i bought an 85 300zx turbo about a month or so ago. for about the last 2 weeks it has been running really poorly. when i start it, it runs rough, and then when i start to accelerate, the car falls of its face, and starts to backfire threw the intake manifold area.

usually after i run the car out past three thousand rpm in first and second gear it will run just fine, whether im in stop and go traffic, or just cruising, but the second i turn the car off, and go to turn it back on it will do the same thing, were it backfires threw the intake manifold.

also about the same time all of this has started happening, i do not feel like i am getting any boost from the turbo.

could this maybe be the bypass valve on the intake manifold creating a vaccume leak at idle, making it run really lean, and making me loose boost?

i had checked the maf and the waveform looked normal, so i dont think it is that...

please help me on this, im really at a lose.

 

Have you done a tune-up yet?

 

i have replaced the fuel pressure regulator, air filter plug wires, cap rotor, fuel filter, but i have not replaced the spark plugs. i did check a coulple of them, and they both looked fairly new.

 

Check timing, sounds like its retarded/advanced a little, has it ever driven good? What did you do to make it drive not so good? Is the timing belt in the right spot? if your cams were not set correctly, this is what will happen, the back fire is due to the spark plug firing when the inlet valve is still open, thus all the combustion enters the inlet manifold. Id say thats your problem, if not perhaps your valves are worn and need reseating, when they wear, the combustion goes past the inlet valves completely.

Id also say you may have a vac leak, but it shouldnt cause too much problems, never has on mine. mine always revs a little higher and gives a slight splutter then goes when positive vac is applied. Never run a turbo with a vac leak too, causes incorrect readings on your turbo, creating over boost and little power.

 

the car always ran a little rough, but not as bad as it has been lately. It has just slowly been getting worse with the colder weather.

I went down to the autozone in town, and they had a Haynes service manual for the 300zx turbo. does anyone know if it would give me enough information to replace the timimg belt? it is getting close to 120,000 miles on it. should i just replace it, if im going to check it?

thanks

 

The FSM should be enough for that job. But buy a haynes manual as you'll need it.

As with vaccume, im pulling most of my vaccum stuff off, its just getting in the way and its a jungle, so ill simplify it a little also to make it a little neater. Things like air recirc valve, fuel pressure regulator solenoid, EGR valve. Just to narrow it down a little, i think its a good idea.

 

Could be the MAF. And the timing belt is about 60k over due. If it goes so goes the engine. It's an "interference engine" meaning it pistons smash into the valves.

 

I am having a similar problem and can't figure it out. Mine idles poorly when you first start it in the morning but will clear up after about 5 minutes. When I accelerate in 1st,2nd,and 3rd the car stumbles until it reaches 3000rpm and then it is like someone flips a switch and it takes right off. I checked the codes and got a fuel temperature sensor code. I replaced the fuel regulator and sensor. Didn't fix it. I replaced the MAF but that didn't fix it. I have also replaced the spark plugs,wires,and fuel filter and it did not fix it. When I changed the plugs I noticed all of them were white so I figured it was running too lean. That is why I replaced the fuel filter thinking maybe it was clogged. I think I was right on that b/c I checked the plugs a couple of weeks after I replaced the filter and they had a nice light black color to them. I went as far as checking the compression on all the cylinders and they are within 20psi of the maximum and all are within 10psi of each other. It is a 87 na and I just can't figure it out.

 

I have had the same problems with my car .
the temp sensor located in the front of the cilinderhead was broken and
at cold start the ECU thinks the engine is already warm and doesn't inject as much fuel
as when the engine is cold ....this couses a verry lean mixture when cold.
just look foor the wiering harnes of the temp sensor and disconect and measure the resistance

it should be at 20 deg-cent/68 deg-F about 2.1.....2.9 K ohm (cold engine)
and at 80 deg-cent/176 deg-F about 0.26......0.39 K ohm (hot engine)

 

good to kknow, thanks Bro. I think that will help trying to fig. my problem out also.