Vincent_35

Alright, this is my last resort I've exhausted many threads across the internet with no luck of finding anyone with the issues that I am having. So here is the details, I have a 1996 chevy k2500 4x4 with the 5.7l engine that currently has about 250k miles on it. The problem I am having is that randomly out of nowhere the truck will not start give it some time about a day or 2 and it starts up like nothing ever happened. the truck will crank over all day but will not fire up. this problem has randomly plagued me for probably the past year. It seems my problems started once I changed out my fuel pump because the gas gauge no longer worked. Swapped out the fuel pump for a precision pump from oreillys and all was good, I had my gas gauge back and the truck worked great and ran amazingly. fast forward to about 3 months later and the truck wont start, I test a few things and realize the pump seems to be bad cant remember how i diagnosed it but i swapped the pump for another precision pump and the truck fired right up. fast forward to about 6 months later and the truck doesn't start again. This time I refused to swap the pump again because the job sucks, so I researched no start issues and went with a couple of easy quick fixes which were top of coolant because it was low, and replace the Ignition control module (ICM). Did all that and the truck fired right up, i was thrilled to not have to drop the tank again. fast forward to about 2 months later I drove my truck to california from arizona about 400 miles for a wedding stayed for about 4 days truck drove fine and started fine the entire time till the last day i was ready to leave and the truck didnt start. I was annoyed but tried every trick that i have tried in the past couple times which were, swap ICM, top off coolant, swap fuel pumps, swap fuel filter, and to no avail. At that point i had to be at work in arizona so i left my truck at my dads and borrowed his truck to drive back to AZ until i can figure out what is wrong with the truck.

My last diagnoses was that the pump was not supplying enough pressure as I was priming the pump and as i pushed the fuel valve fuel slightly trickled out, after swapping fuel pump again i noticed a lot more pressure coming out of the port. Also before i replaced the pump i was able to get the truck semi started with starter fluid but did not sound very good but it was semi running. after putting in a new pump i wasnt getting any sign of a start so i switched to checking for spark. I pulled a plug wire and put it up against the exhaust manifold and cranked it. saw no spark coming out of the plug. Then i pulled the coil wire off the coil and had it partially connected to the coil enough that i was able to see if spark was coming out of the coil to the plug and sure enough i was getting spark out of the coil. At this point part stores were closed and I needed to get back so i left. Next day about 15 hrs later my dad calls me and says my truck started just fine and he drove it around and it ran like there were no issues. This is the part i am not understanding, after that day 2 days later he was going to use my truck to get lumber and it wouldnt start again. he let it sit for a day then the next day it started just fine again. the vehicle is just sitting there and he hasnt touched a thing or tested anything. so literally the truck randomly starts when it wants. Everything I look up for distributor, coil pack, plugs, plug wires, grounding wires, bad pump, crank sensors, all of these that have been fixes for others dont match up with my issues. All these problems seem to show signs of the vehicle running poorly or the vehicle just not running at all or not starting until the issue is fixed. I am at a loss, I have until Nov. 7th to hopefully get this figured out as i will be driving back to hopefully fix this issue and drive it back home.

Im hoping i can get further insight about what else it could be without throwing about a thousand dollars in a full tune up and sensor change on this truck to hopefully get it running consistently. The difficult part about this is I am unable to test or diagnose any problems because the truck is 400 miles away. my dad isnt very mechanically inclined so i can only have him test simple things. any ideas or suggestions will be greatly appreciated, thanks in advance!

Gumby22

Keep in mind that Diagnosis, especially in the case of intermittent faults, is a methodical process, and if you aren’t methodical in your approach, it’s very easy to get lost in the complexity of automotive systems. Despite that complexity, there’s still a specific sequence of events that need to happen in order to start the engine, which means there’s a limited number of things that could be at fault. That list could be a long one, but it’s not infinite.

If you’re really determined to solve this problem on your own, get a cheap OBD2 code reader, a service manual that has wiring diagrams (Haynes, Chilton, subscription to online service info, etc), a digital multi-meter, and learn how to use them. For the money you’ve already spent on parts you could have purchased them all 2 or 3 times over.

Clear your mind of everything you’ve done up to this point and start over as if you haven’t tested or replaced anything. It’s far too easy to think “I’ve already checked/replaced that so it couldn’t be the problem” which can lead to hours of wasted time and more wasted money.

