spaceviolence

Hello all,

A little preface: I am new here, and somewhat new to Z's but by no means new to cars. I have the FSM and have **** near read the entire
thing, I've googled and forumed to no avail, as nobody's problems seem to fit my problem exactly. I've troubleshooted many components and circuits
and fixed ones that were wrong, which I will list later, I've worked on this problem for a couple days and even worked on it in my dreams with no
luck haha.

So I've only had this car for a few months, and in that time it has been awesome, great, reliable, runs like a beast, always starts right up (With
the exception of that occasional vapor lock in the rails), still does but wont stay running. Drove the car the other morning to get breakfast, ran
great, no problems, nothing weird. Exited the cafe and got in and started my car and it started right up but died about 3 seconds later. Was not
successful in getting it to run correctly so drove it home frustratingly running like crap. Will not stay running, runs more like normal in high
RPMs but even then if accelerator pedal held down at a fixed level it will still eventually die. The only way to keep the engine is to keep moving
the throttle. This problem exists regardless of whether cold or hot starting. Disconnect MAF and engine will idle (too low) and run, but will not
rev above 2.5K (duh lol) and dies once throttle is release (will not hold idle.) When engine ran well, all devices seemed to be working correctly,

Idle up did work fine, any time lights or A/C came on engine would idle up correctly.

On to progress.

Checked for vacuum leaks, large ASCD vacuum hose had hole burnt in it from EGR valve tube and was leaking, replaced.
Vacuum line from canister to watercock was brittle and broken, replaced.
Have done a listen check on injectors and all seem to be clicking, will do OHM test and update later.
Checked battery connections, seem legit, grounded to frame and starter.
Checked EVERY fuse, all were fine, anti theft system fuse was always removed and I'd like to keep it that way.
Checked FPR, wasn't squirting any gas so seems fine. *shrug*
Ran a fuel pressure guage T between fuel filter and fuel rail, got 40 PSI primed and ~36 PSI when running. Stays there.
Fuel pump primes perfectly and does run while engine is running. Don't think that's the problem as I've got pressure all the way until and after it dies, fuel pump runs for a couple seconds after engine is turned off as it should as well.
Checked air cleaner. Nice K&N lifetime filter. Seems barely used.
I should add I checked every electrical connector I could get to. I know corrosion is usually a problem on these cars but only maybe one had any corrosion, the rest are pretty spotless and shiny. This car HAD to have been garage kept as everything is in great shape. (Minus some minor bumper and fender/ mild frame stuff underneath due to it being driven off the road into some deep shrubs as previously stated.

So it seems I have ruled out fuel delivery (unless injectors suck) besides, seems that the exhaust is crazy rich at times and lean as **** others. Even when car was running smoothly, It would have a bit of trouble on warm up for about 30 seconds or so, accompanied by missfires upon pressing throttle, is worse the further down and more quickly you move the throttle (would eventually catch up and accelerate to correct engine speed if you held pedal in
place) and then it seems air/fuel ratio would even out nicely, after that, idled great. Not anymore though.

Spark plugs are black, but despite all the carbon the look fairly new, the electrodes are not worn in any way and the wires seem to be in decent
shape. This car runs rich methinks, at least on warm up. Previous owner ran it off the road into some hefty shrubs and let it sit for about 3
years (live in the desert, not many trees) and probably cracked the CAT/Exhaust pipe to muffler/flex pip/whatever so its got an exhaust leak and
probably needs a new O2 sensor on as well. (Light was on when I got the car, due to its age I just diconnected the light as recommended in the
manual)

Ran diagnostics. Got codes. Fixed most problems. Got:

(13) CHTS code, checked harnesses, sensor and circuit and all seems well, resistance is at 4.3 kOhms approximately when cold seems correct for a
cold early spring morning here in the desert (40-50 degress outside), afraid to run car long enough to warm it up to check hot resistance, after I
reconnected all connectors, code went away.
(41) Fuel Temp Sensor: Wire and harness were both misshapen and broken, installed new connector, code went away.
(31) Load switch: turned on lights, A/C, code goes away.
(23) Throttle valve switch/Idle switch. Adjusted TPS, code went away.
(12) MAF code, did not test at this point.

Reset codes, retested and got: Load switch (31) (duh) and (12) AFM.

Checked all wires from wiring harness to computer.
Checked ground resistance for both ground wires, close enough to zero,
Checked incoming 12V to MAF, comes on with EFI relay,
Checked signal voltage at ECU with engine running as long as it would, when engine not running voltage is maybe 1.4 ish, when running its well over 2.0 but not past 3.0, could not check on rev or higher RPMs as engine kept dying.
Checked EFI relay and all associated sensors/switches/solenoids. All are getting power when EFI relay engaged with key ON.
Cleared codes, retested, all codes gone but code 12 for Air flow meter.
BUT WHY if everything seems correct?? (Or am I missing something?)

Cleared codes again, reperformed diagnostics, held throttle at fixed levels to try to get engine to run normally. At 1100 engine seems to run
smooth with no noticeable missing (although engine may just be revolving too quickly to actually tell) however at 1000 engine runs rough and
labored, missing it seems and wanting to die, but wont if i hold it at 900-1000, still really wants to die though. Seems as though the longer held
at a fixed throttle position, the RPM will decrease slowly and steadily until engine dies. Code 12 still shows up. Not immediately, but sure enough, always comes back, even though AFM seems to be within spec.

Results: Still stuck with code 12: AFM.

