I inherited my dad's 1991 F-150 with a 5.0 V-8 and EL4OD tranny. The truck has 46,000 miles on it and it has a miss at part throttle on the highway. I installed new plugs, wires, distributor cap and fuel filter and it runs very smooth at idle but it still has the part throttle miss.

I read in another post to try blocking off the hose going to the EGR valve and driving it to see if that helps. I blocked the hose and it turned the check engine light on but the part throttle miss is gone. I am going to either replace the EGR or clean it and hopefully that will fix it.

Does the EGR affect how the tranny shifts? The transmission has been shifting a little harsh on the 1-2 shift but shifts fine after that and is smooth on the downshifts. When I blocked the hose going to the EGR my tranny issue went away. The 1-2 shift is now buttery smooth. The tranny fluid looks great, doesn't smell burnt, and is at the correct level.

So does the EGR affect how the tranny shifts or is the code from the EGR being plugged affect the other sensors? I thought my TPS may be causing the harsh shifting but now I'm not sure. Does anyone have any input?

 

There is no EL4OD - you probably have the E4OD.

What hose did you block, and how? You should never interfere with the emissions systems. Maintain & repair them (& the rest of the truck), and the truck will run right. It's not difficult or expensive.

No, the EGR isn't involved in transmission control. Pre-'95 E4ODs have lots of problems, so it might simply be time for a rebuild. 46K is VERY low mileage; are you sure it's not 246K? Or has the truck been parked a lot?

Get a Haynes manual (or a '92 Ford service CD) & a cheap digital multimeter(DMM), and test each sensor & actuator.

Also, read this:

 

Unless I'm not reading him correctly, he only disconnected and plugged the egr vacuum line to test it. There's nothing wrong with that.


Rio-
I'm not aware of how the EGR would affect your shifting, but anything is possible. Replace the EGR as planned, and if the shifting improves as an additional benefit, don't question it.

 

My dad bought the truck new in 1991 and I got it when he passed away 9 months ago. The truck has 46,000 original miles on it. I know not to interfere with the emissions and I am trying to repair it. I am not trying to half *** fix it as your implying. I blocked the vacuum hose going to the EGR with a plug and the motor runs smoother and my shifting problem went away. It was a test I read about in another post.

I am trying to understand why the tranny problem was solved when I did this. I didn't think the EGR valve affected shifting so it must be another sensor. I do need to get manual and start testing.

 

Yeah, it's weird. When I plugged the line the check engine light came on and that threw a code. Maybe the computer goes into a limp in mode and disables another sensor that is causing the tranny problem. Like you said, I'll replace the EGR and see what happens. Your post was where I got the idea PK, thanks for the info.

 

Not yet. Like I said, replace the EGR as planned, and if the tranny shifts better as an added benefit, don't question it. If the shifting problem remains, then look into fixing it.


***edit***

Nevermind. We are posting at the same time. lol.

 

The fact that blocking the VACUUM line solves the problem says the EGR is NOT the problem. Don't replace it. If blocking the EGR tube solved it, that would say the EGR needs replacement.

The fault is obviously in the VACUUM portion of the EGR controls, and the roughness in the engine due to unneeded EGR flow is what was making the transmission feel rough. I'm betting the EVR is leaking, causing the EGR to open partially all the time. If you're going to replace anything blindly, replace the EVR. But the Haynes manual tells exactly how to test it. You can buy a hand-operated vacuum pump (like the MityVac) or use engine vacuum. This diagram is only 1 of 3 (or more) EVR functional tests. I don't have the others uploaded, but you can probably find them online somewhere.

.

AZ Online Repair Guide
Look for others here.

 

This is basicly an on off switch for vacuum and if it leaks vac through the EGR opens at idle and the motor runs rough.

New one's 30bucks at ford.



Adrianspeeder

 

I'm not sure how you come to such a positive conclusion, but you're mistaken. If the EVR was leaking, and causing the EGR to be partially open all the time, it would have a rough idle. In fact, that would be the most noticable problem. This vehicle has a smooth idle. The problem is a miss at partial throttle. A leaking EVR wouldn't cause any problem at partial throttle, because the EGR is normally open at partial throttle. By plugging the vacuum line going to the EGR, he confirmed that the problem is in the valve itself, probably a weak spring, possibly a sticking valve. If he had a rough idle, then yes, it could be a leaking EVR, but with a smooth idle, it can't be. He could check the vacuum at the valve with a gauge, and see what it reads, but his results thus far tell me he'll find no vacuum at idle, with vacuum present at partial throttle. If in fact that is the case, then everything up to that point is functioning correctly, and the problem must be beyond that point, and the only things beyond that point are the valve itself, the attached EVP sensor, and the passageway in the intake. The EVP sensor can't cause a misfire, nor can a clogged passageway. That leaves the valve itself.

 

I didn't think the EGR opened until highway crusing?

Adrianspeeder

 

It's easier to define the times when the EGR valve is not supposed to open; when cold, at idle, and at WOT. The most likely situation in this case is the spring inside the EGR has weakened with age, and is allowing the valve to open too fast, causing the stumble, or miss, at part throttle. It won't trip a code because the signal from the EVP is still within range, it's just opening too quickly.

 

Thanks guys. I'm getting some good information here. I think PK has nailed it. The engine runs fine at idle, when cold, and at WOT. I just notice the problem when the engine is warm and at cruising speed.

I'm going to get a manual ,test equipment and an EGR valve while I'm at the parts store. Even if the valve is sticking it could have a weak spring.

 

I think the first thing I would check is all of the vacuum lines. on that age of truck they all need to be replaced anyway.

 

No, you shouldn't replace any hard parts - even vacuum lines - just because of age. If they leak, it's much easier to repair them than to try to replace them. There's less chance of crossing them up.

 

***Update***

I changed my EGR valve and my EVR valve and my miss at part throttle and tranmission shift problems have vanished. I was sweating the tranny issue but she shifts smooth as butter now. I am very happy it's fixed because the miss was annoying on the highway.

I still have a problem with the engine running rough for the first few minutes it is restarted when warm and the exhaust smells very rich. I think I could have a coolant temperature sensor or air temperature sensor that is bad.