QuestionThe truck turns over but dose not start. I replaced fuel pump relay and added water remover to the gas. When sun warms the hood, the truck starts.
AnswerHi Pete,
Well, I can't tell you what is wrong with the vehicle, but I can help you to find out what it is.
I would test the vehicle ONLY when the problem is present. It's sort-of useless to test a running engine for a problem that occurs only when it's not running.
If the battery turns the engine over nice and consistently and does not slow-down or die trying to crank the engine up, I would rule it out as the cause.
Asside from the kinetic energy the battery provides for artificial run, the engine only needs three things to run. Fuel, spark and compression. Compression won't vary enough between cold and warm to make any type of difference here and since the engine does run, we'll assume the cam-to-crank timing is good, so we'll rule-out engine mechanical problems as well. That brings us to fuel and spark.
Checking fuel and spark on the non-starting engine should be a breeze. Best way to test fuel pressure is with a fuel pressure testing gage. In absence of the proper tool, you can find the Schroeder valve on the fuel injector rail or feed line and BEFORE turning the key "ON", release ANY pressure that might be still in the line since the last run of the engine so as not to screw-up the test results you are looking for. Cycle the key "ON" but do NOT start the engine. You should hear the fuel pump cycle on for a few seconds then off. Turn the key "OFF", wait about ten seconds and turn it "ON" again until the pump cycles off itself. Turn the key "OFF". depress the plunger in the Schrader valve again (wrap a rag around the area of the valve to collect any fuel that may spill). If you have a pressure testing gage, hook that up BEFORE you cycle the key for the first time. If fuel sprays from the Schroeder valve, fuel pressure is obvious (the pressure may be low however, which is an argument why you should use a gage instead of a back-yard method. If no gage is available, this method will net results good enough for our purposes). So, if we have fuel pressure, awesome, we can rule out fuel as a possible culprit. No fuel pressure? Need to find out why. Either the relay is not cycling or another sensor is malfunctioning. The relay is obvious, you'll hear it 'click' and the pump will cycle on/off when the key is initially put in the "ON" position.
Spark. Testing spark is simple, just remove any spark plug wire and with INSULATED pliers and hold it close to the engine block or exhaust manifold or ANY piece of engine metal that is clear of any fuel from the previous test. If you have spark, excellent, we can rule that out. If there is NO spark, which I'm betting is the issue, you'll probably find that the crank sensor has a crack in it and it is allowing a small amount of water to enter the circuit and when it freezes, doesn't allow the terminals to make proper contact and when the temp goes up one or two degrees, the sensor makes contact again allowing the engine to run.
When your engine is cold, it is in what is known as 'closed-loop'. This means that the engine management computer only reads a few sensors. The coolant temperature sensor, the crank trigger/camshaft position sensor, MAP (Manifold Absolute Pressure -tests for presence of vacuum) sensor and the TPS (Throttle Position Sensor). If signal is not received from one or more of THESE sensors, the engine will fail to start. In open-loop, ALL engine sensors are read and the fuel mixture and running characteristics of the engine are manipulated based on those readings allowing your engine to operate efficiently.
Thanks for the question, I hope this information is helpful to you.
Fred
www.knucklebusters.us
570-453-0910
