Damn '76 Won't Run!!!!

[Tman]

No matter what I do, something else wears out or I'm not troubleshooting the right areas. I have a '76 with a 2150 Motorcraft 2-bbl Carb, 302. It al started with a rough idle, I had to replace the carb spacer plate because the inside was corroded and getting blow by. Then I began to realize that everything w/ a diaphragm was worn out and rotted, so I replaced teh Distributor advanced Valve, Kick-down valve on back of Carb, the Fuel pump also died and I replaced that. I have new plugs, wires, Distributor cap and rotor. I have Good vacuum, pressure and have No vacuum leaks. At this point, when I start it, it will idle at about 1300 rpm but will eventually just stall, whether its 30 sec. or 2 minutes later. If I try to set the idle to spec. 700rpm, it stalls. if I try to shift down from park from 1300 rpm, it stalls, of course. I have a Auto trans and I am about 8 degrees BTDC and have had it at all different positions, sometimes the idle goes rough, then recovers, then stalls. I realized that the P. S. pump was dead today, so I have to replace that also. Could it possible be the Ignition Module on the Driver side fender under the hood ? Does anyone have any ideas? Its almost May and the Damn thing wont run. ?:?

 

[70_Steve]

I noticed that nowhere in your list of troubleshooting and repairs did you mention rebuilding the carb. What happens when you adjust the idle mixture screws?

 

[2BroncFamily]

Are you sure you have no vacuum leaks? My wife's '76 went through a phase a couple years ago where everything was tired and ready for replacement (ignition module, brake booster and diaphragm, thermostat, carb, and on and on). I was ready to sell the thing, but I'm glad I didn't. You can end up with vacuum leaks in strange places (like the brake booster).

 

[Tman]

I have a buddy working on the truck with me and he is a Carb guy. He has adjusted both sides and it sounds great when its running, then it stalls. We took out the booster venturi and checked the jets, adjusted the float also today. I had replaced the pump diaphragms and the gaskets, yes, but did not do a total rebuild.

 

[Tman]

Yes, i am sure I have no vacuum leaks, we were spraying starting fluid all over the whole vacuum system looking for one. One thing I haven't checked is the valve on the back of my trans pan. Forgot the name of it

 

[NoJoe]

Hi: I would replace the control module they're $20.00 and you should keep a spare if it doesn't fix the problem and you can use needle nose pliers or vise grips on the vacuum hoses to eliminate them, good luck, Joe.

 

[Skuzzlebutt]

Yes, i am sure I have no vacuum leaks, we were spraying starting fluid all over the whole vacuum system looking for one. One thing I haven't checked is the valve on the back of my trans pan. Forgot the name of it

I was going to suggest checking the trans modulator.

 

[Flash69]

I would bump the timing up to 10 or 12 and try that also. Mine is set on 12btc.

 

[Tman]

I have had the timing at 12 degrees and further, it doesn't seem to make a difference

 

[hillbilly delux]

i would replace all your vacuum hoses. i had little holes all in mine. even the ones running to the modulator valve. it may suprise you. i would also check the fuel pump and lines.

 

[Redleg]

Think about the situation. You have checked and rechecked for vacuum leaks and found none. You carb-wise buddy says you are good. The fuel pump is good right? No crud in the fuel tank? Blow some compressed air back through the tank before the fuel pump.

Have you made sure you do not have a fuel starvation issue? Hidden in-line filter or other issue? The next perplexer is the coil. Determine a safe way to check the voltage when it is running and see if the spark goes away when the truck dies. My favorite, which drove me nuts on my EB, was the plate inside the distributor had broken loose and "drifted" the timing at random times. Sometimes ran great, sometimes ran like crap and often stalled. Another issue is the bushings in the distributor shaft may be worn making on the spot point gap changes. If you have a point type distributor, pull the cap and move the rotor button back and forth, there should be no play. If the plastic disc the points sit on moves freely, check to see if the plate is broken. While you are in there, check the shoulders on the eccentric where the point gap moves, if the corners are rounded off, you may have found your problem.

Good luck and keep us updated.

 

[Tman]

I do not have points, I have an Electronic Ignition Module on the driverside Fender. The Fuel Pump is new...before he left he told me to take off the fuel filter and saw it in half just to make sure I'm not sucking up some goo from the tank creating a blockage, since it is a cheap part, I think I'll do that today, although I don't think thats it, we were getting plenty of fuel into the Carb Bowl. We popped the lid off at one point and it was prety close to spec when I measured the fuel lvl in the bowl. I think I am going to replace the Coil and continue on from there...BUT then...shouldn't I replace the Voltage Regulator, Elec. Ignition Module, Distributor, the Alternator is original too, prolly get a new one of those too and while I replace the P.S. pump thats bad, I'll throw on some new belts ...LOL!!!! I have a feeling this is gonna get outta control. Oh well!!! I'll start with the coil.

