Need help with 1986 F-250

Reply

  #1  
Old 10-25-07, 05:08 PM
Member
Thread Starter
Join Date: Oct 2007
Posts: 6
Need help with 1986 F-250

I have a 86 F-250 ,automatic 7.5 liter,W/carburator. On start up it starts and runs smoothly. After about 20 or 30 seconds it starts running irratically. You can press on the gas and it just barely chugs and sputters and back fires if you give it alot of gas. I dont think its a fuel issue. I can spray starting fluid or pour gas down the carb and it doesnt effect it. (It doesnt rev up.) About 2 months ago it was doing the same thing and I figured out that it was the vacuum advance on the distributer. I could unplug the vacuum hose from the unit and it would run smooth without any problems. So I replaced the vacuum advance and it ran fine for about 2months. Now it is doing the exact same thing as before. But when I pull the vacuum line off, it doesnt help like before. Leading me to believe that it might be something else. Or can a vacuum advance go bad that quick and still be bad even with the hose disconected. Im baffled. I took the unit off and it was getting good suction and seemed to hold but that was just testing with my mouth. (: Also when I replaced the vacuum advance the first time it said to adjust it with allan wrench. I did what instructions said but it was hard to tell if anything was turning. But it ran fine for two months so I figured I got it close. Anyway if anyone has some ideas I would greatly appreciate it. Thanks , KHUCK
 
Sponsored Links
  #2  
Old 10-25-07, 06:48 PM
Member
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,768
Could be a number of things, but since you've had some experience with the vacuum advance being a problem, I would start there. Take off the distributor cap so you can watch the rotor.

Then suck down the advance with your mouth (yummy). See if the rotor in the distributor is advancing and retarding as you apply and release the vacuum on the diaphragm. If not, you have a problem in the distributor.

Also check your EGR valve to make sure it's opening and closing properly.

When the engine is idling check if there is any vacuum in the line to the advance. You may have a maverick vacuum supply going to the advance.

Hope this helps,

Bob
 
  #3  
Old 10-25-07, 07:26 PM
HotxxxxxxxOKC's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2006
Location: USA
Posts: 8,044
knuck,

Please refrain from posting this 3 times in two different places.

I deleted a duplicate post you created in the Car forum and will delete the other one that's in their as well.

 
  #4  
Old 10-25-07, 07:51 PM
Member
Thread Starter
Join Date: Oct 2007
Posts: 6
Originally Posted by HotinOKC View Post
knuck,

Please refrain from posting this 3 times in two different places.

I deleted a duplicate post you created in the Car forum and will delete the other one that's in their as well.

Sorry about that- new to site. didnt realize I had posted more than once untill it was to late!
 
  #5  
Old 10-25-07, 08:02 PM
Member
Thread Starter
Join Date: Oct 2007
Posts: 6
Originally Posted by marbobj View Post
Could be a number of things, but since you've had some experience with the vacuum advance being a problem, I would start there. Take off the distributor cap so you can watch the rotor.

Then suck down the advance with your mouth (yummy). See if the rotor in the distributor is advancing and retarding as you apply and release the vacuum on the diaphragm. If not, you have a problem in the distributor.

Also check your EGR valve to make sure it's opening and closing properly.

When the engine is idling check if there is any vacuum in the line to the advance. You may have a maverick vacuum supply going to the advance.

Hope this helps,

Bob
Thanks Bob, The hose does have vacuum on it. So I will suck the advance till it moves or doesn't () You say if it doesnt move I have a problem in the distributer. What would that be? And I'll check the EGR valve. Thanks for the reponse.
 
  #6  
Old 10-25-07, 08:44 PM
Member
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,768
Let me clarify. The rotor itself won't advance as in moving itself. The baseplate of the distributor will rotate, advancing the timing as the vacuum diaphragm pulls it.

You need to watch the baseplate for movement.

Having reread your post on the original problem and how you corrected it, I suspect your problem isn't in the advance, but rather in the supply control for the vacuum advance.

I don't believe that engine is advanced by the vacuum advance at idle, therefore you shouldn't have vacuum in the line at idle.

I'll have to research that to see just what that control is.

Hope this helps,

Bob
 
  #7  
Old 10-26-07, 06:41 AM
Member
Join Date: Oct 2007
Posts: 1
3 things come to Mind
1 - Distributor (common Ford Problem)
( fire it up at night with the hood open and in the dark..see if you see any sparking flashing indicating a cracked cap /bad wires etc) Had an Old ford crew cab that Sounds similar to your problem that I bought for 200 bucks...put a 14.00 cap on it and sold it for a grand!!
2 - Cam Lobe (less likely and symptoms would be a bit different normally ( common Mopar problem in the eighties)
3 - Timing chain/Gear/Belt (seems to me this one is a Chain..sometimes they will idle fine but balk under a load)
 
  #8  
Old 10-26-07, 02:48 PM
Member
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,768
There is a water temp controlled vacuum supply at the front of the engine. Everything considered, that is the part I would look at. I suspect it is passing vacuum to the vac advance on the distributor when it shouldn't be.

