evilstuie

Riddle me this Batman...

400SBC with EFI-connection 24x conversion done.
36lb injectors, XFI280 HR cam, stock 400 bottom end with 5.7" rods and -12cc valve relief pistons, AFR heavily ported heads, 1.6roller rockers, stock 4l60e and convertor.
0411 PCM, vortec timing cover, correct crank sensor, vortec dizzy for 1x cam signal, ls1 harness repinned for SBC firing order, tune file correct (cept for fuel/spark) base cranking spark around 15degrees.

Extremely hard to start the car, 30+ seconds of cranking, and throttle ranges and it will eventually fire up (sometimes)

During cranking, cylinder #1 exhaust port is dead cold. Spark plug works, coil is working, lead is working, injector is working (spark plug has fuel on it when pulled as well)
Cylinder #7 feels cold as well
Cylinder 2 is slightly warm, but only slightly, 2,3,4,5 are nice and warm, 8 is slightly warm.

When the car does fire up, idle vacuum is only 6-7", feels like it's missing, rev it up and throttle response is great, sounds very strong.
Vacuum is steady at idle but low.
Vacuum rises 3-4" when throttle is opened and then closed then reverts back to 6-7"
Vacuum stays the same with pcv valve line, booster blocked, no egr installed.

So my question is...What the F%^& is going on with my motor?
Until I can get it to start easily and idle on it's own I can't tune or drive it.

According to the vacuum gauge stuff I've read, vacuum would fluctuate rapidly if there was a issues with one or 2 cylinders, but it's steady
Low across the board would say vacuum leak, but the manifold gaskets are new and sealed properly, extra vacuum lines blocked off to eliminate from possible causes.
Multimeter and noid tested everything, all grounds read correctly, all voltages are good, battery 13.1 volt.


Any ideas?

kossuth

iTrader: (12)

Che70velle

iTrader: (6)

evilstuie

Hey Che70velle,

I made sure to adjust all the valve using a method I found on you tube, installed everything and just turned the engine a bit each time and tighten everything up until it was just catching on the lifter, then 1/2turn to pre-load the lifter.
They're hydraulic roller lifters, they'd been installed before, but I didn't bleed them down/out or anything because they had sat for about 3-4 weeks before reinstalling them in the motor after a rebuild.

I had a mechanic mate come and watch me do it to make sure I did it right so I'm fairly confident I did it right.

That being said I'm out of any other options, so I miight back them off each 1/4 -1/2 turn and see if I can any increase in vacuum or easier starting, as I'd rathere have some lifter noise and know where the issue is than a phantom problem.
I'm going to get the compression and leak down testers out today and just check before I adjust them, and also pull the rocker covers and crank it just to make sure I haven't wiped a lobe somewhere.

Che70velle

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Darth_V8r

iTrader: (4)

I've seen from time to time when somehow a coil pack gets reversed or flipped so the sparks fire in the wrong order. Typically I see that when the brackets are relocated. Also check for bent pins on your coil subharness connectors.

evilstuie

Well it just gets ******' weirder...

Apologies for the language, but I'm lost...

Coil pack are correct as I've tracked PCM pins back to the coil plug connectors, not the bank connectors

I swapped 1 & 3 packs and plig leads to see if it made a change, it didn't.

Pulled plugs 1&3 and checked the plus themselves were firing, and confirmed the spark is VERY strong.... Also don't shortcut and try 2 plugs at the same time, as the weakest link may be you and you'll feel firsthand the strength of the spark.....

Got my mate to also crank with my thumb on the plug hole, it felt like more suction than compression, but the throttle body/throttle was closed at the time, so that made sense.

I pulled the valve covers off to make sure a lobe hadn't wiped and everything looks good, all valves moving and appear ok./....

As far as I can tell, everything spark fuel and air is a go....
The crank reluctor can only go on one way, and even if cam sensor/vortec dizzy was fucked, it would still go after 4 seconds of cranking, so short of a crank sensor wheel being cut wrong, i really dont know what to look for to solve this....

Darth_V8r

iTrader: (4)

Damn. I was going maybe something simple. Usually when wrong cylinders are firing you backfire through intake.

It seems like you have been very thorough too.

Is there a spare ECU you can try?

pantera_efi

iTrader: (1)

Hi Evil, sound like a common problem WHEN the Cam Sensor in not wired correctly.

TRY a reverse of the TWO outside wires on the cam sensor. (push- to -seat)

Lance

evilstuie

I do have a spare, I'll have to use a different tune but it had started on that one before, it's worth a try.

Cam sensor is avortec dizzy, I got the pin assignments from Mike at EFI Connection as below:
Cavity A must receive 12V.
Cavity B must be connected to ground.
Cavity C is the signal wire. You will test for signal voltage on this wire.

