So I took my S5 'Vert out of storage this week. This week I took it down to the shop to clean it off. I scrubbed the car down, and pressure washed it off (just the exterior), went to start the car, and it won't start unless I floor the gas pedal, and then it barely starts (see video below).

I pulled all four plug wires, I have a good healthy spark on each one. Put the plug wires back on the first rotor, wouldn't start or even catch at all. Put the plug wires back on the second rotor and pulled them off the first, then it would run barely, like it did before.

Checked around for loose or wet electrical plugs, couldn't really find anything. I did find one plug just above the water pump, three wires, that fell apart when I grabbed it, terminals fell out of connector. Not sure where it goes. Wire colors on the harness side: Brown/Black, Brown/White, and Green/Black. Wire colors on the engine side: Yellow/black, Blue/Black, and Black. I think it might be for the MOP, but I'm not sure. Anyone know?

Just checking to see if anyone's run into a similar issue before, before I tear into the engine harness looking for something.

Video of the car running:


The connector that came apart on me:

 

OK, I found an engine diagram with wire colors... Looks like that connector is for the OMP position sensor. Still doesn't help me with matching the wires back up or with my one-rotor condition though lol.

 

Usually error codes point to a bad connection between the ECU and the various sensors. With that being the case, have you checked for error codes so the ECU could perhaps tell what your problem is?

 

Your ECU has gone into limp mode because the OMP is unplugged (or, as far as the ECU is concerned, the OMP has failed).

 

Limp mode makes it run on only one rotor? I thought it would just return the timing to base or something...

Does anyone know which way the two sets of wires are supposed to line up? As in which wire to which wire? If someone could look at their car that would be greatly appreciated! The connector just fell apart on me, so I don't have a clue...

 

The car is at the dealership I work at, so I won't be able to pull codes until Monday. Wish I had thought of it though lol

 

Thanks to a local member texting me a pic of his plug, it looks like it goes like this:

ENGINE SIDE OF CONNECTOR <> OMP SENSOR SIDE OF CONNECTOR
Brown/Black <> Black
Brown/White <> Blue/Black
Green/Black <> Yellow/Black

His car is a T2, but I'm hoping they're the same

 

S4 and S5 colors are different btw, so hopefully that text is of an S5.

 

Well, seeing as how s4's didn't have an e-omp to begin with, I think it's a safe bet that those are s5 wire colors/locations.

Anytime you run on one rotor, I always change spark plugs and check coils for spark on all 4 wires. It's quick and easy to troubleshoot the ignition system, before moving on to fuel and compression.

 

Yeah, was an S5 obviously.

I do have a good spark on all four wires. I'll take a look at the plugs tomorrow too.

 

Right...for some reason my brain decided to read TPS instead of OMP .


Just ignore the idiot in the corner and go about your merry way.

 

Got a chance to look at the car again this morning.

I disconnected the battery for about half an hour, wired up the OMP sensor properly, and tried to start the car. I'm getting the exact same symptoms, barely runs, doesn't want to idle.

I grounded the single green check connector by the trailing coil to check for codes, but there are no codes. Any other ideas?

*Edit: Overheat Exhaust Light is on as well...

 

Have you done a compression test yet?

 

Haven't checked compression yet, but it drove awesome on Saturday to the shop, I shut it off with the key like normal, washed it, and now have these symptoms. So I'd be surprised if it was compression, but I'll check. Just the way it's acting really seems like an electrical issue

 

**** me.

Just pulled a plug out of the rear housing, three strong pulses.

Put it back in and pulled a plug out of the front housing, one strong and two weak pulses.

Gayyyyyyyyy

 

Possible stuck apex seal? Or not likely since it ran fine on the way to the shop?

 

Well without researching enough, I threw some ATF in the front housing yesterday, let it sit for a day, but no dice. I'm not surprised. Might try some GM top engine cleaner this weekend, we use it to remove carbon deposits on the Gen IV 5.3's with active fuel management, seems to work well. I'm hoping that's all it is, will have to remove the exhaust manifold this weekend to get a good look at the seals

 

Apex seals don't "stick" while in service. They stick from sitting for months or years.

 

That's what I figured..

In any event, at the end of the day I have no compression on two faces. Motor is coming out this weekend.

 

Bummer. Sorry dude.

But, this is why I always say that the number one rule of rotary engine troubleshooting is a compression test (even a poor man's ear test). These things can let go at any moment for no reason at all so if you have any major issues you always start there and then work backwards to the harder-to-test stuff like fuel, ignition, timing, tuning, etc.

 

You still could have a stuck apex seal as it will stick if left not starting for a long time. ..and it's a high mileage motor so there's a good amount of carbon on the rotors (good reason to premix).

Try this. Nothing to lose and won't damage your motor anymore than it is.
Look for a large vacuum hose and get a bottle of water. Have the engine suck it in and this will
push water into the combustion chambers. This produces high temperature steam and will loosen any carbon and hopefully loosen the apex seal IF it is stuck. Have someone keep the revs up to keep it from stalling. If all goes well, change spark plugs.

 

If you search on the forum, thers's a bunch of ATF threads. I wouldn't use ATF as whatever is in the chemical mixture, it softens coolant o ring. It does soften the carbon but if you plan on not rebuilding a good motor, I'd be against that.

Out of cusiosity, I had some spare o rings and sprayed some ATF on it and left sitting a couple weeks. After cleaning it off, you can feel a bit "spongy".

 

Yeah i regretted throwing ATF in there after I read up on it... but my plan from the start with this car was to swap a 1J or LS in... haters can hate all they want. I was just hoping to get one more year outta the ol' rotang

 

People shouldn't say what they think YOU should do with YOUR car when THEY'RE car is running like **** as they're typing what HE thinks you should or shouldn't do. Really like to see they're car when they're criticizing others.

 

This from the man who doesn't know the difference between "they're" and "their".

Sorry, I couldn't help but point that out.