Trouble starting one dry plug
 

SO i am working with my son on a 1986 NA RX7. We bought the car with no engine or transmission. None of the wires were cut on the car, but none were labeled either. We bought a used eng and trans that was supposed to be in good shape and it did appear that way. So after connecting everything up - wires and hoses, filling with fluids, we fired it up last weekend. It ran for a few minutes- lots of oil smoke, then quit. We had no fuel pressure so i put in a new pump- . now while cranking we get between 40 and 50 pounds. The car seems to want to start if i shoot it up with starter fluid- it will run up thru the RPM's till it runs out of that.....then i check thee plugs and three of them are wet like it's flooded, the lower front plug is always DRY!- it doesn't even smell like gas. Which injector is responsible for this? I am thinking if i solved this problem, maybe it would start and keep going? Any help would be appreciated. Lots of experience with engines, none with rotaries! Pat

Am i wrong to assume that all four plugs ought to be getting gas? If ONE isn't is that a bad injector or is this a mechanical problem? any advice? Thanks

This is an odd one hotrodin. Since the injectors don't directly squirt fuel into the rotor chamber the fuel should be mixed with air as it gets sucked in the side port on a 13B. The secondary injectors mix into the same stream as the primaries, so if one plug is wet they both should be.

But they ain't.

Sooooo...first thought isn't a good one...there's something that fell down the intake and is blocking on of the inlet ports near that plug which is keeping it from getting fuel wetted. Got a borescope? You might want to pull the dry plug and see if there's something obviously wrong at the ports in the side plate. Beyond that, this one has me stumped too. Hopefully someone with more rotary experience than both of us will chime in.

Good luck!

I will be the first to admit i don't know anything about rotary engines- i do know that there are 4 intake ports going down into the engine, so i figured each one discharged to a different part of the cylinder....so i thought if one of the injectors wasn't working, that's why one plug wouldn't be getting any gas. They wouldn't have four individual intake pipes if they discharged at the same place would they?

Just got good measure I would pull all of the injectors and clean and test them. Weird that one plug isn't wet but the others are, maybe the one dry plug is the only one firing? Check spark on all four plugs. After that put a little oil in the bottom plug holes and see if that works.

i wished i had sent the injectors out for cleaning before i put the upper intake on!

Don't worry, you will be able to do the whole thing completely blindfolded after a while.

maybe it's one of the upper injectors that are easy to get at? can't be the back one...gotta be the front one- or maybe the lower front one- i'm sure the intake runners don't "cross" each other...if i knew it was the upper one i'd just send that one out for testing. has anybody on here ever taken one of these engines apart? somebody must know which intake port would feed the bottom front plug?

The upper injectors are the secondary injectors. They only kick on at ~3500 RPM. The 2 under the UIM (Upper Intake Manifold) are your primaries. They run throughout the whole RPM range.

I'll bet you got it fired up last weekend on one rotor, and now the rear housing is flooding and the front is starving for fuel.

My guess is dirty injectors. It wouldn't hurt to send out the injectors to be cleaned. Or if you have a pick n pull near by you may be able to swipe a few.

After you get the injectors cleaned i'd clean the rails and purge the fuel line.

You really should send all the injectors out for cleaning, once the upper intake is off they are all right there for you to get access to. The upper intake is really only a handful of bolts to take off. There are four intake runners the two rear ones feed the rear rotor and the two front ones feed the front rotor. The two spark plugs are in the same chamber so they both get fed from the two intake runners, so even if one runner was blocked somehow both plugs would still receive fuel.

So how could one of the plugs be dry and not even smell like gas and the other one was wet? I actually can start the car- it will run nice for about 5 seconds, then quits- then 3 plugs are wet like it's flooded, lower front one is always dry.

I did actually put a new fuel filter on it last weekend and a new fuel pump, then i put a long hose into a bucket and pumped about a quart of gas thru it. I will probably pull those injectors and get them tested.

The 2 forward plugs (L1 and T1) are inside the same combustion chamber so you tell me. Maybe its just enough fuel getting through to wet the trailing plug.

https://cimg5.ibsrv.net/gimg/www.rx7...6753a3dc8.jpeg
Well i pulled out all 4 injectors. pretty crusty/rusty. definitely OLD. While removing the upper intake i found a two prong connector NOT attached to the 2 project sensor? switch? on the left underside of the upper intake. I don't know what that one does, but i'm sure it didn't help to not have it hooked up. I guess i'm going to get these injectors rebuilt. out of curiousity do the upper and lower ones have the same flow rates? As in do i need to remember which one came from where? thanks pat

From the factory, all 4 injectors are the same.

You could only be firing on that one plug. Have you checked spark on all four?

Doubtful because the leading plugs both fire at the same time, and the engine would have to fire for the plug to be dry.

anybody know what the sensor is for that wasn't plugged in?

Quoted for the truth.
that being said, have you tried changing plugs? Stop focusing on why one plug is dry. Check resistance on your injectors and make sure they havent failed. Perform a poor man compression check and listen to what it sounds like.
you got this, read up, you can get most rotary engine to run, even with a failed "cylinder". Rotary concept is same as piston. You need air and fuel, some spark and a minimum compression lets say 85psi for both housings to run.. Test all that you can concerning this and you will find where it's not passing. From there you research more or ask another question on the forum.
You won't find better instructions readily available from this forum. Seek and you will find.

well the lower injectors are both 12.5 ohms resistance and the the top ones were 2. so my haynes repair manual says it ought to be between 1 and 3 ohms....so unless there is something different about the lower ones, i would say they are just shot....

Agreed! And even if they are not, the control system won't actuate them with that high a resistance value anyway.

Are you planning to stay with the stock control system, or change it to something more modern? If staying with the stock ECU, then swap the injectors for new ones. If not, you might want to see what injectors are recommended for the new ECU and replace all four at the same time.

Yeah at the very least all of the injectors should have the same resistance 86-87 all came with low impedance, and used resistor packs. Pull all the injectors, get the number off the side, and let us know which ones you have.
••84-85 13B NT low square center 680cc orange 195500-0900••86-87 13B NT low square center 460cc red 195500-1350••86-87 13BT low square center 550cc tan 195500-1370••88 13B NT high square offset 460cc red 195500-1350••88 13BT high square offset 550cc purple 195500-1370••89-91 13B NT high oval center 460cc red 195500-2010••89-91 13BT high oval center 550cc purple 195500-2020

new ones are big bucks...i'm going to see if these can be rebuilt. there is a shop in Schenectady NY that rebuilds injectors...so these are going in the mail today. I'm keeping the stock ECU for this car.....Our other car is a turbo 1990 model that my son uses for drifting....we are looking for a Halteck for that one...

our injectors were the 195500-1350 ones...all the same...

Ok so your using high impedance injectors. Your bodies year came with resistor packs. You either need to remove the resistor packs, or run low impedance injectors with the resistor packs.