Hi .. You are probably here because you are looking into buying or already own a ford f250 and would like a thoughtful review of what to expect from someone who drives this rig .. I always troll these sites looking for info but never actually post anything myself ..

well today that all changes as I would like to share what I have learned in hopes that it helps other truck enthusiasts.. Also if you drive the beastly idi please share your experiences to expand the knowledge base .. And yes i expect many blown britches over my recommendation to use ether .. Nothing can stop me now make my day .. so here goes ....

I am talking about the 6.9 idi diesel n/a engine In Xl trim .. only buy this truck IF .. you get satisfaction from children pointing and referencing your 'monster truck' .. you don't mind guys frequently stopping to tell you 'hey ! Nice truck' .. you like being able to throw 5 dollars on the cashier checkout and telling em diesel on pump one and actually be able to get somewhere .. BUT you must be a decent mechanic to own this one .. because .. this is a 30 year old vehicle that almost certainly has been abused .. if you can’t do your own maintenance .. Just pass .. Taking this to the shop for repairs would cost a fortune .. Fortunately the parts are pretty inexpensive if you do you’r own upkeep it’s a fairly inexpensive vehicle to keep up ..

now .. what I like best is the sound of the engine and it’s reliability .. it is clanky just like a diesel should be but also sounds like a giant V8 .. because .. well it is .. I get amazing fuel economy with 35 inch bfg ko's .. 25+ if I baby it on the freeway .. 15 if I mash the gas all day .. the gas cost is like driving a little hybrid soda can car but with huge power and awesome road presence .. going green never felt so good !!.. with granny low 4 speed and lock out front hubs I can go literally anywhere I shouldn't go in terrain I would describe as only impassable ..

I accidentally drove into a recessed clay mud lake and drove .. dirtily .. out .. I went mudding and took a wrong turn downhill into an abandoned culvert leading to a cistern with standing water pooled up and successfully drove through basically .. washed out river road condition up an insane steep mud grade backwards .. To go any further i would have had to drive into the cistern pit of pooled water and even then there was insufficient room to turn around .. So .. I just mashed the metal pedal to the floor and drove it in reverse back up that insane hill somehow .. in pure mud .. I have never once managed to get stuck or stranded ..

the engine itself is entirely mechanically operated except glow plugs .. starter .. Alternator .. and fuel shut off switch .. when I bought my truck it had sat 10 years with a blown clutch that in turn had destroyed the throw out bearing and pilot bearings .. had dry master .. no brakes .. and a tank of ancient oil sludge in it for fuel .. the drivetrain was slamming and grinding and whining terribly .. but the day I bought it .. unfixed .. I successfully .. and dangerously i might add .. hauled a trailer 15 miles to the shop to begin repairs .. no brakes .. old gas .. torn out clutch .. the bellhousing was sliced clean through in a few spots from fragments of the old clutch swinging wildly in there .. but she made it ..

after 4 straight days and nights and 600 dollars in parts (also when doing an expensive overhaul like this use promo code “VISA” at advance auto parts online .. with the card and select pickup in store // the “visa” deal is 50 dollars off purchase of 150$ or more .. This may now be expired i don’t know .. but last time i used it it was still good .. No guarantees but try it for yourself .. Place your orders in 150 dollar increments (155-50=105) to save a ton of cash!) so after 600 bucks in parts (actually 900-300) she was purring smooth and pulling hard ..

that is just it with these old diesels .. you MUST be a good mechanic .. because although these trucks are super tough .. they are also super old .. and as a result of their toughness the previous owner may have done zero maintenance and you must count on replacing many parts to bring it up to great running condition .. though with a 'b rating' of b50 at 300k .. you can count on your truck to drive 300-800k miles before an overhaul once fully repaired and restored and properly maintained .. and driving long on the cheap fuel wise and sounding and driving awesome ..

I have an unknown number of miles on my motor .. probably no less then 150k and no more then 300k .. none of the tach odometer or speedometer work .. though the gas hand and temp gauges do function .. and that's all I really care about anyway ..

I have had to repair .. clutch .. throw out bearing .. pilot bearing .. brakes master .. clutch master and slave .. rear drum parts .. batteries .. starter .. thermostat .. radiator .. block heater hole plug .. hoses .. belts .. parking brake cables .. one fuel injector .. injector o rings and return lines .. filters .. brake lights .. high beam fix .. fuel selecting valve .. Rear U joints .. tires and rims ... well I guess that's not that much really .. and I knew up front that I would have to spend at least a thousand dollars in parts as well as alot of wrenching ..