Things I haven't checked yet:

CAS (is getting voltage but havent checked actual sensor yet)
Dizzy/Ignition
Injector impedance
Cylinder compression (don't have compression guage, will rent one this week.)
Timing Check (don't have timing light, will rent one, will rent one this week.)

I do plan to do these in the next couple days and will include results below.


Questions:
FSM says with 12v on D&E you should get 1.6V at B & Ground +/- .5V I get about 1.4V so that seems right.
FSM says blowing air thru should get 2-4V. I get 2-3 with engine at idle (Didnt remove AFM, did tests from harness @ AFM and @ ECU harnesses.
Seems right, right?
This being the case, is it possible my ECU had suddenly gone bad as I ate breakfast that day or does anyone have ideas?
Could my timing have jumped?
Are CHTS as they go out, intermittent/work sometimes/not othertimes?


Follow up: Sorry for the length of my post, I hope you all will appreciate my detail rather than become frustrated by it, as it has been opposite for me in my experience. (Never enough details given to help fix problems in forum posts) Also thanks in advance for anyone who takes the time to read and respond. Also, don't grill me or troll me, if you think I've missed something or am wrong, just lemme know, I'll appreciate the knowledge. As you can tell I've really taken the due time to do the correct research and troubleshooting as well as taking the time to write this in a cohesive, coherent and professional manner. Thanks.

spaceviolence

I adjusted the idle screw on the Idle up solenoid valve, backed it out enough that the engine would actually stay running (incorrect but i wanted to warm up the engine), was able to take it for a short drive, at first, smelled very rich. During the drive, if I give it any throttle that puts it under a load, it misses horribly and bogs down. Let off the gas and it idles crappily at about 500 RPM. Still has power like it used to in but struggles with more throttle. I guess I should say its still got torque, but any load other than normal driving, and it misses. NOW I'm thinking back to the fuel system, but i've got good pressure, I guess I should OHM the injectors next.

I should add that I tested for spark on #1 and all seems well, blue spark most of the time. Took off dizzy cap, rotor spins, doesnt look horrible, I do get spark.

spaceviolence

Unplugged AFM, went for a drive, idles correctly, has plenty of power, but obviously not above 2K RPM.

The self cleaning circuit doesnt seem to be working. only gets up to .04 - .05 V after engine is turned off. Is that correct? Thought it was supposed to be 12V. Either way, tested AFM signal voltage at ECU harness and read 2.4 @ 1.1K RPM, 2.8 @ 2K, got it up to almost 4V with a large rev. Seems correct to me, maybe i'm wrong? ECU starts reading voltage around 2V up to 7V if i'm correct, and also correct me if i'm wrong but voltage should be within 1-5 V?

Also, CHTS is weird. At first, with engine cold just now, couldn't get a resistance reading on any of my ranges on my multimeter. After engine warmed up, got ~0.70 kohm, which seems to correlate to ~122 F. Tested continuity from CHTS harness ground to frame and nothing, also to ground in the AFM harness, since they intersect, and still nothing. No continuity. Does anyone know if the sensor is grounded thru the head? if not, my results make perfect sense, which i'm leaning toward since it is a 2-wire type.

rogerz

seems like I answered this but maybe forgot to push the post button so here goes again.

unlikely the maf. you need to put a screwdriver in there and break the wire for them not to work they are a very simple device. If you find a junker take the maf - any maf from z31 work on any z31

Unplug the O2 sensor. run it if that fixes the issue you know the problem. the rich smell etc really points at that.

ChTS normally won't stop it running but will make it run badly at certain temps.

get some freeze spray (radio shack maybe). next time it dies freeze the ignitor (power transistor). If it starts you know that issue. some transistors get flaky when old and hot.

It seems to be an intermittent issue related to engine temp. above are the most common.

Just replace the chts. cheap fairly easy. google a post on how to do it without taking everything apart. I have done that on every z31 I've known with great results. when you do it use a new connector (same as FI can find really good ones off older volvos at junkyard) cut the oval connector atop the engine off and solder the new connector to that. eliminates one more questionable item.

if you put in your general location you may find someone willing to help near you. ie if you near seattle glad to take a look and I have a MAF and ignitor for testing.

spaceviolence

I do appreciate the advice, I'm gonna go try to get a junker AFM right now, failing that, I will pick up an ECU if available and MAF cleaner. I WISH I was in Seattle, too bad. : / In response to your response however, it isn't an intermittent problem, it happens whether the engine is cold or hot. Which is what has me stumped. It idles fine without the AFM which makes me question it, and with the AFM connected, lower RPMs are horrible and higher ones the car runs like normal, but very hard to even get it to higher RPMs while driving without it dying. It is VERY hard to keep this thing running with idle screws and everything set in original positions. Raised, its manageable, but still really sucks with AFM connected, and without it, obviously cant rev above 2K.

rogerz

well you say hot or cold yet you say you drove and it happened so what is it. you start it cold it runs 3 minutes and dies..
you may not want my advice but disconnect the O2 sensor and see if problem solved. do it cold or you burn your hand. do this before you go out whizbanging around with other stuff
and then the igniter.

spaceviolence

Its both. I was just trying to describe the symptoms in detail while driving and also idling, with and without AFM. The condition always exists as long as AFM is conected, without AFM seems normal but wont rev past 2K (for obvious reasons) <-- why I'm thinking AFM but who knows, I still need to do Timing check and compression check.. I went out to tinker and unplugged the O2 sensor but made no difference.

When you say ignitor are you referring to the power transistor? The freeze spray along with some MAF cleaner are next on my list.

Maybe I can snag an ignitor tomorrow at the yard along with AFM and ECU.