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96 x90 revival
Hey folks, been at it for a while and I'm pretty familiar with the platform.
Picked up a x90 with a fuel pump issue and put in a new pump? and filter and got it running. 123000 on the clock 4x4 auto.
Had a few code knocked them out.
The problem I'm having is that it won't stay in closed loop.
I have read the fixkick site quite a bit due to the plentiful info. Thanks,
I have everything checked out and I have this problem.
At idle The primary o2 sensor reads .09vdc and won't toggle as it should. ( we later lean the 0.09v is a typo, and is 0.9v ( that is 1v = stuck high full rich, 0v = lean 1v = rich)
Then the short term fuel trim (long is better) tries to correct until it goes of the scale and shuts down and goes into open loop due to insufficient temperature? (who's temperature, air, coolant or 02 heater?)
No engine codes DTCs, I've checked all sensors related and it's all good , checked fuel pressure 40psi and 50psi(wrong) with the vacuum of the regulator.
I can trick it buy creating a vacuum leek by pulling off the evap nipple, to plenum, and get the o2 to toggle and stay in closed loop, but it's idling high (how high?) at that point with a vacuum leak.
I'm leaning toward a bad ECU (it's not that as I learned) as I have ran out of tests. (no , there are many other tests)
I can list a bunch of things I have done and tested. Try me. ( why leave out facts and tests?)
Thanks again I really appreciate all this knowledge in info your offering..

tech, edited above. accuracy.
welcome X90 that is very cool car, those are. 16valve engine and with MAP sensor and OBD2. sure.
02 front does swing, in fact stuck at or newer zero , (no cracks exhuast flange or exh tunnel #4 crack as is so common that crack. sucking in air and o2 goes to 0vdc and fuel goes full rich.
where did you see the temperature error?
that is good trick, pulling vacuum hose and leaning, the mix.
id say ECU is ok, never heard of any 96 up ecu fail ever (proved)
what is idle fuel pressure.? exactly
is FPR tested fully , from key on to idle and then gunned to WOT for 1 second?
its rich for some reason,
leaking injectors? (do leak down test on them?)
the maf dirty will read low and go lean , never does it go rich, (for sure easy to test with voltmeter to prove not it)
take off the exhaust tin shields yet, exhaust MAN, and gander at it? for cracks.
ever have bad gas in it?
that is it for now, i bet ECU is okay. EFI us rich for 2 reaons , it is rich ! or the O2 sensors caused (0v is no good), and 02 is bad or exhaust leaks doing that.
for sure you are on track, !!!
i forgot to say, are you sure the 02 front sensor heater element works, but again, the OBD2 reports that if current goes to zero, and is bad 02. or wire fell off it;
odb2 will in fact set DTC codes for any heater dead, or shorted
It's a 16v wit ha maf.
O2 gets stuck at .09 (but no, the first post was wrong, the O2 is at 0.9v (1v) so now all this makes sense, knowing first post was wrong.
The temp error is from a generic obd2 scanner tourque lite
50 PSI is wrong.
You had mentioned that an ECU can go bad and fuel out of control in the track fix data
Fuel regulator holds vacuum and regulates fuel well , shows 50 psi when pulling vacume source off
New maf and reads ok on the scanner
Have not checked under the heat shields to check for header leak.
New o2
Any pictures of common cracks in manifold?

Thanks for helping me build a better checklist .
50 PSI is too high. (are you at or near sea level)?
keyon pressure and idle PSI? "Snap-on" tools meant? 50 pSI is wrong, and pressure matters big time on all EFI and for sure this year.

Any ECU is bad, if and only if, all inputs are good and 1 or more outputs are bad. (just like any computer really)
The crack.
I showed this crack only for your wrong post in post 1, at 0.09 (0.1v that is) no the O2 reads, 1v, or (o.9v and you used the wrong decimal point on post 1) ok got it now. 02 front stuck high stuck full rich.

