Engine/Transmission (1998.5 - 2002) High Idle

[garylmoore]

Nope, you need to load test it.
Means measure voltage drop right to left while cranking.

Okay I want to get this right. Compare the voltage of both batteries while the truck is being cranked?
Can you give me an idea of how much difference in voltage would be a problem?

 

[garylmoore]

The temp sensor is easy to check with a multimeter. The only hard part is accessing the connector.

That is under the drivers' side battery tray correct?
I am checking continuity?
Good = a reading, Bad= shorted to ground?

 

[GAmes]

That is under the drivers' side battery tray correct?
I am checking continuity?
Good = a reading, Bad= shorted to ground?

Yes it is under the left battery. The test is a resistance test. For mine the spec is 9k-11k ohms at room temp (75-80f). Yours is probably the same. Chapter 8C in my manual.

 

[Ozymandias]

Okay I want to get this right. Compare the voltage of both batteries while the truck is being cranked?
Can you give me an idea of how much difference in voltage would be a problem?

Less then 0.5-1V, just put the leads of the multimeter on both ends if the cross over cable, it will directly measure the drop.

 

[garylmoore]

The Alternator Is showing 14.4 volts at the positive stud.
The Temperature Sensor resistance is showing 18k at the connecter.

 

[GAmes]

The Alternator Is showing 14.4 volts at the positive stud.
The Temperature Sensor resistance is showing 18k at the connecter.

Assuming the batteries are receiving 14.4 I would say the system is working

 

[garylmoore]

The last time we checked, the batteries were still drawing 13.1 volts and idle was still 1500 rpm.
In the morning, I'm going to clean every connector and ground in the charging system and install the new serpentine belt.

 

[garylmoore]

Less then 0.5-1V, just put the leads of the multimeter on both ends if the cross over cable, it will directly measure the drop.

We had a reading of 0.15 volts under load on the cross over cable.

 

[Ozymandias]

We had a reading of 0.15 volts under load on the cross over cable.

Sounds very good, so your cable is 100% up to the task

 

[garylmoore]

The new alternator came in yesterday, good news.
At one point we had an output of 14+ volts on the original alternator. This morning the alternator read 13.5. Last night I went through the entire charging system cleaned every contact that had anything to do with it the batteries and alternator. That included both engine grounds and the driver's side was a lot of fun (that right there was sarcasm in case you didn't catch it).
Nothing has changed, I'm still running a high idle anywhere from 1300 to 1500 rpm. I am thinking that the engine computer is taking the reading off of the alternator itself, because the batteries are up. The last time I checked they were about 13.7 volts (because they're new batteries).
Unless that alternator is not charging because the batteries are where they need to be and the voltage regulator (which I assume is inside the alternator) is showing them to be charged, then I'm thinking the alternator has to be bad.
It could be that the higher alternator reading we had earlier were from bad batteries in the meters because we ended up changing batteries in both after some odd readings.
So. I'm going to install the new alternator because I have run out of time and choices. Gary

 

[garylmoore]

Changed the alternator, it cured nothing.
12.75 volts out of the new alternator.
New batteries reading about the same.
Can anyone tell me how the alternator is commanded on?
This has been a costly and frustrating situation so far.
Any ideas where to go now.
No codes.

 

[GAmes]

I can't speak to an '01 but the 12 valve 2nd gens voltage regulator is incorporated into the PCM. The engine speed sensor (ESS) is what tells the PCM to send trigger voltage to the alternator. Are you positive the high idle is associated with the charging? It could be an ECM flaw IMO.

 

[garylmoore]

No. I am not sure. The 10 month old batteries were replaced for load fail by Interstate, but that, the high idle and that the truck never charged were the only indication that the alternator was the issue.
I also changed the battery temp sensor during this process.

 

[garylmoore]

There is a small connector above the alternator output stud I assume recieves the signal to charge. But everything I have done so far has done nothing to change the situation.
Batteries, battery temp sensor, alternator have been changed with new components, and all connections in the charging system have been cleaned. I do not know where to go from here.

 

[garylmoore]

Is there an idle adjustment screw on the second gen that could somehow have backed off?
Since the batteries are new, could it be that I am not charging because the ECM thinks it is not neccessary? Thanks.

 

[BigPapa]

Not on the 24-valve. Idle is electronically controlled.

 

[garylmoore]

Not on the 24-valve. Idle is electronically controlled.

Any chance the TPS has something to do with the problem?

 

[BigPapa]

Sorry, Gary, I don’t know. I’m not that good with the 24-valves.

 

[petersonj]

Any chance the TPS has something to do with the problem?

Not likely. The TPS ( actually APPS - accelerator pedal position sensor) has an idle validation switch that comes into play when your foot is off the throttle. The ECM controls idle.

- John

 

[garylmoore]

So, any idea at what I should look at next?
Is there any way to find out if the alternator is being commanded to charge?
Or am I down to the point where the only suggestion is to change the engine computer?