24x SBC conversion starting issues

[evilstuie]

Hi All,

I've just rebuilt my motor after some unfortunate block, head and cam damage, and I'm back to where I was previously which is getting the thing to start and run properly.

This time around I made sure the motor was at TDC on compression stroke and set the vortec dizzy in place before lowering the motor into the car, so I'm fairly sure that side of it is correct.

Previously the car would cough splutter and backfire when I tried to crank it over.

This time around (I've only tried twice so far) it almost started, and then just wound over without firing, I'm wondering what else I should check before continuing to try?

I've attached the tune file, along with the last scan I did, as short lived as it was.
Plugs are clean, leads are good, crank sensor was working fine prior to rebuild.

Build is a 408 SBC stock bottom end, -12cc pistons, around 10.8:1 compression, AFR heads, Holley stealth ram intake, MAFLess setup, 28lb injectors, XFI280HR cam, 1.6 lifters, 4l60e transmission and 24x conversion, coil per cylinder etc.

[evilstuie]

So it's starting now, but I feel like the vacuum is way too low, MAP is high, and it seems like there's a vacuum leaks somewhere.
The TB screw is open to about 0.68v for idle.

I haven't done a CASE relearn yet, as i need to get the car to a point where i can take my foot off the throttle without it dying.

Ben is helping out with the tune, but I don't want to waste his time if I still have things to dial in before we log and do a start changing stuff.

The log file is attached of the start up, I had the throttle open to about 10% to get it to 1400-2000rpm to warm the motor up and let everything settle.

Also I've set up the wideband on the EGR wire and set up the tables in the VCM scanner, are these correct?

AFR = ([2811.10]/0.5)+9.8
AFR Error(%) = 100*((([2811.10]/.5)+10)-14.27])/[2811.10]/.5)+10
AFR Error(ratio) = (([2811.10]/.5)+10)/(([2811.10]/.5)+10)-14.27)

Where 14.27 is the stoichiometric AFR.

[Oleblu]

My laptop is down right now so I can't check anything. You should definitely do a crank relearn, smoke test it. And confirm correct fuel pressure.

[evilstuie]

Fuel pressure is definitely good, right on 58psi, as I installed a gauge to monitor with the wideband to make sure the pump is keeping up once I finally get to tuning the upper rpms.

I'll do a smoke test this afternoon if I can, the crank relearn is a little more difficult, as from what I understand I have to rev the car up to the limiter and then release the throttle and let it go back to idle.
Does it need to stay at idle to successfully store the new settings, or is it ok if the car dies, and then I just cycle the ignition for the 15 seconds?

[evilstuie]

Vacuum was sitting around 5-7"hg which is very low, I'm trying to work out what is causing it and how I can eliminate those to identify the roots cause.

So far I have:
Manifold leak - all gaskets are new, all vacuum lines are accounted for and no leaks there, only leaves inside the lifter valley if the clowns at the engine shop have milled the heads or block surface on an angle.
Too lean - The log shows the AFR around 12-13 in spots, I'm wondering if too lean at idle can cause low vacuum, or if it only works the other way (i.e. low vacuum/leak causes leaning)
Timing - I've read if the spark timing is too late it can cause low vac, but from the logs, it looks like it's giving it 36-39degrees advance, so I doubt that's the cause.
Valve adjustment - I went through and rotated the motor by hand about 4 revolutions and adjust each loose valve to zero lash and then half a turn after that and locked them, so I doubt there could be an open valve, but it's possible. Also timing chain was installed correctly, both dots line up perfectly at 12 & 6 o'clock.

All header tubes are warm, so I'm getting fuel and spark to each cylinder, confirmed over and over again that the wiring for injectors and ignition is correct.
Either the tune is wayyyyy out, or there's a ton of air getting in the motor somehow.

I thought I had a vacuum leak before the motor was rebuilt, befcause I only had 10-11"hg vacuum at idle, but the MAP sensor was getting 50-55kpa at idle.
Now with a change from a 110lsa(XR270HR) to 113lsa cam(XFI280) I've got less vacuum, and the MAP is reading around 75kpa at idle.

The only change to intake that was made was the TB screw was opened up to around 0.68v to get the car to start.

[Ben Charles]

If memory serves that?s a 242/248 cam roughly??
75 Kpa around 900rpms is about right...

12-13 is actually rich IMO at idle..I?d run that setup 16.0 maybe leaner

[evilstuie]

If memory serves that?s a 242/248 cam roughly??
75 Kpa around 900rpms is about right...

12-13 is actually rich IMO at idle..I?d run that setup 16.0 maybe leaner

Hey Ben,
Its' 230in/236ex @113LSA from the cam card.

I'm going to pull the intake this afternoon anyway and check the head intake sruface angles against the block and then the intake surface angles, check them for straight edges etc, and then check the clearances with no gaskets and with a gasket on one side, and see if some math plays out to show the problem.

