Slight back fire and stumble!

[Zed Head]

That's a very good point. One could probably estimate a likely range of location on a single cylinder's compression stroke and get a fair idea of where the other five would end up. #1 location - 120, - 120 more, - 120 more, etc. Or you could just eyeball the cam shaft, after multiple shutoffs and see where the lobes end up. That might be enlightening.

We're not trying to tear down the concept, just doing some process development, to help people avoid some pitfalls. Plus it's just a good reason to BS about cams and what they do, and practice reading cam cards (which can be confusing - to me).

[Willoughby Z]

I have searched Google w/o success. I will now try to get info from CZC. You guys always bailed me out when I did my '71 240Z resto. I am learning new stuff here with this 280Z.

Please clarify what you were searching for that was unsuccesful.

[rotorgoat]

I've got a '78 280Z and lately have been having a similar problem with acceleration from a stop. It either quits or hesitates and doesn't seem to have any power until it finally gets moving and RPM up to about 2000. Funny thing is when I first start it cold, it runs like a dream with no problems until temp comes up to normal. Any ideas?? thanks

[ZSaint]

Bingo! You are having the same problem I am having. Runs good when I first start it. After going 6-8 blocks it starts to have small back fire when I try to accelerate. If I punch it, it takes off like nothing is wrong. When I drive it carefully, it pusles and backfires as it takes off and when it is driving down the highway at 45 mph. It is an annoying charactoristic. It is too lean. We have looked for air leaks and found none. We are still lookiing for any ideas that anyone has. I am certain others have had this problem. How was it resolved???????????

[rotorgoat]

Are you running a carburated engine? Mine is fuel injected so I would suppose we probably have different components causing a similar problem.

[ZSaint]

Wrong buffalo breath, I have a '78 280Z. (I have 3 SU's on my 3.0 240Z)We have looked for leaks to see why this FI is running lean. Cannot find any cracks, bad hoses, loose bolts, etc. We have not found the problem yet. I do NOT want to richen the system until we have found the source of this leaness. We have listened to all of the ideas. It is not the timing or the temperate sensor. The timing will not make it back fire and the sensor deals only with a cold motor. Still looking for someone who has solved this problem. Rotorgoat and I really want the cars to be smooth. This bucking at every light is bothersome.

[Zed Head]

Actually the sensor might have an effect at all temperatures, despite what the FSM says. The FSM says it is essentially out of the picture after 158 degrees F, but it's been shown (see BRAAP's EFI work over on Hybridz) that it still does have some effect at higher temperatures. Plus, it would be surprising for your engine to be fully warmed up after 6-8 blocks, so a shorted temperature sensor would be something to look at.

Don't forget fuel pressure, while driving - after 6-8 blocks. Several people have thoguht that they had good pressure but found that the fuel pump was over-heating and losing pressure under load. I've had one in the garage that looked fine for 10 minutes then slowly crapped out. No fuel pressure, no fuel = lean condition.

I've read road test reports from the past that talk about the 280Z EFI system's lean surge problem, even when new. If you read Fast Woman and cozye's threads you'll learn about the typical fix (seems to be more prevalent with the 78 cars) of adding a resistor to the water temperature circuit to richen up the mixture, across the whole temperature curve.

Another possibility is the AFM. My 76 had similar mid-throttle lean intake popping, bucking and stalling, but much worse than what you describe, it was generally undriveable. In my case, a rebuilt AFM fixed the problem.

Take some measurements, cold and fully warmed up and something will probably show itself. You can't get very far with these EFI systems if you don't take measurements.

[ZSaint]

I feel confident it is not a fuel pressure problem. I have a new fuel pump putting out 40#. When I hammer the throttle it will run up to 5500 w/o a miss. Drop it back into high gear and it starts shuddering and popping. One fellow mentioned the server replacement solved his similar problem. I will get a new one and try it. This car runs soo good I just want to solve this prblem. I'll keep trying....