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1999 Mercruiser 350MAG Issues followup

H

highflight2k2

Contributing Member
"I posted last fall questions

"I posted last fall questions about my issues. Thanks to all that replied. I won't recap as I haven't been able to test everything needing testing yet. I just got the boat in the water and engines started today. For those that remember, my task next weekend is to run the engine on a portable tank to rule out bad fuel or bad pickup.

I do have two questions:

#1 How can I test the TPS? I have a meter but I'm not sure how to test much past continuity or volts.

#2 Can timing alone cause RPM fluctuation or inability to spool up even when throttles are mashed?

Thanks again very much."
 
"Jon:

#1 Test the continui

"Jon:

#1 Test the continuity with the TPS disconnected. Turn the throttle slowly and watch for a steady change in ohms. Any sharp dip indicates a dead spot.

Also check for voltage change with the ignition on, engine not running. Voltage should change gradually w/o spikes or dips.

#2 Mashing the throttle tells the computer via the voltage delivered by the TPS that the engine needs more fuel and the timing needs to change in relationship to the throttle position and the amount of fuel delivered by the injectors. In order to deliver the required fuel, timing and spark the computer has to react to all of the input data from the system sensors per the directions of the integrated software program. Your computer just may need reflashed.

My 2004 Nissan Titan would not idle correctly recently. I did the basic checks and cleaned the throttle body to no avail. Took it to the dealer and their service bulletin called for a computer reflash since it lost its idle memory. When I asked how did the computer lose its memory to idle correctly, they could not answer me. It worked for 2 wks. and had to be done again. The tech. said the computer will need to be replaced if it does it a 3rd time."
 
"Well, I guess this can be con

"Well, I guess this can be considered progress...although the motor is not running any better.

Today, I did side by side comparisons of the fuel pressure at the rail. Both were identical, both in the slip and under load. The interesting thing is that the pressure was around 22 psi regardless of the RPM while in the slip. But under load, it was ~30+ psi. So fuel pressure isn't a problem.

I also attached a portable fuel tank with fresh medium grade fuel to the fuel filter inlet. There was no change in the engine's behavior.

I looked at the IAC and TPI. The IAC has most definitely been replaced. I'm not sure yet when or by whom, but the IAC on the port engine still has the original black paint on it while the starboard is nice and shinny. The TPI, although it doesn't look new, has definitely been removed because I can see the screws are slightly stripped. I ask myself if that rules them out or makes them more suspect. I couldn't seem to figure out how to test the TPI. I guess switching them might be the easiest test. I'm just concerned about the screw heads. I think I will wait for my friends at MarineMax to do it.

So the behavior today, regardless of which tank I ran from, was the same. The engine seemed to run fine up to and including ~3500 RPMs. It would struggle at any RPM greater. If I mashed the throttle, it "sounded" like it was trying to accelerate (it even got a whole lot louder), but was being held back. Fuel pressures were up in all cases. I am hoping that dave_n is still watching my thread and can speak to this. Does this still sound like timing to you? Assuming TPI and AIC are good, what else could be feeding the computer bad data?

I just sent my first email of the season to my friends at MarineMax asking them for a list of all the work they have done to it as well as a list of all parts replaced. I'm sure they were happy to hear from me. :)

If anyone has ideas going forward, please let me know. I will reply back when/if MarineMax answers my questions.

Thanks very much!!!

Jon"
 
"Jon:

"The engine seeme

"Jon:

"The engine seemed to run fine up to and including ~3500 RPMs. It would struggle at any RPM greater. If I mashed the throttle, it "sounded" like it was trying to accelerate (it even got a whole lot louder),"

"but was being held back."

Did you check to see if the exhaust flappers were working? It won't accellerate worth a darn if the exhaust is restricted."
 
"I have not. Is there a secre

"I have not. Is there a secret to checking this or does it mean pulling the risers? The thing of it is that sometimes, it will surge temporarily up to almost 4000 RPMs. During these very short periods, the sound of the engine gets "happy". Although that's not the max RPM (4400), I think that is pretty significant. That is what leads me to think it's a logic problem of some sort. Would the flappers allow that behavior?

