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+--- Thread: jerking (/thread-jerking)
jerking - stickerbuoy - 04-19-2014
and we're back with another issue.
Symptoms: Jerks at highway speeds. Fairly sudden, and random (not periodic). Tach jumps down 100 or 200 rpm during that time.
I've had the error code jumper in the whole time, and it's merrily blinking away 12, without pausing or cutting out when the jerking happens.
I tried flicking the brakes (while holding the gas) to see if I could recreate the problem, however, the tach does not jump down nearly as suddenly when I do that.
Problem seems to be fairly temperature independent...
RE: jerking - fixkick - 04-19-2014
bad spark, caused by?
spark wires bad? dizzy cap and rotor ok.
bad ignition coil?
full stall , if engine hits 100 that is a full stall.
is car , A/T or M/T you have 3 listed.
the 5peed will not go to 100 rpm. moving fast. the drive line will keep engine way fast. at stalls.
A/T can stall easy, its pump dies. and it not in neutral.
if the RPM was high, and tacho shows 100 that means the coil ignitor is bad or ignition coil is bad or wires to it bad. (connections)
if RPM was really 100, then tacho didnt lie. it stalled.
RE: jerking - stickerbuoy - 04-20-2014
(04-19-2014, 09:20 PM)fixkick Wrote: bad spark, caused by?
spark wires bad? dizzy cap and rotor ok.
bad ignition coil?
full stall , if engine hits 100 that is a full stall.
is car , A/T or M/T you have 3 listed.
the 5peed will not go to 100 rpm. moving fast. the drive line will keep engine way fast. at stalls.
A/T can stall easy, its pump dies. and it not in neutral.
if the RPM was high, and tacho shows 100 that means the coil ignitor is bad or ignition coil is bad or wires to it bad. (connections)
if RPM was really 100, then tacho didnt lie. it stalled.
It's the red 2-door, as usual.
The tach is not jumping down 'to' 100, it's jumping down 'by' 100 or 200 RPM. So if it was at 3500, it would dip down to 3400 or 3300 very briefly.
RE: jerking - fixkick - 04-20-2014
ok 100 drops. ok..... misfiring. or bogging, 99% jerking is spark related, bogs are like dragging a weight (if the fuel pump dies, on the fly, its a gently drop in power)
spark fail is violent, or if 100% no spark its a violent jerk, (100% ;death of engine power, in an instant is the jerk) misfire causes the engine to shake, a clear sign of misfire.
95 16v engine jerks.
id make sure you don't lose, 12vdc to the EFI parts. first. but the code 12s happened at the jerk so is not lost DC power.
the ECU and distributor must not lose 12vdc on the fly at any time. and no code 41/42 means to me the Dizzy never lost DC power either.
best i cant tell is this is misfire. and that is complex.
my guess is a fouling spark plug. is one running black?
marginal spark plug wire, (run mag wires, bosch or NGK)
i think its spark related.
RE: jerking - stickerbuoy - 04-20-2014
Ya it's a sudden jerk and loss of power, as if somebody really strong was grabbing the crankshaft for an instant.
I will pull the plugs and check them. I've also got a newer set of wires, maybe I'll swap them over too. This car is getting replaced one piece at a time...
RE: jerking - fixkick - 04-20-2014
yes, 1 part at time. this is so common this old.
so the 12 code was flashing during the instant stall or fast gross misfire.
one trick is use a voltmeter (any) at the cig lighter, to see if 12vd (13.3 to 15vdc) is steady at the drop of engine power.
the ECU does flash out 41, or 42 if for 1 pulse in 10 drop out. this tells me, you loosing High voltage , its a HV side spark failure. of some kind.
and the primary side of coil (ignitor ) is ok,
problem is from coil secondary side to spark plugs.
make sure the rotor on dizzy is not off by 1. 1 of 3 ways it fits with junky rotors. use a bosch rotor, it fits one way ,just like the original mitsubishi rotor fit.
http://www.fixkick.com/ECU/92-95MPI-eng-schematic_files/92-95mpi-eng-full-size-huge.png
if one way you get no spark or if one other way, spark is weak and crossfiring, i sure this is ok but needs to be stated.
the 3 ways of the rotor
1: good and aligned to #1 post. (spec rotor)
2: weak spark and too far to jump spark. (china rotors)
3: way to far to jump and can jump 2 ways. bad bad news.
