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Old 07-07-2015, 04:52 PM
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jlarkin.41 jlarkin.41 is offline
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Boat: 1994 Prostar LT1 1:1
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HELP! LT1 Hard Start When Cold

I have done multiple searching on this site as well as some Google searches and cant seem to find anyone with the same symptoms (some hard starts when hot or all of the time).

My 94 Prostar with the LT1 has been great for the 3 seasons I've owned it and has always started up at the first turn of the key. At the beginning of the season this year I had a few intermittent stalls when returning the throttle to neutral after my skier dropped. I figured this may be some bad gas from sitting all winter and didn't think much of it. That problem has not returned since the first weekend out.

However 2 weeks ago I began to experience difficulty when starting a cold engine. I turn the key and it sometimes it fires quickly before sputtering to a stall (500 rpms or less) other times its turns longer than normal but then fires and sputters to a stall. I am able to get the boat running after doing this several times and using the throttle with the pin pulled out to disengage the tranny. After a minute or two of warming up, the boat runs and drives normal and doesn't even hesitate to start back up after the engine has been killed as long as the engine stays warm.

Just before the problem started, I had replaced both my inline fuel filter on the back of the engine and the water separator in the bilge. I had also applied di-electric grease to many of the electrical connections. The next two times I started the boat after the work, I had no problems, then the trouble began.

Things I have checked thus far:
Throttle body and IAC: Both a little dirty but I cleaned them with TBC and re-installed
Spark Plugs-AC43LTS Replaced last year: Some minor fouling which I cleaned with a wire brush, but still look like they are in good shape
Plug Wires:All connections look to be tight, #6 on the Northstar coil had some corrosion which I cleaned off the post. Some still seen inside the boot of the wire. I am not sure if this could be contributing to my problem
Listen for knock or abnormal sounds while running: Nothing that I can hear
Air Filter is Clean and Oiled
Fuel Pump: Can hear it kick on to prime when the key is turned. Don't have a fuel pressure test gauge to see pressures, yet...
Fuel pressure regulator: Good vacuum at the regulator, when the vacuum line is removed, the idle condition changes as it should and settles back out when re-connected.
Fuel filters: The water separator was a direct replacement (numbers match). The in-line was an "upgrade" according to NAPA as they didn't have #23481 that I asked for. This was a match but a better filter according to the guy at the counter.

Next step is to order a fuel pressure gauge and possibly a spark tester.

Has anyone else had this problem or have suggestions for what I should check next?

Is it possible that the corrosion on #6 could be causing this only when cold?

Maybe the "upgrade" fuel filter is causing a pressure loss that is only noticed when starting cold? It didn't seem to matter the first few times I started it up after install.

Any help would be appreciated, this is driving me nuts.
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Old 07-07-2015, 06:19 PM
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It is always a good idea to check or replace the ECT coolant temp sensor when you are having troubles that seem temp related. The one on the front of the water pump is the one hooked to your ECM.
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Old 07-07-2015, 06:31 PM
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jlarkin.41 jlarkin.41 is offline
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Thanks Table Rocker.

Is there any way to test the sensor? Resistance readings across the sensor correlating to temperature? I would like to see if it's out of range before I go the route of replacing parts that may or may not be the issue.

Is it marine specific or is it something I can pick up at Napa?
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Old 07-07-2015, 06:34 PM
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Quote:
Originally Posted by jlarkin.41 View Post
Thanks Table Rocker.

Is there any way to test the sensor? Resistance readings across the sensor correlating to temperature? I would like to see if it's out of range before I go the route of replacing parts that may or may not be the issue.

Is it marine specific or is it something I can pick up at Napa?
Yes, you can test it. There is a table of resistance/temperature on this site somewhere. edit: http://www.mastercraft.com/teamtalk/showthread.php?t=63500

It is an auto part available for many GM models.
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Old 07-07-2015, 09:27 PM
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jlarkin.41 jlarkin.41 is offline
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Thanks. I will have to check after I pick up a better multimeter. Mine is only able to read resistances up to 1k ohms.

I started the boat tonight after I realized this and brought it up to temperature. The values between 120 and 140*F I was able to read and they checked out with the chart. Although this isn't the temperature where I am seeing problems, this makes me think the sensor is probably ok.

I'll check it with another meter tomorrow for the lower temp range.
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Old 07-08-2015, 06:55 AM
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André André is offline
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Try unpluggin it first when it doesn't start.
Seem to remember that when unplug,the computer will use a standard value and adjust the air gas ratio to allow start when cold.
Of course,ICBW...
Good luck!
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Old 07-08-2015, 09:52 PM
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jlarkin.41 jlarkin.41 is offline
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Was able to try a number of things tonight, but the conditions have not improved. If anything it is getting worse.

-fuel pressure: put a gauge on it and the system primes to about 44 psi. After getting it started it idles and seems to maintain roughly 38 psi. Checked for bleed down with no pressure loss for 35 mins or so (although now I have a slight leak from the flare fitting on the fuel pump after removing it)
-ECT resistance: seems to check out with the table provided. Tried starting with the sensor unplugged as suggested, no change.
-plugs: advanced auto had a set of mr43lts so I installed. No change. Seeing spark on each plug wire with a tester.
-plug wires: the wire with the corrosion (#6) is showing very high resistance in comparison to the others. Time to replace with a new set, but I have trouble believing this is the cause of my issue as it certainly did not come on suddenly.

Does anyone have any additional suggestions? Any help would be greatly appreciated.
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Old 07-08-2015, 09:55 PM
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jlarkin.41 jlarkin.41 is offline
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I also picked up some sea foam to run through the fuel system. Have never used it, but I know people who seem to swear by it. Any issues with running it through the LT1?
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Old 07-08-2015, 11:05 PM
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Shaun R Shaun R is offline
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What do the old plugs look like? Sure you don't have a vacuum leak somewhere? And no fuel on the vacuum line for the FPR?
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Old 07-09-2015, 09:32 AM
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jlarkin.41 jlarkin.41 is offline
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Plugs looked ok IMO, the had a little more build up than I expected considering I just cleaned them over the weekend. See the attached pic. To me if anything it looks like it may be running a bit rich, based on the plugs.

There was no fuel in the vacuum line for the fuel pressure regulator. I have not looked for vacuum leaks elsewhere. Any suggestions on where to start?

It seems like even at idle once I get it running, it is idling slightly lower than it used to.
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fuel system, hard start, ignition problem, lt1

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