Hesitation! Fuel, Vaccum?!?!
 

Last night I did some work on the miata one being vacuum lines. I had my boost gauge “T”ed into the same line the FMU and after 7months of it being like that decided that it would be better if I hooked the gauge up else where. Anyhow, I moved the gauge to where the cruise control used to hookup at right behind the TB and finished up new lines for the FMU. Test drove it last night and worked the same as before. However, for some reason today I’ve been getting a decent hesitation (low rpm’s driving normal/slow) that seemed like a fuel issue (loaded up or etc.) a time or two. It may not even be vacuum related but just seems weird it would happen right after redoing the lines.

Current Vacuum Route:
Stock FPR to Intake Manifold (like stock) with FMU “T”ed in-between the stock FPR and Intake manifold. (looked at the greddy instructions and this seems to be the same as recommended).

How do you all have your lines routed? Could it be in injector or fuel pump issue?

*My car has Stock Greddy Setup (within the last 3 months; new plugs, plug wires, fuel filter) I also changed the o2 sensor and some other small things that shouldn’t be related last night when redoing the vacuum lines.

moveing the vacuum line wouldnt cause this.

re-trace your steps.

Verify the FMU's source inst kinked or leaking.

If you still have strong vacuum at idle I would look elsewhere, what else did
you do at the time other than the o2 sensor?

I'd double check the O2 sensor, make sure the wiring is all intact.

I'll check for kinked FMU line but i know its not leaking and I didn't move or disconnect/reconnect any of the fuel line to or from the FMU. The hesitation is here and there; not consistant. I had a exhaust manifold stud back out so i fixed that the rest was stereo/interior that's unrealated. The o2 sensor is connected for sure. I had it disconnected at one point a long time ago when i first installed the kit and after about 5miles it threw the check engine light. I currently have no light on and I soldered all the wires and checked them before shrink wrapping them.

Now that I think of it the car as done it before awhile back and did it a few times and never seen it since (about 2months ago).

Is it a 4 wire? Is the hesitation happening more when the car is cold?

DansC. PMed for a little more help and I suggested this:

do you have an o2 clamp? Have you always had this hesitation? Could just be a lean-tip in.

I ask because you said you just replaced your o2 sensor, when an o2 sensor starts to fail to system tends to run rich.

Replacing your o2 sensor could have cured rich idle and actually lead to a typical lean tip-in.

the ecu will always try to see 14.7 AFR when in a closed loop. which is typically below 4k or when under heavy loads (up hills). So your FMU will be dumping in fuel as your ECU tries to take it away. This causes a hesitation. Lost of us have felt it, including myself.

The O2 Clamp is activated just upon boost and modifies the o2 signal to the ecu and gives it a signal that all is good, so just as you enter boost the ecu will not try to pull your fuel.

Anyone care to comment?

:bowdown: Any idea where he can get one of those O2 clamp thingies?:bowdown:

Some cool dude makes them ;)

shameless plug :bigtu:

I'll be getting one of those from you pretty soon OG.

I heard the guy was old though.

it's not shameless, he's doing us a favor by being smart and crafty.

Shameless plug reference is from WWF wrestling (Mick Foley, Mandkind, whatever you wanna call him).

I am well aware of the service that OG provides to the turbo miata community...that's why I am going to buy my O2 clamp from him :bigtu:

Im sorry if I offended anyone...that was not my intention :)

None taken here; it was a shameless plug.