1999 454 Mag MPI just quits - videos

[PlayDate]

No video necessary ......put it back in Service mode....check the timing and set the rpm higher. It could be fuel but I would like to see what those IACs are signaling. Those things are controlled vacuum leaks which often create the very behavior you are encountering. Yes, I know they are new.

I'm curious how it behaves in Service mode.

 

[douglee25]

My bet is on timing. So close!

 

[370Dancer]

It's not a fuel issue. It's either air or ignition timing. Check to see if there is a microswitch on the shift selector mechanism (usually on the engine). This is used to signal the ECM to advance the timing when the engine drops into gear. Some configurations had it some not - I'm not sure. The second thing is to clean the Idle Air Control Valve- it may be sticking and not moving fast enough to add the needed air to increase the RPM. But didn't you replace the IAC - I seem to remember you did....

the "shift assist" microswitch is found on I/O applications. Service manual says that the ECM performs the function, at least on MEFI-3. (Load anticipation) Yes the IACs are new. Didn't get to it today. May be Friday before I can dedicate more bilge time. Leaning towards timing first.

 

[PlayDate]

the "shift assist" microswitch is found on I/O applications. Service manual says that the ECM performs the function, at least on MEFI-3. (Load anticipation) Yes the IACs are new. Didn't get to it today. May be Friday before I can dedicate more bilge time. Leaning towards timing first.

Also.....I'm sure you have already thought of this but make sure the vents are open on your 6 gal portable tanks. I left one partially closed once during testing and was convinced their were demons in the fuel system.

 

[370Dancer]

This close.
Sure looks like the IACs can't keep up, but they are new. changing them anyways.
Surges (stbd more than port), and still stalls if I close the throttles all the way. Been messing with the physical linkage, but have not touched the TPS adjustments. Trying to set mechanical closure linkage to 0% TPS. Wish there was an easy way to get them swapped without removing the plenum, or removing the right side elbow (V-drives, so the elbow is in front of the flame arrestor). Had any luck getting the throttle body off without removing the afore mentioned big deal parts on a V-drive inboard?
videos of surging and stalling here:

Dropbox - File Deleted - Simplify your life

www.dropbox.com

Dropbox - File Deleted - Simplify your life

www.dropbox.com

Dropbox - File Deleted - Simplify your life

www.dropbox.com

 

[PlayDate]

This close.
Sure looks like the IACs can't keep up, but they are new. changing them anyways.
Surges (stbd more than port), and still stalls if I close the throttles all the way. Been messing with the physical linkage, but have not touched the TPS adjustments. Trying to set mechanical closure linkage to 0% TPS. Wish there was an easy way to get them swapped without removing the plenum, or removing the right side elbow (V-drives, so the elbow is in front of the flame arrestor). Had any luck getting the throttle body off without removing the afore mentioned big deal parts on a V-drive inboard?
videos of surging and stalling here:

Dropbox - File Deleted - Simplify your life

www.dropbox.com

Dropbox - File Deleted - Simplify your life

www.dropbox.com

Dropbox - File Deleted - Simplify your life

www.dropbox.com

Well .....great videos.....I get the sense that it is getting air going lean and then cycling all over again. I like that the ECM senses when it is in gear and adjusts so that is positive.

I presume that at 1500 rpm in neutral everything looks okay and there is no surging and the engine balancer stays in the dead center.....is that right?


I just want to make sure that this is an idle only problem.

 

[ttmott]

This close.
Sure looks like the IACs can't keep up, but they are new. changing them anyways.
Surges (stbd more than port), and still stalls if I close the throttles all the way. Been messing with the physical linkage, but have not touched the TPS adjustments. Trying to set mechanical closure linkage to 0% TPS. Wish there was an easy way to get them swapped without removing the plenum, or removing the right side elbow (V-drives, so the elbow is in front of the flame arrestor). Had any luck getting the throttle body off without removing the afore mentioned big deal parts on a V-drive inboard?
videos of surging and stalling here:

It almost sounds like the IAC is running out of head room. There is a setup for the IAC's - you'll need your scan tool. You want the IAC valve to be between 20 and 35 percent at a stable idle. Some like less. So with the scan tool and the engine at operating temperature adjust the throttle plate opening so the IAC is indicating between 20 and 25 percent open. This is the only way to set the butterfly on the throttle body.

