I have a question regarding the status of the OMP on my 1990 FC. I have put on about 859 miles since I changed the oil last July. When the change was completed, the oil level was exactly at the "F" mark on the dipstick. Today, I checked the oil level, and found that it was only 1/16" below the "F" mark. I am concerned about the OMP and whether or not it is functioning normally, since I was expecting the oil level to be about 1/4" below the full mark. Question: if the OMP has failed, how many miles could I put on before a noticeable problem would arise, such as engine seizure?

Earlier this year, I had started to add ordinary, mineral based 2-cycle oil to the fuel at a 200:1 ratio after learning that S5 OMP's inject less oil into the engine that the S4's. Since then, it feels like my engine has picked up some power, as the acceleration has noticeably improved. The side effect, however, is that I now have a puff of bluish-gray smoke blow out of the exhaust upon startup from cold.

 

For the FD at least, the ecu should throw a check engine code for an electrical malfunction of the OMP.

The oil injectors are augmented by vacuum (or pressure) assist from the manifold. If those vacuum lines are damaged the oil injectors might not be operating as well as they should.

You could visibly check the vacuum lines (which might need the UIM to be removed), or you could have a shop run a "smoke test" to check for vacuum/air leaks.

Generally in our area we are advised to do premixing even if we still have an OMP attached.

This is a precaution for an aged OMP that may stop working unnoticed.

Check the gaskets for the OMP/Keg. Check that the clear oil feed lines to the injectors are not leaking.

General guidance we have is that for a 65 litre tank we should pre-mix 180ml/65l (with OMP) and 360 ml/65l (without OMP)

There is a considerable range of opinions on this.

 

If you have a borescope or a good inspection mirror and flash light, it's possible to remove the leading (lower) spark plug and look into the chamber. On my FD engine I can look in that spark plug hole while turning the engine by hand using the bolt on the eccentric shaft, and see the face of the rotor as it slowly sweeps by. On my engine there is plenty of dark sooty carbon buildup on most of the rotor except a single clean spot near the center/top of the rotor, and it's my understanding that clean spot aligns with the OMP injector.

I'm not familiar with the FC vacuum lines, but the OMP 'vacuum lines' on the FD connect to the intake tract (between the turbo and the airbox) so they are basically a breather line not a vacuum source. I don't think they are built to experience the sort of vacuum or boost that would happen if connected to the intake manifold.

 

contrary to popular belief you likely would never know if an OMP stopped working. out of curiosity i ran my car with no OMP and no premix for over 8000 miles with no added lubrication and the compression was barely harmed during the test. i rebuilt the engine about 20k miles later when it finally dropped into the 70's after nearly 100k miles of rather spirited abuse and began to get cranky about starting when cold.

the engine was running a 70 trim turbo and over 10psi of boost. i was running Atkins classic seals for reference.


i do not condone running without added lubrication though, premixing is always my ideal 1st mod for these cars. the factory injection rate is too low if you ask me.


if you want to be sure, follow the OMP output test procedure in the FSM. then test your oil metering injectors, i've never seen any clog up but i have seen the one way diaphragms fail regularly.

 

Thank you...That's what I wanted to know. I have put some 4500 miles on the engine after I bought the car, but before premixing the fuel. If you didn't have any problems after 8000 miles, then my engine should be fine. I really need to do a compression test so I can get an idea of how wear there is as well as testing the OMP system. For now, at least, I don't have any starting or performance issues.