DENSO injector owners, need a litlle feedback.

[Newlogics]

This thread is for those of you who run denso 660s or 720s and have fuel pressure gauge.

I have recently dealt with several DSMs (including mine) equipped with denso injectors, and found a rather interesting pattern. When car is shut off, fuel pressure drops rather fast (about 20sec to almost zero). At first, I blamed FPR or fuel pump, but after trying several different fprs, and several fuel pumps, I narowed it down to injectors. It seems they're leaking fuel under pressure. That also causes for rough/low idle for a short period of time after a startup (especially warm startup) due to fuel being puddled in the intake mani/runners.

So here's what I need:

If you have Denso injectors and fuel pressure gauge, post here and tell me how long your fuel pressure stays up after the car has been shut off. What fuel pump and what FPR you're running, and if you're see rough idle after startups.
Info would be much appreciated.

Thank you.

Regards,
Paul.

 

[quest49s]

I run 660cc denso's and have noticed the same thing, I also thought it might have been the fuel pump. my FP drops from 30psi to 0 in about a minute. What I have for a fuel system is a walbro 255lph HP, 6- lines tank to factory return, K&N fuel filter, westach FP gauge, denso 660cc inj. and a aeromotive FPR. I too get rough idle only on warm startup after driving, but say I go to class for an hour and come back, the car will still be warm but won't idle like trash. Perhaps cause the fuel has evaporated in that short time. Curious to know if you are on to something , or if we are an exception?

I'm positive it is not my FPR releasing the fuel pressure because I had the same problem before with the setup mentioned above minus the FPR(I had Stock FPR - I know I was overrunning the factory FPR hence the upgrade) Also when you shut off the car it is harder to open the reg. valve cause the spring pressure is stiffer with no vacuum to assist. Thats why I figured it was the Fuel Pump-

I've got a set off stock 450cc's, I can throw those in and see if the outcome is the same as the 660cc, have you tried this?

Anyone else notice this klind of behavior?

 

[bfdahl]

I just installed 660 densos after removing fic 650s and I too can attest to the long soak hard start and rough idle.

mostly its after sitting out in the sun on a warm afternoon.

at first i thought i had done somthing wrong on install, but soon realized it must be the injectors.

Im using stock AFPR and a 190 pump.

 

[jazzyjay]

You need a check valve, aftermarket FPR don't hold the fuel. If you put a nonfactory FPR on the factory injector it will do the same thing. I f you put the check valve before the fuel rail and after the filter, you will notice a big difference.

 

[Newlogics]

You need a check valve, aftermarket FPR don't hold the fuel. If you put a nonfactory FPR on the factory injector it will do the same thing. I f you put the check valve before the fuel rail and after the filter, you will notice a big difference.

I have dealt with plenty cars with Eromotive AFPR and stock/FIC/RC injectors, and haven't seen then release pressure so quick. Besides, that is happening even with stock FPR.

 

[T9S1i]

Im literally in the middle of this install. From 450s to denso 660's My fuel pressure holds fine right now after the car is turned off. Im running a waldbro 255hp and FTS fuel pressure regulator. Give me a couple of hours (first time install) and ill have an answer for you guys if my injectors are also releasing the fuel pressure into the manifold...

 

[Coup D E'Tat]

My Denso 720cc/Supra TT pump/Aeromotive AFPR setup holds pressure like a champ. I can't give an exact amount of time, but it's quite long. Long enough for me to get annoyed waiting for it to go down, anyways

 

[T9S1i]

ok so i installed the injectors, got them to idle properly with dsmlink, went out for a drive and what not. I then stopped the car, popped the hood, and had my friend turn off the car while i stared at my fp gauge. When he turned off the car it was at about 20psi for a bout 30 seconds then it jumped up to about 30psi and stayed there for the 5 minutes that i stared at it. Then i got tired of staring so i went out and did some tuning.

Sorry paul, but my injectors dont seem to be leaking out the fuel. Also i can start the car back up within 15min or so and it fires right up and idles properly... Maybe dsmlink just has my injectors running properly...

Hope this helps

Danny

 

[Mark90gst]

I have denso injectors and nocite the same thing, i have a 255 pump with an aeromotive regulator. It loses pressure really quick, they even would loose pressure with my stock regulator, car always idles like crap. I have aem ems and just cant get it right, but my new 1000cc are on there way so Im throughing these things in the trash.

 

[BaddAssGst]

I have denso injectors and nocite the same thing, i have a 255 pump with an aeromotive regulator. It loses pressure really quick, they even would loose pressure with my stock regulator, car always idles like crap. I have aem ems and just cant get it right, but my new 1000cc are on there way so Im throughing these things in the trash.

Send them this way. I'll throw them in the trash for you.

