QuestionMy 1997 Plymouth Voyager 3.3 engine has 190,000 miles.
Yesterday after about 2 hours driving 65mph, as I was going up a hill, it shifted down and the engine started missing and running on about one or two cylinders. Parked off the freeway and after about 30 min. it started up again and ran fine. About 20 miles it did it again. Waited for about 30 min and ran fine again. I got home by not driving over 45mp. It runs fine here at home. The check engine light came on and the onboard computer reads missfire on plugs. Checked out the coil, seems good. Checked out the catalytic converter, check out good. Mechanics here are stumped since we cannot duplicate this unless I drive for long distance at high speed. Any ideas? Thanks for your help.
Pat Cochran
AnswerHi Pat,
The high speed-long duration running makes me wonder about a couple of things:fuel supply and heat. Could the fuel pump be faltering in its pressure or the fuel filter getting clogged up? You might want to check the pressure (55 psi), and maybe change the filter if it hasn't been done for quite a while.
On the over-heat factor with quick recovery over a few minutes to possibly allow cooling: it makes me wonder whether the crank or cam sensor might be beginning to breakdown, but not enough to set a code? That usually is a fail/recovery rather than a stumble/recovery phenomenon but this might be an earlier phase brought on by the temperatures running higher at high speeds. If it is the case, a code for that will soon show up. (P0320 or 0340, respectively)
Here is a response I gave earlier today with a similar code problem in the 2.5 V-6 engine (but not speed related):
"Otherwise the multiple misfire has lots of possible causes.
The codes are based upon the detection of minor missing which causes subtle differences in the rpm as each cylinder fires to produce its rotational input (crankshaft sensor is the detector involved). The Chrysler troubleshooting manual lists the possible causes as:
secondary ignition wires, fuel pump or fuel filter, injector harness connectors, ignition coil circuit, spark plugs, mechanical engine problem, contaminated fuel, water in fuel, PCM grounds, Injectors, Restricted exhaust, intake restriction, PCM, evap system, EGR system, Air gap at high rpm's, damaged sensor trigger wheel, and intake manifold gasket leak. That is quite a list!
The approach suggested is to check all electrical connectors and wiring, then do the tests in the following order:
secondary ignition
fuel delivery
engine vacuum
PCM power and ground connections
engine mechanical
The first one uses an engine analyzer scope to look at the high voltage pattern, then spray water on the cables to see if it changes. The possible repairs: individual spark plugs, coil or cable replacement
The second one involves pressure measurement and from there a variety of possible solutions
The third involves reading the intake manifold vacuum to see if it is steady at between 13 and 22 inches of HG. and if not the suspects depend upon the pattern shown by the gauge.
The PCM involves checking various wires at the PCM plugs
The last involves engine compression testing and a variety of other mechanical checks.
So I guess that beginning with the ignition wires makes sense unless you have a scope and the experience/knowledge at interpreting the patterns. You might try looking at the wires in the dark with the engine idling, then also spray some water mist on them to see in either case if you see arcing which would be a sign that the wires' insulation is breaking down. Then measure the coil resistances. If it passes that, then focus on the fuel filter and pump.
An intake manifold gasket leak can be detected by applying very brief squirts of starter fluid around the gasket while listening for any change in the idle speed immediately after each squirt.
I can't give you any personal experience with this code situation, unfortunately."
The last part you might check is the exhaust gas recirculation valve. It is supposed to be closed at both closed throttle and wide open throttle. If it is sticking ajar it will lean out the mixture too much. So look for the valve in the pipe running from the right side exhaust manual to the throttle body. When you find the valve notice that there is a flange between the body and the actuator inside of which you will see the stem of the valve with a slot around its circumference. You can move the stem back and forth with the tip of a screwdriver against spring tension in one direction (closing of the valve). If the valve gets contaminated by exhaust wastes they can gum up the stem. So test that it is closing well by the spring alone. If it appears to hang up then put some spray penertrating lubricant on the stem where it enters the body to free-up the motion. That might eliminate this problem.
Roland
