1500 3.9 Problems

Hello, I am new to posting, but have read and found quite a bit of valuable information here.

Anyway, I have a 1996 Dodge B1500 with a 3.9. Actually not mine, but my girlfriends father. This van has left him stranded a couple times. It would run fine, he would go in somewhere and come back out and it wouldn't start and have to be towed. After it would sit a bit, it would start back up and run again until the next time it decided not to start. I have changed the crank sensor, the camshaft position sensor and the last thing I changed was the throttle position sensor. After I changed the TPS, it ran great for a little over a week, only to have it not start once again. But this time it will not start at all no matter how long it sits. Fuel pressure is good, it has spark and will not start even if I hit it with a shot of starting fluid. Compression is good and I have really run out of things to try with this thing. It's very odd how it would run great at one time and then not start the next. Do you think this could be an ECM problem....I don't know where else to look....

Thanks in advance for any help!!

Where did you check for spark, at the coil only? How about the wire at the spark plug end?

Also, just because you have spark on any of the wires doesn't mean you have spark at the tip of the plugs. Since you didn't get so much as a pop when you used starting fluid, I would suspect no spark in the cylinder(s).

If you get spark on the wire end pulled from the plugs then try a different set of plugs. If you get spark at the coil, but not at the plug end of the wire, then change the cap and rotor. BTW, do not use use the cheap cap and rotor or you run the risk of getting misfire codes. Get the cap with the gold or brass contacts.

Thank you for your response alloro! I checked for spark using a spark plug on the spark plug wires. I also installed a new set of plugs and the cap and rotor were recently changed, but are not new, but it does have spark. The thing I was thinking is that maybe somehow the computer isn't firing the spark at the correct time or is somehow retarding or advancing the timing too much? But, I really don't know if this is even possible or not, but assume it is because it does control engine timing? But I do know that the distributor rotor is pointing where it should. Anyway, I went ahead and ordered a new computer for it and hopefully it does the trick....if not, well then it's more money wasted I guess. Like I said, I really don't know what else could possibly be the problem. Engine is in time and has compression, spark and fuel pressure, so you'd think it would start. The reason I squirted it with some starting fluid was just to be sure the injectors weren't the problem, but like I said it was still a no go.

A while back, another thing the van used to do quite a bit was start chugging along. Say if you were stopped at a light and idling, it would just start chugging and running real rough, but then it would clear up after you hit the gas and started driving...don't know if this is related or not really.

I won't get the computer for a few days, but I will let you know what happens. Thanks again for your response!!

The chugging is a classic sign of a bad crank position sensor as well as for your current problem. I dismissed the crank sensor because you said you just changed it. However I should point out that on a Plymouth voyager I used to own, I replace the crank sensor with a brand new one from Autozone and the brand new one was defective. This of course lead me to believe I misdiagnose the problem, when in fact I hadn't. I point this out just in case you want to try another crank sensor.

Thanks again alloro! I just so happen to have purchased this crank sensor from AutoZone. :eek: :banghead: What made you decide to check out the new crank sensor again? It's gonna be pretty upsetting if the new computer wasn't needed and it turns out to be the new crank sensor.

What made you decide to check out the new crank sensor again?

Everything else checked out okay, including ringing out the wiring harness for any loose or broken connections. So I took the chance and bought another sensor from someone else and voilà, problem gone.

BTW, you do know that the crank sensor has to be installed at a correct gap and at a right angle from the flywheel, right?
With the bracket that the sensor comes on, these are usually pretty foolproof to install, but you still need to look around and make sure it's lined up and straight and that the place where it mounts is clean. Comparing the length to the old one (if you still have it) is also a good idea. You did plug the new one back into the wiring harness, I assume? :)

Well, let me get into a little more detail. When this van was running for a while and starting and not starting for a bit, is when the cam and crank sensors were changed....first the cam sensor (same nostart problem after a while of driving) and then the crank sensor (same nostart problem after driving). The thing was, we wouldn't know if it actually fixed the problem because it would always usually restart and run for a while. So, after the final sensor change (TPS) and the main reason I went ahead and changed the TPS is because when it was up and running near the end, it had a pretty bad hesitation. So, after the TPS change, the thing ran perfectly smooth for over a week and we thought we had finally solved the problem. Then, he had just went somewhere....said it was running great, parked it for a little bit and then came out to restart the thing and it would not start and now will not start period. I did compare the crank sensor to the old one and it looked to be identical, although I did not check the actual clearance between it and the flywheel.

And one other thing I attempted to try that I forgot to mention is after the final notstart, I tried to replace the new sensors (one at a time) with the old ones to see if that would at least get it started and that didn't work. But of course I could have been just putting another bad sensor in it's place, but figured since it at least always restarted before, that it might help. I got so frustrated with the thing, that I got tired of working on it and towed it to a friends shop and they have pretty much ran out of things to try with it also. I posted here in hopes somebody might have had a similar problem and have read quite a few threads that are close to what this thing is/has done. :banghead:

Anyway, the last thing I am gonna try with it is the computer, if this don't work, it's time for a new van. :grinyes: I will keep ya updated!

