I am the original owner of a 1990 F150 XLT Lariat, 4.9, 5-Speed 4x4. The truck has 87,000 original miles and has not been used hard or 4 wheeled much and is garage kept. Lately there has been a problem with acceleration where the engine bucks and hesitates. I suspected the EGR system, so I disconnected the green vacuum line to the EGR valve to isolate and test the system, and the truck runs great! Reconnecting the vacuum line to the EGR valve brings the problem back. I replaced the Valve Position Sensor (EVP) with no luck, then the EGR valve with no luck, and then the EGR PVS valve again with no luck. I ran the code reader through the KOEO and KOER tests and everything comes back okay with a code 11 result. I had a similar problem back in 1999 and the EGR valve and EVP were replaced by the local ford dealer service shop, but never resolved the problem, so I took the truck back and then they found the throttle body gasket was bad and that resolved the problem. The truck runs great with the EGR valve vacuum line disconnected. I am trying to do the right thing and keep this vehicle with-in emission compliance eventhough it is not enforced in my community, but if I cannot figure this problem out, I cannot say what I will do to eventually resolve the problem. I will keep this truck regardless what the outcome is.

 

Might be worth your effort to pick up a manual for your truck along with a multi-meter, do the recommended troubleshooting procedures and see what you come up with. Almost sounds like the solenoid is sending vacuum to the egr, even though you replaced it.

Does it do this all day or does it end after a few miles of driving?

Maybe put a vacuum gauge on the vacuum line to the egr, see how much she is pulling, just to be 100% sure there is vacuum present at idle when there shouldn't be.

 

Try doing a search on here for egr restrictor plate. The egr valve lets too much exhaust back in, and it causes bucking and hesitation. The restrictor plate restricts the amount of exhaust going in. My dad's 91 did this too, bucking on acceleration at around 1700 rpm. We disconnected the egr vacuum line and it runs great. Now all we have to do is find time to make the plate.

 

Hmmmmm.......

Well here goes.........

Your stumble might not be a fault of the EGR system per se.
As you previously said..."I had a similar problem back in 1999 and the EGR valve and EVP were replaced by the local ford dealer service shop, but never resolved the problem, so I took the truck back and then they found the throttle body gasket was bad and that resolved the problem.".

The EGR system introduces "extra air" into the system. If you have a vacuum leak elsewhere in/on the motor, the "extra air" from the EGR IN ADDITION TO A VACUUM LEAK will cause a lean stumble.

Here's a fix from an earlier post that might help you, but remember, if you have a vacuum leak, it should be found and repaired.

Even easier than the EGR restrictor plate would be (from an earlier post).....

"Go a hardware store and get a couple of 3/4" diameter fender washers, one with a 5/32" hole in it, and the other with a 7/32" hole in it.
Loosen the tube nut on the EGR valve and slide it back a little and insert the fender washer with the 7/32" hole in between the EGR valve and the flange for the EGR tube then snug it all back up.
This will allow EGR to flow (at a reduced rate) into the system and keep the CEL light off.
Test drive your truck a couple of days. If there's the slightest hint of a stumble or hesitation, do the above again and replace the washer with the 7/32" hole in it with the other washer that has the 5/32" hole in it.

In a sense.....it's an inline EGR Restrictor Plate !!!!

My total cost for this fix was 34 cents....and that was for 2 washers !!!! "

Much easier to install---1 nut*** EGR Tube Nut *** to loosen/tighten
Already fabricated
Hidden from the smog *****' visual inspection

Keep us posted and let all of us know the results.

Happy wrenchin''

Bob

 

Restrictor plate = thick gauge metal, two holes drilled for the bolts, the other for egr flow sized to your liking, however optional, mine has no hole = free

Don't forget the silicone sealer.

 

That's an EGR "block-off plate"

Ain't these motors fun.

Bob

 

Motorhead,
I did pick up a manual and performed the EGR tests before replacing parts, and all the proper voltages were present. The problem does not go away even after some highway driving. I will try a vacuum guage on the EGR valve line and see what I get at idle.

Machinists Man,
I have heard of the restrictor plate here before and was hoping to avoid this route, but now I am reconsidering it. I am noticing the problem at around the 1700 RPM as well.

Truckin Bob,
I suspected a vacuum leak as well and thought of the throttle body gasket as a possibility, and it makes sense due to the "extra air" like you say. I have visually inspected all vacuum lines and they appear to be okay. Any recommendations how to troubleshoot a leaking throttle body gasket? I was thinking of spraying carb cleaner at suspected locations with the engine idling and seeing if there is any change in RPMs. I read about the "washer" restrictor plate and was hoping to avoid that route, but reconsidering that one too. I do agree that if there is a vacuum leak it must be resolved before anything else.

