with that throttle body setup but running 35-45 degrees of timing at cruising speeds seems very do-able. Just seems like it's masking a problem by locking in things the way you are.

I've put as much as 28 degrees to it at the track with no improvement in et. I know its far from ideal timing for cruising, but like I said it has great street manners as well. Here is another crazy fact. I have the IAC unplugged with this 4500 accufab and it runs great like that. Plug IAC up and it runs like crap. Surging and hanging idle. I just unplugged the IAC at it's closed position and let the throttle body handle the air. It's crazy but it works and work well.

[Jgarretts86]

Back to the cranking issue... What's up with it? I guess the crank sensor is looking like the culprit.

[smokeshow]

You need to diagnose the cam sensor issue first. The PCM needs to know what stroke the engine is on during cranking to know when to inject fuel. Seems like you're pretty content with the rest of it, which is fine...but you can't really know what great street manners are until you have those finer points like part throttle fuel and spark dialed in. What's good now will seem like crap later once that other stuff is fixed.

[5FDP]

My comment about the timing wasn't for performance reasons, more so timing for part throttle and fueling for part throttle.