E30drift

I just joined this forum so not sure if this is the exact correct spot for this post, but I couldnt find a 4000 model section in the technical forum.

I just bought a 1986 4000cs in great condition except how it runs. I bought it like this so im not sure how the problem occurred. It is difficult to start and any push on the gas will make it die. Once I baby it up to idle and let it warm up, you can rev it and it slowly climbs to maybe 2500 or 3k rpm all while running really bad. I initially thought it was running rich but at idle it sounds "cammed" so I then change to thinking its running lean. I took the whole intake apart and cleaned it. The little door in the intake was very dirty, it runs better now but still un-drivable. The previous owner replaced the fuel pump and filter also.

With the intake box out but everything else hooked up, I can reach into the bottom where the fuel distribution and intake door is. I can "help" the door move up when I rev it via the throttle body and it runs great, all the way to redline if I want. This makes me think the fuel distribution block is a little too resistive for the arm to move properly? The door and lever move freely but the plunger in the distribution block is a little harder to move independently.

Already checked the "spare" fuse, its good. Another thing that is strange is the mixture adjustment screw in-between the fuel distribution and intake boot is completely stripped out... If someone cranked on the screw could it make it run this poorly?

TEF1701

Any sort of small vacuum leak can cause poor running conditions, especially at idle. Mine runs beautifully until it idles, and then it runs like crap. Still trying to track it down. I would replace all of the small vacuum lines just to be safe. It will probably cost you $10 worth of vacuum hose, but the peace of mind is well worth it. Also check your intake boot VERY thoroughly for cracks. Some can be patched with Permatex Right Stuff gasket maker. The stuff is sticky and has done well to seal a couple of cracks in my boot.

I would be concerned about the plunger in your fuel distributor not moving freely. If it gets stuck at any point it can definitely cause problems. Pull your fuel dizzy, and soak the plunger in carb cleaner maybe overnight. Then slowly pull the plunger in and out. Be careful not to damage the plunger though. The plunger and distributor are a matched set and cannot be interchanged.

That's my two cents, but I'm sure others may have other thoughts.

E30drift

You were right about the vacuum leaks... there are vacuum lines everywhere on these cars. I fixed a couple, cleaned the plunger and distributor separately and fiddled with the mixture screw and it runs very good now. The mixture is not perfect and the timing is a little off still but it drives now! Thanks for the help.

TEF1701

That's awesome news! Its nice when it's a small thing like that. Whenever I buy a used car I always replace every vacuum line, I don't care how much the owner says he took care of it. Small fix for some peace of mind. You can now start trying different things to get it running top notch, such as cleaning the injectors, new plugs, wires, etc. Check out Mr. Injector in Idaho. http://www.mrinjector.us They clean and refurbish injectors for $16 each, plus a flat $5.50 for shipping back to you. He even gives you a before and after report, which can sometimes point you in the direction of underlying problems. My #3 injector was the worst of them all, which explained why that spark plug looked worse than the others. Just a thought if you plan on keeping the car.

E30drift

Thanks for the info! Injectors will get cleaned in the future for sure at that price. I just did cap, rotor, and plugs and im about to to the thermostat because it runs hot. What should these run at? My fan doesnt come on till two marks from the H yet the temp light flashes just before that... Im a bit stumped there. Have any suggestions? Is the fan not working right or the gauge wrong?

TEF1701

Could be an old thermostat that is slow to open. Probably worth it to swap for a new one. I don't have my manual readily available to give you normal temp readings, but my gauge has always sat just below the normal reading, even in the middle of summer. Flush your system and replace the thermostat, and see if that fixes it. It could also be air in the system. Even a small air pocket can cause funky readings. Park your car on an uphill incline and burp the system. My radiator has a small bolt on top for just such a purpose, but you could always leave your reservoir cap off too.