Hello world -
The tall-deer is: can a failed-open ECT sensor cause a no-start with liquid fuel in the intake manifold and tailpipe?
Long version: I have a '94 V6 4WD on which I just finished a complete engine rebuild(long-term project, I spent about two years on it).
Last Thursday I started it for the first time: it took probably 30 seconds of cranking before it started; chugging at first but quickly smoothing out and settling at 1500rpm. I worked out all of the air from the coolant, stopping and starting a few more times over the next several minutes(it never started quite right away, cranking and chugging for a few seconds each time before settling into an idle, but seemed to start better when warm), set the timing at 10*BTDC, and messed around checking connectors, clamps etc while it warmed up. It settled around 800rpm, oil pressure and coolant temperature good, and I took my wife and kids out for a celebratory drive around the neighborhood, maybe two miles, before parking it for the night. I noticed a bunch of black specks/spots on the driveway right by the tailpipe, and assumed it was just rusty crap that had formed over two years of sitting and been jarred loose by the heat and vibration of starting after so long. Compression was 100-105psi all round before first startup. It ran for about 90 minutes in total, and aside from difficult starting it ran just fine(anyway, a damn sight better than it did with a burned valve and poor compression in two other cylinders).
The next day, I went to start the truck and it just cranked for several seconds without catching. It started farting and chugging a bit, puffing white smoke(not steam) from the tailpipe and nearly starting, but would not run after I stopped cranking. Thinking it to be a fuel issue, I pulled the cold start injector and set it in a cup, cranked for a moment and found a very small amount(1/2-1tsp) of fuel in the cup, but then I had to stop to take care of the kids and couldn't get back to it that night.
Tonight I went outside, just for fun tried cranking for ~15sec(again lots of farting and almost-starting but no success), and started testing the usual suspects(in order of ease of access
). Noticed a little stream of liquid in the tailpipe. I tasted it to be sure it wasn't water or coolant, and I suppose it's gasoline mixed with rust... it tasted like shit and I probably now have tongue cancer. I now assume that the black spots I'd seen the day before were liquid gasoline that had run out the tailpipe carrying rust and general filth along with it, fallen to the driveway and soaked into the concrete.
Cold start injector, coil, AFM, TPS all ohm out properly per the FSM, mechanical timing does not appear to have jumped(distributor rotor is where it belongs, anyway). There were no trouble codes.
I ohmed what I thought was the ECT sensor, got 80 ohms(cold engine, ~55* ambient temp) and thought "AHA, bad sensor for sure, problem found"! Loosened the upper intake to get a socket around the sensor, and noted gasoline pooling on the bottom of the upper intake and throat of the throttle body. Anyway, I pulled the sensor, then dangled it in some ~150* water on the stove. It was then that I realized that I had pulled the cold start injector time switch(d'oh). Resistance stayed at 79-80 ohms. I stuck it in the freezer and later checked it, got 40 ohms. Guess that's fine, and I get to put back the expensive sensor and focus on the cheaper one, yay. Too bad that one is even more difficult to reach.
While the CSITS was chilling, I ohmed the actual ECT sensor, which appears to be open. I have yet to pull the thing, because even with the upper intake loose it's still a really cramped spot under all the heater hoses and other crap and I can't get a socket or wrench around it yet, and again I had to come assist with the kids at bedtime. I'm going to head back outside now and see about pulling the ECT so I can verify it's actually bad, but I would appreciate any thoughts you might have as to whether that could be the source of my too-rich almost-but-not-quite-start problem, and why it might've either failed after a first warmup or why the truck started several times with it having already failed but now will not. I wonder whether it would start again if not for the gasoline pooling in the intake.
That's a long read and thanks for getting through it. I didn't want to leave out anything which might have been important.
I've made much use of this forum during the rebuild and appreciate any more help you might have to offer now.
- Ben
The tall-deer is: can a failed-open ECT sensor cause a no-start with liquid fuel in the intake manifold and tailpipe?
