GT40 takes longer to start when warm

lewy2001 wrote: Fuel pressure is the best place to start after you have confirmed spark. One quick simple check is can you hear the fuel pumps prime when you turn the key to on position before you crank the engine. Adding a fuel pressure gauge to GT40 tool kit is the best $45 you will spend

Got one Friday.

Ok fellas. Here’s the fuel pressure test results.

Key on engine off: I charged the pumps and they started at 26. Five min later, 22. I didn’t wait any longer.


Key in engine running 32. 2000 rpm’s 31. Cut it off and it stayed 32. After 5 minutes she dropped to 28. After 5 more minutes 25

The high pressure fuel pump is brand new as well as the fuel filter in the FCC. Additionally, after i let it set for 20 minutes with the key on engine off, It wouldn’t start afterwards. I had to go wide open throttle and it fired. I guess it was flooded.

So thoughts? My reason for the test in the first place was long starts when the motor is warm. It has never failed to start on the water but a 5 second start was common every time after I cut the boat off.

I have not replaced the low pressure pump or the fuel pressure regulator or the injectors but those are coming. Boat is 20 years old. 604 hours.

Thanks for any input in advance.

I was going over page 41 of the GT40 manual and it said 31 + or - 3 was the standard. Shouldn’t the pressure be holding anyhow? Regardless of the standard I’m not sure if pressures supposed to drop after killing then engine or not ?

gun-driver wrote: Follow this link to the reference section and read starting on page 2B-2 it will explain how the fuel pumps and injectors work. Then you can test it properly and report back. Should be 39 +/- 3 when you first turn the key to on, LP should run for approx 2 seconds to prime HP canister. It should hold the 39 psi thru cranking. At idle (not 2000rpm) it should drop to 31 +/- 3 Page 3H-2 is the trouble shooting for the leak down test You will need to jump the fuel pumps for this test but rule of thumb is rail should hold pressure within 3psi for 3 minutes. http://www.correctcraftfan.com/Downloads/Pro_BOss_GT-40_Service_Manual.pdf

Ok I read it. It said if low goto 3H-12 and there wasn’t one lol. Regardless, I ordered a regulator last night and in the morning, I may go Ahead and get the LP pump and maybe even injectors with adapters. That will be about the entire fuel system lol but I don’t wanna be towed so.

gun-driver wrote: Before I went through all the work of changing injectors I would make sure that’s the problem. And the 3H-12 is there its all the way at the end of the manual. Keep scrolling

Ok lol

Might be a silly question on my part but if the boat runs great all day, only acts up when it's been off for a while why do you think the LP fuel pump is causing this?

C_Heath wrote: KENO wrote: Might be a silly question on my part but if the boat runs great all day, only acts up when it's been off for a while why do you think the LP fuel pump is causing this? one of the pinpoint tests referred to (replace LP pump) I think twice, I also think one or some of the injectors are leaking after shut down. Im a newbie tho.

That wasn't just for you, but for anybody who's been suggesting the pump

Now things that you know from the manual are that it should have

39+ or- 3 psi KOEO

31 + or- 3 psi at idle

When testing, the pressure drop should be no more than 3 psi in 3 minutes.

Due to the regulator it will run somewhere between the nominal 31 and 39 mentioned above while running around on the lake depending on engine load. The load affects vacuum, which is sensed by the regulator. This lets it maintain the proper pressure to maintain the same differential pressure across the injectors.

At full throttle there's basically no vacuum in the engine and your pressure would be around 39 psi

Why not hook up the gauge and take the boat for a ride making a note of how it starts cold and what the pressure was at KOEO and then again when idling.

Then drive it a while, park for your normal amount of time and watch the gauge to see what it is just before you're turning the key again and when starting

That's just for some real world numbers and info to go along with the manual test sections.

gun-driver wrote: I agree with Keno If it runs fine at WOT it’s getting enough fuel. I think your problem is either the regulator, timing, or a leaking injector. But first we need some accurate fuel pressure numbers.

Surely will do. Thanks.

gun-driver wrote: I agree with Keno If it runs fine at WOT it’s getting enough fuel. I think your problem is either the regulator, timing, or a leaking injector. But first we need some accurate fuel pressure numbers.

Thanks gun,

Based on my experience, I’ll chime in on KENO’s question above regarding why a LP pump would cause an issue only after warm and sitting for a while.

