Hello all,

I now have the new (reman) engine from ATK installed in my '83. It runs pretty good but is very cold natured. I installed a new fuel pressure regulator and cold start valve this weekend. I also have a new thermo-time switch but have not had the time to install it. Those changes made the car run quite a bit better but it is still very cold natured. When it is cold, you can twist the throttle linkage from under the hood and you will get a hesitation and almost a backfire through the intake. I have adjusted the valves cold, which quieted the valvetrain quite a bit and also set the timing to 8deg btdc. I don't know what to look for next. I guess the air flow regulator, but when I clamp the hose running to the throttle body, the engine stumbles like it should. I don't know if replacing that piece would help. I know the rings aren't seated yet as I have only driven the car maybe 100 miles, but I am frustrated. Once the car is hot, it runs pretty well. Do you all have any suggestions??

Thanks in advance..

Colin

 

When you say it's "cold natured" you mean it's running cold right? When it's all the way warmed up, where does the temp gauge sit? The running temp is controlled by the thermostat, so if it's cold @ running temp, either you have a very cool thermostat, or maybe no thermostat.

As for the car hesitating: it could be the air flow meter causing a mis-mixture of a/f, maybe a slightly clogged injector, or any other malfunctioning sensor. Maybe a sparkplug wire grounding, or a worn cap & rotor.

Are all the parts on the engine new?

 

hes reffering to cold start and why engine stumbles and mumbles durning warm-up...after seeing so many people post about this im starting to think its one of their quirks...mine ran like carp too when it was cold...i never fixed it just sat there for a while giving it gas every so untill engine warmed up enough to run on its own...

 

I think one thing that commonly goes out on the FI L28 is the fast idle when cold device.

Although, I also had a Z that would idle super low when cold and then gradually come up from 400rpm to 800rpm when fully warmed. That Z had a nice smooth idle still and lots of power.

On my Z, when I had small backfires and poor power when cold, two things that I did that each seemed to help a lot where replacing my distributor with one that had a vacuum advance that worked and getting rid of my big throttle body. (installed stock throttle)

AFM cleaning could help too. I swapped mine out for a 'rebuilt' unit I got off eBay a long time ago.

So as a test, losen the little nut at the base of the distributor and manualy advance it. Maybe even all the way (as allowed). If that clears up your cold running stumble, then your vacuum advance is shot. Next step is to fix or replace the distributor.

 

Thanks Guys,

I do have a new distributor cap and rotor and wires. I have a new air flow meter. New plugs too. It has the original throttle body as well as new fuel injectors. The distributor is the original. The original engine had 205,000. The engine is somewhat hard to crank, though it cranks after several seconds of starter engagement. It idles smoothly, but give it a little gas when it is cold and the engine stumbles and sometimes makes a strange noise like a backfire through the intake.

I sounds like my vacuum advance may be faulty given your suggestions. Is there a preferred method of checking this out or do I just need a new distributor? I have spent this much, I guess a few more dollars won't matter.......

Colin

 

you can test the vacuum advance by hooking up a hand vacuum pump, like the kind used to bleed brakes, to the hose connector on the vacuum advance. Give it some vacuum and you should be able to see the advance plate moving. Oh and the distributor cap needs to be off for this so you have a clear view of the advance unit. Also check around inside the distributor for little ball bearings floating around. The advance plate rides on these so when they go out so does the advance. If you see them floating around then you've got a bad dizzy. You can buy a rebuilt one or just source the parts you need from a junkyard. Give your timing a check too. You can pick up a timing light for under $20 to read base timing.