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-   -   gt40 surging (http://www.wakeworld.com/forum/showthread.php?t=794785)

maxx_wake 07-29-2012 8:31 PM

gt40 surging
The gt40 in my Supra is having an intermittent issue where as soon as it starts it will rev up to around 1500 rpm, then drop down to a few hundred rpm. It will cycle this pattern a couple of times and then it usually levels out and runs fine. It usually never happens on the first start of the day but only after it has been run for a little while and then shut off and allowed to sit for a few minutes. I have already replaced the low pressure fuel pump and both relays because I thought they were the problem but no luck. Any ideas?

boardman74 07-29-2012 8:51 PM

Where that is a computer controlled engine I would say you have a computer issue. When you cold start it the computer goes to full fuel similar to an automatic choke in a carb. But when the engine is warm the computer has to map for a warm start. I would say it's a temperature sensing issue since it starts fine cold but starts hard and "hunts" when it's started warm. I am not sure the name of the sensor, but if you call the dealer I am sure they can tell you. Sorry I don't know the correct terms but pretty sure thats could be the problem.

alcarlaw1 07-30-2012 7:00 AM


alcarlaw1 07-30-2012 7:03 AM

as above, try changing the Idle speed control valve, about $60 so worth changing to rule it out as it is difficult to diagnose a fault on it directly. BTW, I have the same problem and will change this valve before trying anything else...

maxx_wake 07-30-2012 7:24 AM

Wow, that thread on correctcraft fan has a ton of good info. It looks like next thing to try is the Idle Speed Control Valve. Thanks for the help!

alcarlaw1 07-30-2012 7:58 AM

no worries. I have a cold hunting problem, so I guess I'll start by swapping the two repays over in case one has gone bad. That said, I have ordered up a replacement ISCV just to rule this out.

dpauly84 07-30-2012 10:34 AM

If the Idle Air Control vale does not fix it, put a fuel pressure gauge on it. Your problems sound exactly like what I experienced last year with my GT40, and it ended up being the fuel pressure regulator. Just giving you some more ideas, in case the IAC doesn't fix it.

maxx_wake 07-30-2012 11:55 AM

Thanks Derek. Based on the info in the planetnautique thread it sounds like it could be a couple of different things that end up presenting the same symptoms. Just for reference I was having a similar issue with the boat a couple of years ago and one day it died and stranded me on the water. That turned out to be the low pressure fuel pump so when it started the surging/loping again earlier this year I figured it was the same issue so I replaced the pump again but no luck this time. I think for $60 I am gonna give the control valve a try and if that doesnt fix it I will move on to trying to catch it when it is surging and checkin gthe fuel pressure.

maxx_wake 08-27-2012 11:32 AM

Well, it wasnt the IACV. I replaced it a few weeks ago but I just managed to get the boat out on the water over the weekend so I figured I would update this thread. It actually did it bad enough this weekend that it died several times before I got it to level out. Back to the drawing board.

WakeDirt 08-30-2012 4:09 PM

What year is the motor?
Do you have the ProTec ignition?

maxx_wake 08-30-2012 6:39 PM

It is a 97. I am not sure on the ignition.

WakeDirt 08-31-2012 4:25 PM

well if you look at where all the spark wires join at a common location mounted to the block, and there is a piece that says Pro Tec, that may be your problem. I had to replace mine to a Mallory ignition and it fixed everything

dpauly84 08-31-2012 6:14 PM

This still sounds like the exact same thing mine was doing. If you don't have access to a fuel pressure gauge you can unplug the vacuum line that goes to it, and put a bolt in the vacuum line, so you don't have a vacuum leak. This will put your fuel pressure at max. Try this after it has been acting up and see if it stops. The regulator is on the right rear of the motor and has a single vacuum hose that goes to the intake. You should have a lower PSI at idle because that is when you have the most vacuum. Under load or at high RPM's you have less vacuum, and this causes the regulator to bump up the fuel pressure. With the hose unhooked, you will have no vacuum and max fuel psi.

maxx_wake 09-01-2012 6:33 AM

I do have a fuel pressure gauge so that will be my next check. I don't know why I didn't check that first but oh well. I am traveling at the moment but I will check the ignition when I get back as well. Thanks for all of the suggestions so far.

WakeDirt 10-31-2012 1:08 PM

Ever get it fixed?

maxx_wake 10-31-2012 6:08 PM

Not sure. I went ahead and replaced the fuel pressure regulator but I haven't had a chance to get it out on the water since then. I am hopefully going to get out this weekend though so I will post back with an update.

maxx_wake 11-04-2012 7:17 PM

Got the boat out this weekend and it seamed like the fuel pressure regulator helped the issue. It felt like there was still a small hesitation once but overall it was much better than it was before.

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