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96 Voyager tachometer goes to zero while driving

I have a '96 Voyager with 3.3L engine. Recently a strange problem has started to occur. While driving the tachometer will drop to 0 and the engine basically quits running. A second or two later the tachometer jumps back up to normal reading and the engine comes back on. No other light or dash indicator changes, only the tachometer. Do I have an intermittent sensor? Which one?

Are you saying the engine stops running but NONE of the warning lights comes on?

If that’s the case I’d say you’re suffering a complete loss of electrical power from the battery. Have you checked the battery cable connections? Both ends of the cables?

No warning lights come on. The odometer and transmission drive position indicators stay lit. The radio stays on. The speedometer continues to read accurately. All other gauges look normal. Just the tachometer goes to 0 and the engine quits producing power for a second or two.

Perhaps the PCM is losing power or has an internal fault?
I suspect that the engine keeps turning at or above idle speed due to the transmission turning it. That keeps the oil pressure and alternator lights from coming on and keeps the power steering going. It also explains the engine restarting on its own when the PCM comes back.

I agree that the transmission continues to turn the engine. Would the PCM loosing power generate an ODB fault code?

Probably not. It needs power to generate a code.

The PCM acts the same as if you had turned off the ignition. No power, no code.

The rear wheels cannot drive the motor with a modern automatic transmission where the hydraulic pump is driven off the input shaft. The trans is in neutral without pump pressure. You can’t push start modern automatics…

That’s funny, the rear wheels of my 2004 and 2006 cars most certainly can and do turn the engine. Going down hills, they turn the engine such that all fuel is cut off. The MAF sensor once failed on my 06 while on the interstate at 80. All engine power was lost, but the steering kept working, as did the alternator and the oil pump, because the engine was being turned by the transmission. (The cars in question are Lincoln LS, but the same except for being rear wheel drive, applies to almost all cars.) All of this was lost when the car coasted down to 20 or so miles per hour.

The transmission has full lock up, so the output shaft turns the input shaft which keeps the hydraulic pump going. Just because you don’t understand it, doesn’t mean it doesn’t work.

It’s not a push-start situation, it’s more like DFCO (deceleration fuel cut-off). Many (most?) recent cars will cut off fuel to the injectors if you take you foot off the gas to coast, above a certain speed and rpm. It saves fuel and reduces emissions. The engine continues to turn due to the car’s inertia transmitted through the transmission, the alternator makes power and the engine makes vacuum, and when you accelerate or slow below the set speed the injectors turn on again.

Since the speedometer and radio stay on, this can’t be a car-wide electrical fault. Since the tach goes to zero while the engine is still turning, you need to look at how the tach gets its information, which is probably from the engine computer. It sounds like a computer problem that is causing the injectors and/or the spark plugs to stop, plus it stops transmitting a signal from the engine to the tachometer.

Some PCMs will generate a DTC when they power back up (or start back up after a reset) that basically says, " the engine was already turning when I powered up, so something must be wrong."

Most of the time the Tach gets its signel from the firing of the ignition system. The fact that the engine quits producing power when the tachometer drops indicates that ignition may be dropping out while the engine is still turning.

I think if the mechanic troubleshoots the loss of the ignition signal, the tach problem will also be solved. The problem could be the Crankshaft Position Sensor, the ECM, the wiring from the CrPS to ECM, power to the coil pack, etc.

Hope this helps to point you in the right direction.

SDWH you’re absolutely right. I didn’t consider the fact the TC was already locked up. Thanks for correcting my oversight without being an @ss about it.

And, saying that something someone just said is impossible (even though it isn’t, and you don’t know for a fact) isn’t being an “@ss”?

Do you think every poster that contradicts something you wrote is an @ss? By your measure, everyone who makes a wrong statement is an @ss? Perhaps your own bias and insecurity is responsible for how you reacted to a post that contains no derogatory comments aimed at you but coincidentally does mistakenly contradict yours. Best of luck to you in life…

No, actually I don’t think that. Nor did I think that my response to your incorrect response was being an “@ss.” Perhaps you are the one who is too easily offended? In any event, I am careful to state the things that I know as facts as a fact, and I am careful to state the things that I only think as things that I think or wonder about. I do wish everyone else would be so careful. Most of the advice on this board is good, but some of it is very wrong and as such very unhelpful.