Crank + Start, dies slowly + on throttle, not VATS -- help?
08-01-2013, 12:11 AM
#1
Crank + Start, dies slowly + on throttle, not VATS -- help?
Oh why hello dear reader, didn't see you there!
Anyway, here's the deal, in bullet points for those of us with short attention spans (like myself):
What happened:
Driving down highway, not on boost. Everything's fine. Car has been running for the last few weeks perfectly. Hit a small amount of boost while passing a car, 2 psi on the high end, and lose throttle response, car felt almost... jittery. Eventually no throttle response at all. Coasted just fine over to the shoulder before I just pulled the key and called it quits. 67,000 miles, by the way.
At one point last week, car didn't want to start, turned out to be a bad connection to ground at under-hood fuse box.
Codes:
Major mods:
Symptoms:
Things I've checked:
It's late and I'm at my wit's end. Short road. I'm thinking possible bad tune or short somewhere going into the PCM. Possibly that fuse box ground again?
Puttin' on my thinkin' cap...
Midnight update: Roommate came home so I had someone to try to start it while I watched the fuel pressure gauge. Seems like before it was burning off the fuel in the rails, which would make sense. So loss of fuel pressure it is, at least most likely. The UPP kits are run by a Hobb's switch to activate the secondary fuel pump, maybe something is wired up wrong?
Anyway, here's the deal, in bullet points for those of us with short attention spans (like myself):
What happened:
Driving down highway, not on boost. Everything's fine. Car has been running for the last few weeks perfectly. Hit a small amount of boost while passing a car, 2 psi on the high end, and lose throttle response, car felt almost... jittery. Eventually no throttle response at all. Coasted just fine over to the shoulder before I just pulled the key and called it quits. 67,000 miles, by the way.
At one point last week, car didn't want to start, turned out to be a bad connection to ground at under-hood fuse box.
Codes:
- P0113 + another PCM code I forget off of my head- IAT sensor high voltage/intermittent voltage. Was not being thrown prior to TT install, thrown day after install. Ordered new sensor, hasn't arrived yet.
- At one point 2 years ago threw a TPS (report) sensor code, cleaned ground and cleared code, never returned.
Major mods:
- UPP TT Kit - installed by local speed shop
- EPP Blower cam
- 2.5" DPs to a 3" exhaust
- LS6 intake
- The all important dyno tune by a reputable tuner (previous tuner for C&S motorsports)
Symptoms:
- Cranks and starts, normal startup before attempting to idle
- RPMs slowly and steadily drop until death
- Attempts to press throttle to keep the engine "alive" result in car dying earlier
Things I've checked:
- VATS = not the issue (both keys work and no security light)
- Fuel pressure - little weak, but enough to start
- Spark - Well it's starting and firing on all 8
- Vacuum - checked every vacuum hose I could think of and I'm still getting -20 to -15 vacuum after startup. Obviously that decreases as it dies.
- No code for CPS, MAF, MAP, or CAS - at least that it's throwing anyway.
- Even after clearing all codes, CEL comes on, but code doesn't display on DIC. (don't have my scanner with me.)
- Let battery sit disconnected for 30 minutes before trying again while waiting on the flatbed.
- Oil scavenge pump works as directed.
- Immediately after this happened I checked the oil. Dipstick had not blown and catch can was still pristine and empty.
- Chassis ground from UPP battery relocation kit was still good. (if it starts up that's the hardest time of draw anyways, correct?)
- Tried running with IAT/MAF removed, no dice. But that could also be from the car attempting to run limp mode with a huge cam.
- Removal of MAF did cause the car to go into limp mode.
It's late and I'm at my wit's end. Short road. I'm thinking possible bad tune or short somewhere going into the PCM. Possibly that fuse box ground again?
Puttin' on my thinkin' cap...
Midnight update: Roommate came home so I had someone to try to start it while I watched the fuel pressure gauge. Seems like before it was burning off the fuel in the rails, which would make sense. So loss of fuel pressure it is, at least most likely. The UPP kits are run by a Hobb's switch to activate the secondary fuel pump, maybe something is wired up wrong?
Last edited by ZipperSuitedSunGod; 08-01-2013 at 12:31 AM. Reason: Moar info.
08-01-2013, 01:31 AM
#3
Well, before it was creeping right around 15-20. Now it's between 0 and 5, so long story short the starts were a fluke and just from the fuel rails.
Self answering question it seems, just wanted to get the thought out there to get some ideas. So tomorrow I'm off to:
- Checking fuses
- Checking fuel tank seals
- Putting a regulator to the regulator and making sure a valve isn't stuck closed.
08-04-2013, 09:38 AM
#5
08-04-2013, 04:53 PM
#7
Yeah I was curious what was going on, ended up being a clog in the fuel transfer... thing. Whatever it's called. So basically over a quarter tank of gas became an empty tank of gas.
08-04-2013, 05:24 PM
#9
Yep yep. Gotta love when you overthink things and the fix ends up being simple. Still kicking those codes though, so I need to check out my IAT sensor, but that should be small work. Thread closed, etc. etc. Thanks for the help!