Thanks for the input.

Jon"
 
"Jon:

Below is a blowup vie

"Jon:

Below is a blowup view by Mercruiser for the 1999 5.7L exhaust system. You want item #7 "shutter". If they are not "flapping" or moving back and forth freely to block lake water backwash, then they are blocking exhaust from getting out. If it is missing then it fell off and down into the "Y" pipe or the previous owner removed it.
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http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=809500%2099&ivar=images/C OMMON/14171.png&inbr=4856&bnbr=290&bdesc=Exhaust+System"
 
"I'm not sure where that w

"I'm not sure where that would be on my exhaust. My boat has inboard drives. Does it still have a flapper or is it handled by the "muffler". I've attached two pictures of the engine room. Let me know what you think. It's all pretty accesible.

Thanks very much.

Jon

149777.jpg
Engine1"">
149778.jpg
Engine2
 
If you have thru hull exhaust

If you have thru hull exhaust I think the shutter would be in the pipe or on the outside on the end of the exhaust pipe.
 
Nice E/room. Is the red one a

Nice E/room. Is the red one a generator? You stated "or is it handled by the "muffler". Perhaps the muffler is the issue. Can it be opened up and inspected? Can you bypass it w/a exhaust hose? That would tell you if it is the problem right away. Car/truck mufflers are notorius for internal baffles breaking loose and rattling or blocking exhaust flow. I heard a Caddy muffler once that would run like it was "sucking" air when throttling up the RPMs and then the drop in RPMs caused the sucking sound--broken internally.
 
"Thank you. It looks nicer th

"Thank you. It looks nicer than it sounds right now. :)

The muffler uses water. I believe all it has is the inlet pipe going down to nearly the bottom of the tank and the output from the top. You can see two pipes exiting. One is a small one that is above the water line and the large one goes through the bottom of the hull. So a backwash of water through the large pipe would siphon out the small one using the path of least resistance. At idle, there isn't enough pressure so he water comes out the small outless. Under load, it goes out the bottom for noise reduction.

But I'll be totally honest with you, I have derived this behavior based on the design and that when they had the manifolds off, I didn't see any flappers. Maybe that would be the next question...is my analysis of the design correct?

Jon"
 
"Ok gentleman...I'm offici

"Ok gentleman...I'm officially losing my mind now. It was a beautiful day today so we went for a ride knowing it would be a slow one. Well guest what...the engine ran like a top. Outside of about a 300RPM WOT difference, it ran fine. Because of this, I ran it longer, expecting it to eventually start having issues. It never did.

The previous test was running the engine off a portable tank. All I did was disconnect the fuel line into the filter inlet, capped it, and connect fuel line from a portable tank. The engine still had it's issues. At that point, I simply reconnected the onboard tank, tested it for leaks, and went home. Nothing changed. I didn't even flush the fuel line from the tank. I just capped it. But somehow, the engine ran fine today.

Any ideas?

Jon"
 
"Jon...

So thinking that it

"Jon...

So thinking that it may now be considered a fuel problem....I know you said thet you checked for leaks but, is there still a possibility that there is a vacuum leak in the fuel line somewhere? Is the fuel pump sucking air instead of fuel from the tank? Thats what it's starting to sound like to me. Check fuel filters for blockage. Cracked fuel line? Dry O-rings inside fuel line connectors? Weak fuel pump not being able to draw from the on board tank because it is too low in the hull and the pump would now rather draw through the leak/crack. The portable tank that you used was maybe at level or even above the level fuel pump. it didn't have to work at all to get the fuel.

Wrench"
 
"I think I ruled that out. I a

"I think I ruled that out. I attached a fuel pressure guage to the fuel rail. The pressure definitely stayed up. I used it on both engines and fuel pressures were the same. My surprise was that it ran fine today after reconnecting it to the onboard tank. When I did the portable tank test, it still ran poorly.

