Techni-Tips – June ’87
Q. My car, a 1980 320i, has been run ning poorly when cold . It stumbles and dies at intersections, has no power and pops in the engine when I try to acceler ate . The car has 85,000 miles on it. The car was tuned 3 months ago, but the tune-up didn’ t take care of the I’ ve taken the car to several shops, but the problem still remains . I don’ t own a gun, but if I did I would shoot the damn thing . Help!
Dick Meldstrum, Seattle
A . For the purpose of discussion , I will assume the following: your car has at least minimum compression of 11Spsi (more or less depending with whom you are talking), the valves are adjusted to .007, plugs are gapped to .028-.030, tune-up specs are right on, the distributor centrifugal advance and vacuum dashpot are functional and there are no air or vacuum leaks.
The sensor plate in the fuel injection control must be adjusted properly and the CO mixture must be right on. The sensor plate is located under the black air boot on the driver’s side of the engine . Re move the hose clamps attaching it to the throttle body and the air flow meter hous ing. Next , remove the two smaller hoses attached to either side of the air boot. This exposes the sensor plate. The sensor plate is a round disc approximately 80 mm (3Vs” approx.) in diameter and 1 mm (%4 appi:ox.) in width . The upper sur face of the sensor plate should be even with the bevel cone in the housing , or slightly below (no more than 1/2 mm) . If the sensor plate is too low or high , then it will need to be adjusted. The easiest way is to remove the 6 mm bolt in the center of the sensor plate and remove the plate . The lever to which the sensor plate is at tached is adjusted by bending the spring down if the sensor plate is too high , or up if the sensor plate is too low. Pulling the springs up is easy but bending down could cause the spring to dislodge.Iusu ally shim a screwdriver underneath the spring and push down with another when perforriling this task . Do you think a good shop manual with pictures might help at this point?! Take the detached sensor plate and place it against a plate glass window. First try one side of the plate against the window and then the other . If the plate rocks, then it is not flat and should be replaced. Reattach the sen sor plate and center it so it doesn ‘t hang up on the sides of the air flow cone.
By the way, most sensor plates get maladjusted or bent from the owners good intentions of putting their foot down on the accelerator pedal when starting the car. Don’t do it!
If the sensor plate is adjusted as it should be, the next step would be to check the CO on a CO Meter . Most shops have a CO Meter and the cost for adjust ment should be minimal . 1980-1983 320i should be measured in the downpipe and matched with the oxygen sensor at about .6% CO (tolerance is between .2% and 1.2%). 1977-1979 320i should be measured at the tailpipe with the air pump hose to the exhaust manifold dis connected and plugged . The average spec. should be about 2% CO.
If all the above checks out, then the fuel cold control pressure should be checked with the car dead cold (8 hours sitting) . This is best accomplished at your favorite shop with current specs for your car.
If all this fails, then the problem most likely resides in the fuel injectors. An at tempt at cleaning them with a fuel injec tion flush hooked directly into the fuel in jection system might work , but the sure fire cure is to replace the fuel injectors.
This may seem like a lot of work just to make your car run right when cold , but you will be amazed at what it will also do for your car when warm!
Q. I’ ve had my 1982 528e tuned and serviced at the recommended intervals, according to the service indicator lights. It dies, surges and hesitates when the car is mostly cold, but when warm also. Do you have any insight as to what the prob lem might be and how it can be corrected ?
Phil Quantum, Bothell
A. I will assume your car has been maintained properly , is presently tuned to the factory specs ., and has no apparent air leaks or ignition wire related problems .
Quite a few of the ETA controlled en gines had/have an increased tendency to build carbon on the back side of the in take valves . The theory of how this hap pens is called “hot soak.” When a hot en gine is turned off a majority of the intake valves will be closed. A residual amount of fuel will remain in the area around the intake valve , intake chamber and intake tube . The hot combustion chamber tem peratures now dissipate into the sur rounding areas. The temperature on the backside of the intake valve increases and the fuel vaporizes and forms a carbon creosote-type substance . This carbon type of substance is very hard and porous and builds every time you shut off the en gine. BMWNA speculates that a small amount of oil seepage from the intake valve guide seals may contribute to this problem .
These same deposits accumulate around the injector nozzles and orifices and, in effect, decrease the flow of fuel through them.
BMWNA has recognized the tendency of fuel deposits to occur in a number of their vehicles . They have at tributed the problem to fuel qualit y and have recom mended the use of fuel addi tives to counter t he negative effect of fuel deposits on engine performance.
In order to increase cus tomer satisfaction, BMWN A has been performing an en gine campaign to correct the problem of carbon deposits resulting from inadeq uate fuel. This campaign affects certain years of the follow ing vehicles: 318i, 325e, 528e, 533i, 633CSi, 733i, 535i, 635CSi, 735i and L7.
This engine campaign has been done to all cars regardless of warranty status as long as it is not a gray market car. It involves upd ating the idle control units and idle control valves to the latest generation units . The campaign assures clean intake valves by removing the intake manifold and cleaning the back of the intake valves and chemically cleaning the fuel injection nozzles .
Once the campaign has been done, assuming your car qualifies and needs it to be d one, it is very important to begin the use of a fuel additive specifically designed to counter the negative effect of fuel deposits. Once these deposits have formed they are very hard to remove. The additive must be used every time the tank is filled to insure proper cleaning.
I am confident the major oil companies are aware of this problem and are designing additives to their fuel to react more compatibly with the new generation of engines being produced today .
This article was originally published in the June 1987 edition of Zundfolge