BUT .. I can put literally pocket change .. if I happen to be broke .. sometimes .. I am a poor redneck .. I can throw couch cushion change at the man at the gas station and actually go places .. the mileage is amazing it's like a hybrid car but huge and loud and cool and I can haul a house easy .. I can put 5 bucks in there and go to town and back .. my old chevy would burn that much gas before I made it out the driveway .. literally .. and I was always sitting at home for lack of funds to go cruising in the cheby .. well now .. I can smoke tires all day cruising and having a good ol' time in the 420 cb inch diesel .. and it sounds so good I often turn off my hi fi super stereo system because my actual truck sounds even better then the radio ..
just as an aside .. as an audiophile .. I will share the magic music combination .. Kenwood stereo deck .. pioneer speakers .. Rockford Fosgate amplifier (the old style not a new one .. look for the ugliest old rockford amp you can find that works .. even if it's rated 45.2 watts it's a beast .. don't mount it under your seat .. these get hot .. mine is under the hood) pioneer sub in a thin sealed box occupying the 5 inches behind your seat .. you may have to make one it's hard to find a super thin box ..

Back to the truck .. things will wear out on a 30 year old vehicle so if you are a good mechanic then this is a great one to consider .. it will give alot to a wise owner .. when things do break it often drives okay for up to several weeks to 'let you know' things just don't blow up .. they give warning and you get out coveralls and get greasy ..

now specifics .. WARNING .. diesel fuel is now ultra low sulfur .. when these engines were designed the fuel was 'wet' and oily now it is 'dry' if you do not add 2stroke oil at fill up you will wear out the injector pump ! This is a 600 -1000 dollar part ! 2stroke oil is only a dollar or 2 at the gas station so put it in there .. also add a good splash of power service diesel additive .. this stuff boosts power dramatically and gives 15% better fuel economy and quiets the engine .. these motors are meant to be driven with these additives modern fuel is not as good as it used to be and your truck NEEDS this .. If you are running low on gas it wont run out while driving unless you go way past E .. It will keep driving past empty until you park and then .. It won’t start because there is insufficient fuel .. I keep a jerry can with a half gallon of fuel in the back as an ohh **** reserve to get started if i run it out of fuel and it won’t start .. If you do run all the way out of fuel , don’t crank on the starter for 5 minutes hoping the pump will prime .. Do this .. Add fuel .. Then hit the key for 5 seconds .. Grab a small twig off the ground Go under the hood to the fuel filter base and push the shreader valve to let the air escape .. Go back in the cab and repeat 5 second crank .. Air purge .. 5 second crank .. Air purge .. Usually takes 4 times to get the air out of the system then it will start ..

The stock headlight high beam wires, and cab pull switch .. are insufficiently sized to carry the current load and can burn the wire .. Melt the switch .. Or in my case melt the fuse block at the high beam fuse slot .. Do yourself a favor and modify this preemptively so you don’t have your headlights go out on you .. Like mine did until i switched em on to lo beam .. Take your high beam wire lead at the lamp at the passenger side and cut it and connect to operate a 30 amp block relay directly wired from the hot side of the unused glow plug relay wire block add a fuse in there and run the 30 amp side to each hot high beam spade in the lamps .. I think they are yellow .. This results in much brighter headlights and more importantly only about 1 amp is drawn instead of 25 going through all that restrictive wiring and switches ..
If the truck sat for years .. Pull the hvac blower motor under the hood and remove the mouse nest that is invariably been built there .. Pretty easy to get to and makes the air NICE and fresh .. then take off the dash pad and remove the mouse house in the middle and vacuum the vents .. This is easy to do .. Only 12 Phillips screws .. Two screws each side in the defrost vents and about 8 screws along under the front of the dash .. A ‘dental pick’pulls the plastic push pin from the vent flappers sides so you can put a vacuum attachment in the opening ..

