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I've been driving my GS again since around March (had minor bodywork fixed), but lately I've had some problems. The car seems to start only when she feels like starting, often leaving me stranded. The engine turns over fine, but never catches. I'll get a ride home, call a tow truck the next day, and show up expecting to tow... then she'll start right up. Also, under hard acceleration, I get a sort of bogging down, but only at full throttle & only in the powerband.

I've got about 150K on the car with about 20K since the swap. I'd been running the stock disty with bad resistance #'s & cam sensor, so I replaced the disty, and saw minor improvements. I've got great spark. Intake's got no problems. Fuel system?
That's where I'm at. I plan on ripping the engine out and going through it thoroughly over Christmas (I've got a valve ticking ), but until then I've got to get moving again. My thought is that the fuel pump's losing pressure - it's stock... so is the Walbro GSS250 still a recommended replacement? Is there any reason to look into "high pressure" fuel pumps?

try replacing your fuel filter. it may be clogged causing this issue.

I replaced the fuel filter a little over a year ago...
The pump's still stock making it one of the few parts I've yet to replace. I'm about to call around for best prices on a pump, so I can get it done before the weekend. Any thoughts on whether the relay could be my actual problem?

Put a gauge in the line and check out the pressure. Haven't heard of the stock pump being an issue as far as pressure goes.

Sounds like the disty to me. Occassional start, most often success when cold.

Updating.
Hopefully some info will be found useful.

I replaced the fuel pump - went with Walbro, tried two new distributors, replaced the crank sensor, and no results. I planned on ripping the engine back out to fix a valve tick and a tranny leak anyways, so I did just that.
Verdict: my timing belt tensioner had worn out/loosened up/whateverit'sjustdead.
Easy fix, so I'll just be cleaning and piecing everything back together once my heads get back.
Main Question: Is there any reason I can't attribute my problem to this tensioner?
Also: Anyone know a secret/special/cheap way to get a hold on a new/clean timing belt cover? Gonna call Mazda and Ford tomorrow.
Extra: Any tips on sourcing an Mx-6 5th gear? I recall (from a few years back) that it had a better ratio and was interchangeable...

Thanks!

A good scrap yard is worth checking out. Won't find anything clean, though. Maybe new.

Not sure why a simple tensioner would cause your reliabilty issues. One would think as soon as the tensioner slips, the timing jumps, and you'd have more clear issues.

That's my thought - slippage caused my first problems: stuttering in the powerband, occasional trouble starting. These progressed to almost never starting. The thing was pretty much just for show.
Guess we'll see when I get it back together.

I'm kinda excited... I haven't been to a yard for my Mx in years!

Well, to start off...

WOOHOO!!!

Yes, yes, she's running great now - better than ever actually.
I gave up/didn't put a whole lot of effort into the transmission 5th gear swap idea.
...but rebuilding the heads completely rid me of that annoying valve tick.
After a few minor issues (vacuum lines dislodging, bare solenoid wire grounding out my fuel injection, etc), she purrs quietly at 750 rpm and revs like a streetbike.

Nitty Gritty.
My starting/running problem was because of that stupid timing belt tensioner. Replacing it allowed me to actually set the timing correctly where it once was impossible (always seemed slightly retarded).
Hopefully someone'll find this useful.
I'm just stoked to be back on the road

glad to hear everything's good, now go out and up our mx-3 rep by beating those hondas =P