 

[douglee25]

At 1500 rpm, shouldn't the IAC be out of the question? If it's surging at 1500 rpm, something else seems amiss?

 

[PlayDate]

At 1500 rpm, shouldn't the IAC be out of the question? If it's surging at 1500 rpm, something else seems amiss?

Yes.....but I created this confusion by asking about 1500 rpm. The videos are all below that.

Tom's answer is the right way to set the Throttle plate.

That said......I am curious what happens if you disconnect the engine coolant sensor to fool the ECM into a cold condition.

 

[ttmott]

Yes.....but I created this confusion by asking about 1500 rpm. The videos are all below that.

Tom's answer is the right way to set the Throttle plate.

That said......I am curious what happens if you disconnect the engine coolant sensor to fool the ECM into a cold condition.

I should fault and an error should display. The ecm will see 0 volts which is below the minimum acceptable.

 

[PlayDate]

I should fault and an error should display. The ecm will see 0 volts which is below the minimum acceptable.

Beyond the error message.....I'm curious what it will do. According to a Mercruiser mechanic that I know.....it was one of his tricks to determine if the throttle body was out of adjustment. The ECM allegedly throws an error but defaults to a cold condition. I have never tried it but it sounds interesting. He said if the surging goes away .....you have your answer.

Frankly.....I believe the Throttle plate is the issue. It is a balancing act between the plate and the IAC. Once that is adjusted......things should get better.

You guys make me glad I have Holley carbs on my boat. I like fuel injection and it is more efficient but it is also far more frustrating to sort out.

 

[370Dancer]

Short answer is yes, this is an idle problem. 1000+ it is stable (enough), but bad for the transmissions.....
Quick closing of the throttles = stall, which is bad for docking......
I have the Fox Gateways, so full time parameter monitoring. I'll check percentage, but I do recall them not being identical. Gotta fly for a couple of days, and then I'll be back on it after Friday's deluge of rain.
Glad to see the troopers are still playing along.
Back in 2017 when I had the California fire boat engines installed, I let the yard "get em going". That was a cluster@#$% by the Myakka shade tree guys, so there's no telling how long I have been fighting mis-adjustments.
Onward

 

[370Dancer]

It almost sounds like the IAC is running out of head room. There is a setup for the IAC's - you'll need your scan tool. You want the IAC valve to be between 20 and 35 percent at a stable idle. Some like less. So with the scan tool and the engine at operating temperature adjust the throttle plate opening so the IAC is indicating between 20 and 25 percent open. This is the only way to set the butterfly on the throttle body.

While 1000 miles away, thinking about this. My understanding is that the value being displayed is not percentage per se, but counts (pulses?) to drive the stepper motor of the IAC. That number is jumping around when it's surging, and so far, the settle down number still hovers around 40-60. Is that the number you are referring to as needing to be stable at 20-35 at idle? Is adjusting the throttle plate opening done other ways besides adjusting the throttle cable end (3300 cables) to make the overall length shorter and longer? Do I care if I start to register throttle position percentage while adjusting? Asking all this before I curl up with Service Manual 23 tonight for some light reading. Pulling the throttle body and flame arrestor is going to be remove the plenum for the hundredth time, or remove the exhaust elbow to get room to pull it off the plenum in place. Either way breaks gaskets and seals.

 

[ttmott]

While 1000 miles away, thinking about this. My understanding is that the value being displayed is not percentage per se, but counts (pulses?) to drive the stepper motor of the IAC. That number is jumping around when it's surging, and so far, the settle down number still hovers around 40-60. Is that the number you are referring to as needing to be stable at 20-35 at idle? Is adjusting the throttle plate opening done other ways besides adjusting the throttle cable end (3300 cables) to make the overall length shorter and longer? Do I care if I start to register throttle position percentage while adjusting? Asking all this before I curl up with Service Manual 23 tonight for some light reading. Pulling the throttle body and flame arrestor is going to be remove the plenum for the hundredth time, or remove the exhaust elbow to get room to pull it off the plenum in place. Either way breaks gaskets and seals.

Lord man - at least curl up with Elon's biography. Actually, I'm reading that now and completely enthralled with what that guy is all about.....
Ok back on track - throttle plates can't close to the body or they will stick - there has to be an adjustment / set screw - If Merc is using the cable it would be unusual and I can't see how any precision adjustment could be maintained. But quite possible.