Long version: I have a '94 V6 4WD on which I just finished a complete engine rebuild(long-term project, I spent about two years on it).
Last Thursday I started it for the first time: it took probably 30 seconds of cranking before it started; chugging at first but quickly smoothing out and settling at 1500rpm. I worked out all of the air from the coolant, stopping and starting a few more times over the next several minutes(it never started quite right away, cranking and chugging for a few seconds each time before settling into an idle, but seemed to start better when warm), set the timing at 10*BTDC, and messed around checking connectors, clamps etc while it warmed up. It settled around 800rpm, oil pressure and coolant temperature good, and I took my wife and kids out for a celebratory drive around the neighborhood, maybe two miles, before parking it for the night. I noticed a bunch of black specks/spots on the driveway right by the tailpipe, and assumed it was just rusty crap that had formed over two years of sitting and been jarred loose by the heat and vibration of starting after so long. Compression was 100-105psi all round before first startup. It ran for about 90 minutes in total, and aside from difficult starting it ran just fine(anyway, a damn sight better than it did with a burned valve and poor compression in two other cylinders).
The next day, I went to start the truck and it just cranked for several seconds without catching. It started farting and chugging a bit, puffing white smoke(not steam) from the tailpipe and nearly starting, but would not run after I stopped cranking. Thinking it to be a fuel issue, I pulled the cold start injector and set it in a cup, cranked for a moment and found a very small amount(1/2-1tsp) of fuel in the cup, but then I had to stop to take care of the kids and couldn't get back to it that night.
Tonight I went outside, just for fun tried cranking for ~15sec(again lots of farting and almost-starting but no success), and started testing the usual suspects(in order of ease of access
). Noticed a little stream of liquid in the tailpipe. I tasted it to be sure it wasn't water or coolant, and I suppose it's gasoline mixed with rust... it tasted like shit and I probably now have tongue cancer. I now assume that the black spots I'd seen the day before were liquid gasoline that had run out the tailpipe carrying rust and general filth along with it, fallen to the driveway and soaked into the concrete.Cold start injector, coil, AFM, TPS all ohm out properly per the FSM, mechanical timing does not appear to have jumped(distributor rotor is where it belongs, anyway). There were no trouble codes.
I ohmed what I thought was the ECT sensor, got 80 ohms(cold engine, ~55* ambient temp) and thought "AHA, bad sensor for sure, problem found"! Loosened the upper intake to get a socket around the sensor, and noted gasoline pooling on the bottom of the upper intake and throat of the throttle body. Anyway, I pulled the sensor, then dangled it in some ~150* water on the stove. It was then that I realized that I had pulled the cold start injector time switch(d'oh). Resistance stayed at 79-80 ohms. I stuck it in the freezer and later checked it, got 40 ohms. Guess that's fine, and I get to put back the expensive sensor and focus on the cheaper one, yay. Too bad that one is even more difficult to reach.
While the CSITS was chilling, I ohmed the actual ECT sensor, which appears to be open. I have yet to pull the thing, because even with the upper intake loose it's still a really cramped spot under all the heater hoses and other crap and I can't get a socket or wrench around it yet, and again I had to come assist with the kids at bedtime. I'm going to head back outside now and see about pulling the ECT so I can verify it's actually bad, but I would appreciate any thoughts you might have as to whether that could be the source of my too-rich almost-but-not-quite-start problem, and why it might've either failed after a first warmup or why the truck started several times with it having already failed but now will not. I wonder whether it would start again if not for the gasoline pooling in the intake.
That's a long read and thanks for getting through it. I didn't want to leave out anything which might have been important.
I've made much use of this forum during the rebuild and appreciate any more help you might have to offer now.
- Ben
). #1 intake was stuck fully open - I couldn't even rotate it, let alone slide it closed. I could overcome the valve spring pressure with my thumbs at each of the "good" valves, but #6 had crept closed at some point and I could not move that one by hand although I did get it down by turning the cam sprocket. It again crept closed over the next few hours.
