I have been working on this for a couple of months on and off. I originally had the problem of 2 cylinders running rich, so I replaced all 8 injectors. Problem worsened, so I put a reman fuel dist. on, all run rich now. Put the old one back on and adjusted lambda, no better. Took off fuel press. reg. and dissasembled, pushed bi-metal stud up .020 of an inch, re-assembled and tapped down to reach 2 bar of fuel pressure per instructions I found. No change. Thought maybe not enough supply pressure or volume so I replaced fuel pump and filter, no change. Replacedcoil thinking spark not hot enough, no change. Replaced ign module, found out it was supposed to have non-resistor plugs, so I installed a set. Did'nt find any vac. leaks either.I also changed the O2 sensor. I need help.I also took the cold start valve out of the equasion. And disconnected the frequency valve.

Wolfgang

 

I had similar issue on a couple cylinders. Changed a lot of what you did. Finally a new set of spark plug wires and double checking their routing to ensure no rubbing and shorting did the trick. The wires are pricey. Might try a look see at night and move wires around with a wooden stick or ruler, etc. while engineis running May be even try and save your existing spark wires and visually check all to verify intact and no spark leakage. Also check the routing and condition of all the injector wiring. Just a few ideas to try before spending more $$, as I know the hard way, it hurts the billfold.

 

Thanks for the reply, I failed to mention that I put new wires, cap and rotor on, and adjusted the timing. No slop in cam timing either.

 

Forgot to post. More than anything that helped my "known to run rich on certain cylinders" engine was:
-Forget what all the forums or auto parts say on spark plugs. These cars will run just fine on resistor plugs. I know, I have wastedhundreds of $$ on plugs to find this out,even more in plug wires.
-I expended a few hours online and found the heat range equivalent of the bosch plugs for my car, forUS marketed plugs, identifiedtwo steps hotter in heat range, found Autolite plugs of that heat range # atWal-Mart for 99 cents each, installed.The two cylinders that seemed to always run a bit cooler orricher than all the others immediately perked to life and after removing and checking three times during 5000 miles, every plug is a perfect white, no over heated look and the car idles and runs better. I also drained coolant and installed 50/50 antifreeze, whatever was on sale, and that stabilized the temp gauge to well under 100`C and generally 90-95 on hot days. This also keeps the engine and plugs working right. New engine 10K miles ago, so I know it is design andnormalquirks/issues to work around, as the rich/cool cylinder plugs occured before and after rebuilt.

 

What was the brand and number spark plug you used ?