My Hoe won't start! Help, please!

[Smitty Smith]

Hello, Im at my wits' end with my Tahoe. I have a '96 Tahoe 4X4 5.7 that will turn over all day long but not start. Details: For a few months now, when I first start up my tahoe and hit the road, it will hunch and punch like the spark is cutting out intermittently when I hold the throttle at a steady spot (about 50mph), until it warms up after about 5 or 6 miles. If I give it throttle or let off, it instantly runs smoothly. Here is the weird part, if I let it sit for about 24 hours without starting, it is next to impossible to start. The engine will turn over all day long as free as a bird but acts like there is no spark. Spark plug tester shows a spark but it looks a little weak. Getting fuel because I can smell it flooding. I have replaced fuel pump, fuel filter, spark plugs, wires, rotor button, cap, electronic module, coil, and throttle position sensor. Every time I can't get it to start after sitting for 24 hours, I replaced a different part of the ignition system and it starts right up...except for today. The coil was the last part I replaced today but it will not even try to start. Still turns over and has what seems to be weak spark according to spark tester. Now, someone please tell me you have had this same problem and can tell me what I'm missing. My truck is stranded at a boat landing overnight.

 

[SunlitComet]

Exactly what electronic module did you replace? And can I assume you don't have a scanner to check for any active codes.

---------- Post added at 06:20 PM ---------- Previous post was at 06:14 PM ----------

Also check grounds on thermostat housing stud and on the back of right cylinder head for damage or corrosion. Also are you disconnecting you battery each ime you channge a part and this is when it starts right after?

 

[Smitty Smith]

Exactly what electronic module did you replace? And can I assume you don't have a scanner to check for any active codes.

---------- Post added at 06:20 PM ---------- Previous post was at 06:14 PM ----------

Also check grounds on thermostat housing stud and on the back of right cylinder head for damage or corrosion. Also are you disconnecting you battery each ime you channge a part and this is when it starts right after?

The module that is mounted on the heatsink right next to the coil. I haven't always disconnected the battery every time I replace a part. I did disconnect it this time just to see if resetting the pcm would make a difference...it didn't change anything. I did have a check engine soon lit before I changed the module a couple of weeks ago. P0137 and P0157 I believe. OBDII reader said low voltage on two of my O2 sensors. After I replaced module, CES light went out. Checked braid attached to back of block, seemed ok. Don't remember what the one on the thermostat housing looked like but didn't notice any corrosion.
Forgot to mention that I also replaced the EGR valve couple of months ago.

 

[SunlitComet]

Inspect ENG-1 fuse on under hood box for terminal damage and give all your harnesses a good wiggle.

---------- Post added at 07:12 PM ---------- Previous post was at 07:01 PM ----------

That fuse feed the heaters for those two O2 sensors as well as feeds the cam sensor. Also ECM-1as well. That feed the crank sensor and also power the ignition control module. I am wondering if you have a fualty crank sensor that is sucking the power out of your ignition system. When you did the spark test did you try different cylinders?

---------- Post added at 07:14 PM ---------- Previous post was at 07:12 PM ----------

Also there should be two grounding wires on the thermostat housing.

 

[carcrz]

Hello, Im at my wits' end with my Tahoe. I have a '96 Tahoe 4X4 5.7 that will turn over all day long but not start. Details: For a few months now, when I first start up my tahoe and hit the road, it will hunch and punch like the spark is cutting out intermittently when I hold the throttle at a steady spot (about 50mph), until it warms up after about 5 or 6 miles. If I give it throttle or let off, it instantly runs smoothly. Here is the weird part, if I let it sit for about 24 hours without starting, it is next to impossible to start. The engine will turn over all day long as free as a bird but acts like there is no spark. Spark plug tester shows a spark but it looks a little weak. Getting fuel because I can smell it flooding. I have replaced fuel pump, fuel filter, spark plugs, wires, rotor button, cap, electronic module, coil, and throttle position sensor. Every time I can't get it to start after sitting for 24 hours, I replaced a different part of the ignition system and it starts right up...except for today. The coil was the last part I replaced today but it will not even try to start. Still turns over and has what seems to be weak spark according to spark tester. Now, someone please tell me you have had this same problem and can tell me what I'm missing. My truck is stranded at a boat landing overnight.

Hey Smitty try this take the distributor cap off and let some one turn the key and see if your rotor button turns all the way around when you crank the ignition, it may be the distributor gear striped. let us whats the outcome

 

[Smitty Smith]

Thanks SunlitComet, I'll check out the fuse. Forgot to mention earlier that I already replaced the crank sensor along with the timing chain and gears a couple of months ago because of this same problem. Thought it had jumped time. TPS wound up getting it running that time.

I'm headed back over there to pick it up today on the trailer to get it home. I'll let everyone know what I find when I get it back home. Thanks for the ideas.

 

[Smitty Smith]

Update! She is running! After I had my truck towed about 75 miles home, I bought a new distributor to replace then went to my dad's house to replace it. When I got there, I checked the ground wires like SunlitComet said and found them to be in good shape and well connected. I then decided to try the PCM reset by disconnecting the battery for a few minutes. After reconnecting the battery, I tried to start it one more time and I'll be darned if it didn't start right up!
One more thing I did find while I was looking at the ground braid, the wiring harness connector for the exhaust O2 sensor was against the manifold and was somewhat melted. The connector was in pretty bad shape but the wiring insulation was intact so I don't think that was a player in this but I will have to replace the connector.

Thank you, guys for all your input and now I'll be hitting the road again for another 100000 miles or so. Now it's on to rebuilding the engine for my '75 Jimmy.

Thanks again,
Kevin.