Ok, this thing has me stumped. I hope you people can give me some insight as I know there are some good people here.

Background -- 1996 Dodge Ram 1500 Full Size Van 3.9L automatic and about 60,000 miles. I left a job site and pulled out and while accelerating the engine died. No hiccup or jerking - just 100% quit. I have a Chilton's manual as a guide for the engine elctrical.

I have a Chilton’s book for the wiring and it seems to be accurate. I have a computer diagnostics software package and OBD2 adapter to check for codes and read sensor outputs - plugs right into the OBD2 plug just like any reader or scanner. I also have a logic probe for checking any digital signal outputs or digital circuits. And a volt-ohm meter of course. I have pressure and vacuum test equipment as well.

I have tested as follows -

Absolutely no codes (DTC's) of any type.
No blown fuses - under hood or in dash.

If you crank for maybe 5-10 seconds at wide open throttle, the engine will fire and run for about 1-2 seconds then shuts down. If you continue cranking it is almost like it is just on the verge of running but just will not. I hold the throttle wide open to do this. I can not get it to fire unless I use wide open throttle. There is an output from the throttle position sensor (TPS) using my computer software. There is 5 VDC as supply power for the sensor.

Found low fuel injection pressure - Changed fuel filter in tank (not an easy job) and have 45-48 psig while cranking. Pulled injectors also to be sure they were not plugged. All 6 injectors firing and nice even spray of fuel. I am convinced it is getting fuel.

Checked crank position sensor and found completely open from 1-2, 1-3, and 2-3 contacts and a very small bare spot on one of the wires. Replaced this sensor. Still will not run. I thought this was the problem as I believe the engine starts on the cam sensor but runs off of the crank and cam sensor. I later on bench tested the crank sensor with a 5 vdc power source and logic probe and the sensor removed is working. So a working old sensor and a new one have been tried. Unplug this sensor and you get a code.

Checked cam position sensor and it seems to be ok. Unplug it and you do get a code. 5 VDC as power supply. Also note that the engine will fire - see above. Testing with a logic probe on the engine shows it is outputting a pulse.

The coil test ok for primary and secondary resisitance with volt-ohm meter. Distributor cap, rotor, and secondary ignition wires all look ok - did not do any testing with any type of test equipment. I have no way to bench test the coil. Using a gap type spark tester it does produce a spark.

MAP and TP sensors test ok. Removed the MAP sensor and bench tested it. Has 5VDC as power when on the engine.

Auto shutdown relay tests ok - switched it anyway with the horn relay.

Checked voltage to the primary side of coil while cranking -- about 10.4 volts - not 12 but should be ok and the engine will fire and run for about 1-2 seconds anyway. Also unplugged the O2 sensors as they are heated and on same circuit as the ignition coil. Spark plugs are firing and it seems to be a reasonable spark and engine does run for 1-2 seconds. The 10.4 volts while cranking is still there with the O2 sensors unplugged. I am not sure if this 10.4 volts is a problem because it does fire and run for a second or so. See above. I figure it is due to the power drain from the starter.

Have not checked the idle air control.

Have not checked for sync between cam/crank etc. as I have no tool.

I have not removed or disturbed the distributor in any way except to remove andinspect the distrbutor cap after this problem occurred.

With only 60,000 miles I would expect the engine compression would be OK. It has not shown any lack of power or any difficulty in starting until this problem.

Questions -
Can these engines get out of SYNC without the distributor or crank sensor being removed? Engine has a metal timing chain - not a belt.

Is there a way to do a cam/crank sync without a DRB tool or some other expensive piece of equipment ??

Any thoughts on anything else I might check or have overlooked.?? I am thinking it must be electrical.

I realize it may be the computer ... but I want to be sure everything else is done before that step.

9-13-07 I received a used PCM (engine computer) today. I installed it and still the exact same problem.

Can I give a $20 prizefor the solution ??

Thank you,
DB <------- Dumb Butt

 

When you tested the ASD relay did you just test the relay or did you actually test for power on both sides of the contacts and coilwhile the relay was in place andthe key/ignition was on? Just because the relay is okay doesn't means it's getting activated. Also, are you sure it was the ASD relay you tested and not the fuel pump relay? Both are under the master cylinder.

Did you test the 5vdc crank sensor circuit for power?
Did you check for any compression?
Is your distributor rotor turning while cranking?

 

Alloro --- Thanks for the reply.

ASD relay - Did not actually test the original relay itself but simply switched with the horn relay (same) which I knew was working. Whenthis did not help, I checked this relay for coil and contact continuity - ok. Checked then for power to coil with switch on - ok. Checked contacts with coil energized - ok. Also gets voltage to the ignition coil with swich on. I think this is ok - but I can always check again. The 10.5 volts at the ignition coil is a worry to me though - I plan into check this some more. Low voltage to the ignition coil means low output from the ignition coil.

It is the ASD relay - verified by owner's manual and elctrically for what it powers - like ignition coil. These are not under the master cylinder but on the radiator frame/support at very front of vehicle in a fuse/relay box - very easy to get to. There are several other relays in this box - horn, fuel pump, AC clutch, etc.

Crank Position Sensor - Yes, it is getting power. The sensor outputs a signal back to the PCM. Even put a new one on. The one removed bench tests ok.

