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L28 jumping/bouncing idle, running rough


MapleNuts

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Car is jumping between 0-1000rpm at idle and then chopping up when throttle is applied. Doesn't act like a normal misfire  It's been running great, no previous issues. does have msd ignition system. ive checked all the spark plugs, distributor cap and rotor, coil, and checked all the leads and other wires and everything is good. I don't know if this is a msd issue or ecu. Couldnt find anything on this issue in the forms.

anything helps, both my datsuns are out of commision right now!  :crying:

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This is on a cold start. i'm not pressing the gas when its jumping at idle, untill you see the tac go to 3k.

I do have a problem getting it cranked over. Ill try starting it for like 5-15 seconds  and it wont fire, then i try firing it again right after and it usually starts right up. 

thanks

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Fuel filter, fuel pressure regulator, fuel pump?

 

The stock 1975 280z has an electronic pickup, not points.  You said MSD ignition, so something has been changed.  Not likely to be ignition though since it cranks and runs.

 

Thoroughly investigate fuel flow is my suggestion.

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It doesn't have points,i'm going to get a new cap&rotor just to cover my bases as well as spark plugs.

And ill check all the fuel system, could a injector(s) have gone bad? do they all of a sudden stop working?

If if were timing CGraves, why would it jump out of timing all of a sudden if weren't something more major?

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I have absolutely no idea how the timing on an L28 works as I've never built one but I know on my mustang the timing chain jumped a notch one time and it messed my timing up. I'm not sure if that's a possibility here but it's certainly an idea to keep in the back of your head.

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Check the flex hose between MAF and the throttle body for cracks. Air leaking in with really throw the mixture off.

 

The MAF also has a 'flap door' that is puled open by the volume of air drawn in. The door has an arm that draws a contact over a coated surface that varies the resistance. This signal goes to the EFI and indicates how much air is entering so it can compute the mixture. The arm will scratch a groove in the resistance surface over time and the signal can become garbled. There was a U tube vid on how to adjust the arm to a fresh part of this surface and bring back idle and performance. I'll see if I can find it.

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So i just started the car up to check on everything and its running like i was before. There was a little lag when i first reversed out of the driveway but after that it ran great. Ill still check everything so i hopefully wont run into the problem again.

thanks again for the help guys

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