leans out under moderate to hard accel

[jasonsan]

maybe someone has run into this before///just replaced block for ka24de///re: #1 cyl knock///veh will hesitate under moderate to hard accel until approx. 4000 rpm///under full throttle veh stumbles and upon lifting accel. pedal slowly will gain accel and start to smooth out///i think im chasing a MAF sensor but dont want to spend that money on a new one until im sure///engine runs good and quiet and compression is good///all ecm data using consult shows good specs and test results///occasionaly a/f alpha reads 120-130% which from my experience points to faulty MAF. the parameters set by nissan for MAF fault are very wide and can be faulty w/no DTC's set///i dont have a known good MAF to try///i had this running condition before replacing block and i believe it ultimately led to its failure. anyways, im going to fiddle w/it this weekend more/// any ideas are welcome///ill post later if i find out anymore info
Modified by jasonsan at 10:01 AM 6/9/2008

[jasonsan]

i know egr is working good///no valve deposits///no intake leaks///under light loads veh does fine///only mods is a pop-charger installed///new plugs,wires,cap,rotor,o2 sensor/// note: i am a nissan tech w/8 yrs exp. and my master tech are no further help/// my o2 sensor max reading under mixture ratio test is 0.72v and passes test. however reads 0.00 under accel(hard) and should read closer to 0.9v///need to get back to work

[jasonsan]

okay - before going home im going to pinch off return hose and see what it does under hard accel - it should run rich under hard accel - currently my fuel psi does not drop off so pump should be good - im expecting veh to run rich - next step would be to pull fuel rail and check injector flow rate and spray pattern - if that checks good i just may have to take the dive on a new MAF - just hesitant due to i have two mafs and both provide same running condition but both are just as old

any additional thoughts welcome as i could be overlooking something in my thought process

thanks, Jason

[jasonsan]

pinch off return line - just gives max fuel psi - no significant change - - cleaned all engine bay ground connections = slight change - - engine performance better, not so much of a stumble now, a/f ratio gauge shifted slightly richer and acceleration improved - not able to monitor my a/f alpha (consult @ work) - checked MAF ground = good, no voltage drop MAF signal wire = 0.2v KOEO 1.2v KOER

@ this point i think ill put my chips on MAF has taken a "lean" shift

i put this engine together w/used parts and has approx 160K on it, engine sounds good, runs good (should be better), and still fun as hell to drive ((been sitting in my garage for 2.5 yrs)

think ill save up for MAF and ejoy my ride till then.

Any insight would be welcomed.

[jasonsan]

okay - problem finsally showed its head = checking fuel psi again = normal at idle = approx 34 psi

under accel = drops to 30 psi

found sending unit connections corroded at sending unit topfeed and return nipples heavy rotting

will most likely replace sending unit and pump - unless electrical can be fixed

either pump not getting enough current or pump weak or clogging

its fifteen years old, getting a sending unit/pump assy

note: veh runs great using consult fuel injection active test giving 25% more duty time to injectors

quick fix to run rich - fuel psi during driving = 30-32 psineed more fuel psi

boOM!

[jasonsan]

removed fuel sending unit last night - didnt break anything - HUZZAH!

am putting in new fuwl pump today and rewiring sending unit due to green death . did temporarily rewire last night and still 30-34 psi but gauge fluctuates very rapidly now

the quest for fuel continues...

[danielsan]

what do you mean by sending unit???

i have sort of the same problem, its either my maf or low fuel pressure. i dont have the special tools to check fuel pressure though.

im guessing i could test it by removing the vacuum hose from the regulator to check if that effects anything.

[danielsan]

oh yeah i have no codes at all other then my speed sensor but thats because my digi speedo does not work.

[jasonsan]

FUEL SENDING UNIT - what NISSAN calls the gadget that holds the fuel pump and fuel level sensor - access in hatch at RR above fuel tank - remove panel and you will be greeted most likely with a nasty/rusty round panel on top of fuel tank and also most likely will have "green death" @ wires into tank.

at my cost (nissan tech) sending unit is approx 175 bucks - not money i wanted to spend - took utmost care to remove sending unit w/o breaking anything.

fuel pressure before repairs = 30-34 slow moving fuel psi gauge (bounced between numbers slowly)

fuel pressure after wire repairs = 30-34 but needle on gauge going crazy (like fuel pump trying awfully hard)

fuel pressure after new pump = 34 idle (steady) 43 (vacuum hose removed to regulator)

when accelerating veh no longer leans out and hesitates/bogs veh now pulls good and a/f meter reads rich

as for testing by removing vac hose = most likely will not notice differencepurchase a gauge and some fuel hose - i got mine from jegs maybe $35