Suggestions for best coil, plugs and wires for 87 Dakota 3.9L

I need to pass California smog again. I would not have any problem but the state has made the test more stringent twice since I bought the vehicle new. I need every edge I can get and I figure getting the hottest spark is a good place to start and would appreciate any suggestions as to which brands might offer the best chance of getting the hottest spark. If anyone thinks that a certain cap and rotor might be better than the ones at the chain stores I would be open to hearing about that also. The cat is an aftermarket one with the stamp required by the state. It has less than 25,000 miles on it. Thanks for any help.


Soo many questions… How is it a 37 year old truck has only 25,000 miles? That’s only 675 miles per year average! How does a 25K mile truck need a catalytic convertor replaced? Why would you suspect this to fail with sooo few miles on it? And why do you think Cali raised the bar on a 37 year old truck? If it meets '87 specs, why would you suspect they have changed?

As far as parts go… buy the best quality you can find in the exact spec the truck calls for. The correct spark plug, not something “hotter”… If the truck came with platinum plugs use platinum. If copper, use copper. Use a quality cap and matching rotor from a quality brand and change the spark plug wires, they deserve it.

Holey Smokes… this engine still has a carburetor on it! Are you sure that is in good working order? Dried out gaskets, cracked diaphragms and crispy-crumbly vacuum hoses could cause you to fail. Check the hoses, the carb’s operation and driveability to ensure the carb doesn’t need a rebuild.

I’d even treat it with Seafoam in the intake and then take a long drive since so few miles are on the truck.


Just to add to Mr Mustangman’s post above:

I would get a cap and rotor with brass contacts, and Beldon ignition wires from Napa, Napa has the brass cap and rotor also… They cost a little more but worth the money… The OEM Spark plug is a Champion copper plus 404 (part #) and set the gap at .035"…

Are you saying the vehicle has 25K miles on it or the cat only has 25K miles on it…

Also, if you show us the spec where it failed emissions that might help us out more, you could have a vacuum leak or something…


What they said. And that carb and vacuum hoses would be at the top of my list to check, my '84 Cherokee had the carb fail, and it was only 10 years old at the time.

I’m thinking the OP meant the new cat has 25k on it, not the truck.

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Thanks. The cat has 25,000 miles. The truck has about 180,000.

The cat has 25,000 miles. Sorry for the ambiguity. The fail is in hydrocarbons. Everything else is OK. I have managed to pass every time, but barely, and have failed multiple times before eventually passing. One time it passed by one part per million on both speeds, 15 and 25mph.

Agree that plugs and cap and wires is a good start. I’d take a good look at the plugs when they come out to determine if they are a little oily at the tip… an oil use problem, or dry but black indicating an over-rich mixture… a carb problem, most likely.

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My sons 92 Civic failed very bad one time, run some Marvel Mystery Oil in it and drove it hard for a few miles on the highway and it passed with flying colors, crazy low specs, one was even 0 on the test, should have took a picture of it back then… lol

This stuff has worked very well in the past on multiple customers vehicles…

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Truck has 180,000 miles. Cat is newish.

The Belden 700387 wires at Napa are $38.99. RockAuto has the exact same wires for $4.83 plus shipping, and are listed under the Economy category. SMP 7656 at RockAuto are listed under the Premium (Best) category and cost $23.99. Napa has a Good Better Best ranking. The Belden 700387 wires are Better. The Belden 69416 are best and cost $169.99, and are out of stock. :thinking:

There does not seem to be a way of comparing the wires in terms of performance, so it seems to come down to an educated crap shoot.


I’d give the Rockauto $4.83 wires a shot. With a decent set of new wires/plugs/cap/rotor, any problem you have passing the test will be caused by the carb or oil burning.

Napa’s are blue wires, I used to call and just say send me brass cap and rotor (if it had a dist) with some pretty blues and whatever plugs… I have used hundreds at least, with out fail, personal vehicles also… But Rock Auto’s could be 20 year old NOS (new old stock), and they don’t look the same color (but pic may not be correct either), I would not buy the $4.83 wires from Rock Auto… you do what you want… I can only recommend what I would do with being over 30 years in the automotive world… But yes the 700387 from Napa is what I recommend…
I think Belden wires are pretty much Napa only, so if Rock Auto has them, then there is a reason why and so cheap…

They are on closeout, for what that’s worth.