Other things mentioned are possibilities, but given what you have been doing and the results from it, I would look at that valve.

Hope this helps,

Bob
 
  #9  
Old 10-26-07, 05:51 PM
Member
Join Date: Jan 2005
Location: Texas
Posts: 478
Two good tools for vacuum advance prblems are a timing lite and a vacuum gauge "teed" into the vacuum advance hose. I'm not positive but all the distrbutors I ever dealt with had the vacuum advance hooked to venturi vacuum not manifold vacuum. ie: no vacuum at idle and vacuum increased as RPM increased.
Mike
 
  #10  
Old 10-28-07, 02:58 PM
Member
Thread Starter
Join Date: Oct 2007
Posts: 6
Originally Posted by marbobj View Post
There is a water temp controlled vacuum supply at the front of the engine. Everything considered, that is the part I would look at. I suspect it is passing vacuum to the vac advance on the distributor when it shouldn't be.

Other things mentioned are possibilities, but given what you have been doing and the results from it, I would look at that valve.

Hope this helps,

Bob
Well I gave it a full tune up . New coil,new plugs.new rotor and cap,new fuel filters. Checked all the vacuum hoses. No help. When I first start it, it will run good and revs up good sitting in park but as soon as it warms up after a minuet or less , it starts chugging and engine speed slows down. Seems like it quits firing on all cylinders to me. And when it starts doing that and you give it more gas it back fires and wakes the dead. Also you can turn it off and imediatly turn it back on and it will run fine for a second or two or three. You can rev it up once or twice before it starts doing it again. Would the control module have any thing to do with it perhaps. All can figure now would be the ECU or the timing chain . What would cause it to do this when it warms up. Then cut it off and restart it right away and it will run smooth for a few seconds before relapsing back to barely running . Kind of like it quits getting fuel. But I can shoot some starting fluid in the carb or pour some gas in and it wont speed up at all. Any more ideas? I guess I'll change the ECU module next if you all think that could be the problem. Please let me know what you all think. Thanks, Khuck
 
  #11  
Old 10-28-07, 05:40 PM
Member
Thread Starter
Join Date: Oct 2007
Posts: 6
Originally Posted by marbobj View Post
There is a water temp controlled vacuum supply at the front of the engine. Everything considered, that is the part I would look at. I suspect it is passing vacuum to the vac advance on the distributor when it shouldn't be.

Other things mentioned are possibilities, but given what you have been doing and the results from it, I would look at that valve.

Hope this helps,

Bob
But would it not effect it if I removed the vacuum advance hose. With the hose off, it still starts and runs well but then starts sputtering and chugging and barely running during idle after it warms up. 1 or 2 minutes on initial start. With the hose off /no vacuum and it still does the same thing?
 
  #12  
Old 10-28-07, 07:51 PM
Member
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,768
Yes it pretty well eliminates the vac advance. At start up is there vacuum in the line going to the advance. I believe that is a mulitport vacuum control valve. Where are the other ports going ? One would the vac source and obviously one to the advance.

Have you checked the timing to see if it changes any at the time it starts acting up?

Some things (that I can think of) relative to warming up would be ignition module, water temp activated control valves, and O2 sensors. The O2 jobs take a little longer to warm up than a minute though. They have to hit 600 degrees.

The ignition modules can be checked at a parts store prior to replacing them. They can be expensive.

I believe you said you had tried adding fuel through the carb without any effect so it shouldn't be fuel related. The whole thing sounds ignition related.
 
  #13  
Old 10-28-07, 08:22 PM
Member
Thread Starter
Join Date: Oct 2007
Posts: 6
Originally Posted by marbobj View Post
Yes it pretty well eliminates the vac advance. At start up is there vacuum in the line going to the advance. I believe that is a mulitport vacuum control valve. Where are the other ports going ? One would the vac source and obviously one to the advance.

Have you checked the timing to see if it changes any at the time it starts acting up?

Some things (that I can think of) relative to warming up would be ignition module, water temp activated control valves, and O2 sensors. The O2 jobs take a little longer to warm up than a minute though. They have to hit 600 degrees.

The ignition modules can be checked at a parts store prior to replacing them. They can be expensive.

I believe you said you had tried adding fuel through the carb without any effect so it shouldn't be fuel related. The whole thing sounds ignition related.
Im going to have the module checked next. I have some other work to do so it maybe a few days before I can get back to it. Thanks for all your input and I'll let you know if it was the module or not. Also I havent checked the timing at that time but I will. Thanks Again, khuck -Oh also, I'm not sure but there may be a slight vacuum at start up. I'll check again.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes