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GT40 engine loping

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lewy2001 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lewy2001 Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2012 at 9:21am
Brian you add the extra rows and I will update.

Looks like I need a new battery the Interstate has been in there since April 2004. Not bad, I can see why you US based people like these batteries.

While I had it out for testing and charging decided to check all the connections on the 50 amp EEC fuse circuit. Cut away the heat shrink from the fuse holder and found the crimped connections were still in good shape. Would prefer to see them soldered and a heavier gauge wire used. No way that wire was ever going to carry 50 amps over that distance to the breaker at rear of engine. But I doubt it draws much more than 10 amps considering the breaker it goes to is only 12.5 amps. Not sure why they would use a 50 amp fuse in the first place.

I will replace fuse holder at least. At the moment contemplating removing this circuit all together. Will chase this wire back under dash and see where it goes before ending up at the EEC 12.5 amp breaker. I will email Correct Craft and PCM and see if they can provide any info on retrofit mentioned previously that replaced this circuit.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2012 at 8:04pm
Just an update on the loping problem (since I started the thread). Now that we have had warm weather, it is hot start loping all the time with the following conditions:
1. Ambient air at least 75F (was 91 yesterday)
2. Engine hot (have pulled 2-3 sets in the course)
3. Boat sits with engine off for about 30 minutes with engine cover closed (while other two boats at course take their turn (boat rotation)). Gets quite hot (no air flow) in the bilge. If I rotate with only one other boat, then the 10-15 minute with the engine off is not long enough to cause the problem.

When engine is started, immediately starts loping, and most of the time it is severe enough that the engine stalls. The way to "resolve" it is to run the engine at a high idle (usually over 1,000RPM) for 30-45 seconds or so before dropping back to idle.

I have checked the ECM and there are no codes. I also have a fuel pressure gauge and a vacuum gauge on the engine. When it is loping, the vacuum pressure goes up and down (expected since the RPMs are going up and down). The fuel pressure goes up and down between about 32psi to about 37psi (also to be expected since as the vacuum changes, the pressure regulator will change the pressure).

What I expected to see is pressure dropping below minimum (32psi?) during loping, but it never did that, so it appears that the injectors are getting correct pressure at all times.

I have:
* cleaned the throttle plate
* cleaned the idle speed control valve
* run injector cleaner fluid through the fuel system
* Confirmed that the tube in the FCC is good (if it wasn't, I'd see low pressure)

At this point, I don't think it is related to fuel pressure, so the next thing is air.

I think the next thing I will do when the symptoms appear is to pull off the idle speed control valve (ISCV). Of course, that will make it run at a high idle (which might be the same as cracking the throttle slightly to rev at high idle, so that could mask if the ISCV is bad). But I might be able to look into the plunger in the ISCV when I first start the engine to see if it is moving open and closed. That would tell me if the ISCV is what is moving and causing the loping.

If so, the next thing would be to see if it is the ISCV or something before that. Does anyone know what voltage the ECM sends to the ISCV? I'm wondering if I could put a volt meter across the leads (when it is loping) and see if voltage is fluctuating.

Anyway, I'm getting lots of loping in these warm conditions, so will advise what I find out.


Gordon '96 Ski Nautique, GT40
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lewy2001 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lewy2001 Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2012 at 8:40pm
Gordon sorry about the threadjack

That sounds like a good plan for the ISCV. Pinpoint test 3E10 in the GT40 manual gives you all the voltage readings required. Some of the readings require a breakout box on the 60 pin computer connector. When I was testing mine I found it much easier to look at the operation of ISCV than measure the voltages. Although I was looking for a bigger problem than just the rolling idle.

Another possibility could be weak spark. If you prove you have air and fuel it may be the next place to look.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2012 at 8:58pm
Hey Mark, no worries. I'm just glad that you found your problem with no starting after hard runs. At least if that happened to me at the north end of the slalom course, it would just amount to rowing to the other end where the launch ramp is. I would NOT want to be way out on some big lake somewhere knowing that could happen. :-)

I did have a question for you. When you pulled the ISCV, you said it idled with a slightly higher idle. Do you remember about what RPM it idled at? And also, how much does the ISCV move when you turn the ignition on? I'm curious as to if it moves to a different position between hot and cold. I guess I'll pull it and see what it does when cold when turning on the ignition, and then try it again when it is hot. Next weekend the weather is going to be back to normal temperatures for this time of the year (low 70sF (21-22c) rather than the 90sF (34-35C) we had yesterday, so I may or may not have a loping problem next weekend.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lewy2001 Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2012 at 9:06pm
Gordon I remember watching it actuate by just turning the key on and off. My engine always idles around 1000rpm for a short period on initial start before dropping back to 650-700rpm. The high idle is due to the ISCV being open. With the whole assembly removed the idle speed was just above the 1000rpm maybe 1100rpm from memory.

