GT40 engine loping

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.

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....

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.

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.

Lewy, would you mine weighing in here with the problem and fix:
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=25584&title=poor-mans-gt40-diagnosis

I can add a new row in the spreadsheet for EEC Relay.

Thanks! It's in my Amazon shopping cart! :-)

lewy2001 wrote: This is the Code Reader Gordon the book that comes with the code reader has a lot better run down of the fault codes than the GT40 manual in reference section. .

Thanks Mark. One question: Does it come with a cable to plug into the port on the GT40, or do I need to order an extension cord for it? I have a compter-based ODB++ reader and of course the plug for that looks nothing like the one on the GT40.

Thanks,

lewy2001 wrote: Plugged the code reader in and found a continuous stored code 15 (Power interruption to EEC computer).

What code reader do you use?

east tx skier wrote: My understanding of it is that the wire from the battery is eliminated entirely (not just replacing the wire with a fuse with another wire without one).

Correct. Hope I didn't suggest to the contrary.

lewy2001 wrote: Joel where is the on/off/bilge toogle switch located in the engine bay or up at the dash?

Up at the dash in my case. The switch cuts off all systems in the boat including the push-button/keyless dash which is a parasitic load on the battery. Relevant only to the 2000+ "smartpod" boats but probably not terribly unlike the ignition breaker on the older boats.

I remember when I went to test-drive this boat they still had the positive lead with the inline fuse at the battery. It gave us trouble on the test drive so the dealer I bought it from explained the fix to me and had it done before I brought the boat home.

Just took another look at the wiring and my 12.5 breaker is definitely unmolested. Both connections on it are still plasti-dipped from the factory. Both wires on the 12.5 run neatly into the wiring loom, complete with the woven protective sheathing on them both. There's no way this fix involved that breaker directly in my case- could someone have messed with the wiring on your boat? If not, perhaps the unfused side of the 12.5 breaker is powered via the dash somehow and that's why the new wire on my boat goes forward. Donno.

The red wire with the crimped eyelet on the 60 amp breaker (in the picture) is the ONLY non-factory wire/connection on the whole thing FWIW, and it does go forward to the dash area on my boat.

Thanks, Joel. I think I have someone lined up to do the fix for me for lunch and some beer.

Joel would also like to see the pictures or original bulletin. It does seem a complicated way of powering the EEC when there already is the main battery cable located right there on the power assist solenoid.

Lewy, just as an FYI there was a service bulletin (?) released a while back which eradicates that extra power wire and inline fuse. Essentially the power is instead wired directly to the fused side of one of the push breakers above the engine computer. That inline fuse in the battery compartment is a common source of GT40 problems but I always thought it went to the fuel pump relay. Learn something new every day! I can snap a pic of my wiring on that bracket if you want as I had the fix done by the dealer.

Wow, all I can say is I'm damn impressed with what you guys have come up with so far- lewy and slmskrs especially. Great work so far. I have nothing to add, but I'm staying tuned because this is a really interesting thread!

Well, playing role as mechanic is very tuf as repairing of vehicle is not so easy task. As to repair this engine loping is also very difficult, for it auto mechanics plays an important role and there are many online reviews for it.