Crazy Ignition Timing
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Crazy Ignition Timing
I have a 1977 Ford F250 with a 400 cubic inch engine. The engine, which was rebuilt, came from a 78 or 79 F250 and has about 45,000 miles on it since the rebuild.
A few days ago the Distributor Stator died, which meant the engine wouldn’t start, so I replaced it with a new stator. After everything was back together I started the engine with the vacuum line to the vacuum advance being choked off with needle nose vice grips for timing purposes. I then set the timing at 10 degrees BTC. The engine didn’t seem like it was running as smoothly as before, but I left it at 10 degrees. However, when I took the vice grips off the vacuum line to get vacuum to the vacuum advance the truck started back firing and stumbling. The truck wouldn’t idle unless someone used the throttle to keep it running.
<O
Because the engine would backfire and run like crap when the vacuum advance had vacuum and because when the engine was being started it wouldn’t crank smoothly I knew the problem was that the engine had too much timing advance even thought the timing was set correctly
<O
I checked everything at least three times and everything was correct. I checked the following:<O
Everything was right so I decided to tune the timing by ear with the vacuum advance connected to the vacuum source. After I dialed it in by ear the truck ran like it use to and revved fine. I then checked the timing with the vacuum advance working and at idle the advance was 10 degrees.
<O
So it seems the problem is gone, but I don’t understand the timing thing. After 55 years of being a gearhead and playing with ignitions probably more than a thousand times I’m not understanding what the deal is with setting the timing with the vacuum advance connected. The only thing I can think of is that the cam degreeing/timing is off. Can someone straighten me out on this weird timing setup?
<O
Thanks in advance.
A few days ago the Distributor Stator died, which meant the engine wouldn’t start, so I replaced it with a new stator. After everything was back together I started the engine with the vacuum line to the vacuum advance being choked off with needle nose vice grips for timing purposes. I then set the timing at 10 degrees BTC. The engine didn’t seem like it was running as smoothly as before, but I left it at 10 degrees. However, when I took the vice grips off the vacuum line to get vacuum to the vacuum advance the truck started back firing and stumbling. The truck wouldn’t idle unless someone used the throttle to keep it running.
<O
Because the engine would backfire and run like crap when the vacuum advance had vacuum and because when the engine was being started it wouldn’t crank smoothly I knew the problem was that the engine had too much timing advance even thought the timing was set correctly
<O
I checked everything at least three times and everything was correct. I checked the following:<O
- Spark plug wiring and firing order (13726548).
- The timing at 10 degrees without vacuum advance (used two different timing lights).
- The coil for correct voltage and resistance.
- The module for correct ignition voltage and resistance.
- Reconfirmed the stator assembly part number.
Everything was right so I decided to tune the timing by ear with the vacuum advance connected to the vacuum source. After I dialed it in by ear the truck ran like it use to and revved fine. I then checked the timing with the vacuum advance working and at idle the advance was 10 degrees.
<O
So it seems the problem is gone, but I don’t understand the timing thing. After 55 years of being a gearhead and playing with ignitions probably more than a thousand times I’m not understanding what the deal is with setting the timing with the vacuum advance connected. The only thing I can think of is that the cam degreeing/timing is off. Can someone straighten me out on this weird timing setup?
<O
Thanks in advance.
Last edited by hooperdoski; Oct 2, 2012 at 06:39 PM. Reason: cut & paste problem
Elder User
Joined: Jan 2004
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From: NW Kans
id love to help but it seems like you probably know more about ignition than i do. Is it possible you have slop in thetiming chain? i bought a pickup and set the timing on it and you could watch the timing swing 14 degrees with the timing light.
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Or are you talking about 14 degrees full advance meaning the centrifugal advance was fully kicked in by revving the engine?
Thanks.
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How could the harmonic balancer slip. It's keyed into the crankshaft.
Fleet Mechanic
Joined: Aug 2010
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From: Cranbrook, Ont., Canada
I believe that with age the harmonic balancer can slip on the rubber that separates the 2 pieces. I've seen this and have had it done to me on the Dodge that I owned. An R/T charger and a 390 fairlane. Stumped me and the guys I was hanging with. I got a hold of a master mechanic at a Dodge dealership and he put me on to checking this by trying another balancer. Just my thoughts.
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Popajon, glad you explained. I never thought about the rubber causing the balancer to slip. I'll put that one in the memory book.
Wish there was a way of checking it before replacing the balancer.
Thanks.
Wish there was a way of checking it before replacing the balancer.
Thanks.
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Fleet Mechanic
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From: Cranbrook, Ont., Canada
No worries, just passing on an idea that may help others. I have learnt a LOT from this forum and gotten into some words also. Mostly though you learn a bunch by asking those in the know .. Numberdummy, MikeOOOOooo, just to name 2. There are so many more that can help. John
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Post Fiend
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From: Big Sky Country
If it's ported, it's not necessary to disconnect/plug the vacuum advance because it's not pulling any vacuum at idle anyway.
If it's manifold, it is necessary to disconnect/plug the vacuum advance because it's pulling in an additional 15 degrees +/- of advance at idle.
