99 SN GT40 Fuel Supply

SkiDim sells the engine computer. It's ~600.00 IIRC.

AMB wrote: The second video was without jumpered STO, just running on pumps like normal.   I didn't video the jumpered STO. But a few days ago, I jumpered the STO after the pumps wouldn't prime, and the motor died, and it would not start, with pressure on 40. It's back up the chain a ways. This is confirmation of the engine missing and eventually dieing when the STO was jumpered again. So gas is present, but no spark.. I think it might have been when the battery went dead, not sure. One thing though, as the gas pressure was maintained, I didn't notice the loud hissing noise. I am wondering if that is a vacume noise when injectors don't have sufficient fuel?

Well, this is interesting. With the pumps jumped (and no way they go off), you don't get the hissing sound, you get pressure without any dropping of the PSI (confirmed with the schrader valve out). You don't get loping, but you get rough idle, stalling, hard starts.

So ignition, or a sensor issue that is causing not only ignition issues, but possibly also causing the injectors to misfire?

You could put a timing light on it when it is not starting and see where your timing is (and confirm spark). If your spark is way off, that is one indication. You could also pull the SPOUT connector off, which keeps the advance at 5 degrees BTDC and confirm it is there. The SPOUT connector is near the oil filler cap, and it looks like the extra connector by the STO connector. With the SPOUT connector connecting (with the engine running), the timing should be around 20 degrees (I think).

But probably best to follow the troubleshooting in the manual...... :-)

AMB wrote: I tested with the valve out of the Schrader. I could not remove the one in my gauge, but I blew air through it, so have to assume that air pressure was getting through it. \

Okay, so with the schrader valve out, you tested it (the second video you sent) and the pressure dropped to zero and the engine kept running, correct? Or are you saying that with the STO jumpered and the schrader valve out, you got continual pressure but it still died?

What about the hissing sound?

AMB wrote: With STO jumpered, I started the engine and let it idle. It didn't sound loopy, but I would say it sounded a little rougher than when it is running tip top. Just my ear telling me. As soon as I gave it a little gas, slowly trying to build rpm, it cutout, and I observerd no pressure drop on the gauge like I did before. It was hard to restart, acting like it was flooded, but it did start and the same happened again; missing and sputterring and then cutting out. All the while, the gauge reading about 37 psi on the gauge. This sort of confirms my suspicion that a fuel and ignition problem is happening, simultaneously, right?

Mark (Lewy), PIP is the Profile Ignition Pickup, correct? Is that similar to CPS (crankshaft position sensor)? Either way, it does sound like it could be that; the engine thinks it's off, so opens the pump relay circuit. Also, if it the PIP/CPS is reading wrong, that will mess up timing, etc.,

AMB wrote: I also ordered a Code reader, pre-post of how to make a homemade one. Should have tomorrow. Do I just plug into the STO, turn ignition on? Let me know how to use. Thanks.

If it is the same one I got from Amazon (that Mark recommended), it's really easy. Follow the instructions; you'll need to plug in both the STO and the other loose connector. Easy to pull the codes (and at $25, easier than jumping with a test light or analog meter (haven't had an analog meter in years anyway, but glad to get the info on how to do it)).

AMB wrote: Any test for the PIP? If it is an ECM pin 52 error, I suppose that means I need a new ECM? Where is the best place to buy one of those? I don't even see it at the normal part places.

I don't know on either counts but I suspect there is a test or a way to check the PIP. I'll have to look, but Mark may already know.

On the ECM, I suspect you have to get that from CC or SKIDIM, etc., since it will have been custom programmed for marine applications. Maybe you can get it somewhere else, but you'd have to be able to get the FW (firmware) and somehow get it updated with the CC FW.

I tested with the valve out of the Schrader. I could not remove the one in my gauge, but I blew air through it, so have to assume that air pressure was getting through it.

With STO jumpered, I started the engine and let it idle. It didn't sound loopy, but I would say it sounded a little rougher than when it is running tip top. Just my ear telling me. As soon as I gave it a little gas, slowly trying to build rpm, it cutout, and I observerd no pressure drop on the gauge like I did before. It was hard to restart, acting like it was flooded, but it did start and the same happened again; missing and sputterring and then cutting out. All the while, the gauge reading about 37 psi on the gauge.

This sort of confirms my suspicion that a fuel and ignition problem is happening, simultaneously, right?

I didn't do the volume test, as the gauge while the pump was jumpered, measured a very steady pressure. Is this necessary at this time?