RE: jerking - Trk90 - 04-22-2014
Just throwing this out due to the symptom description...is it possible it could be the TPS without registering a code? I had a similar situation in my 1990 driving at highway speeds. It felt like someone was either nudging the bumper from behind or hitting a 60 mph head wind for a slit second. It was very sporadic in the beginning. Turned out to be a bad TPS.
RE: jerking - fixkick - 04-22-2014
sure IT CAN, and a great question! the TPS idle switch stuck open or closed, but you must drive it hard for this to trip. will throw a DTC for TPS idle.
sure will. but can be very insensitive,
the TPS has 2 parts, the throttle angle and the idle switch
the ECU never reports angle off (called the TP output by suz) only if shorted ground <0.2v or stuck at over 4v all the time.
the ECU thinks wild readings are all driver caused. as surely it can be... or is asking for unflood mode, all very normal and even starting with right foot at 10% throw no codes.
The TPS idle throws if idle is low, for a very long time, HOT, and fails to see the switch closes.
same with stuck open. it watches RPM and MAP for a long time. and if the readings (long time checked) are incongruity to the switch, bam.
my guess is his mech. set the idle calibration wrong and on the hairy edge. (didnt use the 3 feelers like the book demands) so since on the edge, it fails randomly.
I calibrate mine the torture it to make it fail by blipping the trottle over and over and using the GO /NOGO feelers.
if yous set it late (late open) the TPS ISC idle loop fights your right foot action.
The throttle angle glitch causes the ECU to enter ENRICH mode for every glitch , not a pretty sight that, and no DTC for that.
i never ever mess with that, i use my voltmeter at the moment of the failure, because you cany fix it or find it , if it is not busted.
and trusting the ECU to tell you this is not reliable at all.
after all, its only failing for short time. and the ecu is blind to short time fails, its even blind to intermittant TP angle glitches do to , it THINKS DRIVER is driving funny./
the ECU only finds, dead opens and dead shorts. and not much else, unless very luckly.
id does not find weak map sensors
or other weakness , except that pesky 400s EGR test.
to find a bad TPS, angle output
use a voltmeter on the TP pin,
it must be totally linear with no drop outs, moving it. if it clitches its bad.
on a real scope the glitches are easy to see.
per here
![[Image: glitch.jpg]](http://www.fixkick.com/sensors/TPS/glitch.jpg)
for sure its not his idle switch , driving fast.
just the TP pin per above.
The ecu looks at fast changes, on the TP, if it sees them it activates ENRICH mode. fast. in fact so fast , it beats the pure air slug at the intake head valves.
that is what the TP does, it uses the speed of light (1/2 joking) to beat that air slug (quote, jeff hartman)
with a dead, TP the car bogs with a fast right foot
if the TPS fails, an glitches the ECU thinks (wrongly) that you did move your right foot fast, but in fact you did not.
see?
on carb cars this was a shot fuel sparyed into the venturi.
on EFI cars, its a fast ENRICH mode. for the same reason, exactly.
it stops the bog, drive car car with a dead pump there, accel pump.and see that car bog fast.
the carbon wears out at your favorite speed, if 55 mph is it, bam that wears out.
in the city its the off idle spot. goes bad.
RE: jerking - Trk90 - 04-22-2014
(04-22-2014, 05:32 AM)fixkick Wrote: the carbon wears out at your favorite speed, if 55 mph is it, bam that wears out.
in the city its the off idle spot. goes bad.
Yup! my right-foot cruise control found that spot around 65. In the beginning, it was definitely more sporadic but it become almost guaranteed (which didn't take long) when I replaced it!
I remember verifying the bad TPS
RE: jerking - fixkick - 04-22-2014
sure would. and the part is crazy expensive
my real jeep is $50 or less....
my guess is they last about 150k miles to 200k max
never had one bad below 100k. ever.
thanks so much for helping!!!