So my CEL was flicking on any time I'd drive for more than about three miles, and the car (S5 NA) would put itself in limp mode. Instead of simply turning the engine off and on again to remedy it (durr), I pulled the codes with an OBD1 reader and got 'P 27'. I don't know what the P is all about, but code 27 comes up on the googles as "MOP (General) - Basic Fuel Injection and fixed timing"

The shop manual I found recommends I replace the OMP, buuut those are a couple hundred dollars, and I want to make sure there's not some insignificant thing I may be missing first.

I already checked all the connections and cleaned them off, and went around plugging up fucked up vacuum hoses and such.

Is there some small thing I might be missing? Anyone?

 

You're not missing anything. If the wiring is fine, replacing the pump is basically your only option. A second route would be pre-mixing 2-stroke oil and having the ECU rechipped to bypass the MOP. Pocketlogger offers rechip services for S5 NA ECUs now: http://www.pocketlogger.com/index.ph...age=1&ecu=S5NA. Also keep in mind that the ECU can be damaged when the pump fails, so you'll likely need a new one to begin with.

 

If you keep driving the car, the MOP will probably burn out your ECU. You should unplug the MOP if you are going to keep driving it. My MOP burned out my ECU, just like the guy in this thread. I drove the car 5-6 times after the limp mode started coming up randomly before the ECU burned out. I had to buy a used ECU and a good used MOP. I will be changing over to an Rtek soon to prevent it from happening again.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s5-mop-ecu-failure-diagnosis-710938/

 

you can get an rtek that will disable the mop. It won't fix it though. You will have to disable it in the software otherwise the code will still pop and the car will go into limp mode

 

Thanks for the replies guys! MOP is now unplugged. Guess it's off to eBay... eek.

I like this option! Are there any advantages to a set-up like this other than cost-effectiveness? The MOP is essentially foreign territory for me so far, so I'm not sure how the car would run if it were bypassed...

Also, I've heard horror stories about people frying their MOP an their ECU, replacing one, and then just having the one fry the other until they've burned through dozens. If I just replaced the MOP without the ECU, so you think the chances would be good that if the ECU were bad, it'd fry my shiny new MOP?

 

Be VERY careful buying a MOP off of ebay.

A well recognised forum member in the classifieds may be a better option.

Or, do what I did and buy a used one from rotary performance. I paid $400 for it, but at least i knew it worked and it came with a warranty

 

I think the 'horror' stories are overblown. I have heard of guys burning several ECU's before they fix the MOP. The MOP takes out the ECU when there is an internal short, thus drawing an excessive current and burning a couple of resisters in the ECU. I don't think the ECU burned takes out the MOP. I think this is more a case of getting a bad used MOP the second time. I bet many S5's have met their end of life by MOP/ECU failure, thus I would suspect *any* MOP from a part-out.

The ECU can be opened up and visually inspected. There are pictures in the thread I posted. The damage is very obvious. I have heard that the ECU can be repaired by replacing the damaged parts. I am not that capable with a soldering iron.

Buy an MOP from someone on the board. Test the MOP using the method and chart detailed in that thread BEFORE you install it. Make sure that you buy it with the understanding that you are going to test it and that it must pass the extended test, or you need your money back. That is a fair deal for all. You should be willing to pay more for this arrangement and less for a you-buy-it-you-own-it deal.

My original MOP tested good by the Factory Service Manual tests, but failed in the extended testing. I then bought a used 'from a working car' MOP but they couldn't really guarentee that the MOP was good. It passed the extended tests and has been working for a couple of years. I also had to get a used ECU to replace the burned one.

Good Luck!