I have a 1977 F250 4x4. I don't know exactly what engine it has other than it is a 351M. What I need to determine is what year it is. I've been assuming that it was a 1977, but it actually might not be. It has a HEI distributor that might be bad. It died on the road last week Sunday (10/26) and will not restart. It cranks, but doesn't fire.

I have two questions. The first is how do I test the HEI distributor to see what the problem is. I have no spark at #1 plug.
The second is dependent on what year the engine actually is. I am considering reverting back to the Duraspark ignition system and would need to know everything that I need to do that.

I hate the look of the HEI and the Duraspark is (IMO) just as good.

Thanks
Mike

 

351C, M 400 429 and 460 use exactly the same distributor so finding one that will work should be easy. 351W also uses the same distributor but the Windsor uses the smaller drive gear.

 

I think the DuraSpark is the better of the two. As to year of engine if 351M, '75 up through '82 anyway. If a 400, started in about '71. No external differences, only the crankshaft and pistons differed. Below might help you swapping back. Looks like will need a distributor, harness, module w/ blue grommet, and coil.

 

Thanks Dave & Tbear.
I know there is a difference between the DSI and the DSII. In theory I should need the DSII system as shown by Tbear.
Does it make a difference if I use the DSI or the DSII? I know that Ford changed from the DSI to the DSII in 1977, I believe.
That is why I ask how I determine the engine year identification.
The module was still on the firewall, but I wonder why the HEI was installed in the first place.
I don't know if it works or not. Also, I have the NAPA part number, so I should look up what it exactly is.

Thanks for your help and any additional information.
Mike

 

What color is the plastic grommet where the wires exit the module.

 

Specify duraspark 2, DS1 was what gave duraspark a bad rap. DS2 had all of the quirks worked out. Go with the blue grommet module, it’s the most common, affordable and most reliable. Get the matching duraspark 2 coil, the difference between DS1 and DS2 being something about proper ohms and capacitive discharge VS. multi-spark discharge or something IIRC. But For sure, get rid of the HEI. Yes, everything in HEI is in one self contained unit, and they are cheap to buy, but every one of these HEI units is full of cheap Chinese (failure prone) components and from my experience even the most basic of ford wiring does not play well with anything GM. I’ve also seen the distributor gear on an HEI unit get munched and ruin a fresh rebuild. Again, cheap. Painless wiring has the whole OEM duraspark 2 wiring setup with factory connectors and instructions, and classic industries sells the whole duraspark kit, just specify a 460 351c or 351m distributor. People may talk poop in duraspark but they are simple and I’ve never seen them fail. Mount your coil and module away from heat and use quality US made or manufactured components. Mount your DS2 standing up as well as away from heat, as (urban myth alert) they can malfunction if on thier side, though I’ve never seen it happen myself. Also, carry an extra (blue grommet) module and ballast resistor just in case. I’m running an MSD RTR distributor with a DS2 coil and module and it runs amazing. (400 ford) but will be switching back to a stock, matched 351m/400 distributor for dependability and “over-the-counter” parts store serviceability.

If you live anywhere near northeast PA, I’ll help ya with it. Maybe even give ya some of my spare DS2 crap.

good luck

 

Thanks bear.

I'll look at the module on Monday when I'm at the shop.
The reason I think it is the HEI is because I have power into the unit,
but no spark at the #1 plug.

Thanks Screwtinized. I live in Wisconsin, so your offer isn't very realistic.
I might go to a boneyard and see what I can find.
I'll look at Summit and see what the cost is.
I can do the work, but not a lot of the testing.
As an example, how do I test if the module input plugs are live and active?
Thing like that I'm not overly experienced at

Thanks all
Mike

 

tbear. I checked the module that was still on the truck today and it is a blue grommet.
So, it definitely was a DSII system.
I still need to check the HEI out. But I'm pretty sure that is the issue.

If anyone has any thoughts, I'd appreciate them.

Mike

 

[QUOTE=1941 Ford

Thanks Screwtinized. I live in Wisconsin.

Thanks all
Mike[/QUOTE]

Maaaan off subject, but your state is beautiful and I wish I lived there. I did dairy farming as a kid, and every single cool thing that we did was based upon something we’d seen or learned from the mega dairies in Wisconsin. Now all of the farms in PA have gone away and are housing developments, data centers and strip malls, but I’ve got tons of pictures of Wisconsin and dreams of going and maybe even living there one day. OK back to trucks!

 

Screwtinized. I'm not really sure of the mega dairies anymore. I live in the southeast corner of the state. There are farms, but it seems like they are the old style small mom and pop type. Combined, as in a co-op, they do fairly well. However, not like the mega dairies.

Thanks for the thoughts tho.
Mike

 

A little late to the party, but I believe you've gotten sound advice, Mike. Based on your description, I think it's safe to say your Chinese HEI bit the fortune cookie. Swap it back to DSII and you should be good to go. There's always going to be detractors, but in 50 years of driving with them, I've only been let down one time from a bad module, and it was 30 years old. Nothing lasts forever. These trucks were never meant to last more than 10. The fact we get to drive them today at all is a testament to the engineering that went into these vehicles. The particular year of your engine block will have no bearing on the distributor you get. Just say you want one for a 77 to match your truck and you'll be fine. However, if you want to scrounge around for date codes, there's help online to show you where they would be on a tall deck 335 series engine (351M/400). https://www.tmeyerinc.com/tech/351m-...-xxxx%20blocks.

 

52 Merc: Thanks for the info. It looks like the year of engine is less important than I had thought.
I've also got a 1941 Ford PU (hence my moniker) that has a different year flathead in it. I believe it
is a 1942, but haven't verified it yet. I just know that the distributor and fan location is wrong for a
1941 motor. That's why I was a bit concerned about the engine year.

tbear: Based on your schematic, how can I (if I can) test the output of the module where it goes to the distributor.
The one I have has the one of the wires cut on the input side. I think that is a brown one. I can resplice that one.
However, there is also one on the output side that has been cut. I not sure which one it is at the moment.
Also, there are wires that go to the distributor, but only a red one is hooked up, none of the others are.
Some advice and assistance would be helpful. I'm definitely going to go back to the DSII.

Thanks to all.
Mike

 

You don't need to precisely date it, but if you just want to .....

Using a clean 400 block for example, (the 351M and 400 use the exact same blocks).
Top rear of block, behind the intake manifold, 8M20 is decoded 8 is 1978, M is December, 20 is 5 days to Christmas.
This block was cast "1978 December 20".

Build date, the day the block was filled with goodies like crankshaft, pistons, etc ..... and this date is a stamping.

The same code is used, hence "1979 January 04",

This is a 400 that came out of a '79 F-350 wrecker. Is a steel bolt as a plug in the dipsick hole as it was a 2wd truck and had a dipstick there under the orange sealer, my truck which this may someday go in is a 4wd with dip stick on the side of the oil pan. The bolt used as a plug can be removed if such is ever needed.



My '77 door sticker indicates the truck build as "03/77", I don't know what the stamped engine build date is, likely some time in early 1977 is all I can say.

 

I have a few manuals, but the easiest way to respond is reposting pictures of pages. Looks like I lifted the pictures from @scottscott at post #15 of the thread ..... Duraspark help - Ford Truck Enthusiasts Forums

 

Thanks for the info bear.

What I really would like is how to test the DSII module. As I mentioned, there are a couple of wires that are either cut
or simply disconnected.
I know that I'll need the harness that connects the module to the distributor, but want to know if I need a new module as well.

Thanks
Mike