I've tried cranking without the sensor plugged in and there's no difference. I was told the cam sensor isn't required to run as it just tells the engine whether it's on compression or exhaust stroke, and if the car doesn't start after 5 seconds of cranking it, it would 180 the thing anyway.

kossuth

iTrader: (12)

Hmm.... I would pull all the plugs out of the motor, pull the fuel pump and ignition fuses, and do a full compression test with the throttle wide open. I know it's a new motor, so it's not broken in and the compression could vary wildly, but just need to make sure it's making over 100 psi of compression and you don't have some exhaust valves cut wrong or something like that. That's about the threshold where you get ignition problems from lack of compression. I know you said the vacuum gauge was steady, but I'm almost throwing that test out at this point. This is weird, because if the reluctor was cut wrong it's illogical that it would run at all and as others have said if it was mistimed you would think it would backfire at some point.

evilstuie

See here's the shitty thing, I've found 3 different pinouts for the same vortec dizzy.
Here's a tutorial to diganose a bad cam sensor on a vortec, and it has the wires completely different again:
http://troubleshootmyvehicle.com/gm/...e-cam-sensor-3

I would assume if I had it wired wrong, I would get a DTC error from high/low/missing voltage or signal but there aren't any.
I would go through and just try all combinations, but wouldn't that have a good chance of killing the sensor?


What you have said would make sense I think, if the wires are crossed that would screw up the signal? or would it still work the same, as the 12volt would still be sent to the signal wire when the tab passes the sensor.

evilstuie

Looks like I'll have to wait for the oscilloscope to arrive. Did a quick test according to the previously posted troubleshooting link, and attached the positive terminal of the battery to the multimeter to check the ground. I then went to check the 12volt pin on the connector but forgot to change the battery terminal to ground, but someone registered a reading of 1. something volts....

Maybe the cam signal sensor packed it in, not too sure.
I've ordered a new one to change it over, but maybe that's where the issue is coming from?

Edit: Probably not the cam sensor but a rogue ground wire going to 12 volts, or 12 volts going to ground somewhere maybe?
Or possibly the PCM has crapped itself, even though I can communicate, it primes the pump, and I can successfully load a tune file from HPT.
Is that possible?

00pooterSS

iTrader: (40)

This is a long crappy process but I would hook a timing light to each cylinder and see where it's firing.

Find TDC for each cylinder (one at a time or make marks for each cylinder) and make a mark on your crank pulley and cover or where ever is convenient, then run the motor and see if you're firing each cylinder near the mark or if it's several degrees off (30, 60, 90 for example) and go from there.

Also for long cranking, make sure your fuel pump holds fuel pressure after you shut the key off. If the pressure immediately drops when you shut the key off then the check valve in the fuel pump has gone bad and is letting all fuel drain back to the tank.

evilstuie

That does sound shitty LOL
It also sounds like the only definitive way to test it and make sure its firing correctly, so I guess I'll do that.
Another tool I'll have to buy (didn't think I'd need a timing light anymore) but I didn't really think I'd have need for an oscilloscope during this build either.

Regarding fuel pressure, I know the pressure drops off as soon as I stop cranking, I was under the assumption that was because of the pump/regulator design, the regulator is a chinese Tomei knockoff, but I know it's holding pressure as I crank because I installed a fuel pressure sending unit and gauge in the car to monitor.

evilstuie

Ok, it's really WTF time now...

Pins on cam pos sensor connector should be:
A=GND
B=Signal (return signal so nothing)
C=12v

Mine is different depending on key on/off (just listen)

Key Off:
A= GND Resistance=130k
B= GND Resistance=130k
C= GND Resistance=130k

Key On
A= 13.4v
B= 12.86v
C= 1.15v
What's really f^&*ed up, those are the reading while the negative clamp on the multimeter is connected to the positive terminal on the battery....

Key On (multimeter terminal on ground)
A=0.02v Resistance=130k
B=0.02v Resistance=86k
C= 12V Resistance=90k

I'm not sure where to start with trying to understand why physics and electrical currents etc don't seem to apply to my car, but how can you get a voltage reading on a multimeter across two 12v sources?

At this point I'm tempted to pull the entire wiring harness from the car, and start again from scratch.

It sounds like a ground connected to a positive source or vice versa but I would assume I'd have a wire cooking somewhere for that to occur...

MuhThugga

Is your engine properly grounded?

Che70velle

iTrader: (6)

codyvette

iTrader: (24)

Try running a ground wire from the engine directly to the computer case and clip it on with a pair of vice grips. I kno it sounds screwy but it only takes a minute.

00pooterSS

iTrader: (40)

Like you I didn't think I'd need a timing gun ever again, but I did the above process on a volkswagen that some jack *** tech screwed up really bad and it lead me to my problem. On that car the crank sensor read off the flywheel and the dude put the flywheel on 90 degrees off. Even though it had an asymmetrical bolt pattern he still managed to fubar it.

Or lort, yeah you need to do some serious wire digging.


When I need to do quick checks like that (running a ground or hot somewhere for a quick check) I use jumper cables. Quick and easy. I use them to simulate and engine ground from the battery, power straight to the starter etc. When I need small wires I have a 30ft roll of wire with alligator clips. But most people have jumper cables so it's why I recommend those, makes for a tip people can easily use.. usually.