1993 OMC 5.8 EFI Idle problem, runs on throttle, too rich

[DSmith1234]

1993 OMC 5.8 EFI ChrisCraft Concept 217. Ran great 2 weeks ago, but next trip couldn't get it to start unless lots of throttle, and ran sluggish, way too rich. Didn't get away from dock. So far was told to- change fuel pumps (2), fuel filter, plugs, Throttle Position sensor. All done with no change. Had a Ford pickup with 5.8 that had the fuel pressure reg go out and it ran too rich. Will try that next. All of the old plugs were black and wet with fuel. Can't get an opening to get it to mechanic til September. Thoughts....

 

[matt167]

Fuel pressure regulator and the MAP sensor is suspect

 

[Scott Danforth]

check if the IAC is working

 

[alldodge]

Test fuel pressure 31-39 psi

Check the vacuum hose coming from regulator to see if fuel is present

 

[DSmith1234]

Thanks for the replies, any help is good help at this point. Would really like to get this running before summer is over...Fuel pressure on rail was 40#, no fuel in vac hose on fuel regulator. Map is discontinued, will one from auto or truck work? Can I use Fuel pressure regulator from auto or truck? I can get these local without waiting. Will check Idle air control, but that usually won't cause fuel to dump.

 

[alldodge]

Fuel pressure is good and no fuel in hose, so those items are not the problem

Need to see if there are any codes. OMC is a type that other scanners may not work. I'm no expert but we have yet to find what's causing the issue

On top of the VST there is a line that goes to the intake. If the VST float does not shut off the fuel coming into the tank (same as float in carb) the excess fuel gets dumped into the intake

http://www.varen4u.nl/pdfs/omc/omcstern86-98.pdf

 

[DSmith1234]

Thanks for manual download, that will be very helpful. Checked the float today, works great , cleaned needle and seat. I have an OBD-1 Ford code reader, it's pinned differently, all I get is steady tone. Anyone use a test light or multimeter to get codes? If I knew which wires to hit I could try that. Thanks again for the help.

 

[Scott Danforth]

Thanks for manual download, that will be very helpful. Checked the float today, works great , cleaned needle and seat. I have an OBD-1 Ford code reader, it's pinned differently, all I get is steady tone. Anyone use a test light or multimeter to get codes? If I knew which wires to hit I could try that. Thanks again for the help.

Your boat motor is not OBD1

 

[DSmith1234]

Understand not OBD1. Reading thru manual its OMC MFI. A specific code reader. Still struggling along, checking sensors. MAP, IAC, TPS, Fuel Pres Reg all seem good, no fuel in reservoir vent line. Guess I'm stuck waiting for shop to get an opening. Thanks for the replies.

 

[alldodge]

Sure wish we had more knowledge to help out

 

[DSmith1234]

Yeah, manual says start by reading codes. Waiting for shop to read codes and diagnose.

 

[Renken2000Classic]

This maybe? :

TechMate Pro marine diagnostic tool, marine code reader

https://www.rinda.com/acro/Engine_Support_2023.pdf

Rinda Technologies Inc.

I didn't see "OMC", but Volvo/Penta (same thing?)

This popped up too, may have some resources in those posts? :

Anyone have experience with the Volvo Penta/OMC 5.8L EFI engine?

I am embarking on a project to convert a pair of marine 351 Windsor engines to EFI. I've just found out that Volvo Penta in cooperation with OMC offered these engines for a few years but are relatively rare. I am most interested to know what design they used for the intake manifold, and if they...

forums.iboats.com

 

[alldodge]

I don't think OMC can use Rinda, but could contact them for advice

 

[DSmith1234]

Thanks for the replies. Great information in the manual. I can get the boat in to get it checked in September, but the date slipped due to high demand. Reading thru the manuals and trying to test things as best I can. Without a code reader I'm shooting in the dark, but did try a Coolant temp sensor yesterday. Seemed to be a little better, started at 3/4 throttle and eventually got it to run at idle, then started to lope and then died. I read the MAP could be at fault, but that sensor is discontinued, are there any sources for a replacement? Willing to throw a few parts at it since they all look original.

 

[Scott Danforth]

MAP sensor comes from one of 3 places. Little River, Standard Motor Products, or BWD. Their catalog links are in the electrical forum sticky

 

[DSmith1234]

Ok, got it in to the shop, they checked everything that controls engine. Came up with bad computer , part # F4FF-12A650-JB or 3854889, which is out of stock. They couldn't find it anywhere. Any place to send it in for repair?

 

[matt167]

F4FFis a 1994 Ford part number and 12A650 I’m pretty sure signifies it’s an ECU. it’s not going to be an automotive part. But I bet it shares logic boards with a Ford EEC IV of which there are several companies that can fix those. A long shot but it’s your only shot… the EEC IV ECUs are plagued with issues as well

 

[Scott Danforth]

Can always yank the EFI BS and drop in a holley 650

 

[DSmith1234]

Ok, so took to local shop, checked all sensors and diagnosed as bad computer. Finding no matches online, buttoned it up and sent it home with me to keep looking for a replacement or send it in to be repaired. After watching many online repair videos on Ford EEC-IV units. I removed it and started checking for bad capacitors. They were still in good shape, but the pin 46 ground circuit was broken. Having done some board repair on some home computers I repaired the broken trace. Long story short it fixed my problem. Started right up and ran just like nothing ever happened. Hope others with this problem see this and have a successful outcome.

 

[alldodge]

Ok, so took to local shop, checked all sensors and diagnosed as bad computer. Finding no matches online, buttoned it up and sent it home with me to keep looking for a replacement or send it in to be repaired. After watching many online repair videos on Ford EEC-IV units. I removed it and started checking for bad capacitors. They were still in good shape, but the pin 46 ground circuit was broken. Having done some board repair on some home computers I repaired the broken trace. Long story short it fixed my problem. Started right up and ran just like nothing ever happened. Hope others with this problem see this and have a successful outcome.

Great news, happy dance