I have a 96 Tahoe, 4x4 5.7L that will crank but not start. Leading up to this point, there was a few mornings where the truck would start, but when it did, it was as if there was a weak start when she did fire. I am not a mechanic so I apologize if this is confussing. When the truck did start, she would run just fine. Now, she will not start, cranks fine, but no start. OBD2 code, was for a bad Crankshaft Position Sensor. I replaced the sensor and cleared the code. Still no start. I pulled the rotor cap and button, the rotor cap had some corrosion on the pins and the button was burnt at the metal tip and plastic. I replaced both of those. Still having the same issue. Moved on to the ignition coil and module, replaced both and yes, still not starting. I have used a meter to test the new coil, new module and both check out good. I have metered the wiring to the crankshaft postion sensor and from the sensor to the corresponding pins on the Power Control Module. I am 5 days into this mess and I am at a stand still. Any help would be greatly appreciated. Thank you.
96 Tahoe 5.7L Crank No Start Please Help
- Thread starter allenpsu
- Start date
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MO Viet Vet
Full Access Member
First thing to do is check for spark and fuel. As long as you have a good battery and the engine spins fast enough when cranking then if you have compression, spark, fuel and is in correct timing, then it will start.
If you have a spare spark plug you can remove a plug wire from one of your plugs and plug in the spare plug and hold the threads of the plug against metal to ground it and then crank the engine, you should see spark across the gap. You can also unplug wire and hold close to the tip of the plug using insulated pliers and see if spark jumps from the inside of wire boot to the tip. If you see spark then you are halfway there.
You can use carb cleaner and spray a small amount down the throat of the throttle body and if it starts when you do that then you have a fuel delivery problem. Then we can go from there. But the engine needs to spin normally when cranking to go further.
If you have a spare spark plug you can remove a plug wire from one of your plugs and plug in the spare plug and hold the threads of the plug against metal to ground it and then crank the engine, you should see spark across the gap. You can also unplug wire and hold close to the tip of the plug using insulated pliers and see if spark jumps from the inside of wire boot to the tip. If you see spark then you are halfway there.
You can use carb cleaner and spray a small amount down the throat of the throttle body and if it starts when you do that then you have a fuel delivery problem. Then we can go from there. But the engine needs to spin normally when cranking to go further.
I left that part out of my initial post. I do not have spark. I only checked for spark at #1 plug. I also used a test light at the ignition coil connection from the rotor to test for spark and I had no spark there either. Since there is no spark at the coil, there would not be spark at the plugs, right? Does this rule out my distributor being the problem? A friend mentioned possibly something is bad with my Power Control Module, is this a possibility? Thanks again for the help.
MO Viet Vet
Full Access Member
I would open up the distributor and look at the wires from the pickup coil to the module you replaced. Have been known to break at the pickup coil from age. You are correct that no spark/signal at the coil would account for no spark at the plugs. Broken wire at the pickup coil would not send the signal to the crank sensor.
May have a PCM problem but is rare.
May have a PCM problem but is rare.
Spark is generated at the module by the coil, it is Altered in time by the PCM IIRC. CKP sensor on the front of the timing housing would control the spark in this case, check wiring from there...... Pull the wire off the coil tower and test for spark there as coil wires go bad also.....
my next step tomorrow is to test for spark at the coil "tower" this might be a dumb question, but in order to test the cable from the coil to the rotor, do i test the cable at the end that connects to rotor or at the end that connects to the coil? I am reading in the Haynes manual that the "pick up coil" is only found on 95 and earlier models. This being a 96, is there not a pick up coil? If I am not getting spark at coil, what is my next step? Knowing that i do have a new CKP and all the wiring is reading correctly. If the coil is not showing spark, what direction do I go in next.
96+ has a CKP sensor mounted in the lower drivers side of the timing cover, it is referred to a 9x crank signal and it triggers the spark like the pickup coil used to do.
If you have spark at the coil, your coil wire may very well be bad (new wireset, Cap, Rotor -get Delco parts for the cap/rotor)
If you dont have spark at the coil tower, check wiring from CKP sensor and perhaps ohm out the coil on that sensor to make sure it isnt open, also could pull it and inspect for damage to the end of it as your last step in troubleshooting.
If you have spark at the coil, your coil wire may very well be bad (new wireset, Cap, Rotor -get Delco parts for the cap/rotor)
If you dont have spark at the coil tower, check wiring from CKP sensor and perhaps ohm out the coil on that sensor to make sure it isnt open, also could pull it and inspect for damage to the end of it as your last step in troubleshooting.
The issue needed up being corrosion on multiple wired to and from the PCM. My upper and lower intake manifold gaskets were leaking as well as my timing cover. Decent price quoted by the mechanic so I had them do it. My question is what, if anything, can I do as a flush or cleaning after knowing that those gaskets were leaking. Anything to prevent damage to the engine?
I have another question. I got the Tahoe back from the shop last night. I drove the truck home and there were no leaks, everything looked good. This morning was a cold morning so I went outside and started her up to let her warm up before leaving for work. About 10 mins later I came outside and noticed about a 6inch puddle under the truck between the fwd part of the engine and the fan. I opened the hood and there wasn't anything that I could see leaking, specifically looking to see radiator hoses and the area around where the manifold gaskets could be leaking. I did notice that there was residual coolant in the bottom of the fan shroud. I am hoping that this is spillage if from when they drained my coolant to replace gaskets? By the time I made it to work, only 7 miles, there was no more leaks. Also, for the time I have owned the truck, 5 months, the temp gauge has never read above 140 degrees. Any thoughts?
was the puddle just water or was it coolant? if it was just water its possible it was condensation, if your temp gauge doesn't read above 140 you may have a faulty temperature sensor or the gauge itself could be bad or out of calibration
