jon9116

Well fellas,

I am stumped on this cel… dreaded P0171. Please read fully before directing me to stickies.
Back story. Purchased an 01 prelude that was tastefully modded but had its issues. It had lurching issues, died at low rpms on idle after warm and consistently had a cel light of p0171 and the occasional misfire cels. So I’ve researched the hell out of these issues for the past months. The car runs fantastic its just this reoccurring CEL bothers the heck outta me.

I’ve read over the idle issue/cel issue sitckies several times and done what I could to fix the problems which actually worked, BUT I still have this P0171 CEL.

Items I have replaced
- Replaced rotor/cap (would not start one day, this fixed that)
- Plugs & wires (getting a healthy spark)
- Main Relay (had the no start problem after the car was warmed, sat 10 mins in the off position, then would not start. This solved that)
- Replaced aftermarket throttle body with a stock one (was thinking bigger TB and non-oem could cause CEL for P0171. This also added the FITV where as the aftermarket did not have one). One thing that could throw me off here is the new OEM TB was off an OBD1 prelude where mine is an ODBII. So what that means is the map sensor is not on top of the TB like they are on the OBDII. To fix this I mounted the map sensor elsewhere, ran vacuum line from the TB to the mounted map sensor.
- All Sensors replaced (TPS, MAP, both O2’s)
- IACV
- EVAP 2 way valve

Items previous owner replaced (engine related)
- JDM engine swap (H22A)
- Intake(injen)/Header( DC)/Excaust (greddy evo2 muffler was replaced with vibrant stealth)
- Magnaflow Hiflow Cat
- All vacuum lines, wiring harness, ect (everything needed for a basic engine swap)
- EGR (aftermarket)
- Injectors replaced

Services Done
- Valve Timing adjustment
- EGR ports drilled and cleaned along with EGR
- Fuel pressure tests within spec
- Vacuum test within spec
- Compression test in spec
- Carbon cleaners through gas tank and vacuum line

Can anyone think of any other possibilities causing this? Again, car starts up great, idles great, runs great. I get great MPG but this dang CEL won’t stop haunting me.

motoxxxman

you said fuel pressure tests. did you test pressure with the engine off? and with the engine idling, and with the engine idling with the vacuum line disconnected from the fpr?

also you said injectors were replaced. do you know if you used the right injectors? preludes have had 240, 290, and 320cc injectors. early obd2 used 320, later obd2 used the 290. maybe your ecu is set up for the 320's, but you are running 290's?

have you checked ignition timing adjustment?

do the sparkplugs show a lean condition? or any signs of detonation?

thirsk66

iTrader: (2)

Are your spark plugs gapped to the correct spec of 0.44? The injectors you replaced, are they stock injectors or aftermarket ones? Also have you inspected your intake system for leaks? And you are using 91 octane for your prelude? I know its a dumb question but thought I would ask anyways.

minilogoguy18

Sooooooooooooooooo many parts replaced that have nothing to do with the problem.

Are you SURE that valve clearance is within spec? Too tight of valves will cause this, valves will open too much drawing in too much air causing a lean running condition. Are both O2 sensors OEM or aftermarket junk? Is the throttle position sensor set correctly and has its range been checked with a good DMM by SLOWLY opening the throttle and watching the change from about 0.45V closed to 4.5V WOT?

Fuel octane has nothing to do with this btw, you can run 89 in these cars with the stock engine and the knock sensor will tell the PCM to retard the timing and nothing will change other than a small loss of power that is hard to notice. Why waste time too with cheap plugs that need to be gapped and will be dead in 10k? Just buy the recommended NGK/Denso platinum plugs that are listed on the sticker under the hood, they're good for 100k+ and do not require gaping.

motoxxxman, the distributor is fixed and the ignition timing cannot be adjusted manually, the PCM controls timing advance/retard based on CKP,CYP and KS input.

DCFIVER

Pressure is only half of the measurement. You need to check fuel volume.