Technical Car Experts Answers everything you need: Extremely High RPM in neutral

Showing posts with label Extremely High RPM in neutral. Show all posts

Wednesday, July 11, 2012

Idles Fine but RPM jumps in drive mode?

2004 Dodge ram will idle fine but RPM jumps in drive mode.

Also it feels like truck pulling forward when coming to stop.

WHY THIS PROBLEM IS NOTICED?

This issue is already been noticed many as times at our repair garage.As per your problem described this is caused by the torque converter clutch staying locked up when you are stopped.
In the front of the converter there is a disc clutch that is turned on at certain times to give a mechanical lock between the engine and trans.

BUT WHY IT FEELS LIKE TRUCK IS GETTING PULL FORWARD WHEN STOPPED?

First of all i will say your dodge cummins engine is very powerful engine as compared to other vehicle model engine.

On most of engines a locked up converter clutch will cause the engine to die when you come to a stop, but the Cummins has enough power that it will stay running,Even though converter clutch is locked.

EXACTLY WHY THESE HAPPENS?

As per vehicles electrical working procedure when you come to a stop.The ECM(engine control module) sees the increased engine load and just ramps up fuel and boost to keep the engine running.
And that is what makes you feels like truck is pulling when you are trying to stop.

But with this same condition if you shift the shifter up into park or neutral it quickly relieves a huge load on the engine, and this cause RPM surge issues.
That is why you may have noticed the RPM's jump up a bit before settling down to normal.

OK,I UNDERSTOOD THE THEORY OF THE PROBLEM.BUT WHAT PART IS EXACTLY FAULTY?

The problem which you mentioned is caused due to faulty/worn out sticking valve in the valve body, bad converter clutch solenoid, leaking seals on the trans input shaft, or the converter itself.
As per details you dodge truck model uses 48RE transmission.
As per our garage vehicle repair experience Usually on most of 48RE trans this same types of problems are caused by a failed converter.

SO SHOULD I REPLACE THE CONVERTER OR DO SOME TROUBLESHOOTING?

First confirm the problem.other then converter issue,i have also mentioned some other possibilities.
The problem like sticking valve in the valve body, bad converter clutch solenoid, leaking seals on the trans input shaft.
So start inspecting and checking this possibilities too.

FROM WHERE TO EXACTLY START TROUBLESHOOTING?

First remove the valve body and make sure there are no valves hanging up. If ok then replace the solenoid pack at that time since the valve body has to be removed to do it and it's already apart, and at that point the problem would either be the solenoid or converter. Since the solenoid pack is cheaper and easier I suggest replace it then and hope that takes care of it, but if not then you know the converter and input shaft seals will need to be replaced.As that's the only possibility left.

OK,WHERE IS THE SOLENOID LOCATED?

The solenoid which you need to replace is converter clutch solenoid.There is also one more solenoid located there,its called Governor solenoid.You don't have to replace governor solenoid,but the converter clutch solenoid.

The governor solenoid and transducer are used together with the ECM to control governor pressure, governor pressure controls upshift and downshift timing.But governor solenoid is not the issue in your case.

You have to replace the replace the double solenoid on the silver bracket on the right side of the valve body, above the governor solenoid and transducer.

The converter clutch solenoid is located on the right side of the valve body above the governor. It's a double solenoid mounted on a single silver bracket as mentioned earlier.The solenoid comes with the trans internal wiring harness. This is the solenoid that can cause the problem you are noticing.

WHAT IF REPLACING THE SOLENOID IS NOT HELPING?

First i suggest to replace the converter clutch/overdrive solenoid .Its the second one on the bracket is overdrive.That should take care of the problem.But if that doesn't take care of it then you know the converter itself is the problem and will need to be replaced. Because Solenoid is cheaper option and converter is costlier one.I suggest replacing the solenoid first and confirm the issue.

WHATS THE PART NUMBER OF SOLENOID AND CONVERTER.AND WHAT IS THE COST OF PARTS?

As per part service manual.It states

Part number for converter clutch/overdrive solenoid is 52118500AB.
&
Part number for converter is R2118868AC.

And for the cost the solenoid pack runs about $120 and torque converter runs about $400.

This details will help.
Thanks.

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1999 Merc Optimax 200hp RPM goes High?

RPM stays there for few minutes then goes up.

At our boat repair Store we have seen several issues that could cause this type of scenario.

Sticking air regulator,
Or the fuel pump not keeping up with demand,
Or fuel pump is slow to react to throttle changes.

Its recommended to get the following test done:---

Get "Leak Down Test" done on the cylinders,
Compression and spark test also needs to be done.
Ignition test also should be done.
Do the self test on engine.
Inspect air compressor and fuel rails, test air system with shop air per tech service.
Inspect the injectors,if dirty clean them.If worn out replace injectors.
Inspect throttle position sensors.

If all this basic tests goes well then, attach the pressure gauges to the engine and test the air and fuel pressures under load. The fuel pressure should not "flinch" when the throttle is gagged, the air might do "One" wiggle.

ON many such cases its seen that Cylinders gets damaged,

These engines are very susceptible to cylinder damage.

The cylinder gets damaged due to water in the air lines, remove the lower air cross over hose and look for signs of water and corrosion, if present, more investigation is required.

To confirm the problem with engine,get the dyno test done.

Can i use Diagnostic tool to confirm the issue?

Yes you can use,but it will not detect the exact accurate fault in such cases.

There are lots of testing you can do before the "Diagnostic Computer" comes into play. In this case most of all issues are apparent in the mechanics and not in the electronics.

HOW TO DO LEAK TEST?

The leak down test and load test each cylinder. The load testing of cylinders require disconnecting each coil Pack one at a time and testing for the load change in the engine to determine that all cylinders are pulling their own load. It also shows if you have any issues at all with a particular cylinder.If you notice any problem with a cylinder,then it has to be replaced.

Getting this possibilities checked will help.

Thanks.

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Thursday, February 9, 2012

high rpm in neutral? Inconsistant high RPM in neutral?

You could have a problem with the throttle cable.Inspect the cable that connects the foot pedal with the throttle body to make it go "zoom, zoom". Its also possible that the inside of the throttle body is gummed up with dirt, dust, varnish and soot. Clean the throttle body with throttle body cleaner liquid available at local auto parts store.Take off the air intake hose, and spray everything inside there until it is clean and shiny. Be aware you may have trouble starting it the first time after cleaning.But once it starts and runs properly,then for second time it will run smooth like before.

But if that is not helping,then problem is faulty TPS.Throttle position sensor located in throttle body.

To see how throttle body looks,see the image shown below :----

Also there is IAC idle air control valve motor on throttle body.If it gets dirty,the same problem will be noticed.Try cleaning the idle valve first and see,if that is not helping,then it has to be replaced.

Other possibility is vacuum leak.
To access the vacuum leak method by professional mechanics is use starting fluid. Simply spray around the engine with it running ( not on the exhaust ) and listen for a change in engine noise. Once You have found the area, turn the engine off and check for cracked vacuum hoses or leaky gaskets.

This will help.

Thanks.

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