84 930 turbo engine problems
 

Ok guys... I am not new to porsche cars at all, and pretty good backyard mechanic, but this one has me stumppppped.

My 84 turbo when under load misses out and pours black smoke... most of the time. It is cis injected of course and I am pretty familiar with it... had lots of 911sc's, 928's, etc... vw's etc... you get the idea.

I have check, I BELIEVE, all the vacuum leak posibilities, checked the airbox for being broken, changed plugs, played with fuel mixture, everything under the sun that was obvious to me. When it is really cold out, hence right now, it will run down the road and the turbo will kick in and run ok... not perfect, but not pouring smoke. When its warm out, such as noon today, it barely stumbled through town with out turbo and would look like a diesel with the turbo kicked it.

It was suggested that a fuel pump may be out... I was told it has two. Thoughts?

Also, it will rev up just fine without a load when it is acting up... no smoke, etc... just not in gear or with a load behind it.

It starts perfect, idles perfect, no other issues.

I had a cis 911 onetime that had a stopped up fuel filter that would make the car rev fine without a load but crap out with a load... Any thoughts there?

But, under load, I get black smoke... i believe is fuel (not oil) and that leads me to believe it is getting fuel...

My tach is acting up too... but not in series with the engine issues... I though maybe spark was cutting out, but that doesnt make much sense because it will always free rev without a load... the permatune box doesnt care if there is a load or not... it doesnt know. So i think spark is ok and I have a fault tach wire or something... thats for a nother day.

i am lost... I am game for any ideas... fuel pump? Sensors? (i unplugged the 02 sensor... but it isn used in full throttle anyway... and doesnt make any difference in my issues now).

Low fuel pressure? Cloged filter? Un obvious vacuum leak under pressure?

Please help.....


todd:mad:

930's do like to run rich. But this sounds far too rich, that causes contamination of the oil which is really, really, bad news.

With CIS, you can't adjust anything other than the idle mixture (which has only a tiny efect on the rest of the range on a 930) without knocking plugs around in the WUR, modifying it to be adjustable or having an adjustable one in the first place.

930's don't break air-boxes - there's too much volume in the intake plumbing for backfires to have much effect, to say nothing of the 8 pound, cast, pop-off valve which turns out to be completely unnecessary - just ask anyone with a Kokeln, Ruf or 965 et al intercooler... :)

Stock 930 has a front pump and a rear pump. Car will run lean - in "limp-home" mode, it'll make no power - if a pump is out, because the dead pump will impede the flow from the functional one.

I think I would start by baselining the CIS control and system pressures, bleed-down time, and pump delivery rates (together). As it smokes worst under load, I'm wondering if something unpleasant has happened to the boost enrichment circuit in the WUR and it's kicking in too soon, or something like a split diaphragm...

Posting on the 930 forum would probably get you more 930-specific advice.

Tach acting up?; could there be a charging issue, messing with the system?

I will check fuel pressures today... Being dumb for a sec... "WUR" ? Help me out there... its early sunday morning. I havent looked real hard yet, but can I pull a vacuum line or something to prevent the turbofrom kicking in to try the idea of boost coming up to soon? I check the alternator, it is 13.7.... all the time except for idle and it drops to 13.5 or so... no real change.... evn plugged a cigarette meter in and drove around the block to make sure it wasnt acting weird off and on... or ground breaking as the car traveled or flexed...

I am lost....

I'd start with the Warm Up Regulator by checking cold and hot fuel pressures. I think they tend to go to higher pressure when they fail which would make a lean condition with CIS, but I guess it could have some failure that makes it drop pressure.

Sounds similar to the problem I had described here:

http://forums.pelicanparts.com/porsche-911-technical-forum/148707-89-911-930-running-poorly-5mpg.html?highlight=warm

I was a bad warm up regulator...