HELP 99 SAN limp mode and surges at idle

[99SAN]

Ok, here is the story. I purchased the boat 2 years ago with blown head gaskets. Removed engine and was going to put a reman back in but for the same price I went with all aftermarket piston, rings, cam, bearing the whole 9 yards and let a local performance engine builder build it for longevity. This was spring 11 when I put the motor back in. (I'm a pwc mechanic so most of the stuff I can do) After installing the motor it wouldn't run, found the fuel pump relay was bad and the ecm wasn' getting power. I fixed those problems and the engine ran. Now that the engine runs it would run but die after 20 seconds. Found a plug wire was backwards. That was all last year and it wasn't running properly then. It will start and idle but surges at idle from 500-1000 rpm and when I try to rev it up it will not rev past 2000 like it is in limp mode. I took it to a local boat mechanic and he said he fixed it but I couldn't get a straight answer to what the problem was ,he said that he couldn't get the computer to hook up to the boat. Now my question is how do I check to see why its in limp mode and what kind of computer do i need to read all the faults. In the pwc world, we have a computer that reads all the sensors while its running. Any help will be greatly appreciated. 2 years owning the boat and its never been to the water.... Im in birmingham,al and if you know of a "nautique" mechanic close i will take it to them. Im desprite right now... thanks

[Double D]

Sounds like what mine was doing and mine was an injector driver on the ECM so my two injectors are sharing a driver. I dont understand why he wouldn't tell you what fixed it......


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[99SAN]

well I think he wouldn't tell me becuse he didn't fix anything, he said I had a 2 plug wires backwards but said that wouldn't matter.... how did you make 2 injectors share a driver?

[Double D]

well I think he wouldn't tell me becuse he didn't fix anything, he said I had a 2 plug wires backwards but said that wouldn't matter.... how did you make 2 injectors share a driver?

Since I didn't do that part of the work, I'm pretty sure my dealer wired them to the same location at the ECM. Im told the ECM is meant to drive a 4 barrel throttle body and mine was only two.

The way we determined it was a bad driver was we could see the gas spray sputter at the one injector when it was pulsing. We switched the wires and the other injector did it, which pointed back to the ECM.


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[99SAN]

how do i check for codes manually?

[AirTool]

how do i check for codes manually?

There is a fairly dumb tool out there that is rare to find, maybe expensive, and generally not very helpful (so people say). I think it would be helpful IMO.

I think I have seen them on ebay but right now can't remember the name of it. I'm sure you can find it.

Also, (i believe on this site) are several nice documents about the ford engines including ignition, wiring, and limp mode. The tester should be mentioned in the ignition book.

[Nautiques_NZ]

Any Ford car dealer that has been around since the early 90's should have the unit needed for diagnostics, Same gear as used in 5.0/5.8 Mustangs from the 90's. Just got to find a tech who has been around long enough to know how to use it!

[99SAN]

I downloaded the complete manual last year but it doesn't say anything about self diag mode., do you plug the computer in on front of the engine in. the square triangle plug?

[crobi2]

A '99 SAN is a great boat, congrats on getting her, hopefully you'll be on the water soon.

Couple of things I can think of right off:

First, I am assuming this is the GT40 motor.

Is the big red light on the dash on? This is the one that lights up for limp mode.

The surge at idle can sometimes be caused by a dirty/stuck idle air controller.

To retrieve the computer codes you can try to get an old STAR tester off ebay, or you can buy an equus 3145 from Amazon for $25. There's only a few codes that the computer will throw out by the way. The ECM is the EEC-IV just like someone said that is found on old ford mustangs etc. It's a great ECM and has been somewhat modified by PCM for boating (no oxygen sensor, etc).

Why did the engine have blown head gaskets?

Last, but probably first, since the engine is running, you might want to get a fuel pressure gauge and hook it to the schrader valve on the fuel rail. If your boat has the FCC (fuel control cell) the filter could be clogged from sitting, there could be a hose defect inside the canister, or the low pressure or the high pressure pumps could be having problems. A gauge with a schrader hookup will set you back about $30.

Good luck, keep us informed!

EDIT: yes, sorry - it's the triangle shaped plug.

[99SAN]

Thanks sure the reply, I changed the fuel filters and thee pressure is 40-50lbs seems like a usher air control valve and yes the red light is on, is there anyway to temporarily disconnect thee limp mode sensors , thanks

[Chexi]

Where do you plug the equus tester in. I can't find a plug that would mate with it.

[AirTool]

Thanks sure the reply, I changed the fuel filters and thee pressure is 40-50lbs seems like a usher air control valve and yes the red light is on, is there anyway to temporarily disconnect thee limp mode sensors , thanks

There are only two limp mode senders: Oil Pressure and Coolant temp ...these two should be separate from the sensor/sender that communicate with your dashboard. PSL (pressure safety low) are normally closed so you would disconnect that one -> oil pressure. TSH (temperature safety high) are normally open so just disconnect the lead. Before you disconnect the coolant, let me know if it has two wires or one wire.


I'm 99% sure limp mode will not throw the MIL light on or set a code. If there is anyway possible you can get it up to cruising speed, you are not in limp mode.

I'm pretty sure neither of these switches are your problem.

[AirTool]

There are only two limp mode senders: Oil Pressure and Coolant temp ...these two should be separate from the sensor/sender that communicate with your dashboard. PSL (pressure safety low) are normally closed so you would disconnect that one -> oil pressure. TSH (temperature safety high) are normally open so just disconnect the lead. Before you disconnect the coolant, let me know if it has two wires or one wire
I'm 99% sure limp mode will not throw the MIL light on or set a code. If there is anyway possible you can get it up to cruising speed, you are not in limp mode.

I'm pretty sure neither of these switches are your problem.

Adding more detail:

There are only two limp mode senders: Oil Pressure and Coolant temp ...these two should be separate from the sensor/sender that communicate with your dashboard. PSL (pressure safety low) are normally closed so you would disconnect that one -> oil pressure. TSH (temperature safety high) are normally open so just disconnect the lead. If your coolant sensor has two wires, look for the other one. You may actually have three total for the coolant. One switch for the ECM, one sender for the ECM, and one sender for the dash if you have a temp gauge. Only the one wire temp switch initiates limp mode.

The oil and temp switches should have a tan/black wire....they are in the same loop - grounding the lead sets off limp.

I'm 99% sure limp mode will not throw the MIL light on or set a code. If there is anyway possible you can get it up to cruising speed, you are not in limp mode. Limp rev limit is 2700 rpm.

I'm pretty sure neither of these switches are your problem.

[AirTool]

Where do you plug the equus tester in. I can't find a plug that would mate with it.

To connect a tester - there are two plugs coming from the ECM harness: 1) a 4x2 prong connector and 2) a single wire connector

The 4x2 plug has the following wire colors: pink/green, blue/orange, purple/black, and gray/red

The 1 wire connector has a white/purple wire.

Maybe you need to build a crossover lead to get you from equus to STAR.

[99SAN]

if the light is on and it's in limp mode why wouldn't one of the two sensors cause this? The rough idle i can deal with but the limp home I have to look into, friend has a dd gt40 and I spoke to him today and he said his has a irratic idle and has been riding for 2 seasons, just worried about the limp home mode