Under hard acceleration in 2nd or 3rd there seems to be a lack of power in he 2500 to 3500 range. I remember something about fuel pressure and shims but can't find anything in the archives.

Thanks
Sean

 

hold on sean i'm working on a cheap upgrade to ditch the cis system. i wont be selling it but will help others.

 

how cheap??? I'm interested...

 

Does "in the 2500-3500" range mean its ok above and below that range? How long since filter was changed? Can you measure control pressure? Once I sorted a bad WUR out, and a couple of new injectors, I have NEVER had anything but good response out of my car.
jp 83 Euro S AT 49k

 

JP, the whole fuel system except lines, accumulator and distributor are new. Control pressure is correct. The engine revs pick up nicely until about 2500 then slow and then pich up again at about 3500.

Lance, I'm interested. I have long trhought that even just replacing the WUR with something more modern would help things.

Sean

 

Have you checked the action of the distributor? A lack of vacuum advance would make lower RPMs feel boggy.

 

Glen, I did check that when I remove the vacuum line from the distributor at idle, the idle rate increases. I assumed that this means there is freedom of movement for the parts inside the distributor.

Sean

 

OK. So you've got the one vacuum line that actually provides a retard and a mechanical advance under the rotor. I suggest checking this system with a timing light. Do you have the info on this? (No books at the office for me.)

 

Sean, did you re-seal the CIS "U" housing? There is a gasket that runs the full length of the housing and in my case that was a prime contributor to the kind of behavior that you describe.

 

Dave, not sure what the CIS "U" housing is. Can you explain further.

 

That's the housing that the fuel dist. and TB sit on top of, essentially the induction path between the air plate and the TB. It is comprised of an upper and lower half, sealed by a gasket. In my case the gasket had aged and in one spot had been blown out by a backfire.

 

right know i'm in the research stage should be ready by feb. 06. i crack open my cd manuals. i'm making up a parts list. the smart thing is to start looking at the l-jet 4.5 efi sharks. get the basics down. and then see what modern parts can be plug in the kit. I'm thinking l-jet fuel rail injectors, and a gm Maf instead of the restrictive Afm that uses a metal door to read the air flow. thats the first thing the 951 guys ditch to get extra power. like i said i'm still in the research stage of the kit.

 

cant find my copy of Watson just now, I find him indispensable in working on CIS. Have you checked fuel flow rate is ok? ~1350cc/30 secs. Does the engine go through the problem phase and start pulling properly again? Does it do it stationery and under load? Your test of pulling the vacuum off the ign distributor may not be valid - the idle may have changed due to extra air coming in through the line. I would pull the cap, fit another tube to the fitting and suck on it - you should see something move. Also check that the rotor can be turned against a spring and it snaps back when released. A frozen mechanical advance can do similar things to what you describe. Also check that the air plate moves smoothly and doesnt bind anywhere in its travel. Has ANYTHING been changed lately, between when it was OK, and when you noticed the problem? Start backtracking through any work done and re-check it all.
jp 83 Euro S AT 49k, recent new tank, pressure line, accumulator, pump, filter, fuel hoses

 

Found Watson. Under "stumble or sag on acceleration" he gives possible causes as Sticking or binding air plate, Incorrect pressures, or unequal injector flow. Under pressure he list 928 as system 65-75psi, warm control 41-46. Under sticking air plate he suggests checking for same clearance all around. If this is ok, but plate does not move smoothly, it needs dismantling and cleaning internally . He notes that the fulcrum assembly is the ONLY part of CIS that can safely be dismantled and reassembled without damaging it.
Is it possible that in replacing parts recently you have introduced some crap into the system? Twice in my time with my car (5 years now) it has developed a misfire on one cylinder, which once located I could cure by popping the injector line off the injector to relieve pressure. My wrench reckoned this was a sign of dirt in the distributor getting trapped in the port to a line - relieving pressure allows it to fall back again and open the line. It will have to get considerable more frequent before I will go for a rebuild here.
jp 83 Euro S AT 49k

 

JP, tThanks for all the comment and advice. I will check the movement of the air plate. The injectors are new so I don't suspect them. I will also re-check the operation of the advance per you suggestion.

I may be faced with pulling out the whole air plate / tb / plenum assembly to check.