 

[Black95TSIawd]

How does fuel get pudled in the intake mani when the injectors are on the way end of the runners? I have denso 560's(evo 8 injectors) and dont see this rough idle problem. On the other hand i only have a 190 pump and stock fpr.

 

[BaddAssGst]

My motor is going in tomorrow so I'll be here with an update as well. Denso 660s, Walbro 255, and what looks to be an older model Aeromotive. Not completely sure.

 

[GSX]

I believe this not to be a problem with the injectors, nor the FPR, but rather with the seal at the fuel pump. I'd bet that in most cases where this is seen, that the car has a aftermarket fuel pump ... and that the rubber o-ring sealing the pump to the assembly is responsible for fuel pressure bleeding off. Plus some other issues such as prolonged cranking when starting the car are also characteristics.

BTW, I have the same parts as originally listed (ie. Denso 720s, Aeromotive FPR, Aeromotive Filter, Walbro 255).

Any opinions on this? I am way in left field?

 

[Newlogics]

I believe this not to be a problem with the injectors, nor the FPR, but rather with the seal at the fuel pump. I'd bet that in most cases where this is seen, that the car has a aftermarket fuel pump ... and that the rubber o-ring sealing the pump to the assembly is responsible for fuel pressure bleeding off. Plus some other issues such as prolonged cranking when starting the car are also characteristics.

BTW, I have the same parts as originally listed (ie. Denso 720s, Aeromotive FPR, Aeromotive Filter, Walbro 255).

Any opinions on this? I am way in left field?

Initially, fuel pump seal was my first suspect as well. However, I have tried Stock, Denso and Walnoro pumps, all with new seals and got the same result.

 

[93jdmlaser]

I have denso 660s, rewired holley 255 and I run a sx regulator with a guage on it. When I turn the car off its takes a long time for the pressure to go back down. I never stayed out long enough but it is a while.

 

[Newlogics]

Judging by all replies here, it is obvious that the problem is not full-sweeping, even though there does seem to be quite a number of people having same problems.
I will look into it more and see if I can definitively narrow it down to injectors. Who knows, may be I just got unlucky with all the pumps I've tried. (which would be a surprize. I once had to exchange tree alternators from autozone because I kept getting faulty ones)

 

[T9S1i]

Hey paul, in my first response, i had let the car idle for about 5-6 minutes before i turned it off to check the fuel pressure. But now when i drive the car around and turn it off and then try to start it again within an hour i have to crank the car for longer to get it to start. Is this the problem that you are talking about or is this just characteristic of larger injectors? I didnt get a chance to see my F/P, but ill try to see if they hold pressure if i turn the car right off instead of letting it idle for a while.
Also we can check it out at the shop on tues and see exactly what you are talking about

Danny

 

[T9S1i]

I also noticed that most people that have complained about this problem in this post are using aeromotive fpr's.... could that be the problem?

 

[Mark90gst]

I dont think that it is the regulator because I have put them on honda's all the way to my own 300zx TT and I have this problem only on my dsm, when i put my 1000's in I will tell you guys if it changes.

 

[Coup D E'Tat]

I also noticed that most people that have complained about this problem in this post are using aeromotive fpr's.... could that be the problem?

My Denso 720cc/Supra TT pump/Aeromotive AFPR setup holds pressure like a champ.

....

 

[Newlogics]

It's not FPR, guaranteed. I've swapped several ones, including barnd new stock one.
At this point, it's either pump or injectores.
I've replaced pumps and seals with no visible results. I'm yet to replace injectors.

 

[Mark90gst]

Thats it, Ill finish this, this weekend I will start my car with the fuel rail bolts out, shut the car off and quickly pull the rail out of the head and see what happens, done as simple as that. Then well figure out if the injectors leak.

 

[Newlogics]

Thats it, Ill finish this, this weekend I will start my car with the fuel rail bolts out, shut the car off and quickly pull the rail out of the head and see what happens, done as simple as that. Then well figure out if the injectors leak.

Be carefull. Fuel pressure will pish injectors out and spill fuel all over.

 

[GORBS88]

I have stock injectors and walbro 190 pump and have the same problem....car starts great cold but once warm is hard to start and idles like crap for first few seconds.....i have just learned to deal with it....

 

[Mark90gst]

I have stock injectors and walbro 190 pump and have the same problem....car starts great cold but once warm is hard to start and idles like crap for first few seconds.....i have just learned to deal with it....

i will be carefull dont worry.. im not new to this game watsoever. Fuel pressure can be equal danger. My car also runs like crap on a hot start for a few seconds and I hate it. today i watched my Fuel pressure gauge after i shut my car off and it held for about 15-30 seconds and then right down, started it and you could smell fuel.