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Won't start when hot

1995 Buick Regal, 128k miles, 3.8L V-6.
Problem: When running errands around town, car will temporarily not start after 3rd or 4th stop. Vehicle cranks, has spark, has fuel pressure at fuel manifold. No codes on computer (Wish it was a '96). Car will start normally after cooling off (generally takes at least 45 minutes). No problem driving to work, parking all day, driving home. Have not tried long distance driving since problem arose, due to concern about being stuck for awhile far from home. Have determined at EGR valve is NOT a part of problem.

Sample situation: Drove 5 miles to town. Shopped for 15 minutes. Drove 2 miles further with 5 minute stop. Drove another 2 miles with 5 minute stop. Drove 1 more mile and stopped for 30-40 minutes. Car would not start. Cranks strongly, has spark and fuel pressure (don’t know if fuel getting to injectors). Still would not start 30 minutes later. Left car for several hours. Started promptly and ran normally on return. Weather condtions - 90 F, low humidity. Problem has been occurring for several months. No computer codes to dive guidance.

It may be a leaky injector(s), flooding one or more cylinders over time. When you then let it sit longer, it evaporates and everything is fine again.

Try running some good cleaner through the gas tank to see if that helps.

What exactly she does when does not start ? Does it cranks and stumbles or it does not even tries ? You may have spark, but you will need to check the cam sensor because timing may be off. You may want to try this tests on the cam sensor. You have to locate it and it will be a pain to get to it.

1- Disconnect the CMP sensor wiring harness and connect an LED test light between CMP harness terminal C (white wire with black trace) and battery ground.
2- With the ignition ON and the engine off, verify that the test light illuminates.
If not as specified, repair or replace the fuse and/or wiring.
3- Carefully connect the test light between CMP harness terminal A (brown with white trace wire) and C (white wire with black trace) and verify that the test light illuminates.
If not as specified, repair the CMP harness ground circuit (terminal A(brown with white trace wire)).
4- Turn the ignition OFF and disconnect the test light.
Next, connect suitable jumper wires between the CMP sensor and CMP sensor harness. Connect a DC volt meter to the jumper wire corresponding to CMP terminal B (red wire with black trace) and battery ground.
Start the engine and verify that the voltage signal is 5–7 volts.
If it is not as specified, the CMP sensor may be faulty.

You had mentioned that you have fuel pressure, But how much?

First you need to find what it should be then you need to have it checked when this happens.

Unless you have the guage and know how to use it (safely) have a compitent tech. handle it.

One other thing that you could check is when this happens remove the fuel cap then try and re-start the vehicle.

How do you know it has spark?
How do you know it has fuel pressure?

What I believe is happ0ening is that you’re thermally cycling some component that has become sensitive to temp cycling. Often those will be components with coils. Coils are coated with a varnish-like insulation that becomes brittle over time after being stretched then contracted repeated as the copper beneath them expands and contracts at a higher coefficient than the insulation. The insulation develops microfractures that open when heated and close when cooled. When open, they allow shorting of coil windings and decrease or eliminate the coil’s ability ot function.

The temp cycling happens because every time you shut the engine off, =the fan stops running and the coolant stops flowing and the underhood temperature rises, and every time you start the engine again the coolant flows, the fans turn on, and the temperature drops. The areas in and around the tops of the combustion chambers, the exhaust manifolds, and the exhaust components are hundreds of degrees hotter than the area under the hood, and alll that heat dissipates and heats up the underhood space.

Components that contain heat sensitive stuff include coils, injectors, igniters, and some sensors. And if the engine isn;t cranking at all when it’s not starting, you can add to the list as PRIMART SUSPECTS the starter motor and the solenoid that engages it to the flywheel and enables the motor circuit.

So, I’ll ask, how do you know you have spark…when it ISN’T starting?
How do you know you have fuel?

This car has a problem with PCM (computer) shutting off the injectors. Sometimes you can reproduce the problem by slapping the PCM (Out of the glove box) while it’s idling and see what happens. 95’s still set cam and crank codes.

Could be any of an assortment of problems. The first thing I’d probaby check is the engine coolant sensor. This is used by the computer to determine the amount of gas to inject. If it is inaccurate when hot, but ok when cold, the computer will not inject the correct amount of gas when the engine is hot, and the car won’t start. Ask you shop to check this. I don’t have any experience on your make/model, but on most econoboxes, it is usually pretty easy to check.

Clarification of terms, et al. Buick starter motor engaes and turns engine over energetically. Sometimes engine will not crank (start) at all, a few times engine will crank and stumble. In example in previou post engine cranked and stumbled briefly 3 times before not cranking at all. I assume this is because available fuel was exhausted Spark present at ignition cables; nothing between cables and spark plugs. Fuel pressure at fuel rail; specific pressure unknown, but does not seem weak. Of course, vehicle will not “misbehave” when left with technician, despite his best efforts to duplicate conditions under which problem occurs. Spurgear