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

[Mr_Roboto]

Interesting, does the inhg go closer to 29" when you close the throttle more. If that reading is accurate it seems like you're near the stalling point.

 

[Thirdgen89GTA]

Interesting, does the inhg go closer to 29" when you close the throttle more. If that reading is accurate it seems like you're near the stalling point.

Can't close the throttle at all with the MAF plugged instantly dies. W/O Maf plugged in, it will hit 2300rpm-2500rpm and hold steady without any throttle at all. IAC counts are much lower with the MAF unplugged too.

 

[Thirdgen89GTA]

Example of datalog with MAF unplugged.

No throttle from me, it goes straight to 2800 and will stay there on its own without any real difference in IAC.

 

[Turbocharged400sbc]

wow low manifold vac even at that rpm ...steady?

.71v seems like too much from my memory

 

[Turbocharged400sbc]

block off brake booster, just in case the diaphrams leaking.

god its acting like a vac leak

 

[Turbocharged400sbc]

wait the datlogger shows 29" but the PIDs show 9"? wtf?

 

[Thirdgen89GTA]

wait the datlogger shows 29" but the PIDs show 9"? wtf?

Yes, I'm not quite sure where the vacuum reading in the upper left comes from.

I think it might be a reading from when the car is off?

I don't know, I'd have to take a look see with the key in Run and the engine off.

 

[Turbocharged400sbc]

okay that would probably be the key on barometric reading don't worry about that

 

[Mr_Roboto]

Yes, I'm not quite sure where the vacuum reading in the upper left comes from.

I think it might be a reading from when the car is off?

I don't know, I'd have to take a look see with the key in Run and the engine off.

That seems logical, we are ever so slightly above seal level. Atmospheric is about 29.9 InHG at sea level.

 

[Thirdgen89GTA]

wow low manifold vac even at that rpm ...steady?

.71v seems like too much from my memory

Reading up on that last night. The tps is non adjustable because the pcm calibrates it on every start. As long as the TPS reading is between .5-.9v the pcm will take the reading and call it zero percent.

And it does look like I'm going to have to drill the air bleed hole larger to get enough minimum air to idle.

The only thing that still has me scratching my head is the super high idle with the maf unplugged. I would thin it would still stall regardless if it want getting enought air to run.

 

[Turbocharged400sbc]

if you think its the air bleed hole, stick a feeler gauge at thelip of the blade to hold it open more and restart. thing is none of yer logs show it maxing the IAC steps to 255 like it wasnt getting enough idle air.

 

[Thirdgen89GTA]

if you think its the air bleed hole, stick a feeler gauge at thelip of the blade to hold it open more and restart. thing is none of yer logs show it maxing the IAC steps to 255 like it wasnt getting enough idle air.

160 is max iac count on LT1s

at times ive seen the logs hit 130 just before it dies from lack of throttle.

the iac counts when im giving the car throttle arent worth much.

 

[Thirdgen89GTA]

The first, with the falling pink IAC line is the car in speed density. IAC falls as it tries to bring the idle down, but the car continues to idle high.

The 2nd is the car in with the MAF plugged in, The IAC counts remain about 100-110, but I'm already giving the car between 6-8% throttle JUST to keep it idling.

The 3rd is with the MAF plugged in trying to start the car with no input from the pedal. As idle falls below 900, the IAC ramps up to 160 before it fails and the car stalls out. This happens within just a few seconds. The Blue line is the MAP. The black vertical line is where all the snapshot data is coming from.

I'm learning as I'm reading, and perhaps their isn't a mechanical problem.

The base tune came from MadZ28, when I compare the tables between the Stock 95 F-body M6 tune I have, there are ZERO changes to the speed density tables. Its actually scary how little was done. The only changes made were to the Spark advance tables, no fueling changes, nothing. I figured that since he has so much experience with LLoyd Elliot tunes that he'd be able to get it running well enough but instead I am basically running a stock tune.

Thankfully, I have TunerCAT and am wiling to learn to tune it on my own as soon as I get a wideband in there. But first I need to get it running.

 

[Thirdgen89GTA]

And last is a short snapshot of me trying to keep it going by giving it throttle when it starts to stall, and then lifting.

The IAC count here is pegged at 160.

The vertical line here is two snapshots from the valley and peak of the graph indicated by the vertical line.

The only thing that really annoys me is the massive idle speed w/o the MAF plugged in.

