Irratic Tach - no power

aplvlydrtybird

Registered User
Ok question for you guys. Driving the car last night on the way home from a friends, there is this little civic with underbody lights on it trying to plan with me in the turbo sc...so i "theoretically" dont turn down the opportunity, and walk all over him, but as i get to about the end of third i loose all power and she falls flat on her face.

Tach goes all over the place and has no power, but doesnt die.

Tach is still operation somewhat but doesnt follow the revs of the engine.

I limp it home and pull codes this morning

511- rom fail = car has a chip
212- loss of tach/spout circuit
216- coil 2 primary circuit fail

replaced the ICM because it seemed to be pretty common problem obviously. Didn't solve the problem. but now i have a spare. The icm is mounted on an aluminum bracket due to engine changes, and battery ground/engine to body ground is located at the bottom of the bracket where it is bolted to the head. I'm assuming there isn't a grounding issue, it has been this way for a while without problem.

Looked at the hb and it didnt appear to be wobbling any direction, and i completely pulled apart the wiring for the icm, crank and cam sensor to see if there was a wire fault. nothing appears to be wrong there.

Then i disconnected the battery in an attempt to clear codes, left it off for about 2 minutes, then unplugged the cam sensor and started again. tach obviously wan;t working and it seemed to have a little better response, but still not great, so i am wondering if it is the cam sensor im looking at or not. i wasnt sure if the sensor was pulled and is supposed to run great or not.

Any help would be appreciated, i kind of have to figure it out cause i am hoping to go to the iowa sc/gtp clash on saturday. perfec timing
 
When my harmonic balancer was wobbling and ready to let go it damaged the crank sensor and caused a similar scenario. It would idle ,but, had very little power. It gradually got worse til it was evident what the problem was. Tach also would drop out and come right back. I replaced my balancer, crank sensor and cam sensor together. May not be your problem ,but, I'd check it out anyway.
 
i guess not 100%, but it was brand new I picked up a cam sensor for s&g's worst case its preventative...i will put it in later let you all know
 
put in the new cam sensor let it run for a couple of minutes and nothing changed does it need to idle for an extended period of time to relearn???

could this be a crank sensor???

i stared at the balancer again and it still doesn't appear to be moving
 
Since you've done a bunch of mods. You should check to make sure your crank sensor wasn't damaged from being mounted without sufficient tolerance. I would also consider that the vane (bolted to the back of the balancer) may have come loose (since you've probably had it on and off) and hit the crank sensor.

Note that the failure mode with the cranks sensor failing is simply no ignition. Without the crank sensor the DIS and the EEC can not figure out when any cylinder is at top dead center, so it won't fire anything.

I would check to make sure the vane on the back of the balancer isn't loose, and make sure the sensor isn't damaged. You should be able to get at it pretty easy if you lay under the car and work from the bottom. (assuming turbo piping isn't in the way).

I would check all your wiring as well, In particular the main harness piece that runs from the coil pack, under the blower to the crank sensor, to the dis module, and around the block to the passenger side firewall. Make sure some heat didn't get on it and damage something.
 
I would check all your wiring as well, In particular the main harness piece that runs from the coil pack, under the blower to the crank sensor, to the dis module, and around the block to the passenger side firewall. Make sure some heat didn't get on it and damage something.

I was thinking that there might be a problem with the wiring, so i will contact Ryan Sunquist to see if he has a good harness.

I will check the balancer again, today wasn't all that fun working in the pouring rain. i can get my hands on it from up top too.
 
checked the balancer again, doesnt appear to be loose, the back metal ring that the ckp gets its signal from is tight. i took out the ckp and it doesnt have any physical damage.

and there are 2 cylinders not sending spark at all and its the two furthest most to the drivers side. pulled the wire while driving and nothing coming out of em, all the others work fine.

so i can imagine its either the wiring or a defective coil. but could a coil do that to the tach??? cause it to not operate properly? everything acts like a dis but i have a new one on and still no difference. thats why im suspecting a wiring.

only other thing i have done recently is clean out my k&n and "recharge" it, but i did pull the maf and nothing changed.
 
