1994 5.0 Cobra EFI stuck at 25% power

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jimbrodigan

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Found The Problem On Mine....its Fixed.....

Found The Problem On Mine....its Fixed.....

Check for exhaust restrictions. I had the same symptoms. Removing the exhaust elbows, I discovered one flapper valve missing. I scoped the crossover tube but couldnt see anything in there. Removing the drive and looking in the transom bracket where the exhaust bellows connects, I could see the missing flapper valve stuck up flat against the opening, restricting exhaust flow. had to break the valve in two pieces to get it out but that fixed it.
 

gadget73

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Jun 20, 2009
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Re: Found The Problem On Mine....its Fixed.....

Re: Found The Problem On Mine....its Fixed.....

Disclaimer: never worked on an OMC/Ford 302 EFI engine, all of this comes from general Ford 302 SEFI experience, which I know this system is based on. If any of this data is wrong, I apologise. Also, please be aware this stuff assumes that there is a supply of known clean fuel, clean fuel filters, and good ignition parts in place. It also assumes that there are no other obvious problems such as the busted exhaust flapper thing mentioned above. Check that stuff before poking and prodding at the EFI junk, since more often than not, its not going to be the problem.

When checking the timing on a typical injected Ford motor, there is a connector that must be unplugged to set the base timing. Usually its right next to the distributor in the harness going to the TFI module. If these use a remote mounted TFI ignition module (looks to be the case judging by the pic of the distributor) it will be near the TFI module. Connector is a small black thing with two wires on it. Unplug it, and set the base timing to factory specs. Timing marks are stamped into the balancer, may need to wire brush them to find it. Do not use the groove on the balancer, its unrelated to setting the timing. Also be sure you're on the BTDC side of zero, or it will run real bad. TIming is set to the flat edge of the timing pointer. You should also hear a difference in the idle with this plugged in vs unplugged. It can be connected with the engine running without breaking anything. If you watch it with a timing light, you'll see the timing marks move with the connector in place.


The EFI system also has a total of 3 temperature sensors. The coolant temperature sensor is a two wire affair for the ECM. Looking at these exploded diagrams, its front port side of the lower manifold, item 69. There is the temperature guage sensor, single wire thing, front stbd corner of the lower intake, item 25. There is an air temperature sensor two wire thing on the lower manifold behind #5 injector, item 28. Not sure which of these OMC uses for their low power mode, but if you're unplugging the wrong one, it might cause problems. Most likely its going to be the coolant temp sensor though. The two ECM sensors are easy to test with a voltmeter, charts for expected value relative to temperature can be found here:

http://fordfuelinjection.com/?p=10

Key on, engine doesn't need to be running to check this but it won't hurt. Values will drift as it warms up though. WOuldn't be a terrible idea to check it engine cold and engine hot to see if you get sane values.

If they're using a MAP sensor, the vacuum line must be connected. I don't see one in the diagrams anywhere, but its a flat black thing, about the size of a deck of cards with one connector and one vacuum line. This determines engine load. With no vacuum, they typically run horribly rich.

TPS should also be checked. Its mounted to the top of the throttle body and has 3 wires. If its using typical Ford wiring on the sensor, meter from ground to the green wire. You should see about 1v with the throttle closed, and it should smoothly increase to about 5v WOT, with key on and engine not running. Idle voltage is OK anywhere from .8v - 1.2v but its normally roundabout .9-1.0.

Fuel pressure at idle with the vac line on the fuel pressure regulator (item 60) is 30-35 psi, no vacuum is 40-45 psi. At WOT, I'd expect to see 30-35 but 29 isn't going to cause any problems.

Injectors are usually not an issue, and if one is bad you'll usually feel a dead miss, or have a rich running condition that can be tracked to one cylinder. Assuming these are typical Bosch injectors used on all other Fords of that era, they're cheap and easy to get at parts stores. Need to know which color the top of the injector is to size it properly, but you don't have to pay OMC prices for one.

Is there an engine diagnostic connector on this thing anywhere? If its of the typical Ford type, you can pull codes with a test lamp and a jumper wire. Not sure if the codes may be tweaked per OMC spec, but it surely looks like a regular old Ford EEC IV brain to me, probably with an altered program but there isn't anything special about that computer.They're quite durable, and almost never the source of problems on an EFI Ford.
 

Ocean 22

Seaman Apprentice
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May 26, 2009
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Re: 1994 5.0 Cobra EFI stuck at 25% power

fourwinnsfive , have you been able to find the problem with your engine? please share with the rest of us.
Thank you
 
Joined
Jun 28, 2009
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Re: 1994 5.0 Cobra EFI stuck at 25% power

Thanks for all the detailed help everyone. I have been swamped with work the last few weeks and unable to make it to the boat. I am going to head down there tomorrow and start with the purple and black wire and see if I am lucky enough to have the same problem. I will keep you all posted.
 

Ocean 22

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May 26, 2009
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Re: 1994 5.0 Cobra EFI stuck at 25% power

Have you been able to repair the problem? please post an update.
thank you
 
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