1989 Ford Bronco • V8 4WD Automatic • 120,000 miles

I got my truck smogged today and the NOX was off the charts high. The tech told me that my hot combustion chamber was responsible for this. I had my cat changed and he said it was something in my egr system. I was wondering how I could diagnose and repair this. Hopefully just cleaning the egr valve?
January 11, 2011.

You can check the valve with a vac pump and see if it holds vac. The thing you realy want to check is the vac line going to it and make sure it dont have vac at idle.

Could a problem with this system lead to rough idle. Cause the care will idle rough then regular sometimes

Jan 11, 2011.
Yes if it has vac at idle it will make it run very rough. But that sounds like a sticking egr valve, but make sure it dont have vac at idle.

If the EGR valve is not opening the exhaust gas will not recirculate and will form oxides of nitrogen Nox to increase due to excessive combustion temperature over 2500F deg

Jan 11, 2011.
I have never seen a egr stuck closed that would make the engine run rough, now if it stuck open then it might not even idle at all, as far as hi combustion temp yes this is true but it only rises under a load or constant hi idle and when this happens it makes this sound we old timers like to call spark nock, this is what an egr gets rid of. Keep in mind this is a 1989 truck.

Detonation/pinging/spark knock all smells the same- High NOx is normally caused by an EGR problem. And Yes I've seen it shut closed in my 43yrs in this business. Open or shut closed you gonna have a problem

TO: Rjohnsn Clean out the EGR valve this is the only way to find out and make sure its functioning correctly- BTW You sure the vac hose is hook-up to the correct type vacuum such as ported/VV/intake

Jan 11, 2011.
Your dogging me and then telling him the same thing I allready told him to do. And buy the way I told him in laymens terms. You need to look at my replies and maybe his to, he says in his massage and I quote-(hopefully just cleaning the EGR valve) would fix it.

By the way rasmataz we have all seen a stuck egr valve. Nobody ever said they dont stick. And just cuz you claim you have been in the business for 43 years dont impress me ive seen certified tecs that dont know a screwdriver from a hammer!

I have never seen a egr stuck closed that would make the engine run rough: It won't-but will increase the Nox and cause it to detonate/ping-like throwing marbles in a tin can-

When he comes back you take it from there-No I'm not trying to dog you, its my job as Sr. Moderator to assist, we work in here as a team-When it gets tough we moderators/experts will link-up and answer the question paid or not-

Jan 12, 2011.
Dude why do you keep saying things I have allready said? Are you reading what your typing. Dident you read the part where I said thats what us old timers call SPARK NOCK!And thats only under load. If working proper it closes at idle(no vac)opens at throttle(vac)if letting gas pass by then you get high nox& bad ilde. Its just an egr valve omg. P.S this man just needs to clean the egr valve and check the vacuum solenoid.

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