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Problem with OMC 5.0 EFI engine (see video)

C

Chris Craft

New member
Hi, this is my first post here and I hope that i will get some help with my engine.

It´s a OMC V8 5.0 EFI engine from 1994.
When I accelerate up to about 2800rpm the engine starts to twitch, just as it does not get enough with fuel.
You can se the problem here on the video i captured yesterday: http://vimeo.com/25830326

I have changed:
low preasure fuelpump
spark plugs
ignition cables

But the symtoms will stand.

Could it have anything to do with the “eletric box” which is red marked on the picture.
DSC_0033copy.jpg

My Best Swedish Regards
Daniel
 
hmmm... I don't know too much about that EFI Ford OMC setup, but it sure sounds control related.... it's acting like a rev limiter.... I think I have a 94 manual - will have a look later if I do
 
I think you could have a broken wire. Get someone to hold the throttle while you move your wires around. It sounds like when the engine torques up it looses contact resulting in the engine falling back to recontact again repeating itself.
 
i´ve changed the fuel filter, it doesn´t help :(

about broken wire, i don't think that because if I put my finger in the air intake the engine goes good. so it must have something to do with either the fuel or the air. and I think it´s the fuel.
It could be the Map sensor, but it´s booring to buy one for about 150-180 bucks if the problem stays...
 
I wonder if cleaning the throttle body and any related sensors - maybe check with the Ford guys on a car forum - Mustangs of that era probably have similar stuff
 
My guess is a bad TFI module. It sits on the side of the distributor and converts the Hall effect signal into electric pulses. Very easy to swap and not expensive.
 
o2batsea said:
My guess is a bad TFI module. It sits on the side of the distributor and converts the Hall effect signal into electric pulses. Very easy to swap and not expensive.
Click to expand...

i will check the TFI modul tomorrow. can I test if the TFI modul is bad or is it just to buy a new one? Do you think it's more realistic that the TFI is bad than the MAP senor?

Thank you all for your commitment to my problem.
 
I have the same problem. I have the EFI diagnostic manual. The engine at 2500-2700 rpm goes to s.l.o.w mode. Is a safety feature if it detects high temperature in water above 200 F or low oil pressure. they are two sensors one under the distributor on the left top and the other on bottom right for the oil. you should have a tan and black wire on them. I replaced both according to the book. I cannot get that engine out of the slow. mode. By the way is pin # 24 on the ECA ( computer). I wonder if anyone knows if I can jump the system or disable it somehow??
 
By 1994, this should be Volvo Penta, no longer OMC.

Start by getting the serial number, and look for Volvo Penta data by serial or model number.
Perhaps order an OEM service manual for this particular engine model.

I believe that the ignition triggering would be photo eye, not Hall Effect. (I could be wrong on that)

The irratic stumbling is too consistantly timed to be a connection issue, IMO.

.
 
karistos said:
I have the same problem. I have the EFI diagnostic manual. The engine at 2500-2700 rpm goes to s.l.o.w mode. Is a safety feature if it detects high temperature in water above 200 F or low oil pressure. they are two sensors one under the distributor on the left top and the other on bottom right for the oil. you should have a tan and black wire on them. I replaced both according to the book. I cannot get that engine out of the slow. mode. By the way is pin # 24 on the ECA ( computer). I wonder if anyone knows if I can jump the system or disable it somehow??
Click to expand...

Hi,
is it any different if your engine is hot or cold? My engine behave the same, hot or cold. I also have a problem that my oil pressure sinks after awhile but then suddenly it will come back upp to 40-50psi.
I have replaced the oil pressure sensor, maybe I should try to replace the oil pressure switch to? Or maybe I'm in need of new oil.
Today I ordered a new distributor cap and rotor that will arrive on wendsay. The old one was very rusty.

I also find out yesterday that my engine is from 1995 not 1994 which I believed first :)
 
Chris Craft said:
i will check the TFI modul tomorrow. can I test if the TFI modul is bad or is it just to buy a new one? Do you think it's more realistic that the TFI is bad than the MAP senor?

Thank you all for your commitment to my problem.
Click to expand...
Do you know what a MAP sensor is and why it is part of the system, or are you just throwing words out there? Your engine is set up with 1980 vintage Ford EFI as found on several million automobiles. If you want to be sure, just order all the engine sensors from NAPA and see if that solves the problem. ACT,MAP,TPS, MAF, and the IAB are less than a hundred bucks all together.
 
o2batsea said:
Do you know what a MAP sensor is and why it is part of the system, or are you just throwing words out there? Your engine is set up with 1980 vintage Ford EFI as found on several million automobiles. If you want to be sure, just order all the engine sensors from NAPA and see if that solves the problem. ACT,MAP,TPS, MAF, and the IAB are less than a hundred bucks all together.
Click to expand...

