04 Z71 silly trans swap, no start

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1low4x4

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hey guys, my buddy blew up, well he burnt up 2nd and 3rd gear in his 4l60, and his crew cab 04 z71 with a 9 inch lift and 20 inch wheels on 35 s. so we brought it to my house and pulled out the transmission, which of course consisted of transfer case, drive shaft, exhaust, cross members, it was a bitch and a half. Got it to my transmission guy, he rebuilt it, new converter. We got it back yesterday and started working on it at 6 p.m. Got the transmission back in and torque converter bolted down, everything back in its place as it should be. Starter, o2 sensors, linkages, harnesses, vent lines,and I double checked everything about 4 times. Toward five quarts of fluid in the transmission with the truck off, as instructed, and got ready to crank it.


well the truck will cycle just like normal, starter operating, serpentine system turning, sound normal but it just won't fire. I touched absolutely nothing on the engine, and he drove a truck to my house the other day so I'm hesitant to say something else failed but it could have. We had to lay under the truck for about 2 hours with a water hose getting all the mud out from underneath it, on top of a 4 hours he spent with a pressure washer days before. the absolute only thing I think could have happened, is either maybe the fuel pump went out somehow, or we got water and some important connector. I can't tell if it's throwing any codes, but I have a code reader that we will put on it today after work.


I got up on the engine and pulled what I think is the main fuel line coming from the back of the motor up to a rail going over to the other side of the engine and then down to the rails. pulled it off with those special little clips I had from my last truck, stuck the hose in a small bucket and had him cycle the engine. On first try, the fuel pump dumped out a little bit of fluid, maybe a quarter cup, and then immediately stopped as he was cranking. The second time he hit it it did not pumped at all.then we waited a little bit, and tried it again. Did the same thing, it pumps for about 2 seconds and then stopped for the duration of the time he was cranking. I don't know if this is normal, like if it just give them enough fuel to fire over and then pump small when the motor starts, I do not know. Or is it supposed to pump a steady stream regardless.

it's hard for me to believe that this is related to our transmission swap, I don't think we painted any wires up there between bell housing, I mean everything is working as should, engine cycling but just not firing.I'm not sure about the ignition on these things, I know they have their own coil for each cylinder, but I don't know how that works. Thoughts?
 

yevgenievich

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With ignition on, fuel pump cycles for few seconds then quits. However during continous turning over of the engine it should keep running. Check if it has spark. If it does then next step is to jumper the fuel pump relay and try again
 
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1low4x4

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Thanks. Is it like tbi, needs spark to trigger fuel?
 

1low4x4

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Also, forgot to add that I tried swapping out different relays in place of the fuel pump relay.

What's the most effective way to check for spark, and if no spark where to check next? I'm not familiar with the new stuff.

So nothing we did in the trans swap could've causedthis? 02 Sensors, trans harness, etc....nothing on engine was ever touched
 

yevgenievich

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O2 sensors and trans harness will not stop it from running. It is possible that it thinks transmission is in gear(if it has the range selection on the shifter at the transmission), but I am not sure if that will tell the computer not to fire. You can unplug the connector just to try.

More than likely one of the sensors ( crank position etc...) got moisture in the connector or failed in some other way. There is spark tester that can be used, but just using a spare spark plug at the end of the spark plug wire with the tip grounded should be good enough indication if spark is present.
 

1low4x4

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Jesus Christ. Last thing I need is to be chasing bad sensors on this pos.
 

1low4x4

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Well I read an article on those crank sensors and now fully understand how important they are. Basically tells engine when to fire. I had so much trouble with the starter abd moving it up and down and round I could've messed up or unplugged it
 

foamypirate

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Well I read an article on those crank sensors and now fully understand how important they are. Basically tells engine when to fire. I had so much trouble with the starter abd moving it up and down and round I could've messed up or unplugged it

Reading through, I was going to mention crank sensor. It should be on the back on an 04'. Looks like you are probably on the right track.
 

Don5

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Jesus Christ. Last thing I need is to be chasing bad sensors on this pos.

^Good Luck Brother! Bring plenty of patience for this particular project. Sorry I can't help with the new and improved stuff.:popcorn:
 

1low4x4

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thanks for the help guys, got home today and drop the starter and sure enough a wire was cut on the crankshaft sensor harness.it was broke right at the connector, so I soldered it back together and voila, we got a running truck
 

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thanks for the help guys, got home today and drop the starter and sure enough a wire was cut on the crankshaft sensor harness.it was broke right at the connector, so I soldered it back together and voila, we got a running truck

good news, it's nice when issues solved easily
 

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