Random jerk in motor

[YukonandtheHOE]

That's what I was trying not to do... It's like 700 bucks for the updated injection. More wasted money if that's not the issue. I've already dropped way too much in this already trying to make it a daily driver that was dependable. I'll lose money like crazy now if I sold it... Plus the injection

Their under 300$ last time I checked, and it doesn't cost anything to whip the TB off just to see what you got.

 

[sarge77]

The 4.3 in my S10 would do the same thing. It would feel like the engine died for a split second and not just a single cylinder misfire. It did this after I had floored it (accelerating, merging, passing...) then went back to a steady cruise. It would do it just once. If I gave it a little throttle, like just enough to accelerate a bit but not downshift, then settled at a steady cruise, it would do it once more. I could stop, shut it off and restart it and it would fix it until the next time I floored it then cruised.

Your 350 is essentially the same in the front and probably has the same timing cover with the sloppy manufacturing tolerances. The CKP sensor doesn't have a very wide tolerance for spacing from the crankshaft. Some covers put the sensor too close, others too far. Most were too close which is why the spacer was introduced. Of course, there's also variances in the CKP sensor manufacturing itself to further exacerbate the problem.

With my issue, all was fine until the crank moved enough radially at high RPM to contact the sensor. My guess is that this threw it out of whack and the PCM kinda resorted to a base map to keep it running normally. Applying throttle causes a change in RPM and the PCM alters the timing, so this is probably where the hiccup occurred. It's like the PCM just cuts all ignition activity then resorts to it's base map which gets it running again. This happens so fast because of the processor speed of the PCM, so it doesn't seem like a single- or multiple-cylinder misfire and more like a quick "key off/key on" action.

If you still have access to that MAC scan tool, have a CKP Relearn performed after you inspect (and space out if necessary) the CKP sensor. You may be able to fix this with no parts cost.

Thanks I'll will definitely try this.

 

[sarge77]

OK so pulled the crank sensor and no signs of wear. Cleaned it and connector really good. Took for drive still jerks. So just for good measure I swapped the fuel filter. The other did not feel clogged and the fuel looked fine but I swear to you where the truck jerked 4 to 5 times on an eight Mile ride to town before... after It I made it into town, through town, another 10 miles before the first jerk. All the way back home only one jerk. I did find one thing I hope one of you can help me with...I found an electrical connector just hanging that splits off the crank position sensor wire harness. I took a pic I'll try to load. It is the only other connector coming off the wire harness it's red and blue.... Anybody have a clue what it should be hooked too. I looked everywhere and didn't find anything.

 

[sarge77]

Their under 300$ last time I checked, and it doesn't cost anything to whip the TB off just to see what you got.

You were right guess I was looking at dealer prices. Just hate to pull that thing to find it's already been swapped or replace it and still not solve the issue.

 

[east302]

Think this is it on my 98. It's hard to see, but in the first picture the harmonic balancer is on the right. It plugs in just down and behind it. My skid plate is in the way or I'd get a better shot of it.










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[sarge77]

Think this is it on my 98. It's hard to see, but in the first picture the harmonic balancer is on the right. It plugs in just down and behind it on the passenger side. My skid plate is in the way or I'd get a better shot of it.










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Thanks! Anybody got an idea what sensor this is. I'll check tomorrow for that connection but I sure didn't see it earlier maybe it was left off the motor swap.

 

[east302]

Pretty sure it's the crankshaft position sensor.


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[sarge77]

Pretty sure it's the crankshaft position sensor.


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No that's right behind the harmonic balancer...I pulled it earlier. Big plug. Don't know what that is... It's on the other side of the oil pan.

 

[east302]

You were right guess I was looking at dealer prices. Just hate to pull that thing to find it's already been swapped or replace it and still not solve the issue.

I just swapped mine.

If you take off the throttle body, you may be able to see what type of clips are holding the ends of the injector lines into the manifold. The original style had two black clips that you squeeze to release the injector. The multi port doesn't have them and has a small wiring harness at each injector.

I would think that if the injectors were installed incorrectly (into the wrong ports) that you'd have a noticeable misfire.




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[sarge77]

I just swapped mine.

If you take off the throttle body, you may be able to see what type of clips are holding the ends of the injector lines into the manifold. The original style had two black clips that you squeeze to release the injector. The multi port doesn't have them and has a small wiring harness at each injector.

I would think that if the injectors were installed incorrectly (into the wrong ports) that you'd have a noticeable misfire.




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Alright worth a try next weekend. I will say this when I first bought the truck it had this jerk but it was barely noticeable. But over the year I have owned it had grown to this horrible jarring jerk.