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Rockymtn 12-04-2012 04:16 PM

1993 Prostar 190 with LT1 motor rebuild or replace?
I own a 1993 PS 190 stars & stripes (blue and white), that we have loved for the last 7 years. The boat has some signs that itís getting older, who doesnít? However, my biggest issue is the boat has become undependable. What I mean by that is I can depend on it to stop running in the afternoon so I guess itís very dependable, in a bad way. I have had many diagnoses, one of which is vapor lock and have tried a number of things like wrapping the fuel lines, leaving the cover off when we stop, etc. nothing works. I suspect the 1200 plus hours on the LT1 may have caught up to the old girl. So this brings me to my questions. If you owned this boat would you rebuild the LT1 or would you replace it with something different? If you say something different what motor would you put in its place? Last question, anybody have a recommendation for a boat mechanic in Colorado?

Thank you in advance for the suggestions and recommendations,


Kyle 12-04-2012 04:26 PM

It doesnt sound that it is necessary to REBUILD that engine.

I would first do a compression check.

Next I would start with the fuel system and the ignition system. Honestly I would run the boat up to operating temperature on the trailer in the lake or on the hose at the house. I would make the boat do what it does and stop running and not restarting. DO NOT put yourself in a situation of being stranded on the lake in the winter months unless you have a for sure way of getting back via another chase or follow boat.

Then I would check fuel pressure, ignition spark, and do a real good overall check on the two systems.

I would be willing to bet that if you rebuilt your engine that you would have the same identical problems as you do now with a new power plant.

Save your money and check out the fuel system and the ignition system first. It may also be some kind of sensor that the LT1 has such as a Throttle position Sensor, mass air flow, or some kind of temp sensor or sending unit.

Also I would check to see if there is some kind of kink or some kind of blockage on the pickup in the tank.

madcityskier 12-04-2012 04:49 PM

The man is wise beyond his years. Also wise beyond mine, as I would have to chase down a thread on each one of these things, one item at a time. Actually, I'd probably try to get my old man out for a week to help me get it right, and then plan to run it hard for a couple days buying food and drinks along the way as a thankyou. I have however known a guy who had major work done to find out the "engine" problems" were problems getting the fuel to the engine. Start with the cheap and likely fixes prior to spending big on large ticket items that may not help.


Thrall 12-04-2012 04:52 PM

So it runs for a pretty much set period of time then craps out, won't start and will re-start once the engine cools down?
First, no vapor lock. Pressurized fuel systems (EFI) do not generally vapor lock.
Sounds electrical to me and the experience I had with my '96 LT-1 years back was similar to what I decribed above.
DOes it die out quicker, the warmer it is outside?
Mine ended up being a bad ECM. Boat would run great until the engine bay got heat soaked, exaggerated in AZ heat. Then no power to the fuel pump. Turned out the fuel pump driver in the ECM had an irrepairable short that would short out with heat.

Rockymtn 12-04-2012 05:08 PM

Thrall, you're spot on, and yes it does die out quicker the hotter the day. How hard is it to replace a ECM?

jakethebt 12-04-2012 05:19 PM

I will give you $500 sight un-seen...

Seriously you have one of the most desirable ski boats and engine combos out there. You have the best looks, hull and EFI.

I agree it does not sound like a rebuild. There is some good advice here on the electrical and fuel delivery side.

The other issue that the early LT1s suffered from was the cooling system was not routed properly and air bubbles developed in the upper part of the engine. On a hot day, this could be giving you temperature spikes, especially after you sit for a few and get heat soak. There is a very simple fix for this and it is pretty easy to tell if you LT1 has the fix. It basically deals with a pass over tube being on the front or rear of the heads. There are a couple of threads here that talk about it, one that even has a part number and a dealer in some place like MN that ships the parts total for around $25.

jakethebt 12-04-2012 05:20 PM


Originally Posted by Rockymtn (Post 893991)
Thrall, you're spot on, and yes it does die out quicker the hotter the day. How hard is it to replace a ECM?

ECM is plug and play on the back of the engine. Not hard at all. It is probably an expensive part if you dont need it, so I would not suggest buying one unless you are convinced that is the issue.

Kyle 12-04-2012 07:42 PM


Originally Posted by jakethebt (Post 893994)
ECM is plug and play on the back of the engine. Not hard at all. It is probably an expensive part if you dont need it, so I would not suggest buying one unless you are convinced that is the issue.

Agree 100%

I would chase down all other sensors and sending units first before just throwing parts at it.

It very well could be an ECM but the last thing that you want to do is start throwing pointless money away. Its a lot easier to throw away money on pointless speakers that get used than buying sensors and replacing good sensors with new sensors or a good ecm changed out for a new one.

A compression check would only tell you for sure that the engine is still fresh.

I wonder if someone that is way smarter than I would have some kind of electrical schematic to measure voltage at the pins on the ecm when it is acting up. This kind of schematic would help you diagnose the problem correctly.

1redTA 12-04-2012 08:58 PM

this may help with some of the sensors

Jerseydave 12-04-2012 09:00 PM

Start with a compression test, but since you didn't complain about performance when it does run then I'm guessing the mechanics of the engine are sound. (Also, if it doesn't use any oil then no need to rebuild the engine)

If it's not overheating just before it quits, chances are you have a sensor or other computer related issue. I believe any good MC dealer could scan your system or use an ohm meter to check each sensor to see where the problem might be.

My '93 LT-1 has a slight stumble on acceleration and also starts hard when the engine is hot, so I'm going to try a TPS (throttle position sensor) and go from there.

A '93 S & S with LT-1 is really rare, so you should try to keep the boat as stock as possible.
Is yours a powerslot trans or 1:1?

Oh and post some pics, your killing me! :D

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