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Retrofit 88 BII tach into 85 with 94 2.3 Engine?


kishy

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This is a little...un-straightforward...

I'm putting an EEC-IV twin plug 2.3 into my '85 Ranger. Electrically, with regard to the engine harness, ICM, ECM and so on, think of it as a 93/94. It's going to be a hodge-podge of parts, but for these purposes...it's a 93/94.

Currently, my truck does not have a tach in the cluster, and I have an aftermarket one that just kind of rolls around tucked on the top corner of the dash by the A-pillar. The tach is not aging well (it sticks in cold weather), and I'd like the cleaner look of a tach in my cluster.

Because my truck is an 85, I can only take a tach/cluster from up to 88 and have it physically fit. I found a 1988 2.9EFI Bronco II at a local yard. It has a tach.

What I would like to do is take apart the Bronco II cluster, take out the tach half of the cluster, and add it into my 85 cluster replacing the face that has the warning lights and fuel gauge. I do not want to use the entire Bronco II cluster because my truck does not have the light panel in between the left and right halves, but the Bronco II does, and I do not want to retrofit that.

So the core questions here are:
1 - Can the tach be transplanted into my cluster physically? Period Ford clusters are usually pretty modular and come apart into interchangeable chunks, in my experience.

2 - Is there a way to make the tach from the 88 V6 accurately display the RPM of the 93 4-banger? I've read something about needing to change which contact is grounded in the tach (?), but also read that the tach signal is different between the TFI distributor engines and distributorless...so I'm not sure exactly what's up here.

Thanks
 
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85_Ranger4x4

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I don't think so much. The tach side is kind of made into it, I am not sure what kind of shape it would be in if you removed it.

You would also need to get a module to adjust it so the V6 tach will work with your 4cyl, not sure they ever put tachs on 4cyl first gens.

You can swap the speedometer though. For a 2wd there isn't a whole lot to miss in the "message center" 4hi, 4lo, EMISS and brake fluid light maybe? I would be tempted to just go the later cluster and gauge bezel. Shran has a really nice writeup in the tech library on how to put a tach into a non-tach truck.
 

kishy

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Hmm...alright. So the 85 cluster does not "pull apart" into modular pieces that can be stuck together like funny-shaped Legos, then?

If the write-up you refer to is this one: http://www.therangerstation.com/how-to/interior-and-interior-electronics/ford-ranger-tachometer-install/
I read it before asking my questions, because it doesn't answer them :(
But then, how many people are trying to hook up the 88-and-down factory tach to the twin plug engines? I'd have to guess not many since Google can't find people running into the same questions.

If the speedometer can be swapped, that's workable. I can buy the junkyard whole cluster, swap the speedometer (it is MPH, I need KMH, plus my odometer), then that should be more or less usable.

I don't want anything to do with the message center though. My cluster surround trim is the silver finish, not the woodgrain, and I'm not interested in swapping that out at all. I'll take apart the junkyard cluster in the yard and see what I can figure out before I'm out the $$ for it.

I'm planning to wire up the EMISS light, which my truck does have, to act as the CEL once the 93 EEC-IV is in place (neither here nor there, but it's nice that there's an unused bulb spot hanging out there waiting to be used for something).
 
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kishy

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Actually yes, that's great, thanks for digging it up.
I can see that the "message center" is a removable module held in with screws, so presumably (oh I hope) I can move my warning light cluster (the 4 individual lights) from my cluster into the 88 cluster, swap my speedometer into it, screw around with the pinouts to get it to match, and then have the result I'm aiming for (solving question 1).

Question 2 is still on the table...tach signal. Not sure what all is going to go into that. Next step at this point I guess, since the physical fitment is doable, is going to be to get the cluster and go from there. I know I'm going to be running a wire into the engine bay to get the tach signal (more likely re-routing the one I've already got), I'm just not sure what tinkering will be needed to make it give a good reading (if 4cyl vs 6cyl is the only issue, that shouldn't be too bad...)

This thread is good info too, I think: http://www.therangerstation.com/forums/showthread.php?t=135668
But the thing throwing me off is: "on Ford's later EDIS units (including my '94), there is a generic/standardized tach pulse emitted by the ignition system regardless of cylinder count."

What is unclear to me is: the "generic/standardized tach pulse" that my ignition will be generating...is that pulse identical to one of 4cyl, 6cyl or 8cyl "traditional" coil tach terminal readings? Or is it something different from all of the above?
 
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kishy

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I went and picked up the cluster.
Unfortunately, there is no viable way to retain the dash bezel with the 4 warning lights, short of cutting the clusters apart and melting them back together the way I want them.
I will have to find a truck that can give me the bezel I need in the colour I want (silver, not woodgrain). I prefer the look of the 4 indicators separated but I'm sure I'll stop crying about it eventually.

Question still stands:
What is unclear to me is: the "generic/standardized tach pulse" that my ignition will be generating...is that pulse identical to one of 4cyl, 6cyl or 8cyl "traditional" coil tach terminal readings? Or is it something different from all of the above?

