codytheoutlaw Posted May 16, 2014 Share Posted May 16, 2014 I have a hesitation off idle and backfiring through the intake. I checked the timing and it is set at 11 degrees, but when I rev the engine at wot off idle, the timing will retard to 0 degrees or less, then advance back above 11+ degrees once the backfiring clears up. I checked the vacuum at the port on the throttle body, and i get 15 inhg when revving and 0 at idle. I pulled a vacuum line off the intake manifold and the car started to idle at 1,100 rpm, but it will rev like it's supposed to. It also caused the timing to retard to 0 degrees, but it advances when I rev it. The vapor canister and egr have been removed and the lines are capped off, but other than that, the vacuum lines are all in the original locations as far as I can tell. Any ideas what could be causing this? Quote Link to comment Share on other sites More sharing options...
codytheoutlaw Posted May 17, 2014 Author Share Posted May 17, 2014 I hooked my vacuum pump up to the vacuum advance and it isn't holding pressure. I assume that is at least one of my problems. Can I buy a new diaphragm or do I need to replace the whole distributor? I haven't had any luck finding a diaphragm for it. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 17, 2014 Share Posted May 17, 2014 Read the reply to your post on zcar.com. Quote Link to comment Share on other sites More sharing options...
codytheoutlaw Posted May 17, 2014 Author Share Posted May 17, 2014 Read the reply to your post on zcar.com. I did and I replied 2 days ago, but since I'm new, a mod has to approve my post. For whatever reason, they aren't approving it, so I came here. This post is a continuation of that thread since I can't post in it without approval. I went ahead and ordered a new distributor and new injector plugs. They should be here sometime next week, but until then I'm open to any other suggestions and tips for a new z owner. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 17, 2014 Share Posted May 17, 2014 I pulled a vacuum line off the intake manifold and the car started to idle at 1,100 rpm, but it will rev like it's supposed to. It also caused the timing to retard to 0 degrees, but it advances when I rev it. The vapor canister and egr have been removed and the lines are capped off, but other than that, the vacuum lines are all in the original locations as far as I can tell. Any ideas what could be causing this? Is there a T fitting on the vacuum line to the distributor? It sounds like you're getting intake vacuum to the vacuum advance mechanism, at idle, from another source. The fact that timing drops to zero when you remove the hose indicates that. It also shows that the vacuum advance mechanism might be working correctly (11 degrees is right for an automatic transmission car), although it should hold vacuum, so may have a hole. The new distributor will have the same problem unless you find out why the vacuum hose is actuating the vacuum advance. You were almost there. Quote Link to comment Share on other sites More sharing options...
codytheoutlaw Posted May 17, 2014 Author Share Posted May 17, 2014 At idle, the port the vacuum advance is hooked to has 0 vacuum, and 15 inhg when revving. There is no longer a t fitting on the line going to the distributor because the vapor canister has been removed. The port that connects to the EGR valve has been capped off as well. Doesn't the 280zx have vacuum and mechanical advance? I'm assuming the timing is retarding to 0 degrees where the vacuum advance is supposed to be activating, then the mechanical is taking over and bringing it back up. That is the only thing I can think of that could be happening. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 17, 2014 Share Posted May 17, 2014 You're right, there is a centrifugal mechanism, advancing timing with RPM, and a vacuum mechanism, advancing it with intake vacuum when the port is open. What happens if you disconnect only the hose to the vacuum canister on the distributor? It's not really clear what hoses you're disconnecting that cause the idle to increase and the timing to drop 11 degrees. If there's no vacuum on the hose to the distributor hose, then nothing at all should happen when you disconnect it, since it won't be a vacuum leak and it's not pulling on the advance mechanism. Try to isolate cause and effect, specifically. Quote Link to comment Share on other sites More sharing options...
codytheoutlaw Posted May 18, 2014 Author Share Posted May 18, 2014 Nothing changes when I disconnect the hose on the distributor. The vacuum leak that is dropping the timing, is on top of the intake manifold. I believe it went to the vapor canister, but now its just capped off. I just assume the timing is dropping because of the 400 rpm increase and no vacuum advance. Quote Link to comment Share on other sites More sharing options...
codytheoutlaw Posted May 22, 2014 Author Share Posted May 22, 2014 I found my problems. The thermo vacuum valve wasn't hooked up and the dashpot on the dizzy was bad. I had never seen the tvv before since it wasn't hooked up when I bought the car. I noticed it when I was changing out the dizzy and googled what it was. I hooked it up and its idling and revving smooth now. I'll take it out tomorrow for a test drive to see how it does. Quote Link to comment Share on other sites More sharing options...
codytheoutlaw Posted May 23, 2014 Author Share Posted May 23, 2014 I think my ICM might be bad. I bought a distributor for a 1980 and it came with the ICM with 1 connector on the top, but my old ICM has 2 connectors. It has an injector style connection on the side. What is the purpose of that second connector, and why does my 1980 have it? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.