No start issue

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Chadewing

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Big piney Wyoming
Ram Year
1996
Engine
5.2
I have a 1996 ram 1500 with a 5.2 bought the truck and the ecu was bad replaced it now truck will start but won't stay running longer then 3 or four seconds the after 3/4 times trying to start nothing still turns over but no fire good fuel pressure volts good sparks great but what I have noticed is that the tach won't come on I have a 99 Durango that had loose wire to the cluster and would do the same thing start and run for a second then die fixed the cluster she runs Awsom so any help getting my truck going would be nice my number is 3072319277 if anyone can think of anything
 

dudeman2009

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2001 1500 Sport with enough electrical modifications to make my brain hurt
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Magnum 360
I have a 1996 ram 1500 with a 5.2 bought the truck and the ecu was bad replaced it now truck will start but won't stay running longer then 3 or four seconds the after 3/4 times trying to start nothing still turns over but no fire good fuel pressure volts good sparks great but what I have noticed is that the tach won't come on I have a 99 Durango that had loose wire to the cluster and would do the same thing start and run for a second then die fixed the cluster she runs Awsom so any help getting my truck going would be nice my number is 3072319277 if anyone can think of anything

First, was the pcm (ecu is fine, just terminology differences) the same year and engine size?

If yes, try holding it at a high idle for a few minutes with the gas pedal. Sometimes after doing work on mine where I have the battery disconnected for a long period of time, it will fail to idle properly for the first minute of operation, but after that it never has a problem until I 'clear' the pcm by removing the power.
 
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Chadewing

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I have tryed that tryed to give it a little gas just seems like if I give it gas then it won't fire at all
 
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Chadewing

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If I leave it alone for about 30 min then try again it it starts for a few seconds the dies
 

dudeman2009

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Any codes being thrown?
 

dudeman2009

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I think I has something to do with the tach not working

Thw tach gets its input from the PCM over the CCD bus. There is nothing wrong with the bus if the other gauges are working, there is something wrong with the PCM or its sensor inputs.

Since it wont stay running lets just pretend that it wont start, it just cranks.
You have spark and fuel as evident by its attempts to run, but it wont stay going. There could be four reasons.

1. not enough air
2. not enough fuel
4. poor spark
3. bad sensor input causes PCM shutdown.

These are listen in order of easiest to check.

First, pull the brake booster line and try to start it. If that fixes the problem, you probably have a bad IAC valve.

If that doesn't work, spray brake clean or ether into either the brake booster line or throttle body while trying to start. If that works, you have a fuel delivery issue. Check your injectors and or fuel line pressure.


If none of that works you need to check the spark plugs, wires, distributor and coil.

To check the coil, get a multimeter out. Probe between the two pins on the bottom side of the coil, you should get about 1 ohm, if its within .2 ohms your great. Then check from the tower to a pin, should be anywhere between 11K and 15K ohms, within .3K ohms is ok.

If that tests good, well you are looking at trying to figure out if the PCM is the right one for this year and engine size truck or not.
 
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Chadewing

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So I just went out hooked up the battery and it started and revs up to I'm guessing around 4000rpm for about five or six seconds then died started again five or six seconds then died now won't fire again
 

dudeman2009

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I'm kinda thinkin I might be the fuel pump

If you don't want help, don't ask. I gave you a list of things to try, easy things that shouldn't take more than 15 minutes. Basic things that rule out whole sections of the engine and its management, and will help everyone else on here help you figure this problem out. Sure the fuel pump can cause this kind of operation, but so can a bad sensor input, or a bad pressure regulator, or even debris in the line. Before you even bother with the fuel pump you need to rule out the much easier and cheaper problems.

You said the old PCM was bad, but not who made that determination or why they came to it. Was it because the gauges didn't work? Was it throwing codes for it? Was it physically damaged? or was it just not starting, and now with the new PCM it starts but only for 5 seconds.

I'm not trying to be rude here, but I gave you a list of things to try. You came back saying nothing more than you did in the original post. You started it, and it died, now it refuses to restart.

