Questions about idle speed on 4.3GXI-E on startup

[stouchton]

Been trying to diagnose a hard start condition on 4.3GXI-E.

Boat has twins, so easy to compare how they act on start. Port engine starts fine, and revs idle initially then settles back to 600rpm. Starboard engine DOES NOT raise idle at start, and tries to simply start running at 600rpm.

I assumed this was a simple IAC problem, and replaced IAC. The new IAC pintle was shorter than original (retracted position) and engine started with a raised RPM then settled back to 600rpm. I assumed this meant it was working correctly and now was fixed. This was not the case, for it still wants to start at 600rpm and does not increase idle rpm to start like it did before (or like the port engine does).

So my next step is to hook up the MEFI4 scanner and see what the engine is telling me. I am just trying to educate myself first so I can better understand this. I have been thru the workshop manuals without any real explanation on start sequence. So I am assuming that engine temp is responsible for startup idle rpm?

When cold, it starts easily at 600rpm (no rev at startup). However, warm/hot it can be cantankerous.

Now, a piece of forensic info - I had to replace the power steering actuator which is mounted to starboard engine. Access was nill, and I was crawled in around the starboard side of starboard engine. Highly possible I disturbed something on the starboard side. Is the ECM temp sender on that side? I could not located it in any of the workshop manuals.

Thanks in advance for any help or insightful thoughts.

 

[alldodge]

Above me, maybe @muc or @dubs283 or @Fun Times might have and idea

 

[dubs283]

Based on provided info my WAG is map sensor issue. Without any diagnostic tool info its very difficult to determine

Depending on style of efi and style of map sensor its possible the map sensor is either dislodged from its seat in the manifold or if a divorced sensor there is an issue with the reference line from the manifold to the sensor (disconnected, broken, blocked, etc...)

With the diagnostic tool check for any active and stored faults and with engine running look at data items. There should be a definite difference in map and baro numbers. If still suspect of the ect data items will tell you quickly what the ecm reads from the sensor

 

[stouchton]

Thanks for getting back to me. My next step is to see what the ECM has to say.

I forgot to add that once started, it runs like a dream. WOT hits 4500rpm, which is exactly what it should hit. No idling issues. Just simply a finicky start, which is more difficult when warm.



On a side note, I have the OBD Diagnostics software and adapter. I see a lot of folks prefer the Rinda Techmate. Am I good with what I have, or should I change up to the Rinda?

 

[cyclops222]

Have you recorded all the data possible of the good engine on a cold start up ? Should point out some problems if possible / recordable.
Record on a smartphone all the computer running cold and hot data. Compare that to the other engine.

I just noticed you REALLY have at least 2 bad conditions. Cold start AND a finicky warmed up problem.
Have you pulled and checked ALL sparkplugs ? 1 or 2 intermittent plugs will drive you crazy. Been there.
Do you do any P M or recommended parts ?
What year is the engine ? Year of the boat ?
Leaky gaskets will cause similar problems.
Do Racerone test of all cylinder compressions. We have no data numbers to give advice on.

 

[stouchton]

Have you recorded all the data possible of the good engine on a cold start up ? Should point out some problems if possible / recordable.
Record on a smartphone all the computer running cold and hot data. Compare that to the other engine.

I just noticed you REALLY have at least 2 bad conditions. Cold start AND a finicky warmed up problem.
Have you pulled and checked ALL sparkplugs ? 1 or 2 intermittent plugs will drive you crazy. Been there.
Do you do any P M or recommended parts ?
What year is the engine ? Year of the boat ?
Leaky gaskets will cause similar problems.
Do Racerone test of all cylinder compressions. We have no data numbers to give advice on.

Sorry, I did leave out some things, and I like your thinking - which is what I was looking for. I am a retired EE who has worked on engines for 50 years so I get trapped in my own thinking!!! I wish I could find a flow chart on the ECM to see what it is trying to do.

I will be recording data this week. Boat is a 2004, engines original with 500 hours. All PM is done, new plugs, wires, cap, rotor end of last season. Ran fine last fall - no issues. This does get a little fuzzy because you don't pay attention to it - but I think it initially ran fine this year. I had no operational issues catch my attention until a couple weeks ago (Boat has been in the water since April). I went out to anchor for a couple hours and starboard engine would not restart (crank, no fire). Was coming back up the bay on the port engine, tried starboard again and it started. Ran fine. Since then it has always started, but not always on first try and not always happy - instead of advancing idle on start (like I think it should) it just tries to come up running at 600rpm. When cold this is not an issue, when warm it is finicky (which is backwards in my head).

I changed the IAC and noticed the new one had the pintle retracted, so I knew it was going to start on a high idle. It did, and backed the idle down so I knew the ECM was controlling the IAC at least in one direction (being a stepper this should indicate control in both directions). At the time, I did not realize there was an IAC reset procedure - figured it was a closed loop system and should set the idle speed if all was well. This might be part of my problem!

I will post back with data - I just wanted to make sure I was not overlooking some obvious thing that would prevent advancing idle at start. Wonder if my new IAC is stuck? Easy enough to check.

 

[alldodge]

The no start after sitting warm for couple hours can be vapor lock, but might be something else

Sounds like you have Diacom software and both are Rinda's

 

[cyclops222]

I am leaning to a chafed / rubbing wire insulation. or a coming loose wire connection.
Next time it refuses to restart. have a spare spark plug handy and work gloves. Pull off the easiest sparkplug boot. Put the spare plug in the boot and make a good GROUND CONNECTION. See and hear good sparks occur. Easier to see after sundown.
Test will tell if gas or ignition problem. Could also look at each sparkplug for 1 or 2 ODD looking ones.

 

[dypcdiver]

Swap ECU;s and see if it follows the ECU, might give you a clue.

 

[stouchton]

Appreciate all the responses, problem is solved.

It was the IAC.

My diagnostic software had too steep of a learning curve for me - it is the OBD Diagnostics based on ScannerPro. But it showed me enough to realize both engines were attempting the same start sequence, and had the same running parameters except IAC position.

Port engine walked up to 1500rpm on start, and backed down to 600rpm. Starboard simply stumbled to life at 600rpm. Both ECU's were commanding the IAC's to open. Of course the starboard would react to slight opening of throttle plates, so this led me to assume I had an IAC issue (I was hoping it was not an ECU driver issue!).

I removed the starboard IAC and the pintle was stuck extended about an inch out from the body. I could not move the pintle at all. On my old IAC I could move the pintle - took a bit of force but would move in and out. My new IAC would not budge.

I replaced my new IAC with another new IAC. Engine now starts properly - when started it revs to 1500rpm and backs down to 600rpm.

So I should be good - except for figuring this ScannerPro software out - lots of corrupted data and for the life of me could not figure out how to graph the parameters I wanted to see!

 

[stouchton]

Also, in response to Alldodge - I am worried I might have had 2 problems. Did not have time to take her out and then let her sit for a few hours to check hot restart. I did attempt hot restart in the marina, but it only sat for a few minutes. So next week I will check this out.

 

[alldodge]

Scanner Pro is good software (I have it also), but for the most part it just tells you want's going on right now, it doesn't read codes