GM Having teething issues with new LT1 build, need some advice.

Thirdgen89GTA

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Engine is in, car all sensors hooked up, and car is doing some strange stuff.

If you attempt to start the car with the MAF plugged in, it revs to about 2k, then dies unless you start feeding it throttle. You need an initial surge to keep the engine going, but if you slowly lift off throttle it will settle to a 900rpm idle with about 5-7% throttle. However, remove your foot and it dies immediately.

After everything I've read that sounds like a MAF issue, or a vacuum leak issue. I haven't ordered a new MAF yet, but thats the next step. The reason I haven't is that when the engine is started the MAF AFGS readings seem correct. about 5-10gm/s varying by idle speed.

So the recommendation is to pull the maf plug and start the car. Well, then it starts right up, but the idle is insanely high, 2500-3000rpm.

The parts:

11:1 LT1
Ported stock heads
Ported LT1 intake
Lloyd Elliot 231/239 110lsa cam
Long tubes
new plugs, wires, O2s, knock sensor, IAC motor. Still original TPS, and MAF.
MadZ28 base tune loaded. INJ Constant is correct for the SVO Redtops adjusted for 43psi base pressure.

I tried to search for a vacuum leak, but every port is sealed tight. Spraying carb cleaner anywhere made zero difference in idle.

Fuel pressure checks out, steady 45psi on the guage.

All injectors are firing, checked with a noid light for signal, and ohm'd the injectors, all checked out good.

Opti is a brand new GM unit.

TPS voltage is reading accurately. Smoothly goes from 0-100% on the TTS logs too.

If anyone has TTS Datamaster, I have logs I can post if you'd like to see them.

Engine is currently open header, so I am not sure if the knock retard is applicable, its pretty damned loud. I don't have a y-pipe fabbed up yet.

No codes at all.
http://home.comcast.net/~thirdgen89gta/cars/datalogs/start1.uni
http://home.comcast.net/~thirdgen89gta/cars/datalogs/start2.uni
http://home.comcast.net/~thirdgen89gta/cars/datalogs/start3.uni
http://home.comcast.net/~thirdgen89gta/cars/datalogs/start4.uni
 

Thirdgen89GTA

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Open header? So what about the O2 sensors?
They are in and the readings swing like they should. But the car hasn't even gotten warm enough to go closed loop for very long. It went cl a few times but still would not run with maf plugged in.
 

Mr_Roboto

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Try taking a small vac line loose and seeing if it lets you idle right. If it does, then you probably need to drill a small hole in the TB unit or enlarge one if it's already there. The reasoning behind this is that you have increased the air flow of your engine at idle, so the IAC can't open far enough to keep the engine from stalling (higher VE means you'd pump more air, and in turn you need more air to maintain an idle RPM.) Check your IAC position in the logs, and sanity check your MAF readings as well. This is on the presumption it's a new cam and heads
 

Thirdgen89GTA

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Try taking a small vac line loose and seeing if it lets you idle right. If it does, then you probably need to drill a small hole in the TB unit or enlarge one if it's already there. The reasoning behind this is that you have increased the air flow of your engine at idle, so the IAC can't open far enough to keep the engine from stalling (higher VE means you'd pump more air, and in turn you need more air to maintain an idle RPM.) Check your IAC position in the logs, and sanity check your MAF readings as well. This is on the presumption it's a new cam and heads
MAF reads about 6-10gm/s with 7% throttle to get it idling at 900rpm or so.

I had planned on upgrading to a F-body MAF later on anyways, but with the fun trying to diagnose it I bought an F-body MAF anyways. I imported the F-body MAF tables into the tune but haven't had a chance to try it yet.

The IAC counts with the MAF unplugged were about 50-70.

With the MAF plugged in they quickly ramped up to 120-130.

Its new everything really. Not a single part remains from the old engine except for the steam tubes, valve covers, and accessories.
 

NOMIEZVR4

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I'd stick a boost pressure tester on the intake snout to really sniff out any leaks...don't go insanely high on the pressure...but if there are leaks..you will find them.
 

Thirdgen89GTA

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egr valve off its seat causing vac leak?
All emissions deleted, and turned off in the tune. I did wonder if it was leaking from the block off plates, but couldn't find anything with a can of carb cleaner.

The TB is a stock ported unit, brought up to 52mm. I swapped in a stock 48mm LT1 TB, but it made no change.

I hate being able to work onthe car weekends only. I have it stored up at my Dads house, and its about 40 miles north of me. So I can only really work on it weekends, its too dark by the time I can get out there during the week, and its stored outside.
 

