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Amedee, Dodge Technician
Category: Dodge
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Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1996 Dodge Ram 1500 4 x 4 Automatic, 5.2 V8. Did a

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1996 Dodge Ram 1500 4 x 4 Automatic, 5.2 V8. Did a transmission replacement. While doing that , the wire came of the CKP sensor. Installed a new sensor and the engine started right up and ran for about 5 minutes. After that it would just barely idle and whne given any throttle, it would die. Thought the new CKP died so put in aniother one. Now it won't even idle. Only way I can get it to start is by using Clear Flood Mode and then it fires and dies. Fuel pressure is at 50 psi. Whne I did get it to idle, it would run very rich and could only get 6 inches of manifold vacuum. I tried plugging every vacuum fitting and no joy. The Map sensor reads about 4.4 with KOEO. Also did a smoke test and found no vacuum leaks.

Hello and welcome!

My name is ***** ***** I can assist you with your question.

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NO codes in the computer?

Does it run better on alternative fuel if you were to disable the fuel system?

Customer: replied 10 months ago.

No Codes. Haven't tried alternative fuel but can hook up my pressure injector cleaner. The fuel is fresh and volume and pressure are good. The Short Term Fuel trim when it did idle was over (-20)% so obviously running very rich.

Try disconnecting the electrical connector going to the crank sensor and see if the engine starts and runs of if it starts and runs any better (allow for longer cranking time). Also, check the distributor sync in your scan tool while the engine is running.

Customer: replied 10 months ago.

I have tried disconnecting the crank sensor and engine will not start. I know that some Chrysler products are very sensitive to CMP/CKP sensors. But two new sensors?

No, I dont think the crank sensor is bad.. although that is possible. We need to try and figure out if this is a base engine mechanical problem or an ignition related issue.

Customer: replied 10 months ago.

Well, I know it gets fuel and spark. I have not touched the didtributor but could have disturbed some wires when trying to plug the CKP back in behind the distributor. Here is something odd though. With the first new CKP it would at least idle, rough but idle. With the second new one it will not run at all.

You might want to replace it under warranty just to be sure thats not an issue

Customer: replied 10 months ago.

The CKP? I did that this morning :-)

I know.. I was just suggesting to do it again..

You can also check the signal from the camshaft position sensor inside the distributor as well as checking the distributor sync to ensure things did not get out of alignment when doing this recent repair.

Another possible cause would be a damaged flexplate causing an irratic signal or reading from the crank sensor as the engine is running. This could have been done by accident when doing the transmission replacement.

Customer: replied 10 months ago.

Possible, but it ran fine for a couple of minutes before all this started.

I can scope the CMP but not sure about the distributor sync whne engine is not running. I just did a relative compression test, triggering of the cyl 1 injector. Please have a look at the screenshot.

Thanks for the upload! Are you able to scope the crank signal?

Customer: replied 10 months ago.

According to the wiring diagram that I have, pin A8 of the PCM is the crank signal. All I get when cranking is a straight 4+ volts, no wave at all.

YES, I just double checked. That is the correct pin. Provided you are on the right wire and pin going into the PCM, this is most likley the issue.

Customer: replied 10 months ago.

Since I can't get to the CKP connector, I am measuring right at the PCM, Grey and black signel and purple and white 5 V reference. Are these after market sensors known to be a problem?

YES, but I dont think thats the problem. I suspect there is a wiring issue from the crank sensor to the PCM

Customer: replied 10 months ago.

OK. can I run wires direct from the crank sensor to the PCM to eliminate that problem? There are only 3 wires - 5V Ref, Ground and Sense. Correct?


Customer: replied 10 months ago.

Thanks for the pic! Which circuit or where do you have this hooked up to?

Customer: replied 10 months ago.

Hooked up to line A8 of the PCM (CKP sense) The on off times seem a bit strange.

Why is that?

Customer: replied 10 months ago.

On other vehicles that I have worked on, the on and off times seem nearly identical. Even now, the engine will not start.

Have you tried checking the cam signal? Can we check that while the engine is cranking real quick?

Customer: replied 10 months ago.

Let me go and hook up the scope. By the way, what should the manifold vacuum read while cranking?

That is a very good question. It depends on if you were to seal off the throttle body air tight. If you dont do this, it would only pull a few inches of vacuum. If you seal off the throttle body nice and tight, it should get up to double digits pretty fast while cranking.

Customer: replied 10 months ago.

Here is the screen shot of the CKP/CMP. Yellow is CKP

It looks good to me but youl want to verify that to a good known cam/crank wave form. I think has good known wave forms you can access.

Are you able to upload a video of the engine cranking over so I can view it?

Customer: replied 10 months ago.

What exactly would you like in the video. Also, The Vacuum while cranking over is only about 2 inches. Would this not make the MAP think that it is operating at high throttle and cause the fuel to be pouring.

I would like to hear the engine crank over. I would also like to view the engine from the front of the vehicle watching it crank over and listening to it. You would need an assistant to crank the engine over while you take a video.

If the engine compression is good and vacuum is normal and the ignition timing is dead on or close to being correct, but the MAP sensor is not getting a good signal or sending a good signal back to the computer, it would simple prevent the PCM from either pulsing the injector open or yes, causing them to open up more than they should. All you would need to do is disconnect the fuel system and see if the engine runs on starting fluid. It should very well run on starting fluid no problem when doing this test. If not, something else is wrong that needs to be adressed.