I'll be honest, you sound like some of the guys I went to school with. They liked to look at a problem on a truck (I went to school for diesel technology/mechanics) and without testing very much of anything, just start guessing at what the problem is. They are known as parts throwers, they guess what is wrong, put a new part in and see if that fixed it. If not, they guess again, the cycle repeats until the problem is fixed or their limited knowledge is exhausted. No one wants them working on their cars or trucks, because they cost everyone a lot of time and money. Sometimes they get it right on the first try, that does happen, but when it doesn't time and money are wasted.

Instead of throwing parts at it, test it first. There is hardly anything on an engine that can't be tested for proper operation, even by the home gamer.

I'm willing to help you. Thats why I said anything in the first place, but you have to work with me.
 
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Chadewing

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Ok so I thought it was the the fuel filter changed it out if I start it and rev it to the nuts it hits about 5500 rpm I think for about 6 seconds so bought a fuel pressure gadge it's about 45 pounds consistent no madder of anything so I was curious about some other thing on the engine now when it fires up and runs I have a stethoscope I put it on the injectors after a few seconds of it running it they quit pulsating why would this happen
 
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Chadewing

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Sorry dudeman I'm not ignoring you and I went threw your list and found out about the injector problem
 

dudeman2009

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Sorry dudeman I'm not ignoring you and I went threw your list and found out about the injector problem

I'll start by saying that no apology is needed, I wasn't offended, I just let loose a little bit. Sometimes I forget that people on here aren't as self righteous as my old co-workers. I'm happy to help almost anyone, even my old co-workers, at least the ones that didn't go around and brag about how they solved the issue to everyone else.

I do apologize for being short with you, it was unnecessary and rash.

Since we know that the injectors are cutting out after a few seconds, and then the engine dies. The fuel pressure is good, the injectors are working, before they shut down it runs well enough to rev that high. We can go with the ignition system being good, as well as getting enough air. Since the injectors shut down we can probably rule out any low fuel issue.

Since it only runs for a few seconds, before the PCM shuts it down, i's be looking at sensor inputs. Its highly unlikely the new PCM is damaged as well.

One of the critical sensor inputs is the crankshaft position sensor. If the PCM doesnt receive input from this sensor within 3 seconds of operation, it shuts down. Then the engine freewheels until friction brings it to a stop.

It will still crank in this condition as the PCM only shuts down the ASD relay. The ASD relay controls spark, fuel injectors, and I believe the fuel pump relay.

Since you also have no tach, the crankshaft sensor is very suspect as that is what the PCM uses to determine the engine rpm.

I would check your crankshaft sensor. It is possible that the connector has been damaged or unplugged. It is a hall effect sensor that uses a chopper gear to determine crankshaft position. If the little reed inside has broken off, or it has been smacked hard enough, it will need to be replaced.

Attached is a picture of the location of the sensor. It is located on the passenger side of the engine right beside the transmission bell housing.

If you wish to test the part before throwing one at it, take a multimeter and check the following.

On the connector that plugs into the sensor, the tab is the top of the connector. Take your multimeter and connect the negative to a known good ground (the battery negative will work as well) Then probe the rightmost pin (violet/white) and have someone turn the key to run but do not try to start it (you can pull the starter relay if you feel like it). You should read right near 5v. If that is good, set your multimeter to resistance or continuity, and keep one probe on a known ground and use the other lead to probe the middle pin(black/light blue). Turn the key to run, you should see near 0 0hms or a beeping (this will not hurt the PCM as it is used to seeing a 4-5v signal on this pin and nearly all Digital multimeters use a 3.7v probing voltage. If both those are good, then the wire leading to the PCM is good (with exception of the leftmost wire, that is the signal wire and cannot be tested without pulling the PCM harness)

If you wish to test the crankshaft sensor, though it is not nessesary, you will need to have someone hand crank the engine, while the key is in run while you are back probing the wire while plugged into the crankshaft sensor. You would be probing the remaining pin (grey/black) and with the multimeter attached to a good ground and in DC volts, you would be looking for a 4-5v pulse as the engine is hand cranked.

Just note, back probing with a paper clip will damage the weather seal on the connector, its best to use a proper back probe tool, even then damage is still possible.
 

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