348 hot start issues

I have a 348 that starts and runs fine when cold, but warm it up and shut it down and it is a mother to get restarted. I mean it cranks fine but doesn't start. sometimes it pops out the exhaust, stumbles,
after about 5-8 tries it starts and runs like nothing ever happened. it runs and idles perfectly.
any ideas on what might be the problem?
thanks!

This can be a symptom of a dual-mass flywheel starting to fail. When hot, the damping-greease is less viscous. The drive shaft, damping grese and the DMFW are used in place of a heavy balacing weight at the front of the crankshaft in americam V8 engines. The the 348/355 the shaft between the crank and the clutch and the DMFW are used to control crankshaft vibrations.

When the first cylinder fires (successfully) the drive shaft twists, and has plenty of time to reach the DMFW and return that twist back to the back end of the Crank. This end of the crank has the timing position sensors, and a failing DMFW can cause the timing pulses to arrive early (BTDC) and create negative amounts of power input, causing the motor fo fail to catch.

Alternately, this could be a Digiplex problem.

One can tell a DMFW issue if the 3K-4K RPM range has developed a rattle in the gearshift lever. One can also tell by looking for grey greas seeping from the clutch observation port under the clutch.

OK, it starts fine when cold.

Have you tried re-starting it the moment that the engine is shut off (when hot)?

It takes a few minutes for a failing component like a fuel pressure regulator to bleed off fuel pressure, so a quick re-start will test if you have a fuel pressure leak.

Likewise, you'll want to spray in some starter fluid with the engine off but hot to see if she starts up easily that way.

Until you perform those two tests, you'd just be guessing at your problem/cause, likely costing you money and time while upping your frustration.

thanks guys, I'll start testing things.
it's pretty much a solid problem, car just needs to warm up and it happens every time.
Wonder if putting a timing light on #1 plug wire when it's in a hard start mode would help figure out what's wrong.
I'm taking your advice and doing the easy tests first though.
thanks again.

I was going to ask if you've done what we should always start with first, and that's Reprogramming the Computers? So many times we've seen a simple Relearn Run on the Adaptive Logic Chips fix a driveability issue. If the answer is yes carry on with the other suggestions as they are spot on, if the answer is no, back up and start at the beggining.

On the Fuel Pressure Regs....pull the small Vacum Hoses at the Manifold End and Look for Raw Fuel (if you see raw gas that's a bad thing). Then put a lenght of vacum hose on the Reg End & pull a vacum with a cheapy vacum pump, if they hold vacum they're ok.

On the DMFW..that advice is also spot on...and if you hear a strange rattle from the rear on shut down you can bet the flywheel needs grease. About 40K miles best case scenario is about as far as a flywheel gets before it needs attention, especially in light of the fact that the factory has upped the specified amount of grease twice since the 348's were first introduced..

No, I didn't do the re-learn thing???
what do I need to do to accomplish that?
thanks,
tim

To run the "Relearn" - with a cold engine - unhook the Battery (not the kill switch, the battery itself)Ground Cable for about a few minutes....this clears the computers of stored data...reconnect...turn on key & turn off accesories...radio, AC, etc....then...without touching the gas throughout this entire cycle, start the engine & let "idle only" for approx. 10 minutes...by this time the engine should have gone from all the way cold thru heating up and the fan cycle, then you can shut down the engine and after a few minutes take the car on a road test of normal driving. This process clears the chips & restores the computers to a "Baseline Model" of codes that the computers then use to determine basic driving vs hard driving. What happens with Adaptive Logic Chips is that after many drives without a "relearn" they can become polluted or over run with info...and lose the original baseline parameters. The Baseline is also corrupted if the Battery goes dead or is disconnected and the 10 minute relearn is not run upon restarting the engine. Any corruption of the baseline parameters can & often does cause starting and/or drivability anomolies.

After the relearn, if you still have the starting issues then move on to diagnoising the other issues described above.

HTH's

To reinforce JRVs message::

After a day or a weekend at the track, my F355 engine (2.7 ECU) is somewhat unhappy running down the interstate at 65 MPH until it gets 50-100 miles under its belt and relearns that the throttle is not being floored every other 5 second interval for 5 seconds. It will idle just fine, run flat out just fine, but it is quite unhappy with the 2000-3000 RPM band, shaking and rattling various things in the exhaust system.

I have followed this over the last 3 years and found out several parameters of the ECU and its learning process.

You, as a driver, can accelerate the relearning process by holding the throttle with extreme precision. You must hold the throttle absolutely still and hold the engine within 250 RPMs of any given point for at least 45 seconds, and repeat this over the whole range from 2000 through 3000 RPMs and most of the lower throttle opening band. If you know of some hills that take those 45 seconds to traverse, you can accelerate the learning at various throttle openings.

You can tell when the ECU has learned any given 250 RPM band, because the engine becomes crisp (and in my car the exhaust vibrations go away) and takes tiny increments of throttle and converts these into immediate thrust. Once the ECU has learned several of these 250 RPM bands, it sort-of automagically adusts the intermediate ranges at least until it gets some learning time in those bands.

If you just drive the car, it might take a bunch of miles for the learning (adaptive) logic to figure out what state of tune the engine is in and adapt to its current state (and the gasoline in the tank).

Note to self: do not try to teach the car ECU new tricks when running 106 octane race gas, it gets very grumpy when you refill with 93 octane!

You're Funny Mitch,

Yes guys....you CAN actually "teach the computers new tricks"...as Mitch states,...we should probably start a new thread on this & get deeper into the mechanics behind it all,the advantages & disadvatages, and then put it into the Tech Section after all of our input.