1995 Civic EX coupe, JDM B20b block, LS head, P75 LS intake manifold, GSR 60 mm throttle body, B20z (CR-V) exhaust manifold to stock '95 civic EX cat-back exhaust. LS manual transmission. P75 ECU non-socketed or chipped.240 cc injectors, stock fuel pump. Purchased car six months ago and prior owner did all swaps.

Posted here a couple weeks ago about lean condition: https://honda-tech.com/forums/honda-...-idle-3303080/
Posted this concerning dyno tune: https://honda-tech.com/forums/engine...ssion-3303847/
Posted this ECU question: https://honda-tech.com/forums/hybrid.../#post51366673

Adjusted idle screw so that the engine is no longer stalling. I tested injectors by pulling each injector harness off one at a time and listened for drop in idle. Three of the four cylinders dropped very evenly and one not as even as the others but idle still dropped significantly. I removed and cleaned injectors by adding pressure + bake cleaner + engaging/pulsing with a 9 volt battery. Reinstalled injectors but no change in lean idle issue. I smoke tested intake & exhaust but no leaks seen, I pushed air into tail pipe and sprayed soap water on flanges/connection/donut seals and no leaks seen. Purchased a used Denso MAP sensor ($8) and waiting for it to arrive. Compression tested an all cylinders are between 205 and 210 psi. Leakdown test performed day of purchase and engine is healthy.

Barring an issue with the MAP sensor will an adjustable fuel pressure regulator help this lean issue? I know a socketed and Hondata s300 or Neptune with a dyno tune is the best way to go but it cost $1k and not into spending that much, Not looking to add power and the tuner shop I brought it to told me that he wouldn't expect to see much gain unless adding larger diameter headers and exhaust + tuning.
The previous owner installed a fuel pressure gauge above the fuel filter and it reads around 38-39 psi at idle and drops 5-6 psi under load. My Hondash live data is showing 40-42 psi at idle and 36-38 psi under load. Not sure where the Hondash takes it's reading from or if it's accurate.

 

You need to find out why that one cylinder is running different (worse) than the others. Start by swapping the injectors around.

Fuel pressure should follow the manifold pressure due to the compensating vacuum hose on the fuel pressure regulator. At idle the manifold is in vacuum so the fuel pressure should drop. At wide open throttle there is less vacuum so the fuel pressure should rise. The reason for this system is to keep the pressure difference across the injectors the same through different conditions, since they are calibrated for a certain pressure difference.

There is no fuel pressure sensor. The computer is showing you a phony number derived from the MAP reading and assuming the fuel pressure regulator is working to spec.

There's no reason to use an adjustable FPR in what is basically a stock setup.

 

They all drop the same now after cleaning the injectors. Even prior to cleaning the drop in the number one cylinder was significant just not quite as much as the others but very close.

Thanks for the explanation...makes it easier to understand.

.

Makes sense

I was advised to try running it for a few days with the FPR vacuum line pulled, cap both FPR and TB ports (max fuel delivery) and see if there is a change in stumbeling/low idle. I did that today and it hasn't stumbled, stalled or dropped in idle. Idle (no load) did raise a bit: (900-1000 rpms). I purchased a new phone and have to download Hondash app to check o2 volts and fuel trims..I intend to do that tomorrow.
I also purchased a used, tested MAP sensor ($8) and will install that when it arrives to see if it helps.

Fuel pressure seems to be an issue with B20 + obd1 swaps: https://www.google.com/search?num=50&site=&source=hp&q=honda+b20+obd1+%2B +adjustable+fuel+pressure+regulator&oq=honda+b20+o bd1+%2B+adjustable+fuel+press&gs_l=psy-ab.1.1.33i21k1j33i160k1.2631.28932.0.31862.47.44.2 .0.0.0.1570.7903.1j15j4j2j3j1j8-1.27.0....0...1.1.64.psy-ab..18.23.7093.0..0j0i131k1.t6stngSEWmI