 

[trailpsycho]

Sounds alot like what others described in the past when their trans modulator goes south. How long did it sit as well? Bad gas or water in the gas can cause wierd difficult to diagnose issues that seem like vacuum or timing issues. IF you do have bad gas, a carb rebuild is probably in order as they can "cheese-up". Good luck with it. Hang in there, it will get better.

 

[Jeepster]

Dont throw parts at a problem.

If you suspect the tranny modulator just pull the vac hose and plug it. If still stalls not the modulator.

Vac pumps work for checking vac lines. inexpensive and decisive. The Gauge tells you if the line wont hold vac. Good test for the modulator also. If it holds (vac)its good.

If the engine starts to stall, dribble some fuel or starting fluid to see if it stays running..if not, its not fuel pump or lines. if yes look at the lines and filter.

cheap volt meter will tell you if you are loosing power to the coil.

save some money and buy a tool instead of parts.

 

[Pa PITT]

I've just went thru this with a little tractor ...It'd run great for a few minutes ...mine even up to 20 minutes then it'd die if I didn't choke it I worked on it forever ....started with bad old fuel but mostly trash would cover the tank outlet
I had changed the filter the 1st filter was not nearly as bad as the last one I changed out .....now it runs good ...
If I were you i'd get some fuel that I knew is good and run your bronco on it for several minutes ...
I also like the ideal of replacing the old ECM the other one can be a spare..If it's good ..
Most parts houses have a good line like BWD 1st line..then same part no. with an "X" after the part no. that is much cheaper .....In this situation I'd get the cheap one ....match the color of the plug....

 

[Redleg]

Concur with jeepster about buying tools instead of parts. It is probably something simple. A low end multi-meter is a handy tool and is kind of fun to learn how to use (in a sick way) and can save you money. Be careful dribbling gas into a carb while it is running. A gas fire from a coughing carb is an ugly thing.
Make sure the distributor is not worn out and is still tight.
Keep at it, you will scratch your head and think to yourself, "how the heck did I miss that?"

 

[Tman]

Well, I had a Fluke meter on the coil and it said 6-8 volts, it crept up from 6 to 8. Just got home from Napa, bought a new Coil, Ignition Module Box and Voltage regulator. I figured, might as well replace them, god knows they may be all original. We shall see, I need to check the Vacuum Modulator too, to make sure its not bad, I have had to replace almost everything that had a diaphragm in it. ?:? :-X

What are the symptoms of a streched timing chain???

 

[cgbexec]

A 31 year old vehicle is prone to failures, especially if some of the parts are old. I agree that buying some tools is a good investment.

An engine needs 3 things to run:
Air - This needs no explanation.

Fuel - The fuel system is very complex when looked at as a whole. Since you are getting fuel into the float bowls and you say the carb looks good, then I guess you have eliminated this. Hopefully the fuel is good and not old.

Ignition - This covers a whole lot of parts from the distributor, spark plugs, timing, coil, module +++++.

Look at each system as a whole and ask yourself questions about what would cause an engine to run at idle, but stall under a load?

In the end, I vote vacuum leak, fuel or Carburator. That is usually the culprit for running fine at idle but not under a load.

Chris B.

 

[Jeepster]

To check a timing chain for slop. Pull dist cap, then with a socket on the crank nut turn the crank by hand just till the rotor turns, then stop and turn the crank the other way. I think if the crank/harmonic balancer turns more than 1/4" before the rotor moves the other way the chain is stretched and should be looked at.

The symptoms would be out of time engine/lack of power/pinging?(more advanced) some slop can be adjusted with turning the Dist.

Dont over look the use of a cheap vacuum gauge To help figure the health of your engine. It can help pin point a multitude of sins.

 

[Tman]

Well, we just did that test you are speaking of Jeepster, this weekend, we put the wrench on the crank nut and watched the rotor as it turned, it seemed to be ok. When I had my meter on the coil, I was only getting between 6 and 8 volts...is this low, shouldn't I get 12v ? Thanks for the reminder to think of all 3 systems separately cqbexec.

This is just getting very frustratiing, the weather here in Michigan is getting nice and I can't even get my rig on the road and I just don't have the experience to troubleshoot this problem, if these new parts don't do it, i'm not sure what the hell I'm gonna do =(