[Slick Nick]

My taco like most others came with just a speedo and no tach so I bought a cluster a while ago from same year truck but it turns out that it was for a 6cyl and not a 4cyl. So instead of revving to 5500 it only revs to 3500rpms. I have been looking for the past year for a cluster with a tach for a 4cyl and for the life of me cant find one. Well I did on ebay but some jackass outbid me in litterally the last 2secs and paid way too much for it (120 bucks). Well i really want my damn tach to read the correct rpms so is there a way to make this one work or do I need to find a cluster for a 4cyl? If thats so does anyone know where I can find one?

 

[Chris D.]

the truck itself wont rev past 3500 or the tach itself?

I read somewhere, maybe on here where someone was able to mod the tach dignal to make it work..

but for the life of me I cant find it.. anyone?

 

[Slick Nick]

the truck itself wont rev past 3500 or the tach itself?

I read somewhere, maybe on here where someone was able to mod the tach dignal to make it work..

but for the life of me I cant find it.. anyone?

No the damn tach wont rev past 3500 but im sure the engine rpms are actually 5500. I did the math and its pretty close to 2/3 what it should be. Makes sense since a 4cyl is 2/3 of a 6cyl.

 

[Slick Nick]

so if its only reading 2/3 of the electrical impulses from the ignition shouldnt there be a way to change that?

 

[Enola Gaia]

I've seen it claimed that it may be possible to do a workable 'conversion' by replacing a resistor somewhere on the circuit board. I don't know for sure if anyone's proven this to (a) work and (b) be cost-effective.

 

[Slick Nick]

Is there anyone in CT thats done that or know of anyone thats done it?

 

[Enola Gaia]

Check with the guys who've been recently discussing this ...

http://www.customtacos.com/forum/showthread.php?t=105789

 

[Enola Gaia]

You might also contact CT-zen yosh2000 to see if he ever found a way to convert / modify his transplanted cluster ....

http://www.customtacos.com/forum/showthread.php?t=80469

 

[yosh2000]

nope, never found a way, rolled the truck before i had a chance!!

the tach does get the impulses from the motor, and you are correct, it is 2/3 of the actual rpms cause it was from a V6. enola is correct, you are going to want to change the resistance somehow, but dont ask me how specifically, i have no idea on the cluster.

only thing i can think of is to install a pot meter. that way you could drive at what you know is close to redline and adjust the pot to read correctly? again, dont ask me how or where to install the pot, i dont know. but i do know the pot will vary the resistance and allow you to dial in the correct rpms.

i know i didnt give you much, but hopefully i helped point you in the right direction!

 

[Slick Nick]

What kind of shop might have the knowhow or the ability to do something like this?

 

[Chris D.]

automotive electrical shop, search the yellows for speedometor repair or something along those lines..

 

[Slick Nick]

automotive electrical shop, search the yellows for speedometor repair or something along those lines..

Thanks Chris...are there any names that you know of that might be reputable?

 

[Chris D.]

I remember reading on a few sites here and there when searching for the same basic thing reguarding tach drives by a place in Stockton CA called Speedometor electric..

 

[Slick Nick]

I remember reading on a few sites here and there when searching for the same basic thing reguarding tach drives by a place in Stockton CA called Speedometor electric..

Thanks I will check into it tomorrow.

 

[Enola Gaia]

I did some digging on this issue to try and get to the bottom of it ...

... and I'm starting to think the whole 'resistor to correct for a 4 / 6 tach swap' thing is an urban legend.

The reason is because I've consistently found two things:

- *Nobody* who's recommended a resistor trick for the purposes of correcting the tach in a 4 / 6 instrument cluster swap can claim (or point to) an instance of it actually being done *for that purpose*.

- The only *actual* tach-related resistor mod I can find was developed for adapting a *6-cylinder* tach to give correct readings after swapping in a different *6-cylinder* engine.

