Hello, I have an 86 NA that I've been fighting with for a couple years now. Essentially it ran fine, but then one day it wouldn't hold idle, you'd have to keep your foot a bit on the gas. parked the car and started fixing various things I found wrong but it never wanted to run again. I posted the whole story here if you want to read it, but I am trying to put everything back to how it should be so the car will run. https://www.rx7club.com/new-member-r...fc-na-1155920/

I'll just list everything I've replaced or tested recently,
fuel injectors; rebuilt (all within 1cc)
fuel pump; new
FPR; new
fuel filter; new
fuel flow; good
MAF; new
temp sensors x2; new
CAS; FSM test for resistance; good
leading and trailing spark; good (+12v to igniters)
TPS; reading 900-4k ohms, lightbulb test for adjustment from FSM as well
compression (cold) 75psi front 70psi rear
plug wires; new & tested good

I did a vacuum leak smoke test with a homemade tester, did not see any smoke but I'm starting to doubt, got new injector seals on the way and will replace soon.
and there was probably other things I've done but this list is what is 100% for sure correct.

whenever i remove the plugs after trying to turn the motor over they are wet with fuel. I can get it to run by using the adjustment for the butterfly valves on the throttlebody to give it a lot more air, but it runs super rough and smokey. (white smoke, grey smoke? I can't tell, its not blue smoke and its not coolant. unburned fuel is my guess)
thinking it was the TPS I've been trying to trace electrical issues, but just today I decided to build the lightbulb tool to set the TPS correctly, and it should be. trying to start it now with the butterfly back to stock and still getting a ton of unburned fuel. it sputters like its gonna start which is better than before I set the TPS but still not starting.

when I opened the ECU it looked mint, can they just go bad? also going to test the manifold absolute pressure sensor next but I need to buy a vacuum tester. thanks for any help!

 

Have you tried new plugs and wires? You said the coils were good, but have you verified you've actually been getting spark?

Have you verified timing?


You said rebuilt injectors. You bought a set of injectors that was already rebuilt, or you rebuilt the injectors that were already on the car?

 

This is taken from S5 manual F1-77, but S4 ('86) should be similar. Is your BAC working correctly? It's possible it has become stuck over time and needs a cleaning. If you turn your key to ON and stick a mechanics stethoscope to the BAC, I think you should be able to hear it clicking/vibrating.

 

it has new wires, and I have like 4 sets of plugs, visually checked and I'm getting good spark. verified timing via marks on the pully and checking the position of the rear rotor.
I brought the injectors to a local rebuilder and he told me they were all within 1cc. 1 was stuck open but it was fixed.

 

I forgot to mention the air injection, BAC and other emissions parts were removed by the previous owner. it has worked fine in the past without. thanks though. 👍

 

Does the car hold idle once it's warm?

One thing people often delete with the emissions equipment is the thermowax. This part is responsible for holding the idle high while the engine is cold, then once warm it disengages and it idles at around 750.

If you let the engine warm up, does it idle better / lower?

 

it will only idle if I increase the amount of air via the butterfly valve adjustment. I've run it till it was fairly warm but no change. also it is rough though the rev range so I suspect this isn't an idle only issue. and correct, it has no thermalwax or fast idle cam. when it did used to run it was a bit smokey at the start but went away pretty quick once the engine was warm.

 

Hate to be that guy, but have you compression tested the motor? Doubtful this is the case, but you can never be too sure. The fact that this occurred out of the blue makes me wonder

 

lol yeah just did it last week, when cold is 75psi front 70psi rear. last month when I was running it and it was rough and smokey at about 1000rpm, when I cut the fuel pump (I have run my own fuel pump power and switch)it revved up to 3k before it died. but it smoothed out and ran well for that 1.5 seconds before it died. thats what makes me think its putting too much fuel in, just can't figure out why.

 

Have you checked fuel pressure? Could be a bad regulator causing rich mixture.

Should be like 28-34 psi at idle, and then slightly more if you pinch the vacuum line. I think. The actual spec is in the manual.

 

it is a new regulator, but that doesn't mean its not faulty. had a pretty steady flow of fuel at the return line as well. If I test on the input line of the fuel rails, or even at the filter would I get the same reading?

 

Reading should be after filter, before fuel rails. Exact distance from filter or fuel rails isn't important.

 

Another thing to check, since your car is an 86, is your resistor pack for the injectors. The 86-87.5 cars used low impedance injectors with a resistor pack, near the intake filter. I'm sure there's a procedure for checking this in the FSM, but if it's faulty, your injectors could be seeing improper voltage (either too high or too low) and cause a fueling issue.

