OK. I have searched the forum and have not seen a post with a problem identical to mine. This one is on my '95 V6 (it seems to be the problem child, it is actually my wife's, but I inherited the care of it when I married her so now I consider it my own).
Anyway...this only happens occasionally and I am stumped. Every now and then the Tachometer will go nuts and jump around for a while. Usually jumps from 0 to about 3000, back and forth. Sometimes it will jump around for a few minutes, then drop down to 0 for a long time, then it will start jumping again. At first I thought it was just a faulty gauge, or connection, whatever. But I noticed when it is jumping around like that, the engine seems to "shudder" I guess would be a good way of describing it. Nothing major, but noticeable. Like say I'm going down the interstate and I have the cruise set on 70. The needle starts jumping and the engine just doesn't feel right, kind of like it is missing or something. I do have a CEL, but I haven't checked the code yet. I plan on going to AutoZone this weekend to pull the code.
Anybody got any suggestions or tests I could try to diagnose this?
P.S. I am having the t-belt, water pump, & seals changed next weekend as the car has 113k on it (I know, I know, I'm overdue.)
I also don't have any idea the last time the spark plugs/wires were changed, if they have ever been changed at all. I plan on doing that myself if I can get to them and if I can get my hands on a torque wrench sometime soon.

 

On models w/ distributors, the ignitor generates apulsed voltage signal that the instrument panel interprets as RPM. I think you have a coil over plug (COP) system, which is probably similar. In any case a failing coil, ignitor, or spark plug may cause a spurious signal that upsets the instrument panel rpm detection circuit. That CEL may be indicate a miss on a cylinder which would tell you which cylinder has a defective component. I would start w/ a new spark plug for that cylinder and see if that fixes the problem. Next you might move the COP to another cylinder and see if problem follows. If yes, then a new or used COP would be needed. I think they are pretty expensive.

good luck

good luck

 

Thanks Texas. I'm seriously hoping it is merely a spark plug. I am pretty sure the current plugs need to be replaced. I'm going to AutoZone tomorrow & pull the codes for the CEL. I'll update.

 

TexasHonda, a COP system does not have a distributor/plug wirescorrect? The V6 does have a distributor with plug wires running from itself to the plugs so I don't think it is a COP system. I think Honda started using the COP system on the 2000 V6's.

 

So I went to Autozone yesterday & pulled the CEL codes with their scan tool. It gave me 2 codes: P0725 (engine speed input circuit malfunction)and P0141(Oxygen Sensor).
So.....TheAutoZone gave various "troubleshooting" for the P0725listed as follows:
Definition
Engine Speed Input Circuit Malfunction - ECM to TCM
Probable Causes
1.-Open or short circuit condition
2.-Poor electrical connection
3.-TCM/PCM communication error

The PCM has determined that a malfunction exists in the electrical circuit for the engine speed input.

Definition
Engine speed input circuit malfunction
Explanation
Open or short circuit condition
Probable Causes
1.-Poor Electrical Connection
2.-Check communication error
3.-Failed CKP sensor

Definition
TCC does not engaged
Probable Causes
Check ignition system for faults

Definition
Engine speed input circuit malfunction
Probable Causes
1.-Short or open circuit condition in the CKP circuit
2.-CKP sensor malfunction
3.-Harness or connector damage from TCM to ECM

Definition
RPM input-Lock-up clutch does not engage
Probable Causes
1.-Poor connection at ignition coil
2.-short or open ignition coil wire
3.-Failed ignition control

Definition
Engine speed signal circuit

Definition
Failed crankshaft position sensor signal
Probable Causes
1.-Open or short circuit condition
2.-Poor electrical connection
3.-Mechanical condition
4.-Faulty crank sensor

Definition
Engine speed signal from ECM to TCM missing
Probable Causes
1.-Open or short circuit condition
2.-Poor electrical connection

Definition
Engine speed input low to TCM
Explanation
Vehicle in drive throttle more than 12%-Engine speed
Input to TCM from PCM incorrect
Probable Causes
1.-Poor connection between PCM and TCM
2.-Open or short circuit condition
3.-Failed TCM or PCM

Definition
Engine Speed Input Circuit Malfunction - CKP Sensor
Probable Causes
1.-Open or short circuit condition
2.-Poor electrical connection
3.-Failed CKP sensor

I'm sorry for such a long post. I just wanted to include EVERYTHING that was on the print out from AutoZone. As I mentioned earlier, I am going to be replacing the plugs/wires soon.Does anyone thinka bad plug or wirecould be causing this? Anyone think the O2 sensor trouble code will go away after I fix whatever is throwing the P0725 code?

 

I have had similiar engine behavior on a 4 gen, turned out to be a faulty idle air control valve.

 

Thanks zexkid37.
OK so I'm pretty new to this aspect of the engine.I see the IAC isattached to the throttle body. My Haynes gives instructions fora "check" procedure. Looks like I may need an adittional tachometer to check it. I'll have to see if I can find one of those around here.
Anybody else got any suggestions on what could be causing the CELcode(s)?

 

My 97 Acura TL manual lists P0725 as an ignition coil fault. I'm pretty sure the P codes are standard codes, same for all vehicles, so you may have some faulty info from AZ, but I could be wrong. Since you have a distributor, a coil fault is a distinct possibility. In that case the rpm signal is generated by ignitor as I described above. Coil is usually cheaper than the ignitor. A faulty (usually won't start car) coil can be detected by measuring primary and secondary resistance w/ a precision VOM against specification.

The fault is very similar to faults I've had w/ engine speed (ignition coil). The wiring problem is possible, but low probablity. Check your wires and harnesses.

I wouldn't worry about the O2 sensor fault until I got the engine miss/rpm problem fixed. It may go away on fixing the rpm problem.

CKP fault generates a separate fault code, P0335.

good luck

 

I think you are right about the fault codes being universal. Here is a site that shows general descriptions of what all the codes are supposed to mean: http://autorepair.about.com/cs/troub...l_obd_main.htm
It says the same thing as AZ about my codes, but I do not doubt it could be wrong and you could be right! Couldn't a faulty ignitor/coil tecnically be listed as a problem with the "engine speed input circuit"?
By "precision VOM" do you mean a multimeter that can read volts & ohms?
Sorry for all the questions. I just really would liketo get this thing diagnosed this weekend when I am at my dad's house with the car .

 

VOM

Volt
Ohm
Meter