Hello folks,

Got my motor back together, went to fire her up and she keeps dying on idle. If you run her past 1200 rpm the thing runs the **** if you go below that you hear the IAC starting to suck in and it dies off.

On my scantool,it's not showing a Crank Reference signal,could this be a problem. Obviously,it's working because of the fact that the RPMs,etc show.

It has had a new TPS,IAC,Crank Sensor,pickup coil, and map sensor.

Only other thing it could be my dad was saying is,since i changed the timing chain,etc there is some anti-freeze in the oil and it was running rich for awhile,could the oil be to thing causing a shutoff to be initiated from not enough oil pressure at low RPMs?

Thanks for the help,
Brandon.

 

https://dodgeforum.com/forum/2nd-gen...tart-help.html

 

My truck starts though.

 

To answer that question regarding coolant / lack of oil pressure, the answer is: NO.

That is not what's going on here.

Under normal circumstances, IF there's no CKPS signal (crank reference) it will not run- AT ALL.

The CKPS is the master clock for the entire EFI system. The entire system is timed, based around that one sensor so, if it's not working, the PCM is programmed to execute the AUTO SHUTDOWN command thus NO PWR to anything. This cuts power via the ASD relay in the PDC.

Now, here's what I think 'MAY' be the root cause based on the information that was provided:

WE know that you put the motor back together and:

A. It runs fine at higher RPMs so long as your foot is on the gas. Is this correct?

B. When it idles it dies right out / does not stay running. Is this correct?

IF the answer to the above two questions are YES, then, there's a very good chance that there's a SYNC issue here and, what that is, is a large offset between the crank and the cam sensors at the PCM program level in which case, you will have to take it to a dealer to have your CAM re-timed to your CKPS values along with resetting the SYNC offset value in the PCM to fine tune the timing of the EFI / fuel delivery system.

At certain RPMs this can lead to what your seeing on your scan tool as well. It will LOSE sync.

What I don't know is:

Scratch my earlier comments, I just found out what you did by re-reading it two more times.

Ok, if you put back in the OEM CKPS and CPS - it will run fine and, that error will go away.

The reason why your having issues is, the NEW CKPS and CPS are NOT putting out exactly the same waveform as the OEM ones and, if your going with aftermarket sensors, this can be a PITA to remedy. I recommend to use ONLY OEM for those two sensors. There's some history here that I have posted on in regards to what I am saying but, I don't have time to re-state it now.

Moving on: you will most certainly have to have your PCM adjusted for those two sensors because, both are out of sync with what's programmed into the program at the PCM level. You can not change this without using a DRBIII or DART tool to reprogram the values.

While some of the more expensive tools such as the 9K snap on tools will allow you to change / program the value however, you will have no way of knowing what is the best value without running it on a scope / rack rig.

The dealers have this tool and, they can tune it precise to the best value to ensure the timing is on and that the sync will not lose lock.

CM

PS: Brandon: do this simple test first: place the OEM sensors back in and re-test. If the issue subsides, LOSS OF SYNC was the issue.

That air sound, that's an indication there but, for now, just start with those two and see what we got.

 

Hello,

Thanks for your reply. The Crankshaft Positon Sensor was replaced before I obtained the truck, once I got it I replaced the timing chain, and I stupidly took out all the valves. So the entire top end of the motor was re-built.

I also tried to reset the distributor to and stuff via my scantool, but I am not sure how it works (it's a snap-on solus).

I changed the oil today and it ran for approximitly 40-45 minutes at idle before it died, which at that point it started running fine over 1,200 rpm again. Let off the gas and it instantly stalled out.

TPS voltage was 0.82 and Fuel pressure was at 46 psi.

 

Something is out for sure here and, the problem is, that too many things were changed to rule any of them out.

But, here we see that it ran fine for 45 mins at idle and just dies out.

Q: any codes / idiot lights?

This still could be loss of sync here. Have you MONITORED the fuel pressure 100% up to dying? I'd like to rule out the fuel supply as a starting point.

Really there's only a few things that will cut the engine like that:

Fault in fuel system

Fault in ignition system

Fault in timing system (loss of sync) which, both this and ignition faults would lead to the idiot light illuminating on the dash.

TEST:

Start with fuel system first as it's the easiest to rule out. MONITOR pressure over time. IF psi is 49 psi ± 5 psi- rule the pump out.

Check coil primary and secondary OHM test.

CHECK: voltage at coil INPUT*

* This is an operational test. Monitor the input voltage to the coil over time while running.

START there first and let's see what we got.

NOTE: you will most likely have a tough time using that Snap On tool. I am not trying to put you or the tool down here but, it's not really the ideal tool for this application.

Will check on the status tomorrow.

CM

 

Thanks,

Yeah I know the snap-on sucks.

When you first turn the key on it builds about 34 psi of pressure, when you start the truck it will bounce between 30-50 the entire time, almost seems like a pressure regulator? It might cause the problem.

Fuel pump is 3 weeks old; replaced by PO.

It's also straight piped at the moment, I am going to weld my exhaust up tommorrow night, I am going to double check the fuel pressure and put the exhaust on and I'll see what happens.

Thanks for the help.

 

So the only problem is it won't idle, right?
I doubt very much it a crank sensor problem. You should be able to set the sync with your Solus. When you select cam/crank sync rotate the distributor until it reads 0%.
Will it idle on a cold start or does it only happen when the engine warms up a bit?
Fuel pressure does sound a bit iffy. unplug the vacuum hose on the regulator and see if the pressure stabilises?
Does the O2 sensor switch from rich to lean? sometimes a bad O2 sensor cam make it run so rich or lean that it won't idle. You can try unplugging the O2 sensor and see if it makes a difference.

Good luck.

 

It idles good until it warms up, yes.

Thanks for the reply; will try that stuff tonight.

 

There's the issue right there- that pump is bad and is not operating within spec. PSI rating should be constant- should not vary more than 5 psi.

By varying 20 psi- that is four times the MAX allowable deviation.

NOW, let's just hold on just for a second and ask ourselves what ELSE would also cause that....ok.

Answer is: VOLTAGE DROP at the pump input will cause the pump motor to drop RPMs, thus leading to LESS OUTPUT, thus resulting in a pressure drop.

The reason this comes to mind is:

You have a new pump- so the PO claims / proves. Chance of the pump failing - 50/50- not unlikely but, leads one to check the supply voltage to the pump first before condemning the pump.

Just measure the voltage at the connector and see if there's fluctuation. There's two methods of doing this and they are:

1. operational

2. non operational

In Test No 1. you will tap into the harness by backprobing and run vehicle and monitor voltage

Test No 2. Backprobe the connector, turn the key to <ON> five times. Note voltage output deviation.

If at anytime during test a sudden drop / loss of voltage- there's an issue with your supply feed which, the first place I would check is the fuel relay in the PDC.

IF voltage is steady- the pump is the root cause.

CM