I have a 95 F-150 with the I-6. It has had a real rough idle and just doesnt seem to have any power at speed. 130K on the odometer.

I pulled codes and the only one that came up was a knock sensor.

Where can I find the sensor and how hard is it to replace.

BTW, cleared the codes and it came back

Thanks in advance for any help

Scot

 

The knock sensor is between the distributor and the coil, on the drivers side of the block. However, I doubt that's your problem. The engine has to be completely warmed up before testing, and you have to goose the throttle to WOT when it tells you to during KOER testing, otherwise that code comes up.

 

I had read about that and was pretty confident that I performed the procedure correctly. Checked it again after getting home from a 30mile drive and got the same code. When I reved the throttle I may not have hit WOT so I will try again this afternoon. I'm starting to think injectors. Is there any way to test the sensor.

Thanks for the assistance.

Scott

 

Injectors are a common problem with the 4.9L, but your symptoms don't suggest that they are your problem. At least not to me. Dirty injectors typically will cause a stumble off idle, almost like you're running out of gas, with bucking, etc., as well as an occasional miss when cruising at part throttle, say around 35-45 mph. It almost always clears up under load, or at high speeds, though. I know that doesn't make sense, but it's true.

Another common 4.9L problem that is a frequent cause for a rough idle is a leaky intake manifold gasket, usually where the number one cylinder tube in the lower manifold meets the head. The vacuum leak created causes an occasional lean miss. You could try spraying WD-40 around the area and see if the idle goes up briefly. If it does, you've found the problem.

You also might have a sticking EGR valve. You could try disconnecting and plugging the vacuum hose to the EGR valve, and see if that makes any difference. Or better yet, attach a vacuum pump to the valve and slowly apply vacuum to it while the engine is idling, and see if it makes the engine stall. If it does, it's working properly.

Another thing I would test is the IAC solenoid. It's mounted to the side of the throttle body, and looks like a small can. With the engine idling, unplug the two wire electrical connector that goes to it, and see if the idle changes. When the engine is cold, it should almost kill it. With the engine warmed up, it should not make much difference at all.

Now, with all that said, I'm thinking you may have multiple problems, especially if your poor idle even happens when it's cold. Based on what little I know about your personal situation, I'd bet that you have a vacuum leak at the intake, and a clogged exhaust/bad cat.

 

Thanks for all the suggestions. I have my work cut out for me today. Under load the truck pulls fine. Your descripition on injectors is exactly what is happening. 35-45 letting off the gas or easy acceleration it feels like a miss.

FWIW, on a cold start it idles fine, symptoms show up after the idle speed drops down from the initial start.

I'm going to go over everything you suggested

Thanks again.

Scott

 

Okay, then let me revise my opinion. lol. I'll bet you have dirty injectors, and a clogged exhaust. What works pretty good for the injectors is this (I've done it personally): Go to the automotive section at Kmart, and look for their fuel system additives. You will find one brand that unfortunately, I can't remember, but it comes in a gray plastic bottle, with a copper colored cap. They should have two sizes, the small is around 12 ounces, and the large is arouns 32 ounces. Buy 2 of the large bottles. Run your truck so that one of your gas tanks is near empty, and go to the gas station. Pour in both bottles, and add 5 gallons of gas (NO MORE THAN THAT!). Now drive it around for an hour or so, and then let it sit overnight. If your injectors were dirty, you will notice a big improvement when you go for a drive the next day. If the problem is better, but not completely solved, you can do the same thing again. If that still doesn't completely cure it, it's time to buy a set of injectors. Injectors aren't cheap, but that fuel system cleaner is, so do try it twice before replacing the injectors.

As far as your exhaust goes, get yourself a vacuum gauge, and do this:
1) Attach vacuum gauge to manifold vacuum source.
2) Warm up engine.
3) Observe vacuum at idle.
4) Leave engine idling for 10 minutes. Do not touch anything on the truck during this time. In fact, go inside and fix some coffee.
5) After 10 minutes, observe the vacuum.

If the vacuum is the same or higher, you don't have any resctrictions. If the vacuum gauge has dropped, you do have a restriction. The more it drops, the greater the restriction. If it drops 1" or more, you have a serious restriction. 2" or more and you might as well have the exhaust welded shut. Keep in mind that a rich exhaust will clog up cats in a hurry.

 

Thanks again. Rear tank is empty. Injector cleaner going in today.

Any suggestions for aftermarket cats/exhaust. The truck has treated me well. Time to put a little money in it so that doesnt bother me at all.

Noticed I'm getting a oil leak from the rear main so I'll be doing a teardown this winter. 130K on the odo. Any suggestions for upgrades when I do a rebuild. I haven't found much info on building up the 4.9l Lots of stuff for V-8's. I probably just don't know where to look.

Here's one for you for all your assistance on this board

Scott

 

There are parts available for the 4.9L (Clifford Performance), but you don't want them. That engine just wasn't designed to go fast (although I did see an altered truck do an 8 second 1/4 mile at Pomona once with a 4.9L!). It's a great workhorse engine, and will last you as long as you own the truck. Your engine really has the best mechanical parts in it already. You have what basically is a factory header, and a good fuel injection system. I have the same truck, and what worked best for me was adding a K&N FIPK, and an ECM chip from JET. My cat is original, and I haven't looked into replacements yet, so I really couldn't make any recommendations, but I am pleased with my exhaust. I bought and installed an Edelbrock RPM cat-back system, that has two pipes that exit behind the passenger side rear wheel. More than anything, it gave it a very respectable exhaust tone. It's not real loud, but it sounds healthy. I didn't really notice any difference in performance, but my vacuum is higher at idle, which means the engine is breathing better, and my gas mileage went up slightly.

 

Injector cleaner made a huge difference. Couldn't find a bottle that matched your description though so I ended up buying 3 bottles of the Outlaw brand. It was cheAP (3$ / 20OZ) and had the best looking bottle

Let is soak as suggested and noticed a huge improvment this morning.

I'll test vacuum as soon as I can track down a guage.

Thanks again for the helpl.

Scott

 

Excellent! Glad to hear the news!