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View Full Version : Older Supras- Stalling/Vapor lock/killing



selle92
07-26-2006, 04:25 PM
I've seen in the past, numerous topics on this. Been reading up on the posts with problems others have had, as I have also had these problem since I got my boat last spring.

I talked to my local MC dealer about some issues I've ben having when I went to get a new Solenoid for my boat not too long ago. I explained that I have an older inboard that has a carb. Mentioned when it was hot outside or if I have been pulling skiers/boarders for a hour or so, the boat wouldn't fire back up if shut off for a little bit. Well, unless I opened up the engine cover and let it sit for 30 mins or so (longer if hot/humid outside).. I noticed others have had this problem too and have posted on it- and seemed to have been mentioned it could be impellar problem, plugs, or vapor lock, etc... Not just issues posted on vapor lock after shutting down, but also boat stalling issues or hesitating.

Well, my problem started mostly when it was hot/humid outside and progressivly got a little worse up until a week ago. It was to the point where after out for an hour or so, the boat might just kill at idle on the way into docking.

He said, I'd really need to bring it in to have a diagonstic check to be for sure what is going on, but mentioned it could be the carb, could be a water flow problem, could be the impellar, or some boats do occasionally have a vapor lock (however said if VL- it should cure itself rather quick by opening up the housing or fanning it)- Fanning did work last year, but got worse and didn't work for me now.

Not wanting to really take it in, I've been self diagnosing it myself with the help from my neighbor and reading the other problems/solustions people have had on this board that seemed to be similar situations.

First off, we thought it might be a carb issue (Vapor lock). Now, bear with me.. new to learing about engines and this is coming from my neighbor. He though possibly, with the heat (outside or when engine got warm) that maybe, just maybe the carb was expanding and a needle was either dripping fuel.. causing a flood, or possibly the carb itself just needed rebuiliding and might be clogged up.

However, after playing with it one day after it was out running for awhile and we parked out front of our place to just swim and hang out with the neighbors.. we checked it out. It didn't appear to be leaking fuel from the needles and wasn't flooding. However, it didn't fire up like it should have. Engine was hot, so it seemed to be some sort of heat issue. (maybe thought electrical too).. So, after digging around in there with the engine cover up.. of couse 10 mins later it fired right up. No smoke and idled just fine. We kind of ruled the carb out as it was purring good and not sputtering or hickuping at all, but we still didn't know what the root cause was for the issue.

So, a few days later.. Wife and I are out in the boat. Only ran it for about 10 mins and anchored out in the middle of the lake. We started drifting as it was really windy, so I pulled anchor to move back to the other side. However, boat didn't start- yet again. I did notice the engine temp was in the 180s.

So, as I sat there with the engine cover up- drifting to the other side, another boat came up and asked if we were having troubles (yet again, going to be towed in). Said yeah, the boat seems to just keep overheating. Didn't know if it was truly the carb or what was going on. As soon as that, the engine fired (temp was then at 165) and I thank the guy anyways coming to our rescue. He said to check the impellar or possibly the Thermostat as he had an older supra before. We pulled into the dock as we needed to go somewhere at that time anways.

another 2 days later. Brother came over to wakeboard. Wasn't real hot out and the humidity finally kick the bucket. Thought for sure, we'd be ok out for a few hours. About a hour into it, boat started acting up again. Noticing the engine temp.. we were up at 175-180 again.. when all of a sudden it went up to 200 and I just shut it down. Watched the temp and when it got back down to 160, I fired it up..as soon as I put it in drive, temp went down to 150 (so I thought the impellar was working just fine).. we headed in after that.

Getting sick of this (not to mention the embarrassement of being towed in 3times this year- and even worse when all other boats- minus my neighbors comp-on lake are MC's or Nautiques) and being unsure if it was safe to go out anymore, I finally caved and brought it in.

Sure enough.. Impellar needed replacing... Like someone else mentioned in another post, it worked- just not perfectly like it should have been.
But, that was only part of the problem. Water lines were also clogged with a bit of impellar peices and some lake debris...Again, Just part of the prob. Once new lines and raw water pump/gasket/impellar were replaced- they fired it up again. Still with water flowing good, the engine temp climbed and ran hot.

Next up... T-Stat.. Low and behold, that was another problem and probably my biggest issue with stalling and what I thought was vapor lock. Now, this is a MC dealer telling me this.. and I don't know the difference, but he said I had a 160degree T-stat in there... said I should be running a 140 degree one (anyone know or care to comment on this?).

From the way I understand it, I was Always running too hot with the 160. I don't know, but when I put it back in the lake yesterday, she hummed like a swiss watch, and did feel like it was running a TON better. I haven't got on it for an hour or more yet to see if there are any stalling problems or non starting issues after I shut down, but according the my service guy.. unless its 90 & humid, it should not happen again... and possibly not even then. He did say my gauge readout was just a bit off, but not of concern as the gauge was reading just a bit higher than the actual engine temp- ( it may show 145degrees when the engine is actually at 140)

Just thought I'd share my little sage for any others having similar problems or concerned with vapor lock or stalling out... The T-stat might be something for you to look into.

anyone know about the Thermstats and care to comment? I would be interested to know more about this.

Is a 140 correct for a 351 PCM?... should it have been a 140 all along? Did Supra put in the 160s back then.. I don't know if mine had been replaced since I bought a used boat early last summer.

Hope some of this may help others.

Joe

OUI
07-27-2006, 10:45 AM
Mine (454) runs at 140 and I've never had a problem with stalling - vapor lock - or not starting. Vapor lock comes from excessive heat so it makes sense that running at 160 and above could be the cause. Cheap and simple fix if it is the problem.

selle92
07-27-2006, 11:22 AM
Went out last night for about and hour.. just a sunset cruise with the wife and kid, but opened it up a bit for 2 5-10 mins stretches. Gauge never went over 150.. so I figure engine was running at 145 tops at its highest.. No problems what so ever and she was running really good.

I know it was mentioned in another post that these things I just had replaced are pretty east to do yourself... Will have to look into learing how to do them myself next time, but to me, this was money well spent at the shop. Does suck when they go thru the list and the parts total was about $30.... and my bill was closer to $300. But, not knowing for sure what it was.. I'm just glad to be out on the lake again with a stress free mind about how she's gonna run.

neardana
07-29-2006, 10:18 AM
I finally determined my problem. From 1991 through 1994 PCM used an electronic ignition module made by Pro-Tec. The ignition module has been known to be faulty since 1994. The problem is hard to diagnose because the failure slowly increases in frequency. The electronic ignitiion module is not properly shielded so it receives other electronic signals from the engine which shuts it down. The problem increases when the unit gets hot. Eventually it resets itself. The fauilure is a function of usage over time.

The module is not manufactured anymore nor is a replacement. PCM has a few left, but only sells those to owners with fuel injection because the two are interrelated. For others (carbs), the solution is a Pro-Tec Ignition Conversion Kit (part no. RK107025A). The kit replaces the electronic ignition module with a distributor and coil (still electronic ignition). Skidim sells the kit for $455. I installed it in about an hour and have had no problems the past 2 weeks (12 hours on the water).

delbert
07-29-2006, 11:08 PM
Had the same issue with the protec on my 1991. I posted about it a while back and dealer replaced the protec with the kit from PCM. The boat ran great after that.