If you go over to YotaTech and track down the thread(s) on a 3.0 3VZ - to - 3.4 5VZ (6 to 6) swap on a PreTaco done by YT member Mt Goat, you'll find a detailed description (with pics) on adding a resistor to the tach circuit so the OEM tach will read correctly off the 5VZ's sensor / circuit. The addition of the resistor was done to sort of 'recalibrate' for the voltage on the tach line, not the 'number of pulses'.

Mt Goat (and others @ YT and / or TTORA) refer back to the Pirate 4X4 FAQ, which lists such a resistor mod - still **for the specific purpose of adapting an older 3VZ-related cluster to read rpm's on a swapped-in 5VZ**.

This mod has apparently worked multiple times for this '6 / 6' swap. I've found mentions / suggestions at other forums (like here on CT) that resistor modding should help with a '4 / 6' swap. In *no* case have I located an actual report of it being done and / or working for a 4 / 6 swap (of either engine or cluster).

I'm not saying I've reviewed every possible server / forum / thread on the whole 'Net. I'm just saying that I spent long enough to convince myself that among Tacoma folks all tangible paths lead back to the Pirate 4X4 FAQ - never to anything proving this can (or has been) done with respect to a 4 / 6 swap.

... So I'm calling it an urban legend until someone steps up and provides substantive proof it *can* work or that it *has* worked for someone doing a 4 / 6 swap (engines or clusters). :thinking:

 

[02TACO7714]

v6's only rev to 3500? that seems really low.

 

[01rocktaco]

v6's only rev to 3500? that seems really low.

THIS is why you read a thread before posting in it :brickknoc

The tach is just showing that the engine is reving to 3,500 RPMs because the signal is different between a 4cyl and 6cyl. The engine is actually reving normally.

 

[02TACO7714]

i did read it, I thought that he meant the tach redlined at 3500. I just misunderstood... my bad

 

[yosh2000]

... So I'm calling it an urban legend until someone steps up and provides substantive proof it *can* work or that it *has* worked for someone doing a 4 / 6 swap (engines or clusters). :thinking:

but dont you think it is ironic that the rpms are exactly 2/3 of what they should be? this simple fact leads me to believe that the rpms have to be getting pulses or at least some timing. and therefore couldnt that timing be adjusted by more/less resistance?

not trying to argue w/ the great enola, just trying to hash this out....let me know what you think!

 

[Enola Gaia]

but dont you think it is ironic that the rpms are exactly 2/3 of what they should be? this simple fact leads me to believe that the rpms have to be getting pulses or at least some timing. and therefore couldnt that timing be adjusted by more/less resistance? ...

It's not ironic - it's entirely predictable. I suspect it's totally beside the point as well ... :thinking:

It seems to me the real issue is how (i.e., on what basis) the tach unit converts the incoming sensor signal into a measurement of rpm's to be displayed on the tach face (by moving the needle).

If the rpm's were 'computed' solely on the basis of the amount of voltage on the input line per se (e.g., 1200 millivolts = 1200 rpm's; 3500 millivolts = 3500 rpm's; etc.), then yes - I could see how manipulating the amount of voltage would affect the tach reading.

But I don't think that's what's going on here ... It seems to me the calculation is based on number of pulses - each one of which is recognized as a *change in voltage*, not an amount of voltage.

Changing the overall 'voltage throughput' on the incoming line shouldn't have any effect on the number of changes in voltage detected on the line (at least not until you reach some point where the modified voltage is such that the changes defining a 'pulse' become impossible to 'read').

To use a very crude analogy ... It seems to me that adding resistance might make the incoming signal 'weaker' (voltage-wise), but do nothing to change the rate at which the modified voltage fluctuates. 1200 'weaker' pulses would still be 1200 pulses counted (with whatever equivalent reading being displayed on the tach face).

I don't claim to know exactly how the circuit works, and I'd be happy to stand corrected ... At this point, though, I still can't see how modifying the line voltage is supposed to affect the number of 'pulses' (which I'm pretty sure is what's being used as the basis for the rpm reading).