Mechanics

ENGINE STALLING IN VARYING CONDITIONS

1995 Dodge Van

Engine Performance problem
1995 Dodge Van V8 Two Wheel Drive Automatic 210000 miles

My Ram B2500 318Y engine has been stalling out for the last couple of weeks. The Check Engine Light has never come on during any of the episodes. At first I had a hard miss; I replaced the plugs, plug wires, dist. Cap/rotor and ignition coil. It rand great for several days then began to stall out again. It will die at any speed or condition (idle, at steady speed and while accelerating). Prior to stalling a slight miss occurs, at first it's intermittent then becomes more noticable and then it will stall. At idle it will just die suddenly.

When the engine is cold it usually will start and run for a few minutes, or long enough to make a short trip and get home (8 or 10 minutes). It will restart if you crank it immediately but then the stalling returns. The engine will run between stalls for shorter periods after each stall (1 minute, 30 seconds, 10 seconds, 3 seconds.) Until it will not fire at all. I get a strong crank as long as the battery lasts.

I checked flash codes several times and got 12, 14, 24, and 55. I replaced the MAP sensor and have not had the 14 or 24 since. I also replace the temp gauge sending unit because it was cracked and the IAC because it was excessively gunked up.
Avatar
Jiminfl
March 2, 2010.



Immediately after stalling, before it will start back up, check for spark. If it's missing, suspect the crankshaft position sensor. If you do have spark, this sounds like a plugged pickup screen for the fuel pump. The fuel supply system is not monitored by the engine computer. This problem acts up more often when the largest volume of fuel is flowing through the screen, ... Which is during coasting.

Caradiodoc

Caradiodoc
Mar 2, 2010.
My 96 b2500 still stalls out. If I blip the gas it will hesitate a little before the idle smooths out. If I let off the gas smoothly it goes to idle with no problem. It will run until it get up to temperature then a miss develops. Since my last post I dropped the tank and cleaned it. I cleaned the pickup screen and replaced the filter with the OE replacement. I have spark when it won't restart. I checked the crankshaft position sensor and cleaned it (some oil and gunk had worked past the rubber seal). I also checked and cleaned the sensor under the rotor in the distributor.

It is very important to my family that I get this fixed. This is the only vehicle we have that will hold all 7 of us. Please give me your best advice as to how to proceed.

Thanks.

Tiny
Jiminfl
Mar 3, 2010.
Since spark is there when it won't start, that is real helpful to know. That indicates the crankshaft position sensor is working and the Automatic Shutdown (ASD) relay is turning on. That leaves the fuel supply system which is not monitored by the engine computer.

Next I would connect a mechanical fuel pressure gauge to the fuel rail on the engine and watch what happens when the stall occurs.

Caradiodoc

Caradiodoc
Mar 4, 2010.
I was wrong when I told you I had spark. I checked fuel pressure and I have fuel when it stalls. The spark is gone. (I pulled the coil wire off the distributor and cranked the engine). I get a miss just before it stalls after fully warming up. If I blip the throttle I can make it stall once the miss starts. It will also stall when revving moderately (like when it cuts off while driving). Also, the rpms will drop while keeping the throttle open and it will hesitate when giving a little more gas. After it stalls the first time it will restart then stall several times before I get the extended crank/no start condition. After it cools down completely it will start and run fine until it warms up then the cycle starts again.

Tiny
Jiminfl
Mar 5, 2010.
Dandy. No spark should be easier to find. Do you have a '95 or '96? No information on the sensors is listed on Chrysler's web site and I don't have a service manual for a '95. This info. Is from Chrysler's site for a '96.

Start by suspecting the crankshaft position sensor. It's on the top of the transmission bell housing, next to the engine block. Normally it will set a diagnostic fault code and turn on the Check Engine light. There could be a code memorized even though the light isn't on. Do you know how to check for codes? That will lead you to the proper circuit.

I can't find the test procedure for the sensors. Start by measuring for 5.0 volts on the violet / white stripe wire. If it is missing when the ignition switch is on, the crankshaft position sensor or the camshaft position sensor is shorted. The camshaft position sensor is in the distributor. Turn the ignition switch off, them unplug both sensors. Turn the ignition switch back on. When the 5.0 volt supply is shorted, the Engine Computer shuts it down to protect it. It will not turn on again until the short is gone AND the ignition switch is turned off and back on.