Thirdgen89GTA

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you sure the cam was installed straight up and not adv/retarded excessively?
it's installed dot to dot with the crank at 12 and the cam at 6. The teeth are too big to let you be off. It's also a new lt4 timing set which doesn't have any adjustability in cam position. Sprocket only fits one way.

Rotated several times to verify the timing was correct. Lined up at 12 and 6 every time.
 

Turbocharged400sbc

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its fucked, 3800 swap time.

get a mech vac gauge and see if the vac ready is really jumping around or if its artificially low.

other poss is thats not a 1 bar map
 

Thirdgen89GTA

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its fucked, 3800 swap time.

get a mech vac gauge and see if the vac ready is really jumping around or if its artificially low.

other poss is thats not a 1 bar map
Factory original map sensor. Suppose it might have possibly gone bad.

Will have to rent a vac. Guage next weekend.
 

wolfe

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Is the tps set up correctly? I know some of them you have to check with a volt gauge to make sure its giving the correct reading when closed.
 

Turbocharged400sbc

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just because TPS looks smooth through a slow data Scanner... hooking it up to a good glitch capture dso will still usually show dropouts that cause lots of odd issues.
considering the age of yours it might not be a bad idea to just put a new one on.
there's no chance that you tighten down a rocker and pushed a valve into a piston is there?
 

Thirdgen89GTA

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Is the tps set up correctly? I know some of them you have to check with a volt gauge to make sure its giving the correct reading when closed.
just because TPS looks smooth through a slow data Scanner... hooking it up to a good glitch capture dso will still usually show dropouts that cause lots of odd issues.
considering the age of yours it might not be a bad idea to just put a new one on.
there's no chance that you tighten down a rocker and pushed a valve into a piston is there?
Valve lash was set at zero + 180*. That was what was recommended for the LS7 lifters. I had them submerged in oil before installation, and manually drove the pump with a screwdriver before setting lash. Is a consideration though. I suppose a compression test would reveal that.
 

Turbocharged400sbc

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ideally with any cam that exceeds OEM valve lift you should be setting the lash or tightening those rockers with the cylinder at the closer to bottom dead center lobe base circles
 

Thirdgen89GTA

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Why, every time I've ever heard of having lash set its always been make sure that both valves are on the base of the cam and off the lob. Which is usually on the compression stroke.

If the piston is on the compression stroke near top dead center wouldn't it be almost a guarantee that the I/E valves were flat on the base of the cam? I know there is a bit of overlap with this cam, 66°.

I've always done them on the compression stroke ATDC so I could set the lash for both valves on the same cylinder at the same time.
 

Turbocharged400sbc

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ideally you do it on the compression stroke with it near bottom dead center so there is no chance the valves can push open and hit the top of the piston like it can when most people set it near TDC compression
 

Turbocharged400sbc

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with the lifters pumped up and having to bleed down you end up opening the valve a lot farther than it would under normal conditions
 

Mr_Roboto

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I don't think it's a vacuum leak, I think it's actually the opposite problem. You may not get the idle down much below 900 just because of the fact that you're running a decent bit of overlap. I ran into this problem with a 305 TPI where I used a throttle body that the IAC passage got covered up on. After that it's possible you may be able to fudge the fuel trim and timing to bring the idle RPM down lower than that. Is it choppy at all at 900 RPM?

Bump your IAC counts to say 180 or so and see if it gets any better, or as said pull a SMALL vacuum line. if either of those work you may need to enlarge or add a hole in a TB blade.
 

Thirdgen89GTA

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Its kind of hard to tell right now. Its dumping straight out the headers, so there is a ton of noise.

Its actually quite smooth at 900. You can definitely hear a cam, but its actually quite smooth compared to what i expected.

It has less overlap than a CC306 does.
 

Mr_Roboto

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Interesting, how many inhg or what's your kpa level at 900? I would try bumping the IAC counts and seeing if it goes away, then tune from there when you don't have your foot glued to the gas. At some level messing with idle fuel and timing is a pain in the rear. Whatever you do don't try and do it by O2. With as much overlap and being open headers, your odds of it working remotely well are pretty slim.
 

Thirdgen89GTA

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Interesting, how many inhg or what's your kpa level at 900? I would try bumping the IAC counts and seeing if it goes away, then tune from there when you don't have your foot glued to the gas. At some level messing with idle fuel and timing is a pain in the rear. Whatever you do don't try and do it by O2. With as much overlap and being open headers, your odds of it working remotely well are pretty slim.
Wasn't planning on doing anyting based on O2's till I got a Wideband in the car and did the Wideband hack to log it with the rest of the PCM data. O2's right now are basically in open air.

Here's a 'snapshot' of the log. Its taking from the "Start4" log in the OP. I could probably export the logs into CSV format if anyone wants them that way.
 

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