Rpm sensor?

[Chexi]

The saga continues. So here is what is going on. My boat will run fine. Then the rpm Gauge will suddenly redline. The motor will not be racing up, but the tach will jump to past 6000 rpms. Just after this, the boat will lose power, and often stall. We surmise that something is giving the ECM the wrong rpm information. Then when the boat thinks it is going into redline, it cuts fuel or spark as a safety mechanism. This sequence keeps happening, but the problem is intermittent. Once it starts, it keeps getting worse. Is there an rpm sensor that could be bad?

I've replaced rotor and cap, fuel relay, tp sensor, map sensor, idle speed control unit, fuel filter, plugs and wires, and tested both fuel pumps (33 psi) even when the problem is happening.

[AirTool]

Here I go not knowing about Fords again. But the RPM should be calculated using the pulses from the crankshaft position sensor.

Usually they won't run at all without it working but if the sensor is goofy, it might go crazy like yours is doing.

Is there one of those on that model? check the pcm parts info.

[AirTool]

Here I go not knowing about Fords again. But the RPM should be calculated using the pulses from the crankshaft position sensor.

Usually they won't run at all without it working but if the sensor is goofy, it might go crazy like yours is doing.

Is there one of those on that model? check the pcm parts info.

There is a Profile Ignition Pickup in the distributor that feeds the pulses for the tach and ECM. There is not much that can go wrong. Take a look under the cap and see if you can see it all. Make sure the ring has all the vanes and they are clean, etc. Make sure all the wires are good, etc. There is a schematic of the tach system on page 278 of 302 in the GT40 manual.

Did you have Buxton's or the other dealer put a code reader on the system?

[Chexi]

Hahahahaha. Read the codes? Neither of the dealers I took it to bothered hooking it up to any testers. Waste of time they said. Well, Buxton said they can't on GT-40s... which is true to a degree, but you can hook it up to a star tester. It's a PITA, and only tells you a little bit, but it can eliminate things.

I have opened up the distributor. It was a rusty, corroded mess, which prompted me to replace the distributor and rotor. I also replaced all the wires, and plugs, used dielectric grease... But the vanes are a rusty mess too. I can't figure out how to pull them. I'm thinking now that it's TFI or the stator/hall effect/PIP, since these are all involved in rpms and ignition firing.

[Chexi]

In case it didn't come across this way, thank you AirTool. I was laughing sarcastically because I really wanted and asked the dealers to hook it up to a tester and they wouldn't. Doing so probably would have saved me a few hundred dollars and a lot of hassle so far.

It looks like changing the PIP on this thing is a bear, requiring removal of the entire distributor.

[DanielC]

Running a tachometer is a pretty basic electrical function. The tachometer just counts the ignition pulses on the primary side of the ignition coil, and divides by 8. It is the same basic system used since electric tachometers became popular in the 1960's.

Ignition systems still function the same way they always have. A battery is connected the primary coil on a transformer, and the magnetic field is allowed to build. At the right time, the battery is disconnected, and the magnetic field collapses, and a high voltage current is induced in the secondary windings, and a spark plug fires. The transformer may be a single coil, firing eight times for every two revolutions, multiple coils, that fire only two out of the eight plugs, or even coil on plug system, with one ignition coil per cylinder. It is still a coil, and a switch.

The Ford GT-40 engine uses the same basic output signal that would be generated by points, and a coil in an older engine. I think it is a little more than a resistor, that buffers or limits the output from the ignition coil. I would think that if the engine runs fine, the signal has to be good, or the engine would not run good.

On a 2000 boat, you might have a problem with the gateway box that goes in between the analog outputs of the engine sensors, and then sends digital information to the gauges. I do not know how much of the information is changed from the outputs of the engine, to the digital information the gauges need.

[AirTool]

In case it didn't come across this way, thank you AirTool. I was laughing sarcastically because I really wanted and asked the dealers to hook it up to a tester and they wouldn't. Doing so probably would have saved me a few hundred dollars and a lot of hassle so far.

It looks like changing the PIP on this thing is a bear, requiring removal of the entire distributor.

It came across properly especially after the dealer comment. The star tool is what I'm talking about and (from what I've read in the manual last night) it won't necessarily point to your problem (especially the PIP and gateway) but it will tell you many loops that are good.

Way above you mention replacement of the distributor and rotor but I think you mean cap.

DanielC's explanation is great. Two comments though: 1. I'm not sure any problem with the gauge(s) is the snag here. I don't know what the tach is doing and might consider disconnecting it. I too don't know about the gauge outputs, but I don't think that is the problem. I don't think there is a gateway box between the system and the tach. The schematic shows the tach getting the feed from the TFI (EEC-IV) 2: The firing of the plugs is probably just as he says, but the PIP info is going to be used to determine timing advance and be a significant variable for calculation of fuel delivery. That is probably why you have the hunting problem. BUT, i'm not sure it is a distributor problem. I'm thinking the problem is in the ignition module or the ECM. Some auto stores can test the ignition module. Find one and have it tested. If it shows good, probably the ECM if fouled.

I believe the rusty PIP is working. If there is a separate plug for it, just unplug it and I'm pretty sure the engine will die.