I also ordered a Code reader, pre-post of how to make a homemade one. Should have tomorrow. Do I just plug into the STO, turn ignition on? Let me know how to use. Thanks.

Any test for the PIP?

If it is an ECM pin 52 error, I suppose that means I need a new ECM? Where is the best place to buy one of those? I don't even see it at the normal part places.

Al yes still run the low pressure output test. Just so you can rule that out as a cause for your problem.

As slmskrs Gordon mentioned can you confirm if valve was removed from Schrader Valve body? When that pressure gauge went to zero.

You have confirmed that with the STO jumpered and engine off you can move, wiggle and jiggle wiring without stopping pumps. This confirms that the power side of the fuel pump circuit is fine. You also previously proved that the wiring from fuel pump relay to pin52 of ECA connector was good. So the problem must be the earth that the computer is supplying to the fuel pump relay from pin 52.

I think you may have done this before but do it again.
Start and run the engine with the STO connector still jumpered to earth. The pumps should continue to run and fuel pressure should remain at around 35psi at idle. If the engine continues to run correctly with correct fuel pressure it confirms that the earth on pin 52 from computer is the problem. So it is sounding like a ECM computer fault.

But there is one more issue and that is the PIP signal from distributor could be the problem and the computer is shutting down the pumps(by removing that ground on pin52) because it thinks that the engine has stopped.

The second problem you seemed to have developed where it will crank but not start even with 40 psi fuel pressure. This may also be related to the PIP sensor because it is the signal that not only tells the computer the engine is running but also generates the spark with the TFI unit and computer.

It would be nice to see if your computer has any stored codes for loss of PIP output.

Do the above tests and report back. It may be worthwhile purchasing that code reader that I linked to earlier in thread to help isolate the fault. It will most likely be cheaper than any other engine part you ever buy.

Yes when I jump the STO, the pump runs, pressure is at 40, not 35 as the video shows when the motor runs, and I wiggled every wire in site, along with the 2 negative grounds on the back of the block. I cannot get the pressure to change or pumps to not run when it is jumpered.

No I did not do the output test, my thinking was that my problem seems to be the pumps not running at all, not that they have variable output. When the pressure starts bouncing around and engine gasps. 9 out of 10 times when this happens and I turn the key back on, the pumps do NOT prime. Would the low pressure pump run randomly on / off or just have reduced output when going bad? My thought was that the pump motor would either run or not run, and when I jumper it, the pressure seems to stay up with no fluctuation, so I deduced that it is a ground or power wire shorting, or a switch/sensor or something not working properly. It was just my WAG while I had a couple hours to work on it today.

I did some research on the pump output test, and I see 10 seconds and 16 ounces, and 15 seconds and 1 quart. Not sure which one is correct, it would seem that if 10 seconds = 16 ouces, then 20 seconds would = 32 ouces or a quart.

I can do this test if you think a bad pump can run/prime intermittantly. I just thought the non-priming indicated something else was shorting out.

I don't know why both sides of the wiring on the low pressure pump were acting as though they were ground wires... that I am wondering about.

The low pressure pump has a red and a black wire on it, connected to green/yellow and a black wire, so I believe the postive is red and ground would be black.

Lewy, if reading these symptoms of the pumps not priming you feel that the pump test is still a go, I will check it this week.

and the other reason I didn't test volume was that when the engine stopped running, after the pressure bounced around, the pressure on the rail went up to 40 after I jumpered the STO, and the motor would not fire at all. It seemed like there was no spark, and the pressure gauge said there was 40 psi in the rail, so that to me meant there was gas present.

I put everything back together, after checking continuity of some of the items like relay to 60 pin, 60 and 40 pins to ground, etc., both relays are over 10 volts, etc..

Started it up and ran ok, but seemed to cut out as I was giving it a pump of gas..

First Test Run

Pumps were priming, etc. Then I ran again, primarily wiggling everything and when it cut out, the pumps were not priming at all. At the time, I was wiggling wires behind the 60 amp breaker. I think it was just coincidence, as I could not replicate. I could jump pump to STO and they would run and I could hear gas in the tank returning. You can hear the hissing sound again, and as far as I can tell, it is coming out of the air breather. After this stall, then engine would crank and no fire. I jumped the pump on STO and got the pressure up, but still no fire, not even a sputter. I jumped the kill switch, and no different. Seemed like the engine had no spark, the pressre on rail was 40. ?Let it set, changed out relays, and then pumps primed, but same result as video.