You want the engine to idle with a minimum IAC percent open - stalling is the engine not getting enough air during idle conditions. So the IAC at a minimum duty cycle gives it plenty of head room to recover low RPM conditions or dropping the boat into gear or the alternator loaded down. Air flow through the IAC is not linear relative to it's position. Combined with the IAC reacting the ECU will advance timing to recover also. As long as your base timing is correct there is nothing more to do there. If you are having issues getting stable values set the timing to fixed; If I remember there is a wire that goes to ground to prevent advance in the timing. You or @PlayDate probably knows what that is.

The 40 to 60 is way too high based upon a maximum count of 100. There is no reason for the IAC to pull air out (close down), it should only add air to achieve idle recovery conditions then return to what you have it set at so a minimum reasonable count is best. Obviously, air quality conditions change so the IAC needs to have the capability to remove air but that is not really a dynamic condition or large swings.

One more thing when you start narrowing on the throttle blade position relative to the IAC percentage keep an eye on the TPS - If it is one of the earlier adjustable GM style ones you will need to tweek it's voltage after you make a throttle body adjustment.

My head is all around the Holley EFI systems so I may have terminology wrong here but the principals are the same.

 

[PlayDate]

Okay for your reading pleasure. Yes....it is on a supercharged go boat but the procedures are correct for a Mercruiser big block. If you think we argue a lot on CSR you should see the discussions we have on OSO. This discussion is actually pretty good.

"How to adjust IAC & TPS" On Merc EFI - Offshoreonly.com

General Q & A - "How to adjust IAC & TPS" On Merc EFI - I have pulled this from FAST's web site on Idle speed. Hopefully this will help people understand a little more. With the FAST system you have the option to make adjustment to the programing. As you will read the orginall throttle position...

www.offshoreonly.com

I do like Holley EFI systems.....they make it very straightforward. We used FAST EFI on go boats for years but Holley seems to have taken over.

 

[370Dancer]

Tracking. I have no reason to believe that the yard gorillas didn't mess with the idle stop screw during "commissioning" of the 2017 engines. So, I'll be yanking the TB, probably by removing the plenum. Hate messing with those RTV'd up exhaust gaskets at this point.
I frequent OSO as a lurker and former local promoter for the 4th of July Suncoast Offshore (or whatever Lucy calls it now). You can't swing a dead cat without hitting a late model MAG MPI in that group. Good thread, thanks. There's another one about the "relative" adjustments I'll have to re-discover.

 

[PlayDate]

Tracking. I have no reason to believe that the yard gorillas didn't mess with the idle stop screw during "commissioning" of the 2017 engines. So, I'll be yanking the TB, probably by removing the plenum. Hate messing with those RTV'd up exhaust gaskets at this point.
I frequent OSO as a lurker and former local promoter for the 4th of July Suncoast Offshore (or whatever Lucy calls it now). You can't swing a dead cat without hitting a late model MAG MPI in that group. Good thread, thanks. There's another one about the "relative" adjustments I'll have to re-discover.

I think Tom is right and the IAC is out of headroom. Adjusting the TB to let some air in will solve that and hopefully the problem. I know it is a pain to take the thing apart again.

OSO is a great place for things like this. Some of those guys have way too much money to spend. While folks on CSR bitch about buying a rebuilt 454 these guys drop $80-90k on a single engine. In addition .......there appear to be a lot more rip off folks in that world.

 

[370Dancer]

I'm going to take an hour or two today, and see if I can't come up with a tool (mod) to address removal of the TB, and/or adjustments with it in place. I actually have a spare plenum with TPS and throttle body to study. The benefit of having 6 motors go through the bilge in my lifetime.

 

[douglee25]

Technically speaking, why can't we increase the throttle opening just using the cable adjustment, then rerun the IAC calibrate procedure? This would avoid breaking gaskets and prove the whole theory without much effort.

 

[ttmott]

Technically speaking, why can't we increase the throttle opening just using the cable adjustment, then rerun the IAC calibrate procedure? This would avoid breaking gaskets and prove the whole theory without much effort.

The process needs to be done with engine running and hot.
Back in the day - to set the butterfly base opening, we used a specific size drill bit as a "feeler gauge" and that was done with the Throttle body removed.