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View Full Version : 1997 LT1 starts rough, stalls then fires up perfectly?


raleydog
05-24-2012, 08:02 AM
I have a 1997 Maristar 225V with the Lt1 w aprox 600hrs. This is my 3rd year owning the boat and it has been absolutely flawless until late last fall. After a session on the river, the boat had sat at the dock for about 30 min after shutting down. Upon restarting to put it on the trailer, it ran very rough and surged in idle up to about 1600 rpm. I gave it some throttle in nuetral and it seemed like it just wouldnt take it and stalled. I refired the engine and it ran instantly perfect once again. This has never happened again until the past weekend.
Same scenario exactly. Engine was hot (160). Boat sat for 30 min or so, then upon restarting to put it on the trailer it ran rough and died. Turned the key to restart after stalling and it ran as perfect as ever.

Any thoughts or ideas on this? It almost seems like the feul is vapourizing or a sensor wasnt working for a moment but being completely EFI theres not much I can check when the problem only exists for 15 seconds or so.

Thanks in advance...
Brent

Farmer Ted
05-24-2012, 08:49 AM
have you replaced your fuel filters lately?

my LT-1 idled rough, replaced the IAC and idled fine

tideengineer
05-24-2012, 09:31 AM
I have a 96 Prostar LT1. If you were in the deep south like me where it gets hot as Hades outside, I would say maybe vapor lock. If we run our boat hard for a while then let it sit baking in the sun with the motor box down, it will spit and sputter and die upon restart. I've had to put a rag over the fuel filter connection before the feul rail, unscrew it and a bunch of feul vapor will come out under pressure. I did this with the blower on and plenty of ventilation....and noone smokes around me. I let it sit for 5 minutes ventilating, then it runs like a champ.

I've learned to use my boat paddle and prop the box open for ventilation while we are off eating or whatever.

I doubt in the northeast that is your problem...and I'm no mechanic, just an engineer who likes to try to be. In the deep south of Alabama...it gets pretty warm :-)

LittleFuss
05-24-2012, 10:29 AM
very similar sounding problems this past year in my 1997 5.7 TBI...Ended up being a filthy fuel tank. If you have not pulled that baby out and looked at it I would. replace the fuel filter a couple of times after you get that tank clean if that is the problem.

raleydog
05-24-2012, 11:40 AM
Thanks for the replies guys. I should have mentioned I changed both fuel filters after the first time this happened. Probably only put 10 hrs on it since. Might be time to have a look inside that tank.
Odd thing is it starts perfectly and runs without even a sputter just after it stalls out from running so poorly. Almost like shutting off the key and turning it back on has reset something. (no engine light either)
I will look into the fuel tank this weekend and grab a new set of filters as well.

raleydog
05-24-2012, 11:42 AM
I have read about testing and cleaning the AIC. Farmer Ted... where is the best place to get this part? and any hints for testing?

Farmer Ted
05-24-2012, 06:54 PM
I have read about testing and cleaning the AIC. Farmer Ted... where is the best place to get this part? and any hints for testing?

I had my boat in for a transmission leak and asked them to look at it, I'm pretty sure this is not a marine specific part and can be purchased at Autozone or Napa

now that I think about it, mine was idling low and often required a little throttle exercise to get it back to normal.

R2 the IAC and it was smooth sailing ever since, may or may not be your problem.

good luck

jakethebt
05-24-2012, 11:16 PM
IAC is idle air control valve?

In the auto world, they usually fail open and then give you trouble when it is cold outside by allowing in too much cold air in the engine at idle. Does it operate different in a boat?

lt14me
05-26-2012, 06:14 PM
Last year, upon start up on my lt-1 it would idle right around 1500 rpm and then settle down, i replaced the IAC on the throttle body and it solved the problem it was worn at the end.

JimN
05-26-2012, 08:52 PM
IAC is idle air control valve?

In the auto world, they usually fail open and then give you trouble when it is cold outside by allowing in too much cold air in the engine at idle. Does it operate different in a boat?

Same thing- these are car engines but it shouldn't idle rough if it fails- it should increase the idle speed, but that's about it (if it fails open).

JimN
05-26-2012, 08:54 PM
To the OP- do a compression test and check spark intensity. If the plug wires are original, replace them- they should have been replaced long ago. BTW- how old are the plugs?

raleydog
05-28-2012, 08:49 AM
Thanks for the ideas guys.... Compression check was done upon purchase and all numbers were good and equal. New Taylor wires 3 years ago and new plugs start of the season. Popped the sender and fuel tank looks great as well.
Ran it for 8 hrs Saturday and not even a hiccup. Ran like a brand new boat as always.
This has only ever happened twice and sitting at the dock for 30-45min after a session.
I would like to change out this AIC for good measure anyways. Do any of you guys have the part # by chance. There is no local Mastercraft dealer in my area.

JimN
05-28-2012, 11:05 AM
Thanks for the ideas guys.... Compression check was done upon purchase and all numbers were good and equal. New Taylor wires 3 years ago and new plugs start of the season. Popped the sender and fuel tank looks great as well.
Ran it for 8 hrs Saturday and not even a hiccup. Ran like a brand new boat as always.
This has only ever happened twice and sitting at the dock for 30-45min after a session.
I would like to change out this AIC for good measure anyways. Do any of you guys have the part # by chance. There is no local Mastercraft dealer in my area.