Test Run 2

I also changed the non-pump relay just for kicks, no difference.

I noticed two things, there was a platic plug on top of manifol in back that has a tube attached to it, this was out of the manifold, so I plugged back in, and no change. This is very easy to remove and I probably did this while wiggling wires.

Second, there was a wire connector that was not plugged together, I have no idea what it does or why it wasn't connected, I plugged it together and no change in performance. What is this?




I guess another thing, I unplugged the low pressure pump wires, and took apart the plug, and I tested for continuity to see which was ground, and they both act as if they are ground, meaning, the meter went to the right all the way, like it does when you complete a circuit. Shouldn't I have gotten volts on one and ground on another? I turned the key on, so should have had power, right?

Oh well, enough for today, I am still in a good mood.

I am 100% convinced that there is something that is cutting off power to the pumps on a random basis, and I also believe that power to the ignition system is also getting cutoff, to explain why the engine will not start when there is 40psi on the rail..

Now if I only had a clue what it could be!

It will not be simple to jumper the plugs from fuel pumps to direct +ve and earth as they have nice waterproof style connectors with the pins recessed behind housing. Would almost need the correct male or female connector to make sure of good contact.

HIGH PRESSURE PUMP CONNECTOR


It is a valid test but I would only contemplate after what we discussed previously.

lewy2001 wrote: With the STO jumper installed and fuel pressure gauge connected. (Without valve inside Schrader housing.) I do not trust the readings on your pressure gauge until you do that. The fuel pumps keep running while wiggling wiring loom, relay connectors and tapping circuit breaker terminals. And the fuel pressure stayed around 40psi. Correct??? This will confirm that pumps are running and there is fuel available in the rail. NOTE ENGINE OFF KEY ON. So you can hear pumps. If that was not clear.

and this also.......

lewy2001 wrote: Also check the output of low pressure pump as mentioned previously. This is achieved by disconnecting the high pressure pump electrical connections at FCC. Remove fuel hose from low pressure pump to FCC and place it in a container. Install the jumper to STO terminal it should pump about a US Quart in around 15-20 seconds.

AMB wrote: What color line is postive on the low pump? I imagine that getting that crossed wouldn't be a good idea! Thanks

I don't know without testing. Fastest way is to unplug the connector. Then with your multi-meter on Ohms, first make absolutely sure the power is off on the boat. Touch the two leads together to make sure you are getting zero or nearly zero resistance. Then put the one lead somewhere on the engine (ground), and the other lead to one of the connector pins from the relay. If it is zero or almost zero resistance, that is the ground side and the other side comes from the battery.

You can then see how the plug from the relay plugs into the plug to the pump, and therefore tell which side of the pump side plug needs to go to ground, and which side needs to go to the battery.

Here are some pics of the panel, Schrader, and my home made lake setup.
The STO and 60 PIN coupler are not in place.

What is the power assist relay? Sorry.

FYI, if the engine is off and the pumps go on and off (wiggling wires, etc.), the PSI is going to stay the same since the bleed down is slow. Pressure should never drop fast if the engine isn't running.

I havent checked the output of the low pressure pump. I think I should do that test outside the garage, and that won't happen tonight.
Mabye late Saturday or Sunday. I am tied up until then...

Should I try to start the engine and test the schrader pressure with the valve out or just jump the STO? When I jump the STO, with valve in, I see 40 psi continuous. Only with engine running does it jump around..

I spoke to the dealer in WA tonight, and they said to check the fuse off positive battery, which I don't have, and check the kill switch. I can jump the kill switch, but it is only 2 years old. I have wiggled it around some while the pumps don't prime, and didn't seem to change anything. They also gave Silver Spray high marks for working on GT40's, so if I don't figure this out over the weekend, it seems like they could be a final sanity measure..

I took the ECM stem out again.

Tested the relay and 60 and 40 to ground with wiggle test. No breaks.   Also wiggled the main ground on back of block.

Tested relay purple/red and is over 10 volts like manual sates.   So does that mean all the in lime breakers are good tool?

What is the breaker box that the manual alludes to? It says to install breaker box and then test.

AMB wrote: but we have mid-80's today and I should be skiing vs wrenching in the garage!!!!

I feel you here, Its supposed to be nice all week/weekend and my boats at FFM for a transmission rebuild. I guess I should have got it up there sooner. Who knew.