It's very confusing. There has to be an intermittent problem. Can anything mechanical be intermittant on an EFI engine?

Thank you.

Jon"
 
"Please clarify just a bit...

"Please clarify just a bit...

[ Outside of about a 300RPM WOT difference, it ran fine. Because of this, I ran it longer, expecting it to eventually start having issues. It never did. ]

Am I to understand that all appears to run fine now? Original problem is cleared up if not exactly defined? Or is there more to do now?

If all is well, but you see 300 rpm difference in top rpm of the two engines, that could be simply normal or due to slight prop differences.

??? In other words, any further action needed now except to moniter the situation for effect?"
 
"David, you are correct...and

"David, you are correct...and so is Guy I'm convinced. The engine ran perfectly smooth and RPMs came up. But there is a WOT difference. The interesting thing with that is I only have to put the port throttle at approximately 2/3's to match the starboard. If I mash the port at that point, it has much more to give above the WOT RPM of the starboard.

I'm think of getting http://tunertools.com/proddetail.asp?prod=MEFI-Scan. I think I will find a difference in something that is preventing it from reaching a similar WOT RPM. Both props were computer reconditioned so I'm hoping they are similar enough to not cause the 300+ RPM difference. I wonder if I'll see the TPI having a different value.

Funny thing is that I am supposed to meet Wednesday with the dealer to go over the issues with the engine. I think my boat is playing a joke on me. But I'm thinking, since I'm confident its not mechnical, that I would offer to them to just give me $500 and we'll call it even. They will spend at least that bringing in their "expert". What do you think?

Thanks.

Jon"
 
"The $500 would help repay you

"The $500 would help repay your aggrevation, but still not fix the "problem?". Get it if you can.

I guess you could switch the props just for effect and to satisfy any possible concern.

Good luck, and keep us curious folks informed of whatever you find."
 
""...switch the props...&#

""...switch the props..." Not if one is counter rotating.

A throttle limit mismatch can be adjusted, can't it?

Jon:

What is the one specific thing from the problem onslaught that has changed recently to cause the boat to run right? Think about it and remember it for future repeat of the same issues.
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"[ Not if one is counter rota

"[ Not if one is counter rotating. ]]

Ooops! I was asleep on that one! Thanks for the awakening. My only twin engine craft had two standard rotation outboards, and my mind had that in gear as I replied."
 
"Guy, I've been racking my

"Guy, I've been racking my brain and the problem is that nothing has changed. After I ran it on the portable tank, I went back to the slip, disconnected it, reconnected the onboard tank, did a leak test (switch on/off/on/off/on (to get the pressure up) first then ran it for a couple of minutes in the slip only), and finally removed the fuel pressure guage from the fuel rail. At that point, I closed everything up and left. Saturday, we just hopped on the boat and left. I got to the end of the no wake zone and punched it and she went.

The only crazy theory I could come up with is that when I removed the fuel pressure guage after I ran it again, the rail pressure was disapated through the guage port. Could that have jossled something lose in the rail that maybe was limiting one injector? Far fetched but I have nothing else. :-(

As frustrated as I've been, I'm more so now because it seems to have fixed itself. Very bad timing with the meeting with the dealer scheduled for Wednesday.

Thanks.

Jon"
 
"Jon:

Gremlins are a PITA t

"Jon:

Gremlins are a PITA to find. Dirt or granular varnish, looks like rust or sand, over time in the fuel rail maybe?"
 
"Ok. I did some side by side

"Ok. I did some side by side comparisons and I've uploaded two images of the data. The left log is the port engine and the right the starboard. The file named NoSpool file is when the issue happens and at WOT, it won't spool up. The Spool file is another point in the same log file where the engine did, for a short time, spool up.

The first thing that struck me is that first off, the IAC values on the SB engine at high throttle is always stuck at 150. I assume that is one of its detents. I'm not sure, however, if that is open or closed. When the coolant sensor had a low value (cold engine) and at idle, the IAC value was in the 70's. The IAC equates to choke right?

