Engine Idle - Help!!

[Double D]

Needs some help guys. I will try to make this short and precise so you don't lose track.

Equipment:
1994 ProStar 205
350 CI Indmar, 275 HP
Throttle Body Fuel Injection

History:
July 2009 filled up with gas at Marina. Started running rough at idle so I thought I got bad gas.

My Fixes:
- Put in treatment in Gas.
- Ran tank empty
- Changed Gas/Water Separator
- Changed Thermostat
- Changed Plugs
- Changed Fuel Filter
- Tested Plug Wires

Result:
Still runs very rough at low idle. Stumbles when engaging to forward.

Next Step:
Took it to the local dealer where they did the following:
- Compression Tested the engine.
- Change Rotor and Cap
- Re-gapped the Plugs
- Replaced the timing control module
- Increased idle a bit
- Water tested it and said it was ready.

Result:
It started better and for the first 25 minutes of speeding and no wake it ran fine. We stopped to gear up to ski and the idle began surging, or should I say dropping. The range of idle on the RPM dial would be from 9 to 8, 9 to 8, 9 to 8 and it wouldn't stop. If you tried to put it in gear, half the time it would stall. So now it is running worse!

Next Step:
Returned it to the dealer where they did the following:
- Replaced two carburetor gaskets that were cracked and sucking air.
- replaced a clear yellow rubber vacuum hose for the map sensor
- Changed PVC Valve
- Did another compression check (Perfect)
- Ran the engine in the shop. (no water test)

Result:
Picked it up last night and ran through the same scenario. 25 minutes of speed areas and no wake zones. Speed to the area to gear up and stop and guess what, it still does it. It wasn't as bad at first but it got worse and back to what it was doing the first time. 9 to 8, 9 to 8 on the tack.

I tried to pull my son on the wakeboard with the Perfect Pass and the engine problem is even messing with that now. Everytime he pulls to make his cut it slows the boat down and the engine cant react quick enough and he hits the wake at 3 mph less than he should. I had to pull him manually.

Additional Information:
- Obviously the dealer didn't water test it long enough to get it hot enough
- Running it in the shop wont get it hot enough
- temp gauge shows a hair below 160 when warm and around 140 when cooled.
- I spoke to the dealer while on the lake and they think it might be the Coolant Temperature Sensor. The wire was lose so I fixed that but it did not correct it.
- It did seem to run better after it sat for 15 minutes while I was fixing that wire, but it didn't last. To me that says temperature....

Next Steps:
The dealer is hoping to order a new Coolant Temperature Sensor (not a standard GM part) because they think there may be a conflict between what the gauge is saying and the sensor is saying which is messing with the computer control.

The dealer is perplexed and if this sensor doesn't fix the problem then they said they might start tearing into the engine, and I don't really want that cost.

On a side note:
- It now runs worse then it did when I first took it in
- The dealer has not charged me for the labor during the second visit
- The compression checks show an almost perfect engine.

So here I am asking for some serious assistance from all you. Hopefully someone has been through this problem.

[Double D]

Here are two pictures of the engine I took last night for the dealer so they could figure out which sensor was which.

[helton333]

I had a similar issue, we did all the same and the only thing you haven't mentioned, coil, we changed out - that fixed ours.

[Double D]

I had a similar issue, we did all the same and the only thing you haven't mentioned, coil, we changed out - that fixed ours.

Yep, did not change coil. With the warm up period it makes me wonder how it could be a coil. I don't see that being effected by heat.

[rspiecha]

Do you still have the water/fuel seperator installed??? Spin on filter looking object down below engine level, in front, port side on the rail the motor mounts on. I had mine removed to help a similiar issue when the boat was new. Installed a fuel filter at tank to clean out trash before coming into the fuel pump.

Later on, same problem came back. My final fix was to replace the throttle body with injectors which includes an integrated fuel pressure regulator. The new owner has had the boat for almost 4 years without issues.

Rob

[captain planet]

Yep, did not change coil. With the warm up period it makes me wonder how it could be a coil. I don't see that being effected by heat.

Actually, that might be it. I have had temperature effect a coil on other engines before. The fact that you are shutting the engine off and then it acts up after restarting makes me think this might be the culprit.

[pkreusch]

Unfortunately, coils will break down from heat. A coil will heat up over time and one that is ready to give out will sometimes act that way. They get old and the resistance changes which causes heat which in turn causes more resistance which in turn causes more heat which in turn......well you get the picture.

