I have an 85 400i with 35k miles. the car was running fine today and began to lightly back fire through the intake upon light acceleration. I came to a stop light and it died. Upon restarting the car it was only running on the left 6 cylinder banks. Of course running like crap. I have spark and fuel and compression on the other 6 cylinders. Any ideas?
If you have spark and fuel and compression in correct amounts and at the right time you have a running motor. Ergo one of them is wrong. How much compression? Is the spark at the right time? You have a single distributor so that isn't it. You have a dual contact rotor. That could be it. How much fuel. Enough to choke a horse? Are the plugs soaking wet? If it backfired through the intake it sounds as though either it is lean (No fuel pressure) or there is a cam or ignition (already covered) timing problem. 400's are timing chain eaters and known to slip and have cam timing problems as a result. That is why the compression numbers are important. Since it has 2 independant fuel systems problems in that area are responsible for most cases of a single bank problem. Take the blue grounding plug off which ever fuel distributor has it and remove the intake boot off the bank that does not run turn on the key and see with a pair of pliers if you can lift the air flow plate. Does it have quite a bit of resistance? Or is it limp? If limp there is no fuel pressure. Also if lifted you should be able to hear fuel squirting through the injection nozzles. That should get you close enough to figure out which of the legs of the three legged stool are broken. Fuel, fire and compression. Thats all it takes. Narrow it down and go from there.