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76 280Z Idles great but dies or sputters when increasing RPMs

9899 Views 11 Replies 7 Participants Last post by  j2woodside
The car is a 76 280Z. The story is....I bought it about 5 months ago, it ran really well (maybe a little rich) up until a month ago. Then it started to cut out when I was driving, it seems to sometimes clear up but then it comes right back. It will now idle really well (as it always has) but as soon as you try to accelerate then it cuts out or sputters. If you continue to try to acclerate it will die. If you let off the accelerator then it idles great (as always).

So, here is what I have done thus far.......I have replaced the fuel filter. (did not help at all) I have ran a bottle of injector cleaner in with the fuel. ( seemed to help at first, but did not help). The car has a newer fuel pump and pressure regulator installed by the previous owner. I checked the fuel pressure, at idle it is right at 20 as soon as you bump the throttle it moves to about 25 or a little higher. I have checked to make sure it is getting air and that the air regulator (if that is what it is called) is opening and it opens what seems to be normal.

The previous owner intended on putting in a turbo so, he put high flow injectors and I think had the fuel pressure a little high and stated that it was running quite rich. It does seem to even spit fuel or somthing out of the exhaust ever since I bought it. But like I said it ran great for about 4 months and I did not do anything different it just started having these acceleration problems. Also it does tend to sometimes come out of it but when you start to go up a hill or somthing like that it just wants to die or only idle.

Thanks for any help,

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I would replace the injectors, since you say that the PO put high flow injectors. Then i would search because this topic has been beaten to death.
I can't seem to find answers with searching and I could understand you thought with removing the high flow injectors but, why did it run so good for 4 months and not give the previous owner any trouble?
The symptoms are similar to mine when I had a bad AFM. But you have a lot of other things going on, so it's hard to say what your problem is.

Your fuel pressure is set lower than spec. (~36 psi) probably to offset the high flow injectors. So you don't know what it was when it ran "right" and can't tell if it has changed. Is the lock nut on your regulator loose?

The PO might also have "tuned" your AFM for the high flow injectors, in addition to fuel pressure adjustment.

You're of in a bind with an engine that has been adjusted away from factory spec. and, apparently, no record of where things were when it ran well. You are almost starting from scratch.
Take off the fuel pump and look into the sock/filter on the inlet side. Probably has rust flakes blocking the flow. Also try draining the gas from your tank into a pan and look for rust flakes or varnish.
Thanks for the advice. I will try to check the fuel inlet sock/ filter. Right now I am leaning toward the fuel pump end of things being the problem. ***More Info*** Today I played with the fuel pressure and it seemed to help. Adjusting the fuel pressure made it more reponsive when sitting. Then I went for a drive, it drove fine until it comes under a load. When you hold the throttle steady, the motor begins to surge. It's like it totally cuts out and then gets a surge of fuel and picks up and runs. It was also doing this the last month. Thanks.
Sounds like rust in the system. Exactly the issues I had.
Drop the tank and use either por-15 tank kit or KBS coatings kit. It has the acid cleaner, the rust preventative, and the coating for around $70 or so. Don't use rocks to brake up the rust, it takes forever to get them out, instead use a 2' length of chain.
Or if your afraid that you'll screw it up (like me) take it to your local muffler shop. Typically they"ll boil and reseal tanks although it will obviously cost more this way. Mine set me back $235.
Does the car run properly after the stumble??

idle..... bbbboooggggg... ZOOM?

Look at the part number on the injectors, then google it to find the specs. Without knowing how much those injectors will flow your just guessing as to how to tune your fuel pressure. A wideband O2 would be very helpful too, because your just guessing as to whether your rich or lean when it is sputtering. If you don't plan on putting a turbo on, then your probably better off putting stock size injectors back on and putting the AFM back to stock specs, rather than try to fool around with compensating for large injectors that you don't need. Lower fuel pressure to compensate for large injectors will hurt the streetability of the car because the fuel will not atomize very effeciently, and it will probably actually cost you a few horsepower over proper sized injectors at the proper fuel pressure.
So I thought it was the fuel tank. Until I started to drain the tank. After about seven gallons no rust or crud in the fuel at all. I am starting to think it could be the pump. Sure it buzzes and sounds right but, a friend says I need to replace the pump because the car sat so long (about a year or longer) before I bought it. He says that can wear out the seals or diafram and make the pump bad. He says that also explains why it struggles under load. Any ideas about how to check wheather or not my pump is good? Should I spend the money on a new pump? thoughts?

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