Truck will crank but not start after engine has been shut off after running at operating temperature?

Hi,

We need to narrow things down. When this happens, you either are losing the ignition spark to the plugs or fuel to the engine.

Try this and let me know what you find.

When it won't start, see if it will start using starting fluid. If it does and then stalls, we know there is a fuel-related issue. If there is no change, we need to check for spark at the plugs.

Here is a link that explains how to check:

https://www.2carpros.com/articles/how-to-check-for-ignition-spark

Let me know what you find.

Take care,

Joe

Howdy, and thanks for your reply. I will check for spark and fuel this evening. A repair shop that I took it to did say that the fuel pressure was good, and they were able to duplicate the problem.
After cooling for 5 hours last night, it wouldn't start at all still. This morning, it fired right up.
Someone mentioned the crankshaft sensor. The engine isn't running poorly as best as i can tell and isn't stalling. The only symptom before this started was a longer period of cranking before it started up. However, whatever is causing it is super temperature sensitive. It will not start unless the truck is completely cooled off but runs well when it is hot.

Hi,

The crankshaft position sensor was my first thought, but this doesn't have one. If you have no spark, at the coil there will be a pink wire. It should have power with the key in the run or start position. Check to see if that is present. See pic below.

Let me know.

Joe

See pic below.

I checked for spark on multiple locations and got rapid flashes on my tester, so I believe that I have spark. From the plugs, the sequence was 1 strong flash followed by several weaker ones repeated. The flashes from the ignition coil were always strong. From the distributor cap, the flashes were 1 strong followed by several weaker ones. Some were so weak that I could tell whether or not it was flashing.
When I took it to the shop, they tested for fuel pressure and said that it was within range. I haven’t been able to get some starting fluid just yet though.
What should my next step be?

Hi,

The strong spark followed by weak ones is odd. Are you sure the distributor cap is good and doesn't have a crack at some point?

Joe

The distributor cap looks good so far. I will take it off later today and inspect it thoroughly. When the truck had cooled down and could start, I tested the spark on all the previous areas mentioned in my previous reply. All the sparks were strong with no weak flashes. I am using an inline spark tester for these tests.

Here is what the spark on a spark plug looks like when the engine cranks but doesn’t start. The spark is erratic and inconsistent in strength.

Here is what the spark on a spark plug looks like when the engine starts.

Hi,

If I had to guess (and I don't like doing that), I would say the distributor is failing. Is there any play in where the rotor mounts up and down or left and right in the shaft? Now that I've seen the videos, which is what makes sense. It works and then it doesn't. By any chance, do you have a different known good distributor that you could switch out for a test?

Let me know.

Joe

I do not have another distributor for the time being. Admittedly, I am pretty intimidated by setting timing. Is there any way that I could take it out and replace it and not have to do that?
Would it be worthwhile to try to change the distributor cap and ICM before messing with the distributor?

Here are the videos of the ignition coil spark during crank no start and starting. All the videos have had volume so you can listen to which is which. Maybe this can help diagnose too.

I replaced the distributor cap tonight. It still cranks without starting after driving at just under 210 degrees. Attached are some pictures of the distributor rotor button and ignition coil while I had everything taken off. There was a little corrosion on the inside of the distributor cap (not pictured) on the ends of the inside prongs. The rotor button looks a bit rough, and it’s only been on since May. When I replaced the original in May, the original rotor button was completely flat/not raised and blackened.
Also, I tried to wiggle the distributor clockwise and counterclockwise from the rotor button, but there was very little movement. It did move a little, but very little. Is that how you wanted me to test it?

Hi,

I noticed in the third pic, the orange wire near the coil connector looks burnt. Check to make sure there is no issue with it. Also, I can't tell in the picture where it is leading to. Let me know if you can tell.

Also, you mentioned using a scanner and found no codes. Do me a favor and try doing it this way to see if you find any codes. Follow the directions in this link:

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Joe

For the orange wire, it looks like it is leading to either the fuse box or towards the ECM. I’m not quite sure since the wire goes way behind the engine while threaded into wiring heat shields.
I have run codes that way with both the genuine GM OBD1 Code Reader as well as a paper clip. I get no codes. Just 3 sets of 12 followed by 3 sets of 12.