Motor oil is 11 quarts mobil delvac 15-40 and a tiny drop of stp oil treatment (1/10) of a bottle for zddp additives .. use powerstroke long oil filter .. coolant is low silicate 'carquest brand' full strength diluted with distilled water add 12 oz sca's every 50k miles .. This is sufficient for the 6.9 though if you have the 7.3 you must buy test strips and more closely monitor your coolant to prevent cavitation ..

use synthetic oil mobil 75-90 in manual tranny and chunks .. atf in the transfer case ..

twice a year remove slave clutch then boot and fork .. reach into the quill and pack the throw out bearing full of good synthetic grease .. Replace boot and fork then slave and add brake fluid to the clutch master .. Leave the cap off and pump the clutch .. It will self purge after about 150 strokes .. No need to bench bleed it or overcomplicate the procedure ..
use dana spicer parts whenever possible .. timken bearings .. the rear diff is full floating dana and tough .. replace bad u joints if they squawk .. use only ford dealership thermostat not parts store brand .. put a plug in the block heater hole if it starts leaking .. sold as the 1 1/2 inch dorman in the help section for 4 dollars ..

when my brass radiator began leaking too much I replaced it with one from the bone yard from a 7.5 460 gasser .. it's plastic and aluminum and found on the 7.5 .. it's a 2 row jobbie but they are wider tubes and this one really cools much better then the old pig brass one .. Though the stock brass radiator never overheated this aluminum and plastic one actually feels cold sometimes .. And the old one was just rotted out and leaky.. Not bashing the old radiator it was just old and i do like the replacement .. Plus it sits lower so l don’t sit on it when i work on the engine .. for hoses i spliced a lower hose from an 85 f150 5.0 to the lower hose from the engine with galvanized fence post tube .. the top hose is Is a splice combo combo of the stock idi hose up from the thermostat to a motorcraft part number F5TA-8B274-YD off a 96’ 5.0 f250 the upper hose was similarly sleeved with galvanized fence post tubing .. I could have run out and paid 400 dollars for a stock unit .. but this radiator works better .. is common in the junk yards and the price totaled in at about 60 bucks .. radiator .. shroud and hoses .. plus if I ever need another I can get another one easy used in good condition for like 40 bucks .. trim the 460 fan shroud back about 1 1/2 inches with a cutoff wheel and it works great ..

only use the block heater if it is mid 85 .. 86 .. or 87 motor .. early castings 83 to 85.5 are weak at the block heater and can crack if used too frequently .. The 6.9 blocks have less cavitation issues then the 7.3 .. Mine is the 85.5 model .. but 85 and 86 had old style rocker arms and 87 and later models have improved version .. I hauled a nice set of 7.3 rockers and installed them along with the fresher pushrods into my 6.9 .. best combo imo ..
also look into a 7.3 fuel filter as they have built in water separator 6.9 has a usually bypassed failure prone separator on the firewall .. though I must admit I just run mine with no water separator for years and not been an issue .. but I also add oil to my fuel (NOT MOTOR OIL / only 2stroke oil and power service) .. if you get water in your fuel injection pump with dry modern fuel you will really quickly wear it out .. add oil .. add oil .. add power service ..

my truck doesn't use .. burn .. or leak hardly any engine oil at all .. after 2,500 miles or so when I do an oil change it is usually 1/2 quart low .. still in safe zone .. just near add line .. and my truck doesn't smoke at all when driving or idling only on startup ..

passed emissions easy .. Actually they used 3 different machines and ran the test 4 times because they couldn't believe they were hardly registering any smoke at all .. but .. if you have a bumper rider on your 6 .. just slam the gas and brake at the same time and you'll send em' backing up in a cloud of puffy diesel goodness ..

My recommended combo of engine oil and fuel treatments works awesome .. But be forwarned at 2,500 miles or so the oil ‘honeys up’ i can feel the oil change from flowing freely to really thickening up .. This is probably mainly due to the stp oil treatment mixing with the fuel additives in the crankcase .. The result is that the engine takes longer to rev up and most importantly the fuel economy drops off significantly .. I can always feel it when the oil is past it’s prime and the gas hand starts goes down much faster .. That is why i change my oil at about 2,500 although i’m sure it could go alot longer .. The price in fuel wasted justifies the change sooner rather then later .. Also this is why i don’t use expensive synthetic motor oil .. I tried it one time and it honeyed up just the same additionally synthetic tends to leak through engine gaskets much easier then the dyno stuff ..

don't be a hotrod and adjust the fuel screw .. it won't gain any power .. it will just smoke use more gas and burn down your pistons .. eventually .. there are no good 'mods' to gain power on an idi .. if your wanta rice racer motor to soup up and add chips and all that junk just go get out and get a cummins .. the idi is all it was ever meant to be in stock form and that's plenty .. believe me true duals on a n/a idi is boss .. they can keep their little inline oil leakers ..

