Kenny/77blue:

I have to respond to both of your posts tomorrow because I'm running late for my tee time (golf day). Plus tomorrow I am going to try providing vacuum to the advance via the spark port, rather than manifold vacuum, to see what's going to happen.

I hope you guys will hang with me.

Thanks.

 

That's what i was alluding to in my earlier post, you're pulling in too much advance at idle, connect the vacuum advance to ported vacuum.

It may or may not be your issue, but it's worth a try.

 

I did get a chance to play around a little more with the truck yesterday afternoon. Here's what I did:

1) I did verify the PVS (I call it the VCV) has three ports and the advance vacuum line is going to the middle port, which is the way it's always been. Also, when the engine is cold it runs fine with 8 degrees initial timing with the vacuum line connected to the advance, but once the engine warms up the PVS port opens and the backfiring begins.

2) The reluctor has been checked twice and it has no play

3) I did plug off the vacuum line coming from the PVS and tried using a carburetor spark port to provide vacuum to the vacuum advance and it seemed to work when I drove the truck down my driveway, but when I drove it back up the driveway it backfired like crazy.

4) I did verify again that when the piston is at the top of its stroke the timing mark is right on the TDC mark on the balancer.

The plan now is to do the coil tests again and the module tests again to make sure I didn't miss something. From there I might start throwing money at it meaning I'll buy a new coil and module, which will probably be a waste.

This whole thing doesn't make sense. I mean the ignition system is a very simple/basic thing and the truck always ran fine the way it was setup before, which is the same way I set it up after replacing the stator assembly and that is what's driving me crazy.

Anyhow, I won't be able to touch the truck again until Tuesday unless it rains. I'll update you guys then.

Thanks to all of you for your help.

 

Okay, here's what happened today:

1) Thought a lot and thought about the EGR adapter and its weak point. The engine has an Edlelbrock Performer Intake Manifold and part of the setup for adapting the two barrel carburetor to the manifold is a EGR plate between the carb base and the manifold. The gasket that comes with this Edelbrock setup has a small square hole in it that allows the EGR to send exhaust pressure into a hole in the manifold when the EGR is open. I'm wondering if this weak spot in the gasket could have blown apart because of all the exhaust backfiring.

I didn't pull the carb to see because I have to order gaskets from edelbrock before I can do it.

2) Another thing I thought about is; the truck is not backfiring through the carb, it's backfiring through the exhaust. How does too much advance cause the engine to backfire through the exhaust. Can someone explain that to me?

3) I checked the non-catalytic converter Thermactor System because the Ford Shop Manual suggested that could also lead to backfiring. The pump and air by-pass valve are working fine, but the check valve (the valve where the pressure from the pump goes into the manifold) is not holding vacuum which means the valve is bad.

I don't know how this could cause exhaust backfiring, but it needs to be replaced and that's going to take a week.

If anyone knows how a bad check valve would cause backfiring I'd love to understand it.

4) I rechecked everything including all the stator assembly tests and coil tests and everything was fine, but I did find some other tests for the ignition system, with the module disconnected from the system and two of the test turned out bad.

Because it was close to 5:30 I quit for the evening so that's as far as I've gotten. From here I will be ordering the check valve, the carb gaskets, from Edelbrock, and a new module because the connectors are screwed up from being torn apart so many times. And, I'll also run down the reason those two tests failed, which in all probabilty is a wiring problem.

That's it for now. Thanks again.

 

Your response today prompted me to go outside and check out my truck to see how my thermactor system was set up. I unhooked the vacuum line from the bypass valve and when I reved the engine and let off it produced a loud back firing in the exhaust. Where do you have the vacuum hose for the bypass valve routed? The purpose of the bypass valve is to cut off the air flow to the check valve under high manifold vacuum such as decelleration. It should get it's vacuum from the intake manifold. The check valve is more of a one way valve, it lets pump pressure flow into the manifold but wont let backfires go back up the pipe to damage the air pump.

As far as your advance problem, have you checked your vacuum advance? I noticed that you replace you stator. Have you tried removing you dist cap and applying vacuum to the advance to see what happens? It should advance smoothly and then spring back when you release the vacuum.

Good luck

 

Finally .... It's over!!!!!!!!!!!!!!!! I found the problem
It wasn't the ignition system. It was the carburetor. A plastic piece that opens and shuts the choke is broken so the choke was almost or fully closed all the time during this fiasco. The way I see it, the choke being closed was sending too much raw gas into the cylinder causing the fuel to take longer to burn so with the vacuum advance in the full advance position the rich fuel was still burning when the exhaust valve started opening.

I'm surprised I didn't smell the rich mixture in the exhaust fumes, but the exhaust pipe was outside the garage and I didn't spend any time at the back of the truck.

77blue, I am going to replace the thermactor system check valve because I know it's no good. Thanks so much for checking that.

To all ........ You guys have been AWESOME!!!!!!!!!!! Thank you so much for all the help and ideas. It is greatly appreciated.

 

Oops! Just went out to finalize the timing and the backfiring is back About two hours ago I let it idle for 20 minutes with the vacuum connected to the advance and it ran fine. Plugged the vacuum line and adjusted the timing to 8 degrees and then reconnected the vacuum line and it started backfiring. After that I retarded it back to where it was running good and started the engine, but it still backfired.