Cargo Master
Joined: Oct 2011
Posts: 2,251
Likes: 304
From: Kenner,La.
harmonic balancer timing marks
To check the balancer, remove #1 plug, turn the engine by hand and have someone feel for tdc with a screwdriver in the cylinder and watch to see how the marks line up. Kenny
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Kenny, you're right and I had already done that with a 3/16" dowel, but forgot about it in my last post.
Thanks for reminding me. That confirms the my Harmonic Balancer is good so I'm still confused about what's going on with the timing.
I also noticed today, not that it's related to timing, that it doesn't look like a F250 400 cubic inch engine came with a manual transmission, which mine has. Or, that's the way it seems. I came to that conclusion by looking at different emissions decals/stickers for a 400 on the web.
One other thing I thought about is that some ford engines with breakless distributors come with a dual vacuum vacuum advance, but I believe the single vacuum vacuum advance on my truck is the right one. Has anyone seen a dual vacuum vacuum advance on a 400 distributor?
And another thing I had read in the factory/shop manual, but haven't been able to find it again is that the module is setup in a way where it can adjust or change timing under certain conditions. Maybe it had to do with a Duraspark III distributor, which I haven't looked at yet in my search for where I read the piece about the module changing timing. Does anyone know anything about a module changing timing?
Thanks.
Thanks for reminding me. That confirms the my Harmonic Balancer is good so I'm still confused about what's going on with the timing.
I also noticed today, not that it's related to timing, that it doesn't look like a F250 400 cubic inch engine came with a manual transmission, which mine has. Or, that's the way it seems. I came to that conclusion by looking at different emissions decals/stickers for a 400 on the web.
One other thing I thought about is that some ford engines with breakless distributors come with a dual vacuum vacuum advance, but I believe the single vacuum vacuum advance on my truck is the right one. Has anyone seen a dual vacuum vacuum advance on a 400 distributor?
And another thing I had read in the factory/shop manual, but haven't been able to find it again is that the module is setup in a way where it can adjust or change timing under certain conditions. Maybe it had to do with a Duraspark III distributor, which I haven't looked at yet in my search for where I read the piece about the module changing timing. Does anyone know anything about a module changing timing?
Thanks.
Cargo Master
Joined: Oct 2011
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From: Kenner,La.
timing
Hooper, Are the timing marks on the balancer, or are they on a bracket . If they are on bracket there may be another groove on the balancer. Also some ignition systems require a "shunt" to be plugged into the ignition harness, if you have that style of system that is the only to get the correct timing. Try to talk to a Ford dealer mechanic about this , maybe one of the "old timers" is still there. Kenny
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Kenny, it has the degrees on the balancer.
Also, on Tuesday, I did have an old Ford Mechanic (my brother) come by and he was baffled too. After going over everything with him time an time again as a last ditch effort, because the symptoms were that there was too much advance, we timed it by ear with the vacuum line connected to the vacuum advance. It worked perfect and when we put the timing light on it again it showed 10 degrees advance with the vacuum advance connected to vacuum.
The truck was running great that day, but this morning I had to take the garbage down to the street for pick up, at which time it ran fine, and while I was unloading the garbage can, with the truck idling, the engine started backfiring again. I barely got the truck back up to the house and into the garage.
The reason it ran fine taking the garbage down was because the vacuum to the advance is controlled by a thermostatic switch in the vacuum line so while the truck was idling during my unloading the garbage can the thermostatic switch got warm enough to open thus sending vacuum to the vacuum advance.
Bottom Line ...... More frigging fun under the hood (YUK).
Also, on Tuesday, I did have an old Ford Mechanic (my brother) come by and he was baffled too. After going over everything with him time an time again as a last ditch effort, because the symptoms were that there was too much advance, we timed it by ear with the vacuum line connected to the vacuum advance. It worked perfect and when we put the timing light on it again it showed 10 degrees advance with the vacuum advance connected to vacuum.
The truck was running great that day, but this morning I had to take the garbage down to the street for pick up, at which time it ran fine, and while I was unloading the garbage can, with the truck idling, the engine started backfiring again. I barely got the truck back up to the house and into the garage.
The reason it ran fine taking the garbage down was because the vacuum to the advance is controlled by a thermostatic switch in the vacuum line so while the truck was idling during my unloading the garbage can the thermostatic switch got warm enough to open thus sending vacuum to the vacuum advance.
Bottom Line ...... More frigging fun under the hood (YUK).
Cargo Master
Joined: Oct 2011
Posts: 2,251
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From: Kenner,La.
timing
Hoop, Are you sure that the reluctor on the distributor shaft has not loosend up, a friend of mine had that happen. Your brother may have already checked that. It appears that the ignition is out of phase. Which means the relationship of the primary signal and secondary signals are not compatiable when it goes to advance. Have you tried by passing the controls and using "ported" vacuum, your brother could set that up.
Good Luck Kenny
Good Luck Kenny
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How many ports are on your pvs? Some of them have 3. The purpos is to apply manifold vacuum to the dist. if your engine overheats while ideling. I believe top port gets manifold vacuum, middle goes to dist and bottom is ported from carb. Maybe the pvs is hooked up wrong or defective and opening up too much and advancing your timing too much. You could try bypassing it and just running a vacuum line directly from your carb to distributor.