Engine cranks, but only starts after letting off key? - I'm perplexed

I was thinking heat soak possibility as well, but that doesn’t make sense with the ignition switch since it’s in the cab and doesn’t see heat from the engine.
Guessing they didn’t actually hot test it at the shop, if you immediately have the same repeatable condition.
I would have bet dead spot on the ign switch as well, but maybe some adjustment to the ign switch will get it right. May have been that all along? Spitballing at this point.

Ricko1966 said:

Covered in post 12,he needs to do as in post 4 and eliminate all possible wiring and switch problems.

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It's stored at the shop this weekend but I'll be sure to mention it to the shop first thing Monday morning so they can try that. The good thing is it's starting every time and running normal, just acting a little odd with the switch when up to temp.

Battery is older, but voltage is good and cranking normal

Now leaning towards maybe something heat soak related under the hood. IGN module or even coil.
Coil windings expand as they heat up. Could need just slightly more power when warm/hot to do coil things and it gets that power as the draw is released from the starter motor.
Don’t recall, if you said dist coil has been replaced recently or not.

Even though you have a “modern” squarebody, lol, it’s still going to me more subject to experienced diagnosis rather than most shops/mechanics now who are frequently only having to do computer diagnostics and replace parts.
Idk how old school your shop is, but finding someone who is experienced in old cars may be more beneficial.

Grit dog said:

Now leaning towards maybe something heat soak related under the hood. IGN module or even coil.
Coil windings expand as they heat up. Could need just slightly more power when warm/hot to do coil things and it gets that power as the draw is released from the starter motor.
Don’t recall, if you said dist coil has been replaced recently or not.

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The whole distributor assembly was replaced which I assume includes the HEI coil. I’ll have to double check that.

The switch issue seems to have developed after they fixed the vacuum leaks and replaced the distributor. Makes me wonder if putting the original distributor back in would shed any light.

The lead tech is an older gentleman, along with the shop owner. They seem to be familiar with TBIs and older vehicles in general. They’re always super busy and have a good reputation locally. They’re definitely being tested this time.

creich68 said:

The whole distributor assembly was replaced which I assume includes the HEI coil. I’ll have to double check that.

The switch issue seems to have developed after they fixed the vacuum leaks and replaced the distributor. Makes me wonder if putting the original distributor back in would shed any light.

The lead tech is an older gentleman, along with the shop owner. They seem to be familiar with TBIs and older vehicles in general. They’re always super busy and have a good reputation locally. They’re definitely being tested this time.

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Did they put a whole new distributor in it or just a cap n rotor or?
Sometimes it’s the oddest thing. That’s why electrical gremlins are called gremlins. For instance son’s mustang was throwing cam sensor codes and running poorly. New cam sensors didn’t fix it. It was alternator diodes causing it. Was totally stumped and read one thing on the web that pointed me to that.

Grit dog said:

Did they put a whole new distributor in it or just a cap n rotor or?
Sometimes it’s the oddest thing. That’s why electrical gremlins are called gremlins. For instance son’s mustang was throwing cam sensor codes and running poorly. New cam sensors didn’t fix it. It was alternator diodes causing it. Was totally stumped and read one thing on the web that pointed me to that.

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Whole new distributor top to bottom.

creich68 said:

Well....the ignition switch has been replaced. The shop drove it to test cold and hot starts. Everything seemed to be back to normal according to them.

I picked it up this afternoon and stopped at the store on the way home. Seems to run normal. Came out from the store, same issue...cranks while holding key and starts immediately after letting off.

Called the shop and owner said come back. Was able to replicate in front of him. He said there is some adjustment in the switch for the contact points (I'm taking his word for now) and that he will pull the switch back out Monday morning and check eveything again. He's convinced it has to be the switch. I'll have my popcorn ready for Monday.

Bummed I'll miss the local 80s-90s car show tomorrow morning but there's always next year!

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I have had mis adjusted ignition switches do the same thing. When you install a new switch you have to test it a few times to get it to work correctly. The mounting holes are slotted. I have admittedly never owned a TBI truck so I can't help you if that system is causing the problem.

I had the same issue with my 88 suburban . … I actually changed to a different column with tilt and a new key tumbler and problem solved starts right up every time as it should

Battery wire to distributor (ignition feed while cranking)
Pull that wire off, put positive lead of voltmeter on that terminal, ground your other voltmeter lead, look for 12v (this wire is a constant "hot"),
Once confirmed then turn key on, again confirm 12v, then while cranking...that wire should have 12v WHILE CRANKING....if not, and when you release key it goes back to 12v then that's why it's firing as you release key
Knowing mouse chewed wires and everything butt connected....probably source of issue
Plus, not much room back there and its dark so wire harness could've been spliced incorrectly.

Good evening friends!

It's been quite awhile since I gave an update, mainly because it's been a long journey. The latest and greatest...

Long story short the shop replaced the ignition switch a second time. Still having the cranking issue intermittently, so the shop looked over the wiring and put in a Delphi distributor/ICM as they suspected the aftermarket distributor installed in May could have been causing part of the problem. After a few back and forth trips, the suburban was starting as normal. No more cranking and starting after the key was let off. However....

Since the new ignition switch and distributor have been installed, it's intermittently losing partial power (feeling sluggish off and on, slightly rough running) and throwing the dreaded code 42. Shop kept it a couple more weeks and found the vehicle would act up whenever the tapped the PCM under the dash. So much that every time they tapped it, it would run rough. So they replaced the PCM with a new AD Delco unit and swapped the PROM over from the original PCM. That seemed to resolve everything. Running well, no hesitation, no cranking issues. Drove it about 100 miles after that and Sunday morning on the way back from the grocery store it started feeling sluggish intermittently and showed code 42 once again.

It will be headed back to the shop Monday morning. I will say the shop has been eating the labor ever since the original diagnosis in May and standing behind their work to fix it. However, I just want my suburban to return to normal again. My confidence in driving it anywhere across the country on trips has definitely taken a hit.

Besides the new distributor, ignition switch, coil, ICM, PCM...are there any other components in the ignition circuit that could cause code 42 and the intermittent issues? I can't think of anything other than the wires and connectors themselves.

Racking my head over here since the only thing I've touched on the suburban before these issues started was removed/re-installed the radio after having it restored in April - literally the very first drive after re-installing the radio and all hell has broken loose. Any prayers, advice, or criticism is welcomed if it helps me put these issues behind before camping this fall lol

I will add that with the exception of the ignition switch, all other parts replaced so far have been AC Delco/Delphi to rule out less reliable aftermarket electrical parts.

code 42 only sets if there is a wiring issue with the bypass (black/tan) or est (white) wires. could be an open or a short to ground, bad connection at the ICM, or stray voltage from a plug wire touching one of the wires or a bad plug wire or distributor cap letting voltage out and it is causing one of those 2 wires to see unexpected voltage. it occassionally sets if the ICM is bad.

The wiring is old as well. Quite within the realm of possibilities that the harness and the connections are getting less than reliable. Just another thought, sorry.

gmbellew said:

code 42 only sets if there is a wiring issue with the bypass (black/tan) or est (white) wires. could be an open or a short to ground, bad connection at the ICM, or stray voltage from a plug wire touching one of the wires or a bad plug wire or distributor cap letting voltage out and it is causing one of those 2 wires to see unexpected voltage. it occassionally sets if the ICM is bad.

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Are there any wires/connectors behind the radio area that I could have damaged when I removed/reinstalled the radio? Or is it just a coincidence that it started acting up right after I reinstalled the radio?