I have a 90 vert and ever since I have owned the car it will go into "limp" mode after about 18 minutes of driving. When I get the codes out of the car it gives me "27" which I have come to learn is the OMP. So this past weekend I had the car up on blocks and did the test on the OMP to see if it had the proper OHM's running through it and unfortunately it did. I ran through the entire diagnostic test that I got from the online manual and everything checked out.

Now here is the real kicker. Now still after about 18 minutes of driving the car will go into "limp" mode. But now if you turn the car off it will reset itself and I can drive the car another 18 minutes before it goes into "limp" mode again. Inevitably I could probably do this forever, but to say the least it is annoying.

My Questions: Has anybody had this problem? If so, how did you fix it? Could it possibly be the ECU messing up?

Any help would be great.

 

Uh...how about replacing the E-OMP as an answer???


-Ted

 

Well I believe the OMP may be working. Does it make sense that the car can driven 18 minutes before the ECU finally puts it into "Limp" mode? If the OMP was out wouldn't the ECU put it into "Limp" mode a little earlier? I have made sure all or most of the grounds are connected.

 

Uh, stock ECU's rare fail.
The most common failure is due to a short from a bad wiring harness.

The E-OMP is a known common failure.
The "quad" leads might ohm out right, but if the position sensor gets confused, it's still "bad" (according to Mazda).
The reason you're getting a consistent 18 minutes is because you're probably driving the same route all the time???
The E-OMP will trigger an error code once you go over 25mph; I believe this is in the FSM?


-Ted

 

So you think its a bad connection in the wiring. You can drive the car like a race car or baby it and not push it past 3k or leave it sitting. A little after 18 minutes (18:07 to be exact) the car goes into "limp" mode. So if it is bad wiring harness, would the OMP still get the proper voltage readings out of it? I have read that neither the ECU or OMP are likely to go out, but is seems odd that the car goes into "limp" mode like clockwork. Wouldn't the ECU run all of its checks on the car faster that 18 minutes?

 

No, I still think the E-OMP is bad.


-Ted

 

What is the E-OMP?

 

E-OMP = electronic OMP

my car did this too... I just got really tired of the whole system and blocked off the OMP and went aftermarket ECU

 

so you just got a new ECU and took out the OMP. Or did the new ECU fix the problem?

 

new ECU = stand alone, not stock.

you can't take out the OMP with the stock ECU on S5s (89-91) or you'll just run in limp mode all the time.

the harness wires going to the OMP might be bad, did you check those?

 

I ran through all the proper diagnostic tests and the OMP plug and ECU were both reading out the proper voltage. Which makes me believe it could maybe be the ECU messing up.

 

did you do these tests after the 18 minutes and the MOP had triggered the ECU or ???

I agree with Ted, I think you have a bad MOP

 

if you have any doubt that your MOP (previously referred to as OMP) is doing its job, you should premix in the meantime. err on the side of caution.

I also had a code 27 a while back, with the limp mode, and it was even more sporradic than yours. sometimes my car would go a week and no code. other times it would limp every day. I scored a used s5 MOP for like $50 on ebay. I pluged in the electrical connections and set the MOP in a safe place in the engine bay. code went away. I drove this way and continued to premix for a good few months and the code never returned. deciding that the new MOP was good, I unbolted the old one fom the engine and intstalled the new one fully.

 

I did that and a blew my EGI fuse on the first run out

I thought that was just cause you shouldn't do that... but maybe it was something else.

 

No I did them after the car had been sitting for over 24 hours. I thought maybe that after the engine heated up to a certain point it did something to the connections, but that doesn't make sense, because it doesn't have to do with heat, it is purely based on time.

 

Probably more based on use than time.

 

That's what I was origanally thinking, but I can drive the hell out of it for 18 minutes and while the car is still moving turn it off and back on and drive it hard again for 18 minutes. This process can go on at least 4 times. Could the ECU be cycling through its tests and on every nth test could it spit out this code?