as i said much earlier i would not spend a lot of time trying to diagnose idle and rough running issues. your engine is sick.

your compression will cause drivability issues that you're partially seeing. it may have other issues like timing, TPS, vacuum leaks, fuel system cleaning, etc. but the engine is going to mask much of that and make it very difficult to figure out what is doing what.

if a customer brought me a car with 60psi on a rotor i wouldn't spend an ounce of energy trying to make it run right before addressing the engine concern.

 

 

"Only runs good when cold". Is that a symptom of a bad water temp sensor/connection? IIRC. Then again I don't really recall... Also could be a bad cat.

 

Certainly not a bad cat, there isn't one in this exhaust :P

We'll look into the coolant temp sensor connection next time we get to work on it, although we did experiment with unplugging it (which made no difference)

I'll check the continuity with my multimeter next time I see my buddy

Our next line of investigation is to check the timing (we ran out of daylight today after doing the brakes and running through everything fuel related with this motor)

 

If you get frustrated I got a ..ahem..Car ..for sale..( I hate pluggin stuff,especially on a tech thread,so just PM me if you get Real stuck!)

 

the brake booster line has a check valve in it, so that vacuum test told you nothing...

 

Does it really?

Well Sh*t, I didn't see one in the line.

We'll do another check tonight.

Does it really matter which line we pull it from long as its not the booster line? any suggestions?

 

the restrictor is formed into that hose so you can't see it, so yes that figure is useless and probably your upper end spectrum in which 15"Hg is quite poor for a stock port engine.

in the second video it sounds like the engine started running on one rotor. was it backfiring or just coughing? if it is backfiring then the second rotor is getting fuel but either no ignition(fouled spark plug or arcing wire) or compression(intermittently sticking apex/side seals). if it is just coughing then it is probably lacking fuel, such as a faulty primary injector or injector wiring/clip.

even when it was running "ok" it sounded sickly.

start with the basics, change the spark plugs/wires and fuel filter. or address the compression issue, but i doubt you want to since you seem to be totally ignoring that and plan on running it until that low compression chamber grenades or the one carrying it along does. if the minor tune up doesn't help then i would do another compression test after the issue occurs, if the compression is still as it was when cold then i would suspect a primary injector clip is broken and failing when the engine is warmed up.

of course no one wants to hear this little bit of advice either... if the engine is original it is not going to last very long, these engines are 25 years old, carbon caked, using inadequate worn out 3 piece apex seals. ie ticking timebombs unless it was well cared for and low mileage.

 

To go with what RotaryEvolution said, it will be a lot cheaper to pull it apart now and replace some soft seals, springs, and apex seals, rather than a housing, rotor, iron....etc etc...

 

Good to know, thanks for that


We're not necessarily ignoring your advice regarding the compression, it's just not our motor. Although with your advice we have convinced the owner that a rebuild is necessary and he is budgeting for a rebuild over the winter, we're mostly trying to get it to run so he can drive it to better storage

 

Basically what he said, its not my car, I'm just trying to help get it running.

 

then honestly the best advice i can give is it sounds like a faulty injector clip. the engine does not sound as if it is backfiring but the video could be misleading.

on the passenger side of the car there are capped off nipples near the secondary fuel rail. get the engine to the point where it begins to have the issue and get a can of carb cleaner and a 3' section of vacuum hose. uncap the front port and attach the hose, hold the throttle up so that the engine doesn't stall and just tap the nozzle on the carb cleaner to pump some into that port.

if the engine struggles more and seems to want to stall, remove and cap that port and move to the rear port, rinse and repeat. if either front or rear causes the engine to run normally for a few seconds then that side of the engine is not receiving fuel from the primary injector for that rotor.

the primary injectors are located under the intake manifold so you will have to remove the whole upper intake to get to them.

if the clip for that injector looks broken i simply recommend replacing it with a generic bosch EV1 clip which can be found at most auto parts warehouses. if it is an '87.5 model you can bypass the offset lug by cutting it off the injector so the clip will fit(i do not know where to source a high impedence denso style clip for the late series 4's).

but even if you do get it fixed and running reasonably the engine is still in need of help and make sure he knows that.

if the engine is backfiring loudly when the problem exists i would start by changing all the spark plugs and wires, if that doesn't fix it then the problem is inside the engine and cannot be readily fixed. though the car should be drivable it will be very difficult to drive running on the reserved rotor.

