1997 Ski Nautique Ford 351PCM Won't Start

[Smindustries]

Ok I see what you're saying now. Does the negative lead go into the COM jack or the other jack? I will do these tests today if I have time then.

Plug the leads in and test a battery. If the voltage displayed is positive, they're hooked up correctly. If the displayed voltage is negative, swap them.

[97nautique*]

Plug the leads in and test a battery. If the voltage displayed is positive, they're hooked up correctly. If the displayed voltage is negative, swap them.

Thanks.

[functionoverfashion]

I wouldn't lose sight of that other manifold. That should be replaced before it does the same thing as the other side. Not to be alarmist, but I feel you were lucky it wasn't worse on the side you already replaced.

[97nautique*]

I wouldn't lose sight of that other manifold. That should be replaced before it does the same thing as the other side. Not to be alarmist, but I feel you were lucky it wasn't worse on the side you already replaced.

Yes thank you, I have been thinking of getting a new one within the summer.

[gun-driver]

I wouldn’t wait long you were already lucky, you can easily bend a piston rod on a hydro locked motor.

[97nautique*]

Ok thanks, I will.

[97nautique*]

Heres what I did with the sensor tests. The negative lead was in the COM jack during all the tests, anything measured in ohms was tested at 200, and anything measured in VDC was at 20.
- The limp mode sensor came out with 54.3 ohms. This was with a ground and ignition off. With the ignition on I got 12.14 volts. Way off from the tests in Peter6000's video.
- The ECT sensor had .5 ohms which is fine. When it had the ignition was on I got 4.57 volts, off from the video's results. When it was PLUGGED in with the ignition on it had 1.3 volts.
- The AIT sensor had .5 ohms which checks out. When it had the ignition on it got 4.57 volts, off from the video again. When it was PLUGGED in with the ignition on it had 1.3 volts.
- The MAP sensor had .5 ohms which is good. With the ignition on it got 5 volts, same as video. I didn't have hertz, but when I measured the center wire (output) it gave me 2.5 volts which is the same as the video.
- The sensor connected to the throttle body had an idle output at .7 ohms (same as video) and at WOT it had 4.7 ohms. Also when I accelerated the throttle it went up with it gradually (good). The orange wire on the sensor gave me 5 volts which also checks out

Heres the video I used that Peter6000 made, https://youtu.be/hFmI-_B9IVs, thanks for this Peter.

Please get back to me on what I should do with this information. Thank you.

[SilentSeven]

If the limp sensor is out of range, I would disconnect it as he suggests and try again. Also suspect is the 1.3v on plugged sensors with the ignition on.

How well have you checked all your grounds - end to end? As a quick test, you might take a jumper cable and connect it directly from the block to the battery as an alternate path and retest.

This is a fine mystery. Sorry you are in the middle of it. Peter's video was super informative; that's a keeper.

[97nautique*]

So to be clear, I disconnect the limp sensor and test it same as I already have. The ground I used for all of the tests was the battery.

When you say check my grounds, should I be checking the sensor grounds and connections?

I've already checked and cleaned the major high current grounds, and I've cleaned and dielectric greased maybe 65% of the reachable connections.

Peter's video was very very helpful and thanks again for that.

[SilentSeven]

Well, the electrical testing is getting beyond my hands on experience. But when I see 4.5v when the harness is unplugged and and 1.3 on the same connector when plugged, my intuition says something's off. Power in is only as good as the ground back. By connecting a jumper cable from the block to the battery you effectively rule out any corrosion or other hidden issues in the ground return. You could argue that it wouldn't crank if the ground sucked and I wouldn't have a great counter argument. But in the end its an easy test.

And with that said, this doesn't tie back to the 'you have to advance the throttle to 50+% and crank to start the boat'. My GT-40 would light off every time with zero throttle. I'd read the PCM manual and see what it says on start problems. Some engines have a start circuit - ie / timing and injector cycle change when not started' - wondering if this engine has one and somehow isn't being triggered.

[Peter6000]

Limp mode 50ohm is too high and is pointing to a bad oil pressure switch, 12V with ignition on proves the point. This is not your problem right now and should not have any effect.
Does the red check engine light in the turn on with ign-on engine-off?
I would disconnect both just for a test.

ETC, you measured 1.3V ignition on sensor plugged in,
what was the engine temp at that time?
Did you run the engine before the test?
If yes this is most likely ok
1.3V would reflect 140 deg double check this reading on a cold engine 70 deg should be around 3V

ACT same as ETC, the fact that it shows the same readings makes me think the engine was hot and both are ok.

For the MAP try to find a multi-meter that can measure HZ

TPS looks ok

Did you check the Idle air bypass valve on the throttle body it should go open with Ign on and move smoothly when turning Ign on/off.
Also make sure the bypass air channel is clean on the throttle body.

If that checks out it only leaves fuel injectors, ECU or a mechanical problem internally. However most of these would also cause problems during operation.
Are there any other symptoms like unstable Idle or power?
Is there a difference between hot and cold start?

Peter

[Peter6000]

In my video I measure 4.5V at 80 deg F on ECT and ACT this is because I use a different ECU on the OEM setup this should be around 3V at 70 deg F, a table can be found in the ProBoss sevice manual page 14
Peter

[97nautique*]

I'll try to answer most of your questions, but if I don't just ask again.

- Check engine light is off with engine off and ignition on. Which seems weird because from memory I'd tell you it'd be on but I guess not.

- The engine temp may have been around 120-140 because it was 90 here and the boat had been run about an hour or two before as well as being in the sun.

- Like I said the engine was run to temperature after a ski about an hour or two before my tests.

- I did not check the idle air bypass yet.

- The boat has stable power at idle and running around the lake around 30ish.

- On a hot start I do not need to advance the throttle it seems. I can't really confirm this because sometimes when it's hot it'll start normally and sometimes I need to advance the throttle. Just this morning I went down to the dock and I started it at idle and it fired right up which mystifies me because it was dead cold.

[Peter6000]

I'll try to answer most of your questions, but if I don't just ask again.

- Check engine light is off with engine off and ignition on. Which seems weird because from memory I'd tell you it'd be on but I guess not.

- The engine temp may have been around 120-140 because it was 90 here and the boat had been run about an hour or two before as well as being in the sun.

- Like I said the engine was run to temperature after a ski about an hour or two before my tests.

- I did not check the idle air bypass yet.

- The boat has stable power at idle and running around the lake around 30ish.

- On a hot start I do not need to advance the throttle it seems. I can't really confirm this because sometimes when it's hot it'll start normally and sometimes I need to advance the throttle. Just this morning I went down to the dock and I started it at idle and it fired right up which mystifies me because it was dead cold.

Check engine is off because your oil pressure sensor does not produce a short when pressure is low. Thus will nor effect performance. I would replace it anyway.
And check to IAC valve I may post another video on that later.

Sent from my SAMSUNG-SM-G870A using Tapatalk

[97nautique*]

Ok thanks, I'll check out your video if you post it.