I searched all the threads for tachometer before I posted this so I feel I've done some due diligence.

My tach works sometimes and is accompanied by codes 11 and 12 (and 55).

My strong suspicion is that it would have to be the crank sensor, wiring placement or something down there. I have class in the morning so I can't go examine tonight but if this is a common issue or anyone has experience, I'd love to hear from you.

NO MIL (sometimes referred to as CEL) is illuminated.

-ultra

 

Crank sensor, wiring, or tach are general probabilites. Very lightly tap on sensor while idling and see if tach goes crazy. Then try pulling or movingwirign around to see if dies out.

 

Mine seems to stick every now and then but if I just tap the dash presto it works again.

 

had the same issue and also the ac would quit cooling at the same time.replaced the brushes in the alternator and fixed both problems..

 

WOW, wild that you mention it, my AC quits cooling now and then too.

What in the world could the alternator have to do with it?

Well, now that I think of it, the alternator voltage appears to be a bit low sometimes too...

Alternator?????? Too strange. Any theory behind this solution?

 

To strange for me. JMHO

 

If you want to dig into your Alt. yourself Fixinrams and Genos have a brush and bearing kit, but when you are in there take a good look at the diode pack and the slip rings.

Floyd

 

Man, I wouldn't even know what to look for when looking at a diode pack.

I usually just buy the cheapie lifetime alternator then sell the vehicle before warrantying it.

I'm not selling this truck though.

I'm quite excited about the potential for it actually.

 

Crank sensor tells the ECM (or PCM, whatever we want to call it) that the engine is running. If the ECM doesn't know the engine is running, it will turn off accessory systems. No A/C, no charging, no tach, and so on. Not sure how the alternator would affect the crank sensor from picking up the signal, but thats not to say that it can't. I'd check the harness to the crank sensor, and check the gap to the balancer first before replacing anything.

 

I can't find the sensor...

I saw someones posted picture where it was on the front of the crank and I looked and I don't see it.

It has one because the tach and AC worked briefly after I got it...

 

Ah, completely on the other side.

This has 3 wires which I take to mean it's a Hall-Effect unit and not a regular magnetic sensor.

49 bucks for a DuraCrap one.

Dealer must be 100 or so, eh?

It's a pretty good bet that is what the problem is. I can't easily tap it or wiggle wires with engine running due to fan and such but maybe a good rap on it will make it work and then start engine and find out.

-ultra

 

No luck. Tapping it makes no difference. I wish I had some way to diagnose this besides total replacement but these 3 wire sensors don't lend themselves to testing, do they.

There is a high-pitched tone before cranking when listening under the hood. When I wiggle the sensor connector the tone changes and a relay seems to click somewhere inside the drivers fender.

If it wasn't for the speedo and a few other gauges, I'd just disconnect the whole ecm, wire the AC the way it should be, get an external regulator for the alternator or maybe just a one-wire alternator and such. I really need a tach and speedo though.

 

its fine with me if you dont think the alternator fixed this problem for me.just a fix i have proven on one truck to absolutely fix this problem.i feel like as much as these forums have gave me good answers that i owed it to you guys that helped me so much to post what i have found to be a fix in one situation,and it absolutely ended the problem,no question.use this info if you wish,or analyse it to your satisfaction,but guess what,it works sometimes!!!!!

 

Actually the code that accompanies this is "no crank signal detected during cranking" (11) which is not a time when the alternator would be creating any significant voltage or lack thereof.

I am going to have to go with the likelihood of this sensor being bad on this but I don't have a scope to really test it.

I'm going to install it really clean as I test I guess.

Of course I am ready to admit my mistake or surprise if it ends up being another component.

The alternator was creating great voltage right before this.

 

guys, I must say that some information that I really could have used is that my vehicle doesn't have a crank sensor.

How come no one came up with this info?

Most of you guys know more than me here...