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Discussion Starter · #1 ·
I'm getting ready to go after the AFM, but I would like to describe my car's symptoms one last time because I have forwarded all your previous ideas to my mechanic and it has helped. He suspects my AFM now ... but that is after I spent $1000 putting in injectors that did no good. Okay...
Symptoms:
The car cycles from running smooth to kind of dropping out and running rough a bit, then running smooth again. It is around 5 seconds between each sputter, but it can run steadily rough at times. Sometimes it seems to me that it is running smooth just as I stop at a light, and once it has sat at idle about 10 seconds later it starts acting up. The idle moves back and forth during this just a bit. It is digital dash and hard to notice because each bar represents a range, but it generally stays at the 750 bar, and occaisionally rises to the next higher bar or occaisionally drops to the lower bar. HOWEVER, although it is most noticable at idle, if I rev it to 1500 rpms I can still feel it. I think it continues doing it at higher rpms, but it is hard to say. It feels like a miss, but one mechanic said it isn't really a miss, but bad combustion. It does drive fine, except that it seems to bog down a bit when cold. It's hard to say though, because I never rev it above 2000 rpm when cold. My mechanic tested the exhaust and said it is running lean -- that it dropped right off the chart. He also tested my fuel pressure and said it was fine (though I am considering changing the pressure regulator anyway). It feels to me like the idle is wandering a bit, but would that explain the mild shake/sputter at 1500 rpm? Or maybe he tested the fuel pressure at a time that it wasn't acting up enough to really tell. Or is it possible that it IS something electrical, rather than in the fuel system or the AFM, etc? I don't know. I'm not very knowledgable about cars.
What I have replaced:
Plugs, cables, dist & rotor
Injectors (Nissan)
Aux air regulator
The car:
83T, driven 14K miles between 1983 and Nov 1998. It was stored covered in a garage and driven sometimes every few weeks, and sometimes every few months. I have put 4,500 miles on it since then. I ran it pretty hard at the start to try to clear it out and ran plenty of cleaner through it. The plugs, cables etc. did improve things, but there is still a problem.
 

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Discussion Starter · #3 ·
RE: Please let me describe my prob one last time!

Definitely sounds like a mixture problem to me, but before you replace the AFM,

1. First thing to check for is vacuum leaks. The most common leak on 280zxs is the boot between the AFM and the Throttle Body. These boots often develope large cracks in the folds that aren't noticable without close inspection.

2. Try disconnecting the O2 sensor and run in Open Loop mode. If the car runs any better, your O2 sensor is obviously fried.

3. Try disconnecting the EGR valve. Any improvement in running indicates a bad valve.

4. Disconnect the boot from the front of the AFM and you can depress the flap inside while the engine is running to mess with the mixture. Pushing on the flap will richen the mixture. Permanent mixture changes can be obtained by removing the black cover to the AFM and rotating the spring inside, BUT make sure you mark the original position of the spring.

Hope any of this helps.
 

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RE: Please let me describe my prob one last time!

Brian,
I would check and clean electrical connections, IE:
battery , grounds etc. If the F.I. doesn't get the proper
voltage it will run bad. I would also check all vacuum
hoses as well. I would also take off the distributor
cap , then try to move the distributor shaft side to side - check for play- wobble.
The rough idle when cold sounds like air regulator.
 

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RE: Please let me describe my prob one last time!

Ok, Brian.
Evan has some good things to check. I would concentrate on cleaning the AFM, like I said before, and check your EGR to make sure it is not stuck in the open position. Your test this very easily by using your fore fingers to go under the EGR cover and open the valve. If it does not move, then it is either stuck open or shut and you should change it. It is described better in the Haynes manual if you have it. The O2 sensor is a good check, but my gut feeling is that's not it. Don't change it for the sake of it, you have done enough of that already, or if you feel you must change something, there are always engines for sale. just joking. good luck and don't let your mechanic change anymore stuff and charge you an arm and a leg. Where are you? Maybe someone around here can tell you of a good Z mechanic, if your's isn't a Z mech., and he can give you some help with his experience.

Later,
LuZZifer
 

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Discussion Starter · #6 ·
<b>RE: Please let me describe my prob one last tim

Before you spend any more money, i would take it to a Nissan dealership. If not, find a mechanic by referral that does good work. But either way, i would buy a repair manual to your car so that you will understand the parts and the function of the parts in the car.
I remember once this shop was telling me that the cause of my problems was my map sensor. He was going to charge me $300dollars to repair(part was $60). I said no way. But since i remembered not finding A MAP SENDOR in my manual. I just took my car.
Also you could have tested those injector, before replacing them and save money.
 

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Discussion Starter · #7 ·
RE: Please let me describe my prob one last tim

check all the electrical connections in the engine compartment. i had a similar problem and took it to a dealer. he wanted to replace all kinds of stuff (was going to cost me about $1500). i cleaned every connectoin that i could find, to no avail, but then i noticed one more (amf sensor/sender i think). i opened it up and there was just gobbs of corrosion and gunk in it. so i spent about $2.50 on some electrical cleaner and it ran like it was brand new! haven't had any trouble with it for about 5 months. just a suggestion
 
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