I have an 88 rx7 with a 13bt swap done, all emissions removed. The engine ran fine when I pulled it a couple months ago to do a Light weight Flywheel and Clutch assembly along with a transmission rebuild.

Now when I start it it starts fine then just dies after a couple seconds. If I give it any gas after I start it it will instantly die, but if I go more than half throttle it will rev up. When it does rev up the engine sounds like it doesn't want to and makes a spuddering sound like it was missing. I found that if I get it warmed up it will barely idle, but again foot on the gas and instantly die.

I have done some research and found that It could be something to do with the AFM or a vaccum leak, I swapped the turbo AFM with a good NA AFM and still the same problem (but im not really sure a NA AFM would even work) I am not sure how to test my Turbo AFM to see if its good. I looked for any vaccum leaks and found none. Checked the resistance on the TPS and it was within spec.

Any input on what my problem could be would be appreciated.

have attached a video of what happens when I start it with my foot off the gas

 

Did you upgrade the fuel system to T2 standards such as the fuel pump?

An NA AFM will suffice as far as starting the car and trying to idle.

Is the turbo engine a USDM or JDM?

 

I am using a walbaro 255 pump, with stock 550cc injectors, and I recently replaced the fuel filter. The engine is a USDM
thanks for the reply

 

unmetered airleak

.. between afm and turbo , or between turbo and throttle

if s4 make sure the small hoses off the intercooler hooked up to the ABSV and the ASV
( note.. some jap engines will lack the ABSV and will only have one small nipple off the intercooler )

if s5 check the plastic air delivery pipe off the turbo to the intercooler is not cracked

 

Okay so I couldn't find any vaccum leaks in the system. I did some tests and I found out that the AFM is good the TPS is gogood CAS is good, fuel pressure is a little off in that the fuel pressure regulator doesn't seem like it is working. I looked up a test and it says if you un hook the vaccum to the regulator the fuel pressure Will go up compared to if it is connected. Fuel pressure reads 45psi when running with it connected and disconnected. I ordered a new rregulator for good measure buy I'm not sure if it would be causeing my problem.

Any other tests or things to checheck would be appreciated.

 

45 psi is not within spec for an unmodded car.

 

well if you match the s4 NA body to a walbro or larger pump then it will push a standard reg to max lift and run pressures like this at low load and flood

the turbo car ran the two speed pump circuit and can get away with it

you will need an aftermarket reg to fix this

with s4,, you can get two variations in the fuel rails depending on markets
( counter current and co current )
depending on which one you get,, sometimes it is possible to exchange the fuel reg for another dampner and then fit an external reg on the firewall
and thus drop the pressure some so the standard ecu will cope.. usually about 38 on the static setting , with no engine vacuum

 

This would make a lot of sense because when I try to flutter the gas when starting it will seem like it is getting too much gas and when it actually starts for those few seconds its a big cloud of smoke that comes out the exhaust and it smells like straight up gasoline.

Some more info on the car, OMP removed, and im running and aftermarket FMIC. Running a S5 turbo on stock wastegate pressure.

 

Would this diagram be a good example to go off of when doing an aftermarket regulator? thanks

 

yes, parallel fuel system is good for those with large injectors and stock s4 rails

the stock serial arranged rails work fine for stock injectors though
so ( depending which s4 rails you have ) really only need to add the extra dampner to s4 rails and then hang the reg as last in the queue

s5 rails make things more tricky , it has less need to be parallel ( more volume in the rail itself )
but has welded in dampner and regs, which need to be cut off and welded over to do properly ( or aftermarket rails ) ,
though there is tricks you can do if you wish to avoid that

it is important in both examples that you do not retain the old reg and stack the new reg on the rear of that serially

 

I am running S4 rails currently. From what I gather from what you are saying there is two different kinds of S4 fuel rails? Anyway this is how mine it set up. fuel goes through the fuel filter then up the pulsation dampener then through the primary fuel rail, then from the primary fuel rail it goes up the the secondary fuel rail, through it, then through the stock pressure regulator, then returns to the fuel tank.

I am running the stock 550cc injectors right now. I plan on running 750cc all around in the near future (summer time of next year) my question to you is should I go ahead and do the parallel fuel system now with the 550cc injectors? Would doing a Parallel system on my stock 550cc injectors still solve the pressure issue I have currently? That way when I upgrade to 750cc injectors I will have the best setup possible to up the fuel pressure.

 

Also What are the difference between running a parallel system compared to the stock in-series system?

 

the parallel system assures equal pressure at all injectors ( it is a ring main system )
this is needed on s4 as the volume in the rails is marginal
and so large injectors opening may effect the pressure at the injectors downstream

so yes, if you are growing your system incrementally
it is good to build your system as parallel while you are mucking about,, no sense doing it twice

by your description you have the stock reg on the secondary rail. and this is good news as another dampner will readily substitute onto the end of the rail to replace it so you can fit an external reg

to do it as your diagram, you need a reg with two supply ports
but if one is used up as gauge then you use another splitter Y ( or T ) to bring the lines together into the one port

 

ps,, while you have the UIM off , cover your LIM openings with a towel ETC
,, very easy to lose things down there while mucking about with secondary fuel rail

 

So you are saying if I have another pulsation dampner I could use it to substitute the fuel pressure regulator on the secondary rail?

What exactly does the pulsation dampaner do? And how does it work? Is it bad to have two pulsation dampaners? Or good?

Thanks for your help by the way

 

the dampners are spring loaded diaphragms that absorb the variation in rail pressures when the injectors operate
essentially they reduce the hammer,, and the noise of the injectors

the s4 dampner got a bad rep for fires
but it is a simple matter to check both still have the little screw in the end
and fit the later plastic cap , or daub of RTV to the screw to prevent it falling out
and then there is no issue

two GOOD pulsation dampners will not hurt anything
and the second one makes an easy substitute instead finding a banjo bolt that will fit in place of the reg
you can then mount the external reg on the firewall and it will work without hindrance from the stock reg
( ie, you will be able to drop the fuel pressure lower than what you have now )

 

I just spent 200$ on a adjustable regulator I installed it just like in the picture and I'm still having the same problem.

 

have you backed the fuel pressure down to 38 psi on it? that is about where the stock ecu is programmed for

is the old reg entirely removed.. if not you cannot achieve pressures lower than before

 

So just to update, I realized I had the injectors plugged in backwards when I put the engine in. Yes I know very stupid mistake I am still face palming myself.

I did set the fuel pressure to 38psi and the fuel system seems to e working now.

BUT a new problem has risen. It does idle and such, but when I drive it and apply more than half throttle to WOT the car sputters/bogs/backfires ALOT. It doesn't really matter when I do it throughout the rev range but it is the most potent around 3500rpm. I checked the ECU ground to see if it was clean and the bolt was tight. I think it might have to do with the TPS? I will go take a look at it again and do some resistance testing on it.

side note: when it idles sometime it revs up slightly by itself when I am out of the car. It will only rev it up like 200-500 rpm more each time it does it but im not sure if it is suppose to do that.

 

to fix the 3800 rpm throttle hesitation properly you have to resolder brass crimps
and add an extra strap to them and bolt it down at the ecu mounting points
in the shield, instrument and ecu earth wiring bundle just out from the ecu main plug

 

I just realized that the second pulsation dampner I installed on the secondary fuel rail (in place on the stock fuel regulator) is on the outlet side of the secondary fuel rail. In that it is not being fed fuel it is outleting fuel. My question is would the pulsation damdampner still work like this?