First LS Swap in a Jeep - Won't Stay Running
 

Hey all,

I've been a lurker around here and only used the forums for searching and research since I started my LS swap project 2 years ago. 2 months ago, I finally had accumulated all the parts and started my LS swap in my 98 Jeep TJ. I'm done with all the fab and wiring and I went to test fire but it won't stay running. I've checked everything once, twice and three times over.

When I crank it, it fires up strong and then shuts down after 1 second. Like the injectors fill the cylinders one time with fuel then shut down or something.

I have an LQ4 with a Gen III PCM (Blue and Green long skinny connectors) that came out of the same Chevy 3500 express can with a U VIN.

My fuel delivery system consists of an RCI aluminum 15 gallon tank with a stock 97-98 Jeep TJ fuel pump with the fuel pressure regulator removed and the Novak fuel pressure regulator bypass kit installed (provides 60 psi out) then into a Corvette filter/regulator with all -6AN braided lines to a fuel gauge on the fuel rail. The gauge reads 55-58 psi at all times, when the key is turned on, while cranking and after the motor stops.

I'm using a PSI HAR-1015 harness and yes I have 12V when in the ON and ON while Cranking position to the red wire off of the fuse block. I have the cab ground secured and tested with a good ground, I have the engine bay ground, grounding to the rear drivers side head ground. That is grounded to the Jeep tub. The tub is grounded to the battery and there is a 4 AWG ground from the battery to frame.

Jeff Lowry at Performance Specialties went through the tune and turned off everything that wasn't needed. VATS is Disabled in the tune and he confirmed this. He also set it up to default to speed density if the MAF wasn't functioning, I believe.

Here's what I have checked so far...
- MAP Sensor is plugged in (extended off of a bung on the bottom of my intake but sealed and is reading on the scanner's live data stream when cranking)
-Brand new crank position sensor installed (24x as it's the black one)
-Brand new fuel injectors (stock but new, none the less)
-New plugs and they are gapped at .035
-New Accel ceramic plug wires
-New MSD coils
-Checked all the grounds (inside harness, engine bay, battery and frame-OK)
-I have 12V when on and cranking on the red wire on the PSI harness
-Brand new fuel (Sunoco 93 octane in the tank and half tank)
-55-58ish PSI at the fuel rail at all times even when cranking(Viewing through an inline gauge on the rail)
-Fuel relay clicks on when key is turned to ON then turns off, but then turns back on as soon as it cranks, stays on
-Battery in Jeep is charged. Showing 12.4 Volts when OFF
-Sprayed starting fluid into the intake and the Jeep runs well, so that tells me I have spark as needed, also tells me I have a fuel delivery problem somewhere too.
-MIL/CEL - no codes being thrown other than it can't see the front bank of O2 sensors since I'm running open headers still with no exhaust... so I didn't install the 02's in fear of burning them up.

I've went as far as taking the red wire on the PSI harness and connecting straight to 12v battery to rule out the PCM shutting down after trying to start. Same thing happens. It runs for one second, shuts down.

I just swapped out the fuel injector for new OEM ones as the old ones sat in my motor in the fuel rail for two years. I built the motor with a cam back in 2015 and the motor has been on an engine stand every since. I figured they were probably jelly inside so I replaced them to rule that out.

Here's what it does. It does start for a second and then shuts down.

I'm at a f'ing loss here.... what else could be causing it not to stay running?

YouTube Video of it cranking, starting and shutting down...

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Is there any way you could share the file (tune). That might help a lot.

I just emailed Jeff at Performance Specialties to see if he can send me the tune file. I'll let you know.

Here is the link to the tune file in Box.com where I uploaded it. It's in HPTuners file format.

https://app.box.com/s/u58n5htqpfe7je53pod9ncl94veuu2oh

Do you have a constant 60 psi of fuel while cranking? Monitor pressure and see what it does as soon as it fires. Also, It won't be a bad idea to check injector pulse with a noid light.

I swear that is how my swap was behaving before VATS was deleted. It would do the same thing as in the video.

That is a DBW harness from PSI , same one I used. In the second pic you don't have it hooked up?

I'm picking up a noid light after work to test injector pulse. I watched the pressure and it stayed at 58-ish PSI while cranking. Should it drop then come back to 58 or hold constant?

It's hooked up. It's plugged into the Torque Rush X-Link DBW adapter and then into the harness, its just tucked under the fuel rail.

http://www.torquerush.com/x-link.html

But if it was VATS would it still stay running when spraying starting fluid into the intake? It runs great by doing that, fires fine, idles, etc. Spray more fluid and it revs up like it should. Wouldn't VATS keep the coils from firing the plugs?

I think VATS just cuts the fuel off. So yes to you question.

I picked up a noid light today and tested injector pulse. I have injector pulse while cranking and while it's running for a brief moment.

I have 58 psi at the rail and it drops to about 52-ish psi while cranking then comes back up to 58 psi as soon as it fires.

I checked all my grounds, took them off and cleaned the metal under them then reattached the nuts/bolts holding the grounds on to be sure.

My battery is showing 12.60 Volts when nothing is running. It drops to 9V while cranking then the Alternator is showing 14+V as soon as it fires and turns over for a brief second.

Could it be low voltage while cranking causing these issues?

I disconnected the battery from the Jeep and put an 8 amp trickle charger on it for the night to see if it helps tomorrow.

I don't think it's a battery issue, as it does start up. There's something else going on. Was ecm tuned for cam and all mods etc?

There is a base tune in it for now so it should actually start and run. Maybe not perfect but at least start and idle with the tune that is in the computer now.

Do you have all your vacuum lines hooked up, it sounds to me like it needs air, adjust the throttle body butterfly open more.

Unplug the MAF and give it a try.

Yes. All my vacuum lines are hooked up. I have one going to a check valve for the brake booster via a 1/4" NPT bung on bottom of the intake, then an 1/8" NPT bung for the catch can/PCV. The others are capped off.

Tried that and no difference. I also tried unplugging the cam sensor too. Still nothing.

"I picked up a noid light today and tested injector pulse. I have injector pulse while cranking and while it's running for a brief moment."

I take it your fuel pump runs constantly while the ignition switch is on. The question is when is the loss of injector pulse? Is it before the engine quits running or certainly after when the crankshaft stops. You previously said that you could squirt fuel in the air intake/throttle body and the motor would keep running. It sure sound fuel related to me.

Loss of injector pulse happens as soon as the motor stops. The fuel pump primes the rail and then shuts off with the key in the ON position. Once I crank it, the fuel pump kicks back on and then shuts off at the same time the motor stops.

It does sound like fuel related. With the pedal all the way to the floor during start up it bogs down and dies faster.

I pulled the plugs and they were brown as if it's getting too much fuel.

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There is definitely no issue with the crank position sensor if the pump comes on while cranking. You can also verify by checking to see if tach is registering any signal, as when my CKS went bad, I had no signal.

as far as cam position sensor, I believe that the computer uses it only on crank up, and then swaps over to the crank sensor. Correct me if I'm wrong