If I get a chance this week I will make a video of what mine does and you can then compare it's operation to yours.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2012 at 9:22pm
I'm a bachelor next weekend (wife and youngest daughter will be out of town), so it will be a Nautique orgy--tons of skiing, and all sorts of work on the boat (prop shaft alignment), replace heater core hot water circulation pump with bigger pump), pull analog tach (it bounces all over the place and when I slug it, it settles down so I figure there is something loose in it--don't care too much since I have Stargazer, but a couple of drivers haven't given it enough throttle to engage because sometime my analog tach can read 4k rpm when it is not up to 3k).

Anyway, hoping it is warm enough that it will lope since I can spend a lot of time at the pond playing around with it. My engine does the same thing (initial start idle around 1k rpm and then drops down to 650-700). It sounds like when the ISCV is wide open, it is around 1k and with it removed, it is a bit over 1k. I don't know if I'll get loping at 1k or not since cracking the throttle will keep it running (above loping RPMs) until it stops. But if the conditions are right and it starts loping, I want to immediately pull the ISCV off and restart the engine and see if 1). there is still any loping, and 2). whether the ISCV valve "lopes" (moves open and closed). I guess the other thing I could do is to manually block off some of the air flow with my thumb (after taking the ISCV off) to slow the engine down, and then see if it lopes at the normal "loping RPM" without the ISCV.

The next would be spark, but I don't know where I'll look for that. I guess I could put a timing light on one of the plug wires and see if a spark is always firing or not. But I'll do the ISVC tests first.

Good thing the boat runs great otherwise. And I can always avoid the problem by either opening the engine compartment when at the dock if the engine is going to be off for more than 15 minutes, or just skiing more (pulling someone every 15 minutes). So not a major problem, just annoying (and embarrasing when it is my turn to pull someone and it stalls when I'm trying to back up out of the dock....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2012 at 9:45pm
Mark, if you are able to take a video, that would be great. But please don't go out of your way to do so.

Thanks,
Gordon '96 Ski Nautique, GT40
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lewy2001 Quote  Post ReplyReply Direct Link To This Post Posted: April-25-2012 at 6:32am
Gordon got some work done on the boat today and managed to get some video of idle speed bypass solenoid. Not great quality but should give you something to compare.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: April-25-2012 at 11:07am
Originally posted by lewy2001 lewy2001 wrote:

Gordon got some work done on the boat today and managed to get some video of idle speed bypass solenoid. Not great quality but should give you something to compare.



That's PERFECT! You even plugged the port with your fingers to bring the idle down. That is exactly what I'll do. I know we wouldn't be able to see it in the video, but I assume you can see the valve close slightly after start (where the idle would normally go from around 1000 back down to normal idle speed).

Anyway, thank you so much for doing that. I really appreciate it. I'm really hoping it is warm enough this Saturday that it will lope so I can do that test!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: April-30-2012 at 11:36am
Wasn't warm enough to lope this weekend until we were pulling the last person (and the wind was coming up so we were in a hurry to pull them). So no chance to pull the ISCV.

Just curious, has anyone with the (hot) loping problem replaced their injectors (and still have the problem)? Someone on the dock mentioned doing that for his truck and it ran so much better. Don't think that would be it, so I'm curious if anyone has replaced theirs (where'd they get them, part number, etc.), and if so, do they still have the loping issue (something else to eliminate from the mix).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: May-03-2012 at 1:45am
As an FYI, for any of you that haven't been following the "99 SN GT40 Fuel Supply" thread, what is interesting here is that AB has got a loping problem, but the source seems to be completely different. But listen to the loping sound. I'm trying to figure out if there is any correlation related to our cold start and hot restart loping issues. Here's the video he posted: http://www.youtube.com/watch?v=0hihpHcuNvY

What's weird with his situation is that the loping has the same type of frequency (RPM oscillation), except his fuel pressure gauge makes no sense, whereas mine does exactly what I would expect it to do, higher PSI when the vacuum drops with RPM drop, and goes back to around 32psi with higher RPM (and manifold vacuum).

Anyway, for any of you following this that didn't see this, it is interesting since it is a different kind of loping problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: May-19-2012 at 5:17pm
Just an update.

I did two tests today. The first was to jump the fuel relay to ground so that the pumps stay on. The idea behind this was to run the pumps for about two minutes to see if the flowing fuel somehow cooled down (assuming it was hot fuel causing the loping). So when I knew it was going to lope (hot, sitting for a while with the engine cover closed, I jumped the pumps (I already had it wired so I could jump them without opening the engine compartment) and let them run for about two minutes. When I started the engine, I still got loping.

The second test was to take off the idle speed control valve and check two things: 1. See if the valve was moving back and forth (which would cause the loping), and 2. place my fingers over the ISCV air opening to slow the RPMs back down to idle speed and see if it would lope.

