I've stumped myself, and a few other forums and groups.

1986 5spd n/a

To put it quick and basic: Used to run fine. Developed a hesitation problem when playing in the 4k range. Soon after developed a problem hesitating more often, and idling rough. Fuel pressure regulator was faulty (fuel coming from a hose that shouldn't have it) which I have just replaced, and now it will start then immediately die, sometimes idles for a few seconds (also dies immediately if I give it gas.)

What I have done:

Alternator puts out 14V
Hoses from the FPR are all replaced.
Vacuum lines on and near idle control solenoids replaced.
Idle-control solenoids click when I apply 12V to them
Engine idles and revs to 2.5K fine when I remove the MAF, or when the MAF is plugged in and not a part of the intake (not metering air)
From the maf test above, I can conckude timing and spark and fuel delivery is not an issue
ECU codes show fuel temp sensor and nothing else. FTR is not the issue, so I've been told.

I'm about to give up. I'd be willing to treat whoever can help me to dinner and some beer if I can get this sorted and on the road again. I'd like to have something to drive to work on Monday!

I made another post in a different area here: https://www.zdriver.com/forums/300zx...-around-40900/

 

How does the MAF test cover timing, spark and such? Either way, it's always a good thing to check the basics:

Spark
Fuel
Air

So regardless of if you think timing, spark, fuel, air are fine, still check. It may be something simple that you would've overlooked otherwise. Have you checked your fuel pressure? especially after replacing hoses?

Also if the Fuel Temperature Sensor is reading incorrectly that could very well be a cause.

Start with those, see if that gets you anywhere for starts.

 

Valid points, my fault for not expanding a little more:

The Fuel temperature sensor is most definitely not the cause. These were an over-engineered piece added to the car by Nissan to negligibly increase fuel pressure when the fuel itself has reached a certain temp. Being that some have removed it, and others suggest it does nothing, I'm going to roll with it.

I've checked spark. Timing LOOKS fine based on some docs I have on how to replace the timing belt. I previously had the timing belt tin off so I know it's still good.

Fuel pressure is interesting because originally I thought that's what it was. I don't have what I need yet to test it. If there was something wrong with fuel delivery (and potentially other mechanical woes) the engine would not successfully idle and rev up to 2.5K in "limp home" mode

Now, I'm by no means a pro, I'm just a 21 year old software tester. I MUST be missing something stupid, cause I tend to overthink things.

I've got one tip thinking it has something to do with the idle control system. Thing is, I don't know how else to test it other than what I've done; replace all the vacuum lines, and apply 12v to the solenoids and I hear a "click"

 

I wouldn't throw out the Fuel temp sensor just yet, maybe put it on a back burner for now, if it is reading incorrectly that could be causing faulty pressure at wrong times.

Timing, you say you had the timing belt off recently? have you checked to see if it's off a tooth or so? This can happen fairly easily.

Fuel Pressure, check it. up to 2500 isn't a very large feat, limp mode causes the engine to dump more fuel in so it still might be able to reach that 2500 in limp mode, where as if there isn't enough pressure when everything is as it should be, that could cause the problems here. you should be able to get a fuel pressure gauge at any automotive store, and it will be helpful down the line as well.

It doesn't sound like it's the idle control system either, that normally would cause rev limitation problems, not all out dying. but if you would like to test it, download your FSM here: XenonZ31 Reference
and just follow the directions.

Hopefully that gives us a good enough start to get us going in the right direction.

 

Hmm, ok. I'll go get a pressure gauge and try it out.

The timing belt was not taken off, I was just inspecting it since I had no idea when it was replaced

 

Good luck! Keep us posted on the results!

 

Results! :
What does it mean? It just keeps dying when I start it

 

so we're back to basics here. Same three things:

Spark
Air
Fuel

Now it looks like the pressure is acting a little weird, but that might just be because it won't fully start up. You said you changed all the fuel lines right? could it be you might've done something incorrectly there? Have you checked to see that your fuel pump is getting full voltage?

What about spark? have you had a chance to inspect your spark plugs and see what they say? You can tell a lot on how your car is running by how your spark plugs look.

 

Fuel pump gets 12v when priming, 4.5v after it's primed, and 9.5v when cranking (won't start cause it's unplugged of course) is this ok?