[Image: 3_12_11_18_6_20_05.jpeg]
02 front is 1v stuck high, just round off number, like this 0.9 is 1v. O2 stuck high right.
the ECU sees that and then sets trim fully lean MINUS MAX long term trim.
that is what the ECU does, its job is to trim fuel at all times not WOT. not cold, but yes, idle and yes, light easy cruising
the ECU stuck at max, NEGative trim, and the FPR reading wrong will over inject, the FPR range is 41psi to 21PSI end to end, and is never at 50 at any time.
the Fuel pressure varies from, 0 vacuum to 26"inches HG vacuum range, and 50 is not part of that SCOPE ever.
I made this curve to prove how the FPR works, at key on the spring opens the valve at 41 PSI, (the FSM even says that clear as day)
The variances keyon only, is only altitude.
the data is my 96 , 500'ft sealevel readings.
36 to 21PSI end to end, and 30 at idle
a savvy mech nows that 22 year old FPR just love to fail and some even stick as I play with my fancy $30 hand vacuum tool I can move the PSI fuel pressure to any point on that curve below, and if the valve sticks ,(can do) the pressure reads wrong.
you can test it or buy a new one for $60 your car your call your wallet and time. oK?

[Image: reg-graph-mpi-g.jpg]

here is spec on car (FPR really) offiical spec, and is poorly done not showing altitude corrections (IMO)
the books also states " keyon pump turns on and the FPR opens at 41 PSI " clear as day.
my guess is the left side below 36PSI is at high altitudes.
I also know that newer FPR sold today are sold with newer tighter spec,'s by USA EPA rule sets)
96-98 16v FSM specifications Rail pressure: (pg.6E3-A-36-37)

Static: 36-43 PSI, keyon, not started ( you may have to key on 3 times to build enough pressure, pump runs on 3 seconds)
Running: 30-37 PSI , idling. (where does 40 fit in here, answer IT DOES NOT)
Residual : minimum 25 PSI , after 1min. drop test. (key off while running drop test)

no you tell me where 50 PSI reading fits in any part of the spec. (the answer is , it does not)

one more point on FPR, and WOT
at WOT (wide open throttle, there is no fuel trims O2 live corrections, it leaves closed loop.
so injection rates are only governed by MAF (air flow) and the FPR
did you know that?
your PFR is bad.
your return line is packed up.
your PUMP is 2 times illegal GPH rated and the shunt test skipped by you is, at 80-100psi not 55, oops wrong pump.

I'd for sure have stopped at 50PSI, and then did test to find true cause, for sure, but do ask .
if the shut test passed,
then id remove the return line , put hose there and other end to a bucket, OMG pressure is ok. now, and i find crushed metal return line right frame rear, omg,
the last guy was a WHEELER. max.
Sorry the snap on fuel pressure gauge reads 40 psi ( idling hot????) and then when you pull off FPR nipple, the(NO) vacuum it reads 50psi (50 is WRONG )
(why leave off the fac t that key on pressure was 50,? why)

The coolant temperature is reading correctly via my obd2 scanner. ( is it to hard to say I see scan tool shows 180F? and holds there?)

If the header was cracked I would think the o2 sensor would read on the lower end and not stuck at 0.9 volts (true but your first post stated, (0.09v) and was typo sending me in the wrong direction.0
and I can watch the short term fuel try to minus fuel while in closed loo till it gets past 20-25% and then go into open loop. At that time the scanner message says open loop due to insufficient temp.
avoid short term trim, this changes faster that humans can see, oK
use only LONG TERM FUEL TRIM and win! says a tech, editing this.

I have a used ECU coming tomorrow wish me luck and if not I will be prepared for more testing. (if does same thing)
Well the replacement ECU I have does the same thing. Aaaaaarrrrrrgggg
if the inputs to the ecu are wrong, so will be those outputs
EFI is a computer, and as one , uses those rules.

Quote:"Sorry the snap on fuel pressure guage reads 40 psi and then when you pull of the the vacuum it reads 50psi"
this is backwards, why is the FPR reading backwards?

that is correct, 0.9v is stuck high, not stuck lean. (THE 0.09Volts in post 1 was wrong) ok, got it. now.
the FPR reads wrong,

you have no idea how the FPR works and how it must work from 0 HG to 25"HG do you, you say you do but do not,
the proof is , 50 PSI is not part of the range of any FPR, here. ever.
41 psi is par, not 50. ever, unless wrong pump used (2x GPH rated) or bad FPR or return line to the the tank is clogged or pinched in 4wheel drive event.
the 9 tests were not done (only 2 done and both fail) IDK what to say wrong is wrong? done wrong and the wrong pressure not recognized as wrong)
the 3 tests only on FPR not done
the shunt test not done
the 4 injector balance test not done if all above pass ! but leakdown tests fails.

the answer is in POST 6, fully and extensively
just for you check it out.

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