94 Nautique - uncommanded limp mode

[bradb]

My 94 Nautique - 5.8LFord PCM - throttle body fuel injection is having problems going into limp mode, but nothing seems to be wrong. I warm the boat up well, and it usually happens on the first or second ski... I shut it off and start it up again and it usually runs fine for the rest of the day. Sometimes it will run fine for a week, and other times it will happen 3-4 times a day. The temp and oil pressure are fine. I've contacted my dealer who had the following suggestions:
1) Change the plugs/wires. Check for corrosion on the coil posts. Check for bad connection. Done...
2) Disconnect the temp/pressure sensors one at a time (keeping a careful eye on everything!). Done...(ie. I think the sending units are fine).
3) Replace a coil pack. Bought a new one, and tried it on both sides replacing one at a time. Didn't help.
Lastly, they suggested replacing the whole computer unit... It's a bit of a pricy item ($900CDN), so I'm a little reluctant, but I'd really like to get to the bottom of this annoying problem. Does this sound like the next logical step? Any other ideas?
Thanks for your help.
B

[skinautique]

Does it happen more on hot days? The boat could be vapor locking. Is it the pro ski engine? What exactly does it do and when? Loss of RPM's?

[bradb]

Temperature doesn't seem to be a factor... It does it all year, in all kinds of different conditions. I'd say most days we ski it's only around 15 - 20 degrees celcius. It's the Pro-boss engine. It goes into what the manual describes as limp mode... Ie anything over 2400 RPM and the engine shakes and backfires... It's to let you know somthing is wrong... It runs fine under 2400. I believe it somehow changes the engine timing to run rough... The pressure and temperature sensors go into the computer, and if anything is wrong (too high temp, or too low oil pressure) it kicks into limp mode. I'm not sure exactly how it works.
There is a spacer block between the computer and the coil packs which are meant to stop the coil packs from heating up too much and shorting out or somthing... That's about all I know.
Thanks,
B

[skinautique]

I don't know what to tell you short of taking it to a dealer to troubleshoot. Good luck and let me know what it is/was.

[lawrence]

My '91 did that last year because of a bad temperature sensor. It is debuggable while it's happening, but no otherwise. The next time it happens, open the cover and remove the wire from the temperature sensor, and if it runs fine, you need to replace the sensor (or maybe the connections are corroded or loose). If that's not it, then try the oil pressure sender. If that is still not it, I fear that you need a new computer...

[bradb]

I've had both the temperature sensor and the oil pressure sensor disconnected and it has still had this problem... I'm not looking forward to getting a new computer, (especially without knowing for 100% sure that it will correct the problem...) Is there anything else that it could possibly be?
Thanks for the help,
B

[lawrence]

As far as I know, the only two triggers for limp mode are low oil pressure and high temperature. It's possible that if the system voltage is too high or too low, it could happen, but otherwise, it's new computer time.

[SolidCitizen]

Hi Brad, did you ever get your problem resolved? I'm curious about your solution because my '94 ski open bow (5.8 PCM EFI) is running pretty rich...the plugs became greasy black and there's continuous blue/black smoke when on throttle. I'm thinking my problem is a faulty MAP sensor.

[nms1991]

the ignition module is going bad it is under the coil packs make sure the new one is a sheilded module when you buy the new one. The sheilded version has the coil packs on top then the sheilded part of the module then the ignition module it self.

[nms1991]

SolidCitizen check your temp you are running at it should be 160 degrees. But if you suspect it is a bad map sensor you can get one from Napa for a TBI chevrolet truck because it is a standard map sensor from GM. You also may want to check your fuel pressure it should be 14 to 17 psi.

[bradb]

SolidCitizen,
I changed he computer, and I thought it was fixed! It ran for about a month with no probs.
BUT... It has since gone into limp mode twice since. I use the boat every day all summer, and it's behaving MUCH better than last year (last year, it would do it every second time out). It is such an intermidant problem, I'm at a bit of a loss as to what to do... (so is my local dealer!)
B

[SolidCitizen]

Brad, sorry to hear the new ECU didn't fix it 100%. I think nms's comment about the ignition module was towards you.

nms, thanks for the suggestions. I will check the fuel pressure. I've never noticed temps rising above normal, and it runs rich even before running it hard.

The PCM engine is a Ford...does it really use a GM throttle body?

[nms1991]

SolidCitizen what I ment is if the engine does not reach proper temp (too cold) the computeer stays in warm up mode, running rich and faster than normal idle. The posible problem is it could be debris in the thermostat keeping the thermostat cracked open. But if you are running at 160 degrees it could be high fuel pressure. No it is not a GM throttle body the system uses GM sensors, the tbi unit is a Holley unit. But if you have to take into a dealer there was a PCM service bulliten in 94 or 95 about adjusting the TBI unit.

[SolidCitizen]

Nms, its definitely rich-smelling even after a long warmup. I'll look into a possible stuck thermostat. Last Friday I changed the fuel filter and was looking over the throttle body and noticed it indeed uses GM parts. Thanks for all the info! I'll probably have at a dealer soon and I'll mention the service bulletin. I also noticed what could be blue-ish smoke coming out of the exhaust (it was hard to tell if it was blue or black) while I was fake-a-laking. If I'm burning oil, I guess the fuel smell could be from blow-by. I hope its not that, especially since the boat has less than 200 hrs.

[patpend]

I had the same inadvertant limp problem on my '92 sn. I first cleaned all the high voltage coil wires. Problem went away. Came back a year later. Unhooked the temp sensor. Problem went away. Came back again. Went back and recleaned the coil wires. Problem gone. Any arcing at the coil connections confuses the computer via stray EMF.