I did not see the iscv moving back and forth when I started it. And when I blocked the ISCV air port to slow the RPMs down, there was no loping.

The most interesting thing was after these tests. I put the ISCV back on, we finished packing up to leave. I went to get the truck, and my ski buddy idled the boat to the launch ramp. I found out afterward that when he started it to idle to the ramp, it was loping.

So, with the ISCV off, it did not lope (even when I blocked the air port to drop the RPMs to idle speed). However, when I put the ISCV back on and the engine was started five minutes later, it loped.

Based on that, I'm questioning the ISCV more now. I looked at the movement of the ISCV packed up to leave when I got home, and it appears to be a little jerky (not bad, but it wasn't super "smooth"). So I may try cleaning it again (I tried when I replaced the heads but didn't power the valve so it would open).

If cleaning doesn't help it, I'm wondering if I need to get a new one.

Anyone replace one, know how much they cost, and where you get them (haven't checked skidim yet)?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: June-16-2012 at 8:28pm
HOT LOPING PROBLEM SOLVED!!!

It was the ISCV (or whatever everyone here calls it, in the car forum I'm on, it's the idle speed control valve). I pulled mine and checked operation, cleaned it out, etc. Seemed okay, but I couldn't get ride of the hot loping. I managed to find the exact replacement from RockAuto for 1/4 what the marine folks wanted (exact same PN, etc.) so figured I'd go ahead and get a new one. I checked its operation with the old one and they seemed to do the same thing. But I put the new one in anyway just to see. I've had the boat out about six times but it has not been too warm / didn't really have perfect storm conditions so no loping problem. So I didn't know if I fixed it or not, until today. Today was the perfect storm. Mid 90s ambient, three boats in the pond (we only allow three at a time and we do boat rotation). When it is hot and my boat sits hot for 20-30 minutes (while the other two boats take their sets), I have always gotten loping, all the way to stalling. Anyway, hot, lots of the boat sitting around and going through the course every 30 minutes or so for some 5 hours. But it never loped. The idle might have been a tad rough (I think that is just a hot fuel issue), but idle never fluctuated more than 25RPM or so.

I wasn't sure that was the solution until today, when with the old ISCV it would have been loping like mad, stalling, etc..

I'm a VERY happy camper and can finally close this thread!!!!

Thanks to everyone for all of their input, etc. Especially to LEWY; he took great video of the ISCV and let me know that I could run the engine with it off, etc. That helped a lot. Also to TomT in San Diego, who has documented his loping (and not loping) for probably 25 outings.

Happy Nautique'ing everyone! It's gonna be a great summer!!
Gordon '96 Ski Nautique, GT40
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: June-16-2012 at 8:38pm
BTW, I can't seem to edit the GT40 spreadsheet, so here's the info:
IACV PN: e9se9f715eb (off the original valve)
http://www.rockauto.com/catalog/moreinfo.php?pk=945342
$55.79 + shipping
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luchog Quote  Post ReplyReply Direct Link To This Post Posted: June-17-2012 at 12:38pm
2nd and 3rd post first page...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: June-17-2012 at 1:36pm
Great Point!! Agreed it was mentioned up front. I pulled the valve immediately when I got that info, cleaned it, checked operation, which seemed normal. Problem remained but only with those specific conditions. Pulled it again, cleaned it again (while opening and closing it), watched video of others with it, confirmed movement was the same. Wasn't any obvious problem with the operation, so in order to not to just start throwing parts at the problem to see what sticks, I did a lot of other checks, tests. In the end the valve was the problem and the only way to tell was to put a new one in. And of course there were other suggestions which I also followed, so while I now wish I had just replaced it at the beginning, I know my pumps, pressure regulator, etc. are all working well, I learned a lot more than I previously knew about the system, and hopefully this thread with all of the various suggestions, etc. will help others hone in on the problem (whether it be the valve, the pressure regulator, pump, relay, ECC, etc.).

Also, I was able to source a much less expensive valve (which is why it made it easier to just go buy one and try it. :-)    I'll spend $60 to try something, but hesitant to spend $225 or more when I can't tell if it is bad or not. So I'll do more checking first. :-) Anyway, again, thanks to everyone for the suggestions, etc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bri892001 Quote  Post ReplyReply Direct Link To This Post Posted: June-18-2012 at 10:38am
Great you fixed it! I'll edit the spreadsheet with this information.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1994nautique Quote  Post ReplyReply Direct Link To This Post Posted: July-14-2012 at 12:27am
Is this on a port fuel injection or throttle body?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slmskrs Quote  Post ReplyReply Direct Link To This Post Posted: July-14-2012 at 2:22am
Multi port fuel injection.
Gordon '96 Ski Nautique, GT40
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