Intermittent crank no start issue, out of ideas

[HumbeeH3]

I have a 2007 H3 with approximately 150k miles, recently developed a strange intermittent long crank & stumble and sometimes crank no start, only happens after the engine reached operational temp and I let it sit for 20-30min while I'm at a store or something. Cold start is fine and immediate stop and start is fine too. It also starts on second try no problem. Truck runs great otherwise. Here's a list of things that I've ruled out either because I've inspected/tested them or replaced them:

New Spark Plugs
New Coils
New Fuel Injectors
Checked Fuel Pressure/Fuel Pump (within spec)
Checked Head Gasket/Compression (within spec)
New Intake Manifold Gasket (torqued to spec)
New TB Gasket
Cleaned TB
Ran Seafoam Through Intake
New Intake & Exhaust Camshaft Sensors
Inspected Camshaft Solenoid
New Crankshaft Sensor and CASE relearn
Checked EVAP purge valve by disconnecting from throttle body and seeing if hard start persists, it does.
Trucks runs great, LTFT at 0% when idling slightly positive when driving but within spec.

I've read plenty of folks who had issues with their ignition and anti theft system, but it doesn't seem to fit my symptoms.

Any other ideas?

 

[Mr_Rich]

Pass Lock? After my 3T hit 100K I started having no start but all it affected was starting. All other electrical was good. I had to do the 10 min relearn cycle often. Not a batt term prob either.

 

[Happy Hummer]

Just off the top of my head sounds like a heat soaked problem or drain back issue to tank. I do agree anti theft and battery terminals.

 

[Jeepwalker]

I'll toss out a few ideas:

1) Yeah, it does sound like Passkey. The 20 min wait is the key sentence there. (failing switch ...batt connections??)

These probably aren't it, b/c you've looked into them, but I'll put them down as possibilities anyway,

2) If your fuel pump doesn't build up pressure fast enough (going bad?). When I've had fuel pumps go bad, the problems became apparent when the pump was warm/hot (not cold). Which might explain why it starts cold but not so well when warm. That's one possibility ...and something to investigate. Esp if it's an old pump.

3) On some vehicles, a faulty fuel pressure sensor (on pump) can keep a vehicle from starting (long crank) and then it'll start when the ECM see's enough oil pressure. Could be the sensor doesn't work as well when it's warmed up. Again, not sure if that could be the issue or not. Might be something to see if shows up on a scan tool.

4) Crap in the tank which gets sucked onto the filter as you drive. But overnight some of it falls off allowing it to start fine in the AM, for example. That doesn't really explain why it runs fine once you get it started ...but just tossing out a range of possibilities that cross my mind. ????

5) IDK if you've cleaned out the throttle bore or if it would even do it, but a heavily carbon'd up throttle blade/bore can make vehicles run/start poorly. I'm assuming you probablby looked at it already given what you've done so far. But it is easy to overlook. Also ...make sure when ya put the rubber snorkel boot on the throttle body, it doesn't get folded over under the clamp allowing some fresh air to be pulled around where it's folded over. Someone (previous owner) did that on mine. I can see it would be easy to do if a guy was sloppy and in a hurry. But that would (and did ...on mine) throw off the airflow that was being metered by the MAF sensor.

6) A couple other possibilities might be a cam or crank sensor starting to go bad.

It could be the pass-key though ...the 20 min wait time is the telle-tale there. Quadruple-check your battery connections and grounds (body grounds too). On my H3 the ground below the driver's foot was corroded in the jacket. That ground is close to the door and window module ...which affects the windows, door locks and maybe security. Once I fixed that I've never had a window or lock/security issue since in some 5 years or more. Could also be the key switch is going bad. That was another common thing.

Best of luck finding it. If I think of something else I'll drop it below. Let us know what the issue turned out to be once you figure it out ...so we can all be a little smarter.

 

[Happy Hummer]

Totally agree

"Best of luck finding it. If I think of something else I'll drop it below. Let us know what the issue turned out to be once you figure it out ...so we can all be a little smarter."

And with how dumb vehicles have become to work on we need all the help we can get!

 

[Jeepwalker]

And with how dumb vehicles have become to work on we need all the help we can get!

Agree'd. They've only gotten worse since our Hummers were made. That's one thing I really like about the H3. It does what you want, not too many 'modern' nanny's.

 

[Teahead]

change your your battery terminals asap.

Solved at least 3-4 CEL codes by doing that. Plus awful transmission issues.

 

[alrock]

If it's the passlock issue the security light should show on the dash.

 

[4speedfunk]

Passlock failures are common. I've repaired many of them. Next time you get a crank/no start...check the dash to see if the Passlock icon is flashing. This is a definitive tell-tale that the passlock module has lost communication with the BCM. Wait a half hour try it again...it will usually start. The passlock module is inside the steering column, and its bolted to the ignition key lock cylinder. You can get a replacement key lock cylinder on Amazon and I recommend getting the AC Delco version (around $100). I normally replace only the electronic piece on the end of it. This small connector is the culprit, and I have never found anything wrong with a key or tumbler on the five or six H3's I've repaired. Replacing the entire unit requires more disassembly, and its much easier to leave the lock cylinder in place and replace only the connector. Why they don't sell just that piece is a mystery to me. Once you get it repaired, you must do a passlock relearn (Youtube it) ...pretty easy. This should last another ten years or more.

If the passlock light is not flashing...then it could be anything. Looks like you went with the nuclear option on the motor, so it could be any number of those items you previously replaced. Given the random long crank or crank with no-start, I would strongly take a look at your previously replaced items and make sure everything is properly installed and tight. Next I would look at the fuel pump relay. This guy is in the fuse panel under the hood. Relays can get corroded and sticky, causing the issue you describe. Its cheap and easy to get to. Find another relay nearby (wipers?) with the same amperage and swap it out...see if that fixes your problem. Of course if your wipers don't work right, you'll know that was it.