[rspiecha]

Here is a related thread about sensors on the boat.

http://www.mastercraft.com/teamtalk/showthread.php?t=4458&highlight=1994+Prostar

[Double D]

Do you still have the water/fuel seperator installed??? Spin on filter looking object down below engine level, in front, port side on the rail the motor mounts on. I had mine removed to help a similiar issue when the boat was new. Installed a fuel filter at tank to clean out trash before coming into the fuel pump.

Later on, same problem came back. My final fix was to replace the throttle body with injectors which includes an integrated fuel pressure regulator. The new owner has had the boat for almost 4 years without issues.

Rob

I still have the F/W separator on the boat. I will put that on the list once the sensor and coil don't fix it.

Thanks!

[Double D]

Actually, that might be it. I have had temperature effect a coil on other engines before. The fact that you are shutting the engine off and then it acts up after restarting makes me think this might be the culprit.

Unfortunately, coils will break down from heat. A coil will heat up over time and one that is ready to give out will sometimes act that way. They get old and the resistance changes which causes heat which in turn causes more resistance which in turn causes more heat which in turn......well you get the picture.

I never figured that. I will suggest this to the dealer and see what they say.

Well, I mentioned it to the dealer and he doesn't think that is it. He figured if it was the coil the engine would lose power at any speed, and its only idling bad. I did mention that when I used the PP I lost power but when I hold the throttle in position I don't. Also, at full speed across the lake, its fine.

Thanks!

[JLeuck64]

Check your grounds...

Engine block.
Behind the dash there is one ground that is known to cause problems if it is loose. Especially when a boat has PP installed...

[Double D]

Bumpidty Bump Bump.... Still waiting for the sensor but now that the 4th is over, and no boat trip, still looking for more ideas....

[blackcreek]

Get your hands on an inductive timing light, you can probably get one at auto zone rent-a- tool or an old school mechanic. Run the boat until you get the poor running condition and then with engine running hook up the timing light sensor over each spark plug wire one at a time and check for spark. The timing light strobe will flash slow enough at idle that you can just eyeball each cylinder for proper spark. A good solid and steady flash rules out most ignition related problems except cracked spark plugs. You can also rev the motor and watch the light for any skips or drop outs. When hooked to number one wire point it at the timing marks and check that timing is not jumping around. It sounds like your basic motor is healthy you just need to find the ignition or fueling issues.
I am not sure about your exact throttle body, but you can pull the spark arrestor and check the spray pattern on the injectors while running. I worked on a volvo penta motor that had two injectors in the throttle body, yours might be the same. Both spray patterns should look the same if one is clogged a bit you will be able to tell. You can also point the timing light at the fuel injectors.http://www.chevythunder.com/gm_throt...ction_pg_1.htm After you shut down the motor you also want to check for drips coming out of the bottom of each injector. A leaky or clogged injector will cause idle problems. That is all I can think of, good luck.

[Double D]

Get your hands on an inductive timing light, you can probably get one at auto zone rent-a- tool or an old school mechanic. Run the boat until you get the poor running condition and then with engine running hook up the timing light sensor over each spark plug wire one at a time and check for spark. The timing light strobe will flash slow enough at idle that you can just eyeball each cylinder for proper spark. A good solid and steady flash rules out most ignition related problems except cracked spark plugs. You can also rev the motor and watch the light for any skips or drop outs. When hooked to number one wire point it at the timing marks and check that timing is not jumping around. It sounds like your basic motor is healthy you just need to find the ignition or fueling issues.
I am not sure about your exact throttle body, but you can pull the spark arrestor and check the spray pattern on the injectors while running. I worked on a volvo penta motor that had two injectors in the throttle body, yours might be the same. Both spray patterns should look the same if one is clogged a bit you will be able to tell. You can also point the timing light at the fuel injectors.http://www.chevythunder.com/gm_throt...ction_pg_1.htm After you shut down the motor you also want to check for drips coming out of the bottom of each injector. A leaky or clogged injector will cause idle problems. That is all I can think of, good luck.

Prior to taking it to the shop the first time I used a timing light on each plug to check to make sure there was no erratic behavior. We did detect it once but moved the plug and it went away. The dealer did change out the timing control module during the first repair because they couldn't get it timed properly.

At the time I did the timing light test there was no pulsing idle problem, just a rough running engine.

The dealer said the throttle body spray pattern looks good and sees no erratic spray.

Next time out I will take the timing light and check for dripping. Thanks!

[captain planet]

Sorry D your boat isn't back yet. You missed a busy lake. It was crazy. I hope Don can get it figured out for you.