gldrsh

My 1998 24 valve will not start with out either. Cranks fast but wont start. I have to give it a shot of either then it starts. When it is running the tach does not work but it runs good. I can drive it on the freeway and it runs fine. Tach does not work. Some one told me it is the crank position sensor.

jrs_dodge_diesel

That would be the crank position sensor. I bet your cruise control and A/C don't work either.

The PCM (Dodge computer) uses the CPS signal to know if the engine is running or not. If it does not see that signal, it thinks the engine is not running. And it will not enable the A/C, tach, cruise control, and I think the alternator.

One word of caution, do not use ether on these engines. There have been cases where the intake horn gets blown off when the ether moves past the grid heaters and ignites before it even reaches the cylinders. Very bad idea.

What else is odd is that your engine should start right up. The VP44 only needs fuel and 12 Volts in order to start the engine. Once the engine is started, that's when the computers turn on and take over engine control. Are your batteries fully charged?

gldrsh

Thanks for your reply. The engine cranks fast and the alternator is charging. The check engine light also is on. I will take it to Autozone to get it scanned.I drove it yesterday and it runs great. I have not tried the cruise or AC. It just wont start without either but runs great afterwords and the tach doesn't work and check engine light stays on. The check engine light came on after I was washing the engine compartment with running water. I did not notice if the tach wasn't working at that time because the truck sat for a long time in storage. And I don't remember if I needed either at that time when I started it.

SIXSLUG

Word to the wise, stop using ether. Unless you have unhooked the grid heaters you are toying with a potential burst of the intake system and a very high bill to repair.

Mine do not cycle right now cuz it is so flippin hot up here.

Get the CPS checked out and follow JR's suggestions.....

jrs_dodge_diesel

Another problem with ether/starting fluid is it can start burning early in the cylinders while the piston is still going up due to it's low ignition temperature and ability to burn fast. This is pre-ignition and causes higher than normal cylinder pressures and has been known to crack piston rings.

gldrsh

I went to Autozone to get the codes retrieved and when he he tried to get the codes his scan tool read no connection to data link connector. He suggested there may be a fuse for the OBD connector. I never had that happen that the codes could not be retrieved. Also the engine surges when I put it in gear and it is hard to keep running. It does smooth out once I start to drive it and it idles fine even in the drive position. The truck will not start with out either. And why would the grid heater even cycle when it is 80 degrees outside? Trying to diagnose the problem myself and only the administrator giving his suggestions, I am leaning towards just replacing the CPS but thought it would be good to get the codes read. Any opinion on some fuse for the data link connector?

jrs_dodge_diesel

I highly doubt there's a fuse on a OBD port. Fuses are only used on power supply lines and circuits, not data lines coming from the PCM.

It sounds like you may have a few problems going on, and your symptoms point towards a faulty PCM

What does your voltmeter on the instrument panel read when the truck is running?

Also you can isolate the VP44 away from everything else (sensors, ECM, PCM). Just give this site a read and do the no start tests. If you do perform those tests, do not use the ether. You need to figure out if the VP44 has problems or not, and the ether could give you false indications. Like I said before, the VP44 only requires 12 Volts to start and idle.

VP44 Diagnostic


Again, use that ether with care. Too much will lead to cracked rings and bad compression. And cyclinder compression is very important on diesel engines.

SIXSLUG

Easy now, we didn't break your truck, just trying to help......good luck!

gldrsh

Thanks for the link for the vp44 no start condition. I did not have time to read it now but I will. The volt meter in the dash is a little over the middle and appears normal.The Autozone person is not a mechanic and I don't have my own scan tool. Maybe I will try a different Autozone. If it is the computer, why would the engine run great once I start driving it? The truck was also running when he plugged in the scan tool. Maybe the engine has to be off before the scan tool is plugged in. But I will read the no start link,thanks.

jrs_dodge_diesel

Because the Dodge PCM cannot control the engine. That is largely the job of the Cummins ECM and the VP44 computer. The Dodge PCM controls most the truck's auxillary functions (HVAC, auto transmission, lights, instrument panel, etc). On the gas engine Rams, the PCM is also the engine computer, and will shut down the engine if it loses the camshaft position sensor since it will not know when to fire the plugs or injectors.

The VP44 computer has the ability to function on it's own, or with the Cummins ECM. The PCM may be inhibiting the VP44 by sending the incorrect (or none) signals, thus preventing your engine from starting without a different fuel source initially.

gldrsh

I did not know there are two computers. I am more familiar with the 94-97 12 valve trucks with one computer. It is located on the passenger side by the air filter somewhere. Where are these computers located? And the tach doesn't work; wouldn't that be the crank position sensor?

jrs_dodge_diesel

Dodge PCM is on the passenger side firewall.
Cummins ECM is located on the drivers side of the engine block.
VP44 computer is mounted on top of the VP44 itself.

CPS could be the cause, but with the other symptoms you posted, I'm leaning toward a bad Dodge PCM. CPS signal passes through the ECM to the PCM and then to the instrument panel.

The Cummins is unique since the VP44 is timed to the crankshaft by gears, so the base timing is always fixed. The ECM, and sensors adjust the dynamic timing and injector duration after the engine starts and is running. This is why the Cummins can start without a working CPS or a dead PCM. The gas engine Rams cannot do this.