Archived 98.5 24v electrical demons ''Help me"

[Mavric]

My 98.5 24 Valve recently started taking longer for the wait to start to light up and turn on the fuel pump. That didn't bother me much but now sometimes when you start it and just barely touch the throttle it races wide open 3200RPM. And when you do it in gear it takes off wide open out of control and I slam the brake it stops doing it then when you take off it is in limp mode 1200RPM only. I'm confused because it doesn't do this all the time only about twice a week and then it goes back to normal. It seems like the ECM might be booting slowly or a sensor is causing this problem. I have an Edge comp and it does this also with it turned off. Any advice?

 

[klcammie]

first not only turn Edge off unhook it compeatly. To see if it does it again. Then go to http://www.bluechipdiesel.com/. There are instructions and steps to check out the ECM, lift pump and injection pump. Also check battery voltage and all grounds. There is one by the pass. side battery that is for the ECM and needs to be clean and shiney.

 

[Missouri Mule]

You mite want to take off connectors off ecm/pcm/vp44 and spray with electronic contact cleaner (lubricating type and drying type). Intake air sensor can be cleaned with rubbing alcohol.

 

[JR]

Definitely sounds like a bad ECM. Per Chip Fisher on Blue Chip:

RPM GOES UP ON ITS OWN, OR WAIT TO START LIGHT IS DUMB, OR THE SUPPLY VOLTAGE TO THE APPS AND MAP SENSORS IS ERRATIC OR OUT OF RANGE, OR YOU HAVE DELAYED 12V POWER TO THE LIFT PUMP AND INJECTION PUMP, OR YOU HAVE A 606 CODE
A few callers have remarked that the RPM goes up on its own, typically above idle, so we have them check that the voltage on the blue with a black tracer signal wire (on Dodges) coming from the APPS, doesn’t go up when the RPM goes up, which confirms it is NOT the APPS. Do the same test if the engine tries to run away as soon as you step on the throttle. No it won't blow up. This test is described under “Dead Pedal” above. If the idle speed goes up on its own, or the RPM runs away when revving up off idle, AND you have a GOOD APPS, then you do have a bad ECM. If it revs up on its own from an idle, you can also do the “No Start” test three, and if it idles smoothly and at the same speed dependably, then it means the ECM is the cause of the problem. If it does it above idle, you'll have to read the APPS signal voltage when driving.




The other strange symptom or indicator of a bad ECM is when the truck won’t start until the wait to start light goes out, or it comes on when driving, or when it shouldn’t.




New for 2012 is a problem where the sensors that get their supply voltage from the ECM are lower or higher than the required 5.0 volts. SOME of the time a bad ECM with any of these symptoms will set a 606 code to make you feel more confident in your diagnosis!




Another new one for the summer of 2012 is delayed start, caused by the ECM delaying the signal voltage to the fuel system relay, which is described in "Hard Start Hot......" above. Do that test and you will know if the ECM is to blame.




These are the only four symptoms that I have seen or heard of, SO FAR, that necessitates replacing or repairing the ECM. The good news is that these unique symptoms have been eliminated every time by repairing or replacing the ECM. You only need one of the symptoms described above to determine that the ECM is bad. The only other way to diagnose an ECM is to try a replacement, if diagnosing a Dodge. It doesn’t seem to matter what transmission, year or engine rating the test ECM comes from, with or without a crank sensor, as long as the above symptoms go away with the borrowed test unit. I have had many callers do it this way, so I feel confident you won’t hurt anything as long as you remember one thing, PLEASE. When installing any ECM, be SURE to ground it to the engine FIRST, before connecting the big plug. This prevents any problem from static electricity or a voltage spike getting into the ECM which can blow away the software and or computer inside. Yes the test ECM may set codes, but if it doesn’t have the above symptoms any more, then you know a replacement or repaired ECM is in your future. I don’t have any experience with Ford or Freightliner ECMs, which may indicate they are better quality, but they are very different and not interchangeable with Dodges as they have twice the number of wires going into them.

http://m.bluechipdiesel.com/site/vp44_diagnostics.html?imz_s=945k1fjvgjaccrue5f419t5uo6