weird fuelling problem,,,rpm's hang

[Hootguy]

2005 2500 4X4,,,

Truck is having a stange problem no local shops can figure out,,then again,,they dont know much about these trucks at most dealers,,

The truck starts fine,,,but when you rev it up in neutral or park the RPM's go up to 2500 or so,,then hangs there and slowly comes back down,,i also notice that when you rev it up it doesn't smoke all that much,,and the truck is not as strong,,the local dodge dealer drove it with the scanner on and reported all fueling is ok,,,fuel pressures and the like are suposed to be good according to the DRB scanner,,,the only thing was the clutch fan doesn't seem to come on at the proper times,,,which i would doubt is the problem,,,

Of course the fuel filter has been changed,,,no change,,

This one has me scratching my head,

Hope someone can help,,

 

[MChrist]

I noticed on my '06, that if you stab the throttle in park and take my foot off the throttle by the time the tach reads 2500, it'll rev up to redline and set there for maybe two seconds, then slowly come down. My '98. 5 doesn't do this. This was also before I made any mods.

 

[JJPage]

The rpms do ramp down slowly on the HPCR's, this is normal. It is designed this way to minimize pressure spikes, that can damage injectors.



By design, if the fuel was just chopped off by slamming the injectors shut, all the built up pressure in the rail has to go somewhere. The rail pressure relief valve is a safety, but once it is exercised it is weak, so the pressure is ramped down in increments by the ECM controlled FCA. Now having said that, you could have a sticky FCA, you may try adding some extra lubrication to your fuel to free it up...

 

[CToney]

The FCA is easy to change if it goes bad. Had to change it on my Dad's truck. I have heard that if your rpms stay up for a while between shifts etc that injectors might be bad as well.

 

[cerberusiam]

IMy '98. 5 doesn't do this. This was also before I made any mods.

Don't try to compare the HPCR to a jerk pump system for operations and reactions. It will drive you crazy trying to figure out what is right and wrong. :-laf





The RPM hang is normal as the ECU is trying not to blow the rail and relief valve, and, on a manual it keeps the turbo spooled instead of the typical drop rpms and smoke till it spools again. A lot of the reactions come from emissions controls built into the ECU.



A smooth ramp down with a few small bumps on the tach is normal. A jerky ramp down with several long plateaus is not a good sign.

 

[sag2]

When the RPM hangs while driving, you have a bad injector(s). While stopped it's pretty normal.

 

[Hootguy]

the hanging rpm's are in park,,but i'm talking a long fluctuating rpm hang,,,nobody has been able to figure it out,,

 

[AH64ID]

How long?



Like its been said some hang is normal, and no smoke is also normal.

 

[JFulford]

My 05 has the same hang, but with longer "stops" on the way down. I also have longer start times AND, at speed on the highway, I've noticed weird hangs letting off the pedal(delay action, feels like it it missing). I've got a couple of guys telling me injectors?
150K on a stock system.
Thanks
jeff

 

[Hootguy]

as soon as we changed injectors in my buddy's truck everything went back to normal...