My Bonneville (over 130,000 miles) has very recently started refusing to start… sometimes. Usually, it cranks, turns over, and runs beautifully. Other times, it takes up to four minutes of intermittent cranking and turning over before it starts; then it runs beautifully. It happens when the engine is both warm (open thermostat) and cold (around freezing).

I think I hear a new sloshing or a medium-pitched rattling under the hood. Or maybe I'm just making myself hear things that aren't there, though.

Possibly relevant history that I can remember:

• Around 60,000 miles (or so I'm told): Transmission replaced.
• Over 75,000 miles:Bought the car.
• Sometime in 2007:Starter blew for the third or fourth time. Tow truck'* jumper cables melted. Smart mechanic replaced starter and battery cables to fix the problem permanently.
• Summer 2008: Started getting intermittent check engine light, that would turn on for a day and then shut off: P1078 ("Transmission component slipping"); same smart mechanic said that it shouldn't be a problem. Still continues to this day, though not as frequently.
• ~116,400 miles: Realized that documenting repair history was a good idea. Kicked myself.
• ~116,400 miles (early July): "Rusted through" fuel filter replaced during oil change. Fittings sealed.
• 117,289 miles (late July): Disaster. Upper intake manifold burst. Replaced it, all soaked spark plugs and ignition wires, missing coolant, and contaminated oil. (Obviously, this fixed the coolant leak.)
• ~123,000 miles (September): Oil change. Lubrication points sealed. Passed state emissions test.
• <130,000 miles, few weeks ago: Gas station was out of 87 octane; had to fill up with 89. Seemed like the car ran a little better, faster, and smoother. Back to 87 after that, though.
• ~130,000 miles, few weeks ago: Car wash. Attempted to spray water under the car, out of fear of salt causing rust.
• >130,000 miles (last Monday) - Oil change; down a quart. Lubrication points lubricated. Recommended flushing brown transmission fluid (when I get paid next). Found a tiny transmission fluid leak in the pan, not serious.
• ~130,000 miles (last Friday?) - Problem began occurring.

Any ideas? I found a couple leads by searching these forums. Could it be the fuel pump, or perhaps an electrical problem with it? Maybe a leak or clog in the fuel line? Or maybe even a worn timing belt?

Could be a pile of things.

What tools for testing do you or friends have?
Fuel pressure gauge
Spark tester
Scanner/code reader

Do you have any moisture inside the car, say the carpet always gets wet from rain etc?

We use our brains and Google, as well as my finicky code reader (which I'll get around to hooking up later tonight). I take their advice with a grain of salt; the closest I have to a mechanic friend is a member of my college'* car club.

The spark plugs are fairly new (<15,000 miles, less than seven months old), and I'm not noticing any check engine lights about emissions, misfires, or whatnot (not that that entirely rules spark plugs out).

The inside of the car is always dry. No leaks.

Take a look here and see if this helps at all.

https://www.gmforum.com/t279317/

ECM or PCM issue?.
Moved to proper section, mechanical issues need to be in the mechanical sections for reference please. This section is just a lounge for Bonneville chat.

PCM is possible, not very common though.

Sounds like you should be able to get a good diagnosis quickly.

I like to cheat on the spark test, knowing at least 4 wires and plugs are good, the motor will start and run. My test is to pull one wire at the coil and crank. If you get sparks jumping around, you have spark.

Do your best to check for fuel pressure. The engine will want at least 25-30psi to start, anything less and you'll crank your life away w/o starting.

Try unplugging the maf sensor and using a little throttle to start it the first couple times. By unplugging you'll default to tables and the pcm needs a couple starts to adjust from the sensor values it was getting to the table values. If that seems to correct the issue, then most likely the maf needs to be cleaned or replaced.

Lastly I'd pull a plug and make sure it'* not soaked in coolant. You did the UIM, check the plugs though just in case.

You can also try depressing the gas peddle just a little bit when you crank it. If it starts fine doing that. Check the TPS.

I had a problem simlar to this, it would take upwards of 15 minutes of non-continous cranking to start. Turns out it was the crankshaft position sensor causing all of hte problems.