Thumper33

I have my LS1 all installed and it starts and runs for 1-5 seconds. It doesn't seem to stumble or anything, just turns itself off. I sent the computer in to speartech (the guy who make my harness) and he said it runs his test engine just fine. So I've ruled that out. The only thing I can think of is if I have a sensor that is messed up or something and the computer doesn't like it.

Is there any way to get the computer to tell me anything about why it's having this issue... maybe through the OBDII port? I tried asking it directly, and it just sits there with a blank stare.

Thanks!

Mike

ls1_chevelle

iTrader: (9)

Sounds like VATS.

-Matt

billyjo

I had a vacuum leak on mine when I started it and it did the same thing.

Bill

Thumper33

according to my computer programmer, it's not VATS. He said that the computer is fine and runs his test engine great.

I'll check for vacuume leaks, but I don't think there is anything that's not connnected.

I checked the wiring, and everything I connected on my harness looks good.

I'm not sure what else to check unless I can figure out how to get a code off the computer.

Would the lack of O2 sensors do anything? that's the only thing I can think of that's not connected yet because I need to get it running before I take it to the exhaust shop. That way I can drive it back and don't have to tow it both ways.

Thanks,

Mike

Thumper33

I'm trying to brainstorm here... best I can tell, the computer is turning off the computer. Why would the computer do this?

I don't know enough about this to know why the computer would decide within a second to turn it off. Is it possible that I have a bad sensor that would tell it something's wrong?

Where all should I check for vacuum leaks? I can't find anything that could leak other than the two hoses at the back, and the one near the throttle body.

G-Body

iTrader: (4)

The missing o2`s should not stop it from running, they will set a code/check engine light and maybe put it in a limp home mode, but it will run.

I think I read in a different thread that billyjo found a vacuum leak on the intake gasket.

Start with the basics, does the check engine light stay on when its running? You can check for codes, if a sensor is bad or not hooked up a code should pop up for it. How about fuel pressure, do you still have pressure when the engine cuts out?

Stu Cool

iTrader: (13)

How about fuel pressure?

Pat

bczee

iTrader: (12)

Get a scanner and check to see if you get a reading from all of the sensors and as you cranking or/and running (or as long as it does run).

Thumper33

Alright, that gives me a few places to start here.

1.) if I'm going to buy a OBDII scanner, is there a particular brand or model that is recommended?

How about this one? http://www.partsamerica.com/productd...artnumber=3030

2.) I'm going to buy a fuel pressure gauge to connect to the fuel rail and make sure I have consistant pressure.

3.) If I can't find anything from the two above, I'll pull off my intake manifold and see if the gasket looks good. I can't find any leaks otherwise.

76LQ9TA

iTrader: (1)

Do you have a laptop? I bought a cable and program to scan codes and look at several parameters while the engine is running. You can bring up a screen that looks like a car's dashboard. I bought this a while ago for my 96 Impala. It was about $120. The scanners that run on your laptop will have more features for less money than the stand alone scanners. obd-2.com is the place I bought from. I'm sure there are better scanners out now. Spend some time searching.

ghettocruiser

iTrader: (17)

Hey man... I wouldnt rule out VATs just yet. I know you said it ran a test engine... But when I picked up my donor car, I had the previous owner turn vats off with HP Tuners. We did it and thought it was complete. Donor car started right up and ran fine so we thought we had it.

Went to run my engine once it was swapped...no dice.

I went to radio shack and got some parts and built a vats bypass module. Had to insert a pin and wire back into the PCM (i took it out while cleaning up the harness). It fired right up after that. Ive since ordered a professional bypass box...which oddly enough doesnt seem needed anymore. My car runs with or without it... Not sure what the deal with that is.

Here is my thread on the bypass box I built.

https://ls1tech.com/forums/conversions-swaps/567630-homemade-vats-bypass-box.html

Not saying its your problem...but my VATS system did and is still doing some weird crap.

Justin

Thumper33

I bought the OBDII reader software setup here...

http://www.autotap.com/product_family.asp?FamilyId=260

I assume this will tell me if VATS is tripping it.

It should be here in a couple of days... I'll let you guys know how I like it, and what I find out.

Thanks all!

Speartech

iTrader: (14)

Try to follow thru with checking the fuel pressure, etc. Regardless of what some of these guys might say, VATS is definitely not the problem so don't keep your hopes up for that.

Does the throttle work properly with the key on? How is your fuel system set up?

ghettocruiser

iTrader: (17)

Haha.. I didnt even catch that it was Speartech that you've been working with. I guess if he says its not VATS then it really cant be VATS.

Didnt mean to step on your toes john...had I realized (read more carefully) I wouldnt have suggested that the VATS may not have been taken out correctly.

Check the basics like was said above... Fuel Air Spark... Go from there. Let us know what you find out!!

Justin

Thumper33

How do I test to see if the throttle works with the key on? it's all electronic. Are you just talking about checking to see if it moves the butterfly on the intake?

My fuel system is a aeromotive external pump going through a factory vette regulator and then up to a single inlet fuel rail. The return obviously then goes to the tank from the reg. I checked the railmaking sure that it's got pressure, although I don't have a gauge yet, so I don't know for sure how much it's getting. I'm going to try to do that tonight. Then I can hopefully rule that out.

I'm not banking of VATS for sure. Speartech told me that he doublechecked that VATS isn't on when I sent it in to get it tested.

Thanks for helping out!

Mike

Speartech

iTrader: (14)

That's ok Justin. I know the symptom sounds like VATS but that has been ruled out unless he's using a different PCM than the one I sent him.

Mike. Yes, make sure the throttle blade works properly from the pedal with the key on. That can be an indicator of problems if it doesn't. You should be able to sit there working the pedal back and forth and the throttle body should respond accordingly.

ghettocruiser

iTrader: (17)

When you first fire an LS1...the IAC along with a slight opening in the throttle body keeps the engine idling correct??

Is it possible that his IAC is stuck or carboned up somehow? I dont know squat about the electronic throttles...is that supposed to do something after start up to establish idle?

Man I know how frustrating stuff like this can be. haha. Im really psyched for you to get it up and going...because we've been tinkering with putting an LS1 in my buddies TJ. And I want one in my XJ since Im addicted to LS1s now. So now that more and more jeep guys are turning to the LS1, its getting more and more tempting!

Good luck again man!

Justin

LS1Cobra

Check the fuel pressure sensor on the passenger side of the oil pan. If you don't have that oil pressure sensor hook up the PCM doesn't see any oil pressure and will shut the engine off.

John,
This is Vinnie. I was the one talked to you several times on the phone about my 98 C5 PCM. I finally switched to the 1999 and up PCM programmed with a C5 firmware and I got my motor up running. Of course I had to rewire the wiring at the PCM. Thanks for all your help.

Rodder

iTrader: (2)

Cobra, the sensor on the side of the pan is oil level, not oil (or fuel) pressure. The LS1 oil pressure sensor is still on the back side of the valley where god and Chevy always intended it to be.

LS1Cobra

oops...