GT40 engine loping

I have always had a bit of a problem with engine loping. It will do it when very cold (winter) when launching, and also do it when the engine is hot and it has sat for a while (30 minutes or so with the engine compartment closed). The warmer it is, the worse it is (really bad in the summer).

When it is cold, it can last for 30 seconds or so but then smoothes out without doing much of anything. When it is hot, it can last that long or up to a minute and be bad enough that it stalls. Giving it throttle helps and speeds up it getting back to normal. I have no idean on the problem when it is cold, but I would suspect vapor lock when it is hot. But with MPFI and high pressure pump, I don't know how that would happen.

I have not put a pressure gauge on it to see if the pressure is going up and down when it is loping (I am in the process of replacing my original GT40 heads with new ones, so it will be a week or two before I can put it back in the water and test). I did have my low pressure pump fail last year and I replaced it (made no difference for this problem), and have not seen any problem with the high pressure pump in the fuel canister.

But since it is a continual and ongoing problem, I'm hoping someone has a suggestion.

Thanks,

Idle air control, as Luch suggests

Okay, so I pulled the IAC (ISCV) and cleaned the orifices in the throttle body, including the screen. The ISCV I pulled out of my car actually seats in the throttle body, so it is easy to clean where it seats after you've pulled it out. However, since the valve seat is part of the IAC, I can't clean that part.

My question before I start spaying the inside of the IAC on either side of the closed valve seat, I wanted to make sure it is fine to spray throttle body cleaner in there. I don't want to short it out, so would appreciate advising the best way to clean the valve (and seat).

Thanks,

Gordon

It also comes up with these motors that the fuel control relays can be troublesome.

I've also read that there is some kind of a clear tube within the Fuel Control Cell (if your boat has one) that can develop a crack and cause fuel pressure problems.

Also, fuel pressure regulator has come up as something to check.

But, usually problems that are related to temperature are often electrical in nature.

On the cleaning with a cotton swab, how can you clean around the valve seat since the valve is closed? Is it possible to carefully open it manually to clean the seat?

Gordon,

My 2002 SN GT40 has the same problem. We used the Star Tester to extract fault codes from the engine's computer and the codes were all 11 which indicated the systems were fine.

The next procedure the manual recommends is to check the fuel pressure regulator and the vacuum system. Today we connected the fuel pressure gauge at the wash ramp. (We ski in saltwater.) By the time we pull the boat out of the water and drive to the wash ramp the engine has cooled down enough to have the idle problem. It was unbelievalbe that the engine didn't lope. Tomorrow, we'll be connecting the gauge again.

I have a thread going on Planet Nautique and have yet to have anyone some up with a solution.

Sincerely,
Tom T.

I have pretty much the same problem on my Sport, will be tackling the problem in a month or so, so this thread could be really helpful to me!

It didn't give me any trouble when skiing, but definitely at hot idle and a few times after near open throttle runs.

63 Skier wrote: It didn't give me any trouble when skiing, but definitely at hot idle and a few times after near open throttle runs.

NEVER happens for me during normal operation; only at hot start up when it has sat for a while. Once I give it some throttle to keep it running and once it settles down, there is no problem whatsoever.

Actually, as I write the above, I'm starting to think about the ISCV again, simply because by opening the throttle, it runs better. If the ISCV is having an issue, opening the throttle would "cover up" that problem.

Of course opening the throttle could also cover/mask the source of other problems as well. I wonder if there is a way to get data on the operation of the ISCV if fuel pressure is okay since I have no idea how to test it.

the temp sender can also heat up and send false info to the computer, when its warmed up this may overfuel because the senseor is telling the engine it is still cold...i believe there are 2 sensors, one for the gauge and one for the computer

lewy2001 wrote: I also purchased a ford code reader but it had no fault codes stored for KOEO,Continuous or KOER tests. The EEC does not store a fault code for the ISC-BPA so it is still a suspect.

Is the connector a ODBII? If so, where is it? I have an ODB reader (although for this problem, as you said, there are no error codes. But it would be nice to diagnose other issues.

[/QUOTE]
You can see the solenoid actuate when you turn the key on and off. This is a good test for proving the correct operation of the ISC solenoid........ I also found that with the ISC-BPA removed the engine will start and run with a slightly higher idle. I plan to use this as a test to eliminate the ISC-BPA as the cause of the problem next time it occurs. By removing the ISC assembly you allow airflow behind the closed butterfly via the now open port.[/QUOTE]

Great info!! I will try removing the ISC-BPA (for my car it's called an ISCV) and then starting it when it has the problem. Only issue will be doing it fast enough that it doesn't cool too much with then engine cover open so that it runs normally.

