Check Engine Light and Drop in Vacuum???

[ChewieM16]

ok here another one for u guys. i watch my vacuum gauge while driveing, and itl drop and then the check engine light comes on. it wont happen when the engine is cold, i drove it for about 5-7miles before it happened. when i shut the engine off and turn it back on, itl wait about a minute of driveing before the vacuum drops and i get the CEL.

anyone have an idea what this can be? thanks

-mike

 

[ChewieM16]

oh yea.. i also baby the truck, i dont beat on it often. i accelerate nice and easy.
(its too early to spell correctly.. )

 

[MrShorty]

Have you checked the engine trouble codes? My guess is, as the vacuum decreases, the mixture gets lean. If the mixture goes lean enough, the computer probably is setting a code like "O2 sensor showing lean; system at adaptive limit" or some such. If this is the case, the CEL and the O2 sensor may not be bad; you need to find out why the engine loses vacuum.

Wasn't your X a '94. If so the computer uses OBD-1, which means you can extract the trouble codes using a voltmeter.

 

[ChewieM16]

i got the codes... KOEO is 335, 332 and KOER is 326, 538. 326, however isnt listed in my Haynes book.. all these codes report something with the EGR

 

[MrShorty]

According to my Haynes manual ('83-'92 Ranger and BII):
335: PFE sensor voltage out of self test range
332: Insufficient EGR flow
326: PFE sensor circuit voltage lower than expected
538: Insufficient RPM change during dynamic response test.
It does, as you said, appear to be a problem with the EGR system. I suggest three things to look at:
1) Is the EGR not working because of a vacuum leak. The EGR valve is controlled using engine vacuum to actuate the valve. No vacuum and the EGR valve doesnt' work.
2) Is the EGR valve bad. It's possible the EGR valve has developed a leak in the diaphragm which is causing the vacuum leak and causing the EGR valve not to function
3) Is there a problem with the PFE sensor (backpressure transducer) . The computer uses to PFE sensor to know when to open and close the EGR valve. The codes suggest a problem here.

Hope this helps. good luck.

 

[ChewieM16]

thanks a bunch! ill probably check em all out tomm or sat. ill let u know how it turns out

 

[ChewieM16]

my dad and i rooted the problem down to the DPFE sensor. dealer wants $130 for a new one, does anyone else carry this thing?

 

[TPLYNCH]

Check with Torrie at FordPartsNetwork. Might get it cheap(er).