Crank, no start after transmission+diff oil change and slave cylinder change

[IVBLUEMAN]

Tl;dr- changed transmission oil, diff oil, and clutch slave cylinder. Car started before that, crank/no start now. looks like its not giving signal to the ignition coils or fuel pump, suspect a bad ptu.

As title says, but a little background-

Im a mechanic by trade, but primary background is in heavy equipment/generators. Work on fire trucks right now. So I do know what I'm doing, but automotive is not my specialty.

The car- '91 Z32, 110K miles. Guy that I bought it from got it from a guy who did an automatic to manual swap. Pretty sure he's got youtube videos on him doing it to my car. Need to pour through them, because guy is a moron. For instance only put 3/7 bolts back in between the bell housing and engine, and 2 of those 3 were finger loose. Caught it the first time I bled the clutch and I saw the transmission bucking like a horse lmao. So who knows what nonsense he did in there. I know my buddy I bought it from didnt touch it aside from replacing the radio and speakers.

Done a s*** of repairs on the thing prior to this I can go through, but gonna try and keep it relevant here.

Car ran fine, but had a few issues I need to resolve to have it reliable and in good condition. Ran before I did all of this, crank no start after I was done.

-Coolant leak at the engine-to-engine coolant pipes behind the engine. Waiting on the part, its coming with a new balance tube (which also has a vaccum leak), fuel damper, and fuel lines. Didn't pull anything related to this aside from the balance tube to see if I could find the O-rings at a hardware store instead of ordering them. No dice, put the O-rings back, put the balance tube back on and torqued the nuts to spec. Didn't take any lines or hoses off it when I pulled it.

- Shifter stick was rattling in drive unless you pulled up on it. Pulled center console (was replacing the cigarette lighter too), checked it out- wasn't secured properly and lower grease boot was f***, so the stick would sink down and the control rod would make contact with the drive shift. Was able to secure it in position, fixed the issue. Put center console back in. Luckily no damage to the drive shift or control rod.

-Slave cylinder was rusted to s*** internally. Replaced it. Between that and fixing the stick, what was hard to shift now moves like butter. Bled the clutch (had already replaced the clutch line with one that goes straight from the master to slave, only bleeder is at the slave) until no air and the fluid was solid and not airated. Already replaced the master cylinder, clutch pedal still needs adjusted- way too much free play. Note that the clutch safety switch did not need to be engaged to start it before this- think the guy bypassed it. Slave cylinder also had a ground cable on one of the bolts, unsure what its for, looks like it goes straight to battery negative. Put it back on anyway.

-Headlights stopped working after I blew the ignition fuse a few days prior. At the time I thought the unlabled fuse in the box by the battery was a spare, switched it and the ignition fuse. Turned out the unlabled one was for the headlights. Switched the power window/seat fuse to there, headlights work now. waiting on new fuses for that, no fuse in the power windows slot. Tested every single relay and fuse in the thing figuring this out. All the fuses and relays in both engine bay blocks and the footwell block are good.

-Changed transmission oil and diff oil. Boy were they nasty and old, figure they've never been changed. Noticed the nuetral switch and backup switch wires were just tied to the plug wires, no electrical tape no splices. Just barely connected exposed wire. Butt spliced the nuetral switch wires together, backup switch wire fell right off at the switch the moment I touched it., so Im just gonna replace it. Maybe got the nuetral switch wires backwards or something, but it should only be opening or closing the circuit, so it shouldn't matter. and I dont think either would cause a no-start. Also metal shavings on the transmission drain plug. has me worried, but I dont think would cause this. Filler plug was a b****, and I had to smack a breaker bar with a hammer to get it out, so maybe I accidentally whacked the speed sensor, but I dont see any damage.

I know a bad PTU would cause this, but there were no signs of it going bad before, and I cant imagine anything I would have done that would have caused it to fail.

At a total loss here.

[VStar650CL]

If it cranks then it isn't the neutral or interlock switches causing the problem. Start with the basics, spray something combustible down the intake to see if there's fuel and pull a plug wire to see if there's spark. If there's no spark, the PTU needs a "hard" ground and maybe you disturbed something changing the slave cylinder.

