EGR code fix revisited, shortened version

[cb97alltrac]

check engine light with code 401 or 701. Insuffiecient egr flow. Have read cytroger and other great writeups with pics.
all I did today was disconnect air inlet hose with 4 nuts, this is under drivers seat, and sure enough the egr passageway was totally clogged with carbon as in pictures. Cleaned both with cleaner spray and pipe cleaners. Also removed the exhaust gas temp sensor with 14 open end wrench and cleaned the tip and orifice with spray and pipe cleaner. Spray would come out the now clean intake passageway and vice versa. I did not mess with the egr modulator or egr valve as these were clean in cytrogers post.
Codes now gone! No check engine light. Next time I will NOT separate the big rubber intake hose from the metal rounded intake part before pulling off the 4 wing nuts, as it is hard to put back on and not much room, but does help to take the metal intake part inside to clean it where its warm.

[cb97alltrac]

also replaced the thin gasket at the intake since it crumbled, part no 22273-76010

[Jonny]

I have had code 71 (EGR gas temp too low) on my '91 for 6 years now. A while ago I did exactly as you did, for the reasons you did, had the same blockage at the throttle body as you did but cleaning only this section of the EGR system didn't clear the code. It went away for a few days but came back, just as it has done once every year - a few days after I take the fuse out to reset the light prior to going for my safety inspection! Why it takes several days of driving to reoccur is odd, but that's the way it is on my van. Presumably I still have a problem somewhere upstream.

Glad this short-cut worked in your case. Just wanted to post for others considering this that it is not a guaranteed solution. I need to clean my idle speed control valve soon, so the full EGR system service will be done at that point also. I'll be sure to post the results.

jw

[tbkilb01]

It went away for a few days but came back, just as it has done once every year - a few days after I take the fuse out to reset the light prior to going for my safety inspection! Why it takes several days of driving to reoccur is odd, but that's the way it is on my van.

jw

The problem is still there, computer still detects malfunction per logic. Have you checked circuits for opens or shorts?
Although the Idle speed control valve (ISC valve) does get gummed up causes idle probems.

[cb97alltrac]

It may not be a permanent fix. But check engine light has not come back on after 1000 miles

[Jonny]

Here are some pics of the throttle body of my 91 from the EGR port cleaning project... Yuk, that clod in the lower right side of the intake manifold is a big ol carbon plug in the EGR passage opening.

Cleaning this out did not solve the code problem, although it did make the EGR valve test positive for killed engine with vacuum applied at idle, so I knew the EGR valve worked.


DSCN2663.jpg

DSCN2666.jpg


Back of throttle plate is nasty too


DSCN2662.jpg


So I finally reinvestigated the problem, bought a vacuum pump, started disconnecting lines and sucking on them and here is the culprit in the bundle of spider pipes (for lack of the official name)...


DSCN3034.jpg


It's a bit hard to see, but the pipe going to the R port of the Vacuum Modulator was completely clogged with rust. The pipe going to the P port was partially clogged.

So my theory is that this pipe was the first thing to clog, then because the EGR system no longer functioned and no gas was flowing through the EGR port this allowed carbon to build up and clog that too.

[Jonny]

OK, this is another post (hopefully last) in this thread which I seem to have hijacked!
So, code eventually came back after cleaning out the clogged/rusted pipe pictured in the previous post so it wasn't the root cause either, even though it was clearly part of the problem.
Following the instructions in the service manual (gosh, what a concept) with a vacuum pump it appeared that the EGR Modulator Valve was bust. Most of the scrap yard ones I found over the last few months were clogged with much shize under the filter so I never bought one. Finally I found one which looked like it had been replaced recently - and it has really fixed the code problem this time. Really.

[cb97alltrac]

OK, this is another post (hopefully last) in this thread which I seem to have hijacked!
So, code eventually came back after cleaning out the clogged/rusted pipe pictured in the previous post so it wasn't the root cause either, even though it was clearly part of the problem.
Following the instructions in the service manual (gosh, what a concept) with a vacuum pump it appeared that the EGR Modulator Valve was bust. Most of the scrap yard ones I found over the last few months were clogged with much shize under the filter so I never bought one. Finally I found one which looked like it had been replaced recently - and it has really fixed the code problem this time. Really.

Interesting. Thanks for the post. I'll pick up one at the pick and pull in case my code comes back.

[cvtroger]

cb97alltrac,

Thanks for the shout out.

My code never came back and so I was glad to do that fix.