 

Sounds like vacuum is being applied to the EGR valve at the wrong time. Vacuum to the EGR is controlled by the EVR. Is there vacuum at the green line when the truck is idling? There shouldnt be.

 

MemOrex,
I will try the vacuum test at idle tomorrow after I acquire a vacuum guage. Is the EVR another module that feeds the EGR PVS with vacuum?

 

EVR may be what your calling PVS, my manual has no reference to a PVS.

EVR opens and sends vacuum to the egr valve, its the solenoid on the left under the egr valve.

I also had trouble with the main vacuum lines to the solenoids, from the vauum canister/ vacuum tree on the manifold, easy enough to check once you get your vacuum gauge.

Good luck

 

You're definately on the right track there m90.

A cheap can of carb cleaner sprayed in the right place will reveal a vacuum leak......but you've gotta' be VERY careful spraying a volitile liquid around a hot engine.
If I were you, I'd spring for a throttle body gasket (very inexpensive and simple to replace) and replace it just for the peace of mind. Of course I've been known to "over kill" repairs on my truck.
While you've got the throttle body off, give it a real good cleaning as well as the Idle air control valve. It might put a little extra pep in your truck.

I've got the lean stumble in my truck and can't figure out where it is for the life of me.
The ONLY way my truck is driveable is to have an EGR restrictor washer in the EGR tube along with a 1 to 3 second vacuum delay valve in the green vacuum line (going to the EGR Valve).
We've got pretty tough emissions testing here in California and I have to remove the above 2 "fixes" in order to pass "the test".

There's a ton of places where a vacuum leak (that can effect driveability) can "hide".

Here's some zero cost places to check.

Vac leak at the EGR tube nut
Vac tree loose on the upper intake plenum
PCV hose leaking at either end or brittle and broken (seldom checked)
Coffee cannister leaking
Vac lines going to and from coffee cannister leaking
EGR sensor leaking @ EGR valve
Charcoal cannister purge valve stuck open (or associated vac lines brittle and leaking)
Leaking caps on vacuum tree
Brake booster (or hose) leaking
Upper to lower plenum gasket leaking
Throttlebody gasket leaking
ERG to throttlebody gasket leaking
Air temprature sensor leaking

There's more IIRC but it's still a little early for me yet --- too much time on the 'puter last night.

Keep us posted on what your're finding and if you found/fixed it.


Bob

 

martinez, what is PVS?

Anyway, yes, the EVR is the solenoid that controlls vacuum to EGR Valve.

 

Motorhead,
I got a vacuum guage today and performed several tests. Vacuum to the EGR valve is 0 in. Hg at idle. On the source side of the EVR, I am seeing 21 in. Hg at idle. The numbers include adding 1 in. Hg for every 1000 feet above sea level which in my case is 5,000 feet above sea level.

MemOrex,
In addition to the above idle test, at the green vacuum line going to the EGR Valve, I am seeing 6 in. Hg at 1000 RPM. Should I be seeing this vacuum at 1000 RPM?

Trucking Bob,
I tried the cheap carb cleaner today and I completely understand the hazards involved on spraying a hot engine with carb cleaner from a close call I had in the past. I sprayed the throttle body gasket area and other possible leak points that you listed with no noticeable change in idle. I then tried the vacuum guage testing at a port near the throttle body and on the manifold fitting and got identical readings of 22 in. Hg at idle and 23 in. Hg at 2000 RPM. I did notice that I got only 21 in. Hg of vacuum at idle on the source side of the EVR and don't know if that would be considered a leak being 1 in. lower than the manifold. I cannot find the spec for this in my Chiltons manual, but that is in the "Green" range of the guage scale and I was not seeing any oscillating at any RPM, so I may be okay and not have a vacuum leak. I may replace the throttle body gasket and clean it out like you suggested. I will probably do a quick check of the ignition system, plugs, wires, distributor cap, and rotor eventhough all was replaced at 60k and the plugs and wires again at 78k. I use mostly NAPA parts on my truck, because I know that low quality parts can lead to problems down the road.

 

MemOrex,

My Chiltons manual has a EGR vacuum schematic with a component called the EGR PVS Valve 9D473 on page 4-6, but this schematic is for EGR systems with vacuum amplifier. Now I see on page 4-5 that it is called the EVR solenoid. Thanks for the clarification.

 

Hmmm...in the least it appears the vacuum lines to the solenoid is good, so thats a plus.

When you disconnect the vacuum line to the egr valve and report its running good, do you plug the vacuum line?

I have run a *cough* block off plate, for many years now, no loss in mpg or driveability. I know this would only fix the symptoms vs finding the source of the problem but it would made daily driving less stressful......until you find the problem.