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Discussion Starter #1
I have a 1976 280z and I am having hard start and rough idle where the car keeps dieing on me. When starting the car it wont start right away. When I crank the engine one or two cylinders fire but then it stops. I have to do this several times (5-10 times) until it will start and fire for a few seconds before it dies. The rpms will get up to 500 and bounce around and fall down until it dies. This will happen a few times and will eventually get up to 1000 rpm, run for a little, and die. After about 5 to 10 minutes it will start to idle rough at 1000 rpm and stay idling. I can then gingerly rev it up to 2000 rpm but if I rev it too fast the engine will hesitate and back fire out the intake until it breaks past 1500 rpm. The weird thing is at 1500 rpm and up it runs smoothly with no hesitation. After 5 to 10 minutes the engine gets up to about 1200 rpm at idle and idles pretty good. The hesitation goes away and I can quickly rev the engine with no back firing from 1200 rpm to 4000 rpm. At this point I can turn off the car and start it again no problem. I think the problem is the car wont start unless it is warmed up. I figure that cranking the car over and over letting one to two cylinders fire eventually warms up the car to where it will kind of run. It eventually fully warms up and idles pretty steady and revs up well. Is there something that would greatly be affected by a cold engine? I'm not sure if my cold start valve is operating right. Could that cause this? I feel like that there might be something more too it. I plan on checking for a signal in the connector to the cold start valve and trying to manually hook it up to the battery to see if it will spray anything.

A few notes:

I have checked for vacuum leaks with brake clean and there are not any. I have cleaned all 6 injectors and I have a new airtex fuel pump and fram fuel filter. New spark plugs and new battery. One issue I do have is the fuel pimp will not turn on in the on position but I have hooked it up directly to the battery so it is not a priming problem.
 

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Do you have the factory service manual (avail on line).
read up on the EFI section.
That being said I would look at 35 pin connector and check the temp sensor resistance reading to see if its consistent with the ambient temps you are experiencing.
 

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also you should have a fuel pressure gauge and hook it up as described in the FSM. This is a very useful tool for making sure the fuel is getting to the injectors at the right pressure, which is critical in a fuel injected car esp the Z without a feed back sensor in the exhaust to correct air/fuel mixtures.


The pump will not operate in the "run" unless there is air flow thru the AFM and the micro switch is on from that air flow.


All this is covered in great detail in the FSM. Read it a few times and it will all sink in.
 

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Discussion Starter #4
Thanks Dave M. I do have the FSM and Ive been going through a few things. I guess Ill have to really dive in and go through the whole thing to get everything tuned up.
 

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just read it over and over a few times, its extensive but not complicated. Good luck with it.


We generally tend to look for worse case issues, but most of the time its simple stuff like poor grounds weak battery (from constant cranking), and faulty sensors. Checking things at the 35 pin connector will get you the best quick answer, if the resistance reading are off then you just check the wire harness connectors and then the sensor.
 

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Find the Auxiliary Air Regulator (AAR) in the Engine Fuel chapter. Then find it on the engine, and see if the hose on the side away from the intake manifold is leaking. It sounds like the engine runs better after the AAR closes.
 

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Discussion Starter #8
Update:

I went back to check on the AAR and there are not holes or cracks in the line. I also clamped a few of the lines closed and didn't see a difference. I was able to fix my cold start valve to where I can manually turn it on and off. It helps tremendously with the hard start but the engine still doesnt want to idle. I can start it with the cold start and keep it alive by flicking the cold start valve to rev it up but the rpms drop below 500 and it dies.

The AAR seems like it would be a reasonable cause of the problem since the engine is running lean and after it warms up it doesn't lean out anymore but I cant see any problem with it. Is there anything else that would seal up and stop too much air getting it in after the engine warms up? Or maybe something that allows for more fuel to come in after the car warms up?

Also I haven't checked the plugs, I missed place a tool bag, but I will check them soon.
 

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You could block the AAR off and see if that changes how it runs. It will take some throttle to keep it running for the first minute while cold.

There is one other thing on the Federal model 76's - a second pickup in the distributor and circuit in the ignition module, controlled by a thermo-switch. I don't know if half of an ignition module can fail or not, but there are two circuits there. And the pickup modules have definitely been known to fail. There's a test shown in the Engine Fuel chapter.

You could short-circuit the thermo-switch so that the module runs on the "warm" circuit and pickup all the time. If you just want to go directly to a "fix".
 

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Discussion Starter #11
pdx280:

What thermo-switch are you talking about? I know the switch to the cold start valve (thermotime switch) is broken and that's why I have to manually actuate the cold start valve with a wire I hooked to 12V. If I short circuit that one the cold start valve would stay on right? The only other ones I see are the water temperature sensor and air temperature sensor in the fsm. Is there another that isn't listed in the fsm?