You can probably much more about this than me. What I know about the map sensor is: " The ECM uses the MAP sensor to control fuel delivery and ignition timing."
I thought that the problem is fuel or ignition related. But I have to say no idea.
Napa seems like a good site, I will check it out. Thanks
 
RicardoMarine said:
By 1994, this should be Volvo Penta, no longer OMC.

Start by getting the serial number, and look for Volvo Penta data by serial or model number.
Perhaps order an OEM service manual for this particular engine model.

I believe that the ignition triggering would be photo eye, not Hall Effect. (I could be wrong on that)

The irratic stumbling is too consistantly timed to be a connection issue, IMO.

.
Click to expand...
The boat is 1994 but the engine was made in 1993 Model # 50FAPLJVN
 
It does hot or cold. with load on or without. It seems stack on s.l.o.w mode unless something else is triggering it. I'll try swapping computers with the other engine to see if it behaves the same and the problem is in the wire harness.
 
karistos said:
It does hot or cold. with load on or without. It seems stack on s.l.o.w mode unless something else is triggering it. I'll try swapping computers with the other engine to see if it behaves the same and the problem is in the wire harness.
Click to expand...

ok, same as me then :(
i will try with a new oil pressure switch on wensday.
Do you know were the brown cabel from oil pressure switch and the black cabel from the oil pressure sensor goes? Unfortunately, I have no wiring diagram of the engine.

My engine model is #50FAPHUE and that must be 1995?
 
I have the manuals . Mine are 1993. Both wires are tan with black and go to ECA or computer pin #24. I found in another forum that if you unplug both wires the computer will work fine. I can't wait to try it.
 
ok, but is that so god to do?
engine goes into slow mode out of one reason: something is wrong. Is it really so good to fool the engine that everything is ok?
But I will also try it:) if it doesn't work with new switch, rotor and distributor cap, of course ;)
 
karistos said:
It's worth a try. I am running out of options.
Click to expand...
Have you managed to fix the problem? I have not come somewhere, next step for me is to leave the boat to a workshop: (unless anyone has any other tips? I myself think it's an electrical fault. Maybe a TFI module ... but I can not afford to take a chance to buy new parts that do not fix the problem
 
No yet. I installed new sensors( water and oil) no luck. This weekend I am cutting the wire to the computer to see if that does the trick.
 
Chris Craft said:
ok, hope you get any success. Please tell me if you manage to fix it.
Click to expand...

I cut the wire just before the computer module,( there is a diode on that wire) by the harness and all my problems went away. Boat can now go past 2500 rpm with no problem. It had to be either a bad diode or a short along the wire to the sensors. If you have your wiring diagram locate the correct wire and cut it. you can always connect it back. Mine was A BROWN AND BLACK WIRE ON PIN 24.:cool:
Good Luck.
 
karistos said:
I cut the wire just before the computer module,( there is a diode on that wire) by the harness and all my problems went away. Boat can now go past 2500 rpm with no problem. It had to be either a bad diode or a short along the wire to the sensors. If you have your wiring diagram locate the correct wire and cut it. you can always connect it back. Mine was A BROWN AND BLACK WIRE ON PIN 24.:cool:
Good Luck.
Click to expand...

I disconnected the wire today and the engine goes perfect again:) Are you going to continue the troubleshooting or are you satisfied now?
 
I am very happy that I have my engine back. I took the boat out and span a prop this time. But the engine works good. After the summer i will run a new wire to the sensors including the diode that was in line with them. Enjoy your Summer and I hope other people read this and save their summer.
Thanks the forum that was so kind of posting our threads.
 
ok, I could be happy one day until a new problem arose:mad: when i accelerate upp to about 3000-3500 rpm the temp rises up to about 210-220F.
Before the old problem ocurred I had some problem that the engine temp couldn't get higher than 100F. so I did something with the thermostat. Could it be so that in the first place the thermostat was broken and in a open position and when I then put my fingers on it. I accidentally closed the thermostat so the engine will not get any cooling water?? however I will order a new thermostat tommorow. Hope that it will be better and no new problem will occur this summer.
 
Change your thermostat, Check your impeller of the water pump in your outdrive, also remember your risers get glogged over time. Good luck.
 
more problem for me but I'm not giving up... when I should replace the thermostat housing I accidentally broken the screw mount:mad: So I need to take of the "adapter" and have it welded. And I don't now which size of the ring spanner I should use? See the picture for info which screw I mean.
adapter.jpg
 
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