gmblack3

B0521 Tachometer Signal Circuit Malfunction

Just got home 30 mins ago from work as usual.

I always idle thru the neighborhood in neutral. Right about when I got to my driveway, I could hear/feel the car starting to idle rough. I coasted into the driveway and it died. It would barely restart and only enough to get up the driveway and it died again as I got into the garage.

Found the above code and it did say HC, I have never seen that code before but it does say history.

I gave a quick check under the hood and all spark plugs wires look to be tight.

Any ideas?

gmblack3

Anyone else ever have this happen?

Dan_the_C5_Man

Damn Bryan, I'm starting to think my sig. is all too real. I'll look up the code for you.

* Well, that DTC doesn’t mean a whole lot, other than there is *something* wrong w/ the serial data for RPM display from the PCM to the IPC. (Instrument Panel).

Hopefully it's something simple like a bad connection / moisture in the wiring harness. I remember seeing a few posts a while back and the PCM was just covered in corrosion, and in that case it wasn’t from a leaky battery.

Patches

I researched that code in the manual and it indicates either a bad instrument panel, bad PCM communications due to ?, or a wiring problem wild goose chase that'll need to ensue to chase down a bad connection.

Let me know if I can help. I'm in Canton.

gmblack3

Thanks Dan and Patches.

Going to have a look around the computer, what is the best way to access that? I know its below the battery.

Will also check the o2 sensor wires around the headers.

Patches

Pull the back wheel well cover off of the front passenger wheel well then the cover just behind that. The TAC module is attached to the front of the PCM. The PCM looks like this.

gmblack3

Here is what it looks like around the computer:





If I unplug it will I loose my tune? I think not but just want to make sure.

Thanks!

Dan_the_C5_Man

There is *nothing* you can do to lose your tune, short of having the PCM re-flashed, so no worries there!

Patches

Doesn't look too bad but I'd definitely pull it out and clean it all up while you're in there. Tune will not be affected at all. Disconnect neg. bat. terminal before you pull it.

gmblack3

Also pondering if its a broken spring.

Going to clean the connections of the PCM and see what that does.

Battery is already disconnected, but thanks for the reminder.

Thanks!

gmblack3

Gave PCM connections a quick cleaning even though they looked very clean.

Tried to start it again but its the same. I'm getting a little bit of white smoke out of the exhaust when its trying to run. I had the wife video the exhaust and it seems that there is a little more of the white smoke coming out of the right side.

93Polo

Just kicking out an idea.... But a local tuner built a 382 stroker and when the motor went together everything checked out. However, it wouldn't idle well and wouldn't rev. Turned out the reluctor ring on the crank was magnetized and the crank position sensor couldn't get a good read. Any chance the code and the other problems could be a bad crank position sesnor or maybe another sesnor? I agree with Patches check all the connections.

gmblack3

#1 piston-left (drivers) side fwd

0 psi all others where good

removing the valve cover now and hoping for a broken spring

t56gen3

Ouch!

gmblack3

gmblack3

I put about 10psi of air on the #1 cylinder thru the spark plug hole. Then had to pry up on the spring/lifter, since the spring is broke, to seal the lifter. No noise from the intake or exhaust so the piston and lifter should be fine.

Parts should be here by the end of the week.

Patches

That's very encouraging. Hopefully you'll be back on the road by the weekend.

Thanks for the update.

t56gen3

Glad that's all it is. Don't remember hearing of a valve spring as a weak point....*shrug*

gmblack3

Well today I got the guide plates, rocker arm studs and pushrods installed. Got to wait 4-6 hours for the loc-tite to cure on the rocker arm studs. Will change out the springs and rocker arms tomorrow.

Here are the guide plates, rocker arm studs and the install nuts that have a set screw on top.



Here you can see one guide plate and two rocker arm studs installed. Then you can see where the next set will go:



Right side all done:



Here are the install instructions, I did steps 1-6 and just the pushrod part of 7 today.
http://www.cranecams.com/pdf/438e.pdf

For step #2, I used some carb cleaner (w/ hose installed) and sprayed it into the rocker thread stud boss area with a paper towel below to catch oil and cleaner that came back out. I then used a little air to get more of the cleaner out and a rolled up end of a paper towel to get the rest of the cleaner out.

I took my time as this was the first time that I did this.

Mike Mercury

I'm just getting in on this thread... but are you saying that one broken valve spring - and your engine won't run ?