Bog/stutter/no power issue under load

[Joe]

Many of you remember this problem i had back in november, well it resurfaced last weekend and im going to create a new thread because the last one went OT pretty quickly.

background Series 2 RB25, been in for about 4 years, dedicated track car, have had virtually no mechanical or electrical part failures at all.

problem - between 25-75% throttle, car has inconsistent power delivery. meaning it will begin to pull normally SOMETIMES and very briefly, then hit a flat spot and slow down and remain like that. at 100% throttle there is no power. makes lots of noise, doesnt go anywhere.

what ive tested - boost leak checked the system to 50psi this morning, NO leaks anywhere, replaced spark plugs, recalibrated TPS, redid base ignition timing, checked resistance on engine coolant temp sensor (value changes with temp change too). boost is reading normal (12psi). THERE IS NO MISFIRING. its just flat. no smoke i can see either.

3/6 - replaced fuel pump, still same issue.

I have 11 days to fix this problem.

give me your ideas NICO.

[Sil240]

Try another ECU.Maybe there is a problem there.Kinda funny to go away an come back.

No loose wires or any chaffed wires??

Have you tested your MAF & or CAS?

[mello88]

Do you have CONSULT or similar way to monitor the sensors as you're driving?

[Joe]

Try another ECU.Maybe there is a problem there.Kinda funny to go away an come back.

No loose wires or any chaffed wires??

Have you tested your MAF & or CAS?

i have a mines ECU, little more difficult to do that.

after this happened the first time it went away on its own, i pulled the entire engine wiring harness off and inspected and rewrapped it. no visible damage and it was fine for 3 months.

have not checked MAF or CAS yet, im going to replace the CAS with a buddies but MAF is off a R34 (because of the mines ecu) so i cant replace to test that one.

[Joe]

Do you have CONSULT or similar way to monitor the sensors as you're driving?

i wish.

[Sil240]

Well there is a guy on FA that's selling a mines ecu.Don't know what its programmed for, you may want to look into it.

or

Look into a CONSULT like Mello or a Apexi multichecker.You'll be able to take a peek into what the engine/computer is doing.

[USMCgetsome]

i got the same issue. changed ecu maf recal tps still has bad flat spots but top end is strong!

[eh?]

Junk that ecu and buy a new tps. didn't you have a CAS issue a while back?

[FAST-DATSUN]

do you have good fuel pressure and volume???? sounds similair to what happen when the walbro goes bad.

[Joe]

Junk that ecu and buy a new tps. didn't you have a CAS issue a while back?

you guys are ****ing nuts im not throwing away a mines ecu OR replacing it. IF the ecu is bad im going EMS.

my CAS did go bad but that was over a year and a half ago. it internally ate itself and was giving me HUGE misfire problems. this is just flat. coincidentally that was the last part failure this engine has had lol

Mack, I was starting to think that too. im gonna volume test it tommrow after i do the math on what it should put out lol. pressure at idle is good but its an engine bay gauge, so i cant check it while driving.

[BoostFab]

the problem could also be the feul pump. do you have another to test out?

btw, what does the mines ecu tuned for (specs, peripherals????)

[Joe]

dont know, came with the clip along with a R34 MAF. all i know is they cant be separated lol

i dont think i have a spare fuel pump but i might just buy a new one. my current pump lost its anti drainback valve about 2 years ago i figure its time to toss it anyway.

[eh?]

Do you even know what kind of tune is on that ecu? Or if it was even thrown into the clip?

That's not smart at all.

[Joe]

Do you even know what kind of tune is on that ecu? Or if it was even thrown into the clip?

That's not smart at all.

yea well its been on my engine for 4 years and i have over 2000 track miles on it. thats wide open, slamming the rev limiter, driving my balls off. i dont think its a problem.

it was bolted down on my clip, not just thrown in.

[Sil240]

I don't think you should just Throw away you ECU.You should stock pile like me:-) I've got 3 2 stock and a chipped one.

Maybe you should find someone to borrows or if not buy one and if its not that sell it.

But I would change your fuel pump first and check or try someone else's MAF and CAS.

[Joe]

well i tested my fuel pump.

on the feed side it tested ok (i dont have any way to measure exactally lol)

but i tested free flowing vs. return w/ pressure and its about a 35% difference in flow. i got about 1 liter in 15 seconds of free flow and significantly less than that when i did the same test on the return side.

im gonna replace the pump and see what happens.

[Joe]

brand new walboro fuel pump, same problem.

[gawdzilla]

i'd say bad maf... what color is the r34 rb25 maf?

try getting a replacement or maybe a z32/safc combo. stock rb25 might even work.

[Joe]

shouldnt that cause misfiring tho? not just no power?

its a sliver sticker, E60 at the end of the part number. i think it translates to a N60 maf but im not sure.

[gawdzilla]

i had a bad maf and it gave me weird symptoms. sometimes it would stall at idle for no apparent reason. sometimes when i was driving it would feel like i was stabbing the throttle and the car would surge back and forth.

never got misfire from bad maf.

it seems like you've ruled everything else out so i'd give that a shot

[Joe]

i dont shotgun troubleshoot, i want to test a part to see a failure. not just replace it as "it could be this" thats my last case scenario, thats quickly approaching haha

[Darius]

Have you verified that your TPS is working properly? I think it should read something like 5.0ohms of resistance at WOT and 0.4 at no throttle (obviously not running the motor while doing this ). For a much better description, refer to pages EN-364,365 in the FSM.

[Joe]

its actually measured in volts not ohms, and its .35-.4 closed and 4.0+ WOT

yes im reading that no problem. i havent verified any of this AT the ecu tho, only at the sensor.

[300Plus]

Check the ground on the MAF. Before my intake gasket failed I had an issue that turned out to be the MAF wires got hung up and when I dropped the clutch on slicks, it stretched the ground wire and was making my MAF max out. worth takin a look man... Good luck

[Joe]

my maf is not maxing tho, there is no wall or misfire.

[krayton]

compression test is pretty easy. know nothing is really saying anything in that direction, but just to rule out?

also can look at plugs

[Joe]

im gonna do one as soon as i run out of things to test that are easily replaceable. if the motor is toast theres no way im gonna make the event anyway.

i replaced the plugs first thing, old ones were black and sooty but not bad.

[chockrl]

One of the best diagnostic tools is the Nissan Consult interface. I would recommend the $75-ish for a cable and one of the many free softwares to trouble shoot. You can monitor everything real time, or datalog.

[Joe]

im just gonna plug an AEM EMS in before i got spending money for a consult i wont use for long.

i was PLANNING to do a EMS/turbo/injectors this summer in our off season but apparently the car may have had other plans.

my friend has an RB EMS and a non-running car at the moment i might throw a basemap on there and just start it up to check sensor inputs.

but you are correct, the consult is an amazing diagnostic tool.

[gbaz77]

kamin you sound extremely sure about your maf. not to act as if i know more than anyone, cause i dont, i learned most of my stuff from all of you.

however, my car had a very similar issue. i had an maf that i would have sworn by cause it was $80. i cleaned it and everything, even had it tested with some equipment that could read the airflow. ended up getting a new maf and it solved everything.

just saying, it could very well be that r34 MAF.