The second thing that struck me is the BPW (which I assume is the injector base pulse width...amount of fuel). When the engine spooled, the value was noticeably higher than when it didn't. That supports the behavior I see. When the throttles are mashed and it doesn't spool up, the engine noise most definitely is higher...like the intake is opening and it wants to go but is being held back...not getting the fuel it needs.

Lastly, the GPH is higher when it did spool up. The BPW was higher on the SB at that time. That would be a rich condition right? Would that explain the slightly less RPMs?

So does this point to the problem? If so, what do you think the causes could be? It looks like the computer is not doing what it is supposed to be doing. What would cause it to act this way?

Thanks for any input.

Jon
150957.jpg
150958.jpg
"
 
"The IAC is not for cold start

"The IAC is not for cold start enrichemnt, it's only functions are to control idle speed and to help prevent stalling upon sudden throttle closure. It's normal for it to be fully open (150 counts) when the throttle is advanced. That way it can close slowly and bring the engine idle down slowly to help prevent stalling. I don't think your problem is IAC related in any way.

The screen shots above don't really indicate the problem as far as I can tell. What was the Knock Retard doing during these runs?"
 
"Is the fact that the IAC posi

"Is the fact that the IAC position is so much different idicating anything? Throttle, MAP, and temperature are essentially identical. I didn't see the knock sensor going off. What else would be modifying the BPW and IAC? When it won't spool it is lean. When it does, it is rich. How significant of a difference is the spark advance?

I'm building a second cable and will be doing simultenous logging this weekend. Maybe that will help things out.

Thanks for the info!

Jon"
 
"David, it went exactly as I e

"David, it went exactly as I expected. They bailed on me. Somehow they feel that since they have spent a certain amount of money and it's taken so long, that they are no longer responsible for it because a failure unrelated to the origional problem MAY have caused it even though the problem has existed since last Spring. So they brought their expert in to say that the problem could be unrelated to the work they have done. Well, the only thing they haven't either had rebuilt, replaced, or swapped with the other engine is the rotating assembly and distributor. So they suggested I buy a new distributor pickup sensor...which I did because it was legitamately the only sensor not touched. It, unfortunately, didn't fix the problem.

So now they are just ignoring me will not call me back/respond to my email. Nice huh? Live and learn.

But I'm still plugging away at it thanks to the help from many very knowledgable and helpful people. Speaking of that, thanks very much to Dave N. I spoke with Bob @ OBD Diagnostics today and he mentioned you had talked to him about my problems. He was nice enough to spend quite a bit of time talking to me about my engine problems. You guys rock!

With a little help from a friend, I think my next task is swapping the distributors.

Thanks all. I'll update after that and after some more testing.

Jon"
 
I've been away for a bit.

I've been away for a bit. Sorry no updates. Thanks again for everyones help. Hopefully this weekend I can resume diagnostics.

Jon
 
"Well, it's been frustrati

"Well, it's been frustrating because I haven't been able to spend much time on the engine. You know...family time and all comes first. I did, however, get a second cable build and have ScannerPro working on both engines simultaneously. Unfortunately, I screwed up my initial test and only saved the SB engine log. For those interested, I'm uploading my logs. The NoWake logs are before and after my test runs. You will see that this time, even at full throttle, the engines didn't even exceed 3000 rpms.

I'm going to do the tests again this weekend and have a better side by side comparison. As always, any ideas are appreciated.

So frustrating... Hopefully this weekend I can do a clean test.

Thanks.

Jon

<center><table border=1><tr><td>http://www.marineengine.com/discus/icons/mime_zip.gif""" align=left alt=""application/x-zip-compressed"">
[url=""][b]2008_05_25_NoWake.zip[/b][/url] (88.0 k)</td></tr></table></center>
<center><table border=1><tr><td>[img]http://www.marineengine.com/discus/icons/mime_zip.gif""" align=left alt=""application/x-zip-compressed"">
[url=""][b]2008_05_25_NoSpool.zip[/b][/url] (55.6 k)</td></tr></table></center>"
 
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