And while we’re on the topic of clearing your mind, try to recognize and disregard some of the BS you’re finding on your internet searches. Low coolant will not cause a no start - at least not on your truck as it was built from the factory. A PO could have added some kind of kill switch in the event of low coolant but that’s only something you’ll find through the course of diagnosis unless you’re personally aware of it.

I recommend you start with a basic, but thorough, visual inspection of the wiring in the engine bay and the driver side frame rail where the harness runs to the tank. I’ve been a professional mechanic for almost 6 years now and it’s amazing the number of problems I’ve been able to solve just by performing a visual inspection.

Remove the air intake boot and engine cover (if equipped) and anything else that could be obstructing your view of the wiring. Lift up the engine bay fuse block and inspect the wiring underneath it (recommend disconnecting the negative battery cable for this). Check for exposed battery cables in areas where they can rub on the frame or other components.

Disconnect the battery cable grounds on the body, frame and engine block and clean them with emery cloth or a wire brush. And while you’re at it, disconnect the cables at the battery and clean as needed. Corrosion builds up between the terminals and battery and can cause several problems, including random no-starts.

Once the inspection is done and any concerns are repaired, check for trouble codes, even if the CEL isn’t lit. If the codes seem irrelevant to the no start, write them down anyway because sometimes they can help provide direction.

I’ll do some more digging when I have time to advise you on more specific procedures.

Vincent_35

I probably should've mentioned this in the original post but I do have a code reader and multi meter and quite a few diagnosis tools, the codes I was getting were not really helping. Can't really remember the exact code number but I had a few through this no start process one was egr solenoid low voltage which that code I've had since I bought the truck. Other codes were for crankshaft position sensor both high and low voltage along with O2 sensor low voltage reading. Both the crank sensor and 02 sensor codes I do believe happened when trying to start it with starter fluid because of how poorly it ran. I cleared those codes and throughout the starting processes and driving the codes never came back (besides egr solenoid) but vehicle still randomly will not start.

kevinkpk

Clearing code's won't solve the issue if the problem still exists. What is the fuel pressure?

Vincent_35

I dont know what the fuel pressure is just yet, I bought a fuel pressure tester but I wont be able to test it until tuesday of next week when I drive back to california. I can hear the pump turning on when the truck doesnt want to start and there is better pressure at the valve then before I swapped the pump so I feel the pump pressure should be decent. I've read lots of forums about the fuel pumps in that truck and how finicky they are unless you go with the AC delco pump but at the time when i swapped the pump i didnt have time to order one before i left back to arizona so there is a brand new precision pump in the truck currently. The truck when it has started according to my dad recently runs just fine with no signs of any issues such as rough idle or stumbling when stepping on the gas. according to him the truck has been running lately without any no start issues. keep in mind he has not done any work to it since i was having the no start issues 3 weeks ago.

Vincent_35

I checked fuel pressure, it is good 60 psi in on and cranking. My crank sensor was in pretty bad shape groove cut into it, bought a new one still no start tried using all the shims and took out 1 by 1 and still no start. My scanner is picking up an rpm signal during crank so the crank sensor should be working correctly? I also unplugged the harness to the connector and got no signal so the crank sensor definitely is getting a signal. The truck sounds like it wants to start but still not firing up completely.

Gumby22

Spray a little starter fluid into the intake. If it fires, it’s an injector problem. If not, it’s a spark problem.

Vincent_35

I'll give the starter fluid a try, just finished testing spark and all the plugs are getting spark. Used a spark tester light that plugs in between the wire and the plug and there is spark at all 8 cylinders

Vincent_35

Tried the starter fluid and still no start just the same stumble of trying to start. Going to pull the plugs and see how they look

Gumby22

1) What is the general condition of the wiring?

2) Is the harness looming falling apart (just about crumbles to the touch of it’s old enough)?

3) Are any component connectors damaged (primarily missing retaining tab) and possibly not remaining seated?

4) Any known fixes from the past related to starting and driveability? (Less about who the repairman was and more about what was replaced and why.)

One more check to make, as sometimes the simplest things are overlooked:

The IAC valve.

At the moment, I don’t have time to list all the reasons why it could be causing the problem, but I did a write up on these a while back that explains how they work and how to test them.

Read all of it to know what tests to do.

I realize now I should probably edit it to better organize the info but as of now it’s as originally written.

https://chevroletforum.com/forum/198...urious-101819/