Jfitzg38

S13 redtop sr20 in s13 chassis.

Wiring specialties pro harness.

Stock setup.

The problem:
-idles perfect.
-Can creep RPM all the way up to redline, but under heavy acceleration/boost it sputters/ falls on its face. Won't hit more than 1 pound of boost. If that.

What I've tried:
New OEM o2 sensor
New coolant temp sensor
Replaced/tested TPS
Replaced/timed CAS
New fuel filter
Cleaned fuel tank
New fuel pump (first one burned out, second was defective, this one seems fine) walbro 255
New fuel lines
New injector O rings (top and bottom)
new FPR
Boost leak test
Smoke test
12v direct relay to fuel pump
Checked coilpacks/ switched with known working ones
Replaced igniter chip
New plugs (gapped)
Wastegate is attached
New AEM uego wideband
No major exhaust leaks
Grounds tested and secured
Replaced ECU with known working one
Replaced MAF 3 times with no result
Wiring specialties PRO harness
Mechanical timing is set




Car was bogging out end of last season, found to be clogged fuel filter. Changed that and this season have had this issue continually after.

Once car reaches boost OR under heavy acceleration will sputter/fall on its face.
AFR reads 15-17 on idle.
AFR reads 17+ after heavy acceleration/boost.
Dropping to ~30 psi fuel pressure under heavy throttle/ boost.
Vacuum is at ~11 LBS which it always has been when car ran great
- My next step is to see if the amount of fuel coming OUT of the FPR remains constant when when heavy acceleration is applied. If so I know that the pump isn't supplying enough fuel somehow.

-^^second step after the above (if all checks out) is to replace injectors.

Last step is to drop this thing off at a shop. I lost a whole season of driving due to a constant troubleshooting/replacement game.



Any input is appreciated!

blkvrtswp

BOOST LEAK

Seen it 1,000,000 times

PS boost leak tests rarely work. Block off piping at each end (TB & compressor) and use shop air or bike tire pump to try to get piping up to 20 psi on your boost gauge. You WILL find the leak this way.

PPS my vac is at -18.

brndck

ok are you still on stock injectors/turbo/maf?
bone stock block and head?

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Jfitzg38

I'll definitely try checking vac leaks again, won't hurt anything. Thanks for the advice!


Yup, stock head, t25, injectors and SOHC maf. Super simple setup.

Jfitzg38

I'll definitely try checking vac leaks again, won't hurt anything. Thanks for the advice!


Yup, stock head, t25, injectors and SOHC maf. Super simple setup.

1988montecarloss

I can see it going rich with a boost leak but can you explain how it would go lean? Not trying to be a wiseass but having similar symptoms with my car

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Jfitzg38

Basically car is running lean all the time.

Pressurized system and actually DID find a few vaccum/boost leaks (at IACV, calvle cover and crank breather). Technically these leaks shouldn't produce my effect but went ahead and replaced some hoses (and waiting on a new VC gasket, because fuck it).

I'll update as I diagnose more.

the shocker

Dropping to ~30 psi fuel pressure under heavy throttle/ boost

that's your problem

Jfitzg38

Vacuum leaks taken care of, still no result.


Obviously that's my problem... trying to get to the root of that now.

Running a 40 micron -AN filter, going to be replacing that with a 300zx one to test, then rail/injectors. If no luck going to a shop.

homeslicej2

You either have a blockage restricting fuel flow, or not enough voltage reaching pump. Replacement WIX fuel filter for 300zx states filters down to 10 microns (via Summit Racing website), so probably not your 40 micron filter (could be though). You replaced the FPR (what brand, is it factory?) IIRC, you should be running 43.5psi at FPR at idle with Vac hose disconnected, and about 37-40 psi with Vac hose connected. This pressure should rise 1:1 with boost. Healthy, stock SR20det should run ~20 mmHg of vacuum at idle speed of 750 RPM (+/- 50 RPM). Larger than stock cams will lower idle vacuum. My guess as of now, since you fixed vacuum leaks (what is it at idle now and what is idle speed?), is that you have weak fuel pump/voltage supply/blockage/bad FPR/etc. Double check your Fuel pressure at FPR and test that direct relay voltage at the pump at both idle and under load. Might need to take car to shop and put on dyno to check voltage at pump under full boost/load.

Jfitzg38

Thank for the explanation homeslice, I definitely appreciate your time typing all of that out!

So upon simple review and retracing steps and the basics I found my issue.

I had a (semi-major) blockage in my fuel hardline...pipe cleaned it, blew it out with air, and flushed it. New filter element (which surprisingly wasn't very dirty, due to nothing passing the blockage) and voila.

Car runs great as of now.

Thank you for all the help zilvians!

homeslicej2

Glad to hear! I love the simple fixes, even though they can be problematic to track down.