I have a problem with my rpm gauge. It works normally under most conditions howerver if im in 3rd gear or higher after 5k Rpm its erratic and bouncy. I cant seem to notice it doing this while in neutral 1st or second gear. any idea what can cause this?


Already been changed:

Dizzy cap
Dizzy rotor
Coil
plugs


thanks

 

Hey there, what you've got there is most likely a VSS (speed sensor) on it's way out, or a short in the wires/dash harness/cluster. best thing to do is pick up a vss for it, see if that fixes it, if not, you'll need to trace your lines and check for breaks/fraying. The VSS units tend to break down over time from heat (the grease inside the unit burns and dries out) from the transmission during high rpm driving. Hope that helps (you can find $20 aftermarket vss on ebay if you dont wanna shell out to honda in hawaii, yes I know it's muchmore expensive there)..oh, and greetings from Hilo!

Edit: Now I feel dumb...mixing up gauges like that

 

VSS affects the speedometer from what i understand and RPM is read from your coil everytime its fires so much is each 1k rpm. if im wrong correct me thanks. Im from puna side originally

 

lol, you're quite right...my bad. in that case, when you say you replaced the dizzy parts, is it a whole brand new unit, or did you reuse the position sensors and/or shaft from the old one?

Update: i looked closer and saw that you only changed cap/rotor/coil....you have a bad internal sensor assembly OR too much oxidation on the rotor wheels (sprial/toothed cogs)...youre not getting a good read off the internals anyhow

 

the FSM states on page 11-62 that the crank position sensor detects engine rpm...you should open up the dizzy and check the wires going to the CRANK sensor, and also check the distributor plugs for damage to the connections there. also, when i was forced to replace the shaft oil seal inside my distributor, i found that the oil had swollen and degraded the sheath on the sensor wires leaving the copper bare and covered in oil...screwed with all sorts of things..i ended up dousing the sensor wires and such with electronics cleaner until all the oil was gone, then separating the wires so there was proper clearance between them, then coating them in liquid electrical tape and allowing them to fully dry before reassembling the dizzy. so you might have a similar situation there.

Edit: CRANK sensor is the second one down that aligns with the rotor with the most teeth (looks like a standard gear config)

2x Edit: also this post: https://honda-tech.com/forums/honda-prelude-4/fluctuating-tachometer-i-increase-speed-2360565/

 

great! thanks! i am not to familiar with the insides of the dizzy and im trying to get away from buying a dizzy they are pretty expensive even on ebay. I was actually gonna try replacing my igniter next but maybe i should try the things u mentioned first

 

good luck man.

 

Make sure the ground wire bolted on the thermostat housing is tight...I had the exact issue.

 

thanks ill check that too. I actually had it not hooked up at all when i first put my new build together and my car wouldn't start at all, no fuel pump. so im pretty sure its tight. also i already took my dizzy apart last night and the main shaft that triggers the magnetic sensor was rusty so i sanded it down using 220 sand paper its nice and smooth metal now. Just need to get on a highway to test ill post my results once i fix this issue

 

The tach signal is based off a signal sent from the ignitor (ICM/ignition control module) located inside the distributor. It's usually a blue wire.....

A jumping tach is usually a sign of a failing ignitor or dirty, loose, worn wires or connectors.

Did you replace the ignitor or try to clean up all the contacts on the ignitor while you were into the distributor?

 

I did clean the contacts. Unfortunately i don't have a compatible ignitor. My dizzy is a TEC and I had a HITACHI ignitor which is built slightly different. thanks for the info

 

Is your voltage stable? Check alt.

 

UPDATE:Finally had a chance to do some 3rd and 4th gear pulls. RPM Gauge works Perfectly!


Cleaned contact on Crank Position sensor and The main shaft (which triggers CPS) was rusty which was also cleaned with 220 grit. I did also tighten up the connections going to the ignitor and cleaned contacts at coil. Cant say which one exactly it was since all were don't at the same time. But i do believe it was something with the crank position sensor, its just what i think, as long as it works im happy


Thankyou ALL