If the 5.0 volts doesn't reappear on the violet / white wire with both sensor unplugged, that wire is shorted to ground somewhere or the engine computer is defective. More likely the 5.0 volts will come back. If it does, plug one sensor back in, then the other sensor. If the 5.0 volts goes away when one of the sensors is plugged in, it is shorted and must be replaced.

If you always have 5.0 volts, check the ground circuit. That wire is black / light blue stripe. Expect to see about 0.2 volts.

If the 5.0 volts and ground are always there when the ignition switch is turned on, you can try measuring the voltage on the gray / black stripe wire on the crankshaft position sensor, or the tan / yellow wire on the camshaft position sensor. An old pointer type voltmeter will pulse if a signal is being generated, but I've never done this test so I'm expecting the same results as compared to other engines.

In leiu of these tests, you'll just have to replace one sensor at a time and see what happens. Be aware the crankshaft position sensor has a critical air gap. Old / reused sensors must have a paper spacer installed and any part of a raised plastic rib on the end must be shaved off. New sensors will come with the paper spacer or a plastic rib that will wear off after engine startup.

Caradiodoc

Caradiodoc
Mar 5, 2010.
Thanks for the advice. I replaced the magnetic pickup in the distributor today and no change. I can't find a camshaft sensor in any parts house site. Is the pickup (HE sensor) what you mean? If it is then the crank position sensor is the last thing. I don't have a volt meter so I'm throwing parts at it. At least when I'm done I'll have all new stuff down there. Please let me know about the cam sensor/Magnetic coil pickup/HE sensor and I'll get the crank sensor in and cross my fingers.

Thanks,
Jim.

Tiny
Jiminfl
Mar 5, 2010.
The camshaft position sensor is the one in the distributor. Crankshaft position sensor is a few inches behind it, pushed through the transmission bell housing. Thats the one with the critical air gap. Never heard of an " HE" sensor.

Caradiodoc

Caradiodoc
Mar 6, 2010.
Thanks very much. So I understand what may be happening: The crankshaft sensor may be faulty and this causes the pcm to " get confused" as to the position of the crank as it relates to sending the signal to spark. Right? This all makes sense with the conditions as the engine warms up and the miss begins. Also why it will crank but not fire off until it is completely cooled down.

You mentioned the air gap in the previous post. I pulled the old one out but when I install the new one how do I know if it's set correctly since it's inside the bell housing?

The magnetic pickup coil in the distributor is the cam sensor? I've heard the pickup coil called the Hall Effect sensor because it measures the variation in the strength magnetic field at the sensor as the rotor spins in the distributor.

Tiny
Jiminfl
Mar 6, 2010.
You're right on all accounts. There are two types of position sensors. The crankshaft position sensor used to be a magnetic pickup. It was simply a coil of wire wrapped around a magnet. It sits next to a ring on the flex plate or flywheel. There are holes in that ring. As a hole passes under the magnet, it disturbs the magnetic field that was set up by the magnet in the sensor. A moving magnetic field induces a pulse of voltage, (electrical pressure) in the coil of wire. Those pulses of voltage are what are seen by the Engine Computer. Magnetic sensors are generally quite reliable, and can be identified by having two wires.

Sorry I didn't correlate " HE" to " Hall Effect Switch". Blame it on " oldtimer's disease". Regular transistors use a very tiny current to turn a bigger current on and off. A Hall Effect transistor uses a magnetic field instead to turn the bigger current on and off. The advantage is it can respond effectively to a much smaller disruption in the magnetic field. The sensor still incorporates a magnet. It is usually in the sensor itself, but in the case of Neons, it can be a rotating magnet that passes by the sensor. Hall Effect sensors have three wires. The ground and 5.0 volts powers the circuitry in the sensor, and the signal wire sends the voltage pulse to the computer. Unlike normal circuits, the ground wire for sensors won't have the expected 0.0 volts. The computer causes about 0.2 volts to be there. That's how it can tell the ground wires are not broken.

Magnetic sensors can be heat sensitive typically from the coil of wire expanding and tugging the ends of the wire loose from the terminals. Also, because there is so much wire length, the varnish insulation can break down and adjacent loops can touch each other. That reduces the effect of the magnetic field's ability to induce a voltage. As the voltage of the pulses go down, the point is reached where the computer no longer recognizes them as pulses. This is where cutting out and sputtering show up. Magnetic sensors do not need to have a voltage supplied to power them, although in some applications the computer will apply a voltage to one wire and watch for it to return on the other wire as a means of testing the integrity of the wires and to assist in providing information needed to recognize a defect and set the appropriate diagnostic fault code.

