L28 won't Rev past 4500 with stock base timing
My Z has been parked for 7 years but I'm about to have it going again. I stopped driving because the heater core valve under the dash started leaking.
The car is actually running great, great throttle response but will cut out and misfire at 4500 rpm, even with no load, unless I change the base timing from 10btdc to 15btdc. At 15btdc it seems to rev out fine. I need to pass smog. I'm pretty sure I can set the base timing to 10 and take it in to pass but I would like to have this working correctly.
I can't seem to find a distributor, I know I can send mine out to be rebuilt but mechanically there's really nothing wrong with it. I replaced the vacuum canister which was leaking and got great engine stability and throttle response. I have verified that the mechanical advance it free. I tested the mechanical advance with my timing light by taking off the vac hose and watching the flywheel mark move under throttle. It gets to 10 or a little more from the base timing easily but there's where things start to break up. It even appears to retard from the 10 under further throttle which is very confusing. I doubt that the weights on the advance are moving back in so it feels like I have an electrical issue.
I replaced the cap and rotor before even trying to start it again but I'm not discounting the possibility that they are causing issues anyhow but I would like to see if anyone has ideas before buying any more new parts. The distributor doesn't actually have that many miles on it since it was remanufactured. The vacuum advance was sticking but have since fixed that. I also replaced the coil. Seemed to run stronger through the low rpm ranges after this but didn't solve this particular problem. I haven't replaced the ignition control module, looks like I can get one for $100. Would like to know if anyone has known an IC module to cause this kind of issue.
I don't think fuel is the issue. I did have to have the tank cleaned, put on a new fuel pump, rigged a pressure gauge in the windshield when I was out for a drive and the pressure was rock solid around 40psi even at the highest rpms. Also, rigged the cold start valve on a switch to supply additional fuel, while fuel pressure gauge still attached, under this condition and still didn't rev out. Also, it will rev out with the base timing set high so I'm confident that fuel, air, exhaust flow are not issues.
Any advice would be greatly appreciated. I'm working on a 79 ZX NA GL EFI
Last edited by bman79zx; Yesterday at 06:49 PM.