92 Chrysler 3.3 has a bad shake going uphill or acceleration. It starts and runs smooth. I have had mechanics change the fuel filter, check the engine and transmission codes (no faults found), replace the coil pack, pull and inspect the injectors. No answer so far. Current theory is a cracked wire insulation allowing jumps to ground. Any thoughts or suggestions?
Where do you feel that shaking, the steering wheel, seat, or entire car? If it's a mechanical problem suspect a worn inner cv joint housing, most commonly on the right half shaft. That vibration usually goes away above around 40 mph.
April, 5, 2013 AT 6:37 PM
Thanks for the response. The entire shakes, actually more a jerking as the speed goes up. I find I did not describe the prob as well as I intended. There is a misfire sound, like a plug missing or a broken plugwire. I replaced those with new ones but the misfire and jerking continues. The engine is physically smooth but the ride is jerky going uphill and the engine falters.
April, 6, 2013 AT 12:00 AM
One thing to keep in the back of your mind is the crankshaft position sensor has a very critical air gap. It must be installed as far in as it will go, but with a thick paper spacer stuck on the end. If that is not done it can cause an intermittent dropout of the signal. The Engine Computer won't know when to fire a coil. Normally a total loss of that signal can be identified by watching live data on a scanner while on a test drive. The crankshaft position sensor and the camshaft position sensor will be listed as "no" or "present" when the engine stalls. For a sporadic intermittent and fast problem like you're having a better bet is to use a scanner with a record feature. You press the "record" button when the problem occurs. Since the data travels through the scanner's memory, the recording actually starts a few seconds before you pressed the button. Later the mechanic can play it back frame-by-frame and watch for a glitch in a sensor's signal when the problem occurred.
Most problems like this are due to something related to spark. They occur quickly and clear up quickly. If that is related to anything the computer uses to make spark-timing decisions it will be monitored and a diagnostic fault code will be set if the problem acts up long enough to be detected. When no fault code is set it means the cause is in a part of the circuit that isn't monitored such as the secondary side of the ignition coils, and spark plugs, or it's fuel-related.
Fuel problems fall into two categories. First is the fuel supply side, meaning the pump, filter, and pressure regulator. None of those are going to cause this symptom unless the pressure is low. Normally problems with pressure or volume result in a gradual loss of power, as in over a period of a few seconds, not like instantly turning off a switch. The injector side is different though. Loss of the signal from the camshaft position sensor prevents the computer from knowing when to fire an injector. That will result in a sudden loss of fuel.
Under rare conditions cam and crank sensors can develop a cracked core which makes them generate erratic signals. Those can be hard to identify without a scope. Digital oscilloscopes will allow the mechanic to view the waveforms coming from those sensors but you need a sharp eye to catch the extra little pulses.
The injectors and coil pack share a common 12 volt feed wire. Check the terminals in the connector in the harness between the body and engine. If you pull it apart and put it back together and the problem clears up for a few weeks, check those terminals for corrosion and tightness. That current comes from the automatic shutdown, (ASD) relay. Although those have an extremely low failure rate you might want to swap it with another one like it to rule out pitted contacts. As I recall, the starter relay and the AC compressor relay are the same.