Hey guys,

So I have an 04, and over the past couple month or so I've been having a limp mode issue. First time happend about a month ago, went to start the car, after about 30 seconds or so, my car stopped behaving responsively, my RPM's max out at about 3k, and it accelerates incredibly slowly. Parked it, tried to restart, no difference. I took a different car. When I got back, I went to drive it again (couple hours later) and it drove perfectly.

Drove fine daily for the next 2 weeks or so, then it happened again. Tried to reset the ECU w/ the brake depress trick, didn't seem to work, messed with it for a bit, decided to wait again (had "fixed" it last time). It started driving fine again after a couple hours (I let it sit overnight again). Read up about the OMP, so I checked under the hood, looked like my sohn adapter reservoir was a bit low (still had oil, maybe there wasn't enough weight to push it down idk, so I filled it up).

Now last week, Thursday or so, I was driving on the interstate, about 80 miles an hour, and it went into limp mode again, engine had been warmed for sure, I was about 15-20 minutes into my commute (college). Got it where I was going, parked it, went to class, when I left a couple hours later, drove fine again, got me home with no issues. This concerned me more, since it happened as I was mid-drive, instead of pretty close to startup.

Still my only option at the moment, so I kept driving it, Last Thursday, drove it to school again, limped on me yet again. Left and started fine. Drove it like 5 minutes to girlfriend's apartment, limped about when I got there. Stayed for the weekend, drove it back to my place, started limping at about 5 minutes in again, my oil pressure light came on (gauge read normally). I had read it had something to do with the oil metering pump, so I figured this must be it, but the oil light disappeared after about a mile or so. Still drove it/didn't stop, especially since light disappeared. Got home, checked my sohn adapter, still good, checked my actual oil level, looked on the low end, but definitely still within the bars. Added like a half quart anyway. Started raining, so I stopped working on it.

Drove it again this morning, I noticed that as soon as it got to almost operating temperature it happened again. I was trying to keep it under 4k RPMs, as I had read something about a recall concerning this, did not help, limped at about 3.7k rpms, when operating temperature got to almost normal.

Questions:

I have a sohn adapter, but it was already installed when I bought the car, I'm honestly not 100% sure on how it works, but it gets rid of the need of an OMP correct?

The most common cause of this is OMP failure right? That + oil pressure light indicates this, correct?

I've been having to drive it anyway, it shouldn't destroy anything if I just drive around in limp mode right? I can only go like 62 mph max, but I'm fine driving that on the highway if I need to. Accelerating from lights is a bit more annoying, but I can still deal with it.

Could this have anything to do with compression? My engine is going and it doesn't hot-start, so I'm wondering if it's getting bad enough where I need to replace the engine.

I have no check engine light, but I think my light is broken anyway, because it doesn't pop up w/ the key in the ignition (on start).

Any help? It's kind of a pain to take it somewhere to get it scanned because it won't hotstart for me 95% of the time.

 

Start by checking to see if there are any logged fault codes(any autoparts store will read them for free), then get a rotary compression check before throwing any money at it in hopes it sticks.

 

Can you please restate the problem in 25 words or less.

 

Car = limp mode at operating temperature (highway). Oil light came on, then back off. Caused by OMP? (I have sohn adapter) Caused by poor compression?

 

The Sohn adapter doesn't eliminate the OMP. It just uses a separate oil reservoir instead of the main engine oil. Have you been keeping that reservoir full? Or premixing?

The oil light is oil level not oil pressure.

Definitely sounds like limp mode, which is usually causes by the electronics in the OMP but not the pump itself. Check the wiring to it and get the check engine code read. Ideally at Mazda because not all readers can read OMP codes.

 

Yeah it got a bit low, but still noticeable level in the reservoir. The adapter was one of the first things I checked once I read it could be oil stuff. I have not been premixing.

Yeah sorry, I mispoke there, I assumed it was level (wouldn't have a pressure guage as well as a light). Why I then checked oil level afterwards.

Yeah I'm pretty sure it's "limping", but doing some forum reading, I read that somebody mentioned there being different types of limp mode? Either way mine seems to be having the same symptoms as people who describe a faulty OMP.

Ok, I have to figure out where it is first, but wiring should be from the fuse-box to it, correct?

My major concern is that most people (on this forum) are saying it's the OMP say that it happens after about 10 seconds of running. Mine runs and revs fine until I get to operating temperature, but that shouldn't affect the OMP right? Unless it is supposed to pump in more at higher temps (but not higher revs).

Guess I do need to get it scanned though.

 

Thank you. It could possibly be related to the oil pressure switch. My manuals are all out at the shop. It won’t register as a regular DTC code because it operates as a body switch tied into the dash display. There is a method posted somewhere on the forum to read dash display codes and sensor outputs on the dash without any special tools.

you will need to check for OBD2 codes regardless to see of anything else is going on.

 

Ok, just took it to autozone and got it scanned.
The only code that showed up was for a faulty coolant temperature sensor, which is maybe good news because I found this: Not sure how to tag users or I'd tag him/her.

So this could very well be my problem? It makes sense to me because the car only limps when it's hot, it doesn't do it when cold at all. And from what I've read, OMP would generally cause issues on first startup check (10 seconds in or so).

Also, they had me buy a new thermostat as well, but I don't think I need one right? If my car isn't overheating, the thermostat is likely good? Definitely debating taking it back.

 

Update: I think I finally got to my ECT (couple wires and things in the way, going to be a real pain in the *** to get out). I don't think mine is connected to anything. I felt around the back and it just seems to stick out into nothing. This is supposed to be wired into a plug or something, correct? Going back out to look around some more.

