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View Full Version : 1995 Maristar LT-1 idles a little rough


walterlaughlin
06-22-2013, 05:06 PM
Hi TT folks, I have a 1995 Maristar 200 VRS with the 350 LT-1 Vette motor with fuel injection, about 300hrs on the meter. The motor runs a little rough at idle. Above idle it runs great, it accelerates without hesitation, and will do almost 5,000rpm at WOT. I have only owned the boat since last September, it was sitting for a while so I was hoping a new set of spark plugs and a bottle of gumout cleaner would smooth out the idle, but no luck. I figure the next step is to clean the injectors, any other suggestions? Thanks

towelshoot
06-22-2013, 05:24 PM
I also have a 95 with similar issues - was also thinking the fuel injectors. Would love to hear how to do that. Mine use to start 100% of the time just by a turn of the key without giving gas, but now I need to give a little gas to start when cold.

JimN
06-22-2013, 05:28 PM
Hi TT folks, I have a 1995 Maristar 200 VRS with the 350 LT-1 Vette motor with fuel injection, about 300hrs on the meter. The motor runs a little rough at idle. Above idle it runs great, it accelerates without hesitation, and will do almost 5,000rpm at WOT. I have only owned the boat since last September, it was sitting for a while so I was hoping a new set of spark plugs and a bottle of gumout cleaner would smooth out the idle, but no luck. I figure the next step is to clean the injectors, any other suggestions? Thanks

Check the fuel pressure.

Make sure the plugs are AC MR43LTS and they're gapped properly. If you have the original spark plug wires, replace them- they should have been replaced in about '98. Measuring resistance tells nothing about their integrity.

Scan it for codes- if you see 21, you may have a bad TPS. What's the RPM at idle? If it's lower than 650, your IAC may need to be reparked and this isn't something that can be done correctly by removing it, pulling the pintel out and reinstalling it.

How old is the gas, and was it stabilized before storage?

walterlaughlin
06-22-2013, 08:21 PM
I doubt the PO stabilized the fuel before putting the boat in storage. I have run a couple tanks of gas through the motor since I bought it last Sept. New plugs were installed by the PO, I pulled one out at the time of purchase, but didn't verify they were the correct plugs. The spark plug wires are original so I'll replace those and the plugs and see what happens. I know nothing about how to scan for codes, this is my first boat with a computer. I'll look for some threads on here on how to do that, and how to check fuel pressure. Thanks

JimN
06-22-2013, 08:45 PM
I doubt the PO stabilized the fuel before putting the boat in storage. I have run a couple tanks of gas through the motor since I bought it last Sept. New plugs were installed by the PO, I pulled one out at the time of purchase, but didn't verify they were the correct plugs. The spark plug wires are original so I'll replace those and the plugs and see what happens. I know nothing about how to scan for codes, this is my first boat with a computer. I'll look for some threads on here on how to do that, and how to check fuel pressure. Thanks

Google 'paper clip code scan" and you'll see what you need, or look here- it has been poosted about a million times and still, I don't think it has been made sticky, as requested.

You might want to check the inlet screen on the fuel pump, as well as the filter(s). Also, check the fuel shutoff valve and anti-siphon valve at the tank.

If you don't have a fuel pressure gauge and don't want to buy one, go to AutoZone or O'Reilly's- they loan tools. The gauge should have a purge valve and a clear vinyl tube- this is for removing air from the gauge and it also allows you to take a fuel sample, something I highly recommend before doing anything else. Collect some gas in a clean, clear bottle and let it sit for about fifteen minutes- if you see anything settle out, like water droplets, it means you need to do something about it.

IIRC, the plug gap should be .045"- if someone has this spec, feel free to verify or correct this.

If you do all of this and it's still rough, get a can of 3M injector cleaner and follow the instructions. If that doesn't help, verify the injectors are delivering fuel.

towelshoot
06-28-2013, 12:55 PM
Don't know if you got yours fixed, but I just replaced my Idle Air Control IAC for $33 from Advance, and now it is working perfect again.

walterlaughlin
07-04-2013, 05:48 PM
Don't know if you got yours fixed, but I just replaced my Idle Air Control IAC for $33 from Advance, and now it is working perfect again.

Do you have a LT-1 also, about the same vintage? Do you have a part # / manufacturer name for the part you replaced? Where is the part located on the motor? I have no idea what this part does but if it can fix my rough idling problem for $33, i'm sold

Shilohsho
07-04-2013, 10:57 PM
I've got an LT-1 swapped into a truck and it has caused me trouble in the past like this. For me is was several small vacuum leaks. It is very temperamental with a vacuum leak.

towelshoot
07-08-2013, 05:45 PM
I picked one up at Advance for $33. It was a BWD part number 21755. I worked perfect. I just installed it and did nothing else.

willg
07-08-2013, 05:51 PM
I don't have an lt1, but the Throttle Position Sensor and Idle Air Control Valve can go bad on fuel injected motors and cause problems like you are describing. They are probably the same parts from a corvette of the same year.

Its likely that these are the parts: http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_throttle-position-sensor-bwd_3478300-p?navigationPath=L1*14932%7CL2*14985 and http://www.summitracing.com/parts/smp-ac125/applications/year/1996/make/chevrolet/model/corvette?prefilter=1