ZCar Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
122 Posts
Discussion Starter #1 (Edited)
Hey Guys


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
 

·
Registered
Joined
·
2,342 Posts
perhaps your air flow meter (AFM) is out of whack or needs an adjustment. might be something to look at. troubleshoot the AFM via the FSM

Bon
 

·
Registered
Joined
·
2,007 Posts
Hey Guys


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
The first thing to do is check that crank pulley and make sure that it hasn't slipped. If it has one of my vendors can rebuild it and make it better than new. If it hasn't slipped, then you need to check all the timing, not just the initial. A=Initial timing, B= Vacuum advance, C= Mechanical advance, A+B+C=D. D = total timing. That's what you should be setting your timing at. Your ZX should be getting 42 degrees total at 3500 to 4K rpm. Advance your dist. until you get that figure. Then go back and check your initial timing mark at idle and what it is now on is your new timing mark for after emissions testing. You may have to adjust your idle speed, put it at 900 rpm, not 800. Go out and drive the car and make sure that it doesn't have detonation under any circumstances. If it does then retard it 2 degrees and test again. Repeat if needed.
This method will give you the best horsepower and the best fuel economy for your z.
When these cars were new, then you didn't have to go to such lengths for timing but the dizzy's have deteriorated to various degrees, and the aftermarket rebuilds aren't as perfect as the original factory ones. Z man of Washington
 
1 - 4 of 4 Posts
Top