Rough Idle/Stall after use

1997 GT40 EFI
I just had a rough idle problem - preceded by often running rich, smelly exhaust. Engine hot was worse. Running full speed pulling skiers not a problem except (come to think of it) we were getting the odd malfunction both Perfect Pass and our iSki box (RPM processor) was having issues too every now and then.

It really felt like a compromised ignition issue but the plugs, wires, cap and rotor were all done last year. No codes (there never is!)

> I got a new MAP sensor and absolutely no change.

Then I looked at my rusty distributor and pulled out it. The Hall sensor pickup was loose, clacking against the toothed ring, and it was all getting quite chewed up.

> Replaced the distributor solved the issue(s). $125 rebuilt. Runs great. I forgot to mark things but easily found TDC. Got my timing light, pulled the SPROUT plug out (by the oil cap) and set it to 5 Deg BTDC.

I would say that to avoid problems the distributor should be replaced at the 1000 hr or so mark. According to a Ford forum I read the TFI is also a module that has about the same lifespan.

My GT-40 is on a 97 Ski Nautique, yours being a 99 I think the electronics are pretty much the same. That being said, the ECM does not store engine fault codes for anything other than the secondary ignition stuff, which basically means the sensors like knock, MAP, temp etc. These all give feedback to the engine that the computer uses to create the ideal fuel/air mix. The primary stuff like fuel pressure and ignition timing and components is not captured, so if your relays fail a code will not be stored.

I'm pretty sure you should see good pressure (can't remember the value but check the service manual) when you do a key on engine off test. As well your pressure should be good no matter whether the engine is idling or at full throttle. The buzzing you hear is likely the low pressure fuel pump, you can put your hand on it when you turn the key and you'll feel it vibrate. The high pressure pump should also come on, but it's harder to hear as it's inside the fuel cell. One easy test I did previously is to turn the key from off to on and back 20 times in a row and check that you hear the pump every time. If it misses even once then it's failing and is probably the relay. If the pump comes on but your pressure is low, it could be the high pressure pump is not working or the low pressure pump just isn't pumping any fuel. I have seen a few posts that hinted to that. One thing you could also try is to remove the fuel outlet hose from the fuel cell that connects to the low pressure pump. Run this into a container of some sort and then do your key on engine off test and see how much fuel flow the pump is generating. It should be pretty solid as its job is to keep the fuel cell full. If it isn't, you could have a blockage in your fuel line somewhere or the pump could just be shot. I don't think they are too expensive so if there is any question then you can replace it.

I'm no mechanic but have learned all this stuff as problems have come up over the years, plus my nearest dealer is a bit of trip away. If you've got a good dealer near you then that's always an option for you. I'd say you should definitely make sure you've got a working fuel pressure tester :)

Let us know how you go.

Pete

NautiBrophy wrote: So it dies at high rpms as well. So I did a fuel pressure test after it died and wasn't getting any fuel pressure to the engine. It would sit for 30 mins then the pressure would rise and it would start up again. My question is now: Would the map sensor trip this not allowing fuel to the engine? Or would this be a fuel pump / fuel pump relay issue? Any thoughts? Thanks everyone I really appreciate your help.... what a mess of a memorial day weekend :/

When I was troubleshooting my issues, I never had any problems with the boat running at speed, only idle after sitting warm for a while so it sounds like your issue is different. I also did a fuel pressure test before going to the MAP sensor and discovered my pressure was fine, so if yours isn't then you should definitely look at that problem. There are 2 fuel pumps on the GT-40, the low pressure one which you can see underneath the fuel cell and the high pressure pump which is inside the fuel cell. Either could be bad, but from what I've read on other posts it is more common for the low pressure pump to fail. A good place to start are the 2 relays on the back of the engine, one of these directly controls the low pressure pump and I had past issues of losing pressure at speed and it turned out to be a bad relay. One way to tell is that you should always hear the low pressure fuel pump spin for a second when you turn the key from stop to run, so try this after you get a failure at speed and if you don't hear it, it may not be getting power. These relays are cheap so you can just replace them without too much worry.

Regarding the MAP sensor, I determined this was faulty by reading the engine codes using a multimeter. It was the only code I was presented so it was reasonably easy to read. Other than that I don't know how you actually test a MAP sensor, but I'm sure it's possible.

Let me know if you need instructions on how to get the codes out without a code reader, I believe I still have the document or a link to it. I wasn't able to buy one in Australia so had to find another way :)

Pete

So it dies at high rpms as well. So I did a fuel pressure test after it died and wasn't getting any fuel pressure to the engine. It would sit for 30 mins then the pressure would rise and it would start up again. My question is now: Would the map sensor trip this not allowing fuel to the engine? Or would this be a fuel pump / fuel pump relay issue? Any thoughts? Thanks everyone I really appreciate your help.... what a mess of a memorial day weekend :/

Brophy, it looks like this.

http://www.partsgeek.com/catalog/1987/ford/mustang/fuel_injection/map_sensor.html
On a car it's on the firewall, but exactly where on a PCM I don't know. I would assume attached to a bracket on the motor.

I am aware of MAP sensors on EFI SBF's doing this, I don't see why a gt40 boat motor would be any different. It is pretty much all ford's efi tech.

Hi Jerry,

I'm pretty sure it is a normal Ford part and not PCM specific as I was able to track one on eBay here in Australia using the part numbers printed on the sensor itself. I did enquire at SkiDim as to the cost of a new one and they said it was approx $170USD.

Pete

Had the boat out yesterday and the long rolling starts and poor idling seem to have gone away. Each start was strong and there was no rough idling or any smell of excess fuel. Looks like the MAP sensor was the culprit! Glad to have it fixed :)

benwa43 wrote: I have a 2002 196, gt-40......

No points to check in that engine....

Updating status, it's not a fuel pressure issue. Pressure was constant and as it should be.

I managed to find a MAP sensor locally for a really good price and have installed it. Testing while running on the hose and the engine no longer started rough, however next time out in real load conditions will obviously be a better test.

Pete

I had a look at the vacuum lines, but I will have a more thorough look again for any cracks or bad seals. I know it isn't clogged as I can blow into the tube at the sensor end.

Perhaps you can tell me what this is (see pic), the hose from the MAP sensor goes directly into this white canister and then into the manifold. Is it a filter? If so I would think it can be serviced or cleaned?

Haven't had the boat out yet to do a fuel pressure test during a bad start, but did do a bit of troubleshooting today. I did a KOEO test and it indicated that the MAP sensor had a hard fault. I tested the wires from the ECU to the MAP sensor connector and they are OK, so it looks like I need a MAP sensor. From what I can find in the service manual, this might explain the intermittent rough starts and poor idling when the engine is hot. I do not have any specialty tools to actually test the MAP sensor itself, but since the connections look good and the vacuum hoses also look fine with no kinks, the sensor seems like the most likely culprit. Couldn't find this part listed on SkiDim or White Lake sites so I don't know how much a new one will cost, but will try some local automotive places.

Pete

Pete - Those are great questions. This might be a case where it may be justified to take it to someone who knows those answers. The shop rate you would pay is justified in the knowledge they bring to the job.

JMO

Maybe it is a fuel injector that leaks when it is hot.

Any luck diagnosing this problem? I'm still experiencing the same symptoms and I'm not any closer to a solution. I'm afraid I'll have to take it in to my local certified PCM service center - which is 100+ miles away.

I have a friend that has a 1999 air nautique and is having the same problem and he has no idea what's wrong. He goes out skiing or wakeboarding for an hour or two shuts it down and then starts it back up and attempts to plane the boat out it stalls and dies. Please let me know if you ever figure out this problem.