Do invest in large tires .. because of the low gearing your fuel mileage and road manners are much improved with large tire .. without 35 inch tires your engine will wind way up to cruise at 75 on the freeway with the granny low 4 speed and no overdrive .. much better mileage and you can go highway speeds .. get 35 inch bfg ko's ! I like 35x12.5x16.5 on offset rims .. 35 inch is the maximum tire size without adding a lift on the diesel trucks ..
also this is important .. these trucks are hard on starters and batteries if not started properly .. a real man starts his diesel with ether .. starter fluid .. now .. stop right there ..

you MUST disconnect all the ignition system .. the glow plug relay specifically and check it to make sure it won't turn on .. if you spray starting fluid into your engine with the glow plugs operational you will ruin your engine pronto .. like right now grenade ..

but .. once the glow plug system is unhooked it is 100 percent safe .. and WAY easier on .. your engine (not turning over dry) .. WAY easier on your battery .. WAY easier on your starter ..

Plus you don't even need to plug in the block heater.. it starts just fine cold soaked .. I worked around big truck fleet mechanics and this is how they do it .. online everyone says .. no!! either is horrible .. That is probably because they heard about someone starting a diesel with the glow plugs on BOOM .. but they have no clue .. you only need to giver the snort once in the morning and perhaps after a long shift .. but if it's already been run no more ether is required it will start without glow plugs or starter fluid just fine .. ..

so instructions .. make sure glow plugs are unhooked ! Now I drill a tiny hole in the intake box and plumb a line for a spray can 'straw' and connect straws with heat shrink tubing into a line .. to which I connect a can of starting fluid .. one spirt .. that's it .. a half second if the temp is 45 degrees .. one second at 30 degrees .. Etc .. spirt and crank 10 seconds .. fires up ? Good to go .. if not .. stop and go give it another half second spirt .. repeat .. always fires easy first or second try ..

beats cranking the starter for minutes at a time with a cranky glow plug system .. now go do it .. be a man ..

drive a FORD

 

welcome to FTE,
you have that old girl looking pretty dang good!
you really do not have to add the two stroke oil to the fuel, but if you want the peace of mind adding it that is fine too.
these trucks will run forever if taken care of. my 88 has been rode hard and put away wet many many times, but i stay on top of maintenance and have been able to run her for 494,000 miles so far without ever having to open her up. i have replaced the injectors 2 times, and the injector pump 3 times. although it does need new injectors, it still runs decent enough for a backup snow plow truck.

 

Thanks .. i do body and paint work from my little shop out back .. In between other jobs i grind .. fill and lay fresh paint down .. I do little bits here and there .. I still have yet to tackle the hood and roof but will get around to that before the summer is through .. Actually just today i was laying some body filler down and getting ready for a splash of fresh paint tomorrow ..

Just doing the driver side front wheel well and the back wheel well .. I already did the rear once .. But this winter i hauled about 3 tonnes of coal from Knoxville .. usually a full load only weighs 2 tonnes but it was real wet from rain .. I had her bottomed out and was still passing people on the freeway super overloaded !

But .. I hit a big bump at speed and my tire crunched into that wheel well .. Smashed up all that perty paint ther’ . . Ohh well .. It’ll be all fixed up tomorrow ..

Another thing i did and forgot to mention was that i crawled all underneath and slathered the undercarriage .. Frame .. Axles .. Radiator support .. Springs .. Skid plates .. Ext .. With rust-mort (muriatic acid) to kill the minor surface rust .. Grinded it all off with wire brushes and wire wheels .. Neutralized it with a good fresh water scrub .. And painted everything with whatever black leftover materials i had laying around the shop .. Por 15 .. Rhino liner .. Paint .. Ext .. All black .. it makes a huge difference .. Looks great !! .. These trucks ride high .. So a lot of the underside is exposed when u look at it .. The transformation from rust color sled to blacked out beastly chariot cannot be understated .. Night and day difference ..