True but Napa still carries that same number, it would have to be very old stock, I know that I have bought some very old brake parts that were in very old boxes a few times from RA… Napa will move stock from an old store to the new store…

Just makes me think the RA Belden’s might be knock-offs or something… Just something seems off about it… It would be like buying Duralast items from RA (I don’t remember seeing any sold)…

Calif smog testing … been there, done that! … lol … What part(s) of the test are the most burdemsome to pass for you? HC? NO? In any event, suggest to take a look at this thread for a 92 Corolla with HC readings near the limit. The 92 Corolla is fuel injected, so doesn’t exactly apply to your Dakota, but it does have electronic ignition w/distributor so probably still worthwhile.

Quick summary: I discovered these definitely helped, roughly in this order

  • Retard ignition timing 2 degrees from spec
  • Fresh engine oil
  • NGK V-Power spark plugs (reduces HC)
  • Remove carbon gunk from distributor cap terminals and ignition rotor.
  • Or even better, install a new cap and rotor & new wires.
  • Try to clear as much gasoline from the evap canister as possible. Done by doing a lot of driving. Definitely do not fill the gas tank just prior to the test. You don’t want extra gas flowing into the engine from the canister during the test.
  • I’ve used a “guaranteed to pass” type of gasoline additive sometimes, and sometimes not, just prior to taking the test. Not clear if it had any effect.

My biggest and most surprising finding was that a slightly clogged air filter helped reduce HC levels more than any of the items above. I think that’s b/c of the specific configuration of a 92 Corolla though, which uses the “speed-density” method to set the air/fuel mixture. So a slightly clogged air filter probably wouldn’t work – and would probably make matter worse – with a carbureted vehicle.

BTW, I think cars 25 years and older shouldn’t require tailpipe emissions testing, except perhaps just visual inspection to make sure all the emissions parts remain installed. Here’s to hoping our Calif politicos finally see the light on this issue. They’re up for re-election this year, so now is a good time to lobby them.


I want to thank all of you for replying. Your answers have directed me to brass rather than aluminum contacts on the cap and rotor, and higher end plug wires. On thing that is coming into sharp focus is the coil, currently a Niehoff AL-172, with 1.7 0hms on the primary and 6,960 on the secondary, which i bought at a local chain parts house years ago. The shop manual specifies either a Chryler Prestolite with 1.34 to 1.55 ohms primary and 9.400 to 11,700 secondary, or a Chrysler Essex (gotta wonder who was in charge of naming these things) with 1.34 to 1.55 ohms primary and 9.000 to 12,200 secondary.

The closest I could find that matches these specs is the Accel 8140, with 1.4 ohms primary and 9.200 secondary. Summit Racing allows to search by winding resistance, and states primary and secondary for each coil.

SMP makes the UC16, which I am trying to find the resistance specs for. I think the coil might be the weakest link in this chain.

That seems like too few secondary windings to me. Definitely would be for a fuel injected engine. But there are other factors is the design of a coil which may make up for what seems on the surface to be a low secondary windings count.

If in doubt, best bet is the oem coil from Chrysler. Those two coil specs look more like what I’d expect. Next after that I’d be looking at Summit Racing’s products. Or a used oem coil if you can find one. Just curious, what circumstances led to a non-oem coil getting installed?

Buying the one O’Reilly’s listed for an 87 Dak 3.9L engine.

I just found an old on I had in the Old Parts Department of the garage that specs out at 1.5 and 12K, which is right on the money. No brand, very generic looking The only markings are:
12 V
Use With
External Resistor
Made in Mexico
0405 is stamped on the bottom. the two 0’s are different looking so may be O405, as in O for Oatmeal.

There is no OE external resistor on this truck.

My own truck is older than yours, and uses a conventional points ignition system. It has a resistor in series with the primary circuit when the engine is running. That’s to prevent damage to the points. Your truck use electronic ignition, no points I presume. Those type of electronics usually do not expect there to be a resister in series with the primary side of the coil.

Thank you, George, it’s all coming back to me now, the reason for the external resistor. Do you have any thoughts on using a coil like the Accel 8140, that has the appropriate resistance specs? The only concern I can think of is if the generator can keep up with the demand for more current, if that is a factor.