Its plugged in. I wouldn't be able to drive it if it weren't

rxhevin, I think I will try swapping the TPS out, can't hurt I suppose.

 

this may sound kind of dumb but is there anyway to see if the mass airflow sensor is working properly? my friend had a bad contact in his mass airflow and it ran like crap ( same symtoms you have) only his was completely stock...need less to say one of the wires broke (they were just so old and brittle) that plugs into the mass airflow and it messed everything up..

 

It could be the AFM but I think Ted is onto something here. Normally When you buy different injectors they will not plug into the stock connectors for the harness of a rx-7, especially if it is a kouki(89-91). Did the injectors plug right up? did you have to shave any keyways from the injector? Maybe they are not connected properly. For testing puposes I would put everything back the way it was before and see how it runs. This would give a solid basis to test with.

 

Ok, pop quiz for me.... I just loaned out my two stock 550c turbo injectors to my '88 Gxl buddy. His car runs super with them in, without additional resistor assistance....could we be potentially hurting the electrical system? His injectors are supposedly high impedance. ANY response would be greatly appreciated.

Sam

'87 TII
Blown engine
w/ J-spec hopefully coming
for to kick Honda ***!!

 

i didnt read any of the post but it sounds like what happened to me when i did a temporary PD fix. i used a self tapping srew and some epoxy and i suppose the car wasnt getting enough fuel, it would operate past 1/8th throttle and it just bogged down

Justin

 

Anthony,

my car did the same thing when i put those 720's in it. I bought 10 ohm resistors and everything, the only thing that fixed it was putting the 550's back in. I never did figure it out, if you do...let me know.

-Nick

 

Can't be the secondaries if it screws up under 3800. *Crusty old wiring*? Pull the small plug off the ECU and check the injector wiring with a meter. Put the meter on ohms and get on one injector wire at a time at the ECU and the other end of your leads on the power wire coming into the injector. See what the reading is. Should be around 12ohms as you know. While doing that twist and turn the injector wiring. Your looking for your 12ohm reading to break or go to some shorted condition while doing this. Primary wiring seems to be your trouble spot. Frankly speaking, since the above would require removing the intake, I'd just go ahead and put the original 550's that were in the secondaries, in the primary holes and move the 550's that are now in the primary holes, into the secondary holes. Then put the thing back together. It shouldn't take you more than a couple of hours max to do that and give it a try. If the car runs good at idle and bad at above 3800....;well you know. Just auger in and do it. Uh. You did'nt put the wrong vac hose on the wrong pipe on the back of the throttle body did you? Probably gonna turn out to be a big vac leak somewhere.

 

I've done everything today, except put the old 550's back in the secondaries. I put a new primary fuel rail with a pulsation dampener on, thinking the fuel pulses were causing it. Now, it idles good about 40% of the time, the other 60% it bucks and sputters, and idles rough.

I am going to replace the 720s with the old 550's and see if it fixes it. I do not know if the injectors get their power in series or parallel. Or if it even matters. I even went so far as to get an 87 ECU just in case I could use it. I have to have the larger injectors, or my new turbo is worthless.

Hailers, I only have three vaccum hookups on my intake. Fuel pressure regulator, oil injectorsd, and brake booster. My solenoid rack has long since been removed. There are no vacuum leaks, and it ran bad with both sets of injectors in the primaries. I was going to try to ohm the wires out like you said, but my meter leads aren't long enough. Everything is like it wsa before when it ran good, with the exception of the secondaries. I just wonder if they are confusing the ECU or something. I have them oriented in the plugs correctly, I had to get some low impedance plugs to install them. I have the resistors soldered in correctly, and everything. I don't know what else to do besides put the 550s back in. Maybe I can run the 720's in a seperate fuel rail off a boost switch or something. I'm at the end of my rope.