[IVBLUEMAN]

If it cranks then it isn't the neutral or interlock switches causing the problem. Start with the basics, spray something combustible down the intake to see if there's fuel and pull a plug wire to see if there's spark. If there's no spark, the PTU needs a "hard" ground and maybe you disturbed something changing the slave cylinder.

Yeah, off the bat did the basic checks for air spark and fuel. No fuel, no spark. Ignition coils and fuel pump aren't getting signal when I turn the ignition switch.

Ill check the PTU harness- guy who did the swap moved the PTU, and I had just found it when I had to stop working on it. Hanging loose behind the AC condenser for some god forsaken reason.

[VStar650CL]

No fuel and no spark at the same time sounds like the ECM's power is down. Check your fuses and fusible links, and if nothing is blown then check the ECCS Relay.

[IVBLUEMAN]

No fuel and no spark at the same time sounds like the ECM's power is down. Check your fuses and fusible links, and if nothing is blown then check the ECCS Relay.

Already checked the ECCS relay, it checks out. Checked every single relay and fuse under the hood and in the driver's footwell.

Getting into the passenger footwell today to directly check the ECU. If its on, Ill check codes while im there, see if I can get anything useful. Left the battery negative off when I finished yesterday, was also gonna see if that might reset the ECU and solve an issue.

[VStar650CL]

The main thing is power to all the power pins and solid ground on the ground pins. Measure voltage on the grounds with the ECM powered, anything above 50mV is trouble. There should also be a circuit straight from the ignition switch that tells the ECM to wake up and turn on the ECCS and ignition relays, make sure that input has power with the key.

[IVBLUEMAN]

UPDATE:

Went to check the ECU for codes. Noticed the red LED wasnt on, trying to switch to mode II to check the codes just turned the led on and wouldn't go to mode II and give me codes, but now I get fuel but no spark.

Checked the fusebox again- when I used a power probe to check the terminals at the ignition coils relay (which I already tested), found that its not getting its ground to the relay coil. I believe the ground signal (terminal 2 iirc) is what's switched on it. Using my power probe to give the ignition coils signal, the engine would turn over.

Given that I noticed that the turn signals are also not working now, Im assuming I disturbed some wiring when I was f*** around in the kick panel. Consulting some wiring diagrams, will report back.

Figure for now if I need to move it, I can just jump terminals 3 and 5 at the ignition coil plug at the fuseblock while its cranking/running. Not trying to run it more than a couple minutes like that though- itd just let me move it from my buddy's driveway back into the garage, so I dont have to leave it in nuetral and just push it around.

Couple other finds- anti-theft module was unplugged. Luckily not aftermarket though. Went ahead and plugged it back in.

Power seat plugs were unplugged. Not important, but it did make me mad lol.

[VStar650CL]

I don't see a copy of the '92 Foldout here in Nico, but the schematic shows the supply for the relay coil and relay contacts come from different places. The Ignition and ECCS relays are both switched on by a common ECM pin (16) and both get relay coil power from the same source. See page EF & EC-13 (pdf page 139) here:
https://www.nicoclub.com/service-manual ... 92_FSM.pdf

That boils down to, if the ECCS relay comes on, the Ignition relay should come on too. Since jumping the Ignition relay contacts lets the car start, that means the high side of the Ignition relay has power and the coil circuit is healthy. So all that's really left is a bad Ignition relay or a bad connector/wire at the relay. I'd try a new relay first.

[IVBLUEMAN]

Already put a known good relay in there- didnt do anything. Pretty sure I may have just dislodged some wires when I was messing with the fuseblock. Ill check the wiring to it later.

[IVBLUEMAN]

Okay, so I looked things over and theres an ignition relay in the back of the footwell fuseblock. It was bad, I replaced it. Still doesn't start. Checked the ECCS relay- it stops getting signal at pin 3 at the relay when I try to start it- using a power probe to supply negative to that pin (I believe its the circuit to the ECU) gets it to start, but putting the relay back in turns it off.

