85 Bronco 351W HO Holley Carb:
The Bronco works great all summer and most of the spring and fall when it is above 50 degrees. In the winter 45 degrees and colder, it runs great when the engine is dead cold (about the first 2-3 minutes when it starts up) and when the engine is really hot(after 15-20 minutes). When it is warming up - the choke is off, but it is not completly hot yet the Bronco will stumble when I give it gas. Sometimes it will stall and when I restart it shoots out a cloud of white smoke. I have worked on it myself for 2 years and have had it to several shops and so far no luck. I just got it back from the shop today (it's been there for over a month) and it does the same thing, so it's back in the shop. Here is what I did:

1. Tried three carburators (stock, rebuilt and aftermarket holley) and all did the same thing (adjusted choke, rich/lean, floats, seals under the carb, set the idle, had a shop tweak the jets
2. All new ignition (plugs, wires, module, dist.cap amd rotor)
3. compression is 125 in all 8 cylinders
3. vacuum in intake manifold is 15 (no leaks)
4. new timing - set correctly now running at 10
5. vacuum advance set and working
6. Emission system gone including purge valve and egr valve
6. Plugs are clean, engine runs smooth when it is completly warmed up
7. Gas pressure at 8 - new fuel pump and filter

remember, this happens only in winter and only when the engine is warm, not when it is hot or cold. Any ideas???

 

Do you have the stock air cleaner with the snorkel and heat pipe going down to the exhaust manifold? This system helps get rid of problems like these.

 

yep, It is still original - I replaced the foil hose that goes to the manifold. The metal plate that screws onto the bottom of the exhaust manifold was loose and I tightened it up with some wire. I also checked the little flapper and it works. Made no difference. The engine runs great for having 208,000 miles and has plenty of power, but I have to get this stumble fixed before I get hit. I already have had too many close calls. Any more ideas? Thanks again.

 

take the air cleaner off and see how long it takes for the choke to open up completely. Have you checked the choke thermostat housing? WHen the motor's cold the chokes' supposed to be closed and open gradually as the engine warms up. It may be opening up too soon causing it to stumble till the engine warms up and catches up to the tempature it's supposed to be at where the choke is all the way open. Confusin' enough?

 

The choke comes off in about 3-5 minutes now (is that about right?). I have set it to stay on longer in the past, but as soon as the choke comes off the stumbling problem starts. If I let the choke on too long, the engine seems to have no power. It seems that the choke would need to be on 15-20 minutes to overcome the stumble/stall because that is how long it takes to fully heat up. I even unhooked the wire to the choke to see if the electric assist was causing it to come off prematurely - did not make any difference.

Also, here is some other info about the problem. When I give the Bronco gas and it stumbles and dies, a large cloud of white smoke comes out of the exhaust when I restart it. During the first 10 minutes, if I drive the car at 55-65 mph and let off the gas, it will backfire one loud blast.
Thanks for the ideas, anything else I can try??

 

[updated:LAST EDITED ON 03-Jan-02 AT 10:44 AM (EST)]What doesn't make sense is, you tried all these different carbs and it did the exact same thing. So if you tried all these carbs, I would guess it is not the carb but, I had a problem like this before and it was the four bowel screws where not tight enough on front of the carb (holley). When it was cool it would not run right, but when it warmed up it would run fine. I guess it was leaking internally in the metering block, and when the casting of the carb got warm enough, it swelled up and would not leak till it cooled off again. But like I said, the chances of you finding several carbs with the same problem I think would be rare.

Also, try turning the mixture screws counterclockwise as far as you can while keeping the idle as smooth as possible, and see if it helps at least cover the problem up a little.

 

[updated:LAST EDITED ON 04-Jan-02 AT 02:12 AM (EST)]It might be runnin lean. WHile its hot, close the choke manually (with your hand) if it smooths out then the idle mixture's set too lean. Now white smoke is from the fuel not burning all the way and what you see is gasoline mist. Dont it smell like gas? Now if this dont help none, then i'd focus on things other than the carbeuretor since you've changed it bout what? 3 times? Check the EGR valve-could be plugged up or sticking until the motor's hot. If all else fails, remember, don't

 

I had a similiar problem with my 83 F250 460 auto. I replaced the snokel damper and also the tin work that covers the exhaust manifold as mine was rusted(full of holes). There is also a thermostat inside the air cleaner that maybe not keeping the damper closed. Plus check or just replace the vacumn hoses.
Hope this helps!
460GENE

 

[updated:LAST EDITED ON 04-Jan-02 AT 06:31 PM (EST)]I've fooled with the rich/lean mixture quite a bit. I've tried running her richer and I have tried leaner. It does not seem to help. I have it adjusted about right now. I'm inside the car when it stumbles, but I don't smell gas. Even when I am working on the engine while it is cold and it pumps out the white smoke, it does not smell at all like gas. Sort of seems like a cloud of steam. Strange now that I think of it. The EGR valve with the rest of the emissions junk is disabled/removed.

Vac hoses are brand new, but I need to check the thermostat in the air cleaner. I do know that the little flapper thing is closed when the engine is cold. As for that little tin thing on the manifold, it has holes in it and it was just hanging loose until I put some wire around it. (it's still pretty loose). I'll see if I can get under it tomorrow and check that metal thing. Thanks for the idea.

BTW, I'm past and now I am in the stage. If not for sentimental value the Bronco would be in the Auto Auction and might be pretty soon.

 

[updated:LAST EDITED ON 04-Jan-02 AT 07:24 PM (EST)]you said the emmisions equipment is disconected did you just disconect the vacum hose off the EGR valve because if you have a wiring harness connector conected on the EGR plus a vacum line then the EGR is running continious open. this will cause bad stumble on a cool motor my Bronco II did that to me. Plus your idle vacum you said is 15 that is way to low for a stock motor(which usually indicates a lean condition), it should be 18 to 21. you may have an internal vacum leak were the leak is not detectable on top of the motor but it leaks inside the intake system. My F-150 had this problem between the EGR circuit and the main intake plenum so the truck would stuble because the mixture goes way too lean. Good Luck

 

I'd better check the vacuum again tomorrow. 15 sticks in my head, but I have not checked it for a few months, so I'll give it a fresh checkup. I took the vac hose off the egr valve, and there are no other connections on it. The bronco has been in the local shop since before thanksgiving and the problem can't be found. I'm bringing it home tomorrow to work on it more myself.

I don't know if this is part of the problem, but it pings pretty bad at about 45mph and has no oil pressure at all (when idling) on the stock gauge with 30 weight oil, but runs low normal with 20w50. When it is cold the lifters bang around for 1-2 minutes. The timing is right and high octane gas does not stop the ping.

 

It's pinging because the egr is disconnected. You will have to hook it back up or get an aftermarket carb to make the pinging go away. You can disconnect the vacuum line on the dist to temporarily make it stop pinging and keep from ruining the motor, but it will kill your gas mileage and power.

 

Ok, checked some things out today. First I reattached the plate on the manifold, then I set the mixture a little richer, adjusted the accelerator pump on the carb so when I hit the gas more sprays out. I also dropped the timing back a hair. I tested it once today and it seemed better, less stumble, less ping. I'll test it again tomorrow. BTW the carb is aftermarket.

 

 

I wonder if the harmonic balancer has slipped a little and the timing is set a little too advanced. If you have an aftermarket carb, and it is pinging, then the timing is too advanced, it's running lean, or it's overheating. Carbon build-up in the heads will cause this too, but I would gamble on the timing since you have changed carbs, and have not noticed it's overheating. Keep at it, you'll get it fixed pretty soon I bet.