Idle Surge, Check Gauges

[Mangler]

I just fixed a my problem with the head lights and tail lights turning on with the ignition on only. Fixed the problem ( i think ) by replacing the head light switch. Today i noticed something new. The truck was warm in traffic and started to have idle surge. Light surge at first, but i could notice it. It got worse through the next 40 min. I did not notice any RPM change. It sounded and felt like bad gas. When i got home i let in run and noticed the alternator gauge fluctuate. Not just low, but went high and low. I got a quick "Check gauges" on a high peak.



1) battery voltage off (12. 5 and 12. 6v)

2) battery voltage running - 14. 5v



I let it set an hour and now it doesn't do a thing. I did a few hot laps, and couldn't get it to happen. I am writing this because I am going to hook up the boat in the morning for a vacation, and not sure what to do. I have a chance to get an alternator, but I don't think it is the problem. I have read many posts, but nothing that seemed to have idle issue (possible FCA) and voltage surge. Any ideas?

 

[BGlidewell]

how old are the batteries?

 

[AH64ID]

If the voltage is moving then I would start there. As it's been stated, how old are the batteries? Are the terminals clean, and tight? Is the cross-over cable in good shape? Is the battery temp sensor in it's proper location (under the drivers battery). If those are all good then the alternator could be the culprit. The voltage is regulated by the ECM, but if the alt is failing the ECM may have a hard time regulating the voltage.

 

[Mangler]

The batteries were replaced in July. At that time all grounds and terminals cleaned. I checked all terminals and they are tight.

 

[Mangler]

I just started it, and got it to happen again(rough idle-light surged with alternator gauge jumping high). The voltage at the batteries was changing rapidly, but the range was about 15. 1v to 16. 2v. I remember yesterday when it was running fine it was a pretty steady 14. 5v. The alternator gauge was close to reading "check gauges" on the high side, but never happened. Dome lights surged a bit more than usual. The truck has 114000 miles.

 

[AH64ID]

It sounds like the alternator is having issues.

 

[Prairie Dog]

I had an issue with the voltage swinging up and down very quickly - about three times as fast as the grid heaters. You could see it in the dash lights but it only did it when cold. Eventually found out it was the batteries. They tested good but since they were old and I was afraid they would leave me stranded with the family, I replaced them.

 

[Mangler]

I just started it, and got it to happen again(rough idle-light surged with alternator gauge jumping high). The voltage at the batteries was changing rapidly, but the range was about 15. 1v to 16. 2v. I remember yesterday when it was running fine it was a pretty steady 14. 5v. The alternator gauge was close to reading "check gauges" on the high side, but never happened. Dome lights surged a bit more than usual. The truck has 114000 miles.

 

[Prairie Dog]

Sounds very similar to the failure mode my batterys were causing. If they're orig. then they're due no matter what IMO.

 

[cerberusiam]

The batteries were replaced in July. At that time all grounds and terminals cleaned. I checked all terminals and they are tight.

Have the batteries tested to verify they are still good. Could have got a bad one. If those are good I would go ahead and replace the cross over cable just to be sure. They will corrode inside the ends on the cable and cause all manner of problems you can never see. It may look good and still be the root cause of the issue.

 

[Prairie Dog]

Heck, when I bought my batteries one of them was defective from the start.
Also may wan't to check all the grounds along the inside perimeter if the eng compartment. Since they're just screwed into the edge of the fenders there is always the likelihood that they will corrode. Just running them in and out will do a lot to clean them up and some of them are critical - like the ECM ground on the drivers side.

 

[Mangler]

Update:

Batteries were both tested and good. I verified the Battery temp sensor was functioning. The crossover cable has not been verified. I need a few more parts to complete the new cable.

I drove the truck to work, and everything was fine. Now I am really feel I am further from the solution. Basically I am clearing the ECM and everything seems to be good for a couple days. I did clean a few more grounds, but I still don't feel like I fixed the problem. I will run it for a few days and report back. Thanks for all the suggestions.

 

[Mangler]

Replaced the alternator. No change.

I did get a bit more info on the issue that might help describe the problem. Once started,when idling it gets more of a "rattle" sound (slightly louder than normal)followed by an increase in RPM. So I set the RPM to 1000, then-when the rattle sound occurred the RPM would slightly jump to 1100. The alternator gauge is typically going high from 14 to what I assume is 16, and is never stable-slowly moving around. The gauge will dip down too, but mostly high. No "check gages" yet. I took it to about 2000 and it is still evident, but not as pronounced. I am going to get the parts for the crossover cable today, and will test that. Any other ideas? I still feel it could be the ECM, but want to test it. If it has the same symptoms after replacing the crossover cable, I am not really sure what I should check next. The alternator wasn't bad because it can be standard maintenance. ECM? -not sure.

Thanks for any help!

 

[jhenderson]

Did you go to an auto electrical shop to get the batteries tested? Many parts store workers don't have the proper equipment to thoroughly test the battery, and if they do, they don't know how to use it.

 

[Wingate]

THis actually sounds more like a short somewhere. .

 

[Prairie Dog]

When my batterys were doing the surging voltage thing, they tested fine.

 

[lhungo]

I don't know if you found your solution already but I just went through a similar problem. As mentioned in an earlier response, my mechanic found that the corrosion was in the cross-over wire. I went through a few battery and alternator swaps before we came to this solution. Now my gauge is sitting at a solid 14. 2.

 

[Mangler]

Got a new cross over cable, and no change. I was still thinking ECM. With travel for work and long hours, I needed help. Sooo...

I took it to the dealership, and they say I have a bad ECM, and it will cost me $2200. The check gages light was coming on more frequently, so they were able to verify what i had seen. It sounds like they checked everything I did. I am going to pick it up tomorrow- pretty sure I can replace the ECM for less. Any suggestions where I can get a remanufactured ECM?