Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

[perna00]

So I bought a 95' Four Winns 20.5 boat with the OMC 5.0 (Ford) Inboard. It won't throttle past 3,000 rpms without backfiring. All new plugs, wires, cap, pretty much entire ingition system installed before I bought it. I verified parts and they are new. I'm sure it is with the fuel system so I drained all gas, changed filter, and cleaned connections with no improvements. The low pressure pump and high pressure pump both turn on with the key but the low pressure pump has a very loud whine/grind to it. I'm going to test the fuel pressure of the low and the high but don't have luck finding a fuel tester that registers around 4 psi and 40 psi. Most are high or low range. I'm going to buy a marshall 0-50 (maybe 60, forget the value) fuel pressure gauge and make it into a tester. The gauge is 1/8" npt and I want to get a fitting to thread on the test ports on the fuel line and test port. I'm just getting mixed readings of what size it is. Any one know for sure?

 

[etracer68]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

I would check the firing order from plugs to dist cap first, it could be a bad valve, or bent push rod too. If this is a carbed motor, 4 psi should be all you need, as 40 psi would not let the float seat.

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

The only thing is that the engine runs perfectly smooth up to about 2,250 rpms. After that it has an varied backfire until it is constant around 3,000 rpms; seems like fuel starvation. Idles smoothly as well as responsive under 2,350 rpms. It is a multiport fuel injection system so the low pressure end is under 6psi and the high pressure end is less than 40 psi.

 

[etracer68]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

Ok, its injected, I would still check firing order. You may have a dirty injector too. Can you get at the injectors, to inspect them? Dirty injectors can cause miss fires at that rpm range.

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

The injectors are underneath everything. It would be a nightmare to get them all out to clean them. I just put injector cleaner in them to help if it is a problem.

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

I've read that some people use a tire gauge for testing. I've seen one that is built like a fuel pressure gauge with a thread on fitting with the side bottom for readings. I'm thinking it might even be the same size threading. Maybe it will work?

Also, are the pumps known to get clogged and able to be cleaned to fix or if they aren't working properly, do they most likely need replaced? I'm not sure how common of an issue they are.

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

Well, I looked more into the problem and I found out that a spark plug wire was crossed with another one. I'm hoping that it was my problem. I also checked the timing which is correct but my idle stays consistantly at 950 RPMs. According to the book, it should only be around 600 RPMs at idle. It is mfi so it is non adjustable. Any thoughts?

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

I was reading into the books more and it says for the carb engines, you test the idle rpms in gear. Would this be the case with the fuel injection versions? If so, my 950 rpms in nuetral idling might just drop down to 600 in gear. Any thoughts?

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

I've checked over the forum and it seems like all fuel injected engines are set at their idle speeds in nuetral. It looks like I either need to replace/clean the IAC valve or I have a vacuum leak somewhere. Are the 5.0's known to have any areas that develop leaks?

Also, can anybody tell me what timing BTDC they have around 950 rpm's? It looks like the previous owner set the timing (standard 5 BTDC) for idle, but while the engine was at 950. The tell tale was the white out on the crank. Thanks for any help you can give.

 

[indybleck]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

If I remember right idle doesn't affect timing but timing affects idle. I think it goes set the timing then set the idle. Hopefully some one else will chime in here to confirm or deny.

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

The book said that the idle is non adjustable and the iac is the only component affecting it. I know a decent vacuum leak will also override the stock parameters too though.

 

[MWG2600]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

Use some carb cleaner to check for vacuum leeks?

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

I was spraying it to see if it would affect idle and the only time it did was when I sprayed in onto the throttle body. The only thing was that the air intake filter is right connected to it so I think it did from the alcohol being in the air around it. I'm going to remove the iac motor and see if it is dirty and seating properly.

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

Well, I removed the idle air control valve and it looked decently clean. Now, the IAC valve controls idle but by which sensor does it use reference to determine idle speed? Would it be a sensor like the crank sensor for speed or would it be the MAP determining vacuum pressure? Any help?

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

Well, it is about time to take the boat back on the water to test everything. I ended up getting a basic tire inflator from autozone $10 to test the fuel pressure. The gauge read up to 45 PSI so it was perfect. I had to use a small washer in the fuel test port to make the needle go down when I threaded the tester on. Both pumps are working like normal; well, at least under no load. The only thing I found wrong during the testing was that the power steering system leaks (nothing major). I also was playing with the idle and I found that even though the engine was reading 1,000 rpm's, I could rev the engine up slightly before it would move it off of the 1,000 mark. It worked perfectly smooth after 1,000 rpms so the gauge just isn't registering under 1,000. Testing it in the next few days.

 

[perna00]

Re: Fuel pressure test port size on 95' Four winns with OMC 5.0 MFI (ford)

Well, the engine works fine now except for a knocking sound. I put the info in a new thread. I think the switched wires were the main reason.