6.2MX Cold Start

CrewLounge

My twin 6.2's run so rich at cold start they smoke. And, when warm, they are sometimes hard to start. Any ideas how to correct?

CrewLounge

Black

212rowboat

year? is it both engines?

your engines are expecting a certain fuel pressure... it trims based on that expected pressure.. do the two engines share a common lift pump from the tank?  Is there a chance you've picked up contaminated fuel that has deposited debris (and made obstructions that disallow seating/closing) in the injector(s) basket(s)?

Is this the start of teh season for you? what kind of winterization did you or someone else perform?  did you fog or have them fogged? it could be simply that the MAF is buggered up (on both engines due to fogging), and that simple...

CrewLounge

The engines are injected. I have checked the fuel pressure at the rail and it is 25 psi, what the manual says it should be. I would expect poor performance if I had bad fuel or a bad pump, but it runs great getting up on plane. It just starts rich and once the reach 160 degrees, it clears up.

212rowboat

What year are they? Are they o2 monitored, which is to ask, do they have an o2 sensor in the exhaust?

It sounds like open loop is the issue, but once it closes your good.. temperature is what prompts the pcm to close loop, which is a simple way to say begin trusting the sensors, and achieve operational temperature where detonation is more predictable.. the pcm controls trim prior to closing loop via scripts/tables that do not change...

Do you have a high idle at start?, or, do you have a sputter and a 'want to die' coughing thing going on? ... Did you fog the engines for winterization? ... Did you clean the throttle body at the end of last season or before this one? .. a rich condition can be attributed to a bunch of things.. you've checked rail pressure, so you obviously know your way around.. because of that, I'd recommend you pick up a can of throttle body cleaner and let your idle air control (iac) have a good bath.. if they are gummed up, and the blades closed (at idle), you could simply be squirting more fuel than the engines have air to blend...

CrewLounge

They are 2002's. Idles fine, just smokes excessively til warm. Runs great, but once at operating temp, they both won't start without cracking the throttles up a little. Did not fog for winter

CrewLounge

I have cleaned the iac's in the past with no change. They have good vacuum. One thing I did notice though, is there is black carbon build up on the throttle body butterfly and iac area.

212rowboat

If the engines were fogged at the end of last season, there is a good chance the MAF's are jacked up.. it happens... We would usually expect to see this happen to only one, but it very well could have happened to both- especially if the fog that was used is caustic enough, and sitting on them long enough.. At the very least, I'd pull them and clean them- if you have carbon build-up on the TB, there is a better than good chance you have it on the MAFs, too..

for EFI on MPI engines to work, the PCM has to kick things off with a ballpark trim, that is rich.. it's rich because a predetonation on a cold engine is often a death sentence.. richer is harder to ignite, and the engine is less likely to predetonate on compression or a hot spot inside the chamber if it is south of 13:1 a:f ratio.. Scripts control the trim solely.. those scripts are based off of expectations though- primarily, fuel pressure.

after fuel pressure, which is of extreme importance in EFI/MPI engines, the other sensors that trickle online are the Mass Air Flow or Manifold Absolute pressure sensors... the intake air temperature is important.. the engine coolant temperature is important.. the PCM needs to know the throttle position, so that is important, too.. you may want to break out your multimeter and pull some readings off of the TPS to make sure they jive- but, alas, it's unlikely both engines would suffer from this... all together, these sensors determine the fuel trim based off of calculations the PCM performs......... if those sensors are bordering the outside of an expected parameter, they will NOT kick a code, but they will misbehave and performance will suffer.. The #1 culprit for poor performance, as far as these key sensors are concerned, is the MAF..

here is a cut view of a MAF.. not your MAF, but the technology is similar:



the things are surprisingly delicate... if they ingest something, like a solvent or an oil, they can continue to 'work' (as in not kick a code), but they are in fact toast... they can't be recovered easily, but instead can only be replaced.. the MAF is an absolute key sensor, and comes online and provides data to the PCM almost instantly...

If you have a set of '02 engines that haven't had this thing swapped recently, I'd rec you do it anyway- just for good housekeeping measures... you may find that your problem clears right up by doing so.

Bruce

Having been an auto mechanic all of my adult life, this has me very curious. Everything Drew stated sounds right on, but I just can't get past the fact that both engines are having the same symptoms.  It seems to me that if you were experiencing a sensor error or a control fault, it would be unlikely to happen to both engines in the same manner. Again I'm a auto mechanic, not a marine mechanic, and our boat is a single, I have no experience with twins,   but I can't help but wonder what both motors share in common? 

