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Hatchbacks Chevrolet Metro/Geo Metro Chevrolet/Geo Metro
1692 messages, Last post on Oct 24, 2009 at 5:27 PM
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Replying to: zaken1 (Aug 14, 2009 1:38 am) Thanks a million for taking all this time. It started my day with a bang!
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Replying to: vanillalatte (Aug 14, 2009 2:58 am) |
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Replying to: zaken1 (Jun 19, 2009 2:44 pm)
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Replying to: jessegeo (Aug 16, 2009 1:45 pm) It is absolutely essential that both the head and the valve cover be surgically clean and free of all traces of old gasket material and sealer along the entire sealing surface, before installing a new gasket. This cleaning should include the recesses in the curved part of the valve cover. You can use an inspection light and a screwdriver, solvent, an Exacto knife, dental probes, or similar tools to reach into the corners of the cover and remove fragments. It just takes one tiny chunk of debris to keep the valve cover from seating completely. And after the parts are cleaned; thoroughly check the entire sealing surface for cracks or gouges. The gray formula Permatex RTV is preferable to the high temp red formula; because it is more resistant to being squeezed out of place when the cover is tightened. And that cover does not get hot enough to require high temperature sealer. It is also important to only apply only a thin, even coat of the sealer to the top and bottom faces of the gasket (not to the metal parts); and then wait about ten minutes after applying the sealer to allow it to set up, before installing the gasket in the valve cover. The sealer should still be tacky enough to hold the gasket in the cover without it drooping out of position. And the valve cover nuts should be tightened in a criss cross pattern, going back and forth in several steps between nuts on opposite ends; so the cover can come down evenly. The final tightening should be done with a torque wrench, to 15 foot lbs. Some brands of gaskets may be made of cork, fiber or cardboard. These are inferior quality, and should not be used on this motor. If that is the type of gasket you've been using; find a store that sells a rubber gasket. And be sure they sell you the right gasket for this motor. It should match the shape of the cover, and fit snugly in the cover without needing to be cut or shortened. Also note that there is only one way the gasket will fit; there should be one curved end that matches the curve of the valve cover and the cylinder head. And the gasket definitely has a top and a bottom side. Some gaskets also come with grommets. These grommets go on top of the valve cover, under the cap nuts. If your gasket came with grommets, and they were placed underneath the cover; they would prevent the cover from seating. |
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Replying to: jessegeo (Aug 16, 2009 1:45 pm) |
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1996 1.0 5 spd Been on this one for months- starts fine but can't give any throttle before it warms up, or it floods out. Checked the voltage at the Coolant Temperature Sensor by backprobing. It has three wires: Light Green/Black, which is common and goes to the MAP, TPS, and IAT. Gray/White, which is the signal to the ECM. Yellow/White, which is not shown on wiring diagram, but I assume is the input from the ECM. LtGr/Bk is ground- no voltage. Gy/Wt reads 2.34V when cold, decreases with rising engine temp and finally goes to 0.5V when hot, at which point the cooling fan kicks on and takes it back up to around 0.65V. (With two different CTS units- same within .2V) At anything over 1.0V, the engine will flood and stall if the throttle is opened even slightly. These values seem reasonable if the temperature was around zero- but it's 80. What does not seem reasonable is the voltage on the Yellow/White wire which I believe should be the standard 5V input from the ECM, but reads a steady 9.2V, regardless of temperature and even when not running with the ignition on. If the input voltage is nearly twice what it should be, then the CTS could have exactly the correct impedence, but the output signal would be much higher than the ECM expects, and it would compensate with a mixture richer than Bill Gates. Is it possible that something is creating a field that the wire is having additional current induced in it somehow? My DMM read nearly a volt with the positive probe held in the air near (2 inches) the sensor wires. I hope this is the gremlin I have been looking for since April, but I don't have a clue how it could get 9.2V. Maybe something a little over 12v, yes- but not 9. Anyone see this before? Hints? My crystal ball keeps saying to try again later....
