RPM with no tachometer

[Timothy]

I have been scratching my head trying to figure out how to measure RMSs with no tachometer. The closest I got was trying to find a volt meter that can measure it, but alas my parts store didn't have one.

Then I went to a mechanic who wanted to charge me $90 to check it.

Solution: I used the slow motion function on my phone. First I made sure my car was at operating temp. Then I then stuck a small square of brightly colored tape on center pulley. I then recorded for 15 seconds. I played back the video and counted the revolutions of the pulley marked by the bright tape and multiplied that number by 4. In my case I counted 199 revolutions times 4 equals 796 RPMs. A tad high. I think it is supposed to be at 750.

I think this works, let me know if anyone sees any potential problems with how I measured this.

[ryanprins13]

I have been scratching my head trying to figure out how to measure RMSs with no tachometer. The closest I got was trying to find a volt meter that can measure it, but alas my parts store didn't have one.

Then I went to a mechanic who wanted to charge me $90 to check it.

Solution: I used the slow motion function on my phone. First I made sure my car was at operating temp. Then I then stuck a small square of brightly colored tape on center pulley. I then recorded for 15 seconds. I played back the video and counted the revolutions of the pulley marked by the bright tape and multiplied that number by 4. In my case I counted 199 revolutions times 4 equals 796 RPMs. A tad high. I think it is supposed to be at 750.

I think this works, let me know if anyone sees any potential problems with how I measured this.

You can pick up a tach for like $20. You dont want to? I like having one.
I believe there is a wire that you can jumper and the engine will idle at 750 exactly. Then you can verify that your getting a correct reading from your phone. Im not sure on that though, hopefully someone else can tell me and you if im right.
Theres nothing wrong with 800rpm. I let mine idle at 900-1000.
750 is proper, lower probably isnt nice, but 750-1000 isnt going to have any negative effects.

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[Timothy]

750 is proper, lower probably isnt nice,

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Haha. You should of heard and seen my engine rattle about when i set it too low.

[FestYboy]

Manual trans cars should idle at 625-650, auto cars at 750-800 in park.

[Timothy]

Manual trans cars should idle at 625-650, auto cars at 750-800 in park.

Thanks for the numbers.

[FestYboy]

That being said: at madness, I was able to get "the astronaut's" stock carb b3 to idle under 400 without issue, and a few years back, Scrappy was at around 250 for fun before I swapped him. (Again, a carb b3). I don't think an EFI can get quite as low in most cases, but sub 500 should be attainable.

[WmWatt]

Haynes manual says 750 for manual "base idle". Not sure what that means but you're supposed to have the STI wire grounded. It's what they recommend when setting timing.

[Timothy]

What is a STI wire? I googled it but all I find is something to do with Subaru's.

[dalebwilson]

RPM with no tachometer

The ST1 wire is a single wire with black connector near the brake booster. Do not mistake it for the single wire with the white connector which is for RPM signal. By grounding ST1, the engine is now in diagnostic mode and base timing and idle should be set while the engine is warm. CEL codes can also be checked while ST1 is grounded.


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[firebush357]

I have never adjusted mine but it seems to sit at around 1000 from what I can see on my $15 Tach.

[Timothy]

The ST1 wire is a single wire with black connector near the brake booster. Do not mistake it for the single wire with the white connector which is for RPM signal. By grounding ST1, the engine is now in diagnostic mode and base timing and idle should be set while the engine is warm. CEL codes can also be checked while ST1 is grounded.


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Thanks for the info.

[TominMO]

Thanks for the info.

Timothy, you need to get a Haynes manual for Festivas. Everything you have been told is in there, and lots of other info and pics. It'll save you a lot of time and trouble.

[Timothy]

Timothy, you need to get a Haynes manual for Festivas. Everything you have been told is in there, and lots of other info and pics. It'll save you a lot of time and trouble.

I ordered one from half.com for $2.30. I waited for it to be shipped and just got an email that the seller couldn't ship so I got a refund. I'll have to try again.

[ryanprins13]

There are quite valuable. This is what mine looks like now.

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[WmWatt]

I help my manual last by photocopying the pages I need for a repair so the manual itself doesn't get dog eared and dirty.