Hi,

I just went back through the videos you provided. Either we have a poor connection at some point, or the "new" coil is not good.

Did it do the same thing with the original coil?

Joe

It didn’t do the same thing with the old coil. The old coil was replaced in May 2023 at 140,000 miles as part of general maintenance. It was the original. It did not have the problem until the week after the 4th of July.

Also, the mechanic I took it to a few weeks ago sent me a new report because the old one apparently had a page missing. Here is what the missing page read:
“There are no codes stored. Run the engine and test drive. Engine is starting and running good. Got everything warmed up and shut the truck off. Waited 15 minutes, truck started good. Run the engine and did a hot soak several times before it failed to start. There was no fuel spraying from the injectors, slight drip. Hooked up spark tester and the truck started. Removed fuel filter and hooked up a pressure gauge. Run the truck to get up to temp and did hot soak.”

Also, I replaced the ICM tonight. The old one had a bunch of scratches along the bottom metal plate. The dielectric grease that had been put on in May 2023 was mostly gone. Some parts of the plastic (especially on the edges) were peeling. The new ICM is the same brand (couldn’t get ahold of an AC Delco on short notice) and I used thermal paste from Best Buy instead of dielectric this time. I had read that dielectric grease can cause the ICM to melt, is that true? Anyway, I got it all back together to find that the negative battery cable terminal bolt is stripped so can’t connect the battery. Will get a new bolt tomorrow and will update on start condition now that a new ICM is on when the battery is reconnected.

Hi,

I don't see how dielectric grease would cause that to happen. It isn't a conductor, so it wouldn't cause an overheating issue. Its purpose is to seal and protect from corrosion.

Let me know how it runs tomorrow. I'm interested in knowing. Also, I have a feeling the coil is failing when it gets hot. If there is no ignition, it will shut the fuel down, so that may be what is happening. The pump gets power to prime and then it shuts off until ignition is recognized. Then it powers on constantly.

Let me know.

joe

I got the new ICM and negative battery bolt on. I started it up, drove it around to get the temperature up, parked it, and shut it off when it was at operating temperature. I tried to start it and it fired right up. I let it idle for a bit before shutting it off and trying to start it again. This time, it cranked but didn’t start. I tried another time with the same result. I waited 20-30 minutes, tried to start it, and it fired right up with the temperature gauge reading about halfway between 110 and 210 degrees on the dash. I let it idle some more, shut it off, tried to start it, and it cranked but didn’t start. I tried to start it again about 30 minutes later which resulted in a crank no start.

I see this as a bit of an improvement, but the problem is still ongoing. Another detail, my cranking RPM is 200. How do I check the coil with a multimeter? It’s a bit hard to get off the truck so I’d rather test it while it’s attached. I’ll also check spark again tonight while it’s dark. I’m in Texas so it’s way too hot to do anything during the day.

Hi,

I was thinking about the erratic spark. Have you replaced the pickup coil in the distributor? Take a look below. I attached the directions to test it. See if it passes. That may be the entire problem.

Let me know.

Joe

See pics below.

Well, the pickup coil is a bit complicated. When the ignition control module was changed in May, the tech broke the clip holding the pickup coil to the module and ended up using nylon zip ties to hold it. Since then, that tie had broken from the heat in the cap and I had replaced it with a stainless-steel tie. The pickup coil is held firmly in place by it with no wiggle but is not crushing it. There is heat resistant electrical tape around the tie where it is threaded between the 2 wires of the pickup coil to help mitigate damage to the wires. As far as I can tell, it is secure with no signs of damage except for a small amount of fraying around the yellow wire when it reaches the connection point of the ICM.

Another clue is that the TBI injectors don’t seem to be spraying (dripping at the most) when the engine is starting hot. It seemed to help a bit when I took the cover off to inspect them while the truck cranked. The left injector has corroded wires while the wires on the right one look brand new. Will send a picture in the morning,

I drove it around a bit more tonight and it was able to start 4/7 times when the engine temperature was at about 185 degrees. Not quite the temperature of the original heat problem, but it’s a bit better.

Hi,

This is an interesting one. Let me take a look at the pics you send. Also, if the connectors are corroded, you really should clean them to see if that helps.

Let me know.

Joe