Carver 400 MY engine RPM issue

[km1125]

Will it throttle up in neutral or do you just have the throttle-up problem under load?

Can you check fuel pressure while you're throttling up? I do not believe with throttle bodies that the fuel pressure is tied to manifold vacuum as it would be on a MPI, so I would expect it to be relatively steady around the 20 that you see at idle. If it does drop then I'd be thinking fuel pump.

Have you checked throttle position sensor? Easy test to measure the resistance over the throttle range.

[hausherrs]

Source of the post Will it throttle up in neutral or do you just have the throttle-up problem under load?

When I am having the issue it does it in neutral and underway. Its acting like no fuel is available when the butterflies open.

Source of the post Can you check fuel pressure while you're throttling up?

It dips a little when I throttle up. But its hard to tell by how much. The cheap fuel pressure test guage needle bounces all over the place.

Source of the post Have you checked throttle position sensor?

I have not checked the TPS. Do you have the specs on hand? I can dig them up if not.

Thanks for the help!

[km1125]

Source of the post

Source of the post Will it throttle up in neutral or do you just have the throttle-up problem under load?

When I am having the issue it does it in neutral and underway. Its acting like no fuel is available when the butterflies open.

Source of the post Can you check fuel pressure while you're throttling up?

It dips a little when I throttle up. But its hard to tell by how much. The cheap fuel pressure test guage needle bounces all over the place.

Source of the post Have you checked throttle position sensor?

I have not checked the TPS. Do you have the specs on hand? I can dig them up if not.
Thanks for the help!

I do not have the specs handy (but when in doubt, just compare port to starboard)

Based on those answers, I'd be less likely to think it has anything to do with fuel pressure or fuel delivery to the injector, but more likely a TPS problem or a crank position sensor.

[km1125]

I was looking for an ECU diagram for that engine but didn't find one (yet). With the throttle bodies you may not have a crank sensor at all. If you still have a distributor the ECU could use that as the "crank" reference.

While looking for that info, I stumbled across this. One more thing you can check (for free and a fairly easy test):

He was having problems with the engine not making power and intermittently dying:
He said to take my multimeter, set it to ohms, and plug both leads into the two wire plug coming from the pickup coil. He said I should get between 700 and 900 ohms. I got 2.4Mohms. Checked the starboard pickup coil and got 800 ohms. On this engine you have to pull the distributor to change out the pickup coil, something else I have never done. Jason told me to put the rotor on and turn the engine over till the rotor pointed to the number one cylinder post on the distributor cap that I had laying adjacent to the distributor. I match marked the distributor base to the engine, loosened the bolt holding the distributor in place and pulled it out slowly. I will rotate as you pull it out because of the helix gear. I purchased a pick up coil from NAPA as no local marinas had one. To remove the old pickup coil you need to match mark the gear at the bottom with the slot for the rotor, then drive out the pin holding the gear on the shaft. Once the shaft was removed, the coil at the top was exposed. It was fried/melted. there was corrosion on top of the distributor shaft (not sure why), but I think that caused the coil to fry. Put the new coil in, lined up mark on gear with shaft, installed pin, put rotor on distributor so I could make sure it was lined up with #1 cylinder post on distributor cap, installed the distributor, plugged in ignition module, installed cap, attached wires and fired it up. I was two degrees off, so I set that, and here we are happily on vacation....

[hausherrs]

Quick update. I replaced the fuel pump and the tps. No change.

When I took the old pump off and put it in the bucket i noticed water bubbles in the bucket.

So I'm of to drain the tank next.

[hausherrs]

I think it's fixed. The contacts on the ignitor were badly corroded. Rotor was arching quite a bit to the cap. Metal building up on the contacts. Replaced cap, rotor, ignitor. Cleaned everything. How i found the issue is i hooked up the timing light and noticed it was missing. So i hooked it to the coil wire. I was getting several consecutive missed sparks.

Before i replaced everything it would barely stay running. And if i throttled up quickly it would cough fuel up from the tb and backfire. Once everything was replaced it was smooth. I didnt get to take it out but will tuesday evening after i do the same to the port engine.

Ill update once i take it for a test run.

[hausherrs]

OK so I didn’t want to say anything else until I got to the bottom of this. After all of the above the engine was still having issues. SO I stuck a tube into the fuel tank and drew out about 2 gallons of fuel. It was bad. Smelled a hint of varnish, had a splash of water, and lots of very fine black junk. I thought about having someone come out and cleaning the tank. I decided to go another route.

Removed the Oberg on both engines. And replaced them with Racor 500s. I’ve put 5 hours on them since and no more issues. The Racor on the stbd engine is in the yellow on the vacuum gauge. So that filter needs to be changed already. I also changed the TBI filter and the Little Racor filter. I ordered a filter for the generator that will be in soon. I believe its filter is clogged at the moment. Was running poorly yesterday and wouldn’t restart after I shut it down to re-fuel.

Anyway, on to the next set of issues..

[km1125]

I'd like to hear more from you and others about the pros/cons of "replacing an Oberg with a Racor".

I have read before where there was an issue that was believed to be from putting too much filter ahead of the lower pressure pump, and that is why they use an Oberg or small screen rather than a filter in that location The Oberg or small filter is just designed to protect the lower pressure pump from damaging debris but would not trap debris that could be a problem for injectors, so that's why the second filter AFTER the lower pressure pump.

[hausherrs]

I would be interested in hearing more on that as well. My experience is that my boat runs better than it has in months.

I can tell you that it took a little while getting those fitlers filled with fuel and they can pick up some heat which can lead to vapor lock, but ive had that issues since I bought the boat so nothing new here. Thats on my to-do list.

[bud37]

Quite a little voyage you have had here, nice to see you have cleaned up more than one issue....should be good for quite a while now hopefully......

I know vapour lock can be created by a few things, but have you tried insulating your fuel lines, may get a little joy from that...