I've got a 1978 F250 with a 400m in it. I recently went to the hardware store and when I hopped back in the truck she wouldn't start. I narrowed it to a spark issue, and after putting a new pickup coil in it she fired right up. However, when I rev'd the engine at all it would sputter, backfire and die. I thought I had broken the vacuum advance on the distributor, so I replaced that as well with no change. Now if I unhook the vacuum line leading to the vacuum advance she runs great. Is it possible that I somehow changed the timing while replacing the pickup coil? I've never adjusted the timing before and don't know much about it.

Thanks for the help!

 

Not if you left the distributor in the block while swapping out the magnetic pickup. It's possible you got a faulty pickup right outta the box (happened to me twice, both times from NAPA). The symptoms were just as you described "sputtering and backfiring", as if the new pickup had altered my timing.

Do you still have your old pickup? if so, swap it back in and try it again, if you haven't already done so. Like most every other electrical ignition component they can work when cool then fail when hot. It obviously needs replaced but at least it will let you know if you got a bad pickup from the parts store.

 

D4PZ-12A112-A .. Stator aka magnetic pickup coil (Motorcraft DU-1A) / Available from Ford & auto parts stores.

ALL 1974/79 FoMoCo V8 vehicles with DuraSpark except 1979 LTD/Grand Marquis 351W with EEC (Electronic Engine Control aka onboard computer).

 

Thanks for the info. I'll try putting the old one in cold and see what happens.

 

Ohm out the stator before installation if you can. You want to see 400 ohms - 800 ohms between the ORANGE and PURPLE wires/connections. Make sure the wires going to the stator (inside the distributor) are well connected. Tickle 'em a bit to check the connections.

If the stator is already in, pull the three wire connection closest to the distributor...make sure the male/female spade connections are clean and no green stuff on 'em. Again, measure the resistance at the PURPLE and ORANGE wires going into the distributor. You want to read about the same ohmage as stated above.

Where is your vacuum advance connected? Ported or manifold vacuum?

 

Flatbed - I finally got around to putting the old pickup back in and seeing what happened. Just like you suspected it ran great and rev'd up fine with the advance hooked up. I went back to the store and got a new pickup coil, and it runs even worse that with the first one I got. It won't even idle, but runs fine with the advance unhooked. I guess I'll have to try a whole new brand.

Thanks

 

Just so I am following you correctly...you're leaving the vacuum advance hooked up to the same port when you tried both the old and new pickup coils?

 

sometimes newer parts seem to actually make things worse. I replaced the PCV valve on my truck with a "new one" and it ran much worse, horrible idle. Put the orignal one back in, back to fine. PCV valves are "weighted" to a certain vacuum pressure so if you get the wrong weight, the little piston inside opens up too early and screws up the air/fuel mix - causing more vacuum issues, which causes the PCV to malfunction even more...etc. It's like a feedback loop

 

Do you have a Federated Auto Parts dealer in your area? They are typically locally owned and operated, and from my experience have superior parts to NAPA, often times for less money.

I have given up on NAPA and only buy my electrical parts from Federated. The pickup coil is a prime example, I bought NAPA's "best" and got two faulty parts back to back, I then bought the pickup coil from Federated and had no issues. Even comparing the two it was obvious the Federated part was superior to the NAPA part, with heavier gauge wiring and just overall better construction.....and it was $7 cheaper!

 

HELP! I'm still having trouble with this and I'm completely befuddled. Here's where I'm at:

I tired three different pickup coils, all with a similar result. The truck was running fine with no vacuum advance line hooked up, but once I hook in the vacuum advance it will stall out (sometimes stalls at idle, sometimes it will run at idle and stall once rev'd). I had been running it with the advance unhooked with no issues for a while. Then it sat for a few weeks and recently the truck started to idle like crap, but run fine once rev'd. This is still only with the vacuum advance unhooked, if I hook it up the truck stalls. At idle it sounds almost like a 6 cylinder, but it still idles pretty smooth so I don't think it's dropped a cylinder or is missing spark. This problem has been on and off and only started in the last week or two after the truck sat for a while. I checked the fuel filter, which looks fine. The vacuum advance hose is running from a port on the passenger side of the carb. I tested the vacuum and it gets a reading between 0-5 depending on idle speed. Once rev'd it jumps and holds steady between 15-23 depending on rpm. I believe this is where it should be. I checked the stator and got around 650 OHMs, so right where it should be too.