Now re-read everything again and let it absorb. That manual in the manual section is very handy...if you haven't looked at it. I assume it matches your engine.

Final note, there are some ignition parts on GT-40's that often get "converted" to a new kit. I don't recall the details but maybe you have the infamous problem. BUT, I would have thought someone whould have already brought it up.

I'll try to watch all of your video tonight.

[AirTool]

PS - rusty vanes shouldn't affect performance. The PIP is just sensing the iron passing by. I think the PIP hall effect doodad plugs in and is replaceable.

[Chexi]

Today we put in a new tfi. It fixed the idle hunting problem. Now, when I first start, the engine hunts for idle with decreasing range until it finds the righ idle, which is lower rpms than it was before. Typically 700s. Sounds better too. That did not fix the crazy rpm gauge or the stalling. We then disconnected the rpm gauge and perfect pass thinking may there was a short. Ran great for about 30 minutes, but then problem started again. Then we replaced the ignition coil. The boat then ran beautifully for 3 hours. But then we had some of the same problems at the end of the day. However, before we hooked up the new ignition coil, we popped off the center plug boot from the distributor cap and the pin came with. It was amazing that we were able to run at all after that. It is very possible we have solved the problem with a new tfi and uniting coil (2 problems actually). We'll know more tomorrow. Thank you both so far. I'm crossing my fingers.

[Chexi]

**** it. It's not the ignition coil either. It is dying again while idling and whilmcruising. We can smell unburned fuel when it happens. It's probably a bad ECM, which both dealers could have found if they had hooked it up to a star tester like I asked and like the manual instructs them to do. Instead, I've wasted weeks of my life and hundreds of dollars on this lemon. It's very close to sale, and I'm very close to leaving this family.

[Chexi]

An interesting discovery. On a hunch, I just pulled the safety lanyard off and it did not kill the boat. So i suspect it has been bypassed. I'll look for a bad ground soon, but does anyone know if a bad safety lanyard switch could cause this sort of erratic behavior? I doubt it would cause rolling idle, which still happens sometimes (boat can't find correct idle), but maybe the loss of power and stuttering. It does not usually die instantly though, but rather sputters with epm gauge all over the place and then dying.

[jjgag60]

Remember to make sure you pull the negitive wire on the battery after you change out sensors. The ECU needs to reset itself otherwise it wont "see" the fix you just made. The are pretty smart and compensate for bad sensors or air flow.

[Chexi]

^ ugh. Well I haven't done this. I did have the positive cable off the battery overnight. If that does the same thing as pulling the negative, then my sensor swaps are not the fix.

I noticed something new today. Sometimes, after my boat mysteriously dies, the tach may continue to bounce around. Today, it was kind of quiet one time when this happened and we noticed that exactly in tune with the bounces on the tach we could hear what sounded like either (a) a spark from a short or (b) a relay click. Every time the rpm needle bounced a bit, we heard "tick". So it was like, "tick, tick... tick tick.... tick.. tick". We assumed it was a short and tried to find it, but we couldn't before it stopped. It did this a few more times throughout the day. My friend was convinced it was coming from the ignition coil, MAP sensor, TFI area... but to me it sounded more like it was further forward closer to the fuel rail on the FCC side. Here's the really weird part, sometimes when it does this, it could be like 5 or more seconds after the boat has died, and the boat will fire back up on its own. This only happens if I don't hit the STOP button of course, but if I don't, the boat could turn over on its own if this ticking is going on.

Another question. The idle speed control bypass air solonoid makes an audible noise like a spring when it engages. Is this normal? This is the replacement I put on.

Thanks all. This is so incredibly frustrating. I appreciate all of your help. One of these days, I'll have a working boat.

[Chexi]

Here is some additional info I forgot to post. We also hooked up a timing gun and strobed the spark while running rough. We noticed a few times the strobe just stop right before the engine acted up and finally died. So we surmise that this is a spark problem. Something (either the short or a bad sensor or computer, or something else electrical) is messing with the spark.

[AirTool]

Chexi - I'm traveling tonight and can't study the schematic again. But here are some comments.

1. Disconnecting positive is the same as negative.

2. The schematic shows a resistor (or two) and DanielC mentioned it also. Usually they are a white ceramic block with the resistor inside. I'm not sure they are like this in marine application (because of spark risk) but can you trace out that tach circuit and find the resistor and make sure it is not cracked or the spade terminals loose in the housing? That thing might be working fine until it gets hot and then starts causing problems. It is a stretch but worth a check. I sold auto parts (back in the day - not at Plant 18) and I sold about 10 of those in five years. BUT, those 10 people needed one.

3. When did you do the strobe trick? before or after the Ignition Module replacement? (Did you put it on one plug wire or on the coil wire? On any wire, but more visible on the coil wire, it should beat like a metronome....NOT ONE SINGLE MIS-FIRE.

4. Did you put the paste on the back of the new Ignition Module?

5. There is a ground in the tach loop and probably the coil loop somewhere. Do check those.

6. Do you have a keypad or key switch. I was thinking you had a switch but you mentioned the stop button. Just wondering because the schematic is for a switch and I'd need to think through the differences.

This one is pi55ing me off. By now, I'm thinking you wish you had that pontoon boat.