99 GT-40 TPS settings question

[vortech347]

I have a 99 Sport Nautique with GT-40 engine. Bought it new and from day one it has hunted and died periodically when warmed up and at idle or just off idle.

I have done several things to try to alleviate it with no luck. I've changed the IAC motor and the fuel pressure regulator and tried adjusting the TPS.

I have checked the tps to make sure it works properly and it does. But I have a question regarding the voltage setting vs. throttle position.

In the GT-40 service manual it shows the voltage at 0% throttle should be .50 volts. When I tested it with the key on and the throttle in the neutral position at .79 volts.

The thing that I'm not positive about is what throttle setting is it in really when in the neutral position. Is the manual assuming that is 0% or is it really something close to 10%. I tried raising the voltage up to .90 volts in the neutral position and the boat hunted and died even worse on the water and was harder to start as well. It would take considerable cranking time for it to start when warm.

Obviously, logic says raising the voltage at idle on the tps was the wrong way to go and I'm going to try it at .50 next time out but I was wondering if anyone on here had experienced this or tested the TPS on their GT-40 engines in the same manner.

Do any of you have your boat handy where you could test that and report back?

The colors on my tps are different that described in the manual. I assume that is due to the year model difference and Ford changed the wiring colors somewhere along the lines. But if someone could test the voltage with the throttle in neutral and the key set to run I would appreciate it.

It's been 8 years now doing this and if I could figure it out I would be ecstatic. It's pretty nerve racking idling up to shore or a dock wondering if the engine is going to die right when I need reverse to keep from hitting anything.

Thanks,

Greg

[dwsa]

RE: 99 GT-40 TPS settings question

Hi Greg,

I have a GT40 in my 2001 SN, I also have the same idle surge and today was checking the TPS, the minimum voltage on the TPS is about 0.8 volts that was with the TPS removed. There seems to be little if any adjustment on the TPS, other than adjusting the throttle stop screw. I set the throttle stop to minimum using a paper feeler gage so the the butterfly just touched it, then remounted the TPS and got 0.9 volts. I also read on a mustang website to set the TPS at .98 to .99 volts, will retry this. My idle is better, but not tested on the water yet. Hope this helps... Cheers Greg in Dubai

[vortech347]

RE: 99 GT-40 TPS settings question

dwsa,

I have had it looked at by my dealer now and after making some changes to the TPS setting and throttle stop it is idling better. But we lake tested the boat again after getting it back and after 30 minutes the surging problem came back.

I met the service tech at the dealer and we took it to the lake to do a lake test with the technician present since they could not get it to surge again after the initial fix in their test tank. After about 50 minutes of driving around the lake it did it again. The tech observed the condition and agreed with me that he thinks a sensor is failing intermittently and probably has to heat up to a point of failure before it starts the problem. Using a laser temp sensor he confirmed the boat was not overheating. It stays under 180 all the time on the gauge and usually stays close to 160.

He mentioned that over time raw water pumps can begin to leak air around their drive shaft which will introduce some air into the cooling water which can cause the boat to overheat. It appears mine is okay but it does fluctuate about 10-20 degrees and I have a new impeller and a new 160 degree thermostat.

He mentioned that since the ECM fueling tables are designed around a 160 degree operating temp that it can be an issue but he did not think that was the cause of my problem.

One other thing he tested was to disconnect the MAP sensor. As soon as he did that the engine ran better and surged about 100 rpm up and down consistently between 700-800rpm. As soon as he plugged the sensor back in the problem came back. The thing is once the problem shows up the boat runs poorly at idle and part throttle applications so he thinks it's not an idle circuit problem.

I left the boat with the dealer so he could do some additional testing and get to the bottom of the problem. Mine and his suspicion is the MAP sensor goes bad when it heats up but there could be other issues as well so he wanted to test it thoroughly before giving the boat back.

The dealer has done some things in the past that were subpar regarding service, especially when the boat was still under warranty. They have basically cleaned house of all the management that was around back then and the new service manager is making every effort to make things right. So hopefully, after 8 years of frustration this problem will be fixed once and for all and my next boat will be another Nautique instead of another brand.

[vortech347]

It was the ECM all along

So the tech figures out the problem. With the engine running he could tap the ecm and it would make the problem start or stop by doing so.

The service manager talked to PCM to confirm the diagnosis and they concurred that the ecm needed to be replaced. The service manager also asked for some compensation on my behalf since this has been a problem from day one for my boat. PCM agreed to sell the ecm at 50% of retail which is $300 vs. $600.

The dealer is only charging me for one total hour since they have 1.5 hours into the diagnosis and will charge .5 hour labor to install the ecm. So they basically are charging me half as well.

I'm already one hour at $95 per out for diagnosis so I will ultimately be out $500 for this fix.

It's a compromise that I am okay with considering the age of the boat. I just wish they had been better at diagnosing the problem when it was under warranty.

At this point in time I will be very happy to have my boat run properly so we can enjoy it more.

[dwsa]

RE: It was the ECM all along

Maybe you should first check the connector to the ECM, electronic do not respond to tapping, it's the connections. Make sure you get your old ECM back or they may well flog it to someone else.

[vortech347]

There is probably a core charge

My guess is there may be a core charge which would negate being able to keep the part. If not, I definitely plan to keep it and will be lake testing the boat again to make sure this fixes the problem once and for all.

[vortech347]

7 months later report.

So we were very late this year going to the lake but we finally tested the boat on 2 separate occasions with the new ECM.

So far the boat has run flawlessly. It appears that was the culprit all along.

I am kicking myself for not taking the boat in to the dealer more regularly when it was under warranty so I wouldn't have to pay out of my pocket to fix something that was defective from the get go.

But the dealer made efforts to help and the boat runs like it's brand new after 8 years of not running that way.

For anyone that might have a surging problem have the dealer check the ECM.