One word of caution when it is flooding the engine. I was helping jump a friend's carburetted SN. She has poor/corroded jumper cables (we were doing this at the launch ramp (no dock) from my car). Because the cables were poor, we could get it to barely turn over, but it wouldn't start. Of course she was pumping the throttle, etc. We finally pulled the battery out of her truck, disconnected the dead one, connected the new one. With her in the boat and me on the ramp holding the boat (luckily with the engine cover closed), she then started it. A very loud bang, the engine cover jumped up. We opened the engine cover, and all of the fuel vapor while trying to start had collected in the exhaust pipe/muffler, and blew out the side of the fiberglass muffler! We were lucky the cover was closed! So please be careful if it is acting flooded!!!

Let us know how your tests go. Between all of us, we should be able to figure this out!

boo wrote: Gordon, Regarding the ISC-BPA, the manual states if the valve is bad, upon rapid deceleration there would be an idle problem. That makes sense becuase the throttle body butterfly valve closes completely and the ISC-BPA needs to open to allow air around the butterfly valve for idle purposes. I don't have that problem and it sounds like you don't either. Today, we're skiing again and will put the fuel pressure gauge on the fuel rail at the wash rack. If we can't duplicate the idle loping again today, then I will test the boat tomorrow evening after work when the engine is totally cold. We ski in San Diego. Stay tuned, I'm determined to troubleshoot this issue until it's resolved. I forgot to mention that the fuel pressure yesterday, when the engine would no lope, was 34 psi, which is within limits at proper idle. At idle it should be 31 plus or minus 3. Tom T.

Tom, I don't have the deceleration problem either.

I will have to check to see if my pressure gauge hose is long enough that I could put it on and have it laying on the floor with the engine compartment closed. That way I don't risk it cooling enough to have the problem not happen (like what happened to you yesterday). Hopefully you'll be able to get it to lope when flushing it today.

If your test is successful and it shows constant pressure, then I'm going to do what Mark suggested and have a socket wrench all ready to very quickly remove (or at least break the seal) on the ISC-BPA since that's a great test as well. It may not be until next weekend until I have conditions that will cause it since it's cooling down this week.

Mission Bay!! I hooked up with a couple of members probably 8-10 years ago while on a business trip, took my ski and got a ride on the course there (I'd have to dig around to get their names). If you are ever in the SF bay area, we're www.sccwsc.org and I'd be happy to give you a pull. Same to you Mark although you are a bit farther away than Tom.... :-(

Gordon,

Yesterday, I connected a fuel pressure gauge to the valve on the fuel rail. Started the engine on the wash rack. This was after a morning of skiing and the engine had cooled down during the twenty minute ride from the water to the wash ramp. The engine idled perfectly. This has never happened in the last six months. It always has the loping idle and then it would eventually stall.

This morning, I launched the boat with the fuel pressure gauge connected to the fuel rail valve. Started the boat and it idled perfectly. This has never happened in the last six months, either. The fuel pressure at idle was 34.5 psi. The manual specification is 31 psi plus or minus 3 at idle. Unfortunately, I was not able to check the fuel pressure with the idle loping symptom present.

After skiing for 3 hours today, I trailered the boat to the wash ramp. Started the boat to flush the engine and the loping idle was present. (The gauge was not connected.) Conclusion, connecting the gauge removed the symptom and the engine idled perfectly both times the gauge was installed. Why? I don’t know yet. Was there air in the system that the gauge’s hose bled out? If so why does it only happen when the engine is cold? Why does it go away by turning the engine off and then on again?Not sure but I will go back to the manual’s Pinpoint Test section and proceed with more tests.

Keep in mind that the engine runs perfectly except for the first start upon launching the boat and after it has sat for about 30 minutes. Stay tuned. I will fix this problem.

The course on Mission Bay now has boat guides and turn balls that self adjust up and down with the tide. One of our members invented the stainless steel pulley system. It's absolutely unbelieveably superb. In 2006 we built a new dock, too.