Michael T

Bothe engines? - all I can think of is - bad fuel, low voltage, restricted airflow into the engine compartment.....MT

212rowboat

If he fogged both engines, the mafs could have been affected on both, which tosses readings until the system closes loop and the other sensors start to report, and reconciles the deficiency.. that's all I got, man.. :-)

212rowboat

Does a single pcm control both? If so, I'd pull the connections and hit them with some contact cleaner.

Bruce

Drew I bet you are right, we see that a lot from people that have installed K&N air filters on their vehicles and charged them with too much oil. It still seems strange that they would both act them same though, but for Crew's sake I hope you're right. With a little contact cleaner it'll be a cheap easy fix. 

 I can't imagine a single PCM would run both engines, but hey I learn new stuff everyday!

212rowboat

I got one mote shot in the dark:

Pull your pcv valve and shake them... If they don't rattle, replace them.. there is a chance (albeit slight, and especially so because its both of them) they are gummed up and stuck open, and you're losing vacuum, and siphoning oil off the valvetrain.. Whallah, tough start, rough running, rich, and cleared up by rpm's, and heat due to engine operation..

It's a strange problem, and I think I'm out of ammo by now.. :-)

CrewLounge

PCV's rattle and have good vacuum. I will clean the IAC's, but I'm starting to suspect the spark arresters. Maybe they restrict the intake a bit...

212rowboat

they likely do, as all of them do to a degree, but it doesn't make sense that they would when the engine is cooler than they do with the engine warmer...

IAC's have a tiny motor that is controlled by the PCM, and is a learned process- the PCM opens the needle, or closes it to allow the proper RPM at closed throttle condition.. they are opened slightly more at cold start than they are while warm... the little motor gadget opens it and closes it accordingly..

a lot of folks make the mistake, whilst cleaning them, of messing up the mapping of those things.. if the PCM thought they were completely closed the last time it ran, and you remove them and open them slightly, the PCM still thinks they are closed... or.. vice versa... the vice versa likely being what happens most often..

when you clean them, do yourself a favor and clean them carefully, making certain teh washer goes back in, and that they are closed.. then make certain and disconnect your battery(s), and give everything a minute or so to drain down- then reconnect.. this clears the adaptive memory on the PCM, and it goes back to hard scripted tables, and where the IAC is thought to be closed..

I doubt both IAC's would be jacking you up.. the arrestor is an easy discovery: remove them and try to run it.. the PCM(s) likely didn't lose data or didn't corrupt data for those pre closed-loop tables, but they could have.. it wouldn't be the first time it's happened.. which is why I asked if you had two separate PCM's or just one that controls both engines? ....

this is def a curiosity... I'm anxious to see what you discover!

Bruce

I would think that if it were an air intake issue it would be much more prevalent under higher rpm's? 

212rowboat

Bruce said:

I would think that if it were an air intake issue it would be much more prevalent under higher rpm's? 

in 99% of the case, this can't be argued.... I have seen, though, obstacles in the induction path that create a ton of resistance in a certain range, and when the engine gulps enough air and at a rate that is enough to overcome that obstruction, and it breathes properly.. ever since seeing that for the first time, I look for it.. it was a bear to track down, and I like to think I learn from my experiences.. :-)

I can't imagine what that would be in this case, though, and then- both engines? 

Like Mike said, not having enough air in the compartment could easily cause the issue- but why only at low temperature? 

this is a weird circumstance.

CrewLounge

Each engine has its own PCM, I checked them for codes and the don't have any

212rowboat

Were they fogged?

I gotta tell you, the more I think about it, the more I think mafs... They often go bad without a code, because the filament lies to the iring, registering decent ohms but only because they're entombed in gunk...

CrewLounge

That's what I was leaning toward

212rowboat

Map, Maf... grrrrr.... I need a chart to know which ones use which...

Bruce

Fuel pressure regulator leaking? But on both motors at the same time?? Unlikely.   Still trying to figure what both motors share. 

 I was with Drew on the MAF's if the motors were fogged, but since they are running MAP's, shoots that theory. 

212rowboat

Manifold absolute pressure and mass air flow are different ways to do the same thing... some engines use MAP's, some MAF's...

Mopar uses MAP's a lot... Chebby uses MAF's more often.. I had a discussion with Al a good while back and (wrongfully) extrapolated that these (mercs and volvo marine) were akin to the Chevy way of doing things.. and assumed MAF's... still... If they use MAP's, that's were I would look..



MAP's, it's been my observation, are even more sensitive than MAF's...  

CrewLounge

Thanks Al, I will

212rowboat

one good thing about finding out it's a MAP and not a MAF: the MAP will run the same with or without a vacuum leak- maf, so much..