The dash in my truck is still 100% perfect .. As is the blue rubber floor .. Both shifter boots are 100% .. The seats are 90% and ***** are 100% .. Door pads are removed and inside of the metal door is repainted fresh blue .. The headliner and plastic trim (sun faded) is removed .. I found all new rubber gaskets still springy and brand new looking from a low mileage 97’ f-250 and pulled all of it .. But .. Because i love Meguires 40 .. But also hate armor-all for paint adhesion .. I was in a conundrum .. I have to repaint the inner doors and jams before installing the new fresh rubber .. So i have only done the driver side thus far .. I really like the new fresh rubber !

Back glass has been updated with C.L. Laurence tinted aftermarket sliders .. The front bumper chrome is still nice and shiny .. And the rear bumper is very nice heavy 80’s dual ball with diamond plate top wide nice chrome sides .. Reinforced with 3/8 flat stock underneath .. This looks like it may have been a dealership upgrade .. I don’t know for sure but it is professional .. The original owner used the truck as a trailer hauler for his prize winning Tennessee walking horses .. I was told .. To this day a big shiny chrome stallion rides the hood front and center ..

For striker posts in the door you can use 1/2 PEX plumbing tubing .. And it comes in three colors ! Blue Red or White .. I have White to match the midsection Paint .. Looks great and the doors shut perfect .. I slice the PEX to length .. Then longways so removal of the striker is unnecessary .. You can simply spread it wide over the striker post and it goes back into circular shape .. With the slit facing the inside you can’t even see the seam..

Next mod looking forward to .. after more fresh paint .. is a grill update .. Someone out there has a 2016 or other late model F-250 with the huge chrome “equal sign grill” flanked with the “c” and reverse “c” and giant FORD emblem .. If someone has this .. That has swapped out to a “T-Rex or Billet or Mesh Grill” and would like to donate it to science .. please let me know .. I do crazy retrofits and body work for a living .. So i think i can make it fit .. And make it look proper .. I know about 90% of people with a late model truck love their grill .. But also about 10% can’t stand the blocky look and all that chrome .. I LOVE IT !! And think it would look really great on an old bullnose .. I will pay shipping if you have one collecting dust and would like it to be reborn as a bug smasher ..

I haven’t measured one for fit yet .. But I already anticipate building a new grill inner support structure out of punched hole stainless to resize it .. though to my eye the grill area looks to be about the same .. One way or another .. I must have that boss grill .. it will look so awesome

I will be posting more pics and updates from time to time .. Please add your own review and info about your ide if you would like to or feel free to comment .. Thanks! Leroy

 

Eh, not so much. The big mod for power is called a turbo. Add more air(then turn the fuel up) and you'll get a /lot/ more power out of your old IDI.

 

yes .. a turbo is the sure fire way to kick the mule a little harder .. but my 6.9 has the high compression motor .. so if i ran a turbo i would only be able to give it a slight boost before risking head gasket blowout .. maybe 7 or 8 psi i suppose would be the max .. also i would only be able a single exhaust not true duals .. unless i were to do twin turbos .. and going for 2 turbos when only half of one is required seems like way to much effort when weighing in the increased complexity .. more parts to break or replace .. greater chance of oil escaping the engine through a turbo and running away .. mostly i just don't like the sound of a single pipe with a turbo .. i know .. everyone else that drives a diesel will disagree .. a turbo is considered like mandatory .. but my truck is fast enough for me .. if someone behind me disagrees .. that's their problem not mine .. and they get da smoke

 

I used to think the same. I figured it wasn't worth the extra stuff to deal with, stock was better. Then I got a $500 Banks kit, and it instantly added a good 75 HP, even with the 10 PSI it's designed for. Butt dyno said "this is awesome"!
As far as sound goes, no reason you can't get anything you want out of it. Split the exhaust pipe after the turbo, and you've got duals. Cut out the muffler or add a through-flow muffler and you've got something really cool sounding.

Sure, 8-10 PSI doesn't sound like much(I know you can run that on a 6.9; Banks wouldn't sell a drop-on kit that would blow the head gaskets), but if you think about it, that's basically adding 60% more air to the engine. That's easily 50-60% more power, right there. And it's better than that because at high revs, the engine is trying hard to suck air in and creating a vacuum, so you get /less/ air.

We all have our thoughts about these engines, but I personally find it fun being able to accelerate up a steep hill at 70MPH in overdrive hauling a heavy trailer. Sure, a NA engine is torquey and amazing at low speeds, but when it comes to hauling a trailer, the boost *really* shines.

