Hey guys,
I'm trying to keep my 302 running until the "Ultimate small-block" is ready. It is an '83 302 with a stock motorcraft 2100 2-bbl. I have adjusted it to where it idles nicely, choke is perfect(it cranks easily even on the coldest mornings and then idles without help), it gets decent mileage for a small-engined, heavy truck. My problem is when I drive on interstate, for example, for awhile and then I take an exit.I let off the throttle and let the truck coast to a stop, it WILL cut off. It will do it every time. It cranks easily enough again, but what's the deal? I don't know what else to adjust. I cant't find any vacuum leaks. It only does this after a sustained rpm and then let out of it. It will never do it in around town driving. Any ideas? Thanks a lot!

Chuck

 

When you do get it started again, does black smoke puff out of the exhaust? Trying to determine if it's a flooded condition or not.

 

Chuck,
This used to happen with my 302 as well. I found the problem to be the choke. I live in south texas so for me, the fixer was disconnecting the choke. I still am a bit confused with you however, because you said you start up fine on cold mornings and then idle fine afterwards....is your tranny AOD? If so, do you notice that it makes it into overdrive?
Johnny

 

Sounds like Vapor Lock to me.

 

Thanks guys, I sure appreciate the help.

Franklin, I'm sorry to say I've never paid attention to any smoke or exhaust. It always does this at the top of the exit with people backed down to the interstate wanting to go to work. I'm just more concerned about getting started and getting out of their way. I will look next time. I don't drive it everyday. I have a shop truck (Ford, of course)that I drive most of the time.

F150johnny, I thought it might be the choke as well. But I have had no problems with it starting. BTW, I have a C-6 tranny.

Wildjohn, it could be I guess, but then I thought vapor lock was only a problem in hot waether. I may be wrong.

Guys, I forgot to mention that I have plugged the EGR. It is non-functional, as well as closed off the heat bypass in the manifold. I know I should have stated that but hey first mistake all year. NOT! Anyway, now that you have more info (duh!) maybe it's easier to form an opinion. It only does it after sustained rpm. That's what I don't understand. It gives me NO trouble around town. Hot or cold.

I sure appreciate you guys time. Thanks.

Chuck

 

Get on a long disterted road in Texas somewhere. Then plug up your vacum line to power brakes. This will give you MORE vacum and see if it still does it. Rememer your brakes will not work as well when doing this. Thats the reason for the desterted road.

 

I see a possibility from your previous "confession". Do you notice it does it more in damp weather than dry? If I am understanding you correctly, you put block off plates on the intake manifold gasket heat ports? This is asking for trouble, especially in cool weather. There is a thing called "turnpike icing" and is caused by the cooling effect the fuel has in the carb. The engine can't burn liquid fuel. It has to be a vapor. The heat that flows through the manifold warms the metal surfaces so the fuel will not condense back into a liquid, which causes the engine to run rough. Have you ever noticed how a spray can will somtimes get cold when you use it? This is because the liquid in the can is being turned into a vapor and it has a cooling effect. So even though it is not that cold outside, the carb turning the liquid fuel into a vapor has a cooling effect in the carb area. In damp weather, this can cause ice crystals to form around the butterflies and choke the engine off. When the engine stalls, heat comes back up through and melts the ice and the truck will start. Also it is a bad idea blocking the egr off. I don't like them either because it's just something else to go wrong but, the carb is calibrated to use the egr. If you don't get an aftermarket carb, or an older carb that was designed without egr, the engine will run lean. This can cause pinging on the highway at light throttle.

 

I apologize again for the "confession", Franklin.LOL! I see what you mean about the carb icing theory. It is the same one that an air conditioning system works on if I'm not mistaken. I didn't plug off the heat bypass THROUGH the manifold, but the one that a small tube makes a "u" thru on the top of the manifold. Somehow this was connected to the carb. I just capped it off, and disconnected it from the carb. I had a nagging feeling that it had something to do with the problem.Or maybe the egr. My truck originally had the feed back carb and the crank-triggered ignition. It ran so bad, it was pathetic. SO, I put in an RV cam (old one had a worn lobe), rebuilt carb for a '73 mustang (I have one so I was familiar with it), and a distributor with points which I replaced with a Pertronix ignitor. 100% improvement. This will get me by while I build my 351. This was just an annoying problem. I think I'll go with an Edelbrock carb for the 351. I had discussed this with you before concerning aftermarket and stock 4 bbl. intakes. I sure appreciate your help and time with this. Are you an auto engineer or something? Your automotive knowledge is amazing. I always enjoy reading your replies. I guess I can live with this little annoyance until the other engine is ready(sometime this fall, according to finances). Thank you again.


Chuck

 

 

The "u thing" is a vacuum tube that pulls warm air into the choke housing to help the choke release. If you have problems with your choke operation, it could be traced to this.

No, I am not an auto engineer, I just work on my own vehicles all the time, and I have alot of books and factory manuals. For some strange reason, I have trouble remembering my own birthday, but seem to retain the information I read in the manuals. Replying on this board and actually doing the work is totally different too. I have been frustrated and stumped many times working on vehicles. I would not like to do it for a living!