Why is my tach needle jumping [Merged 9-9] tachometer jump

[Birt96gst]

While I'm driving my tach will start to jump around and my car will start jolt real bad
need help.

Would a CAS thats shorting out cause this or a cloged fuel filter or maybe just maye a cracked intake manifold?

need help fast need my car to get to work tomarrow

THANK YOU

 

[robs90tsi]

Well do you have any of those problems you mentioned?? Also, what is your setup on your vehicle, what mods do you have and how many psi of boost are you running?

 

[96gsdsm]

Could easily be a fuel pump relay going bad, mine went out, thought my fuel pump was bad or my lines were clogged, as soon as I replaced it it ran right as rain. there only like $5 or something and easy as pie to replace ... good luck man

 

[Birt96gst]

my mods are in my profile and the problem is both the tach jumping up and down but not the actual rpms of the motor then about a minute or less after it starts that the car starts to jolt like crazy

the only way I can explain the jolting is like if you hit a curb or speed bump every other second

Mods are listed as follow if you dont feel like lookin
6bolt block
1g big rods
2g pistons .040. over
2g head ported and polished
greddy type S BOV
Upper and lower intercooler piping
14b turbo
magniflow exhuast

 

[96gsdsm]

What your describing sounds very much like an electrical problem, and will probably be very hard to pinpoint and diagnose. I would have to agree with your origional thought of a CAS, but I doubt it would be shorting, my guess is that when your motor was removed for rebuilding someone was either careless with your wiring harness during removal/installiation, or didnt put it back into place properly ... causing a constant rubbing that eventually lead to a short. Thats the exact reason why rubber/plastic grommits are used even for huge 0 gauge wires running through a firewall... it's eventually going to rub off the rubber coat and short. Try visually inspecting your harness as best you can, maby you'll get lucky and find it, and be sure to pay special attention to metal contact points. ... let the search begin

 

[Birt96gst]

my wire job of my CAS was not the very best and when I got it 2 of the wires were exposed at the spot that they come out of the CAS I tried my best to wrap them but I don't think it worked and the remaining wires 2 crack and are now exposed

 

[96gsdsm]

Well there you go man, maby there's moisture trapped inside or maby the wires end up hitting each other somehow in that not too good CAS job.... i would recomend you very carefully remove that tape wrap job (because in a hot engine bay thats definately a ) make sure that all the wires to the CAS are all attatched properly, if not you would want to soldier them back in place (If you don't know how just google it, it's really easy) and when everything is connected properly, paint on some of that liquid electrical tape ... you can pick it up at most local hardware stores or maby, if your lucky, a local automotive store, that should keep a tight seal, and doesnt melt like tape ... good luck

 

[madman]

For a couple weeks now my tach needle is jumping all over the place, my AFC doesn't even register a RPM singnal anymore (not good because it's not making any fuel corrections ) and my car will ocasionaly sputter and give a p0300, multilple missfire, cel, actaully that problem is starting to happen more and more not.

I'm going to take the dash apart tomarrow and check the wires but since I've been searching, I ran across the CAS maybe being an issue. Any thoughts?

Also, if I have a bad CAS would the screw with my timing?

 

[kspharris]

I know that the CAS does mess with the timing. Mine was wayyy off one time and took me forever to figure it out.

 

[Arrow_Runner]

When my CAS was going out, the tach would sometimes randomly drop to 0 rpm for just a split second.

 

[madman]

Could this also affect my vacuum pressure?

 

[madman]

I thought I would update the thread.

Turns out that all my problems were non-related.

The tach needle was jumping becuase of a loose/bad connection were the MAF-T splices into the tach wire at the intake manifold. Fixing this did solve my p0300 issue.

The AFC wasn't registering RPM's becuase of a loose/bad connection at the ECU.

