QuestionQUESTION: I have a 1979 450SL Roadster, 4.5L Mercedes that was a European car and converted for U.S emissions by the original owner many years ago. When the engine is cold and I drive it, the car runs fine, idle is normal, and performance is amazing. When the engine comes to temp and I try to heavily accelerate, the engine seems to “load up” and “spits and bucks”. Normal acceleration from a stop seems to be fine and idle is not effected. I have already replaced the distributor cap, rotor, plugs, and wire set which was needed. I have also purchased an injector cleaner and valve cleaner from a Mercedes Performance catalog and incorporated both into the fuel. I purchased the car late December and drove it home and this problem did not exist. I did park it over the winter, starting and idling 20-30 mins several times during the 4 months it sat.
At first, I thought the EGR was not performing properly but I have checked the operation by removing the vacuum lines, through a procedure I found on the internet, and find that it seem to be working properly. Others have told me that the Cold Start Injector may be sticking and over-fueling under load, but the idle is not effected and I have no signs of smoke.
This is all the information I have at this time. Thank you, in advance, for any suggestions you may have.
ANSWER: if it bogs down under load I would suspect too much air or too little fuel. It sounds to me that it is carb related. You do not mention if the carb has been cleaned or serviced. If it sat for awhile you may have some deposits that are causing improper mixtures under load. If you do not smell fuel then I would look at the air mixture and throat plates. There is also an outside chance you are loosing compression when the engine warms , but you said you do not see smoke so this is unlikely.
Timing and dwell are also key for solid acceleration under load. Dwell is best set by a meter. Have these been checked? Also make sure the vacuum advance on the distributor( if you have it) is working properly.
Good luck and tell me if this helps
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QUESTION: This engine has a Bosch fuel injection system with a "drop plate" design for a mass air flow. I have checked the vacuum on the EGR which is also feeding the vacuum timing advance for the distributor. I will look into checking for vacuum at the timing advance. Do you recommend having the timing and dwell adjusted if this has not been done. Also, remember that this problem did not exsist when I brought the car home in December and it sat for 4 months before I drove it again. Maybe this will mean something or not.
Thanks
AnswerI think you are looking at a fuel starvation problem, if it ran good then something while it sat - changed, either a vaccuum leak from a weak hose, or gunk somewhere in the delivery system. I know you mentioned cleaners used but you may need to have the injectors removed and tested for spray pattern. I guess you could continue to try antother round of cleaners, but again if it was fine prior to the storage, the only logical thought is a fuel delivery issue or air volume issue ( too much, not enough) I would focus efforts in those areas. Mechanical issues don't just appear in storage ( other than rust!)
two other thoughts is to make sure you are not vapor locking the fuel,make sure your cap is venting properly and that all the gas lines from the tank are not crushed or deteriorating in any way so as under load you are not sucking in air.
Keep me posted, i will do some research as well
