Need Mechanic Help

[Monkeyman2500]

I'm a pretty good backyard mechanic but I've run into a problem. First off it's a 79 Ford Bronco with auto trans and built 351m. Truck was running like a top then gas gauge died and ran out of gas while going down the road. Now engine is running a little off and trans is shifting late. Thought it was just the trans modulator but after replacing it still shifts late from 2nd to 3rd. Looked for a vacuum leak with starter fluid and noticed when I sprayed it in carb it would die instead of rev up. I'm kind of at a loss right now. Will start back on it Sunday so if any of y'all have some suggestions I would really appreciate it.

[swim615]

Maybe the problems are related to running out of fuel. It could of had some trash or water in the bottom of the gas tank that got sucked into the fuel system and is clogging things up. Might try changing the fuel filter and clean out the carburetor.

[RED333]

When ya ran out of gas you sucked crap out of the tank into the carb?

Just a place to start.

Beat me to it, I am a bit slow.

Edited November 9, 2013 by RED333

[Monkeyman2500]

I changed fuel filter first thing. The tank was replaced when we rebuilt it. It is a draw type not a sump so I don't think it was trash. Can't figure why it does not rev up with the starter fluid.

[peejman]

Could be that spraying the fluid directly in the carb is starving it of air and causing it to go too rich and bog. I also suspect gunk in the fuel system. The off the shelf in- line fuel filters are really coarse and won't catch fine particles.

[glock55]

need a little more info on what happened: 1) you say gas gauge died what exactly do you mean? did it just stop reading or what? also after putting gas in is it reading correctly?  2) what type of ignition electronic or points 3) did it miss and sputter or die like you cut the key off 4) I would NEVER recommend spraying starter fluid into a gasoline engine just asking for heart ache and misery. best way to find vacuum leak is to keep intake system closed and use an acetylene torch and turn gas on low and move over line ,fitting and suspect joints. do a small area at a time so don't flood area and get false reaction. engine will rev when leak found. also much safer 5) what kind of fuel pump are you running and inline electric add-on? have you checked fuel pressure and volume at the carb?  6) is your choke working properly 7) I would not spend too much time on trans if it was working ok before this gas issue. if engine cannot develop enough rpms or power the trans is not going to shift correctly. 8) the gas gauge dying and running out of fuel leads me to think possible electrical issue. bad ground , ect. this could explain all your issues. 

[Monkeyman2500]

glock55, the gauge has never read right, I thought it may have died or wire got disconnected but I could not be sure. It worked fine after we filled it back up, it was near empty before it died so I'm not totally convinced it malfunctioned. It read correctly after we filled it, we put 23 gallons in it so it still had 2-3 gallons in it. Original ford electronic ignition. It missed and sputtered, did not instantly die. I did not have torch so the starter fluid method is the best I knew. Only sprayed a little bit in carb when I did not find a vacuume leak. I am still using a stock fuel pump, it was new with rebuild. I will get a in line fuel pressure guage on Sunday. I checked choke and seems to be funcytioning. I went to trans modulator first because it was first thing we noticed, but now after driving it a little I am sure the engine is running a bit off as well. It runs good with good power I just can tell something is not quite right. It is just not as responsive and I can hear the idle is somewhat off. When it happened I was driving at about 40mph and it happened all of a sudden. I was on a stright newly paved road so I cannot figure what could have happened.

[McGarrett]

It could also be an ignition problem. I had a weak coil on my 86 F250 351W that took forever to figure out, it ran decent but would take spells of being hard to start and would sputter and stumble sometimes. I kept thinking it was fuel related, fuel filter, carb, fuel pump etc.. It might not hurt to check it out. I know it seems to be fuel related since it ran out of fuel but you never know it could be weak spark, check cap & rotor, wires also.

 

What carb are you running?

[glock55]

I would check the following 1) fuel pump press and volume - ck manual for specs - this will verify fuel integrity 2) ck choke pull off diaphragm - integrity and setting 3) ck rotor and cap for cracks and carbon tracking also check for moisture in cap, and check coil tower for carbon tracking 4) ck ignition timing I think about 8* btdc but ck data plate on truck for spec 5) ford did have issues with ignition modules but just have to swap out if suspect 6) ck pcv valve and hose. if you recheck everything and still cannot locate the issue feel free to pm me for phone number and we can talk over phone. the only thing harder than trouble shooting over the phone is trouble shooting over the internet. good luck

[Monkeyman2500]

Well I've had a little time this morning. Checked the timing and it's dead on. Choke seems to be working well. I put a vacuum gauge on it and it's way off. Pulling 10in at idle, as I increase RPMs the vacuum steadily increases as well. I'm reading it at the manifold. I want to say it was around 20in when it was running before. I will get a fuel pressure gauge on it tomorrow. Also checked main grounds and all good. Also checked cap, rotor, plugs, and coil all seem fine. I'm just lost that running out of gas could cause this.

[bersaguy]

If the truck has low vacuum that can be causing your sluggish transmission issues. Rather than using Starting fluid to check for leaks which if a plug wire arks off you could get seriously injured, use carburetor cleaner. A lot lower flash point but will find a vacuum leak as well as starting fluid while being much safer. You might find your problem in the Ignition Module mounted on the side of the distributor. You will need a 7mm small socket to remove it and look at metal plate on the bottom side where it mounts to distributor. If there is any small spot on the metal plate that does not look normal you need to replace it as a circuit in side has probably burned out. Also I would dump a few bottles of Gas dry in fuel tank to remove any moisture or water you have in the tank. Buying water at filling stations is becoming more often these days with the ethanol levels that older vehicles are not designed for.  Hope you find the issue and can get it corrected.............. :dunno: :dunno: :dunno: 

[Sam1]

Seafoam it and see if that helps.

