Primes, cranks, fires, runs, and dies

[SchreinerM]

Hello all. Short story, it's a 2002 5.3L with NV4500 behind it. I did the harness using the LT1swap advice. Brendan reprogrammed the ECU. I popped a battery in the truck this evening and while it cranks and fires, it won't stay running. I'm looking for some advice on items to check. Here's the long story:

- With the battery in and the ignition on, the fuel pump primes just like my '02 Silverado.
- I pulled the injector fuses, hit the starter and it cranked over just like it should.
- After plugging the injector fuses in, it cranked and fired within a second. Good idle speed, definitely firing on all eight, very smooth.
- After 10-15 seconds, the idle speed slowed and the engine stopped.
- I keyed it off and back on, again the fuel pump kicked on right away. Assuming it was just air in the fuel lines, I hit the starter again and it fired right up. Same story at the first time, great idle speed and smooth running. But again, it died 10-15 seconds in.
- I repeated this process half a dozen times, all the same result where it died 10-15 seconds in.
- After about five start attempts I plugged in my cheap OBD2 code reader. With the ignition on, it did recognize the port and it had one code present P0102 - MAF). I cleared the code. From there on out, no codes were recorded.
- The next time after it fired I held the throttle partially open (cable throttle body) and it ran very smooth at ~2,000 RPM. Same result though, it died in under 20 seconds.
- In total I started it around 20 times, sometimes after it stalled I'd kick the ignition, some times not. Either way, it fired right back up afterward. On approximately five of the starts the idle speed slowed at the same time but the engine slowly stumbled to stalling out after around 25 seconds (like the engine wanted to stay running).
- No codes / CEL at this point.

Any smoking gun you guys suggest checking?

[BR3W CITY]

Whats your fuel pressure, and does it maintain while starting and running?

Throw a meter on the fuel pump and see what its drawing. Do you notice a drop in voltage or a spike/overdraw?

[SchreinerM]

Brewcity, you read my mind. With it killing in short time span, then priming after it killed, fuel pressure was my first guess. I called a friend and he's going to loan me a fuel pressure gauge that we'll pop in the pressure line.

If it's losing pressure, what's the fix?

[BR3W CITY]

See people from WI figure this stuff out (and then figure out how to get out of WI...thats why the trucks gotta run )

Pop the vac line off the FPR and see if it maintains fuel pressure also. If not, the regulator is bad. If it does, have a friend modulate the RPM (and let evertthing get nice and warm). See if FPR bounces, drops off etc.

Then troubleshoot back from there. If the FPR tests ok, see if the pump is not delivering the fuel. The multimeter will tell you what the pump is drawing. Extremeties in draw can indicate a ground problem, shorting, an internally messed pump etc..just depends what your results are.

Start with the easy stuff first. FPR, no obvious fuel or vacuum leaks, fuel pump not starving in the tank, pinched lines etc.

[Flatpat]

I had the hose from the pump to the sending unit fail and caused this same issue.

[chuckmc8]

As others have said, Connect a fuel pressure gauge to the Schrader port on the fuel rail- run on the key and check your PSI- then start it up and watch the gauge as the engine dies and you will know if its a fuel or if its an electrical/control issue.

OBD reader and Fuel Pressure gauge are two things that LS swappers need from the "git-go"

HTH

[casper71]

Take off you air filter and try to start it. I had the same problem, it was my air cleaner causing turbulence with the mass air flow sensor.

[BR3W CITY]

Originally Posted by casper71

Take off you air filter and try to start it. I had the same problem, it was my air cleaner causing turbulence with the mass air flow sensor.

Thats not the filters fault, its the location of the MAF behind the filter. You need enough distance between the entry point and any major bends otherwise it won't have a full sampling. Also why air filter oil is bad, it can get sucked in and cake the MAF.

[tbrown5079]

I don't know if it's true or not but a friend told me an open vacumm line will cause the motor to stall. Something easy to check.
tbrown

[SchreinerM]

Gentlemen, thanks for all the feedback so far. I really appreciate all the help. This afternoon I grabbed the gauge from my friend and connected it at the rail. I took a video of start-up:
https://youtu.be/q4h_11ibwIc

When it runs the gauge reads very similar to my 2002 Silverado. After it killed I left the gauge on the rail and watched for leak down. It did, very slowly (again very similar to my Silverado). Roughly speaking, it was at 40 psi after 5 minutes, 35 psi after 15 minutes, 30 psi after 25 minutes. It did not leak down passed 20 psi.

I did get a P0200 (injector) code this time. Cleared and it did not return.

