Expert: Miami Auto Help Inc Date: 4/2/2008 Subject: No. 1 cylinder barely firing
Question 1992 MB 300E 2.6L. I replaced the head gasket on the car and upon starting I immediately noticed that No. 1 cylinder doesn't really fire at idle. Test drive revealed full power above idle, but returning to idle, No. 1 cylinder still underpowered. I replaced the rotor, the cap the plugs and the wires...all Bosch. I replaced No. 1 injector. Fuel flow at idle for No. 1 is practically non-existent. Under acceleration, the "fan" appears. Line from fuel distributer to injector is clear (I can blow through it). Disconnecting air mass connector increased idle speed but does not improve idle. Car has 145,000 miles on it. Car ran fine before cylinder head came off though would idle rough until warm. Now car also fails to start when at operating temp. At idle, fuel merely dribbles out of fuel distributor for No. 1 with the line removed. I'm thinking fuel filter but unsure. It probably needs to be changed anyhow. But it's definitely ONLY No. 1 cylinder. Removal of plug wire only makes a slight difference. Cylinder is getting tiny amounts of fuel and the spark checks out on the plug. What would cause only number one cylinder to idle badly. Above 3,000 rpm, the problem seems to clear up and in spite of bad idle acceleration under power seems very good and peppy. I do not detect a cylinder cutting out under acceleration. I do not know how to check the fuel pressure regulator or the idle control valve. Although, disconnecting the idle control valve results in a lower and worse idle than before. I noted with all things connected, the engine accelerates slightly to an improved idle speed, but then suddenly drops off to a lower speed.
Answer Are you ASE certified? Or are you just replacing parts?. Have you done a compression test on that inline 6 yet? Also perform a cylinder leakdown test. Once you have done that and I see the results of those tests posted . I will let you know what to do next.
At higher RPMs the miss is not that noticeable. Do the tests and let me know.
Also when you crack the lines at the fuel distributor are you sure that there is only a slight flow and are you sure that it is at #1 . Leave the valve alone. Swap injectors if the miss goes to the other cylinder then you have a bad injector (but I doubt it). Problem could be the distributor. Let me know 1st the test results