[evilstuie]

So the intake is back on, thicker gaskets and a small line of hardening gasket sealant around the intake ports just to make sure. Torqued it to 10ft/lbs left it overnight then torqued it down to 25ft/lbs.

I also replaced the top and bottom o-rings on the injectors, doubled checked all vacuum hoses for cracks or leaks, and made sure the distributor is set exactly on TDC compression at #1 cylinder and aligned perfectly when seated.

And the car doesn't want to start.
The good news I guess is there is no backfiring, just doesn't want to go.
I've tried closed throttle, slightly cracked, flutteirng the pedal, and wide open.
The exhaust pipes on the headers are warmish, so I'm confident there's spark, and there's definitely fuel, but no firing.

Any ideas?

Also I've confirmed with a guy on the thirdgen forums with an identical setup as mine that he had 50kpa idle at 850rpm, and much higher vacuum reading.
If I can get this bastard motor started I should be able to see if I've fixed the vacuum issue.


I also have a set of EV-1 36lbs/[email protected] Bosch part number: 028015586 injectors on order to make sure I have sufficient fuel in the high-rpm if the motor ever makes it, but for now its the ls1 injectors.

[TheMechanic]

Sounds dumb but check the brake booster vac line. Pull it and plug it.

[evilstuie]

Sounds dumb but check the brake booster vac line. Pull it and plug it.

I tried that but no change.
Also I pulled the brake booster vac line off 2 days after trying to start it and there was still vacuum, so the booster isn't leaking either.

[It Will Run.Maybe]

your firing order is still set for the LS not a Gen1 SBC. needs to be changed. firing order set wrong.PNG

[evilstuie]

your firing order is still set for the LS not a Gen1 SBC. needs to be changed. firing order set wrong.PNG

My harness has been repinned for the correct firing order, because as I understood it the firing order was not able to be changed in the PCM. That was why GM repinned the Express Van harnesses as opposed to using the LS1 style harness I thought?
When the PCM goes to fire Cyl#4 on my motor #7 is the one actually firing. Same with when cylinder #2 is fired, it actually fires #3 etc.

[It Will Run.Maybe]

i been doing allot of research on this. about to buy the 24x kit myself with the cam sensor built into the cover. from what i read u have to repin the harness for the injectors and coils and also change the firing order and injection timing in the pcm like in the picture i posted. it was something about the pcm cant actually change it thats why u repin it. but u have to change it in the program so it knows the correct order to do it in still. im posting a screenshot of what i researched.change in tune and wiring needed.PNG

[evilstuie]

Yeah, injectors and coil pins for cylinders 4&7 and 2&3 are repinned to fix the firing order. The 0411PCM has the order hardwired into the PCM so you change it via the wires.
Injector banks in the tune are changed for the closed loop to know which injectors are assigned to what bank, but the firing order table in HPTuners (ECM 14000)...i have no idea if it does anything, I think it's just there as a reference.

[evilstuie]

Well I checked everything and it doesn't want to go.
It almost started once but died before it even got going.

If I stop cranking at a particular time there's a horrible metal bang noise, like the flexplate is about to snap off, but only if I stop at a particular part of the cycle.
It's almost like the firing sequence is off, but I've quadruple checked the injector and ignition wires are pinned correctly to the SBC firing order and cylinders.

Spark plugs are wet, but exhaust ports are warm.
Power and grounds to injectors and coils.
Spark plug gaps set, wires resistant tested and confirmed, leads on correct plugs.

Log attached.

The only thing I have left to try tomorrow is to just try and set timing to maybe 8 degrees in the VCM Scanner tools, and increase by 2 degrees for each attempt and see if it needs more or less crank timing to start maybe?

[evilstuie]

Fuck me!

Checked everything again and had spark and fuel at all cylinders but still didn't want to go.
Pulled the plugs and some were sooted right up, some looked like they'd never fired in their life, but still had fuel on them.

So I opened the plug gap up and low and behold, the bastard started

[80gus]

atleast you know the knock sensor circuit is working!!!

[evilstuie]

Haha, yeah I was surprised at that too. That's the old TPI sensor, I haven't put the Express Van one on yet.

It'll be interesting to see though if there's still knock if I pull 4degrees out where it detected. As it hasn't been calibrated, I'm a little worried if it's picking up something else other than detonation, e.g. valve clearance issues or something.
I've still only got about 8" of vacuum, haven't been able to check on idle yet. It still feels like there's a miss as well when it's on low rpm.

[80gus]

Im watching with interest as im building a 24x big block.

[evilstuie]

started it again today, took a fair few cranks but it went. All plugs are set to 0.045" gap, still feels like a little bit of a misfire, and vacuum is still sitting at 8"HG, but stable. temporarily decreases on throttle, jumps up to 12-13" on throttle release and then back to 8", so it seems to have the right characteristics but just low, maybe its just the cheap vacuum gauge.

Anyway, time to start tuning with Ben and see where we get to.