After that I pulled the return line and ran it into a 5 gallon gas can (just in case their was blockage). I was surprised that fuel comes out of the return line with the ignition on, even when the engine isn't running (in hindsight, it makes sense since the FPR is just a mechanical unit). Made no difference in the run time, so I reconnected it.

Tomorrow I'll grab some alligator clips and check the voltage at the pump. It hasn't blown fuse on the pump circuit.

[BR3W CITY]

Ignoring the gauge, that thing sounds like its hitting VATS cutoff...but if Brandon redid the ECM, I'm at least confident it was removed.

[SchreinerM]

Brewcity, what do you mean by "ignoring the gauge"? Does the gauge or audio make you think something other than VATS?

As promised, I check voltage at the pump today. 11.8V with the ignition on and a very consistent 14.2V with the engine running. When the RPMs drop, the pump voltage drops (not vice versa) never below 12V. Makes me confident the pump is fine.

I swapped FPRs with my Silverado. The Silverado runs fine with the C-10 FPR. The C-10 acts the exact same with the Silverado FPR as it does with it's own. Between the swap and the fuel pressure gauge, I doubt it's the FPR.

While I had the DMM out, with the ignition on I checked all the injectors. All eight were a consistent had 6.9 volts.

I will hit up Brendan to see if he saves any details on the individual tunes. Other than that, any next suggestions?

[ls1nova71]

Does kind of sound like VATS, since it only runs about 4 seconds in the video. You say it ran as long as 10-15 seconds though, has it ever ran longer than in the video? If not, call Brendan and have him check the file, he's only human and sometimes things get missed.

[BR3W CITY]

Originally Posted by SchreinerM

Brewcity, what do you mean by "ignoring the gauge"? Does the gauge or audio make you think something other than VATS?

Sometimes there is too much information in front of me at one time. I don't want to ignore one fix while chasing another.

[chuckmc8]

It takes three things to run- Fuel, compression, and spark at the correct time- you are eliminating each as you troubleshoot.
I think that some parts stores have the 'spark checker' wire that plugs inline of a spark plug wire and lights up when there is spark. My guess is that it stops firing and thats whats shutting it down, If you can find one of those test wires, connect it and fire it up and watch the light and see what happens.
Ive not seen one run for 15 seconds and the vats shut it down either. Usually they just start up and then die.
It may be worth the shipping to box the pcm and send it to Brendan and have it check it. He has done a lot of them for me and never a problem, BUT it is a computer :-)
HTH

[SchreinerM]

I pulled up several videos and using the timer it runs on it's own for seven seconds in each case. My 10-15 estimate was high. Could seven seconds be a VATS issue?

I have dropped Brendan a note via email with all the same details I listed here. If I don't hear back from him in the next day or so, I'll try and dig up his number.

Good suggestion Chuckmc8. I know the adapters you are talking about and will give that a try.

Lastly the friend who loaned me the fuel pressure gauge dropped a 5.3L in a '66. It's an auto tranny truck with a mild tune but he offered to loan me his ECU to give it a try. I'll follow up with news, but I'll keep checking back here for suggestions. Really guys, I appreciate all the help so far.

[Juiced06GTO]

Definitely sounds like VATS was left on. I left it on in my swap by accident, luckily I own HP Tuners and could just reflash it right out!

[BR3W CITY]

Originally Posted by SchreinerM

Could seven seconds be a VATS issue?

5.3L in a '66. It's an auto tranny truck with a mild tune but he offered to loan me his ECU to give it a try. I'll follow up with news, but I'll keep checking back here for suggestions. Really guys, I appreciate all the help so far.

7 seconds is a tad high for vats, but not impossible. Usually it'll only run that long once or twice, then if you keep trying vats won't even let it start.

[vannatta20]

Sounds like a fuel issue. No reason for spark to die off after 10 seconds. Its got air coming in so thats fine. So if it has good pressure id be looking at the injectors. If the engine has been sitting for a long time they get stuck and malfunction. Pull the rail and check for blockage as well. I think its all gummed up and gets just enough fuel to idle for a short time then stalls. If the plugs are dry that will help pin point it(no fuel).If they are wet its a ignition issue.

[earl84]

Just out of left field here, as I only know enough to be dangerous, but I have an older GM car that would do this, and it was just a bad Idle Air Control Valve. It wouldn't run more than about 4 seconds before dying, though. New one cost about $25 and solved my problem. Never threw a code at all. Quick check on Rockauto lists them for around $80 for your engine.

[chuckmc8]

SchreinerM- What was the resolution to this issue? It would be nice if you could post a conclusion and remedy for others who may have the same problem and searching for similar problems.