Tom T.

boo wrote: This morning, I launched the boat with the fuel pressure gauge connected to the fuel rail valve. Started the boat and it idled perfectly. This has never happened in the last six months, either. After skiing for 3 hours today, I trailered the boat to the wash ramp. Started the boat to flush the engine and the loping idle was present. (The gauge was not connected.) Conclusion, connecting the gauge removed the symptom and the engine idled perfectly both times the gauge was installed. Why? Keep in mind that the engine runs perfectly except for the first start upon launching the boat and after it has sat for about 30 minutes. Stay tuned. I will fix this problem. The course on Mission Bay now has boat guides and turn balls that self adjust up and down with the tide. One of our members invented the stainless steel pulley system. It's absolutely unbelieveably superb. In 2006 we built a new dock, too. Tom T.

Tom,

I only get the cold start loping when it is really cold (like air in the low 40s. Otherwise I don't get it (so don't get it very often--a few times this winter).

Okay, your results are just plain weird! :-) On the surface, I'd just call it a coincidence, as it really doesn't make sense.....or does it? What if there is some sort of pressure surge. But when the pressure gauge is hooked up, there is not only the length of a hose that can expand and contract slightly with pressure, but there is definitely air in that hose, and you will compress that air so that when whatever is causing the pressure to drop, the air expands, keeping the pressure from dropping as much as it would without the hose, and maybe it is just enough to keep it from loping?

I'd love to see you duplicate and see if the test results are repeatable. Since it appears that you get cold start loping every time (whereas I only get it when it is really cold), you could try starting it without the gauge connected. If it starts to lope, immediately shut it off, put the gauge on, and restart (I have tried shutting off and restarting a cold loping engine and it doesn't make it better).

So, just thinking out loud if I had the same results, I think I'd do the following (depending on how frequently you are using it, you could do a few tests over a couple of days):

Day one: Start cold, if loping, shut off, quickly put gauge on and restart. If loping stops, either shut off immediately, take gauge off and restart, or wait and do day two test.
Day two: Start cold, if loping, shut off, wait the same amount of time it took to put the gauge on (but don't put it on this time), and restart. If loping stops, the waiting period is what stopped it. If it keeps loping, then attaching the gauge stopped it.

Do you ever have the problem while out at the course when it is warm? If I'm pulling back to back skiers with only a 5-10 minute stop, I never have a problem. But if we are boat rotation (max three boats allowed at a time) so I wait for two skiers or 20-30 minutes when the air is warm, it lopes. If you have the same scenario, you could do a number of similar tests the same day between boat rotations. But if not, then it looks like your only hot engine test is when you are at the flushing station. I will make sure to have my gauge when I go out next time and if it is warm enough, I'll do these tests as well.

It's not cold enough for me to get the cold start loping so I can only work on hot engine loping. For that to happen, the air needs to be at least in the 70s (at least when it happened Saturday, it was around 70 outside).

We're on a percolation pond here in San Jose, But with rain and the water district playing around with the dam, we can fluctuate upwards of 18 inches. We have sub-floats with 3 or 4" diameter capped PVC tubes with a cylinder lead weight with a stainless cable; the cable coming out of a hole in the top. The weight appropriately counterbalances the buoy and has about a 12" travel (depending on how deep or shallow it is at the anchor). It works reasonably well, but we don't have the daily level change you guys have. I was course caretaker a number of years ago and even though the deepest is only about 12', I dove with tanks many times to do repair (visibility on a good day is about 2", usually around a foot). What is the average spread between high and low tides there? When I skied there, you still had the old dock. I told your club president at the time (I skied with him and someone else and I'm pretty sure it was a Nautique) that he and anyone in the club had an open invitation for a pull up here and no-one has taken me up on it yet......

Gordon,

Please check your Private Message Inbox.

Tom T.

lewy2001 wrote: So when the power is reapplied to the solenoid on restart it fails to operate. The more you turn the engine over without it starting the more fuel that will be dumped into the cylinders. This is why it exhibits a very flooded condition on restart and requires the full open throttle to restart.

Just a quick thought. If the idle speed solenoid is failing to open upon hot start and therefore little air is getting mixed with the fuel, if you cracked the throttle slightly to let air in, then it should start rather than just dumping fuel into the cylinders with no start (it would just immediately start racing). Just wanted to check to see that it is not starting when you crack the throttle (at the start, not when it is already "flooded"). If it start when the throttle is cracked open, then it is the solenoid (or something in the line (low voltage, etc.)). If it doesn't start if you crack the throttle at the beginning, then I don't think it is the idle valve solenoid.

Just a thought....