 

it sounds like you really like the banks turbo .. and who wouldn't like more power .. if i had an automatic transmission i would place a great deal of thought into maybe putting a turbo on there .. but truthfully my motor really does go fast enough as it is .. maybe the engine in my truck is just a good running motor .. i hear a lot of folks say they are dogs and slow .. but mine seems okay .. if i run straight diesel without power service and 2 stroke additives .. then .. it really is slow .. and clanky with alot less torqueyness .. but with a good splash of power service and stroker oil .. i wakes right up .. like i put a little turbo on there .. and noticably pulls alot harder .. it pulls trailers like nothings even behind it .. and generally i can just load it up without care .. thing is with the manual 4 speed i stay in first gear for maybe 1.5 seconds .. second gear 3-4 seconds .. 3rd gear for ?? depends .. with a turbo i would be switchin' licks faster then the servos in the granny tranny could keep up .. but .. admittedly if i did have an automatic would probably add the turbo

 

ooohh i just remembered something .. TJC's reference to his rattletrap jogged my memory .. one part in perticular on these trucks is a dead ringer for major league annoying rattle ..

and pure malpractice on the part of ford in 1985 .. i searched endlessly for the source of this perticular rattle .. in the door .. each side had a similar constant rattle that just drove me bat**** crazy .. i couldn't pinpoint it .. everything was tight and seemed secure ..

then i finally discovered the source ..

it's the pull lever to open the door !! .. it is held in place on one side by a bolt (fine) .. and on the other end it is held in place by a tab in a slot (not fine) .. the tab and slot end of it is not secure enough and it rattles endlessly in that 1 mm slot .. this is the chrome pull lever to open the door .. it has a spring in it and one bolt .. it operates the door latch via a hanger rod ..

simply drill a hole near the tab and slot end of the mechanism where it attaches to the door .. insert a small bolt and secure it with a nut and lock washer from the inside .. the way they should have done it 30 years ago !!

voila .. mystery rattle solved ..

 

^^^^ I think I remember putting a piece of bike innertube rubber in that tab-in-the-slot arrangement for the door handle; snugged it up and quieted it down nicely.

 

my 88 has the original banks non wastegated turbo on it too.
put it on with less than 1,000 miles on the truck. don't really know how much boost it makes, cause only have a 15 PSi gauge in it. but i have pinned that gauge many many many times.
i bet that engine has over 100,000 miles on it boosted over 15 PSI.
it used to loose traction and roast the tires in third gear if i came around a turn a little too hard on the throttle.
it is a little better since i pulled the 5 speed and put the C-6 i put in it 14 years ago.
but i also turned down the fuel with the new injector pump, and put a muffler on it

 

well .. it is good to hear that you can safely boost the motor

i'm not at all surprised as it seems just about impossible to hurt the **** thing !!

as for this particular engine though .. i will just leave it alone .. if it needed work or ran like a slug i would definitely address it with a major turbo .. but with it pulling hard and purring like an angry tiger kitten .. i just can't "mess with success" and so i leave it alone

as for adding a piece of rubber in the door handle slot .. that works great too i bet .. just fix the dang ol' door rattler one way or the other

now .. i just have to post a few interior pics

 

What's that tach? Does it use the stock tach sensor?

 

the tach is built into the cluster

it's iss pro from the factory

but it doesn't work because the sensor location just has a big 'bolt' no sensor whatsoever .. probably the sensor quit 20 years ago and they just put in the plug

here is pics of what i am doing today ... spring cleaning .. rock chips .. shopping cart dings .. rust puffs .. and where that nasty tire crunched into the wheel well

 

issopro is not factory, that was previous owner installed. the factory tach looks pretty much like the speedometer does.
factory tach:

 

The plug is what's usually there in no-tach trucks. That's why I asked about this. I'm guessing that either that Isspro install was some project that was never completed, or there's an aftermarket tach sensor pointing at the flywheel somewhere. Most analog tachs of that time wouldn't work with our trucks with the stock tach sensor, since the sensor triggers on EVERY tooth on the IP gear. Somewhere on one of the IDI forums (burners, maybe?), someone recently posted that they found a modern electronic tach that allows you to "program" how many pulses per engine rev to count, and thus they were able to make it work with the stock tach sensor. But most old school tachs are based on spark ignition pulses, and can only be configured based on number of cylinders.