very odd problem

[xkeithx]

ok well when i first got the car, i started the engine and it ran nice and smooth. i drove it home (about 30 miles or so) with no problems at all. then its just been sitting at my house, i didnt drive it, because i needed to get money for insurance so i could register it. but i was taking the car for drives around the block just to keep everything good i guess. then one day i was at a stop sign and it stalled. i started it and the engine ran really rough. i barely got it home, and took out the spark plugs and replaced them with new ones. i also replaced the cap and rotor. then i started the engine and it was running perfectly smooth again. i drove it around the block, and cam eto a stop sign, and the same thing happened. we limped home, which was right around the corner (i was only taking the car for short drives around the block because its not legal to drive) and tried starting it again. the engine was running rough, sounded like only a few of the cylinders were working. and there was a ton of smoke coming out the exhaust pipe.

well yesterday, i went and got a new set of wires. i put them on, and the engine ran nice and smooth.. and there was no mysterious smoke coming out of the exhaust. (it wasnt blue smoke, just gray smoke, i guess burning oil? i dont know). so then today i went to warm up the engine because i wanted to do a compression test. i started the engine , and it was running smooth just like it was last night. but then i was just letting it sit there and idle, and after about 2 or 3 minutes the engine started running rough again, sounded like it was missing, and the idle speed dropped to like 350 rpm or something. i had to keep my foot on the gas to keep the engine from dying, which it eventually did anyways. giving it more gas didnt really do much. so my question is this: why would the engine run smooth for a little while, and then run rough? and why would it only temporarily improve every time i replaced a part of the ignition? anyone else experience this problem?

p.s. i attempted a compression test, and cylinder #1 held air and the other ones all came up 0. then i re-tested #1 and it came up 0 also. so maybe the gauge is broken, i dont know what happened. i'll have to redo the compression test and let you guys know.

[24OZ]

All I can say is that this sounds to be temperature related.

Maybe a vacuum leak that happens when the engine warms up a bit.

Hope someone can offer you a more concise answer.

[2ManyZs]

You didn't say what year car you had or which carbs, but another thing to check is the water control valve. You may be experiencing vapor lock if the water control valve is overheating the carbs and/or intake.

[xkeithx]

oh crappy. its a 78 280z, fuel injected

[Phacade]

-Fuel Filter

-PCV Valve (I honestly can't remember if the '78 had it)

-Fuel Pump

-Drop tank, clean, clean again, reinstall, new fuel.

-Coil

[xkeithx]

ive replaced the fuel filter, where is the pcv valve located?

[2ManyZs]

When it does it again, pull a couple plugs out and see if they are wet with gas. If they are it may be in the water temp sensor, and causing it to flood, or it may have a bad cold start valve (injector), the one in the front of the intake manifold.

If not that it may be in the ignition somewhere, something may be overheating due to excessive resistance.

Those would be the first two things I would check.

[Leeroy]

Ok...very strange...being fuel injected makes it harder...have you checked the sensor in the exhaust (is it MAP or EGO?...anyway...), check it..if it ain't clean or perpect, bin it and get a new one...I'm guessing that when you start it the computer tells the injectors to put in a set amount of fuel, but once you take it for a drive and then stop the sensor kicks in instead of preset values and completely porks the engine over (grey exhaust fumes mean excess fuel)...

Just my 2c, hope it works out!:classic:

Cheers ppl!

[xkeithx]

no , its weird, like.. right now its all cold outside, and it hasnt been started since the day before yesterday. but if i started it now, it would run rough right away. its hard to get it to run smoothly..and it only lasts a little while, then every time after when i start it, it will run rough.

[xkeithx]

yes, my plugs are wet with gas. they are also completely black, it looks like dry ash or something, are the plugs supposed to turn black?

[xkeithx]

it doesnt sound like a blown head gasket, does it? i was worried about that, and i think my compression tester is broken.

[2ManyZs]

Sounds like the cold start injector or the temp sensor is trying to over-enrichen the mixture. Try unhooking the injector on the front of the intake and see if it helps. Take a look at the plugs after you do it and see if they are gas fouled.

If you don't have one already, I suggest getting a Factory Service Manual for your car. It is almost essential when trouble shooting the fuel injection. There are so many tests for each of the circuits it is almost impossible to diagnose a problem without one. It is expensive, but worth every penny.