runs like crap when heats up

[avbad12]

i have a 1976 datsun 280z and it runs ok until it heats up and then starts sputtering and running like $hit! when i stop at a red light, the rpms hover from 500-1000 and eventually the thing shuts off. When i start it again after that i have to give it a ton of gas and then alot of smoke comes out the back. i have replaced the cold start injector and temp sensor and i attempted to replace the mass airflow sensor today but it ran even worse. any ideas? and does the mass airflow sensor need adjusting right out of the box?

[conedodger]

If I can remember correctly, there is a Cylinder Head Temperature Sensor attached to the thermostat housing. The lore used to go like this - the connection starts to get corroded or worn, whatever, the car runs fine until it warms up and then as the heat expands the connector the sensor loses its connection. This sends an infinite resistance signal to the EFI brain and the brain assumes the car is very hot and richens the mixture. You say you have replaced the CHT but did you check over the connection?

The air flow meter should not need adjustment right out of the box. I know that MSA gets their AFM's rebuilt by Bret Industry in Orange and they flow bench set them. I would guess other rubuilders would do that as well...

Bottom line: clean up and check all of your connections.

[KDMatt]

Not a bad place to start. I would also recommend examining the fuel pressure.

I suspect it's possible that as the car is warming up you may be sucking gunk into your fuel filter, so that by the time it reaches operating temperature there's very little fuel making it to the injectors.

How long after the car dies do you try to start it back up again? Does it fire right of way? Continue running?

[DatsunZsRule]

First off, if you don't have a FSM to go through the testing procedures, you will be banging your head against the wall trying to solve it not to mention throwing $$ at things that are not the cause because as you have probably figured out, there are more than just a couple things that can cause a problem such as yours. About the best we can do without actually being in the garage with you is list possible causes for you to test/check.

Another thought that comes to my mind is possibly a faulty Thermotime Switch. The Thermotime Switch is what provides the ground for the Cold Start Valve to make it operate. Once the coolant warms up to a certain degrees, the Thermotime switch should no longer be providing the ground to shut off the Cold Start Valve when that extra fuel is no longer needed so if the Thermotime switch is not functioning properly then that could easily cause an issue like your having so I would look into that as a possible cause.

[KDMatt]

...Another thought that comes to my mind is possibly a faulty Thermotime Switch. The Thermotime Switch is what provides the ground for the Cold Start Valve to make it operate. Once the coolant warms up to a certain degrees, the Thermotime switch should no longer be providing the ground to shut off the Cold Start Valve when that extra fuel is no longer needed so if the Thermotime switch is not functioning properly then that could easily cause an issue like your having so I would look into that as a possible cause.

No offense, but the last time I checked my EFI bible this was a gross misnomer:

IIRC The thermotime switch/cold start circuit is only open while the starter is cranking, but when the key is in the 'on' position, the thermotime/cold-start circuit is open whether or not the engine is cold -- at that point the coolant temp sensor richens/leans the mixture depending on the temperature of the engine.

I however wholeheartedly agree though that a FSM is the most useful weapon in anybody's arsenal.

avbad, http://carfiche.com/manuals023/cars/ has the FSM on a rotation. When it comes up it is highly recommended you download it. You will not be sorry you did.

[DatsunZsRule]

Excuse me if I read his thread wrong but I thought he was having restarting issues as well which is why I listed the thermotime switch as ONE of the possible causes.

"when the key is in the 'on' position, the thermotime/cold-start circuit is open whether or not the engine is cold" Obviously but what I said is true. The Thermotime Switch DOES provide ground to the Cold Start Valve for it to operate and if the switch is malfunctioning causing the Cold Start Valve not to operate like it's suppose to WHILE CRANKING then yes, it could be PART of his restarting problem. I know as I've had that problem on mine and sure enough, I tested my Thermotime Switch and it tested out bad. Replaced it and problem solved but what do I know

Edited April 3, 2009 by DatsunZsRule

[KDMatt]

Hey that's why I said IIRC -- My misunderstanding friend -- I remember having that debate before with someone (as to whether or not the coldstart fires with the key 'on'), consulting the FSM and seeing that the coldstart is only supposed to work during the 'start' position on the key -- (in fact, aftermarket turbo kits in the 70's and 80's utilized the cold start injector during full boost to richen the fuel mixture because it wouldn't have otherwise been firing).

I also took away from this thread that he was having progressively worsening running issues that were making the car hard to restart.

I hate debating wisdom, I really do, but like you, I just don't want to see someone chasing after a gremlin that isn't there.

Edited April 3, 2009 by KDMatt

[DatsunZsRule]

"I hate debating wisdom, I really do, but like you, I just don't want to see someone chasing after a gremlin that isn't there."

Don't sweat it man, we all misunderstand sometimes. It's easy to do especially here because we can't talk face to face. I don't disagree at all which is why I stated "About the best we can do without actually being in the garage with you is list possible causes for you to test/check."

Didn't mean to take your reply to heart man but I'm just trying to add anything that could possibly be related to any of the issues he's having that he can go through and test. My opinion is if you have a FSM and are able to test components yourself (Process of elimination) that won't cost you anything and if it turns out not to be the cause then great. It's one more thing now you can rule out as being the cause.

avbad12, let us all know how you come out and what the cause was

[sblake01]

"when the key is in the 'on' position, the thermotime/cold-start circuit is open whether or not the engine is cold"

Not quite. It operates in the start postion and only for 8 seconds when the engine is cold due the the bi metal coil in it which heats from current flow until it breaks contact. It also won't operate it the coolant temp is 35C or above.

[DatsunZsRule]

Not quite. It operates in the start postion and only for 8 seconds when the engine is cold due the the bi metal coil in it which heats from current flow until it breaks contact. It also won't operate it the coolant temp is 35C or above.

Your right, The start position What the hell was I thinking :stupid::stupid: Good catch

[sblake01]

Here's a better link to a 76 FSM. It's always available:

http://www.xenons30.com/files/FSM/76_datsun_280z.zip

[KDMatt]

Your right, The start position What the hell was I thinking :stupid::stupid: Good catch

I think he was actually quoting me there. :stupid:

I just meant that the circuit was open -- i.e. no power.

Well, the starter of this thread hasn't posted in a while... let's hope everything is working out...