Take the 2-minute tour ×
Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It's 100% free, no registration required.

I am in the process of making a 1977 Nissan 280z road worthy once again after having it sit for about a year. Here's what ive done:

  • cleaned fuel injectors
  • cleaned fuel lines
  • replaced air filter(high flow)
  • Pressure tested fuel pump
  • Passed emissions

But for some reason, once i've run the car for a bit and warmed it up, the engine starts missfiring badly. Its about at 50% of the time when acceleration on first gear; i press the accelerator and it starts stuttering, and the rpm gauge jumps around wildly. The only way past it is to either stop wait for it to pass, or press the accelerator lightly and "ride it out" all the while having it misfire. Once im able to get past this episode it runs fine until i start hitting higher rpms at 3rd and 4th gear. I can't any faster than 50mph on the freeway, as the same thing happens as on 1st gear, but it always happens.

Doing some research has led me to believe it may be either the EGR valve, or the Ignition Coil, both of which i believe are stock.

Suggestions?

Thank you in advance.

share|improve this question
1  
Is the fuel fresh or one year old? –  mikes Jul 16 '12 at 0:30
    
The fuel is fresh, and the fuel system has been cleaned at a shop –  russjman Jul 16 '12 at 15:10
1  
have you checked your ignition timing? –  mac Jul 16 '12 at 17:06
    
The timiing was also checked by the shop. Also, wouldn't i have falied emissions if the timing was off? –  russjman Jul 16 '12 at 17:33
1  
Bad timing would not necessarily cause you to fail emissions. Especially if you're only missing under high load, it may have never happened during the emissions test. –  mac Jul 17 '12 at 15:03

1 Answer 1

Answer care of cgsheen at Desert Datsuns

1st: If you haven't downloaded the Factory Service Manual from xenons30.com, please do it.

Start here (if you haven't already): - Check ALL your rubber. By that I mean all the intake boots & connections, all of your vacuum lines and fittings. Make sure nothing is disconnected, cracked, or broken.

  • Check and clean ALL of your electrical connections on the EFI harness - including the plug and socket to the ECU. Get some electrical contact cleaner or better yet, De-Ox-It...

  • Once you have the Factory Service Manual (FSM), go to the "EC" Emission Control System section and follow the testing and troubleshooting section. You can test every sensor and component, AND it's connection to the ECU using simple tools and the procedures outlined. Don't replace parts unless they actually test bad.

Rationale: EFI systems react poorly to leaks in the boots and to vacuum leaks. That's unmetered air and it'll confuse the ECU.

The electrical connections and wiring in these cars are more than 30 years old, and were never good at keeping the elements OUT in the first place. 90% of the EFI / ECCS trouble I see is electrical. Check and clean all of the electrical connectors - then do it again!

The FSM is easy to follow, the tests aren't difficult at all, and don't require a lot of special tools. If you don't have an electrical meter, buy one at Harbor Freight for $4.00. May not sound like it at first, but going through the EFI troubleshooting / testing section will end up saving you a lot of time and aggravation, and you won't be replacing stuff that doesn't need replaced.

Have you played with the AFM? Has it been opened? DON'T touch it! Most people think they can adjust the AFM and make things work better... You can't. (I'll explain if anyone really needs to know why) If you've changed the spring setting in the AFM - change it back to it's original position. If you can't change it back......

The "2500 RPM" comment has me contemplating something else, but do all the checks, cleaning, and tests FIRST.

share|improve this answer
1  
The "check the rubber" comments are spot-on. –  Bob Cross Jul 18 '12 at 17:04

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.