fc3steve

Alright RX7club, you guys have gotten me this far - hopefully if I type out enough info someone will have some ideas for me on what could be the case with my engine. I feel I'm overlooking something small but crucial.

So, the car is an 86 NA/auto that's been swapped with a S4 turbo motor and 5sp. The shell is in great shape, meaning so is the wiring and such. Not to be ruled out of course but I wanna give you guys as accurate a picture as possible.

The short block itself was purchased off Craigslist with little info about it. I was told it had been rebuilt and had just been sitting since the rebuild. Everything I've seen and tested about the motor itself seems to back that up, but I don't know much about its internal condition, besides what I have been able to test. Compression is around 80psi on both rotors, with three even pulses. I understand that a rebuilt motor with used housings can show lower compression before breakin, so I'm assuming those numbers are decent, at least to be able to get it running. There doesn't seem to be any mixing of oil with water or anything of that sort, and the apex seals looked fresh through the exhaust ports.

The rest of the setup is as follows:

Intake
S4 TII LIM/UIM, S4 NA throttle body (yeah upside down, OMP will be linked with a bike cable), FMIC, BNR stage 2 turbo, S4 TII AFM

Fuel
Walbro 255lph pump, 4 new 720cc injectors from TLF performance (sells Denso injectors that are modified to flow at higher rates by a company called Venom), AEM universal FPR with fuel rails modified to run in parallel (the fuel line splits before the rails and both rails feed into the FPR) and a S4 TII ECU with RTEK 1.8

Ignition
Stock S4 NA ignition system with NGK wires and plugs

Exhaust
RB downpipe to stock cat (for now) and RB 2.5" catback

Okay, so I got everything together in the car about 2 weeks ago and prepared for first start, but it still hasn't come. I believe I have all electrical kinks worked out, TPS voltage set, getting good spark, getting gas in the motor (I can smell it at least) but I haven't had too many signs of life, save for a few pops and weak tries to start, no more than one or two pulses at a time. And those actually happened while my dad and I were trying to set timing and seemed to be way off any mark. And before I realized that my oil injectors hadn't been tightened all the way down and were leaking compression.

Since I've set the timing, I've had no sign the car wants to start. Seems like the spark is firing in the completely wrong spot or the motor is flooded, both of which I have tackled head on. For the timing, after the stock pulley marks weren't giving me any results, I went ahead and found TDC on my motor by looking in the leading and trailing holes of the second rotor and marking the pulley when I could see an apex seal in both holes, then finding the center of the two. That hasn't worked either, but I've been using that mark to time it since. It's about 20 degrees advanced from the factory leading mark. CAS has been lined up, marked up at the top, checked and rechecked. Anytime I pull a plug out and test it I get plenty of spark, the system seems to be working well. There is one curiosity though, the leading and trailing coils seem to both fire at the same time, wherever I set the leading to. Is this ordinary during cranking?

For flooding, I've installed a fuel cutoff switch and have pulled all plugs, spun the motor to clear any fluids, put MMO and ATF in the leading holes to aid compression, etc a few times. I've only done MMO and ATF once each, and I'm apprehensive to do it again cause it just ends up soaking my exhaust mani and turbo. I don't crank the motor over too much with the fuel on to avoid floods anyway - only when I think I have everything ready to go.

The fuel system seems to have some sort of a problem, it rarely holds pressure after the pump is shut off. Sometimes it holds longer than others, but only ever like 15-20psi. None of the lines are leaking fuel, and I really doubt the injectors are leaking internally since I bought them new (or newly rebuilt). However, I was testing the fuel system's ability to hold pressure by clamping the return line with vise grips and bumping the pump up to 80psi or so, and it leaked down ever so slowly until I let go of the return line, at which point it bled down much faster. Later that day I was smelling gas pretty strongly, so I looked and found fuel pooled around the primary injectors, like gas had been leaking out where the rail meets the injectors. So I pulled them out, sucked out the gas, and reinstalled them with a smaller primary rail spacer (I made the one that was in there). I haven't been able to get it to leak since, but the fuel system still does not hold residual pressure. Shouldn't my FPR not let fuel leak past it after a certain point? Or does it seem like I have a different problem? Even if I'm getting a bit too much or too little gas in the combustion chamber, shouldn't I still get some firing events? Also, what should my pressure be set at for a first start? I've been keeping it around 40psi, but I've been up to 50 and down to 30.

The plugs often smell like gas when I pull them, and sometimes there's some on the face of the plug. And when I turn the fuel on and try to start it, the smell of gas is definitely noticeable. Oh, and when I pull the upper manifold off, the gas smell is very strong through the LIM holes. How can I check for a leaky injector? Does it seem like excess fuel is my problem?

This is my first rotary build and I'm not sure exactly what all the motor needs to see to fire. From what I can tell though, the ingredients should all be there. The compression definitely seems strong enough to start, as does the spark if I have it in the right place... I'm least sure of the fuel at this point but it seems the motor should at least be trying or sputtering if the mixture is a little rich or a little lean.

Any input is appreciated, sorry for the essay but I figured I should provide as much info as I can. Thanks RX7club

Valkyrie

Even during cranking the engine rotates way too fast for you to tell which plugs are firing first.

But the leadings should be firing first by a tiny, tiny margin.

Make sure that the leading coil fires twice for every time a single trailing coil fires.

If it doesn't, you've got a wiring problem.

You can also pull a plug on one rotor and use a smartphone to take a slow-mo video and make sure the right trailing plug is firing when each rotor is compressing.

Although to me it sounds like you might have too much fuel pressure.

