Lurching, dead tach issue (warning, wall of text)

[deven.coffey]

Hello all,

Seeing as this is my first post on the forums I will briefly introduce my car.

She's a 1994 blue MTX with about 150k miles, bought her for 1550 off a guy who picked her up at a auction after some kid had her repo'ed. The guy I bought her from said she had a ignition issue that was "Solved" with new plug wires. I've been the owner for about one year now.

The issue: the car will randomly "bump" or do a series of lurches verging on banging at random times while driving. This happens a lot more often (once a day or more) during hot weather than cold (once a week tops). I know it has something to do with the crankshaft position sensor since I also loose tach signal when it bumps. The check engine light will go on and off constantly while driving on the highway.

About a month ago the car totally died on me pulling into safeway and wouldn't idle above 300 rpm, so I killed it, double checked all my fluids, and let it cool down, started right up after about 3 hours of cool down. Took it to a shop who told me it was the crankshaft position sensor and replaced it. The bumping resumed not 10 miles after I picked up my car and was on my way home.

I think it's a DOA sensor but considering how small the chances of that is these days I wanted to ask on here if anyone else knows of this issue and if so, is it actually a DOA sensor and bad luck or is there a larger electronic issue at work here.

Any help would be much appreciated, again, apologies for the wall of text.

Deven

 

[93markVIII]

camshaft sensor then right? the one up top, rear head, passenger side.
dead/dying ones make the tach act weird.

 

[deven.coffey]

would the camshaft sensor also cause the lurching though?

 

[intimdatr]

Yep, did it to me and its violent when it does it. Fresh Cam Sensor and it went away.

 

[rubydist]

a sick cam sensor will result in the tach signal going in and out, so the tach will jump around. depending on what is wrong with the cam sensor, it can screw up the ignition timing, resulting in lurching or jerking on/off.

however, the dis can cause the same symptoms you describe, and I have replaced good cam sensors only to still have the problem due to the dis.

you should start by pulling codes. these issues may not set a code, but if they do that will help you not guess and actually replace the right thing the first time.

 

[deven.coffey]

the codes the shop pulled pointed to the crank sensor when i had it replaced, I'll call them tomorrow and see what codes they are since the technician told me its spitting identical codes right now, just no hard symptoms to go off.

so ill be back tomorrow with codes to run by you guys

 

[hellrazer]

those are the exact symptoms my 94 had when the cam sensor died on me.

 

[deven.coffey]

Ends up it was the cam sensor, the shop it was at just wasn't driving it for long enough to **** it so I had to pick it up monday and **** it tuesday morning myself =p

Is it common for the cam sensor to go right after the crank sensor? (or vice versa?)