 

Sorry. I can't see how it could be the secondaries if the problem is happening below 3800. The injectors are all spliced into a B/Y wire for the power and all have seperate grounds at the ECU when the ECU pulses them (see page 50-22 of the 88 manual on line).Secondaries don't get pulsed below 3800. I understood originaly that it was happening below that figure. Might have misunderstood. If that is the case, then I still say its a short of some sort. The vac hose idea was a WAG. Yup, put the thing back as original and see what happens.

 

Actually it does sputter a bit above 3800. But most of all the trouble is under 3800 at about 1/3 throttle and below. Putting a pulsation dampener back on has made the problem sporadic now. If the original secondaries do not help, I guess I will start looking for shorts in the harness.

 

Wiring 10 ohm resistors in as I was told was a failed attempt. I put my old 550's back in with no resistors and all is well. I have a plan for the 720's, I just need a pressure switch and a couple other things

 

Why 10 ohms??? Mazda only uses 6 ohms. And that should be a high-wattage resistor wired to the power side of the injector. Just some interesting info.

Irv, Keith's dad

 

Low-impedence fuel injectors spec out to 2-4ohms each on average.
High-impedence fuel injectors spec out at 12-14ohms each on average.
You can do basic subtraction, right?



-Ted

 

Yeah, the 550s were around 13 ohms, and the 720s were about 3.What I was told seems right, but it damn sure didn't work

 

Irv, how many watts are they? When I put the 10 ohm ones in, no one told me what wattage ones to use. I think the ones I used were 2 watt ones, the highest I was able to find around here.

 

Whoa, 2-watt "carbon" resistors is too small!&nbsp These things will literally crack and fall apart due to the sheer current.

Amps = Voltage / Resistance
Amps = 12V / 10-ohms
Amps = 1.2A

Wattage = Amps x Voltage
Wattage = 1.2A x 12V
Wattage = 14.4 watts

People have gotten away with 10watt resistors, but I really recommend 20watt ones due to the numbers.

You need to find "sandblock" resistors.&nbsp These are resistors that have a white or tan colored ceramic casing around them.



-Ted

 

I believe I have some of those, they are square and a grayish color, but they didn't have any wattage rating on them. I bought several sets because I was unsure of what to use.

I'm going to go kick my brothers *** for telling me 2 watts was enough!

OK now I get to try 10 ohm 20 watt resistors. I bet Radio Shack has none

 

Hey, you got me again, Ted. Never mind that low impedance injectors might have higher holding current requirements than high impedance injectors. Never mind that 6 ohm resistor packs were used on every 86-87 1/2 RX-7 vehicle that left the factory. Like me, the Mazda engineers cannot do basic subtraction either, it seems. I am sooooooo embarassed!

Irv, Keith's dad

 

You're right!&nbsp I'm not going to even get into the difference between "impedence" and "resistance", but I'm a college drop-out, so you have to excuse the simplified math.



-Ted

 

Well should I try some 6 ohm ones? I believe I know where an 87 TII is in the junkyard if I would be able to use its resistor pack. I'd like to give them one more try in the secondaries before I go and make myself a crude AIC and add them on the top of my intake...

 

I would say get the resistor pack if you can find it. You know the wattage rating is sufficient. Also, they are encased in metal to help dissipate heat. Also, you can mount them in a cool spot (the resistor pack is under the stock air box on an 87). If you wire large wattage resistors directly to the secondary injectors under the intake plenum, the high heat in this area could cause premature failure, even though they are 20 watt resistors. To wire the resistor pack, just bring 12V ignition power to the black/yellow stripe wire on the pack, and then use any 2 of the other 4 remaining wires as power to each secondary injector (Don't forget to check resistance on the selected wires to the common power wire!). Good luck!

Irv, Keith's dad

 

Thanks! I needed to know which wires were which on the resistor pack. You saved me the trouble of asking another question I borrowed the resistor pack off my brother's 86 NA to experiment with tomorrow, and if it works my friend is going to give me his old resistor pack, since he uses a Wolf 3D. Hopefully it will work.