Tach bounces at High RPM

I've run into a strange problem at my first two events this year with my '84 Civic ITC. Haven't changed anything on the car since last fall except for the air in the tires. I basically rolled the car off the trailer after last year (where it ran fine with no problems) performed the basic mechanical maintenance, (oil, filters, brakes, mechanical inspection of suspension & hubs, etc.) and now I have a problem. The car sat outside over the winter here in Wisconsin (cocooned in several layers of plastic/car cover).

At high RPM in 3rd gear (6000-6500) my tach starts to bounce around +/-300 RPM. I can't feel or hear an engine miss, but I can't really be sure. I can't see the problem in second gear, but I also don't spend a lot of time in second gear (downshift, buzz the motor, upshift). The plug wires are MSD and are relatively new as are the coil, distributor cap, and rotor (all stock factory stuff). Plugs look ok. I thought I found a loose plug cap (that aluminum screw thingy on the end of the plug) and tightened them all down but I didn't seem to make a difference.

The only thing that I have ever seen that caused a similar problem was when I had a plug wire fall off during a practice session several years ago. The tach would bounce around all over the place, probably due to electrical interference. That was an obvious problem since the car was only running on three cylinders.

I'll start by changing plugs and wires first since these are easy changes.

I am suspicious of my electrical connections i.e. moisture, corrosion, etc. This will also get checked, cleaned, and sealed with dielectric grease. The car is carb'd so it doesn't have a brain box. I only run the mechanical advance, no vacuum advance.

Anybody had a similar problem and solution?

We had a problem like this at the end of last year. The tach was basically useless above 4-5K. It turned out it was the distributor/rotor going bad.

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Kevin
R2 Racing
'01 CenDiv ITC Champs

I concure. Honda has had problems with the main shaft wearing out on the distributor (usually high milage vehicles) that will effect performance. The tach will go all crazy on the top end. 2nd gen Integras (90-93) actually have a secret recall on the entire distributor (less igniter & coil) on these models, and that they will replace it for free (here in Canada anyway).

They replaced the distributor on my '93 GSR for free http://Forums.ImprovedTouring.com/it/smile.gif

[This message has been edited by racer-025 (edited May 13, 2002).]

I had the same problem with the Nissan Z20 motor. The final fix was replacing the steel gear on the end of the distributor with a bronze one.

The cap, rotor, and coil are relatively new. I replaced them about 1 year ago when I was trying to fix another unrelated problem. I will pull them of and check for corrosion.

Regarding the mechanical aspect of the distributor, would this just effect the tach and nothing else, or would it also cause a drop in power and/or a high speed miss? I don't feel or hear the engine running rough and based on my lap times it feels like it's making the same power as before.

Back in the late '70's my father raced an SSB Mazda RX3. We found that due to the high RPM's turned on that engine and the speed at which the distributor turns relative to engine speed, the distributor bearings would wear out and cause a lot of contact bounce which resulted in a slight loss in power. But the tach would read fine and you couldn't feel or hear a miss. The car just had less power. This made a lot of sense on a car with mechanical points, but is this still the case today with solid state ignition? Or is it possible that I am loosing power and just don't notice it since it has been a gradual drop off?

The distributor is out of my original racecar (130K street miles, 30+ races as a SSC car, 50+ races as a ITB car, 30+ races as an ITC car) so I can definitely believe the bearings are worn out.

I'll give that a shot and post my findings.

Thanks to everyone for the advice!

My Integra did have a loss in performance when the VTEC was engaged (above 5600rpm). It seemed to be a hesitation in spark. It really had no problems (except the tach problem) under that rpm level. However, the average driver would not "feel" the difference, but since my engine saw 8000rpm daily and at least 8500 (rev limit) per week, I noticed the difference big time. I did have a igniter problem previously and it was replace. The coil was fine. As soon as the distributor was replaced, the tach problem was solved.

Deja vu?

I just finished replacing my entire distributor in a effort to shotgun fix the problems that I have been experiencing. Here's the progression of troubles I had last week:

1) Shift light starts blinking, dimly and randomly and then increasing in brightness and in frequency.

2) After three more laps, and in addition to the shift light, the factory tach starts bouncing around between 3k and 5k - starting slightly and then getting worse.

3) Only know did I start to feel a hesitation or bogging as I went into the throttle. Lost all ability to continue a competative race and called it quits.

Several opinions mentioned the ignitor as a weak link in the distributor and others questioned the coil... I replaced the whole thing. I haven't been back out yet, but bringing it up to my 6500 shift point reveales a steady tach, operating shift light and no engine hesitation.

I appreciate all of the responses. A lot of the posts have dealt with late model Honda's but I guess they apply to my older '84 Civic as well. I'll look into rebuilding the distributor internals (pick-up, bearings, ignitor, etc.) or replacing the whole thing with a new unit. I have to look at my shop manual and see what is 'serviceable' on that unit for my model car.

Just my 2 cents: Check and/or clean your ground wires.

My story:
I have a 90 CRX Si, and experienced a very similar problem to what you're having. I know my car is newer, but the problem sounded so familiar I had to respond. The tach just started bouncing around, but with no apparent sufferings on performance. After a while the car did suffer, and eventually quit.

The problem started after having it serviced by a regular "mom and pop" shop for routine mantainence. In trying to resolve the problem I had the car diagnosted by certified Honda techs. and had the distributor replaced. Unfortunately, this too did not solve the problem. It turned out to be a ground wire that was knocked off by the first service station. GRRRR! This was only discovered after much money and time was spent. I suppose It's possible that not having a proper ground caused my distributor to burn out, right?

As an aside: I have since bought a house with a garage and try to do most my own work. (insert appropriate whacky smile here)

Dave
http://groups.yahoo.com/group/NERDS_racing

Round Two.

I have replaced the ignitor, stator, and pick-up. I replaced the spark plugs. Still have same problem. Next items to try will be to replace cap and rotor (these are one year old and looked okay but who knows). I will also go over every ground connection this weekend with a wire brush and silicone (electrical) grease. I have four more plugs wires I can build up (my MSD kit was for an 8-cyl). Any other siggestions? The inside of the distributor (bearings, mechanical advance, etc.) all seemed fine. I could detect any slop.

This is a 84 Civic (carb's) with stock tach, no brain box. There isn't much else to replace. Could the problem be the tach itself? Anyway to test this besides replacing the instrument cluster? There was one left in the boneyard last week so I can get one for next to nothing.

One last note, we have had a very, very cold & wet season so far this year in Cen-Div (Global warming my ass!) I thought the problem might be moisture/corrosion related. I have used silicone spray & grease on the inside of the cap, rotor, and plug wires. I noticed that the problem seemed worse when the weather was dry. The tach didn't bounce as bad in the rain.