What I'm hoping to do (pending that bezel showing up in a junkyard) is to get the new cluster retrofit into the truck before the engine swap happens, so the tach will need to be reading accurately for the 4 cylinder Duraspark ignition. Then, when the engine swap comes later, it will need to read accurately for the 4 cylinder "generic/standardized tach pulse" that people talk about coming from the twin plug ignition module.
 

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You will need some sort of signal converter for what you are doing. Both pieces of information you have about the tach are correct. You can change the reading for 4 vs 6 cylinder but the pulse is different between EDIS and TFI.

If you ground the tach as a 4-cylinder and hook it up to the signal wire for a waste-spark system it will read double because it reads each four firings of the coil as a revolution and your coils fire twice for each cylinder each revolution. Technically four times per cylinder per revolution because of the dual plug head, but I am pretty sure it only looks at one coil.
 

kishy

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You will need some sort of signal converter for what you are doing. Both pieces of information you have about the tach are correct. You can change the reading for 4 vs 6 cylinder but the pulse is different between EDIS and TFI.

If you ground the tach as a 4-cylinder and hook it up to the signal wire for a waste-spark system it will read double because it reads each four firings of the coil as a revolution and your coils fire twice for each cylinder each revolution. Technically four times per cylinder per revolution because of the dual plug head, but I am pretty sure it only looks at one coil.
Good stuff!

So integrating the tach to make it read what Duraspark is doing should be no big deal. The step over to EDIS is where it gets messier.

Probably too optimistic to hope that the tach can be setup for 8 cylinder "traditional" operation, making the double reading from EDIS appear correct? (on second thought I might have that backwards)

Alternatively maybe there is a "half as much" signal somewhere in the harness between the module and the coilpacks...

Also is there a write-up somewhere about changing the tach to set the # of cylinders? Maybe it'll be obvious if I open that half of the cluster up. Google's not helping (querying this site), and usually when that happens it's either because what you're trying to do is so easy nobody has asked, or because it's so stupid nobody has tried :)

Big edit:

I have physical access to both the truck and cluster right now so I checked two things quickly:
-Started truck, it was idling at 1600RPM. Changed switch on existing generic tach to 6cyl, it changed to 1000RPM. Changed switch to 8cyl, it changed to 600RPM (give or take). So the relationship between 8 and 4 cylinders is not 1:2.

-Pulled tach out of new cluster. Found a resistor tightly wound around two posts on the PCB of the tach. The value of that resistor is how you change how the tach displays the signal it receives. Potentiometer to fine-tune it might be the way to go if there isn't a known list of values somewhere.

Related discussion: http://www.therangerstation.com/forums/showthread.php?t=135668

From the Q&A on the tach install write-up..."The EDIS (and waste spark) is going to make it read wrong. 1st Generation's didn't have either of those. They tripped off the coil primary wire." Yes...it's wrong. But can it be made right? Maybe...
 

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I would try to find the wire coming from the computer for the OE tach and hook up there just to see what happens. You might get lucky and have it read correctly from there but it still needs to be grounded correctly for the 4-cyl.

I will admit that I am sick and not thinking super clearly right now, so bear with me a bit.

The difficulties I pointed out are for installing an aftermarket tach that takes a signal from the coil firirng.

The computer-cleaned signal in your harness should come off a crank sensor. It may still read wonky though. My OE 87 tach reads less than double with my 4.0, but it is not accurate. It seems about right at idle, but never makes it above 2K, even if I am free revving.
 

kishy

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I was in a junkyard today and found a 1988 Ranger XLT, 2.3 EFI with the M5OD, with a tach! Unfortunately, the same woodgrain trim, so I couldn't get that.

The resistor is neatly wound around the posts like a factory job, and it's a different value than the one in my other tach. I haven't hit either one with an ohmmeter yet but I can see clear as day that the bands are different colours. Otherwise the tach looks to be the same. I'm assuming the "ground or not" decision for the extra contact peg is done by a wire being present or not in the harness.

The VIN decodes to 2.3 5-speed, so it wasn't a V6 truck that got swapped. I have no way of knowing whether the tach was swapped in after the fact by the previous owner, but this might be an indication that the "no tachs on the early 4 cylinders" thing might not be the case.

No real updates otherwise, just thought I'd mention this here.
 
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The best thing to do (and what the place I got my converter said to do) was to hook up the tach you want to use and a one that is known to work well (aftermarket,timing light with a tach etc) and compare the two readings and then get the converter that works for that.

I used Baker Electronix.

Me being me and thinking "it is easy, just figure the math" I figured it up and the tach was way off. My previous aftermarket one read perfect set at "8 cyl" but I think there is something in the factory tach that makes it read like a 4cyl even though it comes from a 6.

Unconfirmed but mine didn't pencil out like it should have, I tried two tachs, both off of V6 trucks. Both read 2x engine RPM without the converter, and IIRC read 1.5x engine RPM with the converter. I wanted the module in hand before I tore into the truck so it was wrong and I had to send it back in for a reprogram.

Playing with the resistance makes it read right at a certain RPM, its accuracy will degrade as it leaves that RPM.

Dunno about your different ignition though, since mine works in somewhat the same manor as an aftermarket one I think you will be able to get it to work though.
 
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