Lizard928

You need to take a more methodical approach to this. Verify CIS pressures,
verify timing,
verify that you do not have massive vacuum leaks,
adjust base CO
Maybe flowcheck each injector.

Mrmerlin

unless you have the brake booster line plugged then you will have a leak at the booster this will cause a bad idle. Due to removal of the M cylinder

jwillman

Brake booster is still installed and vacuum plumbing connected , at lease as it was when I got the car. Only things out right now are the air filter assembly, brake master cylinder, brake/clutch resoervoir, brake pressure reducers, and clutch master and slaves and associated plumbing.

I downloaded some CIS theory and trouble shooting stuff but could really use a sequential list of stuff to check which would be really great about now. I don't have a CIS fuel pressure test set and looks like that would be helpful to eliminate items if nothing else.

Seems to me that if injectors were the issue I would have the problem all the time yet on some occasions the engine smooths out and runs pretty well. Seems if I had ignition issues those would also not allow the occassional smooth running.

Vacuum and fuel delivery (those multiple items that affect fuel) seem a greater possibility but then I am the new guy and can't really discount anything at this point.

Thanks all for the input and please keep it coming!!

jpitman2

With the brake m/cyl off the booster, does that allow air into the booster chamber? I would plug the vacuum line to the booster to remove that possibility.
jp 83 Euro S AT 52k

tailpipe

In my experiance with resurecting the CIS systems on my cars here first check to is make sure both fuel pumps are working just one pump working will cause your symptoms. hot wire them directly to power on the plus side ground is already hooked up make sure they work second thing is to bypass the fuel pump relay with a jumper wire to guanetee no problems with the relay if you can get the car to run a small amount as its running put you finger on the airsensor plate and push slightly this will richen the mixture if the engine smoothes out then its prolly the WUR that is not working correctly there is an adjustment modification that you can do to make it adjustable in 5 cars i have only had to adjust one. If the car is running but running really rough then its prolly the injectors that need to be cleaned any bosche certified diesel shop can clean them and check the flow rate for you I just had a set done here for me cost me $30 bucks for ultrasound clean and flow test. if the car idles well but dies out around 2500-3000 rpm then its prolly the fuel dis that filled with crud, again you can try the diesel shop ultra sound or take it apart yourself and rebuild it worst case is a used if you can find one
Imho if the car has been sitting for along time and runs somewhat but roughly usually cleaning the the injectors is what it needs most feel free to pm me if you have questions


Paul with lots of CIS cars
5 928s all 78-79
6 vw bunnies
1 924 1977

donithan

has anyone adjusted co mixture infront of fuel distributer if they have it can be very difficult to get it here it ill run again. i had same problem had to adjust it small amounts until it would stay running. just my two cents.

ammonman

Do as Mr. Merlin and jpitman2 have suggested and disconnect the vacuum line at the brake booster and put a temp cap on it. With the MC removed from the booster you have a HUGE vacuum leak. There is an o-ring between the MC and the booster to keep the booster air-tight and ensure it will hold vacuum. If it still idles poorly with that line capped then start following the troubleshooting info you have found by starting with the most basic stuff first.

Mike

jwillman

Thanks all. That makes sense now as I did already buy the new seal to go between the booster and MC when I get it back in. I will try that today.

deptotpr

I see your "Living the Dream"

Wow! 164,800 miles plus + on the motor

Replace spark plugs.

jwillman

I have only owned the car since April (another cheap 928 that had a blown clutch line and would only run with starter fluid poured into it although a did get it to run on her own shortly after that until fuel pump problems) and it has been in the driveway since so the miles are all previous owners.

Car was sold with a extra engine (almost complete) and a box of many other parts that the PO twice removed had procured for an unknown reasons, to me to date anyway. Many of the parts I have ended up needing so far, in tank fuel pump, park brake pads, tie rods so it makes me wonder about the engine now sitting on my garage floor Once it get the engine in the car running a bit better I will figure that one out.

I pulled the plugs and they looked new but a bit sooty so I cleaned them up for now as I could not find Bosch W8D's readily available at the auto stores I tried.

jwillman

Thanks to your posts I was able to get her started and running much more consistantly.

I pulled the plugged the vacuum line at the brake booster and on the 3rd start she stablized at ~1300 RPM and ran relatively smoothly (comapred to the video). Once warm she drops down to the middle hash mark below 1000 which I assume is about 500 and idles there all day long. She still hesitates a bit responding to throttle and I can only get her to accelerate to 1600-1800 RPM before she starts to fumble and hesitate pretty significanlty. Seems the max I can coax out of her right now.

What items should I be looking at next? I am sure there are a ton of vacuum lines that need to be replaced. The vacuum line to the WUR that runs back under the intake distributor is hard as a rock and split at the WUR. Can't see where it runs to so perhaps I need to pull the air dist and get better access to all the lines and take care of them at one time.

I need to order a pressure guage tester set as I know those pressures are critical. Any other stuff while I wait for that?

Thanks all for the support and education!

jpitman2

Without gauges about all you can do is check the fuel delivery rate is up to std - I think I saw 1150ml/30secs for single pump, 1350 for 2 pumps. My 83 gave 1350 on one external pump. I replaced one of my vac advance lines readily by removing one of the inlet tracts - either 1 or 2 IIRC. Only pull these leads ONE at a time, so you dont forget where they go!
Vac connection to WUR is really only to sense WOT so it can richen I think, so plugging that would not affect WUR much, but would reduce air leaks for the better. Might not hurt to put some Berrymans (or similar) in the tank, and bridge the pump relay to try to dissolve some crud out of the system....When my WUR blocked, warm control went up to 60psi, and I could get it past about 20mph, so my money is on that area. There is an article of mine on WURs on landsharkoz, as well as many others on the web. There is a good one on calibrating a WUR on a benzworld site somewhere too.
jp 83 Euro S AT 52k

86'928S MeteorGrey

Carl has a silicone vacuum hose set that is reasonably priced. Available in colors or black. I'd hit that first. Congrats on some progress...

mark kibort

anyone notice the voltage was way low. could be an issue

jwillman

I noticed that as well. I did check voltage with a multimeter at the battery while the car was at idle, 500 RPM, and got 12.85 v. Battery started at 12.5v before I started her.

I have not done all the grounds yet. I have replaced the negative battery cable and engine ground cable and cleaned those gnd points but still have the others to get to.

I did just notice another issue that maybe voltage connected. The headlights raise and turn on with key on and engine off. With engine running I tried the lights and nothing. Connected?