EDIT: it was definitely attached to some wires, I hooked my battery back up and my fans immediately come on w/ key in on position (makes sense cuz ECU is panicking), connector reads voltage as well as continuity so I think the wires are good.

 

If you have a multimeter you can check the resistance of the sensor. It has a defined resistance based on temperature so you should be able to tell if its reading correctly.
Look around for the graph. If you can't find it I think I have it someplace

 

Update again:
Replaced thermostat + ECT sensor, still exact same problem, fine until it heats up, and then it goes into limp mode. I think I'm going to take it to a mazda dealer tomorrow, get them to scan it, see if I can get a different code to pop-up.

While I'm there, fully considering getting a compression test, though I'm sure it's just going to tell me what I already suspect. How much does that run? I remember seeing something about it being around $300, which seems steep to me for basically taking off a wheel and plugging a machine in.

 

300 is steep. The book value is like 1.2 hours of work, so $125?
Anything more is not really justified. Just make sure they actually use a rotary tester.

Is wiring to the ECT damaged? You did say it wasn't connected which is very weird.

 

You don’t have to go to a dealer. Most auto parts stores will check it for free.

just because it happens once it gets hot doesn’t automatically link it to a coolant sensor issue. It could be any number of a half dozen different things, but it will be painful to try and guess your way through. Quit screwing around and see if it has any DTC codes.

 

Oh yeah sorry, I took it to autozone, and got it scanned, told me the only error was ECT sensor. Somebody else mentioned I may need to take it to mazda in order to get an OMP code as a lot of auto part stores don't fully read or something. That was why I replaced those two things.

 

Well sorry for jumping on you. You should have gotten the code and come back here to discuss it first, but it’s your money to keep throwing at it.

The Sohn doesn’t eliminate the OMP. It allows oil to be supplied from the separate tank to it rather than it being supplied used engine oil. So somebody had to take the OMP off to install it. Anytime the OMP is taken off opens up the possibility that the position sensor on it may need to be adjusted. Which if it’s not adjusted in the proper position can cause a limp mode. So the only thing I can thing of is it might be so close to the adjustment edge that it goes off when warm enough. That’s a 100% guess though.

 

No problem I'm not going to get offended at you being snippy, I'm sure there are a lot of dumbasses hanging around here. I just can only really work on this on the weekend, so I was trying to knock things out before I ran out of time for the week again. Thanks for the Sohn explanation as well.

Ok, well that's a pretty good thought. I got it scanned by Mazda and they said it was an OMP circuit #3 error, whatever that is. So I'm guessing that either you are right, or I have a frayed wire somewhere (less likely) or my pump is burned out or something.

Is there any way to test the pump? If so and I don't see any adjustment issues, I'd obviously test mine, and if it's bad I'm leaning towards pulling one off a junk RX8 in a yard somewhere. If this is the case, does it have to be the same year? Or are all series-1 the same? (A quick search tells me that 2004-2008 are interchangeable) Is there any way to figure out if the junkyard pump is still working? If not a new one could definitely be safer. I'll try wiggling with adjustment and checking wires first though.

 

I’m king of the dumba’s sometimes. IMO you should try to adjust the sensor before spending any more money. It’s worth a try any way. Just two screws on the side on the OMP. I can’t recall the thread where it details that. Just mark where it is now so you can get back to that point. When it’s off adjustment the car will start in limp mode. Maybe try a small bit on either side of your mark and see.

 

Here’s a pic. You can see the two screws with slotted holes for the position sensor.

 

Also, if anyone else looks at this car be sure and get the dang DTC code #(s). You’re paying for it, make them give you the specific info.

 

The mazda guys actually scanned it for free for me, but I definitely should have written it down. Just looked at a CEL code list (https://www.rx8club.com/series-i-tec...e-list-212975/), and it was either a P1686, P1687, or P 1688. Fairly confident it was a P1688 for "circuit 3", don't remember high/low flow on anything. Does that help? Still haven't had the chance to take it apart again, just been premixing heavily (+ sohn) and driving it slow as hell. Thank you for the picture by the way.

 

Hi, im actually having a similar issue with the omp aswell and after 2 weeks of reading and re checking wiring i cant get it to work. Fresh rebuilt engine starts and runs fine deleted cat air pump added catless midpipe and removed a/c unit. But when the car starts it instantly gets p1688 CEL. Also to note the car has unstable idle, in neutral clutch out sitting there it bounces between 1000-1500 rpm. But when i press the clutch in it settles down to around 1000 rpm. Not sure if its related or a seprate issue but more info the better. Also i have tried adjusting the OMP sensor position 4 times and no luck.

 

The idle bounce could be the clutch safety switch on the pedal or the clutch could be dragging/misaligned. See if you can get it to react by pushing on the switch by hand, that will confirm it.

I'd remove the OMP from the engine and reinstall it being careful that everything is aligned including the little shaft that drives it. Or, in the worst case, look into getting another OMP to test with?

You can unbolt it by let it dangle by the oil lines.

 

I never even considered trying to reinstall it. and had no idea about a safety switch under the clutch. I work today but tommorow ill go try these out first thing. Thanks for the great tips

 

Well I checked the clutch safety switch and yup it was loose turned it clockwise and clicked in place. Still feels a little loose but the idle settled down . Bad news is I removed the omp, re mounted it aligned and tried again but I'm still getting p1688. The pump seems to be working as oil is flowing through it and up the lines. But I just can't clear this code.

 

not sure if you saw this or not:

https://www.rx8club.com/series-i-tec...6/#post4919746