Customer: replied 10 months ago.

I can get it to run on starting fluid, although rough. Here is something else - I just scoped the injectors. The on time is over 50 ms where It should be less than 5 ms at idle.

Try disconnecting all connectors going to all fuel injectors and see if you can get it to run nice and smooth on starting fluid.

Customer: replied 10 months ago.

Same thing. I can get it to run but somewhat rough and inconsistant.

Then something else must be going on. Either the ignition system or a base engine mechanical problem.

Customer: replied 10 months ago.

I've scoped both primary and secondary ignition. Both look good. I've smoke tested the intake system and found no vacuum leaks, But, what other than the MAP sensor would cause a 50ms injector pulse? Also, looking at the relative compression test, does it seem like there is a mechanical issue? Also, if you look at that relative compression test, see when the injector opens. Seems way before TDC - no?

Almost seems that the injector is open on the compression stroke??

The engine coolant temp sensor and TPS are the other two sensors the PCM uses for injector pulse width. I do know the injector is supposed to open on the exhaust stroke. This is normal. Even if the injector timing was off, then the engine would still run smooth on starting fluid.. which is doesn't. That leaves a base engine mechanical problem or an ignition timing issue. Did you check the distributor sync yet on your live data?

Customer: replied 10 months ago.

When you say distributor sync, are you asking about CKP/CMP sync?

Yes Sir

Customer: replied 10 months ago.

Yes, when it was running it was in sync.

Right.. but it should give you a number. It might be another pid

Customer: replied 10 months ago.

I don't remember that. Are you talking about the angle difference? It was 4. I just did a real compression test. Similar to the relative one. Most at 155, a couple at 120 and one at 100. Not great, but should still run, as it did whne it came in. All the plugs are jet black and fuel fouled.

The fuel fouled plugs are due to the running issue. Either too much fuel or an ignition timing issue like I suspect. I hate to say it, but it may be a damaged flywheel.

YES, the pid for the distributor sync should be 0 degrees plus or minus 2 degrees.

Customer: replied 10 months ago.

I can try and see if it will show while cranking


Customer: replied 10 months ago.

Re: the flywheel, would the CMP/CKP not be out of Sync?

Yes because the crank sensor gets its signal from the flywheel

Customer: replied 10 months ago.

Distributor sync is 0. Ignition timing is about 8 BTDC while cranking. Did a relative compression watching the coil secondary and the firing is right around TDC, so I assume valve timing is ok. The only thing so far that is not right is that the injector pulse is 10 times what it should be at cranking.

What is the TPS and MAP signal at when cranking?

And that still would not explain why this suddenly happened right after this work was done..

Customer: replied 10 months ago.

TPS is .62 VDC and MAP is 4.2 VDC while cranking

Those readings are good my friend.

Customer: replied 10 months ago.

If the MAP is at 4.2, wouldn't it think that you are at almost full throttle? What else could cause a 50ms injector pulse width?

At 4.20 volt that indicates less than 5 inches of vacuum. Again, without sealing off the throttle body, your not going to have much vacuum when cranking.

Customer: replied 10 months ago.

Got it. So, Valve timing is good, ignition timing is good crank and cam signals are good, TPS is good, MAP is good. Just getting flooded with fuel. Before I lose all my hair, what else can I test to see the cause?

I think the plugs are fouled out because the ignition timing is not correct. That is my theory. Distributor cap, rotor, ignition wires maybe? I can opt out and leave this question open for other experts to see if they have some other ideas that may help. Good luck!


Customer: replied 10 months ago.

Just before you leave, would you answer two things fpr me. What should the ignition timing be while cranking and what should the injector pulse width be while cranking. Thank you.

Hello and good morning. I logged off last night before I saw your reply. As far as I am aware of, the manufacture does not release that specific information. It would sure be helpful if they did as it would help us in this particular situation. However, I cannot find this information for this vehicle and I dont think I have ever come accross this information for any vehicle. I am very sorry.

Customer: replied 10 months ago.

First, I would like to thank you for all your help and timely responses. Second , I want to tell you that I found the problem. I usually start with the obvious, but failed to do so this time. I woke up in the middle of the night and had a lucid moment. I reviewed all the information and the low manifold vacuum kept bothering me. Since everything checked out on the scope, decided to see if I had an exhaust blockage. Sure enough, I removed the upstream O2 sensor and the engine fired right up and ran perfectly. Tom.

Hello Tom! Thanks for the heads up and feedback! That is great news! I am glad to hear it is running good.

However, a few things.

First, exhaust does not plug up that fast. At least based on my experience. It takes time for it to cause low engine vacuum. It happens slowly over a long period of time. Based on your description of the problem, it was running good and then 5 minutes later it started running rough. In addition, this would not be related to any of the recent work that was done. So it must be a coincidence? Did you do anything to the exhaust while replacing the transmission?

Either way, I am glad to hear it is running good!!

You are most welcome!

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Customer: replied 9 months ago.

Since the exhaust was taken off during the repair, and the catalytic brick was in pieces, I assume it moved around and plugged the cat.

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