This happened once before when my brother came over. We retarded the timing and connected the vacuum line and it ran fine, but the next morning after the engine heated up enough to open the vacuum to the advance it started backfiring.

I'm so bummed right now. Anyhow, I'm going to change the module and get a new check valve, which will take a week or more, and see what happens.

 

Where are you getting the vacuum for your vacuum advance? Have you disconnected the vacuum advance and tried running the truck without it? If this problem started after you changed the stator I am still thinking you have a problem in that area, maybe your vacuum advance is getting stuck in the advanced position. Try putting a hand held vacuum pump on the advance can and pump it up to see what happens and then release it. It should spring back quickly.

Good luck

 

Hi 77blue. I have used my mityvac to open the advance slowly. If memory serves correctly, I THINK when I applied 5 inches HG (+ or -) (Whatever HG is) the engine wouldn't backfire, but once I got past 8 inches HG (+ or -) it would start backfiring and I think the 8 inches HG gave full or almost full advance.

Additionally, the vacuum advance that's on the engine has less than 200 miles on it and it holds vacuum.

Also, as an FYI, I replaced the module two days ago and it didn't change anything including all the test results that I've tried two or three times.

There is another thing I did which has me wondering even thought it shouldn't have hurt anything. My truck's factory shop manual says the metal part of the rotor that jumps the spark to the spark plug wire terminals inside the cap and those spark plug wire terminals inside the cap come with a special coating on them. I lightly sanded the rotor end and those terminals to clean them up, thus removing the coating, but I don't see how that would cause backfiring and I can't remember if I sanded those things when I installed the new stator assembly or if I sanded those after the backfiring had begun.

After I get done with this post I'll be emailing my brother-in-law, who has owned his own auto repair shop for 30 to 40 years, to see if he can help. I'll update after I've tried whatever my brother-in-law comes up with.

Thanks again ..... Bud

 

I'm still wondering if you have tried running the truck without the vacuum advance hooked up? What do you have to do to get the advance back to normal after it starts backfiring? Shut it off, move dist., pull off hose? Have you tried hooking up a timing light when it starts backfiring to see where the timing is? I am still thinking that it is something related to changing the stator. It didn't do this before you changed it did it? Also check the centrifugal advance, to see if it springs back when you twist the rotor and check the inside of dist cap for carbon tracking.

Good luck

 

My dads sheared the roll pin in the dizzy gear. Never could keep it in time and couldn't figure our why until the oil pump finally fully sized and spun the gear. It just gradually ran worse and worse.

No carbon tracks in the cap or rotor? How about the spark plugs and boots?

 

I did get it running great. Tuesday, midmorning, I contacted my brother-in-law, the guy that has owned his own repair shop for 30 years. Ironically, that morning he had a friend bring in a 77 F250 with the same exact problem. He told me to buy a new distributor because the guys problem was that the stator assembly had too much side play in it that caused the gap between the magnetic pickup coil and the amature spokes to change. I checked my stator assembly and sure enough it had almost a 16th of an inch in side play and using my mityvac the assembly did change the gap when I applied vacuum to the advance. So, I picked up a rebuilt distributor and the truck ran fine. Unfortunately that distributor was making a loud ticking noise so I pulled it out to find out what was wrong and when I turned the gear shaft while holding the distributor the shaft would drag during about 1/3rd of the 360 degree rotation. I think the gear shaft was bent. Anyhow I exchanged that distributor yesterday and tried to get the new into the distributor hole, but it wouldn't fit. Using calipers there was a difference of 0.0035 inch between the diameters of the old and new distributors at the part of the distributor that goes though the hole.

I know that sounds crazy, but it's true. I even tried forcing it with some light tapping with a hammer and a piece of wood. While probably unbelievable, this is just one example of how crazy this whole thing has been. I'm going nuts.

I will pick up another distributor today and let you guys know the outcome.

Thanks

 

glad you found your problem. we set the timing to whatever specs were (i dont remember) with it warmed up and idling with vacuum advance disconnected. then without changing anything, including throttle, you could watch it swing back and forth on the timing light. you could also turn the crank with a wrench a noticable amount before the distributor would turn.

 

The rest of the story (Finally).

Yesterday I picked up the third Cardone rebuilt distributor (the first two were defective). The truck is finally running the way it should. With this distributor, when the vacuum advance kicked in, which you can hear in the idle, the engine rpm's increased a little with no backfire. I felt like I had just won the lottery when that happened.

For the record, in case anyone with the same backfiring issue reads this thread, the problem was caused by the stator assembly. It was the side play in the stator, which can be seen if you push the stator's magnetic pick up coil from side to side. If you have that stator play replace the distributor.

My thanks again to all that have contributed to this thread. This, by far, is the worst nightmare I've ever had with a distributor problem and everyone's help did help me through this and I'm being honest.

Thanks again ...... Bud

 

Hoop, Glad to see it back to normal. Now Mr. Murphy is probably looking for someone else to visit this weekend. Kenny