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Old 01-10-2009, 11:29 AM   #1
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Default stumble/misfire?

I've been searching this board and others for the past few hours now, and I've turned up some good help.

So far, I'm pointing towards:

Fuel pump/filter (and/or)
Igniter (and/or)
Coils


Anyway, my problem is this: When going from vac to boost, my car has started stumbling (sounds like a puttering noise, with minor vibration) and power loss occurrs, untill I finally break the 2-3psi "ceiling" and then the vibrations/puttering/stumbling end and I regain my power.
More recently, the stumbling has occurred while in boost (4-8psi) on WOT, or on tip-in, and also when tapping the gas while idle.
Idle seems relatively normal, although when I increase it, I can tell there is a bit of stumble.
This has recently started occuring (within 2/3 days) and has gotten considerably more noticable/worse very quickly. I haven't modified anything recently, so i'm thinking something has just worn down/failed ^^

There is no CEL, although I have had one for an o2 sensor, and may need to recheck the connections, and reflash the saved cel ****.
Also, no WBO2

I will need to get a fuel pressure gauge, check plugs and run a few other checks, but I wanted to see where this community could point me first.

Mods: Cartech FMU, 15g TDO4, Custom FMIC, Manual Boost Controller (voodoo), MSD Miata Box, HKS SSQv BOV, 305cc Greentop Supra Injectors.

As far as I know, everything else is stock (save for unrelated IE:suspension/rear end)


Thanks again, and I wouldn't have asked if I didnt search all day with varying answers
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Old 01-10-2009, 11:37 AM   #2
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Someone else had a similar issue a couple threads ago, turned out to be the fuel pump.

https://www.miataturbo.net/forum/t29730/

My car drove like **** and was seemed as if it was getting worse and worse. I changed the fuel pump and it was like night and day. Check your pressure.

Vash-
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Old 01-10-2009, 05:12 PM   #3
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Quote:
Originally Posted by Vashthestampede View Post
Someone else had a similar issue a couple threads ago, turned out to be the fuel pump.

https://www.miataturbo.net/forum/t29730/

My car drove like **** and was seemed as if it was getting worse and worse. I changed the fuel pump and it was like night and day. Check your pressure.

Vash-
hah, funny you should bring up the thread, because it was a post in that thread that made me think "****...fuelpump"

EDIT: actually, it WAS yours

thanks, will update later
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Old 01-10-2009, 05:28 PM   #4
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+1 to checking fuel pressure. Also never hurts to put new plugs in a motor and gap them down to ~.020".
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Old 01-15-2009, 03:45 PM   #5
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UPDATE:

picked up a brand new 190lph HP walbro pump, and installed it.

The car sounded great, and drove pretty good, untill it warmed up. Then, the same **** ;p
When I accelerate with a bit of "go" I get stumbling/puttering as I enter boost. Oil gauge doesnt ping around, and I dont think I hear knock.
If I idle while warmed up, it seems like I get a bit of extra vibration/noise.
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Old 01-15-2009, 03:46 PM   #6
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Quote:
Originally Posted by patsmx5 View Post
+1 to checking fuel pressure. Also never hurts to put new plugs in a motor and gap them down to ~.020".
+1
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Old 01-15-2009, 06:03 PM   #7
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Quote:
Originally Posted by patsmx5 View Post
+1
k, plugs pulled and replaced.

They looked pretty good, a bit black, but nothing out of the ordinary.



So, I decided to pull my o2 sensor (why not?) and boom...no CEL.
****, i says, and I checked the CEL again. (diag jumpering)

I am getting the following codes as of right now:

3) G- Signal
17) Oxygen Sensor (output not changing)

Obviously, the O2 is being thrown because it isnt plugged in.
G-Signal = CAS, right?


There are 2 signals that interface between the CAS and the ECU. One is the "Ne" signal and the other is the "G" signal. Both signals are needed to establish ignition firing pulses from the ECU to the Igniter. The code means the ECU is not seeing the "G" signal. It could be a bad connector, i.e. dirty terminals, not engaging, or a bad wire in the harness connector, or a bad CAS.

m.net quote



Still working on getting acurate Fuel Pressure measured. Was waiting on a friend with a gauge that never showed.

Sound like a step in the right direction?
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