Relatively certain that means the ECU is telling it not to start. So im assuming I somehow damaged wiring to either the PTU, CAS, or MAF.

[VStar650CL]

That pin from the ECM is an open-collector driver. I.e., it's an N-transistor which can only pull ground to the circuit, it can't push power. The only power comes from the high sides of the relay coils, and for that reason, if a relay coil shorts, it will almost certainly overload and blow the transistor.

By grounding 3 you're manually being the transistor, turning on both the Ignition and ECCS relays. The ECM can't run at all without turning itself on, so if the transistor is healthy then that circuit should go to ground as soon as you put the key in the run position. The reason it's set up that way is because the ECM needs to wake itself up periodically while the car is parked, to check the fuel tank and evap integrity. The ECCS relay allows it to do that, then put itself back to sleep. I'm not sure on your Z, but on most Nissans from that era the only thing which might make the ECM sleep itself is a theft condition. Otherwise, you probably have a blown transistor in the ECM.

[IVBLUEMAN]

Maybe the ECU is jacked up now? There's gremlins in the electrical, things are even stranger now.

So I forgot that the anti-theft had the relay attached to it unplugged, and I plugged it back in yesterday. Unplugged it and it runs.

BUT

It only starts if I crank it then leave the ignition in "on" position. And then it wont stop, even if I unplug the battery. The only thing Ive been able to do to get it to stop is unplugging the PTU.

I swear, im at my wits end. I have no idea what I could have done to cause this. Maybe the ignition switch is bad now?

[VStar650CL]

I don't think the ECM has any way to know you want to shut down except the ignition wire into pin 45, that comes straight from the ignition switch. If that goes to 0V but the car still runs then the ECM is probably screwed, if it doesn't go to 0V then either the switch is bad or something is crossed in the power wiring. You can determine which by pulling the ignition switch connector and seeing if the run pin on the car harness side goes dead. If it doesn't, something is crossed between the battery and ignition circuits.

[IVBLUEMAN]

Im thinking I crossed something when I pulled the footwell fuseblock. I did switch the rear window defroster relay and ignition relay in case the ignition relay was bad, even though it tested good after I cleaned the terminals (s*** of circ-clean was all I used). Maybe those relays have different open and close settings.

I dont think its the ECU, cause now the red LED on it doesn't come on at all. And in order, what happened with current start conditions:

-crank, no start
-pulled the anti-theft relay attached to the anti-theft module by the ECU, crank no start.
-realized I had the ECCS relay still out. Put it in, starts if you crank it in the start position, then set the ignition switch to the on position.
-now doesn't turn off unless you pulled the ptu plug, plugging or unplugging the anti-theft relay has no effect.

My theory:

Anti-theft was unplugged for a reason. My other repairs allowed the ignition relay to work- so unplugging the anti-theft made it work. But switching the defroster and ignition relays caused the current condition.

[IVBLUEMAN]

https://drive.google.com/file/d/18ht4Xv ... p=drivesdk

Last thing- found this on the ground under where I had the car parked before moving it to the garage- any idea what it might be?

Edit: never mind, thats part of a vape pen lol

[IVBLUEMAN]

One more question (and thank you for all the assistance, you've been a great help)-

If I do need a new ecu, theres a guy nearby me selling one. But its off a twin turbo model. Would it be compatible with my na engine?

[VStar650CL]

Yep, that's a vape coil alright.

I'm sure the TT unit will fit in the hole, but I'm also pretty sure it will have the wrong PROM. In those days it wasn't an in-shop operation, ECM's with different firmware had different part numbers. To DIY it you need to desolder and replace the PROM, or there are places on the net who can do that for you. If you go that route, I strongly recommend adding a DIP socket to the board so any mistake or subsequent change is a lot simpler.

[IVBLUEMAN]

That definitely sounds like more work than is justified just to have a convenient pickup, especially when im not certain if the ECU is bad yet.

Thing is down and not gonna be running till this weekend because Im in the middle of changing the rear engine water and vaccum lines (deciding if I need to pull the plenum). Any bench tests I could do with the ECM not energized or hooked up?