I just re-read your original post. This has nothing to do with the IAC. You wrote "I've had to put a rag over the fuel filter connection before the feul rail, unscrew it and a bunch of feul vapor will come out under pressure." and, being ahead of the fuel pump & engine, I fail to see how this could be an issue with the device that controls idle speed and helps out on hard acceleration. THAT'S ALL IT DOES and as I posted before, your idle speed may be wrong because of a bad IAC but not the idle quality. If it does this again, check for spark on all cylinders to see if you lost several of them. If you lose one, you probably won't notice much. We were running engines on metal stands in the garage at MC training the first time I went and some of us were curious about how much effect we'd see from pulling an injector plug. Nothing. We put out hand on the engine and couldn't feel any difference. We pulled another and still felt no difference. Obviously, there was no load but if you start your engine and it idles roughly, it's not the IAC unless the idle speed is extremely low.

Another thing you will want to do is turn the key ON without starting the engine to see the engine temperature. If you see 200+ and the air temperature is high, start it and watch the temperature drop, noting the change in idle quality. It should correct itself in about 30 seconds.

You can also turn the key to ON, let it sit and wait for about 5 seconds before cranking. This allows the fuel pump to prime the line to the throttle body, which will allow the gas to atomize fully and it won't do this if the pump isn't getting a good supply of fuel. If you removed the line from the filter ahead of the engine and had fuel vapor coming out, that would be vapor lock and I would look for the anti-siphon valve that's supposed to be on the line, at the right angle block on top of the tank. If that's not there, the heat in the bilge can cause the fuel to boil (remember, it doesn't take high temperature for gasoline to boil because of its low viscosity) and cause bubbles in the line.

C'mon! You're an engineer- be methodical.

raleydog
05-29-2012, 07:57 AM
JimN - I appreciate you replying, however i think you have misquoted me. It wasnt me you quoted. My situation has only happened twice now in over 300hrs of use, and when it did happen it only lasted for 5-10 seconds. Its very hard to be methodical when something has popped up for ten seconds or less and upon restarting runs 100% perfect. I am not an engineer, just a Millwright. But its pretty hard to test spark when I dont even have time to pop the cover before it dies, then runs absolutely perfect,
The sole fact that it fires up instantly and perfectly after stalling out is what has me thinking sensor.
I thought I would turn to the forum first and see if anyone else has experienced this before changing out parts. However it does seem the AIC can be a weak point on these LT1's as i cruse through the forums so Im thinking it wouldnt be a bad idea to have a look at it, if anything just for preventative.
This old girl will still hit 47mph wide open. Not bad for a 22 ft Vdrive :)

JimN
05-29-2012, 10:01 AM
JimN - I appreciate you replying, however i think you have misquoted me. It wasnt me you quoted. My situation has only happened twice now in over 300hrs of use, and when it did happen it only lasted for 5-10 seconds. Its very hard to be methodical when something has popped up for ten seconds or less and upon restarting runs 100% perfect. I am not an engineer, just a Millwright. But its pretty hard to test spark when I dont even have time to pop the cover before it dies, then runs absolutely perfect,
The sole fact that it fires up instantly and perfectly after stalling out is what has me thinking sensor.
I thought I would turn to the forum first and see if anyone else has experienced this before changing out parts. However it does seem the AIC can be a weak point on these LT1's as i cruse through the forums so Im thinking it wouldnt be a bad idea to have a look at it, if anything just for preventative.
This old girl will still hit 47mph wide open. Not bad for a 22 ft Vdrive :)

You're right- I thought the other post was yours. DOH!

Next time, open the throttle and see if it wants to run. If it does, goose the throttle and see if it keeps running when you bring the throttle back to the idle position. If it takes a long time to return to the 650 RPM range, remove the flame arrester and watch the tip of the IAC as you open and close the throttle while it's running. It should move (open) when you open the throttle and again (more closed) when you bring it back to idle. Then, shut it off and watch- it should extend to the closed position, then move back a bit in the seconds after shutting the engine off. If it's not moving after shutting it off, you (or someone) will need to check for voltage at the IAC to verify the cause of the fault if that's actually where the problem is.

I don't remember replacing more than a couple of IACs on all of the engines when I was working at the boat dealers. The other IAC problem was in the ECM of an early injected boat, two MEFI series before yours.

If the IAC isn't the cause, look at the crank sensors and the harness. Make sure the sensors aren't too far from, or close to, the star wheel at the crank pulley.

When you stop the engine, had you let it idle for about a minute after running it hard? If not, the engine will be a lot hotter than if you let it idle longer. Try idling a little longer and see if it still does this. If not, I would say it's a heat soak issue and the dash gauge won't show you what the other coolant temperature sensor shows the ECM. If it can't go higher than about 2000 RPM when this happens, it's probably registering overheat, which sends the ECM to RPM reduction. Don't call this "limp home mode", like the car guys do- they have a radiator and boats don't, which means that if it goes into this mode and you keep running it, the engine will probably be badly damaged.

raleydog
05-29-2012, 10:23 AM
No worries Jim! Again I appreciate your helping out.
When this happened 2 weeks ago, I instantly tried the give it throttle in nuetral and it barely responded at all. Went up to about 1600 rpm and nothing more then just died. You may have an interesting point regarding the ECM seeing an overheating condition. Its runs at a consistant 160 all day and I have seen as high as 180 on the gauge after a hot soak. I will try to let it idle for a moment before I shut it down. Could be the issue as both times this happened was after a hard session of running.