J.S.J

I have a 93 FD, street port and using a 2nd gen something or other map sensor tweaker to slow fuel delivery as I don't have a lot of vacuum (14 to 16 in).
Some times I come to an idle and the volt meter I have reading the 02 sensor voltage is reading .9xx. The engine at this point is rich. I have found when I pop the hood latch it drops way down to less than .2xx, lean. I haven't done much analyzing of the situation but has anyone have some experience or understanding of what might be going on. I have isolated it and it is triggered by the micro switch. Sure there are some things within the air system which could cause this reading at the 02 but the exhaust smells lean and rich at the appropriate times. Along with the readings going lean the engine idle smooths out as well. Really nothing surprises me anymore concerning this fuel injection system but just would like some input. I surely need to install a stand alone system and toss the factory ECU but I just haven't yet decided what I am going to do.

InsaneGideon

Call a priest, you car's possessed!

Looking at the FSM, the hoodswitch has nothing to do with the main ECU, unless I missed something in the past. So, I wouldn't be suprised if the problem persisted even after going to a stand-alone unit.

I'd start looking at some user-installed electrical accessories and see if something was mis-wired (not to insult your electrical talent, just suggesting )... or see if your tires ate through your fender-liner and harness shorting stuff together, a la Turbojeff's MAP sensor fiasco.

The hood switch wire is a ground when the hood is open, so perhaps a mis-wired device is pulling a lot of current when it opens and induces voltage in neighboring wires or drops voltage somewhere else (since it isn't intended in the design). Or maybe when it's open it actually helps by grounding interferance being injected into the line by an alarm system's heterodyning transmitter. I know that last part sounds far fetched, but there's a reason why the O2 sensor wire is shielded.

Do you notice the idle/smell change when the meter isn't connected?

Are you sure the hood isn't blocking something, or pinching a hose when closed?

J.S.J

I have tested the micro switch circuit alone divorced from the hood latch and it does what I have said. Mazda it seems to me has a real "need to know" attitude where the service manual is concerned. There information which is contained in the service manual is far incomplete. The inside programing details concerning many details is not shared. I worked for General Motors as a drive-ability tech for 20 years and there is more information in there. What I mean is the way systems act under certain conditions or how they react between each other. I also feel your points are well taken and am going to look in to it. I just passed my Ca. smog testing with the stock ECU. I have the 3K hesitation to the max. I feel the ECU is at fault and am going to look into opening it up and installing a cooling system. A set of computer fans to see if that helps. The injector drivers may getting overheated or the support systems within the ECU may be overheating. The engine runs great otherwise.

J.S.J

I have to confess, I didn't isolate the problem properly. I have moved all my solenoids out from under the intake and the vacuum supply line to the air pump switching valves was being smashed by the hood insulation. Thus it would pump down stream but not up with the hood closed. I just moved the bracket and it's now working great. I am now trying to isolate the source in the ECU as to where the 3K hesitation starts.

InsaneGideon

Yeah, the FSM is pretty vague on the control system. If I recall correctly, some parts in the sensor diagnostics sections are flat-out wrong.

Glad it was a pinched hose. Had it been an actual electrical gremlin, it would've taken ages to diagnose... like the 3k hesitation.

Good luck with that one, BTW. There was a thread some months ago about it where KevinK2 was arranging to borrow a portable multichannel data-logger (or was it a DSO?) and was going to record the injectors' behavior. I've lost track of that, in the mean time...

J.S.J

The 3K is a real pain and I would like to find some way to relay the signal to a heartier set of drivers. I have plans to look at the amperage draw and voltage along with the pulse with. The engine runs so good otherwise. Sure I can get a stand alone but a good one is an investment. I just don't send out things for others to set up. I also am not trying to build a race car. I am only running 7 lbs of boost and for me that's plenty of power. I like the idea of studding the system, learning the root of how the systems operate. Doing things all my self is a terminal illness or a curse but thats the way it is. I really can't see why you couldn't just use the factory drivers as a reference signal and use other electronics to do the heavy lifting. Well another science project awaits. Thanks for the input.