So I've been having lotsa problems recently with my rpms and the tach. It first started out where the car( h22 integra, stock p13, no cels) would revlimit at 6500 rpms, even though vtec engages fine, I had it diagnosed and the guy datalogged it and said for some reason it showed the rpms would drop to 0 around 6500 so that's why it would revlimit and drop out of Vtec, and also my tach was already jumpy. So I go home, and start replacing things, first thing was the Igniter, thought for sure it would fix it but no, no difference at all, tach still jumps and still revlimits at 6500 rpms, then changed the coil, then spark plugs, wires, cap/rotor, all the ignition stuff I could think of except for a new dizzy, only thing I have to try left. I was wondering what else could make the tach jump and have a problem reading rpms? Thanks for the help!

 

I had a very similar problem turned out the battery lead to the alternator was loose, i also heard that problem can be a bad alternator in general, have it tested.

 

Really, how does the alternator affect the tachometer? I had it tested when I first did my swap 2 months ago and they said it was fine. But I'll look into that. Anyone else got any suggestions?

 

your not throwing a CEL?

 

my tach used to jump around... until i replaced the dizzy.

 

my aftermarket tach jumps around when i have the windshield wipers on. lol

 

I think this would apply to you as well but im not sure. I had kindof the same problem with my integra. When i would start it, it would idle at 2500 cold and once it got to operating temp it would bounce between 1500 and 2000 up and down. I changed out a bunch of stuff as well. I finally found out that it was the fitv. Its a piece that bolts under the tb and controls the idle at startup and so on depending on the temp. When i took mine apart it was nasty dirty and the plunger was most of the way out and needed to be screwed back in. Here is a link to the write up i found. i hope this helps you out.
https://honda-tech.com/zerothread?id=1564019

 

yeah i had a similar problem when my alternator was going, tach and speed-o would jump, but eventually stopped moving all together so I got the alternator replaced and problem solved

 

Thanks for the replies, I'll try em. I know it's not the fitv though thats for idle, my car idles fine, the problem is reving through the rpm range, and yeah I'm not throwing a cel, said that in my first post.

 

could also be the ignition switch, or main relay,

does the car cut out when the tach jumps or no?

 

if your car chokes hardcore when the tach jumps, it's more than likely your ignitor. new distributor time

 

The car doesn't choke or cut out at all when the tach jumps, I can rev it up to 6500 rpm just fine with the tach jumping up and down but cuts out at 6500 rpm cause the ecu early rev limits the ecu cause it stops getting an rpm signal. But no the engine seams completely unaffected by the tach bouncing, mostly, it seems like it misfires a little, or is a little jerky but that's about it, but it will cut out of Vtec at 6500 rpm and the tach floats at 0 rpms straight down. Any more help anyone could offer would be nice!

 

i had this problem as well. even at times the RPM wouldnt work. replaced dizzy and that solved the problem!

 

Ok, yeah I've had a dizzy ordered but the shop I ordered it ffrom is having problems and is ending up taking 3 weeks for them to get it because it's backordered, he said it should come on next monday, I just hate waiting that long. Yeah the problem's getting worse, it only really happens at higher rpms, anything above 4k rpms, and it will bounce, and the higher it is the more crazy it will bounce, it's like the spark has to jump a gap somewhere or a signal is jumping a gap cause it's harder for it the higher the rpms are. Hopefully the new dizzy I ordered will fix this, I've already replaced everything in my own dizzy and checked all the connectivity of the wires and still no luck. Thanks to all the help everyone, I'll update when I get my new dizzy.

 

i had an alt go bad and mine did this. since the tach wire comes from the dizzy i would say it could be an issue too.

 

The only reason I can think of that the alternator could do is when it goes out doesn't give power to the battery, so when the batterie's almost dead, the tach starts bouncing, I've had this happen b4, but My alternator is charging my battery to 14.5volts and is always fully chaged, so I don't think it's the alternator. Getting a new dizzy is my last resort, then I'm broke too.