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View Full Version : Looses rpm after several minutes of running


timh
09-03-2007, 02:33 AM
at wot. Can pull forever at 3000 to 3500 rpms, no problem. Cruising at wot, 4900 rpms, after a while, 15 minutes or so, sometimes only 5 minutes, the rpm start to slowly drop to about 3000, then level out. Turn engine off for a minute, and back to normal. Thinking it was a fuel problem, I changed the filter and it seemed to help a bit, but I'm not sure it's fixed. Has anyone had this problem and found the cure. Any help appreciated before I continue on the parts changing route. Can injectors become slow reacting after minutes of wot operation? How about the fuel pump? How do you guys monitor fuel pressure? There appears to be no built in schrader valve. Sorry for the rambling post. Looking forward to your suggestions. Oh, btw, oil pressure and temp are good and stable.
1994 ps190 351 tbi
Thanks in advance

Jesus_Freak
09-03-2007, 04:03 AM
at wot. Can pull forever at 3000 to 3500 rpms, no problem. Cruising at wot, 4900 rpms, after a while, 15 minutes or so, sometimes only 5 minutes, the rpm start to slowly drop to about 3000, then level out. Turn engine off for a minute, and back to normal. Thinking it was a fuel problem, I changed the filter and it seemed to help a bit, but I'm not sure it's fixed. Has anyone had this problem and found the cure. Any help appreciated before I continue on the parts changing route. Can injectors become slow reacting after minutes of wot operation? How about the fuel pump? How do you guys monitor fuel pressure? There appears to be no built in schrader valve. Sorry for the rambling post. Looking forward to your suggestions. Oh, btw, oil pressure and temp are good and stable.
1994 ps190 351 tbi
Thanks in advance

Welcome!

After the drop back to 3000, can you continue there for "forever"? Can you return to WOT again without first shutting off the engine?

timh
09-03-2007, 02:13 PM
Thanks for the welcome and Bless you for your interest.
As in cruising up the river, after the drop in rpms, , it will continue to run at around 3000, for as long as I've ever wanted it too, I guess 15 minutes or so. Returning it to idle and then advancing to wot, it will still only go to 3000, but if I shut the engine completly off, wait about a minute and restart, it will then pull up to 4900 and go through the same cycle again.
If I'm just pulling skiers, we only ski at 3000-3500 rpm, I would never notice a problem. I could open it up for a minute or two, as in getting back to a downed skier, and it would work fine. Hope this better defines the problem.
Thanks again.
Tim

Jesus_Freak
09-05-2007, 03:15 AM
Thanks for the welcome and Bless you for your interest.
As in cruising up the river, after the drop in rpms, , it will continue to run at around 3000, for as long as I've ever wanted it too, I guess 15 minutes or so. Returning it to idle and then advancing to wot, it will still only go to 3000, but if I shut the engine completly off, wait about a minute and restart, it will then pull up to 4900 and go through the same cycle again.
If I'm just pulling skiers, we only ski at 3000-3500 rpm, I would never notice a problem. I could open it up for a minute or two, as in getting back to a downed skier, and it would work fine. Hope this better defines the problem.
Thanks again.
Tim

Yes, better, thanks. There are many here who know 10x as much as I do about ECMs, but since I am the only one "biting" at the moment, I will share my $0.02. If the operation in the "temporarily slowed" condition is smooth and correct, as best as you know it, it sounds like an electronic stop has been reached. Maybe it is rev limiter of sorts reached at 4900 prematurely, or maybe by design. I have zero experience with rev limiting mechanisms. It would probably be worth having your local dealer run the diagnostics to see what alarms, if any, have been triggered. I assume you have experimented with various "pick up skier" speeds to see how high is needed to cause the problem. Just randomly thinking....I guess I would either not go to that speed, or would ask my local dealer to plug in to the DLC.

Hollywood
09-05-2007, 01:52 PM
I don't know much about ECMS (who does???), but I would put a fuel pressure gauge on there and see what it's doing when you lose those RPMs.

timh
09-11-2007, 12:08 AM
Thanks for the replies. The nearest dealer is about 30 miles. Not too bad but I really don't know much about his reputation. I guess I will try him though if nothing else works out. I would like to monitor the fp but I have to find some sort of adapter because there's no factory provided schraeder valve. I'm working on it. Anyone else?

Leroy
09-11-2007, 12:22 AM
Welcome Tim, sure you are guessing either fuel or electrical! The pressure would tell you a lot.

JesusFreak has studied up on '94 era problems lately, JimN will likely be able to nail the problem if he comes on or PM him.

erkoehler
09-11-2007, 12:58 AM
Where are you located in the midwest?

timh
09-11-2007, 12:49 PM
Where are you located in the midwest?

St. Louis area.

f16driver
09-11-2007, 03:00 PM
TimH,
I just noticed your thread and in some respects I now have a similar problem. My thread 03prostar 197 wont start need manual etc http://www.tmcowners.com/teamtalk/showthread.php?t=18887

Started out with a no start issue and now it starts but I cant get my rpm over 3800-4200 range before engine starts popping and/or lossing some power. I've used a fuel pressure gauge on mine during load and for the most part the pressure is staying steady at about 59psi even when I'm loosing power.
Keep us posted if you find anything from the repair shop.

03 PS 197 LQ-9
Va

Jesus_Freak
09-12-2007, 03:28 AM
Welcome Tim, sure you are guessing either fuel or electrical! The pressure would tell you a lot.

JesusFreak has studied up on '94 era problems lately, JimN will likely be able to nail the problem if he comes on or PM him.

Yes, I have been in school, and JimN has been the teacher. Some other classmates (Andre, ETS, Bigbadblue, etc.) have helped as well.