problems getting engine started

[81cuttysupreme]

So my swap is complete except the engine wont stay running. I've already had an initial flash on the ecm and had the vats removed. It is an LS1 block with an LS6 top end. The motor was rebuilt all forged a couple years ago for a procharger set up. I've got good oil pressure, fuel pressure, and spark. The motor wont fire up every time. When it does run it's only for a few seconds and then it dies. The ecm is holding a problem code for the map sensor circuit. "MAP sensor circuit low output." I've checked for vacuum leaks and havent found anything. The boost gauge shows 10in vacuum when the engine idles. I have 5 volts at he map sensor plug. I'm not sure what to check next. Any ideas?

 

[Black Power]

fuel pressure staying up?

 

[Chuck Leeper]

MAP reading is, KOEO.??
Injectors been sitting for 2 yrs ? NE old fuel in them?
Gas tank clean?
Fuel filter fresh?
Fuel pump prime cycle working?
Reworked, or aftermkt harness?

 

[81cuttysupreme]

new gas tank. new fuel filter. fuel pressure at the rails stays between 56 and 58 psi. The injectors did sit for two years, could they be gummed up? Is there something i can do to check them or clean them? Injector cleaner in the gas tank? The pump does prime as soon as the key is turned to the on position. The harness is a re worked harness. The guy that did the harness though did a complete check of it with sensors and a computer. The reading i get from the map is koeo. It gives me 29.80 inHG, atmospheric pressure. I'm not sure what it does yet with the engine running. I can tell you my boost gauge holds about 10 in of vacuum with the engine running. I should probably check to see that the MAP has the same reading.

 

[81cuttysupreme]

I started it last night with the scanner hooked up to look at the MAP reading. The map did pull down to 21 inHG once the engine fired up for a couple seconds. So even though the ecm is holding on to the map sensor code, it appears to be working normally. Any thoughts on injector cleaner? Is it possible to have a bad crank or cam sensor without the ecm reporting the code?

 

[Chuck Leeper]

No crank sensor = no start.
Tuners usually work with KPA, not in Hg. Can you change that on your scanner??
29.80 is about 100 KPA.. so the sensor is reading.
If the injs have been in open air, and/or have had fuel sitting in them, it's highly likely they are gummed/stuck shut.
Once you confirm the VATS is out, then the next is to confirm the injs are OK...
If the engine runs for about the same time each start, I'd guess the VATs is still active.....NE 1 around you with a Tech 2, or EFILIVE, etc?

I clean injectors one way... On the test bench, flow test them, clean them, retest, and replace the wear items....

 

[81cuttysupreme]

it's a 45 min drive to get the vats removed, wich i already did once. if i need to do it again so be it. i'm going to check the resistance on the injectors just to see what i get. the other thing, is i'm not sure if i'm actually pulling as much vacuum as I should be. My cam is 230/240 @.500. Anyone have a good value?

 

[Black Power]

10 in. isn't great but that alone shouldn't be killing the engine

 

[81cuttysupreme]

I double checked the pressure that the MAP is getting when the engine chooses to idle. It reads 16.5 inHG, or 56kPA. Does this sound normal? I'm not sure how accurate the boost gauge is with vacuum. Are there any other vacuum ports besides the ones behind the throttle body, and the two right below/next to the MAP? I have them all plugged. If those are all plugged what else could cause a vacuum leak? bad manifold seal? Something stuck in the manifold? bad TB to manifold seal? I'm going to double check all that stuff again, but I can't think of anything else that could cause this issue??? Brake booster?

 

[Black Power]

what cam does that thing have?

 

[Chuck Leeper]

A 230/240 @ .050 cam is not going to have idle vac much better than the 56KPA U R seeing.
The other issues with the engine may also reduce the vac some.
That cam, and 56 KPA, pretty much says there are no other serious leaks.
Mine is tuned, [I use EFILIVE], and will idle at 50-52KPA. The cam is 222/226 @ .050 in at 113*.

