hey guys,

I have posted this problem before and have still not figured it out. I have a 1993 f150 302 that hesitates at about 30 mph, while cruising. If I plug the EGR, or disconnect the EGR vac. the problme goes away. I have replaced the EGR valve, EGR sensor, and the EGR regulator. Aside from the PCM malfunctioning, is their any other component under the hood that would control when the EGR regulator gets a signal from the PCM?

any response is welcomed thanks

vince

 

No there isn't. Have you checked vacuum lines in the egr system to make sure they are clear?

Do the KOER test again and tell us what happens.

Regards, Robert.

 

If the engine thinks it is warmer than it really is, then when the EGR opens normally the resulting mixture could be too lean which would cause a hesitation, or other drivability concerns.

Just trying to think of other scenarios that would follow this set of symptoms.

Good luck!

 

What happens if you pull the EGR vacuum line but DON'T plug it - you just let it suck air?

 

IMHO

The EGR control vacuum is a small vaccum source.
The EGR valve connects the exhaust manifold to the intake manifold through about 3/8 inch orifice when fully open.
Therefore the premature opening of an EGR can give you all the symptoms of a large vacuum leak without the ability to hear it or see it.

 

all right guys, here is the deal.

KOER test gives me two codes 167 and 225. I have replaced the TPS and do not have any problems with idle--other than a little rough. yesterday afternoon I hooked a vacuum gauge up to the line going to EGR (new vac. hose Rob), taped the gauge to my windshield and went for a ride. The gauge reads no vacuum until I reach about 30 mph (about 5 inches of vacuum or so). If I drop below 30 the vacuum shuts off. Well that is exactly when my truck normally starts acting up. Should my egr be getting vacuum when cruising at 30mph? Steve83, I'll let you no after lunch when I pull the vac and let the EGR suck air.

 

Oh yeh, almost forgot--my engine vacuum is at a steady 18

 

Vince, I don't know if you have tried this or not, but they Haynes manual talks about testing the EGR by taking it off, and applying 5" of pressure to it and says that if it drops below 4" in 30 seconds that the valve is leaking too much. I'm trying to diagnose whether mine has a problem too, and I think part of the issue is whether the right vacuum is getting there, the other part is what does the valve doing on its own. I think if the valve leaks you get rough idle and other problems.

 

Heck if the valve is dirty (sooted up) then it will not respond properly to the vacuum signal.
Taking it off would be a good thing.

 

Duck,
The EGR is brand new. It holds at 5"--the problem seems to be associated with the valve is opening at the wrong time. Should the EVR be triggered at 30 mph while simply maintaining that speed?

 

Yes it should. Go to

http://fordscorpio.co.uk/egrmonitor.htm

and

http://fordscorpio.co.uk/egrsensors.htm

for an excellent explanation into the world of egr sensors. The second one gets technical and explains operation in detail. Look past the later improvements with the double vacuum sensing valves (we don't have those) and just read about the basic egr function.

Also, your vacuum is borderline low. Close off the throttly body at idle with something that won't get sucked in and see if the engine dies.

Regards, Robert.

Edit: the egr valve vacuum input isn't going to "suck" anything. The vacuum input goes to a diaphram held by a spring. As more vacuum is applied the diaphram is pulled back against the spring which opens the valve to let exhaust gas through.

2nd edit: also go to:

http://people.ucsc.edu/~kbrandt/mustang/smog.shtml

 

thanks for the site, it gave me an idea. i think i'm going to crawl behind the engine and see if there is a leak in the egr exhaust inlet pipe.

 

That would simply be an exhaust leak - it (in itself) wouldn't affect the engine. The worst I can imagine that doing is melting the vacuum lines or wiring. But if you can't hear it, it's probably not happening.

 

I was tinking more about the inert gases vrs. pure o2. does'nt matter any way, I checked this weekend and no leaks. I found a freakin' wire broke in my harness up by my radiator though. Guess what it goes to--the o2 sensor. I re-sodered it, but no difference(seems suspicious) PCM?

 

The PCM has now learned how to do without the HEGO, so you have to make it forget & relearn. Unhook the battery for ~5 min, then go for a 10-mile test drive, changing speed frequently. Don't let it idle, and don't set the cruise. When you get home, check the codes again.