MC gremlins

[Matthew Beaubien]

I've had a problem with my '86 5kt for a while now, and seeing as how the weather has been warming up, I've been more inclined for work on it.

It all started a few months ago when I was driving home from work.  About 10 minutes into the drive, the engine started running really poorly.  I was only a couple of blocks from my house, so it didn't leave me stranded, but was very disconcerting.  It didn't want to idle and wouldn't make any power.  At WOT in first gear, it would maybe rev to 3k RPM.  Playing with the throttle while sitting outside my house, it cleared up and started running just fine.  I drove it to work the next day without any problems.  On the way home, it started acting up at almost the exact same spot.  This time, it didn't clear up, and I had a consistent miss.  Playing with the throttle, I could get it to rev up, but a lot of times it would backfire through the intake and the large pressure increase would case the I/C to hit the front of the car (not good).

Further diagnosis showed that pulling #1 plug made no difference.  I tried a couple of different spark plugs and verified spark.  No difference.  Fine, it must be fuel.  So I swapped #1 and #3 lines at the fuel distributor and fired it up.  It still had a miss, but it wasn't on #1 _or_ #3.  I pulled all the injectors and operated the flapper to see the injector pattern/flow.  They were all very close to one another, and if anything, #1 had a bit more fuel than the rest.  During the course of the diagnosis, I replaced the FP relay and pump, and I also tried swapping the warm-up regulator with no effect.

The next step (a couple days ago, and a couple months since the above) was to put a set of fresh plugs in and try to get a better read on the mixture.  It started ok, didn't have a miss, but was running so-so.  It seems lean.  As it warmed up, it was harder to keep it running and get it restarted when it would stall.  There may have been a slight miss after running for a few minutes.  I pulled all the plugs and they had a nice tan to them, aside from #4.  It looked like hardly anything had gone on in that cylinder.  Also, the O2 sensor was reading very lean during the entire time (even without the miss).

So, what is my next step?  Just swap out the fuel distributor?  I don't see how it would have caused the intermittent problem I started out with, and it seems like there is even flow to all the injectors.  It just doesn't make any sense.

Suggestions?

Thanks,

Matt Beaubien
'86 5kt
'73 911E