[Monkeyman2500]

Bersaguy, I'm not sure I have the same distributor your thinking of. I think it's under the rotor assembly on mine, it's a new distributor but I may still check it. And yes I would usually use carb cleaner but was out. Sam, I don't know if the ol seafoam trick is gonna fix this one. :)

[bersaguy]

 

Is this a picture of your distributor system and ignition system?

[Monkeyman2500]

Ok Bersa I thought you ment on the distributor. Yea that was also a new piece. I may still have the old one and that will be swapped tomorrow. Just to check it off the list too. Thanks.

[Monkeyman2500]

Ok got fuel pressure gauge on it holding around 7 psi at idle. Plugs look fouled but ar only a couple months old. Glock I'm sending you a pm

[McGarrett]

What kind of plugs are you running? My Fords do best on the cheap regular plugs Autolite or Motorcraft, don't bother with the expensive platinum, iridium, etc exotic plugs. Make sure to check the gap, I think it is .044 on the duraspark ignition setup if I am remembering right. You may also have too cold of a plug or a weak coil. I have a crane ignition box and aftermarket coil on a 351w and I opened the gaps up to .050.

 

If you have another coil laying around it might be worth trying it to rule out weak spark from the coil. I have seen this happen a few times. I got a later model square type coil and mounted it on the firewall to get away from the engine heat.

[Monkeyman2500]

Well checked coil, replaced plugs, even tried changing power valve to no avail. Thanks everyone for your help especially Glock55. I'm at the point now I think there must be at least one burnt exhaust valve. I will have to take it somewhere at this point I just don't have the time to pull the heads or the experience. Wish me luck

[Superman]

If you have that low of vacuum then you have a vacuum leak somewhere or low compression. Do you have a compression gauge?

 

In my experience, burnt valve isnt going to cause low compression. It will cause the vacuum gauge to fluctuate. Low vacuum is caused by vacuum leak, low compression, or valve timing. Since you checked the ignition timing and it is good, that should rule out valve timing. Use the vacuum gauge on the crankcase and see if you get a vacuum reading. Check the compression, if its low you will have low vacuum.

Edited November 12, 2013 by Superman

[MadMarx]

I had a 2 barrel ford2150  carb on a Jeep V8 that would eat carb to manifold gaskets. That would happen suddenly and the motor would run crappy and have low vacuum. There was one passage way on the bottom of the carb that only got covered by the gasket and was free to the world on the other. Took forever to find. Remove the carb and the phenolic spacer and check to see if either gasket has a burned through spot.

[Dolomite_supafly]

There are very few causes for low vacuum. Timing wrong and a leak. You checked the timing so it is a vacuum leak, put and simple. Did the truck sputter or backfire as it ran out of gas? If so it could have blown a vacuum line off anywhere. Some vehicles even have vacuum lines that run into the cab. Pinch off all vacuum lines coming off the engine and see if the vacuum reading improves. If it does then you have a line that is either off or has a leak. Unpinch one line at a time until the vaccum signal goes bad again and the last line you unpinched is the problem.

 

Vacuum lines are notorious for getting small cracks in them from the engine heat. The crack can be long and not even look like a crack.

 

Also, most carburators have several vacuum ports. Make sure all of them are capped.

 

For checking the gasket use WD40 and spray it around the carburator gasket. If the idle changes, if the vacuum increases or you see blue smoke coming from the exhaust then it is a gasket that has a problem. Depending on the carb a backfire can mess up the gasket and open of places that shouldn't be. And in some cases, like older Holley carbs, it can blow out the power valve.

 

I would not hot rod the truck at all because it is buring extremely lean right now. That can cause some damage if not corrected.

[Monkeyman2500]

Yep I capped every vacuum line on it. No change. I've sprayed around all gaskets with no change. When I spray any around carb opening it wants to die. Vacuum gauge reads between 12-13 and bounces back and forth very quickly. When RPM's increase vacuum steadily rises. When I rev it quickly vacuum falls quickly to zero then jumps back up to 20 then comes back down to 12-13.

[Guest sqlightning]

it sounds like you sucked trash into the carb.  it is dumping fuel in and flooding it when you spray it with carb cleaner/starter fluid.  did you replace the fuel filter on the carb where the fuel line attaches?

[Dolomite_supafly]

Could also be a valve or a love on the cam that went flat. Any unusual ticking noises? I know all Fords do unless they have adjustable valvetrain. The back and forth rather quickly makes it seem like it might be something a bit more serious than a carb problem. When you run an engine out of gas it runs very, very lean right before it dies. And if you are at WOT or close to it the lean condition can damage the valve and seat. Although unlikely it sounds like it is something related to the valve or the cam based on the vacuum gauge bouncing back and forth.

 

Sounds like the carb needs a rebuild and a new base gasket for the carb to start then see what happens.

 

Are you sure you are capping off every line coming off the carb? There are a few that are way under the carb that can be very difficult to see. Also, pull the vacuum line off the distributor when you test the vacuum.

[bersaguy]

Vaccumm issues can drive a person nuts for sure. Could be an EGR valve stuck half open. Could be a bad PVC Valve in valve cover. Might try tapping top of EGR with a hammer to make sure its not stuck. I know this may be reaching but have seen it in the past. You might want to look at your fuel filler cap. If the vent gets stopped up it will create a vaccum in the fuel system and act like a vapor lock............. :shrug: