cliftcrawford

I have an 86 nissan 300zx non turbo. Ive replaced the fuel injectors, wiring harness, etc... complete rebuild on the engine. the car starts fine, runs for a few minutes and just dies. It will restart in about an hour. ive checked the wires on the injectors and oddly enough, i show voltage on both wires - the red and green - which i believe is odd. Someone told my their car was doing the same thing and it was the security system. Is that possible? can it be disabled?

my86z

Have you run the codes of the ecu yet?

cliftcrawford

I looked up two codes; one indicated there was a problem with the air conditioner and the other said there was a problem with the throttle position sensor.

straight hate

Sounds like a fuel issue. I have an 84 na that I converted to a turbo car ran fine when I did the swap, got the tires back on it took it out and the thing would die after running for a minute. then start back up. Relays were good had FP, injectors fired all the basics. Turned out it was the ecu, I know a guy with a 87 na that did a turbo swap, same thing happened to him. I would check the fuel system first.

cliftcrawford

Ive got fuel to the rails. I was afraid it was the ecu. thanks for the help

my86z

Fix the TPS issue first. It may just need adjusting. Then continue troubleshooting if the issue persists.

Another question I have to ask you is........ How old is the fuel filter? I read about you replacing the injectors. But nothing mentioned about the filter.

straight hate

I didnt mean it was the ecu bro, I was just saying I have had that brodlem and I know someone else who's delt with the same issue. 86 is right always try to rectify the codes first, clean that connector and TPS up real good first, put some dilectric grease on that bad boy n' see what happens. Hope for the best and expect the worst. Why all the rebuild work and harness? Do you have a wiring diagram so you can cross reference/double check that everything is hooked up right. I know I tend to rush it when I'm all amped up and ready to drive it and the car has been down for a month or two. Double check the work, maybe you missed something or a pin backed out of a connector somewhere.

cliftcrawford

the car had an injector leak and caught fire. I bought it for $800, had second thoughts but it was in such sweet shape! I replaced the wiring harness and figured i might as well do a rebuild while i was at it. I got a wiring diagram - would you believe from autozone.com! - and the harness checked out. I now have a fsm so that should help..Ill check the tps out. havent thought about the fuel filter but figured if it was the fuel filter, it would still start. thanks for the info.
youre right, i was so damn excited about driving it and then my heart fell right into my *** when it died.

z-hag

if it is not a clogged fuel filter, prolly the ecu.

Z Car Barbie

Yeah. If the TPS (Throttle Position Sensor) doesn't make proper contact, it can shut off the A/C compressor, so this is probably why you're also getting a trouble code for the A/C.

straight hate

Hey Barbie, how does the TPS work with the A/C compressor? Does it share the same signal wire to the TPS? It would have to be a broken signal to even throw a code, right? So my main question is how do are the two related, I could see through the idle up valve possibly it would make a difference, cause I know with my 84 when I turn the A/C on it dosnt want to idle up and compensate for the voltage load. So I dont run it, and TX sucks without A/C! I've have never even heard of an A/C code before, is that like head light fluid or is it an issue with the Z's past 86. And Clift, I would look up n' under the dash to check for any burnt wires and connectors. I dont know how bad it's burnt up but it's a good I dea to check and make sure you dont have any thing shorting to ground, make sure the harness matches the conectors and the pin numbers. I found an automatic harness will not work on a standard car, even though you have the ecu and motor. Wiring is different between the Turboo and n/a, the coil is routed through the harness differently. I found that out the hardway. My coil turned out to have two 12v wires coming in instead of one 12v and one gorund. I had to strip the whole thing out and put the original harness back in. Any ways make sure you have the right stuff for the model your working on. My hands are cramping!!

cliftcrawford

I'll take a look under the dash. I got a harness from an 86 nissan non turbo manual transmission. It hooked up perfectly. I did find that someone had cut the wires (all the green) to the injectors so I had to reconnect them. I cleaned the tps but still getting the same. I guess i will replace the tps. And I still get voltage on the red and green wires on the injectors. That still doesnt seem right!
Youre right about he ac in tx, I lived in west and east texas and life sucks without it.

my86z

have you used an Ohmeter on the tps switch yet? It may just need adjusted.

straight hate

yeah ohm it up! I think it should range from 0.5v, throttle closed, then move smothly up to 5.0v. If it jumps around sporatically TPS is wasted. I'll look @ my 84 tonight and see what the colors are on my wires, and check the manual. So the wire harness is the same make as your 86 right? An n/a with a manual tranny, you havnt done anything other than the injector harness?

cliftcrawford

Yeah. the part numbers matched exactly, all the connectors were perfect. the only problem was the 6 wires for the injectors. I know I keep bringing this up but......... there is voltage on the red wire and green on the injectors. is that normal? shouldnt the green be a ground that the ecu controls the injector with.

straight hate

I'll look @ the wiring scematics tonight and get at you in the morning. I dont have a computer at the house. It should be one line for voltage and one for signal to the ecu and for some weird reason I think the other one is hot too... but dont quote me on it. I' ll see what the injectors on my 300 read. Oh yeah, how long will it run before it dies? Alright I'm outy 5000, catch you guys tomarrow.

my86z

Actually, the TPS on a stock z31 is just a switch. It's not a potentiometer, like many other cars. At idle, there should be continuity (close to 0 ohms) between two of the three terminals on the TPS. as soon as you bring the throttle off of it's stop, the circuit should be open, meaning infinate ohms, on the same two terminals.

