Another "no-tach" thread - Maintenance Forum

Forum Post / Reply
You must log in before you can post or reply to messages.
Another "no-tach" thread
Monday, April 15, 2019 2:06 PM
I restore Ecotec engines for side income here in Las Vegas and am truly a fan of these power plants. To date I have rebuilt just under 100 total between the 2.2 and 2.4 models. I consider myself average intelligence and have no problem admitting fault when I screw up (which I do). I am pleading ignorance and am open to any advice for the following issue listed below. Thank you in advance for looking.

2008 2.2 Cobalt

Fresh engine rebuild.

I was given the core and the engine was installed by owners friends. Car is now in my possession due to a no start complaint.

First resolved issue was no positive wire from battery to starter. It had been tucked out of the way. After correcting, the car fired right up.

The issue remaining is no RPM signal to tachometer. Not only is that annoying, but I cannot perform the CASE relearn (reprogram crankshaft position sensor). I removed the harness and have 5 volts on outer wires and solid ground on center wire. There is an intermediary harness between main harness and sensor. I have the same signals before and after it, so theoretically its not at fault. Upon removing the sensor and inspecting it, I see that the center "prong" was crushed and lying across at least one of the other prongs. Evidently it was forced down when plugged in. I purchased a new sensor (GM OEM from dealership) and reinstalled. Same issue present. No fuses blown. No visible damage to wiring harness and I have spent a lot of time inspecting it.

Using my Tech 2 (authentic not a clone) I cannot complete the relearn process because the step "place foot on brake pedal and hold, start car" is performed but the screen flashes start and idle car. Clearly the ECM doesn't know its running.

Or does it? Going into engine data on Tech 2 I have no RPM. However if I going to ignition data I have RPM signal from the CPK. uuummmm? What is going on?

I have inspected the installed engine and put grounds back into correct locations as well as determining everything else is plugged in as should be.

So my question to you learned people in the Ecotec world is: How can the CPK register RPM at ignition data control and not at engine? I know it could have damaged electronics by not having positive cable connected, but is it likely? If I still have voltage and ground at sensor, is it likely that the bent prong did not damage ECM?

When I say it runs, I mean it runs well . Idle is smooth. Test drive was also good. power seems to be as desired. Cranks longer than it should, but I assume that is a result of this issue. I see that issue often until I perform the relearn, then starts much faster (as intended).

I almost wish it wasn't running so well, then maybe I could be provided a hint from the symptoms.

Re: Another "no-tach" thread
Monday, April 15, 2019 2:47 PM
Forgot to mention

P0335 is the only code present
Forum Post / Reply
You must log in before you can post or reply to messages.


Start New Topic Advanced Search