ALL sensors connected and working?
MAF not in backwards?
PCV system hooked up and working?
Air cleaner not getting blasted w/ fan wash?
Have you tried the start fluid trik to see if there are leaks?

My next "stop" would be a clean set of injs. In tank stuff may work if they are a bit sticky.. Gummed shut, they need to come out and get cleaned the correct way.
While u r waiting on the injs, I'd suggest checking every connector, ground, power source on that harness.

 

[Black Power]

Oh I missed the cam duration. Yeah that's true, I don't think it's a vac leak. If it is, it's not a huge one. I assume you've tried starting it with the maf unplugged?

 

[81cuttysupreme]

i did try starting with the maf unplugged. It wouldnt start with it unplugged. It does seem to be working though according to my scanner as far as it shows airflow when the engine runs. My PCV system is not hooked up completely i have one of the ports open for now. Would that have any affect? The air cleaner is on the back of the procharger. I checked the harness grounds, they were good.

 

[Black Power]

it should start with the maf unplugged. leads me to believe the map is screwed up somehow. Which map sensor are you using? 2 bar? You said the boost gauge shows 10 in/hg but the map shows 21 in/hg?

Also, describe how your pcv system is hooked up. If it's venting crankcase pressure to the atmosphere it's fine, as long as it's not pulling vac into the manifold.

 

[81cuttysupreme]

For the PCV system. I have the two rear ports tied into an air/oil seperator and then fed to the air filter on my procharger. For, now the front port is just open to atmosphere. For the MAP, i just have the factory MAP. 1 bar right? When my boost gauge shows 10in vacuum, the obdII scanner shows 16.5inHG, or 55kPA.

 

[Chuck Leeper]

For the PCV system. I have the two rear ports tied into an air/oil seperator and then fed to the air filter on my procharger. For, now the front port is just open to atmosphere. For the MAP, i just have the factory MAP. 1 bar right? When my boost gauge shows 10in vacuum, the obdII scanner shows 16.5inHG, or 55kPA.

Key on, engine off...What's the MAP sensor read??

 

[Black Power]

yes the factory is a 1 bar for the ls1s

 

[81cuttysupreme]

koeo the map reads 100kPA or 29.9 inHG.

I think I may have come across something tonight.(i hope) Tell me what you guys think. I got my hands on a bottle of starter fluid. I was able to start and keep the engine running by spraying the throttle body with the fluid. It would seem i would be able to keep the engine running until the can of spray ran out if I so desired. My thought is that the injectors are bad, if so probably from sitting too long without being cleaned before storage? When I checked the fuel pressure before at the rails it held steady between 56 and 58 psi. So I'd like to know if you guys would come to the same conclusion based on the results of this test. Is it probable that the starter fluid would overcome more problems than just bad injectors?

 

[Black Power]

I'd say you found it probably. Out of the things an engine needs to run, you obviously have fire, you have compression, and when you add fuel it makes it happen. I'd try the injectors. Since it will run a little bit, I would guess maybe they are leaking down a little bit of fuel when it sits in the rails, which allows it to fire, then maybe when you try to keep it running it becomes fuel starved? Chuck will know this one, lol.

 

[Chuck Leeper]

I'd say you found it probably. Out of the things an engine needs to run, you obviously have fire, you have compression, and when you add fuel it makes it happen. I'd try the injectors. Since it will run a little bit, I would guess maybe they are leaking down a little bit of fuel when it sits in the rails, which allows it to fire, then maybe when you try to keep it running it becomes fuel starved? Chuck will know this one, lol.

Yep. See it most every time a j/y engine is installed. Or, most times that an engine is installed, and the injs are left out in open air w/ fuel in them...............
I've done several conversions....Don't recall 1 that we didn't use clean injs...No point pounding sand in a rat hole, trying to work w/ an unknown...

You can about bet the farm, that if the fuel in the injs stinks, the injs are not going to do well.
Gas these days is so nasty, that the small engine companies are saying to not buy more fuel than you will use in 30 days.. They are also selling small cans of fuel w/o the corn likker in it....