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1991 VR4, 10:1 compression, mildly ported heads, stock turbos, 3" downpipe, 98 SL flashable ECU
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Discussion Starter #1
I have a 91 VR4 with a freshly rebuilt 10:1 compression engine, mildly ported heads, stock turbos, 3" downpipe, no cats, stock cat back, manual boost control. Intended as a fun daily driver, but currently giving me problems.

I'm on my third set of stock injectors and I believe they've gone bad again. Years ago with the originals, I was having trouble with the car being difficult to restart after about 20-30 minutes. I decided the injectors were leaking into the engine and flooding it, so I got some used stock injectors, had them cleaned, put them in and the problem was solved. I then sent out my originals for cleaning to have as backups. I had an injector go bad, so switched back to my cleaned originals and the warm restart problem returned. I’ve just rebuilt the engine, and had those injectors cleaned again while it was down, but now still have that same problem. I though it might be ECU related, so just I swapped in a flashable 98 SL ECU, but the problem remains. At this point, I’m 99% sure it’s those dang injectors again.

I think it’s time to buy some brand new injectors and quit messing around with these 21+ year old stockers. Since I now have full ECU control with Chrome, is there any reason not to get bigger injectors for future capabilities? It looks like I can buy 750cc FIC injectors for less than 370cc RC injectors (closest stock replacement I can find). I have been thinking about upgrading turbos to 15Ts or 19Ts and running E85, which I think would need around 750cc injectors.

Is there any reason not to go with the 750cc FIC injectors now so that I don’t have to upgrade injectors again down the road? Any other suggestions?

Thanks,
Lee
 

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I was in your exact predicament (Minus the vehicle starting issues.), I bit the bullet and just got the fuel system upgraded. Having your fuel system upgraded now so you didn't have to down the road won't hurt anything as my tuner was telling me. Per him "It's better to have it done now before you start throwing upgraded turbos and other mods."

I personally am going with 1000cc injectors with a walbro 450hp fuel pump.
 

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You will like the FIC750's - very easy to work with on a simple setup such as yours. A friend/client of mine has been using them for 3-4k miles now. The first 2k were with just a MAF-T and Pump-E85, and he more recently is still using them with an AEM EMS Series 2. You only need a modest FP upgrade as well e.g. AEM 340lph. Best of luck!
 
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Hi Lee, with flashable ecu there is no reason to not go with a moderately sized injector like the FIC 750

Sent from my SM-G955U using Tapatalk
 

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1991 VR4, 10:1 compression, mildly ported heads, stock turbos, 3" downpipe, 98 SL flashable ECU
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269 Posts
Discussion Starter #5 (Edited)
Now I'm second guessing the size, what's up with FIC's injector calculators? The HP calculator says their 750's will only support 440hp at the crank (or 374 at the wheels) at 80% IDC on E85. If I plug in our stock 360cc injectors, it says they can only support 274hp at the crank at 80% on gasoline - obviously not correct since these things put out 320hp stock.

Should I go with 950s instead of 750s (sizing for future turbo upgrades and E85)?
 

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440/374 figures are on ethanol fuel... 571/485 is the correct "apples to apples" comparison on pump gasoline.
 

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1991 VR4, 10:1 compression, mildly ported heads, stock turbos, 3" downpipe, 98 SL flashable ECU
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Discussion Starter #7
Thanks, yes you are correct, I'm trying to size for E85 in the future. I went back and edited my post to be more clear.
 

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If you are just trying to do it once with room to grow into your future plans, then just get a larger size that is slightly above your goal... but at the same time, take into account what you currently have and what else you will need to upgrade to justify it. For example, are you still on a cast crank or stock clutch?

If you are set on FIC, then the 850's are also nice. They accommodated ~450awhp before I upgraded two more times... (exactly what their calculator shows for 85%). There is nothing wrong with taking things in steps either though.
 
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1991 VR4, 10:1 compression, mildly ported heads, stock turbos, 3" downpipe, 98 SL flashable ECU
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269 Posts
Discussion Starter #11
I was planning to buy from you Chris, but I thought I needed the low Z injectors to work with the Chrome ECU?
I was thinking these: FIC 950cc Fuel Injectors; Set of 6; Low-Z Peak & Hold / Low Impedance Disc Type; Plug & Play - Rvenge Performance & Transmissions

Maybe I'm still more lost than I thought I was. Been researching this for quite some time and thought I had a decent understanding, but now I'm doubting that. I do have a forged crank, ACT HD street clutch, and 300M output shaft, but right now am still on stock turbos. I was thinking all I needed to upgrade the power at this point was injectors, fuel pump, and turbos. Since I need injectors right now, I thought I could get away with going ahead and getting something that would support E85, and at least 15Ts even though I may never get there from here.
 
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I was planning to buy from you Chris, but I thought I needed the low Z injectors to work with the Chrome ECU?
I was thinking these: FIC 950cc Fuel Injectors; Set of 6; Low-Z Peak & Hold / Low Impedance Disc Type; Plug & Play - Rvenge Performance & Transmissions

Maybe I'm still more lost than I thought I was. Been researching this for quite some time and thought I had a decent understanding, but now I'm doubting that. I do have a forged crank, ACT HD street clutch, and 300M output shaft, but right now am still on stock turbos. I was thinking all I needed to upgrade the power at this point was injectors, fuel pump, and turbos. Since I need injectors right now, I thought I could get away with going ahead and getting something that would support E85, and at least 15Ts even though I may never get there from here.
Appreciate that! The low-z injectors are good, but the high-z are a little better tech. Chrome can run either as long as you bypass the resistor pack (easy). Unless you are running a piggyback there's really no harm in moderately sized injectors in the 1000 range. Either injector you have selected will run great, just FYI.
 

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1991 VR4, 10:1 compression, mildly ported heads, stock turbos, 3" downpipe, 98 SL flashable ECU
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Discussion Starter #13
I feel like I confirmed my problem is in fact the injectors again. I don't like pinching hoses because I feel like it causes damage, but did it anyway. After priming the fuel system I clamped off the feed and return fuel lines in the engine compartment. The fuel pressure still slowly fell by about 2psi per minute. I have no visible external leaks in the fuel rail, injectors, or fittings and no raw fuel smell like a leak, so the injectors have to be leaking internally and flooding the engine as suspected. I have no idea how they could pass the leak check when I had them cleaned, but I'm done messing around with these old injectors.
 

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1993 3000GT VR4
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Pull the upper intake manifold and then turn on the pump with the test connector. You should be able to look down the ports and see if any of the injectors are leaking fuel then.
 

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1991 VR4, 10:1 compression, mildly ported heads, stock turbos, 3" downpipe, 98 SL flashable ECU
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Discussion Starter #15
Got the FIC 1000cc high z injectors last week and got them installed Saturday - thanks for the great price and quick shipping Chris!

When I pulled the upper intake there was still fuel pooled on top of some of the valves even though I hadn't ran the car in like a week! Old injectors were definitely leaking. I wired in the new connectors (which I had to tweak), bypassed the resistor pack, changed the injector size and latency to what the FIC data sheet provided, lowered the cranking injector pulse, and she fired up and ran. I'm a total newbie to tuning with Chrome however, and struggling to get things running just right with the new injectors. I've already driven out half a tank of gas logging and adjusting all weekend. I'll continue to search the forum's tuning threads to see if I can figure out what to do. However, the new injectors solved the starting issues and the car starts instantly every time now!
 
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nice!! I recommend those 1000s to anyone who doesn't need bigger anymore unless they are on a piggyback.
 
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