Car starts, runs, I turn off the car, then it wont start back up.
 

Whats going on, i'm a first time poster on here. My car has been acting up and we replaced a good amount of things which we thought might of been bad, The Fuel pump is good, we replaced the Fuel Control unit since we suspected it being bad, fuel damper we thought was bad, we replaced the sparkplugs since those were pretty bad.

Heres where I run into problems, as soon as I replaced the sparkplugs, the car ran really smoothly, I took it for a spin, hopped on the freeway, drove around for a while, came back home, turned the car back off, tried to start it back up and it wouldnt start. About an hour later or so I tried to start it back up and it started up, there was a bit hesitation at first but it started. My buddy things it has something to do with the throttle cable since its slightly loose but I dont think that would be it.

I have about a little bit above a quarter tank of gas, I remember talking to someone who was telling me that his fuel pump would have to work harder and therefore wouldnt' work as well if he was low on gas, he filled his tank up and the car started up fine.

Another thing I'm running into, the cable that runs to the PTU is a little funky, if you start twisting the cables the car starts the sputter but I dont think this would have an effect on the car wanting to start, then not wanting to start after drivint it for a while..

just like you said the ptu/maf/cas all the sensors need to be checked. check all your connections
this happend to me while while driving before.
as your car heats up the copper in the wire expands and can move connections out of place and as it cools they go back i have this happen on my maf and ptu make sur you have rock solid connections

Thanks for responding. I was posting on a different 300zx and someone said he had a similar problem. So do you think a good way of testing this would be to leave the car running for a while, then turn it off, then turn it back on and it shouldn't turn back on since, that ptu is hot right?

I'm thinking that the PTU just needs to be replaced I think. I've tired wiggling the cables while the car is on to see if I'd get any issues but it stays running. Maybe it just doesn't want to start once it gets hot?

first check the PTU harness, for signs of of tampering or repair, then check the connector, i have an odd feeling someone might have cut the harness and did a cheap repair, or the harness might be ate up.

well there was some tape wrapped around the harness but when i cut it all up the wires looked in decent condition. Also I saw a bit of corrosion on the back of the connectors but I cleaned the front of em, could this really have an effect on it not wanting to start? I did see a bit of damage on the cables going to the PTU, that I might have to replace. heres some pics

http://i20.photobucket.com/albums/b2...U/DSC01380.jpg
http://i20.photobucket.com/albums/b2...C01379copy.jpg

http://i20.photobucket.com/albums/b2...U/DSC01381.jpg
http://i20.photobucket.com/albums/b2...U/DSC01382.jpg

http://i20.photobucket.com/albums/b2...U/DSC01385.jpg
http://i20.photobucket.com/albums/b2...titled-1-1.jpg

a loose PTU connection will cause the car to run funny and sputter and hesitate, a bad PTU will downright make the car not run period. (as well as the CAS, but lets rule out the cheap stuff first) if you have access to a spare PTU harness, or the PTU relocation harness i would try it, some of those cuts look fairly deep, but loose connectors in the socket and you telling us that when you jiggle the harness the car responds tells me that it might be your harness.

PTU relocation harness? I was actually thinking of just cutting the one I currently have so I could reposition my PTU somewhere else, is this normally how its done or is there an actual relocation harness that they sell?

for your loose connections you could take a set of needle nose pliers and twist the male ends of the conector a little bit like 10-15 degrees. and they will cause the female connectors to hold in a little better and as hoov said those cuts look a lil deep

the later 94+ z32's relocated the PTU to the left side of the engine bay, because of failures of both the PTU and harness.

heres the courtesy link, but for them you have to buy the PTU and everything else.

http://www.courtesyparts.com/22020-p...tml?cPath=882&

my ptu is next to my air filter i believe attached to a pannel of some sort on the drivers side of the car its kinda weird

it can be moved to over on the fender with the harness you have. i think he's talking about a relocation harness to put it up by the air intake. either is fine. it really only helps for looks. that connection can be very hard to clean. what you need to do is dip each connection that is on the PTU into a cleaner, and scrub each terminal with a piece of metal. you can tighten the connectors in the harness, to grab the pins tighter by just sticking an awl or something down beside them. get them good and tight. the pins need to be cleaned several times, and actually scraped with an awl or something. it took me a very long time to get those connections good again.

