Jumping Tach needle, Lean cylinders, Misfire Options

[MotoFoo86]

On a recent drive back through the middle of nowhere my car started to act up. It began with the tach needle (not the actual engine rpm's) jumping up from the actual RPM's 300-500 rpm. I dismissed it at first, and continued to drive. The Jumping got worse, and the car began to misfire/loose power at the time while the needle was jumping. I reduced my speed and limped her home. By the time i arrived, the needle was jumping consistently every 10 second or so, and occasionly for several thousand RPM. Parked her and left her for a couple days.

Coming back to her today, no symptoms while engine is cold. Upon reaching operating temperature the symptoms started again, tach needle began to jump, engine stumbled while reving. Shut her down, ran a compression test, all cylinders at about 200 PSI. Spark plug reading shows that all cylinders are running lean. Check grounds, all appear to be good (i redid them less then 6 months ago). Fuel pump is obviously working as it can be heard while the car is running.

Already Checked the ECT sensor, it is in spec.

I'm thinking TPS or MAP sensors are the most likely culprit. Any further ideas?

Stock 5sfe with 149k miles on it, manual tranny.

This post has been edited by MotoFoo86: Oct 18, 2013 - 8:54 PM

[cwong]

On a recent drive back through the middle of nowhere my car started to act up. It began with the tach needle (not the actual engine rpm's) jumping up from the actual RPM's 300-500 rpm. I dismissed it at first, and continued to drive. The Jumping got worse, and the car began to misfire/loose power at the time while the needle was jumping. I reduced my speed and limped her home. By the time i arrived, the needle was jumping consistently every 10 second or so, and occasionly for several thousand RPM. Parked her and left her for a couple days.

Coming back to her today, no symptoms while engine is cold. Upon reaching operating temperature the symptoms started again, tach needle began to jump, engine stumbled while reving. Shut her down, ran a compression test, all cylinders at about 200 PSI. Spark plug reading shows that all cylinders are running lean. Check grounds, all appear to be good (i redid them less then 6 months ago). Fuel pump is obviously working as it can be heard while the car is running.

Already Checked the ECT sensor, it is in spec.

I'm thinking TPS or MAP sensors are the most likely culprit. Any further ideas?

Stock 5sfe with 149k miles on it, manual tranny.

i had that happen to me i changed the tps it went away.
then it came back change egr valve and egr modulator.
egr valve i pulled from boneyard modulator i found on amazon for dirt cheap

[cwong]

On a recent drive back through the middle of nowhere my car started to act up. It began with the tach needle (not the actual engine rpm's) jumping up from the actual RPM's 300-500 rpm. I dismissed it at first, and continued to drive. The Jumping got worse, and the car began to misfire/loose power at the time while the needle was jumping. I reduced my speed and limped her home. By the time i arrived, the needle was jumping consistently every 10 second or so, and occasionly for several thousand RPM. Parked her and left her for a couple days.

Coming back to her today, no symptoms while engine is cold. Upon reaching operating temperature the symptoms started again, tach needle began to jump, engine stumbled while reving. Shut her down, ran a compression test, all cylinders at about 200 PSI. Spark plug reading shows that all cylinders are running lean. Check grounds, all appear to be good (i redid them less then 6 months ago). Fuel pump is obviously working as it can be heard while the car is running.

Already Checked the ECT sensor, it is in spec.

I'm thinking TPS or MAP sensors are the most likely culprit. Any further ideas?

Stock 5sfe with 149k miles on it, manual tranny.

i had that happen to me i changed the tps it went away.
then it came back change egr valve and egr modulator.
egr valve i pulled from boneyard modulator i found on amazon for dirt cheap

[Smaay]

this doesnt sound likea MAP or TPS issue, more like an igniter issue. thats what sends the signal to the tach.

[czwalga]

Loose ground, check both battery cables. Had it happen to me at the last race. Would idle fine gave it gas would sputter with the tach jumping and going crazy.

[Smaay]

yes ^^^^ that too