91 CEL

[slhanks4]

I am the proud owner of a '91 Eddie Bauer Edition with the 351W and 140k miles.

A couple of months ago I did a tune up. Replaced the plugs, wires, cap and rotor. Ever since my check engine light comes on within a mile or two of driving. The truck runs just fine, better than it did before the tune up. I borrowed a code reader and these are the codes it gets:

44 | 33 | 77 | 74 | 65

Of these, I believe only the 33 (EGR fault/valve not closing) is the one turning on the light. I looked at the vacuum line going to the EGR valve and found it was broken about 16" from the EGR valve. It is possible I did that while replacing the spark plugs or wires. I got some rubber vacuum hose and reconnected the line at the break, but it still displays the code.

I used a Mityvac pump to check the operation of the valve and it seems to be working properly. At this point, I am not sure what to do. I do not want to just throw parts at the problem.

Any advice/suggestions will be appreciated. Thanks!

[JBfab]

Does the code reader you borrowed have a clear codes function? Clear the old codes and drive for awile to see if it pops up again. Sometimes codes get stored in the computer even though the problem has bin fixed. If your reader doesnt have the clear codes function disconnect the battery for about 15 minutes and reconnect. Give it about 50 miles to relearn and check for codes again.

[Steve83]

Originally Posted by slhanks4

...I believe only the 33 (EGR fault/valve not closing) is the one turning on the light.
...
I used a Mityvac pump to check the operation of the valve and it seems to be working properly. At this point, I am not sure what to do.

Continue diagnosing the EGR system: does the valve's motion translate to the EVP? Does the EVP generate the proper output? Does that output reach the EEC?



If all of those are "yes", then you've proved your original belief incorrect, and that code is either historic or erroneous. If it returns, the EEC is probably failing. Either way: move to another code & diagnose it FULLY.



BTW
I'd start over with a paperclip to pull codes. It's more reliable.

[FordFan021]

i have a 91 xlt myself my check engine light is always on i took it to a shop and got the engine and transmission rebuilt and i asked them about it and they said it was fine. they were gonna charge more money to fix it so i told em it would do for now. its been a year and i check it periodically its been fine ever since.

[slhanks4]

Originally Posted by JBfab

Does the code reader you borrowed have a clear codes function? Clear the old codes and drive for awile to see if it pops up again. Sometimes codes get stored in the computer even though the problem has bin fixed. If your reader doesnt have the clear codes function disconnect the battery for about 15 minutes and reconnect. Give it about 50 miles to relearn and check for codes again.

Ah, yeah...I forgot to mention that. I did clear the codes and the CEL came back on within a mile. Hooked up the code reader again and had the same codes.

[slhanks4]

Originally Posted by Steve83

Continue diagnosing the EGR system: does the valve's motion translate to the EVP? Does the EVP generate the proper output? Does that output reach the EEC?



If all of those are "yes", then you've proved your original belief incorrect, and that code is either historic or erroneous. If it returns, the EEC is probably failing. Either way: move to another code & diagnose it FULLY.



BTW
I'd start over with a paperclip to pull codes. It's more reliable.

Thanks. I didn't know I could check the codes with a paperclip. It's worth a try. It will be this weekend before I can spend any real time messing with this again, but you have given me some good ideas.

[slhanks4]

I wanted to mention that I have fixed my Check Engine Light issue. I had a feeling the root of the problem was the vacuum lines I broke while doing a tune up, so that is what I looked at first. I followed the instructions in this thread Replace your plastic vacuum hoses with rubber. I had broken the EGR hose and the main vacuum source (red) hose at the canister. I had repaired them but then found the hose to the diverter valve was broken too. After replacing all the hoses I cleared the computer by disconnecting the battery for 30 minutes. I have been driving it since Saturday and the CEL has not reoccurred.

Thanks to everyone on the forum who offered advice. I now know more about the vacuum lines and OBD system than I ever thought I would.