Compression - I did not check the compression with a guage. The engine only has 60,000 miles. It does not use oil. It will fire as described but will not continue to run. With low compression I expect to see an engine that will not fire on cranking since that is when compression would be the lowest. Once started, I would expect to see even a low compression engine continue to run. I can always check but expect this to be unlikely.

Rotor - My bad !!!!!! I have not checked this. This is a possibility for sure. I don't know if this would give a code or not.

I am thinking this whole problem may be a mechanicalissue with the timing as there are no DTC's and since I can not find any electrical problem. I am also thinking a weak spark might bethe problem. I have no scope to actually measure the voltage output from the ignition coil.

I knewthere were some smart people on this forum.

Give me a few days to check out a couple of things.

Thanks again,
DB

 

You might want to also check that the distributor is lined up correctly. I've seen them getturned when the shaft is getting insufficient lubrication. To checkit,bring the engine to TDC and pull the cap off. The rotor should be pointing to the #1 cylinder mark on the distributor body. Sometimes the mark is a line labeled #1and sometimes it's a notch cut into the body of the distributor. Also, the rotor should be at or around the 2:00 position if looking down from the back of the engine.

The symptoms your engine has is typical of a distributor that is not timed correctly. Some distributors have just a slot at the end of the shaftand can only go in correctly or 180 degrees off. Because of this, if the shaft jumped out of it's notch it could've gone back in 180 degrees off. Other distributorshave a nylon gear held in place by a pin. If either that pin sheared or the nylon gear stripped, your distributor might still turn but the timing will be off.

When you line up the timing mark with TDC make sure you have the #1 plug out and that you are on the compression stroke. Don't assume that just because the rotor is at 2:00 that everything is fine and dandy.

 

Most auto parts stores will test a coil for you, just bring it to them.

The 12v power for the coil comes right off the ASD relay after going through a few splices. One of those splices could be weak and causing the voltage drop. You could verify this by using an ohmmeter from the ASD relayoutput terminalto the coil wire and see if the reading is more than an ohm or two.

 

Sounds just like our '01. We were experiencing the same symptoms and I checked EVERYTHING. I finally broke down and just started buying sensors and replacing them to see if it would run any different. It ended up being the coil even though there was spark! No problems after that.

 

Thanks for the thoughts Guys

alloro -- I have managed to get out and check the distributor rotor yesterday. The rotor is turning and is firmly on the distributor shaft - and I mean it is snug. There is virtually no play in the distributor gear as it contacts the camshaft. Checked the cap again for cracks, moisture, etc. - no problem seen.

I plan to check into the primary coil voltage next. I will check the wiring to see if there is any resistance causing the 10.5 volts. Maybe I'll try a coil as well.

I did remove the coil and take it to AutoZone but it was very clear that no one knew how to test the coil. I did check it for primary and secondary resistance and it checked right in spec.

Next I will verify that the distributor is lined up on No.1 cylinder. I hope the crank pully has timing marks - would make it a little easier to do. I have not had any backfire or anything like that. But I agree ithas symthoms like it may be a timing problem.

Between work and everything else it will probably be a few days.

Annihilatorx-You probably still saved by just buying parts and replacing. Just think -- you are set for the next problem as well.I have spent a lot of time on this and I am certainly getting frustrated.

The next new car I buy, I am going to get a complete set of sensors as part of the deal.

Thanks for the help !!
DB

 

Sept 16, 2007

Did some more checking today as follows:

Checked the voltage to the coil - 12.6 at the battery ----> 12.6 at the fuse ------> 12.6 at the ASD (auto shutdown) relay ------ 12.5 at the ignition coil when not cranking. This is as good as it gets.

Checked resistance from ASD to the coil -- maybe .1 ohms at most.

Voltage at the ignition coil while cranking the engine --- about 10.6 VDC.

Checked rotor button location to see if it is properly aligned with No.1 cylinder at TDC. Removed spark plug to be surethe pistonwas all the way up ( you can see the piston through the spark plug hole). It is aligned as it should be. This means the timing chain, distributor gear, cam, crank, and distributor rotor are all mechanically linked the way they should be. Spark plug looks good except for some wetness from gas.

Decided to replace the coil -- still will not run

Checked coil wire to the distributor -- Found coil wire to be corroded badly at the center terminal of the distributor cap. Replaced coil wire, distributor cap, and rotor.

OK, It has gas, it has spark, relatively sure it has compression, it is mechanically timed at least close, it has a different computer, every sensor I check tests ok and puts out a signal, and all the wiring needed for ignition seems to be ok.

SO HOW CAN THIS THINGNOT RUN ??

 

Oops I didn't pick up on the fact in your first post that the 10.4 volts at the coil was while you were cranking. Getting 9-11 volts at the coil while cranking is normal due to the drain on the battery from the starter.

Seeing the piston up isn't a correct way to determine TDC. Since the cam turns at 1/2 the speed of the crank, the piston is at the top twice to one rotation of the cam/distributor. Even though the piston is up there, you could be off 180 degrees on your timing. You have to stick your finger in the spark plug hole while the piston is coming up. If you get pressure blowing out the hole will you know you're on the compression stroke.

Food for thought...the used PCM you received wasn't necessarily a working one.

 

Have you sprayed carb cleaner or starting fluid into the intake to see if you can get the engine to fire up?