engine missing, tach incorrect

[BubbaZ71Tahoe]

my 97 tahoe has been running like crap.

the tach is not reading right and it has a miss to it. I am more concearned with what will make the tach read incorrect. I have tryed to find this out but I am confused. Is the tach read off the distributor or the crank position sensor or both?

I plan on hooking my laptop up to it with Auto Enginuity and hopefully I can figure something out.


My dad seems to think that my distributor may be wearing out. It has 193,*** miles on the motor.

As for the miss I could use new plug wires and a cap and rotor.... any insight would be helpful.

 

[BubbaZ71Tahoe]

anyone?

 

[FastOrange]

change the plugs, wires and cap.

 

[Sepiroth]

Is your Check Engine Light on? If it is, get the code read first. IIRC, the tach is read off the Distributor.

 

[Aloicious]

check out the stored codes for sure first. you may find the cause of all the problems there.

the Tach is not ran directly off the distributor in your truck. the signal comes from the PCM as the ignition control signal, it is routed to the ignition control module (which is mounted next to the coil), then to the coil, then finally up to the tachometer.

I have a schematic for the '96, which should be the same as yours, but it won't let me attach it here. if you need it PM me and I can get it to you.

 

[BubbaZ71Tahoe]

once i get off work this week I plan on trying to trouble shoot it.

The SES goes on and off.. I have tryed my stock pcm and my wheatley pcm and i get the same problems.


I will let you know if I need that schematic. My haynes manuel was not helpful in trying to figure it out. Hopefully my autoenginuity will help my out. I know its been a big help for detecting problems on my powerstroke.

 

[BubbaZ71Tahoe]

I used the AE and pulled the codes...
These are the codes with the Wheatley tuned PCM

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I put the OEM computer in and it ran better but the tach is still not reading right.. The live reading off the PCM shows seems to be reading right but the tach is not. I cannot get a SES light after 30 minutes of running the dog **** out of it with the stock PCM

 

[DRAGGIN95]

Like mentioned above the tach signal comes from the ecm, if the ecm show's it correctly, perhap's your stepper motor on the tach in the cluster isn't working right.

 

[Tinbender59]

if the ECM is reading right and the tack isn't. you could have one of two problems, either the tach is shot, or your plugs and wires have wiped out the module, or at the least overheating it and causing it to act up, and really noticeable in the tach. I have had this issue on a BUILT 400 many many years ago. when the wires are bad, not all of the secondary voltage from the coil goes out to the plugs. It has to go somewhere, there is no such thing as "just going away" unfortunately as I learned back then, it is usually reflected back into the coil, and thus into the module, as it is the weakest link. and all of that High secondary energy causes all kinds of weird shi....stuff to happen. Proly what is causing the ECM to act up as well???

 

[BubbaZ71Tahoe]

what module you talking about tinbender? the coil or ingnition?