Map sensor? Motor boggs at 2100 rpms
I recently purchased a 96 prostar 205 SD LT1. The boat has about 250 hrs on it. Here's the problem. When i accelerate the boat boggs down at 2100 rpms. I turn off the engine and restart it and the boat runs like a "scalded dawg" as my father says, pull the throttle back to idle or below 2100 rpms and try to accelerate and it boggs down again at 2100 rpms. Turn the engine off and restart it and it runs great again. It will also bogg down after about 5-10 minutes of running 2500 rpms or higher. I need to get this fixed before i wear out the battery and starter.
Thanks to this forum, here's a list of the things I've done...
-completely drained the fuel tank
-changed both fuel filters
-checked the fuel pump inlet screen (it was clean)
-repaired sender unit (gas gauge didn't work)
-changed oil and filter
I am wondering if I need a new map sensor. Many thanks in advance for any help.
Any Luck with this?
I have been having exactly the same problem with my '95 Prostar with the LT-1.
At EXACTLY 2100 RPMs, bogs down, back off, right back up to 2100 RPMs, but bogs down again. Seems pretty clear that something is causing it to go into 'Safe Mode'. It was running a little hot, so I thought maybe that was it.
After lots of research, I:
- replaced the impeller and made sure closed cooling system is running clear
- drained and cleaned the tank
- checked the pickup screen
- changed the fuel filter
I ran it for a while on the trailer and the temp was stable at 180. I know that running it on the trailer or in neutral isn't a substitute for a real water test, but the lakes are so high here in NJ that they are no-wake lakes, so I can't really test it until later in the week when the water goes down...
Next steps are to:
- change the thermostats if it runs hot again
- pull the Fuel pump to check the screens
- check the fuel pressure
Let me know if you had any luck on your problem. That shutdown at exactly 2100 RPMs makes it seem like an electronically controlled situation more than a mechanical, but I guess it could be electronically controlled based on a mechanical problem...
what is your fuel pressure at the time of the bog?
I don't know that yet. I will try to test it later this week or on the weekend. Need to pick up a tester and get back on the water - I assume that it wouldn't be worth testing that unless it is under load, right?
Update!!! No better - Still not able to run past 2100 RPMs.
I replaced the impeller, fuel filter, drained and cleaned the tank, checked the screen in the tank. Put the boat in the water tonight hoping that it would run normally.
- Started and warmed up the engine
- Ran great for about 10 - 15 minutes, from idle to 40 MPH.
- Temp stayed around 180, maybe a bit higher
- Oil pressure at 35 - 50 when under power, but dropped as low as 10 at idle.
- Started and stopped repeatedly. No problems.
- Stopped the boat, idled a bit, turned it off, restarted, put the throttle down gradually and the problem started again. at 2100 RPM, engine boggs down until I backed off the throttle, then I could go right back up to 2100 RPMs.
- Put the Fuel Pressure Sensor on and started up... Able to get up to speed, well past 2100 RPM. Pressure looked fine - 35 PSI at idle, 38 - 40 while going 10 - 40 MPH. After about 10 minutes, the engine started bogging down at 2100 RPMs. Fuel pressure stayed between 35 - 40, even when the engine wouldn't go through 2100 RPMs.
- Disconnected battery and let it sit for 5 minutes. Reconnected and still had the same problem.
Next up? Thinking about replacing the TPS this weekend, but that is a $50 gamble to see if that helps. The Mastercraft shop at Lake Hopatcong can take a look, spend an hour and $100 to do some diagnostics next week.
Any other ideas?
have you checked for codes? you can do a search here but i'm pretty sure you want to short pins A and B in the diagnostic connector and see if your check engine light flashes any codes. post up what it flashes. you should get a "12" or 1 flash then 2 and then any actual error codes will flash.
also, i know the LT1 has a "reduced rpm" mode that only turns on half of the injectors as a protection mode. i dont know for sure what conditions will activate that mode though, jimn will probably be your best answer on that.
you can check the resistance of the coolant temp sensor at the ECM and see what it reads at the time of the problem. ohm it out at pins J1-2 and J1-29 and post up what you had, i have a chart for that. max on the chart is 212 degrees which is 177 ohms, lowest i'd expect you to see would be about 60 degrees which should be 4450 ohms.
might want to unplug the knock sensor at the time of the problem also.
it would likely be a quick diag with the correct scanner, i'm just trying to throw some things out there you can do without one.
Bartman was the only one who mentioned his temperature being 180 degree or higher. I have the 95 TBI and not the LT-1 but the book says 142 for the TBI and 142/160 for the LT-1. If it were me, I would replace the thermostats or at least take them out and see if the problem goes away with the engine running cold. It is possible that 180+ degrees is just on the boarder line of being too hot.
Several of us with the 95 TBI Maristars have the 142 thermostat and the engine acts up if we try to run the 160 thermostat. The engine will run at 160 degrees but doesn't want restart after it has been shut off.
Interestingly, after running at 180 for a while, when you stop, or especially shut off, the temp goes above 180 (but I don't think it goes above 195). It seems like that may be when it starts... I have it scheduled for Monday at the shop to have them put it on the computer to see what exactly the engine is doing and saying. I am thinking that I should do this anyway, since the boat is new to me, to see if I can get this resolved, and to see if there are any other problems looming out there.
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