Last edited:
The coil does send a back feed signal to the DIS which sends it to the EEC for system monitoring. Either you have two bad plug wires or the coil pack could be shot, but the cylinders affected would normally be the pair thats side by side on the coil pack.

To add to the crank sensor failure, you won't get fuel either as it is used to control injector timing... no signal, no injector firing.

I had one car here that had an intermittent crank sensor. It would run but like crap and would stall alot etc, then run fine for awhile. New sensor, all problems went bye-bye.

Fraser
 
but the cylinders affected would normally be the pair thats side by side on the coil pack.

To add to the crank sensor failure, you won't get fuel either as it is used to control injector timing... no signal, no injector firing
Fraser

Yes the two coils that are not firing are side by side, so i will try and put a coil in tonight, we'll see what happens, either that or could be some faulty wiring.

it doesn't stall on me, i limped it home Saturday night for 20 miles or so. barely made it but didn't die on me. so that's why Im guessing not a crank sensor.
 
still no spark on the same two cylinders after replacing the coil with a motorcraft coil, any other guesses besides wiring? i have to review my schematic again and see what im missing.
 
still no spark on the same two cylinders after replacing the coil with a motorcraft coil, any other guesses besides wiring? i have to review my schematic again and see what im missing.

I have a EEc-IV breakout box that you could borrow if you want to do some troubleshooting without piercing so many wires.
Coil gets it's commands from the DIS. It gets it's supply voltage from the ICRM. If one coil isn't firing, it could be the wire that goes to that coil. See if these diagrams let you figure out the wire. Then you could check for voltage drop and continuity for the wire from the DIS module to the Coil pack.

Coil 1 fires cylinders 1 and 5
Coil 2 fires cylinders 3 and 4
Coil 3 fires cylinders 2 and 6

I have no idea what two farthest most from drivers side means. No set on one side of the engine share the same coil.
From the drivers seat.
1 is on the passenger side, closest to the radiator
2 is behind that on the passenger side
3 is behind that (at the firewall) on the passenger side
4 is on the drivers side closest to the radiator
5 is behind that
6 is on the drivers side at the firewall.


DISwiringGuide.gif

DISTimingDiagram.gif

DISWireLabels.gif
 
Last edited:
cylinders 3 & 4 on the coil are the ones not firing, there are the basically 3 coils that have two cylinders on each. its the furthest most set to the drivers side. see pic

i can get a new dis, crank, and cam harness from Ryan Sunquist tomorrow and try that

it cant be a crank sensor, it wouldn't just affect one set of cylinders...it would be random.
 

Attachments

  • firing order t-bird.gif
    firing order t-bird.gif
    2.4 KB · Views: 35
found the problem!

So i totally ripped apart the entire harness all electrical tape off and everything and found a break in the line wasn't all the way apart yet but almost there, so i spliced in a new wire (temporary) til tomorrow and started up and ran just fine, so looks like i have a few new ignition parts.

but best of all i will be going to Iowa for sure unless of course something else happens....but that never happens with an sc...

seriously though thanks guys for the help and fast replies, its easy to get frustrated on these cars and this is a great community!
 
Then it's Pin 1 on the Coil Pack to pin 11 on the DIS module wire that you want to check. It should not be open, it should be solid wire. Yellow with a Red Stripe I believe.

Congrats on the find. I was looking up the color and I bet that's the one you found.
 
found the problem!

So i totally ripped apart the entire harness all electrical tape off and everything and found a break in the line wasn't all the way apart yet but almost there, so i spliced in a new wire (temporary) til tomorrow and started up and ran just fine, so looks like i have a few new ignition parts.

but best of all i will be going to Iowa for sure unless of course something else happens....but that never happens with an sc...

seriously though thanks guys for the help and fast replies, its easy to get frustrated on these cars and this is a great community!

Glad you found the root cause Keith. Good luck in IA. Be sure to post up your E.T.s
 
Back
Top