The Org - Serving W116 Enthusiasts since 2004!
Started by raueda1, 01 November 2018, 10:03 AM
Quote from: raueda1 on 01 November 2018, 10:03 AMAfter solving a long crazy WUR/fuel pressure mystery my car is running very well. However, it's now cold enough here, 35-40°F, that all the cold start mechanisms should be in play. The car starts immediately but idle is very rough for a minute of so before it smooths out, almost like it's not firing on all 8. I know that the WUR and fuel pressures are all ok. At one point I cleaned the aux air valve on principle. Any thoughts on what to look at? In the spring it's my plan to replace injectors and maybe rebuild fuel distributor. Thanks!
Quote from: TJ 450 on 03 November 2018, 07:18 PMAfter checking the above, I would also check that the airflow meter plate is moving smoothly and that the screw is adjusted. This is assuming there are no vacuum leaks.When it's running roughly, see if you can get it to run smoothly by manually pressing or lifting the plate to see if it is running too lean or rich.Does the engine hesitate or feel like it's going to cut out when you open the throttle during this condition?Tim
Quote from: UTn_boy on 29 October 2023, 05:20 PMWell, contrary to one of the comments above, the cold start injector does not operate until the engine warms up. It ONLY operates between 2-12 seconds max and only when the key is in the start position. The colder the engine is, the longer the cold start valve will spray, but again, no longer than 12 seconds. Conversely, with a hot engine, it does not spray. The thermo-time switch is what determines how long to operate the injector. You mention that the car starts up instantly when it's cold. I'd venture to say that your cold start injector system is ok. The most common failure is the valve/injector itself. They'll either leak fuel externally, or the pintle valve will get stuck open and will constantly spray or dribble fuel into the intake. Sometimes the wiring will flake out, and rarely will the thermo-time switch go bad. You'll usually know if the injector is leaking or stuck open. It'll belch out black smoke from the exhaust, fuel economy will decrease, or there will be a slight miss that can't be rectified through conventional methods. As far as testing the system, there is little to do. With a cold engine, make sure you're getting voltage at the injector when the key is in the start position. In order to check the thermo-time switch, you'll have to measure the resistance of the switch at it's terminals and compare that reading to the temperature. There is a table in the shop manual that shows the correlations between the temperature and the resistance of the switch itself. And of course, check the wiring, and I believe there is also a relay for the system. But again, reading that the car starts instantly when cold tells me the cold starting system is probably working.....but who knows. Just my two cents worth.
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