I have been having some cold start issues and intermittent driveability issues.

First, the truck starts immediately on the first try.

1. When ever I start the truck in the morning, or after it has set for a few hours, the truck will go to a fast idle of about 1500 rpms and slowy idle down to ~750-900 rpms.

2. If I let it idle a few minutes, it start will to die out, but immediately will catch itself and the rpms will raise back to ~1500rpm and then settle down.

3. When driving down the road, tranny in 5th, sometimes it lightly bucks under load.

4. If I press the gas to accelerate (say 3rd or 4th gear), it doesn't pick up speed for awhile, but then it feels like an auto kicking down to passing gear and takes off like it should.

The truck has recently had the oil & filter changed.
The PO put motorcraft wires/Autolite DP plugs in about a month or so ago.
I cleaned the MAF w/ disconnected battery
I cleaned the IAC-it was pretty cruddy
There is no CEL

The truck has an exhaust manifold leak. Could this cause these sorts of issues?

The truck feels pretty doggy, unless it's in 1st or 2nd and has a 3.73 rearend.
From what I have read, the 4.0 should be pretty spunky. Mine is not unless I'm shifting north of 3500 rpm.

Also, I am getting pretty crappy mileage (for a small 4wd truck). Last fill up averaged 14.45 mpg. I don't drive 80mph or do jack rabbit starts. Most of this is highway mileage w/ some city.

I have search for quite a while and got some ideas. Does anyone else have any thoughts on this? Any help is greatly appreciated. Thanks.

 

The high up idle at the first start is normal, just because the truck is cold.

Past that, sounds an awful lot like a vacuum leak of some sort. Do you have the vacuum hubs for your four wheel drive? Those seem to have a bad habit of leaking.

 

Thanks RangerPilot

Ya, I knew that the fast idle was normal for cold start up, but is it normal or necessary after the truck has been running and then shut off for a few hours?

I did some checks for vacuum leaks w/ a can of starting fluid, but couldn't find any, not that I have completely ruled it out.

My truck doesn't have vacuum hubs for the 4wd I don't think. The PO switched to manual hubs and the truck has a shift lever for the T-case instead of the push button SOTF-just the way I like it

BTW: How many Rangers of this vintage came w/o the push button 4wd?

 

Ahh...good previous owner!

The time doesn't so much matter as the temperature. In a few hours, most trucks are back down to cold, and thus require the higher idle at first. Just glance at the temp gauge next time you start it and it does this. If it's pegged on cold, it's normal.

Is it a California truck with EGR?

While I have full faith in your vacuum-leak finding abilities, loss of power, high idle, poor fuel mileage, typically in my experience that points to a vacuum leak or EGR issue.

The 4.0L is quite spunky indeed, no matter the gearing.

 

Sounds like a possible fuel problem. Change your fuel filter if it hasn't been done already. Also, check for vacuum leaks as well.

 

Alright thanks guys.

I just checked for vacuum leaks again w/a can of starting fluid. Still can't find any! Though I did see a few lines that are dry rotted and could stand to be replaced, spraying them with the starting fluid did not reveal any change in rpm-that I could hear.

The exhaust leak that I mentioned is on the driver side and is either the exhaust manifold, Y-pipe connection to the manifold, or where the EGR line connects.

I haven't replaced the fuel filter yet. I did look at it though and it was all rusted up like everything else is. I do plan on replacing that anyhow just so I know it's been done.

Yes, the truck has an EGR valve on it. How do I check to see if it is operating properly?

 

Could this be a DPFE issue? I am not getting any CEL, but decided to check it anyway.

When I tested with KOEO, I got rock solid 5 VDC on my multimeter.

When I checked the Ranger FAQ sticky, I read where it should be 1 V if good or much less if bad. How am I getting 5 volts?

 

I would say start with the basics first. Make sure that you get that exhaust leak fixed. That can cause the computer to do goofy things and cause the truck not to run right.

I would say to start with the exhaust leak and change the fuel filter. Once you have done that, then move on to pinpointing the problem.

 

Thanks MisterCMK

I originally meant to say that the fuel filter is not rusted up and looks like it has been replaced. Though I am going to replace it anyway-they're pretty cheap.

About the exhaust leak. Is there any way to pin point it? I know the general location, but I really don't want to drop the manifold only to find it wasn't the culprit.

 

You can pretty much find it by following the pipes from end to end, checking for spots that are rusted through. If the pipes check out, look at the main connections. Manifolds to Y-pipe, Y-pipe to cat converters, cat converters to muffler, muffler to rest of exhaust. In my experience, gaskets between manifolds and the Y-pipes tend to go out a lot, but it can be anywhere.

 

Thanks RangerPilot!

The leak is either the manifold to Y-pipe or the manifold itself. I'll get this leak taken care of first, then post back if I still have the issues.

 

One little trick is to use sea-foam in the vacuum lines. It will smoke like a **** and show you where any exhaust leaks are.

 

Oh, forgot to mention that you should check the manifolds to y pipe connection. I have an Explorer with the 4.0 (basically same as the ranger) and I have a leak there. Just a tip.

 

Thanks MisterCMK!

That is exactly what I was thinking after I posted. Just run some seafoam, been meaning to de-carbon the engine anyway, and that will show me any leaks.

Thanks again!

 

Let us know how it goes. IIRC the exhaust has ball flanges from the manifold to the y pipe. Some copper RTV works wonders getting that sealed up. The y pipe them has a slip fit with a muffler clamp to the catalytic converter. After that, there is a flange with spring bolts to connect to the cat-back.

On my Explorer, I found that the cat-back connection was quite loose and came off easily without heat or penetrant. A leak that far back will not effect the engine operation like one closer to the manifold would.