Rats. My suspicion is this is indeed fuel-related since the supply system is not monitored by the Engine Computer. You said it runs better when it's warmed up. That reminds me of a recall modification on the K-cars years ago where fuel vapors could condense in the hose going to the MAP sensor and block it. Your sensor should be plugged right into the intake manifold so it won't develop that problem, but that is the one with the biggest influence on how much fuel goes into the engine.
It's odd no fault codes set so far. Any chance the battery was disconnected? That would erase any codes.
The next thing is to connect a scanner so you can watch the sensor readings while you're driving and the problem is occurring. I can watch the oxygen sensor readings to see if they're switching between "rich" and "lean" about twice per second, but for the other sensors, I know what "normal" is, but I'm not experienced in watching them while driving. Engine performance specialists will recognize right away when a reading is wrong, and they will introduce artificial lean and rich conditions to see how the sensors and computer responds. You also want to look at the "long-term" and "short-term fuel trim" numbers. Ideal is all zeros meaning the computer is not adding or subtracting fuel from the factory pre-programmed values, which themselves are real close but only approximate for most conditions. You can expect to see plus or minus 2 or 3 percent, but you don't want to see a high number like 8 to 15 percent. Those mean the computer is really modifying the amount of fuel it needs by a lot, but it doesn't know why. That's what we have to figure out. A high positive number means the mixture is way too lean and the computer is commanding more fuel in an attempt to fix that. Low fuel pressure would do that.
For those cam and crank sensors, the better scanners have graphing capabilities that let you watch their signals. As soon as you see what normal looks like, you'll recognize right away when one is breaking up or pulses are missing intermittently. You have an ignition module too, but I'm familiar with that. Anything electronic is prone to failure just because of the environment it lives in. Heat, dust, and vibration are real hard on that stuff and their connectors.
Most of the other experts here will also suggest connecting a fuel pressure gauge so you can watch it while the problem is occurring. Pressure on Chrysler products doesn't have to be perfectly at specs like on some other brands. On my Grand Caravan, for example, when the pickup screen in the gas tank was plugged, the engine still ran fine with no symptoms down to 20 psi. At 15 psi it started to sputter. Normal is 45 to 50 psi, so that's quite a drop.
The other things to consider are ignition-related, but almost all the time those act up when the engine is hot. The crankshaft position sensor and the camshaft position sensor in the distributor often fail by becoming heat-sensitive, then they work again after they cool down for an hour. There was a common problem in the early '90s with worn bushings in the distributors on Dakotas. Those caused erratic ignition timing which caused running problems.
Saturday, August 1st, 2020 AT 12:51 PM
(Merged)