that being said, i don't think that the PTU is even your problem. have you run the codes on the ECU? this is the first thing to do when trouble shooting the Z32. do a search to find the write up, print out the list of translations, and check on that. it sounds to me like a temperature sensor. check that connection, and it may need to be replaced. what can happen is if the sensor is bad, it's running constantly rich (suggested by the bad plugs), or lean, then when you start it again, it's like trying to start a warm engine with the choke on. i may be a little off, but i've seen that sensor cause this problem.

im not completly sure about the temp sensor switch thing kas because my temp sensor switch was disconnected for the longest time and it didnt have much affect. but still check it!!!

honestly, i dont trust the ECU as much as i used too, before mine died it was running on 4 cylinders, with two coil packs broken, the valve timing was completely off, 4 of the injectors where leaking while 2 of them where not even working at all, the temp senders where disconnected and ECU oil pressure sender was blocked off, but yet there was still no check engine light and no codes being thrown. and how the hell is the temp sender gonna keep the car from running? when the temp sender goes out, the car will run rich yes, but not enough to keep it from running, its designed, so that when the car gets hot it will run rich to help cool the motor, but it wont run soo rich that engine wont run at all, even with it unplugged.

without _______ sensor working properly the computer i believe goes in to saftey mode and runs a base "safe" program. at least thats how most cars work

before changing anymore parts clean and inspect any and all connctors you can then go from there thats what i did and now my never hesitates of throws tantrums

Well the crazy thing is my care use to hesitate up until i changed the sparkplugs. I might try to hit up a junk yard this weekend and try to pull a ptu from there, drive the car for a while and see if it wont want to start on me..

yeah I ran my codes a while ago and I got a code 21 which means "Ignition Signal Circuit" then I most recently ran the codes and I got code 55..so I honestly dont know..

The only reason why I thought it was the PTU was because someone else on another forum said that ended up being the problem for him, I just figured if my car didn't want to start up after driving it for a while, that that could of been it..

How would I check the temp sensor switch? Sorry for all the questions, theres still a lot i'm learning about my car.

well make sure the connecions on it are good if you want get a new temp sensor its like 20 bucks at auto zone

i still believe you have a bad connectin somewhere i had a bad connector that connected the new ptu harness to the old one. i ended up hard wiring them together and getting rid of the connector completly.
my car also had trouble starting it hsitated and threw fit some days depending on weather. i fixed this connector and inspected all other onces and i havent had a problem in over 3 months.

when i first got the car the wind would make my car shut off.
(the maf connector was loose)
also when i got my car turning left would make my car shut off
(the cas sensor was loose)
i fixed these problem with the twisting meathod i mentioned above.
also dielectric grease is your friend get some

thanks man, i'll try cleaning these connectors again and i'll keep you guys posted.

well, you all may be right, but i do believe that the sender going out and the harness being unplugged are different. being unplugged gives no signal, and a bad unit sends a bad signal.

Well we cleaned the connectors, the connectors going to the PTU were clean as a whistle but we sprayed them down anyways and cleaned em. I took the car out for a spin, I drive for about 20 minutes, came back home and the car had no problem starting back up but then again I didn't drive it as hard as I did last time, so that could of been a factor. Plus I think my battery is running out of juice so I might replace that next week.

you may have fixed the problem, but if it happens again, you should keep looking, because driving hard shouldn't cause it to not start.

I refuse to believe I fixed it! lol.. thats too easy man lol. I'm still gonna look into moving the PTU elsewhere in the engine compartment. I thought the problem was fixed when we replaced the fuel damper, and before that it was the control relay box..you know I went through 3 different control box's cause I thought each one was bad? luckily i didn't pay full price. Thanks everyone for the help, I'll keep you all updated on my journey to making my car run smoothly lol.

if you cleaned a lot of connections, it may be likely that you fixed. it' bad connections are a big problem on these. most of my running problems have been fixed by re-doing some connections