One other thing, is that with the earlier nostart problems, the van would always respond to a shot of starting fluid, but that is not the case this time...it just seems dead and doesn't even attempt to start.... :screwy: Also, yes everything is definitely connected like it should be. :D

Well, finally got the new computer and the van started and ran fine for the trip home, but when I got home and turned it off and tried to restart it....it took alot of cranks before it would start. Then once it did start, I turned it off again and hit the key and it restarted instantly...so now I just don't know what's going on with it...really tired of messing with it. I am gonna let it sit now for a few hours and go out and see what happens.... :banghead:

Edit: Went out again and it was hard to start. I hit the key a few more times and then it finally started up. It just makes no sense....when I drive the thing around it runs excellent. :screwy: Now maybe I need to make sure the crank sensor I bought isn't junk? The funny thing is when I first started it after I put the new computer in it gave me a check engine light and it was code 11. :banghead:

When it is not wanting to start, it is acting like an older vehicle that has the timing too far advanced if that makes any sense.

When it is not wanting to start, it is acting like an older vehicle that has the timing too far advanced if that makes any sense.

By this do you mean it pauses and spins, pauses and spins, like the battery is weak; or do you mean that's it's spinning real fast?

By this do you mean it pauses and spins, pauses and spins, like the battery is weak; or do you mean that's it's spinning real fast?


Yea...it's kinda like it's trying to fire but getting "kicked" back when it does....Kind of hard to describe...but yea I think your description of pausing is probably a good one. Seems to turn over easily but then like a cylinder hits and prevents in from turning. So, do you think it would be a good idea to buy a new battery for it or at least have the old one checked out?

I tried to do this work in order to save the owner the cost of taking it to the dealer, but seems now I am just replacing stuff that just isn't helping. I am guessing the new computer did do the job since it did at least finally start after I got it in there, but hell....who knows if the damn thing just finally decided to start for a different reason. This whole ordeal has pretty much made the van untrustworthy to drive anywhere now.

Thanks again for all of your replies!

I'd still put my money on the crank sensor or the wiring harness that feeds it, as the problem.

Van has been driven for the last couple days now, but still has issues. Seems to be starting alright, but now stalls for no apparent reason and still does the chugging thing every now and then like it's loading up.

Here's another list of what I have already changed now:

Computer
Throttle position sensor
Crank position sensor
Pick up/Cam position sensor
Spark plugs
Battery
I have also removed the throttle body and cleaned it.


One final thing I noticed this van doing when I had it running one time is that it was running normal and then all of a sudden I could hear the throttle body start sucking air real hard and it got pretty loud. What in the world would cause this? Wasted alot of money on this thing and kinda hate to start replacing things again especially stuff that has already been changed. I know you said the chuuging is a sign of a bad crank sensor so hell, don't know if I should try another new one or what....it also did the same thing with the one that was replaced. I will check out the wiring for the sensor to make sure it's ok. This thing is driving me nuts...never worked on something and had this much trouble.

all of a sudden I could hear the throttle body start sucking air real hard and it got pretty loud.

How's your fuel pressure at idle and under load?

I have encountered this same problem with two Dodge Vans.One 90 model and one 93 model both with the 3.3V6.I hate to hear that someone is experiencing the same issues with a 3.9,because we now own a 97 Ram2500 conversion van with the 3.9 engine.I never fully found the solution with the other two, except that after I would remove the intake plenum and clean the varnish away as well as clean the injectors the problem would go away.This fix would sometimes last for several months but always came back.I hope you have better luck that I did.

Just to update on this. I ended up removing the engine from the van and found the timing chain was so wore that it was rubbing the side of the block and made a pretty deep goudge into it. As a matter of fact, when I went to remove the upper timing gear bolt, the gear was actually able to slip on the chain. Also had marks on the pistons where the valves had contacted them. I ended up putting a remanufactured longblock in and it starts every time now without a problem. Although, it is still having the chugging symptoms from time to time. :shakehead

If I'd known the timing chain was the main problem in the first place, I would have probably just changed that. But with the valves hitting the pistons and things, I was better off to replace the whole engine. The van was in the shop for a while, but we were told the chain was in good shape....but apparently not.

Thanks for the replies!!

hi,
still having chugging problems--
remove fuel tank and clean it out, also change fuel filter.

Have your checked the catallitic converter. If the converter is contaminated or broken you can get backpressure that will upset the start mixture?
Have you had the codes checked.

This is an old thread but I thought I'd post if it'll help someone out... I had the exact same problems described by the original poster but in my 1997 Chevy Astro 4.3 V6. Tried everything like the original poster but nothing fixed it permanently until I had the fuel injectors (called the "spider" assembly) and the fuel pressure regulator replaced. Hope that helps.