Hall Effect sensors have a lot of electronic circuitry which is inherently adversely affected by heat. Failures can be sudden and permanent or intermittent and will work again when the surrounding area cools down. Heat migrating up from a hot engine can take an hour or longer to dissipate.

I hope you're paying attention. There will be a test later!

When the ignition switch is turned on, the Engine Computer turns on the Automatic Shutdown (ASD) relay for one to two seconds, then it goes back off. The relay sends power to the injectors, ignition coil, alternator field, oxygen sensor heaters, and, most importantly, the fuel pump or pump relay. Fuel should remain pressurized in the supply system for weeks, but in case it bled down, that one-second is enough time for the pump to build system pressure in preparation for engine starting.

When you crank the engine, the computer knows the engine is rotating by the pulses coming from the two sensors, so it turns the ASD relay on again. To hear Chrysler tell it, one sensor synchronizes when each injector fires, and the other sensor determines when a spark plug should fire. That may be true, but if the pulses stop coming from either sensor, the computer turns off the ASD relay and the engine stops running for lack of spark, lack of power to the injectors, and lack of power to the fuel pump. There is a very important reason for this.

In the event of a crash where a fuel supply line becomes ruptured, the electric pump would pump raw fuel onto the ground creating a severe fire hazard. With the loss of fuel pressure, the injectors can't spray fuel so the engine stalls. That results in loss of sensor pulses so the computer turns the ASD relay off. Power is removed from the fuel pump, and it stops pumping fuel onto the ground. The system is very effective and relatively reliable. Ford's version of this safety system is the miserable " inertia switch. It responds rather effectively to potholes and curbs. A swinging pedulum shorts out the fuel pump wire and pops a circuit breaker.

Normally the Engine Computer has time to see which sensor stops sending pulses while the engine is coasting to a stop. It will memorize a diagnostic fault code and turn on the Check Engine light. The codes can be read easier on Chrysler products than on any other brand. Cycle the ignition switch from " off" to " run" three times within five seconds, then watch the Check Engine light. Don't crank the engine or you'll have to start over. After about five seconds, the light will flash out the digits of various two-digit codes. The first set of flashes is the first digit. There will be a little pause, then the next set of flashes will be the second digit. After a longer pause, the next two-digit code will show up the same way. The last code displayed is " 55". That just means that's the end of the message. Some vehicles start out with code 12. That just means the ignition switch was turned off recently.

Once the problem is corrected, the code(s) can be erased with a scanner, (hand-held computer plugged in under the steering column), by disconnecting the battery for a minute, or the computer will erase them automatically if they don't come back after starting the engine about 50 times. Until that happens, the codes will remain, but the Check Engine light should be off. Disconnecting the batery is not the preferred method because a lot of other stored data will be lost, in particular, short and long-term fuel trim adjustment data.

New crankshaft position sensors could have a small plastic rib or strip on the end, about 1/32" high. When you push the sensor in as far as it will go and tighten the bolt, that rib sets the air gap. It will partially wear off from rubbing on the flex plate or flywheel. To reuse it after removal, use a knife or razor blade to cut the remaining part of the rib off flush, then install a paper spacer available from the dealer's parts department. It's a sticky disc the same diameter as the sensor. Many new sensors come with the spacer already stuck on instead of a plastic rib.

As a side note, some other brands, GM for instance, and some models, only use the camshaft position sensor during engine starting to determine which cylinder to fire. After that, the computer just calculates the next one according to the firing order. If the sensor fails while the engine is running, you may never know until the engine is stopped and restarted later. Some engines will not start. Some have a 33 percent chance of firing the right cylinder and will run, but they have a 66 percent chance of firing the wrong cylinder. If the engine doesn't start, simply releasing the ignition switch and trying again won't help because the computer will just keep on following the same firing order. You must turn the ignition switch all the way to " off", then, when you try again, the computer will start over with a 33 percent chance of being right.

Caradiodoc

Caradiodoc
Mar 6, 2010.
Thanks again. I appreciate the info and am ready for the quiz. This will be very helpful next time my wife wants to know why the van isn't running yet.

I'll replace the crankshaft sensor today and gedt back to you.

Jim

Tiny
Jiminfl
Mar 7, 2010.
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