 

I checked that and it was fine according to the FSM. after that I was busy for a while but now I'm trying to fix the car again.
I've since replaced the ECU, which did nothing, but now I have 2 so thats good. It did stay running for a bit once I put my foot on the gas and so I ran around and sprayed a bunch of starter fluid at the engine, but still died out after 30 seconds or so. anyways I had bought new injector seals so I installed those and checked the fuel injectors. I felt like after that it maybe was a little easier to start but I still have to use the pedal. kind of tried to stay running for a bit.
when I pulled the plugs they didn't smell like fuel so I'm starting to think its lean and not rich. it also will continue to run/start if I use the pedal a bunch of times so I don't think its flooding.
Is there anything else aside from a vacuum leak that can cause a lean condition?
edit: tomorrow I am going to get fittings to install a fuel pressure gauge.

 

Definitely sounds like a fueling issue. Have you checked the temp sensor on the back of the stat housing? If that goes bad, the ECU won't enrich the mixture for cold start, so it'll be hard to start/run

 

Just for fun. . put the key in the ignition and turn to the second position. if the air box is removed, you should be able to reach in and push on the vane inside the MAF and simulate air coming through it. When you do that, you should hear the fuel pump kick on. . .This is a good way to check the fuel pump relay.

Measure the BACV resistance and Intake Air Temp sensor resistance.

Use a hand vacuum pump and verify that the oil injector spider isn't a big leaker.

Buy the EGR valve blank off plate and plug the line if you haven't already.

Plug the double throttle valve vacuum line. . . ..Check the water thermo wax valve is not broken.

What messed me up before was the o-ring for the snorkle sealing to the upper intake was pinched and causing a leak. I could tell because it was ever so slightly crooked and not seated after I touched it last.

And what's your confidence in the distributor.. . .I think there is a check in the FSM

 

yes I've replace that one.
my rx7 is a little modified, in the terms that the fast idle and all of the emissions stuff was removed before I got it. The fuel pump is wired to 12v so thats on for sure when i flick the switch, you can hear it wrrrr.
I'm not sure what the air intake temp sensor is supposed to read but they don't make them anymore, and I haven't found anyone on the internet who attributes that to any issues. I've considered it but I'm not paying 100$ for a used one that may not do anything.

No one has ever mentioned the oil 'spider' which i assume is the rats nest of vacuum tubes mostly under the UIM. are they supposed to be filled with air or oil? I think on mine the lower section closer to the OMP have oil in them but the rest looks like air (they are all clear on my car). I will check later. and leaking as in vacuum leak, or putting too much oil into the engine?

there are a bunch of blocked tubes but I didn't remove them so i don't know what they were for. there is a blockoff plate above the exhaust so I assume thats the EGR hole. And I also assume the blockoff plate on the drivers side of the UIM dynamic chamber is the double throttle/thermowax position but mine is removed. It used to start fine without the fast idle and I don't drive it when its cold out anyways.
I just removed the UIM to redo the injector seals the other day, that o-ring is a pain but I know its in properly. I use o-ring jelly to set it in place before I put the elbow on.

and I've done the FSM check on my CAS and it all came out within spec.
the car does run not too badly when I start the car with my foot on the gas, which would indicate to me that I've got compression, spark and some fuel anyways. after running for a few minutes it will idle a bit but then it will die out.

thanks for the help guys, I am going to install a pressure gauge in the fuel line, i was just waiting for the thread seal to cure before I put it back together. I'll let you know the results.

 

well took a while to get the right parts, had to order from online. looks like I'm getting about 32 psi. I can't remember if 28 or 32 was the correct number, I think one is for without the vacuum tube on the regulator? I can regulate the voltage to adjust the pressure as well if I have to. I'm not sure what to check next.
it dosen't seem like there is a huge vacuum leak but its my best guess at this point so I'm going to start going through everything on the intake.
any chance it could be the LIM gasket? I've never removed that one but the UIM and replaced the gasket, replaced the o-ring on the 'neck' but there is a bunch of blockoff plates and vacuum lines to check.
also any recommendations for vacuum tube to replace the old stuff or where to get it for cheap?

 

I had a lot of the same symptoms .. . . .This is what I did.


https://www.rx7club.com/2nd-gen-gene...ption-1154012/

 

thanks, I'd never thought of the oil injectors, no one else has mentioned it in everything I've read. Seems like I have a vacuum leak and that may be the place.

 

https://www.atkinsrotary.com/store/8...G1-14-631.html

I found some other vacuum leaks but I want to get these done as well while I have the car apart. Do I need 2 or 4 of these oil injectors?

 

You'll need 4 of them. 2 go in the rotor housings, and 2 thread into the back of the LIM

There are 2 different oil injectors with 2 different lengths on stock cars. I'm not sure if these OE replacements are a one-size-fits-all, or if there's a separate part #. May be something to look into. On stock cars, the ones that thread into the LIM have more thread than the ones that go to the housings

 

thanks, i'll check it out.