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Replying to: shaggyman1 (Aug 17, 2009 10:20 pm) But there is one other factor here which proves this point: The CTS resistance is highest when it is cold, and drops as the engine warms up. This means that the voltage signal the computer "sees" from the sensor is LOWEST when the engine is cold; and becomes higher as the engine warms up. So if your supply voltage was too high, the computer would get a signal that the engine was hotter than it really is. And under that condition, the engine would not go rich when throttle was applied. Instead, it would go too lean. But you claim the engine is flooding. Actually, I believe you are confusing the behavior of a flooding engine with one that is going too lean and starving for fuel. An engine which is too rich is typically insensitive to small changes in throttle opening; and will easily accept sudden openings in throttle position. A rich engine will also run much better when it is cold than it does when it is warmed up. On the other hand; an engine which is too lean will stall out if the throttle is opened when cold; but will run much better after the engine temperature comes up to normal. So I believe this is what your engine has been doing. Hopefully this will give you a better sense of where to look for the source of the problem. Here's a simple test you can do to prove this: Disconnect the plug to the IAT sensor, and then try running the motor. I bet you'll find that the cold stalling is gone. The IAT sensor is just like the CTS. Its resistance is highest when the air temperature is cold. So when you disconnect the IAT plug; the computer thinks the air temperature is below zero; and richens up the mixture.
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Replying to: jessegeo (Aug 16, 2009 1:45 pm) |
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Replying to: zaken1 (Aug 17, 2009 11:39 pm) The voltage most definately decreases with increasing temperature, which means the resistance is increasing. WTF? How could both my sensors work backwards? And the fan comes on when the voltage hits half a volt- shouldn't it be coming on with some increased voltage? If I disconnect the CTS the fan comes on, which implies that a zero volts signal received triggers the fan circuit. Tried disconnecting the IAT- no change. (It is receiving an index of 4.95V from the ECM) Tried measuring the voltages accross the signal and common ground wires, rather than grounding to the battery- same. It read 2.65V after sitting all night, and decreased as the engine warmed to a minimum of 0.50V, at which point the cooling fan came on. Maybe I drew the wrong conclusion from results, in that the signal of 0.5V is interpreted as zero, the same as if the sensor was disconnected, and the ECM thinks it's a malfunctioning sensor and defaults to cooling fan ON? I'll go and get another sensor today and see what it does. I could swear that when I tested the impedence on that unit it decreased with heat. I am disturbed that the wiring diagrams only show two wires, rather than the three I have. It implies other info may not be precise, either. Anyone with an FSM for 1996 have a table of voltages through a temperature range? My head hurts. Feels like I am dealing with things that violate accepted laws of physics- which implies I may be wigging out in a rather interesting fashion....
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Replying to: shaggyman1 (Aug 18, 2009 8:14 am) In view of this; it sounds to me like you are interpreting the voltage drop ACROSS the sensor as the amount of signal the computer sees. But this is just the opposite of what is happening. The higher the resistance of the sensor is at any time; the more the voltage will be dropped across the sensor. And the more voltage that is dropped across the sensor; the lower the voltage will be that reaches the computer. Think of it this way: If there is a 5.0 volt supply to a sensor circuit, and the sensor has enough resistance to drop 3.5 volts across it; the computer will only see the remaining 1.5 volts. IT WILL NOT SEE THE 3.5 VOLTS YOU ARE MEASURING ACROSS THE SENSOR. Similarly, the lower the voltage drop there is across a sensor; the higher the signal voltage will be at the computer. We know this much; sensor resistance decreases with heat; which will produce less voltage drop across the sensor. So if you are measuring lower voltage at the sensor as the engine warms up; you must be measuring the voltage ACROSS the sensor; rather than the voltage in series with the sensor. And that is the source of your headache. Furthermore, I believe the engine temperature sensing circuit is connected in SERIES through the CTS and IAT; rather than in parallel. I also believe the engine load sensing circuit is also connected in series through the TPS and MAP. And this would further confound your attempts to measure the circuit dynamics. But I see one thing that is not right in what you measured: Disconnecting the IAT should NOT have resulted in no change. If it did; this indicates either a short across the IAT sensor, or else the computer was not responding to the change in IAT signal, because it was in "limp in" mode as the result of a trouble code having been set. Does your "check engine" light come on when you first turn the key on, and does it then go out after the motor is started? If it doesn't come on at all; or if it stays on all the time; then the computer is in limp in mode, and will not respond normally to sensor inputs. In this case, you'll need to clear the trouble codes with a code scanner (assuming your 1996 model has an OBD II engine control system) Trouble codes can only be cleared by disconnecting the battery if you have the earlier OBD 1 system. And you can't tune the motor when it has a trouble code set in the computer. I know scanners are expensive; but there is no easy way around this. Actually, some people say that turning the ignition key on and off about 15 times in succession will clear OBD II trouble codes.
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