My original thought was that the pickup coil that was installed in the truck when she died on me was designed with substantially advanced timing, hence why the motor dies when the advance hose is hooked up with the new pickups. I tried backing off the timing a bit but found that it didn't change anything. I got myself a timing light, and the engine seems to run best with the timing between 20-30 BTC. If I set it at 12 BTC it will run, but the idle drops a few hundred RPM and it lags a bit when revving. I tried retarding the timing all the way to 0 BTC, and it runs like garbage but will still stall with the vacuum advance hooked up. No matter where I set the timing, if I hook up the vacuum advance it will stall out.

I'm at a loss for what could be causing this. Should I just start replacing each part of the ignition (module, coil, wiring etc)? Has the timing chain slipped? If that's the case, I don't think it explains why the vacuum advance stalls it. Any insight is greatly appreciated!

 

 

When I hook the vac advance line in the timing jumps so much that I can't even see the timing marks, so I have no idea where its at. Stalls right out as soon as it starts pulling any vacuum. I pulled the distributor cap and applied some vacuum to the advance to see what was happening inside. By sucking on the vac line I can pull bout 7-8 inHg, which gets the pickup coil to move a little. Nothing obviously wrong in there. Like you said, I don't think its really possible to botch the pickup coil install. I've checked it and rechecked it about 40 million times. I'm not sure if I mentioned before, but when I first replaced the pickup coil I was having this issue and noticed that the rubber diaphragm inside the vacuum advance was cracked. I put a new one on thinking that would fix the issue but there was no change.

I think I'm going to start replacing pieces of the system starting with the ignition module and see what happens, unless anyone has any better ideas.

 

You set the timing with the vacuum line off and plugged.
Set your idle speed per book spec.
Now check and set timing. You may need to adjust idle speed again after timing is set.

Before hooking up the vacuum line you should not have vacuum on the hose if you have the right port on carb and carb is good. If you do have vacuum find out why and fix.
If idle speed is too high it can put vacuum on that port.

Now if no vacuum on the port but still cuts out what it does get vacuum you need to run an ohm test on the pickup coil.
If the wires are broken in a way they only make connection with no vacuum then when the plate moves breaks connection.
Run the ohm test no vacuum then with vacuum motor off and see what happens.
Also is there a ground strap on the plate to distributor body that could be bad / broken?
Dave - - - -

 

All roads lead back to ford-trucks.com, lol. At the end of July I was experiencing challenges getting the ignition timing right in the 400m in my 1974 Ranchero. Similar to right now I googled the problem and it led me to an existing thread on this exact sub forum of ford-trucks. 3+ months later, 130 posts on 10 pages later, I’m left with the exact same problem as this thread.

In summary:
- Dura spark I
- new distributor, coil, ignition control module, HT leads and plugs
- initial timing set at 16*, vac advance plugged
- runs well with a predictable advance curve
- connect ported vac advance and engine misfires when advance kicks in
- connect manifold vac and engine dies like ignition key was shut off
- read up on subject, pointed to stator
- replaced stator, ran well with vac advance, took for 3 mile test drive
- returned home, shut off, engine cooled down
- tried to start, no go, will not run with vac advance again, same as before
- replaced stator again, this time with different brand. Same problem.
- I’m measuring between 475 and 570 ohms across the orange and purple wires depending on which stator

There are 4 resistance tests for the stator described in the Ford Engine Service Manual. I’ve attached a photo. The last two (pin 7 to engine ground and pin 8 to engine ground) are tests between each of the two wires (orange and purple) coming from the stator. The expected value is 70,000 ohms +. I’ve performed this test a dozen times with one probe on either pin 7 or pin 8, and the other probe on either the engine blocky or the battery negative post, and cannot get any reading. I’m not an electrician. Am I performing this test correctly?




TIA with thoughts on how to overcome this frustrating problem!

 

Pulled distributor out without marking the position it was in .