MickeytFC

iTrader: (1)

You're on the right track. I kind of suspect the injectors leaking and you getting a flood condition. I personally would try a pull/push start. I swapped a used motor years back on an NA that wouldn't start and that was the only way I could get it to start the first time.

fc3steve

Well I say that because when I put my timing light on the T1 wire it lights the same place on the pulley as the L1 does.. It should be 15* behind I'm pretty sure, unless they fire at the same time during cranking.

What is the advantage of a push start? I've heard it can be a helpful technique and I've used it on other cars with dead batteries, but do you know the advantage over the starter?

Thanks for the help guys, I gotta test those injectors.. Might try swapping in some stockers for now and see if that works.

fc3steve

Fuel system still loses pressure pretty quickly even with my stock injectors. What would cause this? Might it be something at the pump? or is it my FPR, I haven't been too impressed with this unit so far. If I run 60psi through it and then stop the pump, it drops to 50 almost instantly, 40 maybe 5-10 seconds later, then to 30 and 20 over the next minute. It'll often hold around 20 for 5 minutes... Yesterday it held 10psi all night. There isn't that big of a fuel leak anywhere and I'm fairly sure now that it's not leaking injectors. Why would a brand new FPR let that much fuel by?

DR_Knight

iTrader: (23)

1. are you sure fuel lines are hooked up correctly. I swapped my s4 n/a to s4 t2 and I believe rails are opposite. I read somebody did the same thing and couldn't get their car to start.

2.Did you use s4 n/a or s4 t2 engine harness? alternator plug is on starting/charging harness on the t2 instead of on engine harness on the n/a. two wires need to be switched. When I did my swap 7 years ago, I faintly remember it wouldn't start, and I forgot about changing those two wires. Brown/red or something just to help you search the forums.

3. Timing. Crank angle sensor only goes in X amount of ways due to the number of teeth. would be nice if you could actually compare another crank pulley to determine proper TDC markings since the pulley bolts are offset to only fit one direction. When my engine was assembled by builder, he put the CAS in, so I figured it was properly timed... it was not. I was young, and I don't actually advise this, but I kept taking the CAS out and turning it until it started since I wanted to see it run. I got a timing light the next day.

4.Injector impedence. You say you have 720cc injectors, but are they low impedence or high impedence? You can use low impedence injectors if you have 1987-1988.5 engine harness that has built in injector resistor pack. You can use high impedence injectors if you have 1988.5-1990 engine harness. Check by measuring resistance across terminals of the fuel injectors, or at the harness where it connects to ECU. Refer to foxed.ca rx7 searched on google.

5. Do you have constant spark or does it stop sparking? Can easily check by cranking motor over and check for arc, or plug in another crank angle sensor and spin it just so you don't have to worry about proper lubrication of the engine.

6. Have you tried changing for new spark plugs? I had a vehicle with 1600cc injectors on haltech that would flood, and I had to keep trying swapping in new spark plugs to get it to start while the wet ones dried over time.

7. Coolant temperature sensor. Maybe coolant temperature sensor resistance is stuck at hot range. ECU may see this thinking the engine is hot, and fuel trims are not correct. Refer to foxed.ca rx7 to check coolant temperature sensor resistance testing procedures. Honestly I think it should start with a bad sensor, but would run badly while cold.

8. Boost pressure sensor. Guessing you're using a s4 t2 one. You never mentioned it so I brought it up.

9.Check for vacuum leaks. big vacuum leak and you'll have problems starting this thing.

10.Check fuel pump voltage. Fuel pump should prime with key ignition on which sounds like it is for sure. I just converted to s5 so dont know if s4 is different. but S5 t2 will prime with ignition on, and then fuel pump is triggered by signal of air entering the MAF.

Pretty much out of ideas. Report back and let's help this guy out guys.

fc3steve

Well that was a bunch of ideas! Thanks man, I'll try to reply to each..

For the fuel lines, yes they're hooked up correctly to the best of my knowledge. A single line comes up from the pump, through the filter, and then splits using a fuel block into two lines which then run to the individual rails. On the other side of the rails (front side) those two lines continue and meet at the FPR, and then one return line goes back to the tank from the bottom of the FPR.

I'm using the original na engine harness so I think the alternator should be correct.

Yes it would be nice if I had another pulley.. The one I have still has the factory notches in it, but when I found TDC for myself, the leading mark seemed to be about 20* behind. I've re stabbed the CAS many times, pretty sure I'm doing it right but who knows. I line up the pulley mark with timing pin, align marks on cas, mark the top of the cas so I can see where it goes, and get it as close as possible. Then I twist it and use timing light from there.

I will check injector impedance tonight but I'm pretty sure they're low impedance, matching the car. If I spin the cas out of the motor with key on I can hear the injectors working.

I've only checked for spark once, by pulling a plug, but it was strong and seems to be constant. I'll check again tonight and make sure both leading plugs fire. Haven't bought new leading plugs yet, if they spark outside the motor might they still need replacing?

Will check coolant temp sensor tonight.

Yes s4 TII pressure sensor.

I've checked a few times for vacuum leaks, I don't think that's happening.

My fuel pump doesn't prime at key on, but it comes on fine at cranking, or if I jump it at the pump circuit connector.

Thanks for all the ideas man, I'll post my results later. Still confused on that fuel pressure leak down though.

PinkRacer

I had one that just wouldn't start for me - same story, bought it rebuilt by someone else. Tried and tried, even drug it up and down the road to bump start it, it wouldn't run when you put the clutch in, only when being pulled in gear. Gave up and took it out and tore it down.

Had 3 issues:
- One housing should never have been reused. It was gouged to ****.
- One rotor had 3 stuck side seals.
- The torrington bearing in the front stack had been improperly installed and had dropped - got completely chewed up in trying to start the engine.

Since you seem to have consistent compression, the first two likely haven't happened to you.