 

Hey this may be a dumb question but how the heck do you guys unplug the primary injectors or check them for power, they seem unreachable with the intake in the way.

 

i said it right before you asked.

you can also backprobe the ECU to check for 12v with the key on at the injector signal wires, but i suspect you will wind up needing to remove the upper manifold anyways. even a 12v reading can be misleading so i prefer to just knuckle down and go for the root.

 

 

What happened on checking the Water Thermosensor? It should read 2 to 3 volts w/key to on at pin 2I w/key to on. Fully warmed engine should read .4 volts w/key to on.

 

I ran out of daylight,

If you watch the first video it shows once the engine got warm and started acting up, that disconnecting the TPS allowed it to rev freely while having it connected made the engine run like crap.

Even though the TPS allowed it to rev freely you still think it may be the temp sensor?

 

The TPS, when unplugged, causes the ECU to default to a full throttle position.

 

hate to be "that guy" but most of us, i think would have hooked the hose for the vacuum test up to the engine. it IS interesting that i think you hooked it to the metering pump spider and it has vacuum in it

 

So what should i conclude from that? That the TPS is not the problem? You believe temp sensor?

I have no clue what i hooked the thing to, i dont know rotarys well, it was a vacume hose and it looked like it ran down into the engine somewhere :S

If i have to go back to his house a third time to do a vacuum test, please just tell me where the heck i should plug this dam thing in

 

Pin 2G of the ECU is G/R and this is the input wire from the TPS. It should read 1 volt w/key to on and the engine as hot as it can possibly get. It could read this value at the sensor but that doesn't necessarily mean it has the same reading at the ECU where it is most important. And the TPS needs to range from 1 volt at idle (engine fullly warmed) and progresses up to about 4.5 volts or so when the TPS piston is fully extended. And the climb from 1 volt to 4.5 volts should be smooth and completely free of bumps or gyrations from the meter. An analog meter (w/needle) is a much better method for testing this range than a digital meter as it is not sensitive enough nor quick enough to indicate possible dead spots. And taking the Thermosensor reading is important as it might be way out of spec.

 

Ok i'll test it next time I'm there.

The reason i even suspected TPS was we fired her up today and it immediately started acting wonky even cold. Then it smoothed out and ran ok-ish until it warmed up, then started acting wonky again.

I'm still kinda confused how disconnecting the TPS would resolve the issue if the TPS was NOT the issue. Like how would the TPS being disconnected resolve a Thermosensor issue, I thought the temperature impacted how much fuel it injected.

 

Because if you disconnect the TPS it tricks the engine into believing it is running at a higher rpm which then means the ECU then makes certain adjustments.

 

this isn't rotary specific, but you took the hose off the intake, and just put the vacuum gauge on the intake. cap the hose. just like any other car.

you could also use the boost sensor hose, which might be simpler, on the passenger side shock tower, there is a little black sensor, it should say N327 on it, with a vacuum line on the bottom of it. follow the vacuum line to the intake, pull it off the intake, put your gauge on the intake, and test away

 

well, the metering jets do enter late into the intake stroke and will still pull vacuum, so i suppose that does work but i also wouldn't really consider that an accurate vacuum source either.

strange that it sounded like a lawnmower in the first videos but sounded a bit different in the later videos, not so much as if it was running on a single rotor otherwise i wouldn't have suggested ripping the upper manifold off to test injectors.

the TPS however does cut fuel to the rear rotor if it thinks it is on a deceleration so it makes sense that a faulty TPS would be the main culprit. i would start by checking voltage at the green wire off the TPS with it still connected, engine fully warm, engine off key on. do a sweep and it should read 1v at closed throttle up to 4.6v at 30% throttle, if the signal breaks up at all then the TPS is bad.

with the TPS disconnected the ECU will default to open loop, so it will not cut fuel on decel which is why it acted differently/better. decel fuel cut is to improve mileage, reduce emissions and eliminate backfiring/afterburn.