 

I don't know what changed, but now it idles at 500. I can SOMETIMES rev it up, but 99% of the time it dies

help. please.

 

Used this guide: XenonZcar.com Z31 Z31 Crank Angle Sensor

And it failed the last step. Should I jerry rig a fake harness?

 

Did you do anything differently right before it started to idle at 500?

When you say the last step, do you mean this guy?

"Lastly add a jumpper wire to Pins 2 and 3 of the Crank Angle Sensor Plug and test for continuity on Pins 8 and 17 on the 20 pin connector at the ECCS unit. You should have 0 resistance in the circuit."

I'm beginning to wonder if it's a vacuum leak. poor idle, dying. when it's started do you hear any sort of whistling?


If you get a chance, can you pull one of your spark plugs and post a pic here as well?

 

I was messing with the throttle position sensor. Still dies if I give it gas. Idles at 500.

I'll get you pics tonight

 

Here. It's probably way too rich from the few times I've tried running without a maf: http://imgur.com/JHGA1R5

It's worth noting before I replaced the FPR I pulled the same plug and it (according to a diagram) was PERFECT

 

I'm about out of patience with this pig, I'm considering taking her to scrap this weekend if she doesn't knock off the attitude. I was really hoping the 2nd chance I've given Z's wouldn't backfire on me...

 

After reading through this thread, I'd say you need to do more realistic checking / diagnostics...

#1: You said timing "LOOKS" fine? Did you check with a timing light? It should be at 15-20*.

#2: Have you pulled and read the spark plugs? Color? All the same? One look different?

#3: Have you ohm / continuity tested the CHTS, MAF, and other sensors and their wires back to ECU?

#4: When an engine won't rev or has a loss of power (if no mechanical failure), it's usually a spark or fuel issue, caused by electrical component failure, or clogged / failing fuel system components. Check coil, ignitor, dizzy cap & rotor, spark plug wires possibly grounding out, etc.

The FSM has very detailed steps to take depending on the issue. I suggest following those steps. Don't rule anything out until it's been accurately checked, but start with the basics.

A similar Z31 issue that turned out to be a burnt ecu: https://www.zdriver.com/forums/300zx...ed-help-40079/

 

on a side note, I love IMGUR!

back on topic note, yes listen to Nismo. Spark Fuel Air. It's not getting one of those, and it sounds like it's either spark or fuel. The FSM has lots of tests you can run to check this.

on another side note, if you decide you'd rather scrap it instead, let me know, i'd rather take it off your hands than have another Z dead.

 

Ok, I checked spark on each plug.

Re-checked the CAS, and I AM getting positive results.

Got an ECU for a decent price coming in Friday/Saturday, so I will swap them, and if that doesn't solve it, I'll do by-the-book tests on the MAF. If that shows it's working, I'll replace the FPR with an OEM used/known working one.

If none of that works, I'll replace the MAF, even if it passed the above tests, since they are known to pass resistance tests and still fail functionally (from what I've heard, but you know, what the hell)

If none of THAT works, I'll order all-new vacuum lines and replace EVERY single line in the engine bay, as well as a few solenoids

 

I had very similar problems. And I feel your pain.

I would almost guess that it's your fuel pump itself. I replaced everything (maf,cas,chts,fpr,plugs,wires,cap,rotor) I checked fuel pressure twice and got normal readings.

I didn't check fuel volume however. So as a last resort I changed the fuel pump and it finally cleared it up. It now runs like a raped ape.

I resisted trying to change the fuel pump thinking it was going to be a major job. It wasn't that bad. It took maybe 3 hours.

Hope this helps.

 

Wasn't the ECU, although the one that was shipped to be was banged up, I doubt 2 different ECUs would cause the same problem.

 

continue on with the FSM tests. Fuel pump and MAF to start.

 

MAF tested fine


Local z driver dropped by my place and we swapped MAFs, and guess what? It ran fine.

Ordered a wortking MAF online, I'll update when it gets here

 

so it idled correctly and wouldn't die out if given some throttle? Good to hear! keep us posted.

 

ITS ALIIIVE

Replaced MAF, went about 100 mil;es and still strong! Runs better than it did when I got it

 

Great to hear, enjoy the Z m8!