AZ-ZBum

That's normal. You'll read 12V until they activate. Then, they'll ground and open.

Z Car Barbie

Oh, don't forget about the blinker fluid also.

Seriously though, the ECU relies on the Throttle Position Sensor (a/k/a Throttle Valve Switch on a Z31) to determine the position of the throttle (closed, partially open and wide open) so that the ECU can properly adjust the idle speed by altering the air/fuel mixture. At WOT (wide open throttle), the TPS signals the ECU that the accelerator pedal is being floored, which causes the ECU to temporarily shut off the A/C compressor in order to provide more power to the engine (this occurs so quickly that you've probably never even noticed).

So, if the TPS sends a false signal to the ECU that the throttle is wide open, the ECU improperly richens the air/fuel mixture (causing idle, hesitation and/or acceleration problems), shuts off the A/C compressor, and thus gives the A/C trouble code in diagnostic testing.

AZ-ZBum

The TPS does NOT send any WOT signal. It only sends an idle and off idle signal. 5V when closed and 0V when not closed. That is, if the TPS is adjusted properly.

Z Car Barbie

Sorry, I don't understand your point. 5 volts when closed and 0 volts at WOT - the ECU is reading this info., so if the TPS sends NO signal to the ECU, the ECU thinks the throttle position is wide open. Therefore, a faulty TPS can send wrong info. to the ECU (regardless of whether it's actually sending or not sending info. to the ECU), cuz the ECU detects the electrical current, or lack thereof, to make adjustments to the air/fuel mixture and idle speed.

EDIT: Oh, I think I know why you said that now - cuz I said earlier that the TPS "sends" a signal at WOT. What I should've said was that the TPS "controls" the signal at WOT, since the ECU continously detects the signals from the TPS.

straight hate

With the injector wire issue zbum is right I double checkd last night, with the car running red wire is a 12v constant, the green wire is the pulse, so it fluctuates between .01-12v. Because the ecu is constantly adjusting the fuel mixture. Thanks for clearifing Barbie, its amazing how fast you forget this stuff when your not doing it everyday. So do the 84 and 86's have a differnet TPS, my86z was saying that it wasnt a "poteniometer" TPS, I thought the one on my 84 was. I know I was having hesitation prodlems at one point and remeber back probing the TPS with the key on and would get a smooth reading from .05-5.v or vise-versa when you open the throttle plate. Similar to the old pathfinders. But my 300 would never die, it was stalling out and running rich which turned out to be a vacume leak. So in Clifts case the ecu might be thinking the TPS is at WOT shutting down the A/C and running enough fuel to kill it completely, the plugs should be fouled out really bad, right? Hey Barbie you goin' to west coast nationals this year? We started talkin' about it on the 280zx board and the guys were talkin' about everybody from the board rollin in together, are you down or what?

cliftcrawford

Thanks! Youve given me a lot of information! Im going on the attack this weekend!

AZ-ZBum

Are you guys not reading the same information I am?

THE TPS SENDS NO SEPERATE WOT SIGNAL

One more time:
As far as the ECU is concernted, there are two signals sent by the TPS.
1. Closed throttle (foot off the pedal, throttle closed) = 5V because the circuit is completed.
2. Open throttle (foot on the pedal, throttle anywhere from 1 degree open to WOT) = 0V because there is no more continuity.

Stated a different way:
The ECU sends out a 5V signal. If the throttle is closed, it gets 5V back. If the throttle is anywhere but closed, it gets 0V back. There is no third signal if it goes to WOT.

Now, there are TPS's with potentiometers. But all of those are for automatic transmission control. They do not affect the ECU to motor connection in any way, shape, or form.

Now, also for the record, the ECU doesn't shut off the AC. It doesn't care about the AC. If you have the AC going, you want it going for a reason. Because it's hot outside and you want cold air. WOT or not, the AC will keep going. To date, none of my cars I've ever put on a dyno shut the AC off at WOT. There is a distinct loss of power when you compare dyno pulls with the AC off and with the AC on.

Finally, all this is pretty much irrelevent. A broken or misadjusted TPS will not keep a car from starting. The problem lies elsewhere. AFM, ECU, etc.

Z Car Barbie

"Reading the same information" you are? Where are you getting this info.? Yes, I've read what you posted, but still don't completely agree.

No one is disputing that. You obviously didn't read, understand or chose to ignore my latter post. Again, what I should've said earlier was that the TPS/TVS "controls" the signal to the ECU (regardless, it's still "sending" info. to the ECU; 5 volts or 0 volts, the ECU reads this info. and reacts to it). You cannot convince me that just because there's 0 voltage from the TPS that the ECU doesn't notice it.

Obviously, if the ECU receives a signal from the TPS during closed or partially open throttle, and at WOT, there's NO signal (0 voltage), then if the TPS isn't making contact or "bad" (0 voltage), the ECU thinks it's at WOT.

None of your cars ... well, I've seen dyno results on 8 Z31's with the A/C on and off - only a 3 HP difference if even detected at all. At WOT, the compressor temporarily shuts off and the air/fuel mixture is adjusted so quickly that you don't even notice it.

How do you explain the trouble codes he's getting then? TPS and A/C?

Also, I don't want to argue about this here, because it only confuses people, sends mixed signals, and extends the search time for anyone seeking this info. I think it'd be best if we IM or PM each other to settle our differences, and if you prove me wrong, I'll be the first to admit it, and post it for everyone else to see.