Last fall I fought an issue whereby the boat would startup perfectly fine cold every time. After a good long run and then shutting down and sitting for a while, the boat would actually start up but then die about 1 minute later and I could not get it to start back up until sitting for maybe an hour longer. With key on, engine off I could hear both pumps prime, so initially didn’t think there was anything wrong with either.

Long story short, after fiddling around and hooking up a fuel pressure gauge, I found that when he boat wouldn’t start I was getting zero fuel pressure and when I pulled off the output hose from the LP pump, nothing was coming out. I guess once it had a chance to cool off by sitting it would start working again. I replaced the LP pump and have had no issues since.

So, while this isn’t exactly the same scenario the OP is having, the moral of the story is these LP pumps are strange birds. You might hear one power up, but that doesn’t mean it’s pumping fuel.

cboland wrote: Based on my experience, I’ll chime in on KENO’s question above regarding why a LP pump would cause an issue only after warm and sitting for a while. Last fall I fought an issue whereby the boat would startup perfectly fine cold every time. After a good long run and then shutting down and sitting for a while, the boat would actually start up but then die about 1 minute later and I could not get it to start back up until sitting for maybe an hour longer. With key on, engine off I could hear both pumps prime, so initially didn’t think there was anything wrong with either. Long story short, after fiddling around and hooking up a fuel pressure gauge, I found that when he boat wouldn’t start I was getting zero fuel pressure and when I pulled off the output hose from the LP pump, nothing was coming out. I guess once it had a chance to cool off by sitting it would start working again. I replaced the LP pump and have had no issues since. So, while this isn’t exactly the same scenario the OP is having, the moral of the story is these LP pumps are strange birds. You might hear one power up, but that doesn’t mean it’s pumping fuel.

Maybe you should update that thread from last year, here'a a link to it

Skip the part about pulling Pete around on a tube in a bikini though

link

cboland wrote: Ha. Thanks for the reminder. I’ll do it now. I’d still be interested in seeing what some of our photoshop folks can do with Pete in a bikini on a tube.

Sounds like the challenge is on

You have great advice above. You don't have any leaking injectors or your fuel pressure would fall off quickly. Yours does not it holds just like it should and you are in good shape as far as pressure bleed.

Leave your pressure gauge hooked up and verify you have full pressure when you try to start your engine hot after sitting.   If it still does not start promptly and you have 38-39 PSI you can rule out fuel supply as your issue. You can also rule out flooding due to injector leaks.

Did you clean your mesh screen which functions like a air cleaner/filter and fire suppressor.
If this is dirty you may be running rich with a hot engine making for the hard warm start.
On cold start when checking pressure I usually turn the key on 3 seconds, then off, then on again to see what pressure the pump is offering.   Sometimes one turn of the key does not hit max pressure.
Maybe your pressure relief valve is not working all the time and on your warm starts you are not getting the full 39 PSI. This was mentioned earlier in your thread but I am not sure it was actually checked.

I just read your thread and it sounds to me like you have a good fuel system supply and great advice already.   

Pretty bored here so will do some kibitizing

Any possibility that the cold-start F/A ratio could be happening during hot start?

If so, maybe a temp sensor, wire, or even controller could be at fault.

Quick dirty fix for the LP pump issue: pull the lid, rotate the vanes and reassemble. Dit it with ours and fixed it for maybe another 10+ years?

MrMcD wrote: You have great advice above. You don't have any leaking injectors or your fuel pressure would fall off quickly. Yours does not it holds just like it should and you are in good shape as far as pressure bleed. Leave your pressure gauge hooked up and verify you have full pressure when you try to start your engine hot after sitting.   If it still does not start promptly and you have 38-39 PSI you can rule out fuel supply as your issue. You can also rule out flooding due to injector leaks. Did you clean your mesh screen which functions like a air cleaner/filter and fire suppressor. If this is dirty you may be running rich with a hot engine making for the hard warm start. On cold start when checking pressure I usually turn the key on 3 seconds, then off, then on again to see what pressure the pump is offering.   Sometimes one turn of the key does not hit max pressure. Maybe your pressure relief valve is not working all the time and on your warm starts you are not getting the full 39 PSI. This was mentioned earlier in your thread but I am not sure it was actually checked. I just read your thread and it sounds to me like you have a good fuel system supply and great advice already.

just went ahead and ordered a new LP pump. Thanks