 

[Turbocharged400sbc]

dude it sure is seeming like a vac leak double check your inj sizing and etc in the tune, we gotta figure on a little overlap and a lower than oe idle vac, but it shouldnt be that low.

whats the exhaust smell? rich? clean? changes at rpm/stall point?

 

[Mr_Roboto]

what about a captain obvious question here what about a vacuum gauge to be sure that everything is good with the MAP sensor?

Is the timing more advanced or retarded with the new tune? Also you may need to put more idle fuel in and the vacuum could go up at that point. Just a thought. Start with about 5% or so then add about 2% at a time. Be leery of adding too much, but if you're "seeking" where it's bouncing up and down there's a good chance that's part of your problem. Then progressively bring down the IAC counts and see if you can get it to not stall. You may be out of fuel on the bottom left of the table.

 

[Thirdgen89GTA]

Engine will not run with any tune unless throttle is given. I've tried the stock 95 M6 tune, and the one provided.

Wish I could go out there and try something for 10 minutes, then come back, but still stuck at home today. Hopefully weather will be nice enough tomorrow and I can head up there and try some of things in this thread and get more data logs.

I also have to switch out the pure water in the engine for some regular coolant since the temps have dropped so much, and a possible freezing night is definitely here. No sense in risking a cracked block because it had straight water in it.

 

[Turbocharged400sbc]

yeah make sure you toss a vac gauge on it, and delete the brake booster hose to make sure its not a vac leak source (old cracked/leaky diaphragms dont always make a hiss audible in the cabin)

plug the vac gauge into as many different vac port locations as possible, the one point that has a drastically varying pulsation of the gauge needle may be near the vac leak. you may have to get it near the stalling point.

make sure you get back to us with the exhaust smells as its dieing out or at the held throttle "idle"

i have to believe that the engine is lean from a vac leak looking at the consistently lean NB o2 voltage

 

[Thirdgen89GTA]

yeah make sure you toss a vac gauge on it, and delete the brake booster hose to make sure its not a vac leak source (old cracked/leaky diaphragms dont always make a hiss audible in the cabin)

plug the vac gauge into as many different vac port locations as possible, the one point that has a drastically varying pulsation of the gauge needle may be near the vac leak. you may have to get it near the stalling point.

make sure you get back to us with the exhaust smells as its dieing out or at the held throttle "idle"

i have to believe that the engine is lean from a vac leak looking at the consistently lean NB o2 voltage

The O2's are kind of useless as they are 1" from open air. They constantly read lean unless the engine is held at a high enough RPM to prevent open air from touching them.

Since its flanged I really don't have a way to close the exhaust up with an extension.

 

[Turbocharged400sbc]

ah crap

if you have scrap pipe, you can shove it in there and block the outside with a rag to prevent reversion readings.

your not going into closed loop from the looks of things?

gah everything about this says it has a vac leak...tps closed the damn thing goes to no manifold vac quite quickly

 

[Turbocharged400sbc]

yeah dude the highest yer vac gets is ~15-16 "hg at a rev and throttle letoff. i would expect to see 20+ at a snap rev even with a big overlap cam.

 

[Thirdgen89GTA]

Well, put a mech. vacuum gauge on it. With the MAF unplugged so it would idle, it only had 20" at 2600, throttle blades closed.

With the MAF plugged in, and someone giving it enough throttle to idle @ 900rpm, I had 1" of vacuum.

So I have a huge leak, and its either the intake, or one of the heads.

I had thought to confirm it. If I pull all the rocker nuts so the valves close, and seal the front of the intake could I so a neg. pressure test? If all the valves are closed, would I need a vacuum pump to do it, or could a Mighty Vac generate enough vacuum? If the valves are closed, and all of the vacuum ports sealed, would the intake hold vacuum on its own? Or do the valves leak enough normally that I'd need a vacuum pump to test this?

Mostly just to confirm without lifting the heads off the car.

I have a stock LT1 intake I may swap to to confirm if its the intake or not. But if the head side intake sealing surface isn't flat that wouldn't do anything for me either.

So, how to test the intake/heads for vacuum/sealing issues 101?

 

[Turbocharged400sbc]

smoke a cigarette and blow into the brake booster hose

 

[Turbocharged400sbc]

there is the distinct possibility that you poured it a little too much away and a thin area cracked so look carefully if you did any porting work

 

[Xfirez51]

Have u pulled the spark plugs? Are they all similar or is there one w a different coloring or no coloring? Amazing that a motor would idle w 1" Hg vacuum. Doesn't sound right.