I have adjusted the idle air screw on the throttle body but it only raised or lowered the rpm. All the way in and all the way out didn't an effect on the hesitation or back fire. Is there something else I can adjust to change the idle?
 

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There's an idle speed adjustment screw on top of the throttle body. Big head, turnable with just fingers, has a spring compressed under the head.

The switch is diagrammed on page EE-26. It's only used on the Fed model, not the CA model. One area that Nissan didn't do a great job is showing where the various switches are in the thermostat housing. But there are threads and pictures out there.
 

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Super rich, get some new ones, check the temp sensor resistance AT THE ECU, and compare the values to the FSM for the ambient temps (do this with the car cold).


Hopefully no one has messed around with the AFM.


pull the CSV out of the manifold, hold it in a suitable container so it does not shoot gas all over the engine, disconnect the starter solenoid (single wire with a spade connector) so the starter will not spin over when you turn the key to the start position, see if the CSV fires and then stops when you release the key from the start and stay in the "run" position.


It should only inject when the key is in the "start" and even then only if the temps in the thermostat are under 70f (a bit iffy as to the exact on temp) and even then it should turn off after several seconds (like 9-10 iirc) as the "time" of the thermotime will limit how long it shoot gas.


see if it leaks after firing. I still think its just a faulty temp sensor or connector to the temp sensor, or the temp sensor not connected, or the temp sensor not connected right...


that's why you need to check it AT THE ECU.
 

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Discussion Starter #16
I haven't checked the temp sensor but I know it doesn't turn on the CSV, but I will check it too. They probably only got sooty because I have been manually turning on the CSV. The problem seems like a lean condition until the engine warms up since it backfires out the intake and I can save the dieing idle with a blast from the CSV. Ill mess with it a bit and see if I can help anything.

Also does a putt-ing sound out the exhaust mean anything? There are noticeable puffs of air coming out the exhaust in a rhythmical, random pattern during idle, even after warm. It is continuous but not predicable. Its not very strong but its audible and you can feel it with your hand. Its not a back fire or at least not a strong one and I dont think the car is misfiring either. The engine also vibrates around with the puffs but subtly. Like with the poor idle, the exhaust putting pretty much quits past about 1500 rpm. However the exhaust putt-ing stays even after the car is warm, its just a little quieter.
 

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why have you not checked the darn temp sensor, its the main thing that setups the mixture when the engine is cold. Quit futzing around with the CSV until you have check that temp sensor.
 

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There is a process well documented in the FSM on how to trouble shoot EFI issues. It will take 2 min to eliminate the temp sensor as possible issue. Look at the chart in the FSM and see where the enrichment come from. Pull the 35 pin connector off (engine off) find the pins on the connector (not the ECU) and read the resistance. compare to water temp in engine using FSM as a guide.
 

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one thing what does the fuel pressure gauge read? that was something that was mentioned early on and is a common problem with getting the EFI to work right.
 

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Discussion Starter #20
one thing what does the fuel pressure gauge read? that was something that was mentioned early on and is a common problem with getting the EFI to work right.
Ive gone through and checked a few things so here is what I found out.

The fuel pressure is at 40psi when the pump is running and the system will hold 38 psi when the pump cuts off. After about 5-10 minutes it will drop to 30 psi and after about 30 minutes it drops to about 20 psi. Is this normal? I have a new fuel pump so I doubt the check valve would be bad. My guess is I have leaky injectors since the car will fire up good for just a second and then back to nothing on start up. This could also be the cause of the sooty plugs too.

I went through the factory service manual tests for the Thermotime switch and the water temperature sensor. Like I thought the thermotime switch is dead. The resistance is inifinity the whole time regardless of water temperature. The resistance will bump around for a second on the M-ohm setting in warm water but it isnt any good. Id rather not replace this $75 switch if all it does is activate the cold start valve for a second and I can activate the cold start valve with my switch. Do this do anything else for the enigne besides turn the CSV on for one second?

The water temperature sensor is also messed up I think. The measurements I got were in the 26kohm to 33kohm range so that must be busted too according to the chart in EF-53. This one is about $40 so thats fine if it is broke. Ill post a picture of my results. The Ohmeter was set to the 20k Ohm reading. Can anyone confirm these are bad readings, I dont want to be missing the obvious.

I also conducted the 32 pin connector tests.

Water temp: I do not have continuity between 13 and ground. (I got a reading of 054 which usually means that its close to having continuity so probably just a bad connections somewhere).

Thermotime switch: Pin 21 receives 9V power when cranking

Air regulator: Continuity between pin 34 and ground. Pin 34 receives 9V power when cranking. No continuity between pins 6 and 27.

So far the only conclusion I can see is I probably need to replace the water temperature sensor and hopefully that will fix my car. Anyone have any suggestions?
 

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