Garbage Idle

[jersey280]

Hey guys,

 

Just recently purchased a 1976 280z. Along with the purchase, I bought a recently rebuilt L28 with transmission from a 1978 280z. I personally witnessed it running like a top, within its original 1978 vehicle. I removed the original motor, which would run smooth but suffered from a "warped" head and was burning oil. I installed the new rebuilt motor from the 78, in which i just recently have been able to test start.

 

The engine runs extremely rough and backfires from the intake occasionally upon reving. I have read many topics regarding chasing down fuel issues, or AFM ect ect. I personally witnessed both vehicles run perfectly prior to my ape hands getting involved. I feel that I may be experiencing some sort of issue regarding differences between the 76 and 78 EFI or computer related issues. Does anyone have a suggestion on what could be causing this or more in particular, what things should I look out for when swapping a 78 L28 into a 76 harness?

 

Thanks in advance!

 

 

[NewZed]

You probably lost a lot of viewers with your title.  

 

Sounds like plug wires on in reverse rotation (easy to check), or off one hole (check timing?  what is it?), or a vacuum leak.  All intake air must pass through the AFM.  Even the PCV system matters.

 

The 78 should run perfectly with the 76 EFI parts.  I have a 78 engine in my 76, and I've swapped ECU's, AFM's, ignition modules, and just about any other part you can think of, with no issues.  I check my spare parts by using them.  The 78 AFM even came with a fuel pump relay switch, just no wires in the harness for it (not your problem, just mentioning).

[jersey280]

Zed,

 

Thanks for the response. I get a little confused if I should be putting 76 afm on the 78 l28 or does it matter?

[NewZed]

If the 78 AFM has the internal contacts for the fuel pump relay you can use it no problems.  But the 76 AFM should work fine also.  They're the same except some the 78's don't have the fuel pump control switch inside.

 

You haven't mentioned fuel pressure or any of the basics that might cause a lean condition.  Popping back through the intake is typical of lean..  That's why I mentioned the vacuum leaks.  If the engines ran fine before, don't do anything dramatic.  It's probably something simple.  Might even be that the AFM isn't plugged in, it doesn't have to be to idle  If it won't rev without popping, it certainly won't drive well.

 

If you get lost, the best thing to do is download the EFI Guide and check things at the ECU connector.  You can check that the AFM is properly attached, the coolant temperature sensor isn't shorted, the injectors are all connected,, etc.  All from the Ecu plug.