Hey everyone
So before I start, I just want to say that I have searched this forum extensively before deciding to post, but haven't been able to solve the problem.

Details:
2004 MT with 117000 miles, about 2000 miles on rebuilt engine, running BHR midpipe.

I have been having serious flooding issues when the engine is cold, so much so that it essentially never starts when cold. Even extensive flood clearing hasn't been successful, I've had to hill start it twice now. It has started once when cold, but was only firing on the front rotor, and died quickly afterwards. Hot starting is no problem, and I've experimented with luke-warm starting (?), essentially starting it 30 mins after shutting it off (fully up to temp). It will start, but with difficulty, and often only after a couple of flood clear cranks.

Now I know that flooding is usually due to poor ignition health, but I've replaced the plugs, coils, and wires to no avail. Battery is relatively new, and was tested by the dealership and found to be OK. I installed the upgraded starter a few months back, and it still cranks quickly and powerfully.

Compression is another big cause, but I had the engine tested and compression is within acceptable ranges for all faces of both rotors.
Additionally, there are no misfires at all once she is running, and no problems idling.

My next thought was the engine running too rich due to O2 or MAF sensor failure, which I suppose is still possible. However I cleaned the MAF, and also calculated my highway gas mileage (which I figured would be very low if there was a rich condition). I got 18.5 mpg cruising at 80+ with a somewhat heavy foot when passing. That seems pretty good to me.

I also read about faulty water jacket seals fouling spark plugs and causing flooding, however I haven't noticed any white smoke, and I would think that such a failure would also manifest itself in very low compression numbers.

Other things I've tried: clean ESS, reset PCM (brake stomp method)...

One other thing: Occasionally while driving I get hesitation and bucking under acceleration, accompanied with sporadic P0420, P0661, and P2259 codes. Now I believe this is due to an SSV that sometimes sticks, (there's a fair amount of carbon on it), which I haven't gotten around to cleaning yet. I don't see how this would contribute to the flooding problems, but I figured I would include it for the sake of being thorough.

Any ideas?

 

Incorrect. Eventually coolant leakage will hurt compression scores, but it takes a while. One of these mornings, instead of starting it, crank the engine over a few times with the gas pedal to the floor to keep the injectors off, and then pull the spark plugs. See if they have coolant on them. If coolant leakage is your problem with sparking, you will find coolant on the plugs. If the plugs are dry, then it isn't what is inhibiting the spark.

The other primary cold start problem possibilitity that hasn't been addressed in your list yet is fuel pump failure that is making the fuel pressure take too long to come up. I don't think this is your problem, because if it was then you should have an easy start eventually.

MAF, fuel trims, O2 sensors, and the intake valving have no impact on starting. Fuel trims are locked to a map, O2 sensors feedback isn't used until the coolant temp gets past 160F or so, MAF isn't used until the engine is alive, and all the intake valving is closed at idle and below anyway.


If it isn't a coolant leakage problem, then get a timing light or a spark tester and test for spark on the leading/lower plugs (trailing plugs don't fire when starting). You may need both, spark tester to ensure that the coils are firing correctly, timing light to ensure that the plug itself is firing (since the spark tester replaces the spark plug). Also, check for fuel. If the problem is a fuel delivery problem, then the plugs should be rather dry when trying to start.

 

After that, looking at the SSF might be worth the effort. Mine started easier afterwards, enough that I noticed it. I put it down to the ecu reset, but it could also be related to SSV. If it is not closing, mine was having issues closing or being in the low RPM position, then you have air flowing one way, and fuel flowing someplace else during startup. At least I think that is how it works. So, the stuff above, then clean the SSV. one test would be to make absolutely sure it is closed, then try a cold start.

 

Good idea on how to check for leaking coolant, I'll give that a shot soon. Fuel delivery definitely doesn't seem to be the problem, during flood clearing I can smell fuel out of the exhaust, and I've pulled the plugs to find them soaked in gas.

Also good to know that trailing plugs don't fire when starting, that explains a few things.

 

OK I'll check to make sure it's closed next time I try starting, it's easy enough to do.

 

One more thing, I am running a small amount of premix and have left the OMP fully functional. I know it's one helluva stretch, but any chance there's just too much oil to ignite when it's cold?

 

Nope, not a problem. Lots of people premix with zero added difficulties, even at way too heavy premix rates.

 

I wouldn't think it's a over oiling prob I premix pretty heavy and still have the MOP running to and I have no starting problem. You could have got one or more bad coils out of the box it has been known to happen.

 

Hmm OK well if there's no coolant leakage in the chamber I'll go back and test the coils/plugs again. But wouldn't a faulty coil almost always cause misfires when running?

 

Not necessarily, but I don't think it's going to be coil related. If anything, the added ambient/saturation heat that the coil will see would make a hot start faintly harder, not significantly easier.

 

An option, in the event there is a bad coil, is swap the leading and trailing coils and see if something happens.