 

[boogst]

i have been searching the site for 2 hours now and can't come up with exactly what's wrong with my car.

first off my mods are in the profile. but i have a basically stock 95 2ga, t25 turbo, 10-12psi.

yesterday it started to do this...

above 4k the tach will jump around. either go under 4k rpm them up. or go above 4k rpm sometimes bury itself. usually it's at wot. while driving normal it is fine MOST of the time. every once in a while it will bog and the tach will jump around again. but it's mostly above 4k rpm. if i drive normal, get to 4k rpm and shift it will do the same thing. every once in a while at a red light my idle of 750-800 will drop all the way down to 0 like it wants to die out.

so this is why i am confused... i read posts that said it could be spark plugs and wires. coil pack. sensors. and some say it could be the clutch.

i just put ngk plug wires on a month ago w/ ngk +1 cold plugs... i replaced the plugs today because i thought maybe i fouled them out for using +1 when i don't need them. so after i put new plugs in i took it for a drive to see if that would fix it and it didn't. and when i got home to open the hood to check for things a little bit of smoke was coming out. but i drove for 15 minutes, lots of spirited driving to see if it would do it again and to check other things... so i don't know. like i said at 4g rpm + is when it will bogg and the tach goes crazy. i heard a banging type noise at the same time. could this be KNOCK SENSOR??? i do have the famous lifter tick btw.

did a boost leak test at 20psi a few days ago and had no leaks. it doesn't seem like a boost leak... the tach is jumping!!

i've been worried about the clutch a little.. it does seem like it slips every once in a while. but i haven't smelled burnt clutch. my friend w/ a 1g just burnt his up after 3days of having it so i know the smell real well, .

i don't know what it is and i'm frustrated. i already had to get a starter monday because it came apart. one bolt fell off, 1 gear was missing. , don't ask. then wed. i broke my passenger window so i had to get a window.. then tinted it to match all my windows., first time tinting my self. so i already put $200 into this damn thing this week. not to mention i ordered a hallman es mbc, and a 34mm flapper for my 16g turbo build that i've been trying to do but little stupid things keep coming up or i'm spending money on stupid little things so it's taking me forever to gather all the parts. .

thanks for your time. any help would be much appreciated!

and i figured i would bold some keep points for people that don't want to read everything i put!!

 

[pj91gsx]

Do you have a cel on?

 

[95turbo4life]

I had the same problem with my rpm's jumping in my car. Your transistor pack (as it is labeled) or your ignition control module (as it is called to find the part for it) is either going out or not fully connected. When mine were jumping I would take the connection apart and just blow in the clip to clean it out and the rpms would not jump anymore. The connection is located just to the left of the coil packs. It is a 7 prong connection when you take it off. It should have 3 prongs a space and 4 prongs. Either replace the ICM or clean the connection with some spray from autozone. Let me know how that works for you.

 

[stevo911]

Your ECU is leaking caps pop the ecu out, Pop the cover and look for caps leaking on the board willing to bet its gone.

 

[95turbo4life]

I didn't understand anything you just said but yes you can take your ecu out and look at it to see if anything is melted or burnt. If not make sure to check the ICM like i stated earlier because that was my issue with my tach.

 

[1gDSM4g63]

The tachometer jumps around when I'm holding a stable throttle, i.e. when I'm cruising at 3000 rpm it'll jump back a forth from 3000-3500 rpm after I rebuilt my car.

Don't know if this is due to switching from stock throttle body to a Q45 80mm throttle body without the ISC or it's the 90' gauge cluster. I even replaced my ignition control module, but it still jumps around on my tach, although when I log it on DSM Link it stays stable.

Anybody know what I should check?

 

[steve]

Are you running a 91+ ECU?

 

[1gDSM4g63]

No, I'm running a 90' ECU with DSM Link. There must be something wrong with the gauge cluster. Even though the tachometer is jumped around, the DSM Link log show a stable rpm.

 

[steve]

The ECU RPM count is from the CAS but the Gauge is from the output of the Tach Gate on the 90 coil pack. That signal is conditioned by the 90 noise filter before going to the gauge and ECU.

 

[dees75z]

The ECU RPM count is from the CAS but the Gauge is from the output of the Tach Gate on the 90 coil pack. That signal is conditioned by the 90 noise filter before going to the gauge and ECU.

I think this noise filter is the one bolted to the vacuum distribution bracket on the back of the block???Correct??

 

[1gDSM4g63]

Virtual Tour of a 1G DSM Engine Bay: Noise Condenser

What should I be look for? Replacement?

 

[steve]

That's not it. The noise filter in question is specific to the 90 and I believe bolted to the intake manifold.

 

[tunethis]

I think this noise filter is the one bolted to the vacuum distribution bracket on the back of the block???Correct??

Yes, this is correct.