Factory tachs 101...the real deal.

[bigblock73]

OK folks, with Daves permission, and both his help and Kens, here is a tech article on factory tachs!

http://www.73-87.com/7387garage/inte...achometers.htm

I am now on the hunt for different gauge cluster pics with tachs...so if you got em (and if you KNOW what year it is), please post a pic or two and tell me what they are from.

Thanks Dave and Ken, this will be a time saver for sure when people start asking about them.

[swervin ervin]

Looks good, but let me be a critic for a minute.

You need to change the info about all 86 trucks having feedback carbs. Not true. None of our trucks had feedback carbs except for the ones in California. Unless your truck was built for California, the later Q-jets had the dual capacity pump system only. None of our trucks were computer controlled except for California trucks.

Mike

[bigblock73]

Thanks Mike

I got that info from Dave, maybe he will chime in and put his .02 in the pot. I have no clue on this, I am strictly going by what I hear from the people who know.

Dave?

[apstguy]

Let me also add that the 81-87 California truck did NOT ever come with a factory tach dash. California is special - we get all the crap!

Mike -were all 85 & 86 electronic carbs dual capacity pump? I can't tell if mine is or not.

[swervin ervin]

Yes. I'm not sure on how far back it goes, but I do know 85 and 86 was.

Edit: I seen where you said Electronic carbs. I'm not sure if the computer controlled carbs had the dual capacity pump or not. I'm thinking not. I'm speaking of non computer controlled ones. They came with the dual capacity pump system only. Just one wire coming from the sensor in the thermostat housing to the solenoid in the carb. This I know for a fact.

[apstguy]

I looked in the Rodchester carb. book I have and it says ALL 85-86 chevy trucks came w/ electronic carbs and dual capacity pumps, but I don't trust it. It shows the electronic carb and the solenoid has extra wire coming out of it for the dual capacity pump on it that mine doesn't have. It is weird as everything else is identical.

[BladeX]

Is there a better detailed guide on how to install gauges? or is 73-87's the best guide there is?

I wanted an RPM gauge that'd be nice.

[swervin ervin]

Sorry, don't know where my brain was. Yes, it was only used in 85/86 trucks. It's important to remember, electronic controlled is not the same as only having the dual capacity pump system.

Computer controlled Q-jets have the idle mixture control solenoid too.

[apstguy]

And a TPS. I don't think mine is dual capacity, but I would probably have to take it apart to find out. I think this is one of those gray areas that no one can give a definitive answer to. I'm guessing there were 3 different carbs on these trucks then. Non-computer dual-capacity, computer dual capacity, & computer single capacity. Odd.

[79BIG10]

Originally posted by BladeX
Is there a better detailed guide on how to install gauges? or is 73-87's the best guide there is?

I wanted an RPM gauge that'd be nice.

You can install any tach for your truck. You can mount them on the column, dash etc. Now to get one like the factory style that is where 73-87.com comes in. Also in the Garage section of the site there is 2 versions on how to install aftermarket gauges.

[apstguy]

Sorry about hijacking the thread

[BladeX]

the only ones i saw were clusters not like dash mounted ones.

linkage? 73- 87 garage section. maybe im blind.

[bigblock73]

Originally posted by BladeX
the only ones i saw were clusters not like dash mounted ones.

linkage? 73- 87 garage section. maybe im blind.

Here ya go buddy.

[BladeX]

i was thinking bout a single individual gauge thats mounted on top of the dash , not in the actual cluster itself.

[79BIG10]

Oh ok. Those people just mount them anywhere they want to and are very eas to wire in. One ignition power wire, one ground, one lead to the distributor and finally the last wire to your light switch. This is to light the tach up when you turn on your lights.

[BladeX]

rocket science i dont speak electrcian.

i dont know to even "hook" them up..

lol im mad n00b.

[79BIG10]

If you buy an aftermekt tach they will come with instructions. Most of your tachs are wired like this

Red- Ignition power (when you turn over the key it gets power)
Black- Ground (attach to metal to complete the "circuit")
White- This one connects to the conneection to your lights (I used the wire I had for my old radio that had backlit).
Green- This wire goes into the engine bay and on the driver side of the distributor. There is a place in the cap for this.

[BladeX]

k you rock much easier to understand.

btw i was lookin around its like 25 bucks per 2 5/8th guage? that seems kinda pricey no?

[BladeX]

bump

[bigblock73]

Originally posted by BladeX
k you rock much easier to understand.

btw i was lookin around its like 25 bucks per 2 5/8th guage? that seems kinda pricey no?

I don't think so, but it depends on the brand. I myself like Autometer gauges.

[Prerunner1982]

the sunpro tacks are usually about $25, they arent the big racing tachs or anything, my sunpro has a 3" face diameter. and new.. many moons ago it was $25..

[crossy]

aptsguy & swervin, thanx for that 85-86 input and i have said all along that i am by no means an automotive tech. I would rather be safe than sorry and always have steered people with stock 86's that have stock carbs/ignition & emissions away from factory tachs because of the VSS issue. out of the 5 or 6 of 85's I've had only one had a feedback carb and all the 86's did. the Feedback QJ's have the MCS(mixture control solenoid) sticking out the top of the carb. Does this or does it NOT (I truly don't know) get it's 'feedback' from an ECM that gets info from a VSS like an EFI 87 does?? I do know that when the MCS gets back or bad signals it goes Full rich and although the truck will still run OK it is miserable on fuel mileage & aceleration. I'm NOT a tach god ,just a bit of a guru. DAVE

[swervin ervin]

Dave,

I think you are confusing the dual capacity pump solenoid for a MCS. True, it's in the same place as the MCS, but all it does is control fuel flow to the accelerator pump. The sensor in the thermostat housing sends a signal to the solenoid when coolant temps reach around 160-170 degrees. This then energizes the solenoid and the pump valve opens reducing the amount of fuel going to the accelerator pump by 1/2 the volume. This is all this is for. I'm not sure on GM's reason for this in 85/86 but I'm sure it has something to do with emissions. I figure this is the reason it was only in 85/86, right before they went to TBI.

I've never seen a computer controlled 85/86 pickup. Only heard about them from the guys in California. There were no computers installed in any of these trucks until 87, except for the ones built for California. Most folks think the wire going to the carb makes it a feedback carb. Then they see the wires going to the ESC and also believe it is a computer.

Just so folks know, if you disconnect the sensor going to the pump solenoid, it will be in the dual capacity pump mode all the time, thus wasting gas. This needs to be hooked up and working. I bet there are a lot of owners who have removed this and wonder why they don't get good gas mileage.

[apstguy]

Here is the picture in question - Everything is identical to the bottom figure except the wire & connector B. I believe this would be dual/computer while the top figure is dual/non computer.