V8 Owners, what are your RPM's at around 75mph?

[paulyjsob]

I have an 07 Mountaineer AWD V8 and it almost seems like my RPM was higher. My tach is a hair over 2000rpm at 75mph. I though it used to be closer to 2200. I also get a slight jerking at times at around 50mph going up a slight hill.
Wonder is my torque converter is going bad or a coil is bad.

Thanks.

 

[DavidEBSmith]

How many miles? The slight jerking was the symptom we had that was cured by replacing the plugs.

 

[paulyjsob]

I have 75000 miles. Thanks.

 

[Maniak]

While I can't tell you the correct RPM at 75 I can tell you a web page you can use to figure out where it should be.

Use the gear calculator on 4lo.com and you can enter the tire size and gear ratios to figure the correct rpm @ speed.

You put in 1 for the transfer case ratio and put in the OD gear ratio from your transmission in there along with the rear end ratio and tire height. Now when you enter 75 mph it will kick out what RPM you should be.

~Mark

 

[thebrakeman]

The miss/jerk in a high-gear, low rpm, moderate throttle (before it downshifts) sounds like a plug or coil going bad (misfire). Read the engine codes. If you haven't seen a check-engine light yet, you could have what's called a "pending code". The computer will store codes for potential problems before they reach a certain frequency threshold to throw a light. Or you can simply keep doing whatever causes the jerk, and it will soon throw the light.

At 75,000 miles, if you haven't changed the plugs, it's time to do it anyway. They plugs themselves are good to 100,000 miles. But in case you haven't read, the longer you wait, the more likely they will break upon removal.

 

[paulyjsob]

Thanks for the advice!
I'll start with the plugs next week.

 

[thebrakeman]

Read up on it on this site. There is a good TSB from Ford on how to do this carefully to minimize the risk of breaking. Involves loosening about 1/8-turn, putting in a teaspoon of carb cleaner, and giving it at least 1 hours to wick down thru the threads, and break up any carbon build-up between the plug-sleeve and the cylinder-head. Then you work the plug back and forth, never exceeding a certain torque (?).

 

[Essex4x4]

Why are you going 75mph when the speed limit through most of our country is 65?

 

[JPinUSMC]

If you haven't seen a check-engine light yet, you could have what's called a "pending code". The computer will store codes for potential problems before they reach a certain frequency threshold to throw a light.

Is it possible to read these pending codes with a code reader? I had a hell of a time diagnosing which of my coils was acting up when I was having this problem because the light wouldnt come on. Would be nice to be able to read them once the issue starts.

 

[Maniak]

Why are you going 75mph when the speed limit through most of our country is 65?

It is? Its 75 all over out here.. It really just depends on the part of the country I guess...

~Mark

 

[Maniak]

Is it possible to read these pending codes with a code reader? I had a hell of a time diagnosing which of my coils was acting up when I was having this problem because the light wouldnt come on. Would be nice to be able to read them once the issue starts.

Good code readers/scanners can get this. You can also get it via an UltraGauge. The UltraGauge is like a scangauge (I'm assuming you have seen those) which is just a GPS sized screen that is connected to your ODB-II port. It can show you the current codes and pending codes along with all kinds of other information.

I have an Ultragauge on our honda and I use it to show MPG (instant and avg) plus a bunch of other things. It was nice to be able to see the pending codes when I did have an injector issue.

Last time I checked the Ultragauge with the windshield mount was around $80.

~Mark

 

[thebrakeman]

Yeah, I have the ScanGauge2. Runs around $120 IIRC. It's been great for monitoring all kinds of stuff, expecially when I'm towing. Helps watch torque convertor lockup, trans fluid temperature, engine coolant temp.
But also has a good code scanner, including the ability to check pending codes.
But if you don't need to purchase one, most auto parts stores will run scans for free. Their scanners should be good enough to check pending codes...if the guy knows how to ask the scanner to check those.

 

[jadez03]

Thanks for the advice!
I'll start with the plugs next week.

Read up on it on this site. There is a good TSB from Ford on how to do this carefully to minimize the risk of breaking. Involves loosening about 1/8-turn, putting in a teaspoon of carb cleaner, and giving it at least 1 hours to wick down thru the threads, and break up any carbon build-up between the plug-sleeve and the cylinder-head. Then you work the plug back and forth, never exceeding a certain torque (?).

I posted a thread recently with my experience on this one. It was in my sport trac but the principle is the same. Check it out here.

 

[StevenStebo]

2000 rpm @ 73 mph