Start, stumble, stall, repeat...
10-04-2016, 08:43 AM
#1
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Start, stumble, stall, repeat... This one has me puzzled. It's been my daily driver for 17 years, never a lick of motor trouble with over 250k miles.
1. Running the tune I've had in the car for over 10 years without a change. EGR and AIR deleted, speed density.
2. Have HPTuners connected, which gives me control over EVAP purge solenoid and vent valve
3. Pulled the fuel tank, took pump and canister out, no visual indications of trouble, so reinstalled.
4. Removed fuel rail and backflushed injectors with seafoam while holding them open with 12v
5. Fuel filter required a little effort to blow through, so I replaced it.
6. I literally have like $10 to my name, so I can't afford to rent a fuel pressure tester; I rigged up my compression tester to use as a fuel pressure guage and hooked it to the rail (took the shrader valve out of the guage to be sure I would see pressure drops)
7. Car starts, runs fine for about a second then stumbles - work the throttle, it might pick back up, but only for a second - dies usually with 5-10 seconds of starting
OBSERVATIONS:
8. Battery is fully charged, system reports 13.4v when running
9. No Codes
b. Computer doesn't listen to the MAF anyway, as I have the fail frequency set to 0hz (always in fail state, to force speed density)
c. Logs taken before this issue show that the MAF was registering corretly previously
11. MAP Sensor fluctuates with RPM, baseline while running matches idle reading from a good log
12. Fuel pressure climbs to 60 (as read by the compresson tester, accuracy unknown) when priming and stays there throghout the time the key is on - degrades over time after engne stops running
13. While stumbling, the usual "hiss" of the induction changes to more of a growl, as though it were gasping for air
14. Via software, can observe the IAC commanded and actual change in unison
TESTS:
15. Set purge=100%, vent=open (and monitored their status)
a. Motor ran "ok" for about 10 seconds then stumbled and stalled
16. IMMEDIATELY started it back up
a. Ran for 3 seconds, stumbled and stalled
b. Repeat this many times - always fires back up instantly
17. Play with different states of purge and vent - never get a consistent result
a. Sometimes opening the purge valve nets a few extra seconds, sometimes not
b. Same with vent valve
18. Unplug purge solenoid - get a few extra seconds on the first start, but subsequent starts don't net the same result
19. Using paperclip in place of relay, activate fuel pump to always be running
a. No noticeable change in result
20. Disconnect the purge solenoid (leaving an open tube into the intake
a. Doesn't seem to effect results
21. Disconnect MAF and IAT
a. Doesn't seem to effect results
22. Shoot some ether down the intake
a. Roars to life briefly then dies
23. Via software, force closed loop
a. Doesn't seem to effect results
Ideas? ?
1. Running the tune I've had in the car for over 10 years without a change. EGR and AIR deleted, speed density.
2. Have HPTuners connected, which gives me control over EVAP purge solenoid and vent valve
3. Pulled the fuel tank, took pump and canister out, no visual indications of trouble, so reinstalled.
4. Removed fuel rail and backflushed injectors with seafoam while holding them open with 12v
5. Fuel filter required a little effort to blow through, so I replaced it.
6. I literally have like $10 to my name, so I can't afford to rent a fuel pressure tester; I rigged up my compression tester to use as a fuel pressure guage and hooked it to the rail (took the shrader valve out of the guage to be sure I would see pressure drops)
7. Car starts, runs fine for about a second then stumbles - work the throttle, it might pick back up, but only for a second - dies usually with 5-10 seconds of starting
OBSERVATIONS:
8. Battery is fully charged, system reports 13.4v when running
9. No Codes
10. - ODDBALL CLUE - MAF reads 0 g/s with ignition on, then goes to 2.3 g/s when motor starts running - stays there regardless of RPM
a. Does this even of the MAF is disconnectedb. Computer doesn't listen to the MAF anyway, as I have the fail frequency set to 0hz (always in fail state, to force speed density)
c. Logs taken before this issue show that the MAF was registering corretly previously
11. MAP Sensor fluctuates with RPM, baseline while running matches idle reading from a good log
12. Fuel pressure climbs to 60 (as read by the compresson tester, accuracy unknown) when priming and stays there throghout the time the key is on - degrades over time after engne stops running
13. While stumbling, the usual "hiss" of the induction changes to more of a growl, as though it were gasping for air
14. Via software, can observe the IAC commanded and actual change in unison
TESTS:
15. Set purge=100%, vent=open (and monitored their status)
a. Motor ran "ok" for about 10 seconds then stumbled and stalled
16. IMMEDIATELY started it back up
a. Ran for 3 seconds, stumbled and stalled
b. Repeat this many times - always fires back up instantly
17. Play with different states of purge and vent - never get a consistent result
a. Sometimes opening the purge valve nets a few extra seconds, sometimes not
b. Same with vent valve
18. Unplug purge solenoid - get a few extra seconds on the first start, but subsequent starts don't net the same result
19. Using paperclip in place of relay, activate fuel pump to always be running
a. No noticeable change in result
20. Disconnect the purge solenoid (leaving an open tube into the intake
a. Doesn't seem to effect results
21. Disconnect MAF and IAT
a. Doesn't seem to effect results
22. Shoot some ether down the intake
a. Roars to life briefly then dies
23. Via software, force closed loop
a. Doesn't seem to effect results
Ideas? ?
10-04-2016, 06:26 PM
#4
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I did consider it, but only briefly. My reasoning being that ether brings it back to life when it's stumbling. Therefore, I've been focusing (maybe incorrectly) on it being a Fuel delivery problem.
10-05-2016, 10:24 AM
#6
9. No Codes
b. Computer doesn't listen to the MAF anyway, as I have the fail frequency set to 0hz (always in fail state, to force speed density)
c. Logs taken before this issue show that the MAF was registering corretly previously
10. - ODDBALL CLUE - MAF reads 0 g/s with ignition on, then goes to 2.3 g/s when motor starts running - stays there regardless of RPM
a. Does this even of the MAF is disconnectedb. Computer doesn't listen to the MAF anyway, as I have the fail frequency set to 0hz (always in fail state, to force speed density)
c. Logs taken before this issue show that the MAF was registering corretly previously
Id start there and trace the MAF wires, could be a short somewhere.
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10-05-2016, 12:02 PM
#8
One would think...but there are a lot of wires in that MAF loom that could potentially fray, touch, and cause a short that could create this scenario. I'd be inclined to at least check into it since its free to do so.